NUREG-1890

Evaluating Igneous 

Activity at Yucca Mountain 

Technical Basis for 

Decisionmaking 

Advisory Committee on Nuclear Waste and Materials 
NUREG-1890 

Evaluating Igneous 

Activity at Yucca Mountain 

Technical Basis for 

Decisionmaking 

Manuscript Completed: February 2008 

Date Published: February 2008 

Prepared by 

W.J. Hinze1, B.D. Marsh2, R.F. Weiner1, N.M. Coleman1 

2

Johns Hopkins University 

 3400 North Charles Street 

Baltimore, MD 21218 

 

1

Advisory Committee on Nuclear Waste and Materials 
iii

ABSTRACT 

Eighty thousand years ago a small-volume basaltic volcano, the Lathrop Wells volcano, 

erupted about 20 kilometers south of the Department of Energy’s proposed high-level nuclear 

waste repository at Yucca Mountain, Nevada. Lathrop Wells is one of a series of infrequent 

basaltic volcanoes that have occurred near the proposed repository site during the past 10 

million years. This report presents the Advisory Committee on Nuclear Waste and Materials 

(ACNW&M) summary and analysis of the range of current technical views on the nature, 

likelihood, and potential consequences of future igneous activity at the proposed repository. 

This report responds to the request of the U.S. Nuclear Regulatory Commission in Staff 

Requirements Memorandum M06011B, February 9, 2006. The technical views have been 

abstracted from published literature and public agency reports and presentations. The 

alternative views reflect uncertainties of the igneous processes that have occurred in the region 

and those that are likely to occur in the future, as well as the interaction of these processes with 

the proposed repository. Analysis of the views and observations is based on professional 

judgment and quantitative considerations within the scope of the resources available to 

ACNW&M. 

****** 

Paperwork Reduction Act Statement 

This NUREG does not contain information collection requirements and, therefore, is not subject 

to the requirements of the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.). 

Public Protection Notification 

The NRC may not conduct or sponsor, and a person is not required to respond to, a request for 

information or an information collection requirement unless the requesting document displays a 

currently valid OMB control number. 
iv

This page intentionally blank. 
v

CONTENTS 

Page 

Abstract..................................................................................................................iii 

Contents..................................................................................................................................... v

List of Figures..........................................................................................................ix 

List of Tables..........................................................................................................xiii 

Executive Summary .................................................................................................................... xv

Glossary................................................................................................................xix 

Abbreviations........................................................................................................xxix 

Acknowledgements...................................................................................................................xxxi

Preface...................................................................................................................1 

1. Introduction....................................................................................... ...............3

1.1. Igneous Activity and the Proposed Yucca Mountain Repository...........................3

1.2. Objective and Rationale of Report.........................................................................3

1.3. Scope of Report ....................................................................................................6

1.4. Content and Organization of Report......................................................................7

1.5. Report Preparation Process ................................................................................11

1.6. Constraints on the Report ...................................................................................12

1.7. Previous Reviews of Igneous Activity Technical Bases ......................................14

2. Brief Geologic History of the Yucca Mountain Region ....................................................17

3. Overview of Igneous Activity Processes .........................................................................27

3.1. Introduction..........................................................................................................27

3.2. Origin and Nature of Igneous Activity..................................................................27

3.2.1. Magma Generation..................................................................................27

3.2.2. Magma Composition................................................................................28

3.2.3. Volcanoes and Their Products.................................................................29

3.3. Magma/Repository Interaction ............................................................................31

3.3.1. Nature of Magma Ascent.........................................................................31

3.3.2. Key Features of Magmatic Dikes.............................................................31

3.3.3. Basic Nature of Eruptive Event................................................................32

3.3.4. Magma Interaction with Repository and Waste Packages ......................32

3.4. Dispersal of Contaminated Ash...........................................................................37

3.4.1. How Is Ash Dispersed? ...........................................................................37

3.4.2. How Does Ash Become Contaminated? .................................................37

3.5. Remobilization and Resuspension of Contaminated Ash....................................38

4. Nature of Potential Igneous Events in the Yucca Mountain Region................................41

4.1. Introduction..........................................................................................................41

4.2. Volcanic Analogs.................................................................................................41

4.3. NRC and DOE Perspectives ...............................................................................46
vi

4.3.1. NRC/DOE KTI Agreement on the Likely Range of Tephra 

Volumes...................................................................................................46

4.3.2. DOE Approach to Event Definition ..........................................................46

4.3.3. NRC Approach to Event Definition ..........................................................49

4.3.4. EPRI Approach to Event Definition..........................................................50

4.3.5. Comments on Hydromagmatic (Maar) Volcanism...................................51

4.4. Summary .............................................................................................................52

5. Probability of Potential Igneous Activity ..........................................................................57

5.1. Introduction..........................................................................................................57

5.2. Spatial and Temporal Distribution of Igneous Events..........................................58

5.2.1. Introduction..............................................................................................58

5.2.2. Surface Exposures ..................................................................................58

5.2.3. Known Occurrences of Buried Basalts ....................................................61

5.2.4. Undetected Igneous Activity ....................................................................66

5.2.5. Change in Basaltic Volcanism with Time.................................................67

5.3. Time Period Used in Extrapolation of Igneous Activity........................................72 

5.4. Controls on Occurrence of Igneous Activity ........................................................72 

5.5. Calculation Methods............................................................................................76 

5.5.1. Physical Precursors.................................................................................76 

5.5.2. Proposed Linkages to Other Volcanic Zones ..........................................77 

5.5.3. Expert Elicitation......................................................................................78 

5.5.4. Mathematical and Statistical Techniques ................................................81 

5.5.4.1. Data-Based Approach............................................................81 

5.5.4.2. Locally Homogeneous Spatial and Temporal Models............82 

5.5.4.3. Nonhomogeneous Spatial Models .........................................82 

5.5.4.3.1. Parametric Spatial Density Function......................82 

5.5.4.3.2. Nonparametric Spatial Density Function................83 

5.5.4.4. Nonhomogeneous Temporal Models.....................................83 

5.6. Treatment of Probability in Performance Assessments.......................................83 

5.6.1. DOE Analysis ............................................................................................84 

5.6.2. EPRI Analysis............................................................................................84 

5.6.3. NRC Analysis ............................................................................................84 

5.7. Perspectives on Igneous Activity Probability.......................................................85 

5.7.1. NRC Analysis...........................................................................................90 

5.7.2. DOE Analysis...........................................................................................91 

5.7.3. Probabilistic Volcanic Hazard Analysis (PVHA).......................................92 

5.7.4. DOE Igneous Consequence Peer Review (ICPR) Panel . ......................93 

5.7.5. EPRI Analysis..........................................................................................94 

5.7.6. State of Nevada Contractors ...................................................................94 

5.7.7. Nuclear Energy Institute (NEI).................................................................96 

5.7.8. Other Estimates of Probability .................................................................97 

5.7.9. ACNW&M Observations of PVHA-U........................................................98 

5.8 Summary (Igneous Event Probability)..................................................................98 

6. Consequences of Igneous Activity Intersecting the Repository ....................................101 

6.1. Introduction........................................................................................................101 

6.2. Effects from an Intrusive Event (Magma/Drift/Waste Interaction)......................101 

6.2.1. Critical Magmatic Aspects .....................................................................101 
vii

6.2.1.1. Magma Composition ............................................................101 

6.2.1.2. Magma Viscosity..................................................................102 

6.2.1.3. Perspectives on Magma Viscosity .......................................107 

6.2.1.3.1. DOE Perspective ................................................107 

6.2.1.3.2. EPRI Perspective................................................108 

6.2.1.3.3. Additional Comments on Magma Viscosity.........109 

6.2.2. DOE, EPRI, and NRC Perspectives on the Magma/Waste 

Package Interaction...............................................................................113 

6.2.2.1. DOE Perspective .................................................................113 

6.2.2.2. EPRI Perspective.................................................................113 

6.2.2.3. NRC Perspective .................................................................114 

6.2.2.4. Summary of Views ...............................................................115 

6.2.3. Number of Waste Packages Potentially Affected by Dike Intrusion ......116 

6.2.3.1. DOE Analysis.......................................................................116 

6.2.3.2. EPRI Analysis ......................................................................117 

6.2.3.3. NRC Considerations ............................................................118 

6.2.3.4. ACNW&M Comments on Magma Viscosity and 

Potential Dike Intrusion ........................................................119 

6.2.3.4.1. Magma/drift Interaction Scenarios .......................119 

6.2.3.4.2. Estimating Viscosity using Lava Flows ................120 

6.2.3.4.3. Magma Flow into Drifts ........................................123 

6.2.3.4.4. Quenching Effects on Waste Packages...............128 

6.2.3.4.5. Secondary Venting and Magma Flow in Drifts.....131

 6.2.3.4.5.1. Flow of Magma to Pressurize the Drift.......133 

6.2.3.4.5.2. Initiation of a New Fracture in the Drift 

 Roof or Wall.........................................134 

 6.2.3.4.5.3. Flow of Magma to the Surface in the New 

 Fissure................................................135 

6.2.3.4.6. Overview ..............................................................136 

6.3. Effects from an Extrusive (Volcanic) Event .......................................................136 

6.3.1. DOE and NRC Approaches...................................................................137 

6.3.2. EPRI Approach......................................................................................139 

6.3.2.1. EPRI Analyses .....................................................................141 

6.3.2.2. EPRI Comments on Tephra Dispersal Models ....................142 

6.3.3. ACNW&M Comments on Potential Fate of High-Level Waste in a 

Volcanic Conduit....................................................................................143 

6.4. Remobilization of Contaminated Volcanic Ash..................................................148 

6.4.1. Introduction............................................................................................148 

6.4.2. Characteristics of the Fortymile Wash Drainage System ......................149 

6.4.3. Approaches to Fluvial Sediment Transport and Erosion Evaluation......152 

6.4.3.1. NRC Approach to Fluvial Volcanic Ash Redistribution.........152 

6.4.3.2. EPRI Analysis of Fluvial Transport from Extrusive 

Volcanic Activity ...................................................................156 

6.4.3.3. DOE Volcanic Ash Fluvial Redistribution Model ..................156 

6.4.3.4. NWTRB Comments on Potential Consequences of 

Igneous Activity....................................................................160 

6.4.4. Effects of Transport of Contaminated Ash on Dose to the RMEI ..........160 

6.4.4.1. How Transport Can Result in a Dose...................................160 

6.4.4.1.1. Potential Dose from an Extrusive Scenario..........160 

6.4.4.1.2. Potential Dose from an Intrusive Scenario...........162 
6.4.4.2. NRC Analysis.......................................................................163

6.4.4.3. DOE Analysis.......................................................................164 

6.4.5. Remobilization Summary........................................................................165 

6.5. Summary............................................................................................................166

7. Summary/Conclusions ..................................................................................................171 

7.1. Introduction........................................................................................................171 

7.2. Nature of Anticipated Igneous Activity...............................................................172 

7.3. Probability of an Igneous Event Intersecting the Repository .............................173 

7.4. Consequences of an Igneous Event..................................................................175 

7.5. Uncertainties in Igneous Activity........................................................................176 

7.6. Alternative Models and Risk from the Proposed Repository .............................177 

8. References....................................................................................................................185

Appendix A. Status of NRC Igneous Activity Key Technical Issue Responses (2006).......... A-1

Appendix B. The Programmatic and Technical Activities of the NRC Staff in Reviewing 

Igneous Activity Associated with the Yucca Mountain Project ...................................... B-1

Appendix C. Conceptual Model for Defining Natural Analogs for Future Yucca 

Mountain Volcanism and Expected Consequences......................................................C-1

Appendix D. List of Agencies, Organizations, and Individuals Receiving Preliminary 

Draft of this Report for Their Review and Comment .....................................................D-1

Appendix E. Meeting Agenda for February 2007 ACNW&M Working Group on the 

Igneous Activity White Paper ........................................................................................ E-1

Appendix F. Minutes of the ACNW&M’s February 13 and 14, 2007 Working Group on 

Igneous Activity ............................................................................................................. F-1

viii
ix

LIST OF FIGURES 

Figure 1 Map showing the location of Yucca Mountain in southern Nevada.......................4

Figure 2 View looking south from the crest of Yucca Mountain toward the 

Lathrop Wells volcanic cone and the Amargosa Desert........................................5

Figure 3 Logic chart of components involved in defining the nature of 

possible future igneous events at Yucca Mountain. ..............................................8

Figure 4 Logic chart of components involved in defining the probability of 

future igneous activity intersecting the proposed Yucca Mountain 

HLW repository......................................................................................................8

Figure 5 Logic chart of components involved in defining the consequences 

of a dike intersecting the Yucca Mountain HLW repository 

(intrusive scenario). ...............................................................................................9

Figure 6 Logic chart of components involved in defining the consequences 

of a volcanic conduit intersecting the Yucca Mountain HLW 

repository (extrusive scenario). .............................................................................9

Figure 7 NRC view of risk-significant aspects of igneous activity......................................10

Figure 8 Basaltic volcanism during the period 6 to 4 Ma in the Yucca 

Mountain region used by Crowe (2005) to predict volcanism in the 

following 2 Myr (4 to 2 Ma).. ................................................................................13

Figure 9 Actual basaltic volcanism during the period 4 to 2 Ma in the Yucca 

Mountain region. .................................................................................................13

Figure 10 Timeline of events in the Yucca Mountain region related to 

igneous activity, geological periods of time, and events in human 

evolution. .............................................................................................................17

Figure 11 Elevation map of the southwestern United States showing the 

position of Yucca Mountain and major geologic, structural, and 

topographic features............................................................................................18

Figure 12 Geological Map of the Yucca Mountain Region. ...............................................19

Figure 13 Interpretation of seismic reflection profile across Crater Flat and 

Yucca Mountain...................................................................................................20

Figure 14 Late Cenozoic (16 Ma to present) basaltic rocks of the 

southwestern United States. Note the small amount of basalts in 

the vicinity of Yucca Mountain (CF-Crater Flat). .................................................22
x

Figure 15 Summary of K-Ar and 40Ar/39Ar radiometric ages for the 

Quaternary basalts of Crater Flat. .......................................................................23

Figure 16 Southwestern Nevada volcanic field....................................................................24

Figure 17 Conceptual model of igneous activity..................................................................30

Figure 18 Inferred eruption events at the Lathrop Wells volcano. .......................................30

Figure 19 Schematic depiction of the anticipated repository tunnel (drift) 

containing waste packages within Yucca Mountain. ...........................................33

Figure 20 Identification and linkages of abstractions in the igneous intrusion 

scenario of DOE’s TSPA. ...................................................................................34

Figure 21 Dogleg scenario. .................................................................................................35

Figure 22 Identification and linkages of abstractions in the eruption scenario 

of DOE’s TSPA. ..................................................................................................36

Figure 23 A contour plot illustrating the expected tephra dispersion for a 

violent Strombolian eruption................................................................................38

Figure 24 Schematic diagram of processes involved in ash remobilization. .......................39

Figure 25 Resuspended fraction of deposited material from the Anspaugh 

et al. (2002) equation for long-term resuspension, redrawn using a 

linear presentation...............................................................................................40

Figure 26 Pleistocene and Pliocene volcanoes in Crater Flat.. ...........................................43

Figure 27 Volcanic explosivity index....................................................................................43

Figure 28 The 1968 Strombolian eruption of Cerro Negro Volcano, 

Nicaragua. ...........................................................................................................45

Figure 29 Locations of basaltic volcanoes in the Yucca Mountain region. ..........................59

Figure 30 Photos of Yucca Mountain area. .........................................................................60

Figure 31 Photo of Yucca Mountain area at Crater Flat. .....................................................60

Figure 32 High-resolution aeromagnetic map......................................................................63

Figure 33 Estimated extension rates in Crater Flat basin as a function of 

time and magma volume erupted as a function of time. .....................................68

Figure 34 Age vs. volume of Plio-Pleistocene volcanic episodes in the Yucca 

Mountain region...................................................................................................68
xi

Figure 35 Plot of fissure length (lines) and lava effusion rate (dots) for PlioPleistocene volcanoes of the Southwestern Nevada Volcanic 

Field.....................................................................................................................69

Figure 36 Age and distribution of Pliocene-Pleistocene basaltic volcanoes in 

Crater Flat-Lunar Crater zone (CFLC). ...............................................................71

Figure 37 The number of volcanic events as a function of time in the Lunar 

Crater-Reveille Range and Yucca Mountain areas. ............................................72

Figure 38 Spatial distribution of expected volcanic event frequency defined 

by the Probabilistic Volcanic Hazard Analysis Expert Panel. ..............................80

Figure 39 Conditional dose and expected dose from extrusive igneous 

activity. ................................................................................................................85

Figure 40 Comparison of selected estimates of the probability of future 

volcanic intersection of a repository at Yucca Mountain....................................100

Figure 41 Schematic depiction of cinder cone volcanism and the underlying 

magmatic eruptive column. ...............................................................................104

Figure 42 Relative viscosity as a function of capillary number. ........................................105

Figure 43 Viscosity (μ) as a function of crystallinity (Φ). ...................................................106

Figure 44 Magma phase diagram showing change in viscosity (μ) as a 

function of temperature. ....................................................................................107

Figure 45 Phases in a volcanic eruption column ...............................................................108

Figure 46 Details of the near surface eruption thermal trajectory and the 

possible rheology if the magma quenches to a glass........................................109

Figure 47 The increase in viscosity in response to increasing crystallinity 

during the final stages of ascent for a water-saturated magma 

containing 4 wt.% water. ...................................................................................110

Figure 48 Magma viscosity calculated at 1150o C during near-surface ascent 

and degassing. .................................................................................................111

Figure 49 The solubility of volatiles in magmas is a function of temperature, 

pressure, and the compositions of the liquids and gases..................................120

Figure 50 Radial extent of the Lathrop Wells, Nevada, lava field as a 

function of the duration of the flow event...........................................................122

Figure 51 The extent of flow of a single lava flow on an inclined surface as a 

function of time, flow thickness and lava effective viscosity. .............................123
xii

Figure 52 Photomicrographs of thin sections of samples of lava from Lathrop 

Wells..................................................................................................................124

Figure 53 The penetration distance of magma into a repository drift as a 

function of magma viscosity and as a function of time . ....................................127

Figure 54 Photos of quenched magma. ............................................................................129

Figure 55 The time to grow a quenched rind on a cool surface as a function 

of time for a basaltic magma or lava..................................................................130

Figure 56 Schematic of zones of intruding magma effects in a repository drift 

on the engineered barrier system .....................................................................140

Figure 57 Schematic cross-section through Shirtcollar Butte, Crater Flat, 

Nevada, a Pliocene (3.7 Ma) basalt volcano.....................................................143

Figure 58 Median tephra diameter distribution plotted with spent fuel particle 

size distributions used in TPA versions 3.1 to 4.1.............................................145

Figure 59 Cross-section of a fuel pellet after irradiation in a reactor core. .......................146

Figure 60 Crush-impact experimental results and photo of xenolith with 

basalt rind..........................................................................................................147

Figure 61 LANDSAT Thematic Mapper image showing the Fortymile Wash 

drainage system ................................................................................................150

Figure 62 Landsat Thematic Mapper image showing the hypothesized active 

part of the Fortymile Wash depositional (or alluvial) basin in red......................154

Figure 63 Plot of calculated accelerated erosion following potential tephra 

fall......................................................................................................................155
xiii

LIST OF TABLES 

Table 1 Ages, volumes, and eruptive characteristics of PliocenePleistocene volcanoes in the Southwestern Nevada Volcanic Field ...................44

Table 2 Igneous activity input parameters to Total-System Performance 

Assessment.........................................................................................................53

Table 3 Summary information for completed PVHA-U Drill Holes....................................62

Table 4 Previous confidence rankings for anomalies now reinterpreted 

with data from PVHA-U drilling and dating ..........................................................64

Table 5 Summary of published perspectives on probability of igneous 

activity .................................................................................................................86

Table 6 Summary of the impacts on waste packages and specifically 

containment and controlled-release functions of barriers, for each 

of the three zones for the expected intrusive-release variant case.. .................117

Table 7 Peak discharges at stream gauges along Fortymile Wash. ..............................151

Table 8 Estimated peak discharges (m3/s) along stream channels of 

Fortymile Wash at Yucca Mountain...................................................................152

Table 9 Summary of computed values of mass interception fractions of 

fallout from nuclear tests at the Nevada Test Site.............................................161

Table 10 Summary of views on significant igneous activity topics (organized 

by the risk triplet). This table is a simplification and generalization 

of views that are reviewed in the report.............................................................179
xiv

 This page intentionally blank. 
xv

EXECUTIVE SUMMARY1

Eighty thousand years ago a small-volume basaltic volcano (Lathrop Wells) erupted 

about 15 miles south of the Department of Energy’s (DOE) proposed high-level radioactive 

waste (HLW) repository in Yucca Mountain, Nevada. Lathrop Wells is one of a series of 

infrequent basaltic volcanoes that have occurred near the proposed repository site during the 

past 10 million years. This NUREG report presents the Advisory Committee on Nuclear Waste 

and Materials (ACNW&M) summary and analysis of the range of current technical views on the 

nature, likelihood and potential consequences of future igneous activity at the proposed 

repository. This report responds to the request of the U.S. Nuclear Regulatory Commission 

(NRC) in SRM M06011B, February 9, 2006. The technical views have been abstracted from 

published literature and public agency reports and presentations. The alternative views reflect 

uncertainties of the igneous processes that have occurred in the region and those that are likely 

to occur in the future, as well as the interaction of these processes with the proposed repository. 

Analysis of the views and observations is based on professional judgment and quantitative 

considerations within the scope of the resources available to the ACNW&M. 

Two possible scenarios that involve different processes and consequences can be 

associated with the potential intersection of the repository with igneous activity. The extrusive 

(volcanic) scenario involves intersection of a volcanic-cone-forming conduit through the 

repository to the surface, possibly causing destruction of the waste packages intersected by the 

conduit and dispersal of contaminated volcanic ash over the Yucca Mountain vicinity. Very small 

particles of radioactively-contaminated ash from the volcanic eruption would be inhaled by the 

reasonably maximally exposed individual (RMEI). Current performance assessment calculations 

indicate that the largest dose from igneous activity is from a volcanic intersection during the first 

thousand years after closure of the repository. These calculations suggest that the maximum 

probability-weighted dose is only a fraction of the current dose standard and decreases with 

time. The principal factors in determining risk from the extrusive scenario are the probability of 

the event, including consideration of the probable location of future events and their recurrence 

rate, the number and contents of waste packages disrupted and entrained in the erupted ash, 

the eruption volume and the dispersal of the contaminated ash, the size distributions of the 

waste particles and ash, surface remobilization of contaminated ash by water and wind, and 

inhalation of the ash by humans. 

The other scenario involves intrusion of an igneous dike into the repository, leading to 

possible damage or destruction of waste packages and premature release of the waste to 

infiltrating waters that pass through the repository to the vicinity of the RMEI where radioactive 

materials in the waste could be ingested directly or indirectly from vegetation and animals that 

have taken up the radioactively contaminated ground water. The maximum effect of the igneous 

intrusion scenario is not expected to occur for tens of thousands of years due to slow movement 

of the water from the repository to the vicinity of the RMEI. Present performance assessment 

calculations indicate the maximum probability-weighted dose from the intrusive scenario also is 

likely to be only a fraction of the current standard. The major factors in determining risk from the 

intrusive scenario, in addition to the probability of the event, are the number of waste packages 

affected by the intruding molten rock (magma) (determined by the viscosity of the magma and 

-- 

1

 References to sources of information presented are excluded in the Executive Summary. 

Detailed references to all specific sources of information and views on future igneous activity at 

Yucca Mountain are provided in the body of this report. 
xvi

the magnitude and duration of the pressure upon entry), the extent of dissolution of 

radionuclides by infiltrating ground water, the rate at which ground water transports 

radionuclides to the vicinity of the RMEI, and the amount of radionuclides ingested by the RMEI. 

The risk from these scenarios depends on the likelihood of the occurrence of an igneous 

event during the compliance period of the repository and the effect of or consequences from the 

event. Consequences depend on the nature of the anticipated igneous activity which is informed 

by investigations of past geologic and tectonic activity in the Yucca Mountain region, interpreted 

within the constraints of knowledge of geologic and physical processes. The nature, likelihood, 

and consequences of future igneous activity intersecting the proposed repository make up the 

risk triplet. 

More than a quarter of a century of study of the volcanic history of the Yucca Mountain 

region has provided an almost unprecedented amount of information on igneous activity that is 

useful for predicting future volcanic activity. As a result, the divergence of views among 

investigators regarding the nature of future igneous events is relatively small. General 

agreement exists that future igneous activity is likely to be a small-volume, single-episode 

basaltic volcano similar to the 80,000-year-old Lathrop Wells volcano. Although uncertainties 

remain, this agreement extends to related parameters of the event such as power and duration, 

volume and type of erupted products, size of the volcanic conduit supplying lava to the surface, 

spatial relationship of the eruption to the topographic surface, geochemical characteristics of the 

magma, and igneous dike characteristics from which the volcano originates. 

Recent detailed studies of nearby basaltic volcanoes in the Yucca Mountain region have 

provided an improved understanding of nominal eruptive behavior, including the style of lava 

effusion, that place controls on the nature of the possible igneous event scenarios. For 

example, the conditions necessary for explosive phreatic eruptions (maar volcanism, involving 

heating and expansion of groundwater) do not exist at Yucca Mountain. There is also no 

evidence that maar volcanoes formed near Yucca Mountain during the last 10 million years and 

they are not expected in the future. 

One of the more challenging aspects of the igneous activity investigation is to estimate 

the likelihood of the occurrence of future igneous events. There are no recognized 

contemporary indicators of igneous events that could occur thousands of years in the future, 

sources of magma have not been found in the nearby Earth’s crust, there is no evidence that 

the repository footprint has been intersected by igneous activity in the last 13 million years, and 

the number of volcanic events in the region from which to extrapolate into the future is limited 

compared to other basaltic volcanic regions in the southwestern United States. As a result, 

there is a range of views on conceptual models used to predict probability of igneous events 

and uncertainties exist in parameters used in evaluating the models. Nonetheless, there is 

general agreement based primarily on the location and recurrence rate of volcanism over the 

past 5 million years that the range of probability of an igneous event intersecting the proposed 

repository is from 10-9/yr to 10-7/yr. The assumption of igneous event probabilities larger than 

10-7/yr is inconsistent with the number of volcanic events that have occurred during the past 

5 million years. Moreover, care is necessary in comparing probability estimates because of 

changes in igneous event definitions during the past few decades that have progressively 

included the probability of intersecting dikes and sills of igneous material in addition to extrusive 

(volcanic) activity. 

The consequences of an igneous event are less well understood than other components 

of the risk triplet. The study of consequences from the igneous intrusion scenario has been 

more limited than other aspects of the igneous activity program and there are no generally 
xvii

appropriate analogs. Thus the models and parameterization for intrusion consequence analysis 

are less mature than other segments of the program and considerable uncertainty exists in both 

consequence models and parameters. The principal difference in views of the intrusive scenario 

is associated with magma/drift/waste interaction and the distance that intruding magma will flow 

into the drifts as a result of uncertainties in the viscosity of the magma and the magnitude and 

duration of the pressure upon entry into the drifts. Models that do not incorporate evidence that 

the magma may have relatively high viscosities, consider quenching of magma on the drifts and 

waste packages, evaluate the role of progressive solidification of invading magma, and consider 

potential barriers to magma flow from drift-roof collapse may overestimate both the number and 

extent of damage to waste packages. Additional uncertainties exist in the extrusive scenario 

consequence analysis, e.g., the range of size of spent fuel particles and ash and the effects of 

large floods on the transport of contaminated ash of significance to the inhalation dose. 

Consideration of the full range of current views on the nature, probability, and 

consequences of igneous activity which are summarized in Tables 5 and 10 lead to the 

following general observations: 

1. The nature of the occurrence and consequences of an igneous event in the Yucca 

Mountain vicinity lead to differing professional judgments and alternative views on the 

potential effect of igneous activity on the proposed high-level waste repository. As a 

result, evaluation of risk from an igneous event requires quantitative consideration of 

credible alternative views taking into account geological evidence and their physical 

bases. These analyses will be useful in evaluating risk and determining whether further 

investigations are warranted to reduce uncertainties. 

2. There is general agreement on many aspects of the nature of potential igneous events 

and the range of probability of these events in the future, despite the broad range of 

conceptual models and parameters that have been used to investigate the potential 

effects of an igneous event intersecting the proposed high-level waste repository. The 

consequences of an igneous event on the repository are more controversial and less 

well understood, but these models and their characterization are evolving. The 

significance to risk of differences in these views is not well documented. 

3. Limitations in fundamental information and knowledge of processes result in inherent 

uncertainties in evaluating igneous activity models. For example, the very low rate of 

basaltic volcanic activity over the past 5 million years in the Yucca Mountain region in 

comparison with other areas of the region leads to lower igneous activity probability 

estimates, but increases the uncertainty in the probability of such rare events. 

4. Both the extrusive (volcanic) and intrusive scenario could occur in the vicinity of the 

proposed repository in Yucca Mountain. The extrusive scenario is likely to cause a larger 

risk and the effect is greatest within the first thousand years. In time the shorter half-life, 

more radioactive nuclides in the waste will largely have decayed. The maximum effect of 

the intrusion scenario on the RMEI will not occur for several tens of thousands of years. 

Preliminary performance assessment indicates that the risk from both scenarios would 

be only a fraction of the current dose standard. 

5. Future igneous activity in the Yucca Mountain region will likely be similar to the 

characteristics of the small-volume, single-episode basaltic Lathrop Wells volcano and 

will likely occur within basins as has most of the igneous activity over the past several 

million years in the region. Certain styles of volcanism are not expected. For example, 

the conditions necessary for explosive phreatic eruptions (maar volcanism, involving 

heating and expansion of groundwater) do not exist at Yucca Mountain. There is also no 
xviii

evidence that maar volcanoes formed near Yucca Mountain during the last 10 million 

years and they are not expected in the future. 

6. General, but not total, agreement is that the igneous activity at Yucca Mountain is 

waning, with the probability that future igneous activity based on nearby volcanism over 

the past several million years is in the range of 10-9 to 10-7/yr. The ongoing elicitation of 

volcanic experts in the DOE’s Probabilistic Volcanic Hazard Assessment – Update, 

which incorporates the latest geophysical and drilling data from the Yucca Mountain 

region, will be the most up-to-date, credible estimate of the range of igneous activity 

intersection with the proposed repository. 

7. Significant disagreements exist regarding the nature of the flow of magma into drifts of 

the repository during an intrusive igneous event and the number of waste packages that 

would be damaged or destroyed by invading magma. The “dogleg” scenario in which the 

invading magma breaks out to the surface through a secondary vent after traversing 

along the drifts and interacting with the waste packages is considered to be of extremely 

low probability based on both available evidence and expert opinion. Magma physics 

indicates that flow of intruding magma into drifts would be limited and a secondary 

(satellite) vent branching from a drift (including the “dogleg” scenario) is unlikely to form 

at any time in the style of volcanism expected at Yucca Mountain. 

8. The current technical bases of several aspects of igneous activity appear to be 

insufficiently developed or supported by available information and analyses. These 

include the range of waste particle sizes in the ash and the ash that will contribute to 

inhalation dose, the effects of large floods on the volume and distribution of 

contaminated ash in the vicinity of the RMEI, the amount of waste incorporated into ash 

versus lava during the early eruptive phase of the extrusive scenario, and the 

importance of setbacks of the repository from faults and fractured zones that are likely 

locations for dikes leading to either eruptive or intrusion scenario events. Also, there is a 

need to consider newly available information regarding volcanic conduit widths at 

repository depth. 
xix

GLOSSARY

aa flow native Hawaiian word, pronounced “ah ah”; lava flows typified by a 

rough, jagged, spinose, clinkery surface (Neuendorf et al., 2005) 

actinides heavy elements with atomic number of 80 or greater; the series is 

named for the element actinium, element 89, and includes all 

heavier elements; actinide radionuclides are found in spent nuclear 

fuel. 

adiabatic expansion increase in the volume of a substance during which no gain or loss 

of heat is allowed to occur (Lewis, 1993) 

aeromagnetic perturbation of the main geomagnetic field that is caused by 

agglomerate a chaotic assemblage of coarse, angular, pyroclastic (volcanic 

ejecta) materials; a volcanic breccia 

Alkali silicate minerals that contain alkali metals but little calcium 

(Neuendorf et al., 2005) 

alluvium a general term for unconsolidated materials deposited during 

comparatively recent geologic time by a flowing body of water as a 

fan at the base of a slope 

alpha particle nucleus of the element helium, made up of two protons and two 

neutrons; alpha particles generally do not penetrate very far any 

material, do not penetrate the outermost dead layer of the skin, but 

can damage cells in the body if inhaled or ingested; the penetration 

range of typical alpha particles in tissue is 50-80 microns

AMAD activity median aerodynamic diameter; the diameter of a sphere, of 

density 1 gm/cm3

, that has the same terminal settling velocity in air 

as that of an aerosol particle whose activity is the median for the 

entire aerosol (Shleien et al., 1998) 

amphibole a group of dark, rock-forming ferromagnesian silicate minerals 

(examples include hornblende, anthophyllite, cummingtonite, 

tremolite, and actinolite) 

anomalies variations in the magnetization of the nearby Earth’s crust 

aphyric texture said of the texture of a fine-grained or aphanitic igneous rock which 

lacks phenocrysts 

ash volcanic ejecta under 2 mm in diameter 
xx

asthenosphere the layer or shell of the Earth below the lithosphere, which is weak 

and in which isostatic adjustments take place, magma may be 

generated in this shell, and seismic waves are strongly attenuated; 

it is part of the upper mantle (Neuendorf et al., 2005)

basalt general term for dark-colored mafic igneous rocks, commonly 

extrusive but locally intrusive composed chiefly of calcic 

plagioclase and clinopyroxene 

base surge a ring-shaped cloud of gas and suspended solid debris that moves 

radially outward at high velocity as a density flow from the base of 

a vertical explosion column accompanying a volcanic eruption 

bocca an aperture on any part of a volcano from which magma or gas 

escapes

caldera a large, generally roughly circular, basin-shaped volcanic 

depression formed by collapse after a voluminous volcanic 

eruption 

cation an atom or molecule that has lost an electron and thus acquired a 

positive electric charge (Lewis, 1993) 

clast an individual constituent, grain, or fragment of a sediment or rock, 

produced by the mechanical weathering of a larger rock mass 

clinopyroxene a group name for pyroxenes crystallizing in the monoclinic system 

and sometimes containing considerable calcium with or without 

aluminum and the alkalies (examples include diopside and 

hedenbergite)

committed dose 

equivalent

dose to a specific organ or tissue that is received from an intake of 

radioactive material by an individual over a specified time after the 

intake; for radiation protection purposes, the specified time is to the 

age of 70, which is normally taken to be 50 years for a radiation 

worker and 70 years for a member of the public 

compliance period period of time that the repository must result in a dose to human(s) 

that does not exceed a specified standard dose

corrosion the electrochemical degradation of metals or alloys due to reaction 

with their environment, which is accelerated by the presence of 

acids or bases (Lewis, 1993) 

coseismic simultaneous earthquake activity or simultaneous with earthquake 

activity 

crust the outermost layer (or shell) of the Earth that is roughly 30 km 

thick in the vicinity of Yucca Mountain
xxi

density mass per unit volume (Lewis, 1993) 

dike a tabular (sheet-like) igneous intrusion that cuts across the 

bedding of the country rock (Neuendorf et al., 2005) 

dilatent a change in volume due to change in internal openings 

drift a nearly horizontal passageway in (the repository) 

(Merriam-Webster,1988) 

elicitation a formal, highly structured, and well-documented process for 

obtaining the judgments of multiple experts (Kotra et al., 1996) 

en echelon said of geologic features that are in an overlapping or staggered 

arrangement (Neuendorf et al., 2005) 

eolian borne, deposited, produced, or eroded by the wind 

(Merriam-Webster,1988) 

equilibrium constant a number that relates the concentrations of starting materials and 

products of a reversible chemical reaction to one another (Lewis, 

1993) 

equivalent committed effective dose equivalent for internal exposure; the 

equivalent dose is the product of the absorbed dose, quality 

factor, and all other necessary modifying factors at the location of 

interest; the committed dose equivalent is the dose received 

from an intake of radioactive material during the 50-year period 

following the intake (Shleien et al., 1998) 

equivalent dose is a measure of the radiation dose to tissue where an attempt has 

been made to allow for the different relative biological effect of 

different types of ionizing radiation 

exsolve to separate or unmix from a solid solution into two distinct phases 

(Neuendorf et al., 2005) 

extrusive scenario hypothetical future event in which a volcanic conduit (which 

develops along a dike) intersects an underground repository, 

interacts with waste packages, incorporates some nuclear waste 

material in volcanic ash, and carries it to the surface

felsic an adjective applied to a light-colored rock such as granite or 

rhyolite 

Fickian diffusion the spontaneous mixing of one substance with another when in 

contact or separated by a permeable membrane; the rate of 

diffusion is proportional to the concentration of the substances; the 

theoretical principles are stated in Fick’s laws (Lewis, 1993) 
xxii

fission product a fragment (usually 2 or 3) produced in fission (splitting) of a 

nucleus; most fission products decay by beta-gamma, positron, or 

electron capture decay; many fission products have relatively short 

half-lives (less than 100 years) 

fluvial pertaining to rivers 

geodetic data data pertaining to the position on the Earth’s surface or the Earth’s 

size, shape, and surface deformation 

graben an elongate, relatively depressed crustal unit or block that is 

bounded by (normal) faults on its long sides 

half-life the time needed for a radioactive material to decay to one-half of 

original amount 

high-level radioactive (1) the highly radioactive material resulting from the reprocessing

Holocene an epoch of the Quaternary period, from the end of the Pleistocene 

to the present time (Holocene began 11,800 yrs ago - International 

Commission on Stratigraphy: http://www.stratigraphy.org/chus.pdf)

horst an elongate, relatively uplifted crustal unit or block that is bounded 

by faults on its long sides 

hydrovolcanic term encompassing all volcanic activity that results from the 

interaction between lava, magmatic heat, or gases and meteoric or 

connate water at or near the Earth’s surface (Neuendorf 

et al., 2005)

igneous activity processes involving magma (molten rock) 

ignimbrite deposits of rhyolite ash derived from flowing ash clouds erupted 

from a volcano that flow along the Earth’s surface 

intrusive scenario hypothetical future event in which a basaltic dike intersects an 

underground repository and interacts with high-level waste 

packages

isothermal at constant temperature (Lewis, 1993) 

kernel a weighting function used in non-parametric estimation techniques; 

kernels are used in kernel density estimation to estimate the 

density function of random variables, or in kernel regression to 

estimate the conditional expectation of a random variable 

liquidus the line (or curve) of points in a temperature-composition diagram 

representing the maximum solubility (saturation) of a solid 

component or phase in the liquid phase 
xxiii

lithosphere the outer, relatively rigid layer of the Earth, including the crust, 

which responds to stress by folding or faulting 

lithospheric plate a torsionally-rigid, plate-like segment of the outer layer of the Earth 

lithostatic vertical stress derived from the weight of the overlying rocks 

lognormal distribution a normal distribution that is the distribution of the logarithm of a 

random variable (see normal distribution) (Merriam-Webster 

1988) 

maar a low relief, coneless volcanic crater formed by a single explosive 

eruption; it is surrounded by a crater ring and is commonly filled by 

water (examples in northern Death Valley, Ubehebe Crater and 

associated smaller maars) 

mafic said of igneous rock composed chiefly of one or more 

ferromagnesian, dark-colored minerals (e.g., basalt) 

magma naturally occurring molten or partially molten rock material 

generated within the Earth and capable of intrusion and extrusion 

(Neuendorf et al., 2005) 

magnetic pertaining to magnetic fields 

mantle rock rock existing in zone in the Earth above the core and below the 

crust 

micron micrometer (one millionth of a meter) 

Miocene an epoch of the upper Tertiary period, after the Oligocene and 

before the Pliocene (Miocene began 23.03 Myr ago and ended 

5.33 Myr ago according to the International Commission on 

Stratigraphy: http://www.stratigraphy.org/chus.pdf)

nanostrain 10-10 mm 

neutron activation nuclear reaction between a neutron and a stable element to form a 

radioactive form of the target element; metals that have been 

exposed to high neutron flux, like the metal components of a 

nuclear reactor, contain neutron activation products 

normal distribution a probability density function that approximates the distribution of 

many random variables (Merriam-Webster, 1988)

normal fault a fault in which the hanging wall appears to have moved downward 

relative to the footwall; the angle of the fault is usually 45-90o 

order of magnitude a range of values that begins at any value and extends to ten times 

that value (Lewis, 1993) 
xxiv

orogeny the process of forming mountains 

oxidation originally, a reaction in which oxygen combines chemically with 

another substance; usage has broadened to include any reaction 

in which electrons are transferred; the substance that loses 

electrons is oxidized; the substance that gains electrons is reduced 

(Lewis, 1993) 

paleosurface surface of the Earth formed in previous time 

petrology origin, composition, occurrence, structure, and history of rocks 

phenocryst term used for relatively large, conspicuous crystals in rocks that 

contain crystals of different sizes 

phreatic said of a volcanic eruption or explosion of steam, mud, or other 

material that is not incandescent; it is caused by the heating and 

consequent rapid expansion of groundwater due to an underlying 

igneous heat source 

plagioclase a group of triclinic feldspar minerals of the general formula 

(Na, Ca) Al(Si,Al)Si2O8) 

plate tectonic paradigm theory of the movement of crustal plates on the Earth through 

geologic time 

Pleistocene an epoch of the Quaternary period, after the Pliocene of the 

Tertiary period and before the Holocene (Pleistocene began 1.81 

Myr ago and ended 11,800 years ago according to the 

International Commission on Stratigraphy: 

http://www.stratigraphy.org/chus.pdf)

Pliocene an epoch of the Tertiary period, after the Miocene and before the 

Pleistocene (Pliocene began 5.33 Myr ago and ended 1.81 Myr 

ago according to the International Commission on Stratigraphy: 

http://www.stratigraphy.org/chus.pdf)

pyroclastic clastic rock formed from materials (ejecta) derived from a volcanic 

eruption 

radiation dose a generic term that includes absorbed dose (the amount of ionizing 

radiation absorbed in matter), effective dose, equivalent dose, 

committed effective/equivalent dose (see total effective dose 

equivalent) (Shleien et al., 1998) 

radioactive decay the decay of an atomic nucleus by emission of a particulate and 

electromagnetic radiation; radioactive decay is described by an 

exponential function 

radioactive material any material exhibiting radioactivity (see radionuclide)
xxv

radioactivity a property of some matter whose atoms undergo spontaneous 

transformation in its nuclear resulting in the emission of particulate 

and electromagnetic radiation 

radionuclide an isotope of an element (either natural or artificial) that exhibits 

the property of radioactivity (Lewis, 1993) 

remobilization the action by wind or flowing water to move deposited ash or other 

fine particulate material downwind or downstream from the original 

point of deposition 

Reynolds number the function used in fluid flow calculation to determine whether flow 

is streamline or turbulent; proportional to flow velocity and density; 

inversely proportional to viscosity (Lewis, 1993) 

rheology study of the deformation or flow of matter and the relationship 

between stress and strain, and the responses of rock to 

deformation (Neuendorf et al., 2005) 

rhyolite volcanic form of granite, felsic volcanic rocks 

RMEI the reasonably maximally exposed individual is a hypothetical 

person who (a) lives in the accessible environment above the 

highest concentration of radionuclides in the plume of 

contamination; (b) has a diet and living style representative of the 

people who now reside in Amargosa Valley, Nevada; (c) uses well 

water with average concentrations of radionuclides based on an 

annual water demand of 3000 acre-feet; (d) drinks 2 liters of water 

per day from wells drilled into the ground water at the location as 

specified in item a; and (e) is an adult (10 CFR 63.312) 

scoria large size pyroclasts irregular in form and generally very vesicular 

sedimentary pertaining to or containing sediment (Neuendorf et al., 2005) 

seismicity the phenomenon of movements in the Earth’s crust (Neuendorf 

et al., 2005) 

spent fuel cladding the outer jacket of nuclear fuel elements which contains and 

supports the fuel material, protects the fuel, and prevents the 

release of fission products into the reactor coolant

spent nuclear fuel nuclear fuel that is removed from a nuclear reactor after a period of 

time, either because fission is no longer maximally efficient or 

because some desired product is to be extracted; spent fuel 

contains fission products, actinides formed by neutron capture and 

decay, and neutron activation products, as well as some unreacted 

fissile material 
xxvi

stratovolcano a volcano that is constructed of alternating layers of lava and 

pyroclastics 

Strombolian a type of volcanic eruption characterized by jetting of clots or 

fountains of fluid basaltic lava from a central crater (Neuendorf 

et al., 2005) 

subduction the process of a lithospheric plate descending beneath another 

plate (Neuendorf et al., 2005) 

tabular sheet-like intrusion

tachylite a volcanic glass formed from basaltic magma that is commonly 

found as chilled margins of dikes, sills, or flows

tectonic event a geologic event involving the deformation or fracturing of the 

Earth 

tephra a collective term used for all pyroclastic material ejected during an 

explosive volcanic eruption 

tomographic methods determining the physical property (e.g., velocity) distribution from a 

multiplicity of observations using combinations of source and 

receiver locations 

total effective dose the sum of the dose equivalent for external exposure and the

TPA (also TSPA) total performance assessment of the proposed repository; 

performance assessment is a process which (1) identifies the 

features, events, processes and sequences of events that might 

affect the Yucca Mountain disposal system and their probabilities 

of occurring during 10,000 years after disposal, (2) examines the 

effects of these on the performance of the disposal system over 

the compliance period, and (3) estimates the dose incurred as a 

result of releases (10 CFR 63.2); TPA is the acronym for the NRC 

performance assessment code, and TSPA is the DOE 

performance assessment code system 

transtension a system of stresses that tends to cause oblique extension 

(i.e., combined extension and strike slip) 

viscosity the internal resistance to flow exhibited by a fluid (Lewis, 1993) 

volatile an element or compound that has a vapor pressure equal to or 

greater than 0.1 mm Hg that is not a gas at ambient temperatures 

(Lewis, 1993) 
xxvii

waste (HLW) of spent nuclear fuel, including liquid waste produced directly in 

reprocessing and any solid material derived from such liquid waste 

that contains fission products in sufficient concentrations; 

(2) irradiated reactor fuel (10 CFR 63.2) 

xenolith an inclusion in an igneous rock to which it is not genetically related; 

as used here it refers to pieces of country rock from the walls of a 

volcanic conduit that are carried to the surface during an eruption, 

and often have outer rinds of quenched magma 
xxviii

This page intentionally blank.
xxix

ABBREVIATIONS 

AMAD activity mean aerodynamic diameter (for particles) 

BSC Bechtel SAIC Company LLC

CFR Code of Federal Regulations

CNWRA Center for Nuclear Waste Regulatory Analyses (San Antonio, TX) 

CRWMS M&O Civilian Radioactive Waste Management System Management and Operating 

 Contractor 

DOE U.S. Department of Energy 

EPA U.S. Environmental Protection Agency 

EPRI Electric Power Research Institute 

FEP Features, Events, and Processes 

FGR Federal Guidance Report 

HLW high-level radioactive waste (also see glossary) 

ICPR Igneous Consequences Peer Review (Panel) (Detournay et al., 2003) 

NMSS (NRC’s) Office of Nuclear Material Safety and Safeguards 

NRC U.S. Nuclear Regulatory Commission 

NTS Nevada Nuclear Test Site 

NWTRB U.S. Nuclear Waste Technical Review Board 

OCRWM (DOE’s) Office of Civilian Radioactive Waste Management 

PVHA Probabilistic Volcanic Hazard Assessment 

PVHA-96 Probabilistic Volcanic Hazard Assessment published in 1996 

PVHA-U Probabilistic Volcanic Hazard Assessment – Update (final report to be published 

in mid-2008) 

RMEI reasonably maximally exposed individual 

SNF spent nuclear fuel 

TPA NRC’s Total-System Performance Assessment 

TSPA DOE’s Total System Performance Assessment 

USGS U.S. Geological Survey 

YMP (DOE’s) Yucca Mountain Project 

YMR Yucca Mountain region 
xxx

This page intentionally blank. 
xxxi

ACKNOWLEDGMENTS 

 The authors acknowledge the significant input to this ACNW&M report by the members 

and staff of the ACNW&M and the numerous geoscientists who reviewed and commented on 

previous drafts. The views expressed in this report are solely those of the ACNW&M and do not 

necessarily represent those of the U.S. NRC. 

 
1

___________________________________________________________________________ 

Evaluating Igneous Activity at Yucca Mountain: 

Technical Basis for Decisionmaking 

A Report 

Prepared by the 

Advisory Committee on Nuclear Waste and Materials 

U.S. Nuclear Regulatory Commission 

Given for one instant an intelligence which could comprehend all the 

forces by which nature is animated and the respective situation of the 

beings who composed it — an intelligence sufficiently vast to submit 

these data to analysis — it would embrace in the same formula the 

movements of the greatest bodies of the universe and of the lightest 

atom; for it, nothing would be uncertain and the future, as the past, 

would be present to its eyes. 

— P-S. Laplace, 1776 

Looking south along the crest of Yucca Mountain, Nevada, toward Amargosa Valley 

and the extinct Lathrop Wells volcano. 
2

This page intentionally blank. 
3

1. Introduction 

1.1. Igneous Activity and the Proposed Yucca Mountain Repository 

Eighty thousand years ago a small-volume basaltic2 volcano, the Lathrop Wells volcano 

erupted about 15 miles south of the Department of Energy’s (DOE) proposed high-level waste 

(HLW) repository in Yucca Mountain, Nevada (see Figures 1 and 2). This was the first 

volcanism in the immediate vicinity of Yucca Mountain for a million years, but one of a series of 

infrequent basaltic volcanoes that have occurred in the vicinity of the proposed repository site 

during the past 10 million years. This NUREG report presents the Advisory Committee on 

Nuclear Waste and Material’s (ACNW&M) summary and analysis of the range of views of the 

ACNW&M, the U.S. Nuclear Regulatory Staff (NRC) staff, and other stakeholders on the nature, 

likelihood and potential consequences of future igneous activity at the proposed Yucca 

Mountain repository. This NUREG includes additional information that was not available when 

the report was first published in June, 2007 (ACNW&M, 2007b). An article that summarizes 

highlights from this NUREG report was recently published in Eos (Hinze et al., 2008). 

Considering the documented ongoing volcanism, the proposed Yucca Mountain 

repository could be compromised by igneous activity during its compliance period. Accordingly, 

potential risk resulting from hypothetical igneous activity interacting with the proposed repository 

has been investigated as part of the assessment of the Yucca Mountain site. A risk-informed 

performance assessment uses the risk triplet for this evaluation (Kaplan and Garrick, 1981; 

Garrick and Kaplan, 1995). Components of the risk triplet for igneous activity are: What is the 

nature of a potential igneous event? What is the probability of an igneous event intersecting the 

proposed repository? And if the repository is intersected, what are the consequences of the 

igneous activity to the repository, the stored high-level radioactive waste (HLW), and the impact 

of the potential release of the waste to the environment and on dose to the reasonably 

maximally exposed individual (RMEI) assumed to be residing in the near vicinity to Yucca 

Mountain? Uncertainty in these studies results in a spectrum of professional views regarding the 

potential impact of igneous activity. A review and analysis of the technical bases for the range of 

views to these questions is the subject of this report. 

1.2. Objective and Rationale of Report 

This report responds to the following direction from the NRC in the Staff Requirements 

Memorandum (SRM) M060111B, dated February 9, 2006: 

The [ACNW&M] Committee should provide the Commission with an analysis of the 

current state of knowledge regarding igneous activity which the Commission can use 

as a technical basis for its decisionmaking. 

This report presents an overview of the current, publicly available perspectives regarding 

igneous activity. It is not intended to be an exhaustive study, but a presentation of the major 

components of current views and their principal supporting evidence. 

-- 

2

 Words defined in the glossary are italicized the first time they are used in the report. 
4

Figure 1 Map showing the location of Yucca Mountain in southern Nevada. Also 

shown are the boundaries of the Nevada Test Site and Nellis Air Force 

Range, and the major cities of Las Vegas, Reno, and Carson City (Source: 

U.S. Department of Energy). 
5

Figure 2 View looking south from the crest of Yucca Mountain toward the 

Lathrop Wells volcanic cone and the Amargosa Desert (Permission 

to use this copyrighted material granted by Abe van Luik at 

http://www.thoughtsandplaces.org). 

Accordingly, this report contains no conclusions or recommendations regarding the risk 

from igneous activity intersecting the proposed high-level waste repository at Yucca Mountain. 

Such decisions will be made by the NRC during a review of the license application for 

construction of a repository at Yucca Mountain. The NRC anticipates that the DOE will file for a 

license sometime in 2008. 

The NRC has not established definitive views on igneous activity at Yucca Mountain, 

and maintains a position of neutrality and independence during the pre-license period. 

Nonetheless, the NRC and its contractors have conducted extensive studies of the nature, 

likelihood, and consequences of igneous activity at Yucca Mountain in preparing for the review 

of the anticipated license application. The perspectives reached by the NRC from these studies 

as reported in the published literature and public documents and presentations are described in 

this report, but it is understood that these are not definitive positions of the NRC. Additional 

information about the programmatic and technical activities of the NRC and its reviews of the 

Yucca Mountain Project may be found in Appendix B (also see NRC, 2007). 

Igneous activity describes processes associated with the origin, nature, transport, 

emplacement, and solidification of molten rock, or magma. Magma comes from rock melted in 

the Earth that may rise to the surface because of the net effects of tectonic stresses, density 

variations, and gas pressure. Rising magma may solidify at depth to form intrusions or may 

breach the surface to form volcanoes or other volcanic deposits (i.e., lava sheets or ash flows 

(ignimbrites)). Volcanic and intrusive activity is restricted to regions that are actively undergoing 

sub-crustal dynamic or tectonic processes, and the location of the proposed DOE HLW 

repository at Yucca Mountain occurs within such a region Risks to health may arise if humans 

are exposed to radioactive materials released from the repository during volcanic activity by 

resuspension of deposited or remobilized material or by premature release to ground water of 

radionuclides from waste packages damaged by magma entering into the proposed repository. 

As a result, the DOE has conducted extensive studies over the past few decades to evaluate 
6

the potential risk from igneous activity at the Yucca Mountain site and surrounding region. Other 

interested parties including the NRC also are studying the potential risk from igneous activity. 

Evaluation of hazards and risk from igneous activity over periods of thousands of years 

or more is a major challenge to the scientific community. Long-term quantitative predictions, as 

required in the case of the HLW repository, have been made only in recent decades using 

primarily probabilistic techniques based on past igneous events of the region. However, 

procedures for implementing predictions and the nature of the data used in making predictions 

are not standardized and there are limitations in data and experimental evidence. This leads to 

varying professional judgments with attendant uncertainties and variations in hazard estimates, 

particularly in the case of infrequent, low-volume basaltic volcanism, as in the Yucca Mountain 

region. 

There is a base of knowledge regarding the fundamental magmatic processes leading to 

volcanic activity and near-surface intrusions in the Yucca Mountain region, but many 

uncertainties remain. In addition, it is difficult to determine the existence of low-volume magma 

source zones at their sub-crustal depths as well as the controls on the movement of magma 

through the Earth’s crust which could be useful in long-term predictions of the occurrence of 

volcanic events. 

Estimation of risk from igneous activity is further complicated by differences in views 

regarding the nature and behavior of magma and its potential impact on entering underground 

openings that contain waste packages. Appropriate geologic analogs of consequences from the 

intersection of magma and underground openings do not exist. As a result, both evaluating the 

probability of igneous activity at the proposed repository and the impact of this activity on the 

repository throughout the compliance period have been the subject of extensive investigations 

and considerable variation in professional views. 

During the past few decades significant progress has been made in determining the 

technical bases for predicting risk from an igneous event at the HLW repository. Accordingly, 

the purpose of this report is to present the range of views and their current technical bases, 

including the nature and probability of igneous activity intersecting the repository during the 

mandatory time of compliance, the potential consequences of this interaction, and hypothetical 

radiation doses. 

The EPA and NRC regulations pertaining to the proposed Yucca Mountain HLW 

repository specify that assessment of the performance of the repository provide reasonable 

assurance that the EPA dose standard will be met throughout the time of compliance. 

Performance assessment is used for the quantitative evaluation of the repository. It is a 

probabilistic method that incorporates the uncertainty in the scenarios, models, and parameters 

and involves repeated calculation of the performance of the repository (“realizations”) using 

samples of the input parameter distributions. Cumulative distributions of the results are 

compared to the standards established by the EPA for the repository. 

1.3. Scope of Report 

This report reviews the technical bases for estimating the risk from igneous activity that 

could occur at the proposed Yucca Mountain high-level waste repository during its prescribed 

time of compliance. Accordingly, the scope of this report is limited to the post-closure period of 

the repository. The post-closure period is defined as the 10,000 years following closure, the 

period of time that has been considered in the majority of current igneous activity investigations 

of Yucca Mountain. The Environmental Protection Agency’s (EPA) current draft revised 
7

standards for the Yucca Mountain repository prescribe that consideration of features, events, 

and processes (FEPs), which includes igneous events, shall be based on the 10,000 years 

following repository closure as had been detailed in the current regulation at 40 CFR Part 197. 

This is incorporated into the proposed changes to 10 CFR Part 63 (70 FR) based on the EPA’s 

assertion that data and models used to prepare performance assessment for the first 10,000 

years provides adequate support for projections through the period of geologic stability and 

limits uncertainties associated with speculation of performance over very long time periods (i.e., 

hundreds of thousands to a million years). 

This report provides a review of the current public perspectives taken by the DOE, NRC, 

and other interested parties on issues dealing with the nature, probability, and impact of igneous 

activity on the proposed Yucca Mountain repository. Where appropriate, observations are 

provided on perspectives unsupported by measurement or extrapolated from existing data or on 

perspectives that differ from EPA standards or NRC regulations. Every attempt is made to 

identify uncertainties in perspectives and issues. The State of Nevada has not established 

specific views on the impact of future igneous activity at Yucca Mountain, however, contractors 

supported by the State of Nevada have published several professional journal articles related to 

the probability of an igneous event intersecting the proposed repository. These articles are 

reviewed in this report. 

1.4. Content and Organization of Report 

Chapter 2 is a brief review of the geologic history of the Yucca Mountain region and 

serves as the basis for subsequent chapters on the nature of future igneous activity and the 

likelihood of its occurrence. Figures in this chapter show the geographic location of various 

geologic features treated in subsequent chapters. 

Chapter 3 presents an overview of the principal processes involved in igneous activity. 

Chapters 4, 5, and 6 review the state of knowledge available in documents and published 

materials regarding the nature, likelihood, consequences, and risk from potential igneous 

activity in the context of the risk triplet questions. Chapter 7 summarizes our conclusions. 

The essential components involved in answering each question are shown in the logic 

diagrams (Figure 3, Figure 4, Figure 5, and Figure 6). They include and expand on 

consequence effects of a figure originally published in Crowe et al. (2006). The oval shapes in 

the figure are uncertain elements of the logic flow that are treated probabilistically, while the 

rectangular shapes are decision parameters that have been determined either subjectively or by 

general agreement of the engineering and scientific community based on the inputs feeding into 

them in the logic diagrams. The bold ovals are conditional parameters that are convolved 

(multiplied) to determine the probability-weighted dose as a function of time which is compared 

to the standards of the repository and the irregular hexagon is the performance assessment 

probability. 
8

Figure 3 Logic chart of components involved in defining the nature of possible 

future igneous events at Yucca Mountain. 

Figure 4 Logic chart of components involved in defining the probability of future 

igneous activity intersecting the proposed Yucca Mountain HLW 

repository. 
9

Figure 5 Logic chart of components involved in defining the consequences of a dike 

intersecting the Yucca Mountain HLW repository (intrusive scenario). 

Figure 6 Logic chart of components involved in defining the consequences of a volcanic 

conduit intersecting the Yucca Mountain HLW repository (extrusive scenario). 
10

The NRC has reported risk insights for various aspects of igneous activity and scenarios 

and the NRC has assigned relative rankings of medium to high significance to waste isolation 

(NRC, 2004). A number of these rankings are illustrated in Figure 7. For example, the 

probability of an igneous event is considered to have high significance with respect to waste 

isolation. Wind speed and direction are considered to have medium significance to waste 

isolation. 

Figure 7 NRC view of risk-significant aspects of igneous activity (After Hill, 2007). 

The NRC’s (2004) risk insights were generally framed around the risk triplet. Risk 

insights were stated in terms of a scenario, essentially as a statement of the feature, event, or 

process that might exist or occur in the post-closure repository system. The risk insights 

baseline provided context for understanding the likelihood that the feature, event, or process will 

exist or occur during the compliance period. The baseline also included a discussion of the 

consequence of the feature, event, or process, in terms of its beneficial or adverse effect on the 

waste isolation capabilities of the repository system. Effects on waste isolation subsequently 

affect the estimated dose to an individual, in other words, risk. Although individual risk insights 

are supported by quantitative analyses, classifying the risk insights by relative significance to 

waste isolation was more qualitative. Staff judgment was used when combining information 

from different analyses. The NRC evaluated significance relative to the waste isolation 

capabilities of the repository system. Three criteria were considered (NRC, 2004) in evaluating 

the significance of the risk insights: 

 • Effect on the integrity of waste packages; 

• Effect on the release of radionuclides from the waste form and waste package; and 

• Effect on the transport of radionuclides through the geosphere and biosphere. 
11

High significance is associated with features, events, and processes that could (1) affect 

a large number of waste packages; (2) significantly affect the release of radionuclides; or 

(3) significantly affect the transport of radionuclides through the geosphere or biosphere. 

Medium significance is associated with a lesser effect on waste packages, radionuclide 

releases, or radionuclide transport, and low significance is associated with no or negligible effect 

(NRC, 2004). 

The summary and conclusions reached in this ACNW&M report are presented in 

Chapter 7. A listing of the status of NRC key technical issue responses and the agencies, 

organizations, and individuals receiving an initial draft of this report for their review and 

comment, plus the agenda and minutes of the Working Group held on February 13 and 

14, 2007, are provided as appendices. Other appendices include the NRC’s programmatic and 

technical activities in review of igneous activity associated with the Yucca Mountain project 

(NRC, 2007), and EPRI’s new report on conceptual models for future volcanism at Yucca 

Mountain and their expected consequences. 

1.5. Report Preparation Process 

This report has been prepared by members and staff of the ACNW&M with the 

assistance of a consultant who is an expert on igneous activity and magma physics. An initial 

draft of the report was sent to the NRC, the DOE, the State of Nevada, and other stakeholders, 

and to a group of external experts in related disciplines for their review and comment (see the 

list in Appendix D). Subsequently, the stakeholders were invited to a working group meeting 

convened by the ACNW&M to discuss igneous activity at Yucca Mountain and to provide them 

with an opportunity to recommend appropriate revisions to the report. Specifically, stakeholders 

were requested to address the following questions: 

• Does the ACNW&M report address the risk-significant topics related to igneous 

activity at Yucca Mountain? 

• Does the report capture the range of views of the interested parties with respect to 

the technical bases for decisionmaking on these topics including definitions of 

volcanic events, geologic periods of interest in predicting probability, igneous activity 

probability, magma/drift interaction leading to both extrusive, intrusive scenarios, 

potential consequences for the risk from a high-level waste repository, etc.? If not, 

the positions detailed in the report will be clarified from published position papers in 

the final ACNW&M report. 

Additionally, at the working group meeting a group of distinguished experts on the 

various aspects of igneous activity and high-temperature processes provided an overview of the 

challenges facing technical decisionmaking on igneous activity at Yucca Mountain and a 

description of the status of knowledge of relevant volcanic features, events, and processes. The 

experts also participated in a panel discussion on the completeness and quality of the content of 

the ACNW&M report where they commented on the following questions: 

• Has an effective and accurate understanding of the various views on volcanism been 

identified and documented in the report? 

• Have the risk significant topics regarding igneous activity been identified? 

• Are the technical bases for positions taken for determining risk from igneous activity 

at Yucca Mountain scientifically correct? 
12

• Are there risk-significant topics regarding igneous activity that have not been 

adequately addressed considering the current state of the science? If so, how can 

they be addressed? 

The public also was invited to present their comments on the draft. All of the comments 

and results of the discussion of the working group were reviewed and considered by the 

ACNW&M as part of finalizing the report. 

1.6. Constraints on the Report 

There are several constraints on the report and its conclusions that limit the technical 

bases for decisionmaking regarding igneous activity. These include the following: 

• Critical decisions about the design of the repository and waste packages that may 

affect the probability and consequences of igneous activity are not final. For 

example, there is as yet no decision on the maximum temperature of the repository. 

This decision will affect the distribution of waste packages and the areal size of the 

repository, both important parameters in establishing the probability and 

consequences of igneous activity. Pending decisions about backfill of the drifts, the 

alloy to be used in construction of the waste packages, and the use of an inner 

canister also are important to the effects of igneous activity. (Note: Although 

changes in the areal footprint of the repository could affect probability calculations, 

the tendency for dikes to follow pre-existing faults or to be influenced by topographic 

effects could compensate for this by diverting dikes away from emplacement drifts.) 

• Ongoing DOE and NRC studies that relate to the probability and effects of igneous 

activity have not been included in this report. The DOE, for example, is currently in 

the process of updating the 1996 Probabilistic Volcanic Hazard Analysis (PVHA – 

96) with a new expert elicitation using data from new geosciences investigations 

(PVHA-U). The NRC is conducting studies of eolian (wind) redistribution of 

contaminated ash to the vicinity of the RMEI, the interaction of magma and the 

repository and waste packages, and the significance to risk from secondary satellite 

volcanic vents that may occur adjacent to the main vent of a volcano. 

• Many process models are incorporated into the performance assessment of igneous 

activity at Yucca Mountain, but few of these models have been validated with 

realistic data or simulations. Accordingly, there are limitations in the confidence that 

can be placed in the results of the analyses. For example, the volcanic models used 

to determine the hazard from basaltic volcanism are largely determined from past 

volcanic events of the region, but prediction of basaltic volcanism over several time 

slices within the past 10 million years (10 Ma) in the Yucca Mountain region 

(Crowe, 2005) using previous volcanism and the geologic structure of the region as a 

predictive tool were not notably successful in specifying the location of actual new 

clusters of volcanoes or volcanic fields that occurred within the region over the period 

of the time slice. Figure 8 shows the results of Crowe’s prediction of volcanism 

between 4 and 2 Ma based on the record of basaltic volcanism in the Yucca 

Mountain region between 6 and 4 Ma. The actual volcanism observed from this time 

period is shown in Figure 9. As noted by Crowe (2005) in this figure the actual 

volcanism (results) are mostly unexpected based on the basaltic volcanism of the 

previous 2 Ma. 
13

Figure 8 Basaltic volcanism during the period 6 to 4 Ma in the Yucca Mountain 

region used by Crowe (2005) to predict volcanism in the following 2 Myr. 

Extent of volcanism shown in green (After Crowe, 2005). 

Figure 9 Actual basaltic volcanism during the period 4 to 2 Ma in the Yucca Mountain 

region. Exposed basalts of this age range are shown in green and green stars 

are magnetic anomalies that are interpreted to have a source of basaltic 

volcanism during this time interval. Note the significant spatial displacement 

of much the volcanism during this period from the basaltic rocks of the 

previous 2 Myr (Figure 8) (After Crowe, 2005). 
14

• Studies related to igneous activity at Yucca Mountain published in professional 

journals generally are subjected to intense peer review. As a result, data and 

conclusions of journal articles are credible. However, subsequent studies may show 

different results and interpretations of the data. Thus, conclusions presented in 

journal articles, such as those referenced in this report, must be carefully evaluated 

in the light of subsequent publications. A case in point is geodetic data that describe 

the ambient strain of the Yucca Mountain region which has considerable importance 

to understanding and predicting potential seismicity and volcanic activity in the 

region. Geodetic observations prior to mid-1999 that were obtained from point global 

positioning satellite (GPS) observations replicated at intervals showed a strain of an 

order of magnitude greater than indicated by geologic observations which reflect 

mean long-term strain rates (Wernicke et al., 1998). This led Wernicke et al. (1998) 

to conclude that hazard analysis may be underestimated by an order of magnitude. 

However, follow-on investigations suggest that these results may be in error (Savage 

et al., 1999) or represent a geologically recent spike of increased crustal strain 

(Connor et al., 1998; Wernicke et al., 2004). Subsequent GPS studies in the Yucca 

Mountain region are based on continuous observations which enhance the data 

quality. They suggest that the earlier strain rates may be too high by a factor of 

roughly two (Wernicke et al., 2004). 

• The scope of this report is limited to the post-closure period of the repository after the 

underground repository has been sealed off from the surface. Preclosure igneous 

activity is not considered. Although the unlikely probability exists that igneous activity 

could occur during the preclosure period with its resulting impact upon waste stored 

on the surface for aging purposes and emplaced in drifts of the repository as well as 

on workers and surface structures, systems, and components at the repository, there 

is no evidence from precursor indicators that imminent igneous activity is likely over 

the short span of the preclosure period (~100 years). DOE (1999) in its preclosure 

event prevention strategy is designing preclosure structures, systems, and 

components to withstand bounding igneous events, but the NRC (2005a) has 

pointed out the lack of consideration of tephra and ash falls which could impact the 

roof loads and effects on ventilation and filter systems. The NRC (2005a) also has 

written that the DOE should provide the technical basis to exclude hazards from lava 

flows to the potential repository surface operations area. It is unclear to ACNW&M 

why the NRC has preclosure concerns about lava flows. Lavas extruded in Crater 

Flat could not reach the ridge-top location of Yucca Mountain. The genesis of lava 

on the mountain itself at the repository site has an extremely low probability (10-9/yr 

to 10-7/yr) that falls below the cutoff value (1 chance in 10,000) for consideration as a 

Category 2 event during preclosure (10 CFR 63.2). Finally, the genesis of lavas on 

the eastern side of Yucca Mountain where preclosure facilities would be located 

should have an even lower likelihood of occurrence than on the mountain itself 

because there is no evidence of post-Miocene volcanism in Jackass Flats. 

1.7. Previous Reviews of Igneous Activity Technical Bases 

Understanding and predicting the role of igneous activity throughout the lifetime of the 

proposed Yucca Mountain repository has been one of the more challenging topics of the 

characterization of the repository site. Accordingly, progress on the technical bases for making 

decisions on igneous activity has been under review for nearly two decades. The Nuclear Waste 

Technical Review Board (NWTRB) has monitored progress in the DOE program at regular 

intervals and the NRC’s program in igneous activity has held the interest of the ACNW&M since 
15

the inception of the Committee. The igneous activity program of the NRC and the differing 

opinions regarding the results of the program among the State of Nevada, the DOE, and the 

NRC has encouraged reviews by standing advisory (review) committees and ad hoc panels of 

specialized experts. 

The ACNW&M has sent eight letters to the Chairman of the Commission with its 

observations and recommendations on the NRC’s igneous activity since 1989. (Committee 

letters since 1989 are available on the NRC’s Web site at http://www.nrc.gov/reading-rm/ 

doc-collections/acnw/letters/.) These letters have dealt with the importance of a multidisciplinary 

approach to igneous activity studies, magma/drift/waste package interaction in the intrusion 

scenario, the significance of accurate isotopic dating of basalts of the Yucca Mountain region to 

the estimation of the probability of future igneous events, the importance of minimizing 

uncertainties in the results of the studies, and the need for a risk-informed approach to igneous 

activity studies. In addition, the Center for Nuclear Regulatory Waste Analyses (CNWRA), the 

laboratory supporting the NRC’s repository analysis program, has conducted external previews 

of their igneous activity studies (Hill, 1995; McKague, 1998; Sparks and Woods, 1998). These 

reviews have made specific recommendations regarding topics that have received special 

attention. 

The DOE’s igneous activity study program, supported by personnel from Los Alamos 

National Laboratory and the U.S. Geological Survey, has been complemented with external 

peer review panels. In 1996 the DOE completed a 2-year expert elicitation, the Probabilistic 

Volcanic Hazards Assessment, which established the probability distribution of the annual 

frequency of intersection of the proposed repository by volcanic activity on the basis of the 

evaluation of ten experts following the guidelines for expert elicitations set forth in NUREG-1563 

(Kotra et al., 1996). This elicitation is being updated (Probabilistic Volcanic Hazards 

Assessment – Update) taking into the account the considerable amount of new geosciences 

information about igneous activity at the proposed repository. Support for this new elicitation 

came from the DOE’s external Igneous Consequences Peer Review (ICPR) Panel (Detournay 

et al., 2003) which was constituted to review the potential consequences and effect upon risk 

due to an igneous intrusion intersecting the proposed repository. A major emphasis of this 

panel, which released its final report in 2003, was to review the interaction between the intruding 

magma and the repository drifts and to recommend studies by the DOE that would reduce 

uncertainties in the overall igneous activity program. The results of these reviews have brought 

knowledgeable, fresh insight into the program. 

The NWTRB reviews the DOE studies on igneous activity on a regular basis. The 

NWTRB has reported the results of these reviews and suggestions for further studies in regular 

reports to Congress and letters to the DOE Office of Civilian Radioactive Waste Management 

since 2000 (NWTRB; 2001, 2002, 2003, 2004). 
16

This page intentionally blank. 
17

2. Brief Geologic History of the Yucca Mountain Region 

The geologic history of the Yucca Mountain region, including both its structural 

development (tectonics) and history of volcanic activity, form the foundation for understanding 

the past and for predicting future igneous activity in the region. The geological structure of the 

region has a direct impact on the magma source zones and the specific location of volcanic 

activity. As a result, the nature of tectonism is critical to predicting the probability and nature of 

volcanism. As stated by McKague et al. (2006) in referring to the implications of tectonic models 

on the probability of occurrence of a volcanic eruption or igneous intrusion at Yucca Mountain: 

For volcanism to occur, the physical and chemical conditions for magma formation 

must exist at some depth, and a path must be established between this magma 

source and the Earth’s surface. Both these sets of conditions together with the style 

and frequency of igneous activity are determined by tectonic setting. More locally, the 

in situ stress state and presence or absence of faulting and fracturing are factors 

controlling magma ascent through the crust. 

This section provides an overview of the tectonic and igneous activity history of the region. 

The literature on this topic is too extensive to cover comprehensively in this report, but useful 

recent reviews of the subject that contain critical references have been prepared by Crow et al. 

(1995; 2006), Parsons (1995), O’Leary (1996, 2007a), Grauch et al. (1999), and McKague et al. 

(2006), Lipman (2007), and Stuckless and O’Leary (2007). A simplified history of the Yucca 

Mountain region is illustrated in Figure 10. 

Figure 10 Timeline of events in the Yucca Mountain region related to igneous activity, 

geological periods of time, and events in human evolution. 

The State of Nevada and the Yucca Mountain region are located in the Central Basin 

and Range geological province (the Western Great Basin) which is noted for topography 

consisting of generally north-south trending, alternating elongate valleys (basins) and mountain 

ranges that extend into adjacent states and continue south into northwestern Mexico (Figure 
18

11). The geological history of this region is long and complex with periods of tectonic activity, as 

illustrated in the general geologic map of the region (Figure 12). The area was last subject to 

mountain building during the Laramide orogeny that occurred as a series of tectonic pulses 

separated by quiescent periods, from about 70 to 40 Ma3

. The Rocky Mountains, with generally 

easterly-directed thrust faults and folds that extend from Alaska to northern Mexico, originated 

during this orogenic event. The mountain building episode was caused by collision of a 

lithospheric plate off the west coast with the North American plate. The western plate was 

subducted beneath the North American plate at a low angle resulting in the broad zone of 

mountain building observed in the western United States. The sedimentary and igneous rocks

that form the base of the volcanic rocks in the Yucca Mountain region were complexly faulted 

and folded during the Laramide and earlier orogenies (Dickinson, 2006). 

Figure 11 Elevation map of the southwestern United States showing the position of 

Yucca Mountain and major geologic, structural, and topographic features 

(After McKague et al., 2006). 

-- 

3

 Ma is the abbreviation for age in millions of years; Myr is the abbreviation for a duration of time in millions of 

years. 
19

Figure 12 Geological Map of the Yucca Mountain Region (From DOE, 2002). 
20

The Basin and Range province is an active extensional region within the North American 

western Cordillera. It is named for the topographic manifestation of the most recent mode of 

extension which consists largely of block faulting with normal faults typically dipping at a steep 

angle to the west. The current tectonic activity within the region is indicated by its high heat flow, 

seismic activity, recent basaltic volcanism, thin crust, and observed strain rates. Unlike most rifts 

that have undergone normal faulting and lithospheric extension, the Basin and Range province 

is very broad, reaching a width of more than 900 km. Extension commenced about 25 Ma ago 

resulting in a variable amount of stretching across the region with an average total extension of 

approximately 100%. Relatively small magnitude extension in the Yucca Mountain region of the 

Central Basin and Range from approximately 13 to 10 Ma produced the steep (~ 60o

) normal 

faulting that results in the characteristic Basin and Range topography with ranges such as 

Yucca Mountain and basins such as the adjacent Crater Flat basin and Jackass Flats (Figure 

13). The Crater Flat basin is described as a half-graben which is “...the southern extremity of a 

much deeper, broader crustal depression that hosts the caldera of the southwestern Nevada 

volcanic field.” (O’Leary, 2007a). It is shown by the geophysical interpretation in to extend from 

Bare Mountain to east of Yucca Mountain into Jackass Flats. Also see the map by Faulds et al. 

(1994) that describes the geology of eastern Crater Flat basin. The source of the extension 

causing the half-graben is uncertain, but it is thought to originate from the Pacific Plate moving 

northwest relative to the North American Plate. This same force created the San Andreas fault. 

Other forces may be involved, including those related to the movement of the North American 

Plate over the spreading center associated with a plate to the west. There is evidence that an 

early stage of extension may have occurred at the end of the Laramide orogeny as a result of 

gravitational collapse of an overthickened crust, followed by extension related to spreading of 

the continental crust associated with disintegration or steepening of the plunge of the 

subducting oceanic plate. 

Figure 13 Interpretation of seismic reflection profile across Crater Flat and Yucca 

Mountain (After BSC, 2004b). 

In addition to the late-stage normal faults, several other types of faulting have occurred 

in the region. Low-angle normal faults that occur in isolated locations represent an earlier stage 

of extension, but their origin is controversial. The Yucca Mountain region is a complex structural 

belt resulting from its location in the transition between the Walker Lane, which lies on the 

eastern margin of a distributed shear zone, the Eastern California Shear Zone (Figure 11), that 
21

extends north-northwest from the southeastern corner of Nevada, across Nevada, and into 

California, and the Basin and Range province to the north and east. The Walker Lane structural 

feature, dating back a few tens of millions of years, is characterized by north-northwest striking 

right-lateral displacement and north-northeasterly directed left-lateral displacement faults and 

consists of an assemblage of independent structural units. Its origin lies in distributed shear 

forces arising from movements in the continental crust to the west. Both normal faults of the 

Basin and Range province and the shear faults of the Walker Lane are prominent in the Yucca 

Mountain region. 

Several tectonic models have been proposed to explain the origin of the structures of the 

Yucca Mountain region and to assist in extrapolating those features into the subsurface. It is 

their subsurface extent and orientation that have a significant role in relating them to volcanic 

and seismic activity. The models can be classified into three groups based on the principal 

mode of deformation that is incorporated into their explanation: extension, shear, and volcanic. 

This is not surprising because of the overlap in the region of shear deformation associated with 

the Walker Lane, the extensional forces prominent in the Basin and Range province, and the 

massive, intense volcanism 11 to 15 Ma ago. McKague et al. (2006) recognize eleven viable 

models and present a description of and the bases for each of these models employing the 

most recent geologic, geodetic, and geophysical data. They conclude that no single tectonic 

model explains the structural deformation of the region. However, they point out that the active 

faults, high strain rates, and deep faults identified with the shear models are of concern when 

considering the potential for igneous activity in the Yucca Mountain region over the lifetime of 

the repository. O’Leary (2007a) identifies the pure shear (planar fault) model as the preferred 

tectonic model for the region. 

Igneous activity appears to coincide with the Basin and Range province extension, but 

the relationship is variable across the province. Magmatism is particularly well correlated with 

the early stage of extension involving low-angle faulting, but not necessarily with late stage 

normal faulting. The widespread igneous activity over the Basin and Range province is well 

summarized by Parsons (1995). 

 Voluminous felsic volcanism occurred in the Yucca Mountain region ~7 to 15 Ma ago. 

This is the final portion of the extensive “ignimbrite flare up” of felsic, relatively high silica 

volcanism which advanced across the Basin and Range province from the north to the Yucca 

Mountain region. The source of the felsic volcanic rocks is largely from the melting of crustal 

rocks as a result of heat from the mantle and intrusions into the lower crust. The felsic rocks are 

the result of collapse of calderas over felsic magma chambers causing immense flows of the hot 

ash (ignimbrites) and ash falls which make up Yucca Mountain. These rocks which have been 

subsequently faulted by late stage normal faulting and shear faulting of the Walker Lane make 

up the repository rocks. They consist of both welded and unwelded tuffs. The welded tuffs are 

ash flows deposited in a sufficiently hot state that the ash particles welded together. 

During the period from about 9 to 11 Ma the felsic volcanism in the Yucca Mountain 

region transitioned to mafic (basaltic) magmatism. Basaltic volcanism was widespread over the 

southwestern United States during the subsequent period of time and much more voluminous in 

many other areas in contrast to the Yucca Mountain region. At least four known pulses of 

basaltic volcanism occurred (DOE, 2003) in the Yucca Mountain vicinity. These include the 
22

~80 ka Lathrop Wells cone and flows (Heizler et al., 1999), ~1 Ma events (Pleistocene or 

Quaternary4

) in Crater Flat (Figure 15), and multiple events dated ~3–5 Ma (Pliocene) and 

~8–13 Ma (Miocene). No basaltic volcanism is known to have occurred between 5 and 7 Ma. 

 

Figure 14 Late Cenozoic (16 Ma to present) basaltic rocks of the southwestern United 

States. Note the small amount of basalts in the vicinity of Yucca Mountain 

(CF-Crater Flat) (After Perry, 2002). 

Other young basalts in the Yucca Mountain region (YMR) include Little Black Peak 

(~0.3 Ma) and Hidden Cone (~0.4 Ma), located about 35 km NW of Yucca Mountain. Large 

exposures of Miocene basalts occur in Jackass Flats, at Dome Mountain in the Timber 

Mountain caldera complex, and in proximity to the Black Mountain caldera. Miocene-age basalts 

also occur in western Crater Flat, and as a dike complex in Solitario Canyon on the 

northwestern flank of Yucca Mountain. All of these occur within the Southwestern Nevada 

-- 

4

 The Pleistocene Epoch and the Quaternary Period are used synonymously in this document and much of 

the literature on igneous activity of the Yucca Mountain region for the time period between 11.8 ka and 1.8 

Ma. Note that by international agreement the Quaternary formally extends from the present time to 2.5 Ma 

(Intl. Commission on Stratigraphy, 2006). 
23

Volcanic Field (Christiansen et al., 1977; Grauch et al., 1999) which is the site of intense 

episodic, voluminous magmatism and variable intense extension over the period from 9 to 17 

Ma and subsequent waning basaltic volcanism (Figure 16). It covers an irregular area with a 

radius of roughly 50 km generally centered on the Timber Mountain Caldera Complex 

immediately north of the proposed repository. 

Figure 15 Summary of K-Ar and 40Ar/39Ar radiometric ages for the Quaternary basalts 

of Crater Flat. Error bars represent ±2σ. Symbols at bottom of chart are 

abbreviations for each cone (M=Makani Cone; B=Black Cone; R=Red Cone; 

and L=Little Cones) (After Valentine et al., 2006, Figure 2) (σ = standard 

deviation) (Permission to use this copyrighted material is granted by the 

Geological Society of America). 
24

Figure 16 Southwestern Nevada volcanic field. The limit of the Southwestern Nevada 

Volcanic Field indicated by the dashed line (from Byers et al., 1989). 

Several volcanic calderas have been identified as the sources of the 

intense felsic volcanic activity in the field. The Crater Flat caldera is no 

longer generally recognized (After Crowe et al., 1995) (Permission to use 

this copyrighted material is granted by the American Geophysical Union). 

The frequency and volumes of basaltic volcanism have declined significantly since 

Miocene time (DOE, 2003). For example, Jackass Flats has widespread Miocene basalts but 

no known post-Miocene volcanism. Magnetic surveys indicate that additional basalts may be 

buried beneath alluvium in Crater Flat and the Amargosa Desert (Stamatakos et al., 1997; 

Connor et al., 2000; O’Leary et al., 2002; Hill and Stamatakos, 2002; Perry et al., 2005). 

Basaltic rocks have an intense magnetization in contrast to the alluvial sediments of the basins 

and thus are readily mapped by anomalies in the normal Earth’s magnetic field. The magnetic 
25

variations (anomalies) resulting from buried basalts may be either positive or negative 

depending on the polarity of the Earth’s magnetic field at the time the basalts solidified. 

Additional details regarding the temporal and spatial occurrence of basalts dating back to 10 Ma 

are presented in Chapter 5. 
26

This page intentionally blank. 
27

3. Overview of Igneous Activity Processes 

3.1. Introduction 

The logic charts of Figure 3, Figure 4, Figure 5, and Figure 6 show the components 

involved in evaluating the nature and likelihood of future igneous activity at Yucca Mountain and 

the potential consequences of this activity. The consequences are based on both the intrusive

and extrusive (volcanic) scenarios and their interaction with the repository and the waste 

packages. The processes involved in these scenarios are integral to the technical bases for 

decisions about igneous activity at the proposed Yucca Mountain HLW repository. Accordingly, 

this chapter briefly explains processes related to the origin and nature of igneous activity (Figure 

3), magma/repository interaction (Figure 4, Figure 5, and Figure 6), dispersal of contaminated 

ash and its remobilization (Figure 6), and the doses to the RMEI from the contaminated ash 

(Figure 6). 

3.2. Origin and Nature of Igneous Activity 

3.2.1. Magma Generation 

The origin and nature of igneous activity is important to understanding the processes 

that may impact the risk from the proposed Yucca Mountain repository. Knowledge of the 

scientific basis of igneous activity has progressed steadily during the past century, but growth 

has been particularly dramatic in the past 40 years with the development of the plate tectonic

paradigm and rapid advances in the geochemistry of igneous rocks and modeling of magmatic 

processes (e.g., Fisher et al., 1997; Decker and Decker, 1997; Schmincke, 2004). 

Magma is primarily generated at depths of several tens of kilometers in the lower crust

and upper mantle along crustal boundaries where plates making up the outer lithosphere of the 

Earth are colliding (convergent boundaries) or being pulled apart (divergent boundaries) by sublithospheric movements within the mantle. Plates at convergent boundaries may be drawn into 

the Earth (subducted) to depths great enough to cause partial melting of the upper surface of 

the plate. At divergent boundaries, along mid-ocean ridges and continental rifts, lateral 

extension or rifting of the lithosphere moves deep, hot rock upward. This rock then undergoes 

partial melting in response to the decrease in pressure. Partial melting leading to magma 

production in Earth’s mantle also occurs in response to isolated ‘thunder-head-like’ motion. 

Rising plumes of hotter rocks occur independent of plate margins and produce localized 

igneous activity and voluminous volcanism on the continents (e.g., Yellowstone) and in the 

oceans (e.g., Hawaiian Islands). The deep-seated processes giving rise to the magmas 

responsible for the igneous activity in the Yucca Mountain region are not well understood. This 

magmatism probably reflects residual heat effects and chemical variations in the upper mantle 

associated with the extensional tectonics that has been the hallmark of the area for the past 

25 Myr. 

Partial melting of mantle rock produces buoyant basaltic magma, which ascends as 

magma-filled cracks (dikes) and as magmatic plumes (diapirs). Most basaltic magma does not 

reach the Earth’s surface, but becomes encumbered at depth due to solidification or loss of 

buoyancy. In continental terrains, stalled basaltic magma contains sufficient heat to melt the 

already hot adjacent lower continental crust, generating fresh magma that moves upward 

toward the surface as in the case of the volcanism that pervaded the Yucca Mountain region 10 

to 12 Ma ago. This rising magma reflects the composition of the local continental crust, which is 
28

much closer to granite (i.e., rhyolitic) in composition, and is distinctly non-basaltic, as are the 

volcanic rocks making up Yucca Mountain. Volcanism in continental terrains, like the western 

United States (including Yucca Mountain), is thus commonly bimodal, with rhyolitic magmas 

from melting of the lower crust and basaltic magmas from the venting of small, deep-seated 

mantle reservoirs of partial melts. Small-volume basaltic volcanism, as has occurred over the 

past several million years in the Yucca Mountain region, is commonly inferred to be derived 

from small pockets of magma that are formed and triggered into movement toward the surface 

by motion in the mantle reflected by crustal tectonic movements. This magma undergoes some 

fractionation and contamination while traveling upward through the crust. For additional 

discussion about background theory on magma chambers see Marsh (2000, 2006). 

3.2.2. Magma Composition 

The physical nature and behavior of magma intimately reflects its chemical composition. 

All Earth magmas are polymeric solutions of silica (SiO2) diluted by varying amounts of cations 

(mainly, Al, Fe, Mg, Ti, Ca, Na, K, P). The silica content of magma, the basis of all rock 

classification schemes, varies from ~50 to 75 percent by mass reflecting the chemistry of the 

source rock from which the magma was generated. There is a complete compositional 

gradation from basalts with ~50 percent silica to rhyolites (essentially molten granite) with 70-

75% silica. The temperature range of crystallization, the viscosity (or rheology), and most other 

transport properties are strongly dependent on magma silica content. Basalts crystallize at 

much higher temperatures and are much less viscous than rhyolites. This reflects the less 

polymerized nature of the melt forming the magma. The viscosity of a melt increases and the 

melt becomes more difficult to deform as it becomes more silica-rich and thus more 

polymerized. At the same temperature and free of crystals, basalt is a factor of ~104

 times less 

viscous than rhyolite. 

A critical parameter in determining the consequences of igneous activity at Yucca 

Mountain is rheology. The single most important influence on the rheology of any given magma 

is the buildup of crystals as magma crystallizes. Most magmas crystallize over a span of about 

200o

 C in temperature. Crystals build up from none at the liquidus to 100% by volume at the 

solidus. Liquidus temperatures vary from the order of 1200o

 C in basaltic rocks to as low as 700o

C in granitic rocks depending on their composition, depth, and volatile content. Higher 

concentration of crystals strongly increases magma viscosity and as the maximum packing of 

crystals approaches ~50 percent, the magma becomes a rigid, dilatant solid that expands upon 

shear and resists all motion. At maximum packing, as in a cup full of ice cubes, all solids 

(crystals) are touching and cannot undergo shear unless the assemblage expands as 

neighboring crystals move outward and past one another. With magma held within solid rock, 

there is no room for expansion. Consequently, no magma is ever erupted containing more than 

~50 percent crystals of a given size. 

Volatiles dissolved in magma are of central importance in determining the nature of 

volcanism and the risk from igneous activity at the proposed repository. Apart from the 

availability of volatiles, magma composition, temperature, and confining pressure are the major 

factors in controlling the concentration of volatiles in magma. The principal magmatic volatiles 

are H2O, CO2, and SO2, with water the most common primary constituent. The solubility of 

water in magma is a function of water vapor pressure. The solubility is directly proportional to 

pressure and also to magma silica content. A silica-rich magma, like rhyolite, can contain far 

more water than basalt at the same pressure and temperature. Because the solubility of water 

in magma is zero under surface conditions of one atmosphere total pressure, as magma 

approaches the Earth’s surface it inevitably becomes saturated with water and generates 
29

bubbles, much as when a diver gets the bends from bubbles forming in the blood as the diver 

rises toward the surface. Volatiles also have a major effect on the viscosity of magma. Water in 

solution, for example, de-polymerizes the melt structure, greatly reducing viscosity. Adding 5% 

(mass) water to a rhyolite at 1000°C and sufficiently high pressure (several MPa) will reduce the 

viscosity by a factor of 107

. The effect is much smaller with basalt, but still important. Water also 

significantly reduces the temperatures of crystallization. 

3.2.3. Volcanoes and Their Products 

Magmas rise from source regions of molten rocks by buoyancy due to lower density of 

the melt and gas bubbles of vapor and when the overpressure exceeds the tensile strength of 

the overlying rocks. The melts rise largely as near-vertical disk-like slabs or dikes, which are 

typically several meters wide in the Yucca Mountain region. In the absence of pre-existing 

weaknesses in the overlying rocks, the dikes propagate in the direction perpendicular to the 

least compressive stress (Valentine and Krogh, 2006; Keating et al., 2007; Perry et al., 2006, 

Connor et al., 2000). Otherwise dikes tend to follow paths of least resistance, which typically 

are existing fracture zones. The magma may freeze within the crust and stop rising, but if the 

magma reaches the surface a volcanic eruption occurs with the ejection of molten lava, gases, 

and fragmental materials through a vent into the atmosphere (Figure 17). The nature of the 

eruption controls the characteristics of the volcanic deposits and the relative proportion of 

eruptive products. For example, at the 80 ka-old Lathrop Wells volcano the eruption began with 

cone building. Next, the fan-like lava flows that to violent Strombolian activity with episodes of 

sustained eruption columns that deposited tephra over the adjacent region (depending on the 

wind direction) and produced the major portion of the scoria cone. The latter was accompanied 

by additional lava flows as indicated in D. The estimated volumes of the products of the Lathrop 

Wells volcano (Krier et al., 2006) are (1) fallout, 0.039 km3

, (2) scoria cone, 0.018 km3, and (3) 

lava flows, 0.029 km3

 (total volume ~0.086 km3). 

The NRC approach currently assumes that all waste packages entrained in a conduit

would be extruded as volcanic ash fallout. In his presentation to ACNW&M, Sparks (2007) 

noted that the 1973 Eldfell eruption (Iceland) included the simultaneous extrusion of degassed 

lava and explosive activity. Sparks considers this eruption to be a close analog to the eruption 

at Lathrop Wells, 80 kyr ago. Based on observations at several analog eruptions he suggests 

that the magma starts at a temperature ~1000o

 C, but erupts at 1030o-1055o C due to the heat 

production attending the latent heat of crystallization. Insights provided by Sparks (2007) 

suggest that the extrusion scenario for Yucca Mountain should consider that a substantial 

fraction of waste entrained within a volcanic conduit would become locked up in lava flows or a 

scoria cone. Because these features resist erosion over hundreds of thousands of years, any 

contained waste would contribute little or no dose to the RMEI. 

Volcanic cones accumulate around erupting magma fountains. The pile of material 

forming the volcano, in volume, textural detail, and composition, reflects the nature and 

sequence of arrival of the ascending magma. Two convenient measures of the material type 

and of volcanic activity itself are the explosivity and mobility of erupted materials. The most 

explosive and devastating eruptions, by far, involve large volumes (10s to 1000s of km3

) of 

silica-rich and volatile–rich magma (ash flows) that erupt as dense clouds of ash and gas that 

flow along the surface move under the force of gravity to lower elevations. 
30

Figure 17 Conceptual model of igneous activity. Magma rises via dikes (left) leading 

to effusion of magma fountains along the length of dikes that reach the 

surface (center) and finally to focusing magma eruption in a conduit 

resulting in a volcanic cone (right). Arrows indicate vertical component of 

flow (After Valentine, 2006).

Figure 18 Inferred eruption events at the Lathrop Wells volcano. Presented are 

respectively simplified (a) cross-section and (b) plan view of the early stage 

of eruption; also illustrated are the later stage of eruption with cone 

building dominated by fallout (c) and effusion of the eastern lava field (d) 

(After Valentine et al., 2005) (Permission to use this copyrighted material is 

granted by the Geological Society of America).
31

Silicic ash flow eruptions have not occurred in the Yucca Mountain region for roughly 8 

million years (Thirsty Canyon tuffs; ~7.7 Ma). Instead, the region has experienced eruptions of 

small volume silica-poor, basaltic magma. Basaltic magmatic systems characteristically low in 

volatiles, like Hawaii, emit mainly high temperature (i.e., low crystallinity), low viscosity, low 

explosivity lavas of high mobility that can flow considerable distances (10s of km). Flow distance 

depends greatly on erupted volume and terrain slope. On the other hand, basaltic magmas of 

high volatile contents (>~1% by mass) become saturated in volatiles in approaching the surface 

and generate a bubble phase that can expand rapidly, fragmenting the magma into material 

ranging from fine ash (mm) to coarse tephra (cm) or cinders. The overall process is somewhat 

akin to the uncapping of a vigorously shaken bottle of soda. The early phase of the eruption is 

marked by high explosivity with the transport of ash into the atmosphere. Distribution of the ash 

to the surrounding region depends on the intensity of the explosivity and the local 

meteorological conditions. This phase of the eruptive sequence is called the Strombolian 

phase in reference to the Stromboli volcano in the Mediterranean Sea, which has delivered gascharged eruptions of this type. The extrusion of sluggish, high viscosity, low mobility lava flows 

generally follows but can accompany the Strombolian phase (Sparks, 2007). The outpourings 

are generally short-lived (~1 yr) and occur in a single (i.e., monogenetic) episode. Small volume 

(<~5 km3

) cinder (scoria) cone systems of this nature are typical of those in the Yucca Mountain 

region. None of the cinder cones in the Yucca Mountain region are interpreted as polygenetic. 

Because cinder cone events often commence with eruption from a fissure ~1 km long or greater 

(Figure 17), there is the potential that a dike associated with a cinder cone event adjacent to 

Yucca Mountain could reach far enough into Yucca Mountain to intersect the repository. 

3.3. Magma/Repository Interaction 

3.3.1. Nature of Magma Ascent 

Low viscosity magmas flow like thick syrup, travel rapidly in small meter-wide cracks and 

spread rapidly as lava flows. The transfer of basaltic magma in the upper crust, especially 

during establishment of a new volcanic vent, is mainly by magma-filled elastic crack 

propagation, as evidenced by the common occurrences of dikes of basalt in eroded volcanic 

terrains. The rate of propagation is limited by the ability of the magma to flow into the opening 

crack. If magma viscosity becomes too large, dike propagation and ascent stall and magma 

may pool or solidify in place. 

3.3.2. Key Features of Magmatic Dikes 

The features of magmatic dikes that are critical to a Yucca Mountain igneous event are 

rapid rate of propagation, the azimuthal orientation, and the large aspect ratio (length/width). 

Typical aspect ratios can be of the order of 100 to 1000. The dike is envisioned as a thin disk 

expanding upward in all directions from the point of initiation and driven by an internal 

overpressure or buoyancy. A dike one meter thick can lengthen to one kilometer or more as it 

approaches Earth’s surface. The volume of available magma limits the size of any dike as well 

as the number of dikes that can be generated in a single event. Once the dike intersects the 

surface, the internal driving pressure is dissipated through venting of the magma, compromising 

further expansion. Propagation is normally in the plane of the least principal stress, which in the 

Earth is generally vertical, and the strike or azimuthal orientation of the dike is strongly 

influenced by the principal horizontal stresses, whose magnitude and orientation reflect the 

structural makeup of the crust and the prevailing tectonic conditions. These are generally 

referred to as ‘regional stress patterns.’ Local topographic conditions, which alter the local 

stress field, can literally steer the dike to a limited degree as it reaches the surface (e.g., 
32

Gaffney and Damjanac, 2006). BSC (2004a) reports that the topography of Yucca Mountain 

would have little effect on dike propagation. Gaffney and Damjanac (2006) show a more 

detailed analysis of flow focusing given a dike ascending beneath variable topography. 

3.3.3. Basic Nature of Eruptive Event 

The nature of the eruptive event as the dike intersects the surface depends critically on 

the type of magma, its viscosity and, especially, the volatile content of the magma. With the 

amount of volatiles expected for typical basaltic magmas in the Yucca Mountain region, the 

magma will be undersaturated with volatiles until it comes within about 5 km of the surface. At 

the point of saturation a separate vapor phase will form as an assemblage of bubbles to further 

accelerate ascent. The increasing strength of this vapor phase event will eventually fragment 

the magma and form an explosive eruptive column into the atmosphere of hot gas laden with 

quenched particles of magma. The sizes of these particles will vary from fine ash to popcorn-like 

tephra. The strength and duration of an event depends on the volume of magma involved, the 

volatile inventory, the number of eruptive vents, and the geometry of the eruptive system. Lava 

can push out from the central vent through the base of the cone and flow outward under gravity. 

In these eruptions, explosive activity commonly switches back and forth between Strombolian 

activity and eruption of lavas (Valentine et al., 2006, 2007; Valentine and Keating, 2007). 

3.3.4. Magma Interaction with Repository and Waste Packages 

In the unlikely event that volcanic activity would intersect a repository (Figure 19), there 

are several scenarios for potential interaction. The consequences for future radiological 

exposures vary significantly among these. These scenarios are the intrusion scenario (including 

the so-called “dogleg” scenario) and the extrusion (i.e., volcanic) scenario. 

The first scenario, the intrusion scenario, involves hypothetical intersection of the 

repository drifts by a volcanic dike (Figure 5 and Figure 20). An ascending dike could 

theoretically be deflected around a repository by topographic and/or thermal-mechanical stress 

(Hardy and Bauer, 1991). Nonetheless, the NRC, DOE, and EPRI have considered the 

possible consequences by assuming that a dike could intersect and propagate through the 

repository and interact with the waste packages in the tunnels (drifts). As a dike approaches the 

level of the drifts, the crack tip would advance ahead of the magma front. This advancing vaporfilled cavity would be the first part of the propagating dike to reach the drift. The DOE models 

the pressure in this cavity to be negligible because of the very high gas permeability of the 

fractured nature of the local tuffaceous rock (Detournay et al., 2003). 

Detournay et al. (2003, p. 49) also commented on the possible effects of a repository on 

dike propagation, as follows: 

The stress barrier that develops around a hot repository during the intermediate period 

spanning the first 2000 years (since closing of the repository) could cause the dike to be 

deflected so as to avoid crossing of the repository, promote the creation of a sill, or halt 

propagation of the tip approaching the repository if the dike is centered a few kilometers 

north or south. Such protection is time-limited, however; it is therefore conservative to 

assume that the dike would propagate vertically under all circumstances and would 

intersect the repository. The major impact of the thermal perturbation would be to 

reduce significantly the size of the tip cavity ahead of the magma front and perhaps to 

increase the magma pressure gradient behind the magma front. 
33

Figure 19 Schematic depiction of the anticipated repository tunnel (drift) containing 

waste packages within Yucca Mountain. 

The stress barrier described by Detournay et al. (2003) would apply during the time 

when potential risk is greatest. After the first 1000 years, the hypothetical doses from the 

volcanic extrusion scenario would diminish significantly (Figure 39) because substantial 

amounts of shorter-lived radionuclides would have decayed away. 

As the basaltic magma moves upward it may degas steadily or catastrophically. Steady 

release of gas would diminish the volatile content such that the magma front would not likely 

produce violent explosive behavior when it encounters the repository. It would instead flow 

effusively into the drifts. In the hypothetical case where gas explosively exsolves, magma could 

flow into drifts as a two-phase gas-magma flow, generating tephra instead of a magma flow. 

The flow of magma into drifts may slow the progress of the magma front to the surface, but it 

should have little effect on the tip of the dike cavity, which would already have begun 

accelerating given the diminishing overburden pressure as it approaches the surface. The dike 

tip would probably reach the surface in seconds after passing the repository horizon 

(BSC, 2003a). Flow of magma into a drift would lower the pressure in the dike directly above 

the drift, but this would last only as long as it takes for the drift to become filled with magma or to 

become obstructed by a plug of tacky, incandescent tephra. The presence of backfill either 

intentionally placed or as a result of drift-roof collapse, could be beneficial from the standpoint of 

intrusive volcanism because it would minimize contact of magma with waste packages. Backfill 

would not significantly alter the extrusive scenario because if a volcanic conduit intersects a 

waste drift it would likely entrain both waste packages and the backfill itself. 
34

Figure 20 Identification and linkages of abstractions in the igneous intrusion 

scenario of DOE’s TSPA (After Valentine, 2006). 

If a dike reaches the level of the repository, magma would be available to flow into drifts 

at a rate that would strongly depend on the magma viscosity and the rate of magma 

solidification as it contacts the relatively cold drip shields, waste packages, and drift walls. The 

flow rate would also be influenced by frictional losses at the dike/drift interface and partial 

obstruction of the tunnel by waste packages and drip shields. The DOE (2003) estimates that 

magma could fill a drift in about 5 minutes, given a dike ascent rate of 1 m/s and very low 

viscosities between 10 Pa·s and 100 Pa·s. Magma rising at 10 m/s could fill a drift in less than 

1 minute. The filling time depends critically on the magma viscosity and pressure head driving 

the flow, on which there have been differing views (discussion in Chapter 6). For example, 

EPRI (2004) suggested viscosities several orders of magnitude greater than values given by the 

DOE and NRC in modeling of lava flowing into drifts. Other recent work also suggests that 

magma viscosities could be orders of magnitude greater than previously assumed, which would 

reduce the rate of magma entry to drifts (Marsh and Coleman, 2006; 2008). The potentially 

critical effects of quenching and solidification on waste packages and drift walls have not been 

fully evaluated by the DOE and NRC. 
35

A variation of the intrusion scenario for magma-repository interaction has been proposed 

whereby magma might fill a drift and create enough pressure to generate (at a distance from the 

entry point) a secondary dike to the surface as illustrated in Figure 21 (Woods et al., 2002). This 

so-called “dogleg” scenario may affect a large number of waste packages. The key factor here 

is whether the magma has the ability to fill the drift quickly and re-pressurize it to the extent of 

nucleating a new dike elsewhere along the drift, in spite of the initial flow continuing to the 

surface. This proposed process arose from the observation that magma sometimes also erupts 

from separate, secondary vents in the neighborhood of the original central vent. This “dogleg” 

model was analyzed by BSC (2003a) which considered the propagation of pressure and stress 

through the dike system and the effect of magma cooling. Detournay et al. (2003) considered 

the propagation of either a magmatic or pyroclastic “dogleg” scenario to be improbable, but 

recommended further analyses to assess the impacts of this process on repository 

performance. The viability of the “dogleg” scenario is treated more fully in Chapter 6. 

Figure 21 Dogleg scenario. Schematic of the steady flow geometry that may enable a 

steady basaltic eruption to develop (dogleg scenario): (a) with flow along 

the original dike; (b) with magma being diverted along the drift before 

surfacing along a new fissure; and (c) with magma being diverted along the 

drift and into the main access drift from where it vents to the surface (After 

Woods et al., 2002) (Permission to use this copyrighted material is granted 

by the American Geophysical Union). 
36

The extrusive igneous scenario involves the intersection of a tephra-cone-forming 

volcanic conduit with the repository drift (Figures 6, 22, and 24). A volcanic vent is the surface 

expression of a conduit. The transition from flow in dikes to conduit flow occurs early in an 

eruptive sequence, and vents form under various conditions. In low-viscosity basalts, the 

transition may occur when narrow parts of the dike freeze followed by mechanical and thermal 

erosion of wider sections as the flow is repartitioned (e.g., Bruce and Huppert, 1990). A key 

difference between a volcanic conduit and a dike is that the conduit is much smaller in diameter 

(tens of meters) than a dike is long (kilometer scale). Given a repository drift spacing of >50 m, 

a conduit could directly intersect only one drift along with a relatively small number of waste 

packages within the cross-section of the conduit. Due to the perceived complexity of the 

processes involved, both the NRC (Mohanty et al., 2004) and DOE (2003) assume that the 

small number of waste packages (approximately 1-10) entrained within a conduit would be 

completely destroyed and the contents carried to the surface and ejected as contaminated 

tephra of varying particle sizes. The degree to which ceramic or glass waste forms could be 

reduced to fine particulate materials in a volcanic conduit is uncertain, particularly during the first 

1000 years when the waste packages and waste forms should still be relatively intact. The 

manner and degree to which the fragments would be incorporated in volcanic tephra also is 

uncertain, but would involve magma quenching. 

Figure 22 Identification and linkages of abstractions in the eruption scenario of 

DOE’s TSPA (After Valentine, 2006). 
37

3.4. Dispersal of Contaminated Ash 

Ash emitted during an extrusive event that erupts through the proposed repository may 

contain fragmented radioactive waste. The contaminated ash will contribute to the dose to the 

RMEI primarily through inhalation (Figure 22). If the ash is not contaminated by radioactive 

materials, and is present in sufficient concentration, it can cause respiratory problems, but these 

will be minor and transient in healthy individuals (Calabrese and Kenyon, 1991). Accordingly, 

studies of the impact of ash on health effects associated with the Yucca Mountain repository 

have been directed at radioactively contaminated ash (DOE, 2002a). 

3.4.1. How is Ash Dispersed? 

Contaminated ash would in essence be dispersed in the same way as uncontaminated 

ash from a violent Strombolian eruption. The ash plume consists of a vertical high-speed jet, of 

which the volume and vertical extent depend on the power and duration of the eruption. The 

mixture of gases and particles rises adiabatically to an altitude where its buoyancy is neutral; 

i.e., where the plume temperature is the same as the ambient temperature (DOE, 2000). At that 

altitude, further dispersion of the ash depends on meteorological conditions. Wind has a firstorder effect, and meteorological conditions that impact the crosswind movement of gases and 

particles have a second-order effect (Wark et al., 1998). 

Dispersion of ash particles by meteorological conditions can be modeled and predicted 

in several different ways. The Suzuki model (Suzuki, 1983), which is generally accepted as 

representing the dispersion of ash from a violent Strombolian eruption, correlates well with 

reported data on ash fallout (Suzuki, 1983; Hill et al., 1998). The basic premises of this model 

are as follows: 

• Movement of dispersing particles in the air is random. 

• Small particles diffuse both vertically and horizontally in response to local 

concentration gradients. 

• The scale of horizontal turbulence is much greater that the scale of vertical 

turbulence. 

The Suzuki models involve turbulent diffusion by combining several theoretical diffusion 

formulations with empirical observation instead of using the Fickian diffusion equation that most 

Gaussian models employ (e.g., Wark et al., 1998). 

3.4.2. How does Ash become Contaminated? 

The dispersed ash from the postulated extrusive event would be contaminated by the 

incorporation of spent nuclear fuel particles over a wide range of sizes as well as by weakly 

volatile radioactive compounds. Incorporation depends on the relative densities of ash particles 

and spent fuel particles. The major constituent of spent fuel is uranium dioxide, which is about 

four times as dense as volcanic ash, so that incorporation of this material would result in 

relatively dense ash (Jarzemba, 1997; Jarzemba and La Plante, 1996). Less dense 

radionuclides, although likely to adhere to or condense on ash particles, would not increase the 

ash particle density significantly. 

Suzuki postulates ash particles from a violent Strombolian eruption with a mean actual 

diameter of about 1000 microns and standard deviations of 1000, 4000, and 20,000 microns. 

He also postulates ash particle densities between 0.1 and 2.4 gm/cm3

, but includes in his model 
38

particle densities up to 10 gm/cm3

. Assumptions about ash particle diameter and density are 

important to modeling both the direct air dispersion as well as the remobilization of ash particles 

by wind. As expected, particles of larger mass as a result of size or density will fall out of the 

eruption plume closer to the vent. Suzuki (1983) models the footprint of the plume of smaller 

(1000 to 4000 microns) ash particles as extending as far as 60 km downwind. The range 

postulated by Suzuki encompasses the Jarzemba and La Plante (1996) assumption that the 

density of contaminated ash could vary up to 5 gm/cm3

. 

Figure 23, provided here as an example, shows a sample of Suzuki model output 

produced by modeling an eruption at Irazu volcano, Costa Rica. 

Figure 23 A contour plot illustrating the expected tephra dispersion for a violent 

Strombolian eruption. The plot coordinates indicate location of the 

deposited material with respect to the eruption site. Wind is blowing from 

right to left. The vertical axis is in a northerly direction; the horizontal axis, 

easterly. The numbers refer to universal transverse Mercator UTM grid 

locations; units are meters (Source: 

http://www.cas.usf.edu/~cconnor/parallel/tephra/tephra.html#input). 

3.5. Remobilization and Resuspension of Contaminated Ash 

Remobilization refers to the movement of ash from the initial tephra deposit to the 

vicinity of the RMEI, and is accomplished by either wind or water. Resuspension occurs when 

deposited ash becomes airborne and can be inhaled by the RMEI. 
39

After deposition, the loose ash in a tephra sheet would be exposed to surface processes 

Particles with activity mean aerodynamic diameter (AMAD)5

 larger than about 100 microns, as 

well as particles with density greater than about 5 gm/cm3, would generally fall to the ground 

before reaching terminal velocity (Wark et al., 1998). Settling of these particles would most 

likely be within tens of meters of the eruption vent. Smaller and less dense particles could then 

be remobilized. Precipitation, wind, and ephemeral surface water flow would begin to erode, 

rework, transport, sort, and redistribute the finer-grained ash. Intense, ephemeral floods 

associated with major storms have the potential to extensively erode tephra deposits, but the 

large flood discharges also can transport radioactive materials long distances, to the vicinity of 

the RMEI or beyond. Fine-grained materials can be moved to the vicinity of the RMEI where 

they can be resuspended by surface winds and inhaled by the RMEI. Current models assume 

potential health effects from both the inhaled ash and ash incorporated into soils and foods 

grown from those soils. Particles containing radioactive material of AMAD 10 microns or less 

contribute more than larger sized particles to calculated doses because of the patterns of 

deposition in the human respiratory tract (Figure 24) 

In NRC’s TPA code, version 4.1J, wind was treated as unidirectional, always blowing 

toward the RMEI. A more realistic treatment of wind is now being incorporated in version 5 of 

the NRC’s TPA code. Most of the volcanic ash would not be contaminated, and only particles 

with AMADs less than about 50 microns would be lofted by the wind. Radioactively 

contaminated particles of AMAD 20 microns or less contribute more than larger sized particles 

to calculated doses because of the patterns of deposition in the respiratory tract of humans. 

Larger particles would contribute only minimally to a RMEI dose, if at all. 

Figure 24 Schematic diagram of processes involved in ash remobilization. 

-- 

5

 Movement of particles is often modeled by giving particles the radial dimension they would have if they were 

spherical particles of density 1 g/cm3

. This is the activity mean aerodynamic diameter, or AMAD. 
40

Anspaugh et al. (2002) have developed both a short-term and a long-term model for 

resuspension and the dispersion of resuspended material. Anspaugh et al. (2002) point out that 

there is at least an order of magnitude uncertainty in any long-term model of resuspension. 

Anspaugh (2004) points out that very little deposited material will be available for resuspension 

15 or more years after the particles are deposited (Figure 25). This suggests that several 

decades after an eruption, little resuspended ash would be available for inhalation by the RMEI. 

Fraction Resuspended/20 Miles

1.E-11

1.E-05

2.E-05

3.E-05

4.E-05

5.E-05

6.E-05

7.E-05

8.E-05

9.E-05

1.E-04

0 5 10 15 20 25 30 35

Time (years)

Resuspended fraction

Figure 25 Resuspended fraction of deposited material from the Anspaugh et al. 

(2002) equation for long-term resuspension, redrawn using a linear 

presentation. 
41

4. Nature of Potential Igneous Events in the Yucca Mountain 

Region 

4.1. Introduction 

The initial question in the risk triplet (Figure 3) – What can happen? is the subject of 

Chapter 4. What can happen in this case is an igneous activity event that intersects the 

proposed Yucca Mountain repository. Events may be initiated directly beneath the proposed 

repository or may reach the tunnels of the repository by dikes associated with the event 

extending into the footprint of the repository. 

The volcanic history of Yucca Mountain, and the changes in volcanism that have 

occurred with time in the Yucca Mountain region, suggest that a future igneous activity event 

would involve a particular type and volume of volcanic eruption and produce volcanic conduits 

of a particular size and shape. This assumption is supported by the geologic and tectonic 

history and the comprehensive site characterization of the Yucca Mountain region that have 

provided information on basaltic volcanism during the past 10 Myr. Additionally, geologic 

investigations of other volcanic regions of similar age of the Basin and Range province and 

volcanological studies of modern volcanoes and their processes contribute useful information 

about the range of anticipated igneous events. There is general agreement among investigators 

on many, but not all, of the characteristics of possible future igneous activity. These views and 

their current status are identified in this chapter. 

4.2. Volcanic Analogs 

To evaluate the likelihood and consequences of an igneous event intersecting the 

proposed repository it is necessary to estimate the type, size, and shape of future igneous 

events, and their location and orientation, The importance of these attributes is illustrated in 

comparing a volcanic conduit of limited diameter to a dike whose length is measured in 

kilometers. Note that a volcanic conduit at repository depth would likely be much smaller than 

the size of the vent at the surface. A dike is more likely to intersect the repository than is a 

conduit. Volcanic vents typically form along dikes at sites where eruptive activity becomes 

locally concentrated, resulting in erosion and expansion of a local segment of dike to form a 

conduit or vent. Accordingly, if the repository were to be intersected by a volcanic conduit, it 

would also be intersected by at least one dike. The orientation and length of dikes is important 

because of the possibility of a dike extending into the repository from outside Yucca Mountain 

and the control these dike characteristics have over the number of drifts of the repository that 

would be intersected by the dike. 

Examination of volcanic analogs, in particular those originating during the past several 

million years (Table 1), provides a practical method for estimating the characteristics of volcanic 

features. The time period used to evaluate future volcanism should be reasonably 

representative of present-day conditions in the Yucca Mountain region. The DOE has 

emphasized the Pliocene-Pleistocene (Plio-Pleistocene) time period6

 for extrapolation of 

events, consistent with the approach by members of the 1996 PVHA expert panel (Geomatrix 

Consultants, 1996). However, several members of that panel considered the Pleistocene 

-- 

6

 The Plio-Pleistocene time period includes both the Pliocene (5.3 - 1.8 Ma) and the Pleistocene (1.8 Ma - 

11.8 ka) Epochs. 
42

(previous 1.8 Ma) Epoch to be the most representative and the preferred time period from which 

to extrapolate. For young (Pleistocene) volcanoes, the presence of tephra cones conceals the 

actual dimensions of the underlying conduit, but provides useful information on the nature and 

volume of the events. Pliocene vents, such as those cropping out in the Crater Flat basin, can 

be evaluated in some detail because they have been deeply eroded, exposing interior cores 

filled with agglomerate (pyroclastic debris). The dimensions of the agglomerate mass provide 

an estimate of former conduit size. 

The volcanic cones and lava flows of Pleistocene age near Yucca Mountain (Figure 26) 

provide direct analogs of the igneous activity events that could occur in the region. The 

Pleistocene volcanic cones of the Crater Flat basin, along with the Lathrop Wells cone, all occur 

in basin areas although two of the eight Pleistocene volcanoes in the Yucca Mountain region 

occur on topographic highs. The dimensions of the Crater Flat basin volcanoes indicate that the 

volume of volcanic material ranges from 0.002 km3

 (Makani volcano) to 0.06 km3 (Red and 

Black Cones), while Pliocene volcanoes in Crater Flat basin and elsewhere within the Yucca 

Mountain region have significantly greater volumes (Table 1). The products of these events also 

provide information on the eruptive power of future volcanic events anticipated in the Yucca 

Mountain region. The presence of tephra (ash) suggests that in addition to Strombolian activity, 

violent Strombolian activity occurred, with plumes of volcanic material injected into the 

atmosphere, during portions of the volcanic events. As shown in Figure 27, Strombolian 

eruptions, and violent Strombolian events which are in the upper range of Strombolian 

eruptions, are in the lower portion of the volcanic explosivity index which is used to classify the 

intensity of global volcanic eruptions. As noted in this figure Strombolian eruptions are the most 

common volcanoes globally and are associated with small volume eruptions of lava and tephra 

(ash). A photo illustrating a Strombolian eruption (Cerro Negro Volcano, Nicaragua) is shown in 

Figure 28. 

The maximum lava effusion rate for the Pleistocene Crater Flat basin volcanoes is about 

1 to 4 m3

/s while the effusion rate of the Pliocene volcanoes is an order of magnitude larger 

(Table 1). Valentine and Perry (2006) have concluded that the total length of the fissures 

associated with the Pleistocene volcanoes, which is the length of the intersection of the 

originating dike with the surface, is less than 2 km, while Pliocene volcanoes are associated 

with fissures (dikes) roughly twice this length. Valentine et al. (2005) have investigated the 

makeup of the Lathrop Wells cone and find that the bulk of the cone is composed of fine grained 

eruptive materials consistent with sustained columns of well-fragmented eruptive materials and 

laterally extensive fallout deposits as much as 20 km from the vent. 
43

Figure 26 Pleistocene and Pliocene volcanoes in Crater Flat. The 80,000-yr-old 

Lathrop wells cone is the youngest volcano in this area. Diagram courtesy 

of Dennis W. O’Leary, U.S. Geological Survey. 

Figure 27 Volcanic explosivity index, showing the position (bold arrow) of 

Strombolian eruptions like those that have occurred within the last 2 Ma in 

Crater Flat adjacent to Yucca Mountain. Violent Strombolian refers to 

eruptions in the “moderate” range of the general description. Note that the 

maximum cloud column (plume) height for Strombolian volcanoes is up to 

5 km and the maximum volume of tephra (including ash) is roughly 0.1 km3

(from Siebert and Simkin, 2002) (Permission to use this copyrighted 

material is granted by the Smithsonian Institution). 
44

The change in rate and volume of the volcanoes and of fissure length is indicative of 

waning volcanism, such as evidenced in the Reveille Range, which is approximately 100 km 

north of Yucca Mountain (Yogodzinski et al., 1996). Valentine et al. (2006, 2007) have 

concluded that the Pleistocene Crater Flat volcanoes are each derived from a single conduit 

(monogenetic) formed in a single eruptive episode lasting only a few years. Field studies 

indicate that there were shallow breakouts or secondary vents from the main conduits that fed 

lava flows (these vents are typically referred to as boccas). Valentine and Perry (2006) have 

inferred that some dikes rise vertically with limited lateral propagation and have a curved, 

convex upward leading edge in a shape similar to a tongue depressor. The occurrence of 

volcanoes on local topographic highs (Little Black Peak and Hidden Cone), without vents that 

intersect the surface at lower elevations, provide evidence for the lack of extensive lateral 

propagation. Most basaltic dikes of Miocene age, as mapped by Valentine and Krogh (2006) in 

the Paiute Ridge volcanic center located east of Yucca Flat (Nevada Test Site), occupy normal 

faults. Similarly, Valentine and Perry (2006), based on geophysical data and field evidence, 

suggest that Plio-Pleistocene volcanoes erupted along existing faults. 

Table 1 Ages, volumes, and eruptive characteristics of Pliocene-Pleistocene 

volcanoes in the Southwestern Nevada Volcanic Field (Valentine and 

Perry, 2006) (Permission to use this copyrighted material is granted 

by the American Geophysical Union). 

Volcano Age, 

Ma 

Rock 

type 

Volume, 

km3

Fissure 

length, 

km 

Lava 

flow 

length, 

km 

Maximum 

lava 

effusion 

rate, m3

/s 

Brief description 

Thirsty 

Mountain 

4.63± 

0.02 

Basaltic 

trachyandesite 

2.28 5 6 80 Broad shield volcano 

with stacked lava 

flows 

Pliocene 

Crater flat 

3.73± 

0.02 

Basalt 0.56 3.6 4 40 Low shield volcano 

with multiple lavas 

Buckboard 

Mesa 

2.87± 

0.06 

Basaltic 

trachyandesite 

0.84 2.5 7.3 100 Large lava field 

Black 

Cone 

0.986± 

0.047 

Trachybasalt 

0.06 0.6 (1.8)a

 1 0.9 Pyroclastic cone 

remnant and two lava 

fields 

Red Cone 0.977± 

0.027 

Trachybasalt 

0.06 0.5 (1.6)a

 1.4 3 Pyroclastic cone 

remnant and two lava 

fields 

SW Little 

Cone 

1.042± 

0.045 

Trachybasalt 

0.03 0.3 (0.8)a

 0.7 0.4 Pyroclastic cone 

remnant, open to the 

south, with single lava 

field 

NE Little 

Cone 

1.042± 

0.045 

Trachybasalt Included 

with SW 

Little 

Cone 

0.2 (1.8)a

 1.8 4 Pyroclastic cone 

remnant, open to the 

south, with single lava 

field 

Makani 

volcano 

1.076± 

0.026 

Trachybasalt 

0.002 0.4 0.4 0.1-0.2 Small lava mesa with 

pyroclastic deposits 
45

Volcano Age, 

Ma 

Rock 

type 

Volume, 

km3

Fissure 

length, 

km 

Lava 

flow 

length, 

km 

Maximum 

lava 

effusion 

rate, m3

/s 

Brief description 

Little Black 

Peak 

0.323± 

0.027 

Basalt to 

trachybasalt 

0.014 0.4 (1)a

 1.3 2 Pyroclastic cone with 

lavas that extend 

from its base 

Hidden 

Cone 

0.373± 

0.042 

Basalt to 

trachybasalt 

0.03 0.3 (0.8)a

 1.6 4 Pyroclastic cone on 

side of butte with two 

lava fields 

Lathrop 

Wells 

0.076± 

0.005 

Trachybasalt 

0.09 0.8 (1.8)a

 1.6 4 Single pyroclastic 

cone with two lava 

fields 

a

 value represents diameter of main cone, which is the source for all preserved eruptive material, representing 

the expected value. Value in parentheses is the total length that could be buried by all eruptive deposits, 

representing the maximum possible value. 

Figure 28 The 1968 Strombolian eruption of Cerro Negro Volcano, Nicaragua. In the 

foreground is a small crater that is emitting fire fountains of magma that 

are feeding a lava flow during the central crater’s Strombolian eruption. 

Diameter of the base of the volcano is about 1.5 km (After Melson (2002) 

from a photo by Robert Citron). 
46

4.3. NRC and DOE Perspectives 

4.3.1. NRC/DOE KTI Agreement on the Likely Range of Tephra Volumes 

 A Key Technical Issue (KTI) agreement related to the likely range of tephra volumes 

from volcanoes in the Yucca Mountain region was reached by the DOE (2003) and NRC. This 

agreement is reflected in a letter from the NRC (Kokajko, 2005) to the DOE. However, in this 

letter the NRC expressed concern that the range of tephra volumes used by the DOE in 

performance assessment did not correspond to the volumes interpreted for volcanoes that have 

occurred in the Crater Flat basin during the time interval used in the DOE’s probability 

calculations. For example the eroded remnants of scoria cones of Pliocene volcanoes in Crater 

Flat basin, which are included in the DOE probability results, indicate larger tephra volumes 

than those accounted for in the current DOE parameter range (BSC, 2003b). However, the 

magnitude of differences between the DOE and NRC estimates of tephra volumes for past 

Yucca Mountain region volcanic events (NRC, 1999) does not appear to affect performance 

calculations significantly (NRC, 2004). 

4.3.2. DOE Approach to Event Definition 

The DOE (2003) evaluated characteristics of volcanic features in their Technical Basis 

Document (#13) on volcanic events. In the PVHA expert elicitation (Geomatrix Consultants, 

1996), the expert panel defined a volcanic event as a point in space representing a volcano, and 

an associated dike having length, orientation, and location relative to the point. Associated 

eruptive products may include ash, tephra, and lava flows. The Paiute Ridge intrusive/extrusive 

center, dated at 8.6 Ma and located on the northeastern margin of the Nevada Test Site 

(DOE, 2003; Valentine and Krogh, 2006), is a possible analog. A study of this center can 

elucidate the relationship between intrusive and extrusive components of a volcanic event. 

Paiute Ridge is a small-volume Miocene volcanic center comparable in volume and composition 

to Pleistocene volcanoes near Yucca Mountain. Like the Pleistocene cones, Paiute Ridge 

igneous activity is believed to have occurred during a brief magmatic pulse represented by a 

single volcanic event. The vents and associated dike system formed in a NNW-trending 

extensional graben, and exposures of the system include remnants of surface lava flows, 

volcanic conduits, and dikes and sills intruded into tuff country rock at depths of ~250 m from 

the paleosurface. Dike lengths at Paiute Ridge range from less than 1 km to 5 km and widths 

from 1.2 to 9 m. At Paiute Ridge parts of some dikes terminated within ~100 m of the surface 

without erupting, while other parts of the same dike did erupt, as evidenced by associated lava 

flows and volcanic conduits. This contrasts with the current assumption by both the DOE and 

NRC that any dike which intersects the repository will vent out to the surface. However, an 

event may consist of multiple dikes; only one of those dikes will feed eruptions, while the others 

might stall just below the surface. This is consistent with field analog studies (Valentine and 

Krogh, 2006; Keating et al., 2007) and is also reported in ANL-MGR-GS000002 Rev 03 (under 

review at the DOE). 

 Volcanic events occurring outside of the repository footprint must have sufficient length 

to intersect and breach the repository. Longer event lengths will result in higher intersection 

probabilities. The mean dike length associated with a volcanic event in the Yucca Mountain 

region is 4 km, and 95 percent of dikes are shorter than 10 km (DOE, 2003), consistent with 

observed volcanic features in the Yucca Mountain region. The maximum aligned-vent spacing 

in the Yucca Mountain region is 5.4 km between Black and Makani (Northern) Cones, and 

volcanic-vent alignment lengths are typically in the range of 2 to 5 km (e.g., Hidden Cone-Little 

Black Peak, Amargosa aeromagnetic Anomaly A, and Red Cone-Black Cone) (DOE, 2003). 
47

The longest proposed vent alignment is the Pleistocene Crater Flat feature with a length of 

about 11 km, if one assumes it represents only one volcanic event. If in fact that alignment 

represents a single event, the effect would be to reduce the Plio-Pleistocene recurrence rate 

significantly. 

Dikes such as those at Paiute Ridge range in length from less than 1 to 5 km. Dike and 

vent alignments of the 3.7 Ma basalts in the Crater Flat basin are no more than 4 km long. More 

recent studies have indicated much smaller dike (fissure) lengths as specified in Table 1 and 

discussed in Section 4.2 of this chapter. 

The DOE (2003) cites Delaney and Gartner (1997) in noting that 97 percent of the 174 

dike lengths measured in the San Rafael volcanic field are less than 5 km. The median of the 

length distribution at San Rafael is approximately 1 km, and the longest dikes are 8 to 9 km. The 

DOE (2003) estimated a measure comparable to dike half-length, the distance from the end of 

the dike nearest the repository to the point of origin (the midpoint) of the volcanic event, using 

information elicited in the PVHA (Geomatrix Consultants, 1996). The mean of this distribution is 

2 km, the 5th-percentile is 0.2 km, and the 95th-percentile is 5.6 km, agreeing well with 

observed volcanic-event features near Yucca Mountain. 

It was noted in Section 4.2 that some dikes have limited lateral propagation. Crowe 

et al. (1983) measured basaltic dikes intruded into tuff at eroded volcanic centers of the Yucca 

Mountain region, and observed dike widths ranging from 0.3 m to 4 m. Most dikes were 

between 1 and 2 m wide. The typical dike-width dimension assigned by the PVHA experts was 

1 m (Geomatrix Consultants, 1996). The DOE (2003) reports that most basaltic volcanoes near 

Yucca Mountain are small in volume and fed by one main dike. Sets of dikes (dike swarm) may 

be present with spacing between individual dikes of up to a few hundred meters. There may 

also be small dikes that radiate outward from the conduit of the main cone, analogous to the 

crudely radiating dikes that are enclosed in near-vent scoria at the eroded Pliocene basalt 

centers of Crater Flat basin. The Paiute Ridge volcanic complex may have as many as 10 

dikes, in addition to sill-like bodies. 

Data from a variety of basaltic fields indicate that the spacing between multiple dikes 

(dike swarm) can vary from about 100 m to approximately 1 km (DOE, 2003). For the Paiute 

Ridge complex, measurements suggest that the mean dike spacing for dikes greater than 1 km 

long is approximately 1 km (maximum 1,440 m; minimum 250 m) (Perry et al., 1998). For the 

3.7-Ma-old Crater Flat basalts, dike spacing is approximately 400 m (Perry et al., 1998). Dike 

spacing in the Yucca Mountain region ranges from about 100 m to 690 m (DOE, 2003). 

The expected frequency of basaltic intersection is 1.7 × 10-8/yr (Geomatrix Consultants, 

1996). If this rare event should occur, the DOE has estimated that an average of 77 percent of 

the basaltic, repository-intersecting intrusive events would result in at least one volcano within 

the repository footprint. This is based on observed vent spacing in the Yucca Mountain region 

and an assumption that the volcanoes could occur randomly along the length of the dike or 

localize near a repository drift. 

Basaltic eruptions begin from dikes that focus into roughly conical (base upward) conduit 

eruptions. The best data on conduit diameters and depths to which conduits extend come from 

observations of basaltic volcanic necks that have been exposed by erosion. However, few 

volcanic necks have been mapped in detail, at least those with the basaltic compositions of 

interest in the Yucca Mountain region. Without such mapping, estimates of potential conduit 

diameters are based on measurements at analog volcanoes (DOE, 2003). The transition from 

magma flow in a subplanar dike to flow in a conduit has been inferred at many field locations 
48

(e.g., Delaney and Pollard, 1981; Hallett, 1992). A planar dike is the preferred form for 

movement of magma through brittle and elastic host rock, whereas a conical conduit is the 

preferred form for magma flow and delivery to the surface (Delaney and Pollard, 1981). Once a 

zone of widening and flow focusing has initiated, the evolving conduit may continue to widen via 

erosive and hydromagmatic processes. Solidifying magma may choke portions of a conduit so 

that only a fraction of the vent may be active at any given time during an eruption. Basaltic 

conduits vary greatly in diameter, depth and geometry. Valentine and Groves (1996) used the 

well-established sedimentary stratigraphy beneath tephra deposits at the Lucero Volcanic field 

(New Mexico) to evaluate variations in conduit size beneath a basalt center. They calculated 

that the conduit ranged in diameter from 3.5 to 10 m. Conduit-size calculations based on the 

proportion of rock fragments in these hydromagmatic deposits indicate that a cylindrical conduit 

up to 40 m wide may have formed in the uppermost strata. A flared conduit could also have 

developed, varying in size from 6 m at depth to 300 m at the surface. 

The diameter of the Grants Ridge conduit in New Mexico (Keating and Valentine, 1998; 

WoldeGabriel et al., 1999) suggests that an upper bound for basaltic conduit diameter in the 

Yucca Mountain region is 150 m. This is a conservative upper bound for Yucca Mountain 

because the Grants Ridge volcanic neck formed during an eruption of <1 cubic kilometer of 

alkali basalt (compared, for example, to the much smaller Lathrop Wells volcano with its 

approximate total volume of 0.09 km3

) (DOE, 2003). The volume of the Grants Ridge eruption 

is reported in ANL-MGR-GS000002 Rev 03, now under review at the DOE (ACNW, 2007). 

Doubik and Hill (1999) used a process that may overestimate the volume fraction of tuff 

xenoliths to estimate a 50-m conduit diameter for the Lathrop Wells scoria cone. Thick Miocene 

volcanic units beneath the Lathrop Wells volcano are lithologically similar, making it difficult to 

assign relative proportions of those units represented by rock fragments of the walls of the 

feeder. Given the limitations on specific data to test the assumptions made by Doubik and Hill 

(1999), their estimate of a 50-m conduit diameter for the Lathrop Wells Cone was used as a 

most likely value for conduit diameter at depth for potential eruptions at Yucca Mountain 

(DOE, 2003). New work to be reported in DOE’s ANL-MGR-GS-000002, Rev. 03 (under review 

at the DOE) supersedes the DOE range of conduit diameters at repository depth with a lower 

mean value based on recent analog studies (ACNW, 2007). 

Based on data from the Yucca Mountain region and selected analogs, the conduit 

diameter for a future basalt volcano was constrained at its lower bound by 1- to 2-m wide dikes, 

and at its upper bound by the 150-m Grants Ridge plug (DOE, 2003). The ongoing PVHA-U 

has been tasked with reevaluating the volcanic event definition used in the 1996 expert 

elicitation. The panelists have been asked to assess the following aspects of future volcanic 

events that could hypothetically affect Yucca Mountain during the next 1 million years: 

• Magnitude of event 

• Intrusive event geometry 

– Dike system length, azimuth, and location relative to point event and dike 

width (similar to the 1996 assessment) 

– Description of dike swarm (e.g., number and spacing of parallel dikes along 

length of dike system) 

– Influence of repository opening on dike intersection. 

• Extrusive event geometry 

– Number and location of eruptive centers (conduits) associated with a volcanic 

event 
49

– Conduit diameter at repository level 

– Influence of repository opening on eruptive conduit location. 

The final report of the PVHA-U is not expected to be published until 2008, therefore this 

report cannot incorporate the revised assessments. Based on ACNW&M observations of 

PVHA-U proceedings, some significant changes are being considered to the 1996 study 

(Geomatrix Consultants, 1996). Most panelists appear to emphasize the nature of Pleistocene 

activity (instead of earlier activity), consider dikes that are shorter in length, discuss the 

possibility of sills, and consider increased flexibility in possible dike orientations. Event 

(eruption) cycles are being discussed, and fewer hidden events are now being considered 

based on the results of drilling of aeromagnetic anomalies that have been interpreted as 

possibly derived from hidden basaltic igneous events. 

The latest estimate of the conduit diameter at the Lathrop Wells volcano is provided by 

Valentine et al. (2007). Using data on xenolith abundance, and assuming a cylindrical conduit 

through the 335 m thick Miocene tuff sequence beneath the volcano, they estimated an average 

conduit diameter of only ~8-9 m. They further reasoned that if the lavas and fallout deposits at 

Lathrop Wells have a similar xenolith content (which is unlikely based on observations) the 

added volume of xenoliths would imply a maximum average conduit diameter of about 21 m. 

Because Lathrop Wells is an excellent analog of a hypothetical eruption through a repository, 

the estimates of conduit diameter by Valentine et al. (2007) represent the most current and 

plausible estimate for Yucca Mountain. A conduit diameter of 21 m would significantly limit the 

number of waste packages that could become entrained in a volcanic eruption. 

4.3.3. NRC Approach to Event Definition 

The NRC/CNWRA, in Connor et al. (2000), noted that the most prominent vent 

alignment in the Yucca Mountain region is the arcuate northeast trending Pleistocene Crater 

Flat alignment consisting of five cinder cones. Three magnetic anomalies are mapped along the 

alignment that reveal the presence of older, buried basaltic lavas. They propose that geological 

and geophysical mapping indicate that the Crater Flat alignment is up to 16 km long and may 

have been reactivated through time. However, recent high-resolution aeromagnetic surveying 

provides no support for connecting the outcropping and sub-cropping vents. The aeromagnetic 

data show no indication of anomalies related to magnetic intrusive dikes connecting the vents. 

The alignment of magnetic Anomalies G, F, and H (Figure 29) provides further evidence 

of NE-trending alignments. At aeromagnetic Anomaly G (Figure 29), drill hole USW VA-2 

confirmed that 3.8 Ma basalt lies at a depth of 119 m. Based on alignment and similar magnetic 

signatures of Anomalies H and F, these anomalies are also interpreted to be related to Pliocene 

basalts. Other vent alignments in the region include the 0.3 Ma Sleeping Buttes alignment, 

consisting of two cinder cones aligned on a NE-trend ~40 km northwest of Yucca Mountain, and 

the Pliocene Crater Flat vents, which form a north-trending alignment of 6–8 vents that erupted 

3.8 Ma ago. In all, five vent alignments with a total of 18 vents have formed or reactivated 

during Plio-Pleistocene time. Six remaining Plio-Pleistocene vents are not included in 

recognized alignments. Four of these are known only from magnetic mapping and one from 

drilling (Anomaly B, basalt of Pliocene age). There may be multiple vents associated with some 

of these anomalies. It is possible that future volcanic activity may produce similar alignments. 

Connor et al. (2000) estimated the probability of future volcanic intersection at Yucca 

Mountain assuming that half of any future volcanic events would not create alignments and 

would only disrupt the repository if they fell within the site boundary, and that the remaining half 
50

would form alignments that could intrude areas 5.5 to 8 km beyond the midpoint of a dike. 

Connor et al. (2000) point out that the three youngest alignments in the Yucca Mountain region 

trend along azimuths 20–30°, parallel to the maximum principal horizontal compressional stress 

in the region (Morris et al., 1996). Connor et al. (2000) also pointed out that existing faults may 

locally control the locations of vents regardless of whether vent alignments develop. For 

example, a normal fault crossed by a strike-slip fault will tend to dilate more at the fault 

intersection, creating additional space for the intrusion of ascending magma. They reported 

evidence of such localization of cinder cones along faults in the Yucca Mountain region. The 

Pliocene aged basalt of Anomaly B (Figure 29) occurs at the intersection of the north-trending 

Gravity and Rock Valley faults in the Amargosa Desert. The Carrara fault basalt is located at 

the intersection of north-trending normal and NW-trending strike-slip faults. The Lathrop Wells 

volcano is located along the trend of the Stage Coach fault, south of Yucca Mountain at the 

intersection with several north-trending faults (Connor et al., 2000). 

The igneous activity parameters used in the most recently published version of total 

performance assessment by the CNWRA are shown in Table 2 (Mohanty et al., 2004). This 

table shows that the geographic orientation of a dike intersecting the repository is assumed to 

be N7.5o

E with a range from N0oE to N15oE. The mean width of the dike is assumed to be 5.5 m 

with a range from 1.0 to 10.0 m and the mean length of the dike is 6.5 km with a range of 2 to 

11 km. Multiple conduits are assumed to form along a dike during a single igneous event, but 

the base case is only one conduit. The range of diameters of the conduit is uniform from 25 to 

78 m with a mean of 51 m. The volume of ash associated with an eruption event is estimated 

using better preserved volcanoes which serve as analogs to the basaltic volcanism of the Yucca 

Mountain region. The NRC (1999) observes that the range of ash-to-cone volume ratios at 

historical analog volcanoes range from approximately 1:1 to 6:1. Based on these ratios and 

estimation of the power and duration ranges of potential igneous events, the ash-volume ranges 

from 6 x 105

 to 3 x 108 m3 with an average volume of 3 x 107 m3. In contrast, the DOE has 

determined an average volume of 1 x 108

 m3 with a range of 2 x 106 to 4.4 x 108 m3. 

4.3.4. EPRI Approach to Event Definition 

EPRI considers the Lathrop Wells basalt center as the best example of a natural analog 

of a future eruption in the Yucca Mountain region (Morrissey, 2006). The original character of 

erupted material refers to the physical state of magma in the conduit or fissure prior to erupting. 

The physical state of magma reflects the composition, water content, crystal content, and 

temperature of magma. These four properties are used as part of EPRI’s criteria for defining a 

natural analog for future volcanism. Other important criteria for a natural analog are volcano 

type and tectonic setting. 

In contrast to the Lathrop Wells volcanic center, the Pliocene basalt centers in the Crater 

Flat basin are deeply eroded and poorly exposed, although they, too, provide valuable 

predictive data for other parts of the igneous scenario analysis (Morrissey, 2006). Lathrop 

Wells, however, is representative of the largest monogenetic basaltic eruption that might be 

anticipated in the future around Yucca Mountain. EPRI used features of the Lathrop Wells 

basalt center to define the following criteria for selecting appropriate natural analogs to future 

eruptions in the Yucca Mountain region (Morrissey, 2006): 

1. Magma composition is alkali basalt with 1.9-4.6 wt.% H2O and < 4 vol. % phenocrysts of 

olivine, amphibole and/or clinopyroxene. 

2. Monogenetic scoria cone. 
51

3. Total eruption volume < 0.1 km3

. 

4. Extensional tectonic setting. 

In addition to magma composition, phenocryst phases and water contents are included 

in EPRI’s criteria. These two parameters constrain the eruption temperature that is a governing 

factor of eruption style. Lathrop Wells basalts, along with all basalts < 1.1 Ma in the Yucca 

Mountain region, are characterized by a crystal assemblage exclusively of olivine and some 

contain clinopyroxene and/or amphibole. Plagioclase phenocrysts are rare in these basalts. 

Plagioclase does occur in these basalts as microcrysts or groundmass crystals indicating that 

these grew at shallow depths during rapid decompression. The absence of plagioclase as a 

phenocryst phase with olivine indicates a lower liquidus temperature or eruption temperature 

(975-1010°C) than if plagioclase were present (Sisson and Grove, 1993; Nicholis and 

Rutherford, 2004). An eruption temperature of 975-1010°C yields a viscosity for basalt of 100-

1000 Pa·s, whereas an eruption temperature of 1100-1200°C yields a viscosity of 1-10 Pa·s 

(Lore et al., 2000). The different viscosities tend to favor different eruption styles. EPRI believes 

phenocryst assemblage to be a vital criterion for selecting an appropriate analog to a 

Strombolian eruption in the Yucca Mountain region. Therefore EPRI’s analog criteria include 

aphyric texture (< 4 vol.% phenocrysts) and phenocrysts of olivine and amphibole (or 

clinopyroxene). 

EPRI found that proposed analogs such as Paricutin, Grants Ridge, Tolbachik, and 

Longuimay are not appropriate because they do not meet at least two criteria. Use of such 

analogs should be restricted to understanding processes associated with an igneous event but 

not to quantify a characteristic property. Analogs such as Basalt Ridge, Paiute Ridge, Boulder 

Dam dikes, and Red Cones in California fit the criteria. Field observations of eruptive 

characteristics at these analogs to the Crater Flat basin may reduce the uncertainty associated 

the intrusive and extrusive scenario. Volcanic fields that have been proposed as analogs to the 

Crater Flat volcanic field include Coso, Cima, Death Valley, Lunar Crater, Reveille Range, Nye 

Canyon, and El Jorollo. Based on only composition and tectonic environment, Reveille Range, 

Death Valley and Clayton Valley may be good analogs. EPRI considers the others to be 

questionable as they include cinder cones with a wide range of composition and eruption type. 

In addition to the above considerations, as part of their comments on the ACNW&M’s 

draft report, EPRI provided a revised description of their conceptual model for natural analogs of 

future volcanism. This material is an addendum to EPRI’s internal report on igneous events. 

Because this addendum may not be readily available in the public record, it is provided (with 

minor editing) as Appendix C to this report, along with its own figures, table, and reference list. 

Appendix C is tltled “EPRI’s conceptual model for defining natural analogs for future Yucca 

Mountain volcanism and expected consequences.” 

4.3.5. Comments on Hydromagmatic (Maar) Volcanism 

The principal condition necessary for explosive phreatic eruptions (maar volcanism, 

involving heating and expansion of groundwater) is a shallow groundwater table in a largely 

unconsolidated, highly permeable medium (i.e., alluvial basin). This condition does not exist at 

the Yucca Mountain site which is an elevated block of consolidated volcanic rocks with a deep 

water table. The depth of the water table is not expected to change by more than 20 to 30 m 

over the next million years as a result of climate change in southern Nevada. There is also no 

evidence that maars formed in alluvial basins near Yucca Mountain during the last 10 million 

years. 
52

McBirney (2005), in a presentation to the PVHA-U expert panel, concluded that the 

probabilities of phreato-magmatic eruption are largely a function of the ground-water level and 

the permeability of the sediments invaded by magma. These conditions have existed in the 

Crater Flat basin and could recur there in the future, but they do not exist on Yucca Mountain. 

The principal hazards of such an eruption in the basin are damage to surface structures from 

ballistic ejecta and base-surge flows. These hazards are limited to a radius of about five 

kilometers from the vent. 

4.4. Summary 

A concise summary of the views regarding the nature of future Yucca Mountain region 

igneous activity is constrained by the lack of published materials that discuss current 

investigations. The DOE (2006) anticipates that changes to the input parameters to 

performance assessment, based on analog geologic data, will involve: 

• Dike length, width, orientation, and number of dikes, 

• Conduit size, and number and locations of conduits, and 

• Fraction of eruptive material in tephra, cone, and lavas. 

There are several areas of agreement between the DOE and NRC regarding the nature 

of igneous events impacting the proposed repository. These are based on geologic analogs and 

the geological and tectonic history of the Yucca Mountain region. They include the following: 

• Igneous events will be of similar nature to the Pleistocene volcanoes of the Yucca 

Mountain region and particularly the most recent volcano, Lathrop Wells. 

Accordingly, igneous events will occur as small-volume basaltic volcanoes that have 

effusion rates, power, and duration similar to the Lathrop Wells volcano. The 

occurrence of high power and volume and long duration volcanic events involving 

felsic ash flows typical of those of Miocene age in the Yucca Mountain region are not 

supported by evidence. 

• A portion of the duration of any volcanism will involve violent Strombolian activity with 

plumes of ash distributed over the Yucca Mountain region. Analogous with the 

Lathrop Wells eruption, fallout from a sustained eruption plume is likely to result in 

ash falls extending to a few 10s of kilometers. 

• Multiple dikes including en echelon dikes are possible associated with an igneous 

event. The dike orientation will be parallel to the maximum horizontal compressive 

stress in the region, roughly spanning an azimuth from N to N30o

E. New work to be 

reported in DOE’s ANL-MGR-GS-000002, Rev. 03 (under review at DOE) ties dike 

strike more closely to pre-existing faults, as supported by analog field data 

(ACNW, 2007). 

• The diameter of the volcanic conduit assumed by both the NRC and DOE has a 

mean value of about 50 m. NRC anticipates a range in diameter of 25 to 75 m, while 

the DOE cites diameters from 15 to 150m. New work to be reported in DOE’s ANLMGR-GS-000002, Rev. 03 supersedes the DOE range of conduit diameters at 

repository depth with a significantly lower mean value based on recent analog 

studies (ACNW, 2007). 

• Any dike intersecting the repository will continue to the surface above the repository. 
53

Table 2 Igneous activity input parameters to Total-System Performance 

Assessment (CNWRA, 2004).

Parameter Mean Value Distribution 

Volcano model (1 = geometric, 2 

= distribution) 

1 — 

Time of next volcanic event in 

region of interest 

5.05 × 103 years Finite exponential; 100.0, 

10,000.0, 1.0 × 10-7

X location in region of interest 5.48 × 105 m — 

Y location in region of interest 4.08 × 106 m — 

Random number to determine if 

extrusive 

or intrusive volcanic event 

5.00 × 10-1 Uniform; 0.0, 1.0 

Fraction of time volcanic event is 

extrusive 

9.99 × 10-1 — 

Angle of volcanic dike measured 

from north—clockwise 

7.50° Uniform; 0.0, 15.0 

Length of volcanic dike 6.50 × 103 m Uniform; 2,000.0, 11,000.0 

Width of volcanic dike 5.50 m Uniform; 1.0, 10.0 

Diameter of volcanic conduit 5.13 × 101 m Uniform; 24.6, 77.9 

Density of air at standard 

pressure 

1.29 × 10-3 g/cm3 — 

Viscosity of air at standard 

pressure 

1.80 × 10-4 g/cm-s — 

Constant relating fall time to 

eddy diffusivity 

4.00 × 102 

cm2

/sec5/2

— 

Maximum particle diameter for 

particle transport 

1.00 × 101 cm — 

Minimum fuel particulate size 1.00 × 10-4 cm — 

Mode fuel particulate size 1.00 × 10-3 cm — 

Maximum fuel particulate size 1.00 × 10-2 cm — 
54

Parameter Mean Value Distribution 

Minimum ash density for 

variation with size 

0.8 g/cm3 — 

Maximum ash density for 

variation with size 

1.60 g/cm3 — 

Minimum ash log diameter for 

density variation 

- 2.00 — 

Maximum ash log diameter for 

density variation 

- 1.00 — 

Particle shape parameter 5.00 × 10-1 — 

Incorporation ratio 3.00 × 10-1 — 

Wind direction - 90° — 

Wind speed 1.20 × 103 cm/sec Exponential; 8.3 × 10-4

Volcanic event duration 4.85 × 105 sec Log-uniform; 1.80 × 105, 

1.30 × 106

Volcanic event power 4.31 × 1010 W Log-uniform; 3.59 × 109, 

5.30 × 1011

Volcanic column constant beta 1.00 × 101 — 

Ash particle size distribution 

standard deviation 

1.00 — 

Relative rate of blanket removal 0.0007 — 

Fraction of precipitation lost 

to evapotranspiration 

6.80 × 10-1 — 

Fraction of irrigation lost 

to evapotranspiration 

5.00 × 10-1 — 

Fraction of year soil is saturated 

from precipitation 

5.40 × 10-3 — 

Fraction of year soil is saturated 

from irrigation 

2.00 × 10-1 — 

Ash bulk density 1.40 g/cm3 — 
55

Parameter Mean Value Distribution 

Ash volumetric moisture fraction 

at saturation 

4.00 × 10-1 — 

Depth of the rooting zone 1.50 × 10-1 m — 

Subarea of volcanic event 

(Model 2) 

2.00 — 

Number of waste packages 

contained by ejecta (Model 2) 

50.677 Beta 1.0, 150, 1.0, 2.0 

Number of magma induced 

mechanical failures remaining in 

drift (Model 2) 

37.40 Log uniform; 1.0, 1402.0 

Areas of disagreement between the DOE and NRC include: 

• The DOE assumes a single eruption volcanic event associated with each dike 

approaching the surface. Each event might have one to three conduits, but each 

conduit might have shallow breakout vents that feed lavas from the lower flanks of 

growing cones. In contrast NRC supports the possibility of multiple vents including 

the potential for flank eruptions from a volcanic cone leading to satellite (secondary) 

eruptions of lesser intensity. 

• The length of potential intruding dikes remains an issue of disagreement. The DOE 

currently uses a probability distribution function of dike length from PVHA-96, ranging 

from 1 to 10 km with a mean of 4 km. NRC considers a mean dike length of roughly 

6 km with a range from 2 to 11 km based on dike lengths interpreted from both 

Pliocene and Pleistocene igneous activity. 

• In the event of formation of multiple dikes, the DOE has considered the dikes to have 

a width ranging from 0.5 to 5 m with a mean value of 1.5 m. Recent analog work by 

DOE indicates that this range and mean may increase at repository depth (however, 

this is not a sensitive parameter in the DOE TSPA igneous consequences 

calculations (ACNW, 2007)). The NRC assumes a wider range of dike widths from 

1 to 10 m with a mean of roughly 5 m. 

EPRI used features of the Lathrop Wells basalt center to define the criteria for selecting 

appropriate natural analogs to future eruptions in the Yucca Mountain region. EPRI developed 

the following criteria (Morrissey, 2006): 

1. Magma composition is alkali basalt with 1.9-4.6 wt.% H2O and < 4 vol. % phenocrysts of 

olivine, amphibole and/or clinopyroxene. 

2. Monogenetic scoria cone. 

3. Total eruption volume < 0.1 km3

4. Extensional tectonic setting. 

Additional summary observations include the following: 
56

Two possible scenarios that involve intersection of the repository by igneous activity 

include different processes and risk consequences. The extrusive (volcanic) scenario involves 

intersection of a volcanic-cone-forming conduit through the repository to the surface causing 

waste in the conduit to contaminate the ash and be dispersed over the Yucca Mountain vicinity. 

The greatest risk from such an event will occur during the first thousand years due to the 

presence of significant quantities of short half-life radionuclides. The intrusive scenario involves 

intrusion of an igneous dike into the repository leading to damage or destruction of the waste 

packages and premature release of the waste to infiltrating waters passing through the 

repository, but does not involve a volcanic conduit directly to the surface. 

There is general agreement regarding the nature of any future igneous event (i.e., power 

and approximate duration of event, volume and types of erupted products, general magma type 

and its volatile content, and the characteristics of the crustal pathways (dikes) for the magma). 

There is also agreement that dikes (which can locally evolve into volcanoes) tend to follow preexisting fault zones where faults exist in proximity to an ascending dike. Thus, current DOE 

plans to avoid existing faults in constructing the repository (setback strategy) will minimize the 

likelihood of an extrusive event intersecting the repository. 

The majority of past volcanic activity in the Yucca Mountain region occurred within a 

basin, e.g., Crater Flat basin, the northern Amargosa Desert, and Jackass Flats, not on ridges 

like Yucca Mountain. Although one ancient (>10 million year old) basaltic dike exists on the 

western flank of Yucca Mountain, no volcanic activity is known to have intersected the 

repository footprint since the surface rocks were deposited 13 million years ago. 

Igneous event definitions have evolved during site characterization and analysis. Prior to 

the mid-1990s, the definition of the event was largely restricted to volcanic eruptions. 

Subsequently, the importance of dike intersection with the repository has been emphasized as 

well as volcanic events. Even more recently, studies of similar small-volume basaltic igneous 

events dating back to 10 million years ago in the nearby Nevada Test Site suggest that igneous 

sills, which are near-horizontal tabular igneous intrusions, should be considered in event 

definition. This evolution in event definition may be important in evaluating published igneous 

event probabilities because of the change in definition from point events to long (dikes) and 

perhaps broad igneous features (sills). 

Finally, the conditions needed to support a phreatic (maar) eruption do not exist at 

Yucca Mountain today and are not expected to exist in response to climate change. 
57

5. Probability of Potential Igneous Activity 

5.1. Introduction 

The second question of the risk triplet, What is the probability of an igneous event 

intersecting the proposed repository?, is the subject of Chapter 5. Considering the limitations in 

knowledge of the past basaltic volcanism in the Yucca Mountain region and the imperfections in 

the understanding of volcanic processes, it is impossible to specify the time and location of 

future igneous activity precisely. The probability of an event is further complicated by the range 

of characteristics of the dikes from the igneous event that may intersect the repository (i.e., 

length, orientation, as well as location). However, it is possible to predict, in a stochastic 

framework, the recurrence rate of such an event within an area encompassing Yucca Mountain. 

The predicted recurrence rate can be translated into the probability of repository intersection 

given the footprint of the proposed repository and assumptions regarding the volcanic zone and 

tectonic models and the nature of the igneous activity. A useful review of the methods of 

prediciting igneous activity at Yucca Mountain and a history of probability estimates is given by 

Crowe et al. (2006). 

The Environmental Protection Agency (EPA) set the generic standard for geologic highlevel waste repositories (EPA, 1993) and confirmed, in the standard for the proposed Yucca 

Mountain repository (EPA, 2001), that an event, such as a volcanic eruption, does not require 

evaluation if the probability of occurrence is less than 0.01% in ten thousand years, i.e., less 

than one chance in one hundred million (10-8) per year. This is roughly equivalent to the 

probability estimated for mass global extinction of life caused by the impact of an extraterrestrial body on the Earth (Crowe et al., 2006). Estimates for the annual recurrence 

frequency of repository intersection by an igneous event range from one part in a million to one 

part in a billion (10-9 to10-6), thus necessitating consideration of the risk from such an event. 

 In evaluating the probability of an igneous event intersecting the proposed repository it 

is important to understand the impact on the standards and the regulations for licensing the 

repository of the change in the time of compliance from 10,000 years to a million years. The 

EPA’s current draft revised standards (EPA, 2005) and the NRC’s draft revised regulations 

(NRC, 2005b) prescribe that consideration of features, events, and processes (FEPs), which 

includes igneous events, shall use the results obtained for the 10,000 years following repository 

closure. This is based on the assertion that the data and models of the first 10,000 years 

provide sufficient support to analyze performance during time periods up to a million years 

without invoking undue uncertainty associated with long term projections. As a result, the 

probability estimates based on a 10,000 year repository lifetime that were made prior to the 

lengthening of the repository time of compliance remain valid and are discussed herein. 

 The logic diagram showing the major components that enter into the evaluation of the 

probability of an igneous event intersecting the repository is shown in Figure 4. These include 

results presented in the previous chapter regarding event definition and the number of events 

that have occurred in the germane region over a specified duration of geologic time. This 

evaluation also requires estimates of the number of undetected events and change in number of 

events with time. Assumptions regarding volcanic zone models and to a lesser extent tectonic 

models also enter into the evaluation as indicated in the logic chart (Figure 4). 

It is useful to understand that the issue of probability of volcanism at Yucca Mountain 

poses an interesting paradox. Crowe et al. (2006) describe this contradiction. The small 

number of past eruptions is the best evidence that the probability of future volcanism near 
58

Yucca Mountain will be small. Had there been more volcanic events to study there would be 

more data on spatial and temporal patterns to project future volcanism with less uncertainty. 

But in that hypothetical case the risk from future volcanism would be substantially higher than is 

the case for Yucca Mountain. 

As discussed below, the volume of basaltic volcanic material near the site has 

dramatically declined over time. Accordingly, the Crater Flat basin volcanic field represents a 

zone of very small activity compared to other volcanic fields in the region (e.g., Lunar CraterReveille Range, NV; Cima, CA; and Springerville, AZ). 

5.2. Spatial and Temporal Distribution of Igneous Events 

5.2.1. Introduction 

The spatial distribution of basaltic igneous events in the Yucca Mountain region and their 

absolute age is fundamental to formulating volcanic zone and temporal models of igneous 

activity used in predicting the probability of future activity at the proposed repository site. 

Geologic mapping has identified numerous surface features, both volcanic cones or their 

remnants and dikes. Isotopic dating of volcanic material has been used to determine their age 

to a high degree of accuracy. Detritus eroded from the topographic highlands (ranges) has been 

deposited in the adjoining basins and may have buried older igneous event features. 

Fortunately, the basaltic rocks have a significantly stronger magnetization than the alluvium in 

the basins. Thus, hidden basaltic features in the basins can be isolated by geophysical 

mapping of magnetic anomalies. However, alternative sources of the magnetic anomalies are 

possible. Thus, drilling on the magnetic anomalies or a representative of a group of anomalies 

to test for the presence of basalt is required to complete the analysis. Basalt samples obtained 

from the drill core are dated to determine the age of the feature. The resolution of the magnetic 

method is limited, so that deeply buried, small, and thin basaltic features may not be mapped. 

Thus, undetected basaltic features may be present in the region. Accordingly, the geographic 

location of surface and buried basaltic volcanic rocks and their absolute age, and the possible 

presence of undetected features, are all considered in estimating the probability of intersection 

of the proposed repository by an igneous event. 

5.2.2. Surface Exposures 

Figure 29 shows the locations of surface exposures of basalts in the vicinity of Yucca 

Mountain. At least four known pulses of basaltic volcanism have occurred (DOE, 2003) in the 

Yucca Mountain vicinity. These include the ~80 ka Lathrop Wells cone and flows (Heizler et al., 

1999) (Figure 30 A), ~1 Ma events in Crater Flat basin (Red Cone, Black Cone, Northern 

(Makani) Cone, and Little Cones) (Figure 30 B), and multiple events dated ~3–6 Ma (PlioceneUpper Miocene) and ~8–13 Ma (Miocene). Other young basalts in the Yucca Mountain region 

include Little Black Peak (~0.3 Ma) (Figure 30 C) and Hidden Cone (~0.4 Ma), 35 km northwest 

of Yucca Mountain. 

The Lathrop Wells cone has undergone extensive research because of its relative youth 

and its proximity to Yucca Mountain. It is the only known igneous activity that occurred in the 

immediate vicinity of Yucca Mountain since the formation of the ~1-Ma-old-cones in Crater Flat. 

Two large basalt flows associated with the Lathrop Wells cone extend east and south of the 

cone and were emplaced during a range of pyroclastic activity (see Valentine et al., 2007 and 

ANL-MGR-GS-000002 Rev 03 which is now under review at DOE) (ACNW, 2007). 
59

Figure 29 Locations of basaltic volcanoes in the Yucca Mountain region. Letters and 

numbers are magnetic anomalies of high to moderate confidence that 

represent possible buried basalts. Drilling at “A”, “B”, “D”, “G”, 23P, and 

JF-3 (not shown-just north of 23P) has detected basalts. Map coordinates 

in UTM Zone 11 Meters, North American Datum 1927 (After Connor 

et al., 2002). 

Pliocene-age basalt flows and several remnants of volcanic conduits occur in eastern 

Crater Flat (Figure 31). Other Pliocene basalts occur east of Little Black Peak near Thirsty 

Mountain, and at Buckboard Mesa on the margin of the Timber Mountain caldera complex. 

Large exposures of Miocene basalts occur in Jackass Flats, at Dome Mountain in the Timber 

Mountain caldera complex, and in proximity to the Black Mountain caldera. Miocene-age 

basalts also occur in western Crater Flat, and as a dike complex in Solitario Canyon on the 

northwestern flank of Yucca Mountain. 
60

Figure 30 Photos of Yucca Mountain area. (A) Lathrop Wells cone (Age is 80 ka 

(Heizler et al., 1999) and height is ~130 m). (B) View of the ~1 Ma old cinder 

cones in Crater Flat, as seen looking northeast from Steve’s Pass at the 

southern margin of Crater Flat. Yucca Mountain is on the far horizon at 

right side of image. (C) Little Black Peak, ~0.3 Ma (in foreground). 

Figure 31 Photo of Yucca Mountain area at Crater Flat. Person at left is standing on a 

dike of Pliocene age in southeastern Crater Flat. The distant cone at center 

is the Pleistocene-aged Black Cone. Between Black Cone and the figures 

at right are the eroded remnants of two Pliocene vents (conduits). 
61

5.2.3. Known Occurrences of Buried Basalts 

Samples obtained from drilling in the alluvial basins show that buried basalts exist at 

several locations around Yucca Mountain, and magnetic surveys also indicate that additional 

basalts may be buried beneath the alluvium in Crater Flat and the Amargosa Desert (Connor 

et al., 2000; O’Leary et al., 2002; Hill and Stamatakos, 2002; Perry et al., 2005). Anomaly ‘‘B’’ 

in Figure 29 was confirmed by drilling to be a Pliocene basalt (~3.8 Ma) buried under 73 m of 

alluvium (Perry et al., 1998; O’Leary et al., 2002; DOE, 2003; Ziegler, 2003). A basalt in 

borehole NC-EWDP-23P located S-SE of Yucca Mountain has a Miocene age (9.48 ± 0.05 Ma) 

(Ziegler, 2003). This basalt lies buried beneath 400 m of alluvium. Another buried basalt was 

penetrated by drill hole VH-2, with a Miocene K/Ar age of 11.3 ± 0.4 Ma (Carr and Parrish, 

1985). Basalt was also found in drill hole J-11 in northeastern Jackass Flats and at Anomaly 

“D” in Figure 29. 

In support of the updated PVHA-U expert elicitation, a 30 × 30 km, high-resolution 

aeromagnetic survey was conducted in 2004 of Yucca Mountain, Crater Flat, Jackass Flats, and 

northern Amargosa Desert by the DOE to optimize detection of buried basalts. The helicopterborne survey was made along east-west flight lines at 60 m spacing. Over flat terrain the 

magnetometer was maintained at an altitude of ~45 m and roughly twice that over mountainous 

terrain to ensure the safety of the aircraft. In a presentation to ACNW&M in July, 2006, Frank 

Perry (LANL) described the new survey as providing high resolution and broad coverage that 

allows better interpretation of buried basalt vs. alluvium and tuff, faults beneath shallow 

alluvium, and relationships between faulting and volcanic features (Perry et al., 2006). Based 

on the new magnetic map and modeling of magnetic anomalies, anomaly targets were chosen 

for further study with drilling using the following criteria: 

• Location with respect to impact on probability estimates (distance from repository, 

impact on event lengths), 

• Sampling of each major cluster or alignment of anomalies, 

• Consideration of a range of potential ages based on differences in burial depth and 

magnetic polarity, and a 

• Balance of “high confidence” vs. “low confidence” anomalies (basalt vs. tuff). 

Seven new drill holes were completed at locations of magnetic anomalies in Crater Flat 

basin, Jackass Flats, and the northern Amargosa Desert. Their locations are shown on the highresolution magnetic anomaly map (Figure 32) together with selected existing drill holes and 

selected geologic features and the repository area. Table 3 summarizes the results of the 

drilling. Four of the seven drill holes penetrated basalt. Only in one case, Anomaly "Q," was 

unexpected basalt encountered (faulted tuff was the predicted source). Preliminary age 

determinations have been obtained revealing that three of the anomalies are due to buried 

Miocene basalt, one is due to Pliocene basalt, two are caused by Miocene tuffs, and one 

anomaly (JF-6) is probably due to faulted tuff (but is possibly due to Miocene basalt). 
62

Table 3 Summary Information for Completed PVHA-U Drill Holes (footnotes 

are interpretations presented by Perry et al., 2006). 

Magnetic 

Anomaly 

Drillhole Location Magnetic 

Source 

Predicted 

Source 

Depth and 

Thickness 

of Basalt 

(m) 

Age (Ma) 

Aa USW VA-1 Crater Flat Basalt 

(basanite) 

Basalt 148 / 62 ~10.1 Ma 

(Miocene) 

Qb USW VA4a Crater Flat Basalt Tuff 141 / >22 ~11.1 Ma 

(Miocene) 

JF-5c UE-25 VA10 

Jackass 

Flats 

Basalt Basalt 77 / >17 ~9.4 Ma 

(Miocene) 

JF-6d UE-25 VA11 

Jackass 

Flats 

Likely tuff Unknown n/a n/a 

I

e

 USW VA-5 Amargosa 

Desert 

Tuff Tuff n/a n/a 

Of USW VA-3 Amargosa 

Desert 

Tuff Tuff n/a n/a 

Gg USW VA-2 Amargosa 

Desert 

Basalt Basalt 119 / 31 ~3.8 Ma 

(Pliocene) 

a Basanite represents a mafic magma composition not previously seen in the Yucca Mountain 

region; the drilled body may be an intrusive sill. 

b Anomalies “R” and “4” are considered an expression of the same basalt; possible 

stratigraphic correlation with basalts of VH-2 and southern Crater Flat. 

c Basalt correlates with basalts in drill holes J-11 and Nye 23P. 

d Likely due to faulted tuffs. Any basalt that may exist below borehole depth of 196 m is likely 

to be Miocene. 

e Drillhole terminated in tuff at 200 m. 

f Similarity of magnetic signatures suggests that anomalies “L,” “M,” and “N” also represent 

faulted tuffs, not a volcanic alignment. 

g Alignment and similar magnetic signatures of anomalies “H” and “F” suggest that these 

likewise represent Pliocene basalts. 
63

Figure 32 High-resolution aeromagnetic anomaly map and locations of holes (solid 

white circles) drilled to determine if the magnetic anomalies are derived 

from basalts. Solid red circles indicate selected pre-existing drill holes that 

provide key constraints on the location of buried basalt near Yucca 

Mountain. Qb=Quaternary basalt, Pb=Pliocene basalt, Mb=Miocene basalt 

(After Perry et al., 2005; Perry et al., 2006) (Permission to use this 

copyrighted material is granted by the American Geophysical Union). 

Hill and Stamatakos (2002) presented a relative ranking of low-medium-high confidence 

in the interpretation of buried basalts associated with magnetic anomalies prior to the highresolution magnetic survey. Their table of confidence rankings shown herein as Table 4 

provides previous rankings by the USGS (O’Leary et al., 2002) and by the expert panelists of 

PVHA-96 (Geomatrix Consultants, 1996). 
64

Table 4 Previous Confidence Rankings for Anomalies Now Reinterpreted with Data 

from PVHA-U Drilling and Dating (After Hill and Stamatakos, 2002). 

Magnetic 

Anomaly 

O’Leary 

et al. 

(2002) 

Geomatrix 

Consultant

s (1996) 

Hill and 

Stamatako

s (2002) 

Source of Anomaly Age (Ma) 

A 1a 0.20b Hc Basalt (basanite) ~10.1 Ma 

(Miocene) 

Q 4 n/rd M Basalt ~11.1 Ma 

(Miocene) 

R 4 n/r L Basalt - interpreted 

similar to Q by Perry 

et al. (2006) 

Miocene 

4 4 n/r L Basalt - interpreted 

similar to Q by Perry 

et al. (2006) 

Miocene 

JF-5 n/r n/r n/r Basalt ~9.4 Ma 

(Miocene) 

JF-6 n/r n/r n/r Likely tuff (Perry 

et al. (2006) 

n/a 

I 2 n/r M Tuff n/a 

O 3 n/r M Tuff n/a 

L 3 n/r M Tuff - interpreted 

similar to O by Perry 

et al. (2006) 

n/a 

M 3 n/r M Tuff - interpreted 

similar to O by Perry 

et al. (2006) 

n/a 

N 3 n/r M Tuff - interpreted 

similar to O by Perry 

et al. (2006) 

n/a 

G 1 0.36 H Basalt ~3.8 Ma 

(Pliocene) 

F 1 0.37 H Basalt -interpreted 

similar to G by Perry 

et al. (2006) 

Pliocene 

H 1 n/r H Basalt -interpreted 

similar to G by Perry 

et al. (2006) 

Pliocene 
65

The results of drilling on anomalies following completion of the 2004 aeromagnetic 

survey reduce some of the uncertainty about buried basalts in the region and can be used to 

update previous probability models. Consider, for example, dataset CFB_plio-quat-Mag 

(Connor et al., 2002), which represents 29 Plio-Pleistocene events (dated basalts + 10 

anomalies that were assumed to be post-Miocene basalts) in the Crater Flat basin. The number 

of basaltic events in this dataset is now reduced to 22 events by eliminating seven anomalies 

(A, I, L, M, N, O, and Q). This lowers the apparent Plio-Pleistocene volcanism recurrence rate 

from 5.5 × 10-6/yr (Coleman et al., 2004) to 4.2 × 10-6/yr., which is also consistent with the 

Pleistocene recurrence rate of 4.4 × 10-6/yr that is based solely on the eight known Quaternary 

basalts that exist in the Yucca Mountain region (Coleman et al., 2004). These results show that 

the new data will influence some statistical-mathematical models by lowering the probability of 

future repository intersection by volcanism. It is significant that no post-Miocene basalt was 

found in Jackass Flats at drill holes JF-5 and JF-6. If buried Pliocene basalts had been found 

there, that would suggest that the Plio-Pleistocene volcanic zone of the Crater Flat basin 

extends through Yucca Mountain significantly increasing the modeled probability of future 

repository intersection. 

The occurrences of buried basalt features help to interpret the pattern of surface basalts. 

For example, the Lathrop Wells cone, which previously appeared to be an isolated volcanic 

event in an area of no prior activity, is now seen as occurring midway along a band of Pliocene 

basalts that extend from the Crater Flat basin southeastward to the buried basalts of Pliocene 

age found at Anomalies G and B. 

The CNWRA has recently reevaluated the geophysical information used to detect and 

characterize buried basalts in the Yucca Mountain region (Stamatakos et al., 2007). Their 

analyses update the initial evaluation of aeromagnetic data provided in the 2002 CNWRA report 

“Evaluation of Geophysical Information Used to Detect and Characterize Buried Volcanic 

Features in the Yucca Mountain Region” (Hill and Stamatakos, 2002). The 2002 report had 

concluded that there may be twice as many basaltic volcanoes in the Yucca Mountain region 

than considered in the original 1996 DOE hazard assessment. These additional buried 

volcanoes could potentially lead to a tenfold increase in probability estimates for igneous activity 

at Yucca Mountain. Stamatakos et al. (2007) concluded that the new DOE analyses have 

reduced the overall uncertainty in the number of past events. Specifically, many of the 

anomalies that were previously ranked as having a high or medium likelihood of being the result 

of buried basalt are now confirmed buried basaltic features while several anomalies ranked as 

having a low likelihood of being buried basalt are now confirmed as being the result of faulted 

tuff. Moreover, the aeromagnetic data and drilling program have identified previously unknown 

Miocene basalt buried in Fortymile Wash (Stamatakos et al., 2007). 

The new DOE information and analyses also support the hypothesis that past volcanism 

in the region was temporally clustered (Stamatakos et al., 2007). The most active of these 

temporal clusters occurred between 3.6 and 4.7 Myr ago when at least 12 to 17 volcanoes 

formed. This leads to an episodic recurrence rate of 11 to 16 volcanoes per million years, which 

is substantially greater than the longer term average rate of about 5 volcanoes per million years 

and an order of magnitude greater than the 1 to 3 volcanoes per million years in the original 

1996 DOE assessment. Additional temporal clusters are recognized for the period between 9 

and 11.2 million years ago and one between 80,000 and 1 million years ago. Based on these 

data, it appears temporal clustering is an important feature at Yucca Mountain that should be 

accounted for in volcanic probability models (Stamatakos et al., 2007). 

New data and modeling of the drill core at anomaly “A” reveal what appears to be a very 

thick intrusion or sill rather than a buried volcanic lava flow or cone (Stamatakos et al., 2007). 
66

This is the first documented evidence of a possible basaltic sill in the Crater Flat structural 

basin. The presence of a sill raises the possibility that, in addition to existing igneous activity 

scenarios in which a dike intersects repository drifts or a volcanic conduit forms thorough the 

repository, a basaltic sill could form within or beneath the potential Yucca Mountain repository. 

However, the potential “sill” was found to be 10 Myr old (Miocene age), and may have formed in 

response to the higher magma volumes produced at that time, analogous to Miocene age sills 

to the east at Paiute Ridge on the Nevada Test Site. There is no evidence of Quaternary-age 

basaltic sills near Yucca Mountain. 

The new DOE data improve resolution of buried basaltic volcanic features and thereby 

reduce but do not eliminate uncertainties in spatial and temporal recurrence rates. Magnetic 

data alone cannot differentiate basalt from faulted tuff in areas with extensive tuff outcrops. 

Magnetic properties of tuffs and basalts are comparable, and without additional information, 

magnetic anomalies arising from fault to tuff or basalt appear quite similar. This ambiguity was 

apparent in interpretations of anomaly Q, which the U.S. Geological Survey ranked as unlikely 

to be buried basalt. The drill hole at anomaly Q encountered basalt at 140–163 m. Thus, areas 

with faulted tuff at or near the surface could contain additional, undetected basalt. This “present 

but undetected” designation adds uncertainty to volcano counts used in probability studies 

(Stamatakos et al., 2007). 

5.2.4. Undetected Igneous Activity 

Some analyses of the probability of igneous activity at Yucca Mountain (e.g., Geomatrix 

Consultants, 1996) provide for estimates of the number of basaltic events in the Yucca 

Mountain region that remain undetected. One objective of the 2004 high-resolution magnetic 

survey was to minimize the number of these events that need consideration in the analysis. 

The basalt of well 23P provides an example of the ability of the high-resolution survey to detect 

deeply buried basalts. This Miocene-aged basalt lies buried beneath 400 m of alluvium but 

nonetheless is associated with a magnetic anomaly, a normally magnetized, linear anomaly 

identified as “U” in Figure 32. On the other hand, there are some practical constraints on the 

resolution of the survey. For example, the Solitario Canyon dike, also of Miocene age, was not 

detected by the high-resolution survey, probably because it is a narrow and discontinuous 

tabular feature (<1 m wide), and the Tiva Canyon tuffs which were invaded by the dike can have 

locally enhanced magnetization that can mask the magnetic signature of the dike. Failure to 

detect these and other Miocene basalts that may be masked by the magnetic signature of tuffs, 

are deeply buried by alluvium, or occur as narrow dikes have no significant adverse effect on 

probability models that are based on the rates of Pleistocene or Plio-Pleistocene volcanic 

activity. The NRC considers Miocene volcanism in some of its probability analyses, but the DOE 

places a low weighting on Miocene basaltic volcanism in its evaluations. 

The DOE (2003) has reported partial burial of Pleistocene volcanic features. 

Nonetheless, Coleman et al. (2004) argue that erosion and deposition during the arid to semiarid climates of the Quaternary Epoch should be sufficiently limited to preserve the surface 

evidence of Pleistocene volcanic activity. Accordingly it is unlikely that Pleistocene events are 

undercounted. This conclusion is supported by the results of the recent drilling associated with 

PVHA-U, which has not found buried Pleistocene basalts. Most of the newly drilled basalts are 

Miocene in age. Anomaly G, and by association Anomalies F and H, are now interpreted as 

Pliocene basalts, which is consistent with the previous discovery of extensive buried basalts of 

similar age (~3.8 Ma) at Anomaly B (Figure 29 and Figure 32). The depth of these buried 

basalts is a function of their age, the elevation of the paleosurface on which they were 

deposited, proximity to paleodrainage systems, and local sedimentation rates since the time of 
67

volcanic activity. The buried Pliocene basalts occur at depths between 73 m (Anomaly B) and 

119 m (Anomaly G). The buried Miocene basalts range in depth from 77 m (JF-5) to 400 m 

(Nye 23P). 

The rocks that comprise Yucca Mountain record an integrated tectonic-volcanic history 

since the ~13 Ma tuffs were deposited by large-scale pyroclastic flows and volcanic ash falls. 

More than 20 years of intensive site characterization studies have included detailed geologic 

surface mapping, geophysical surveys, and construction and mapping of ~6 km of drifts in or 

near the repository. Hundreds of surface drill holes of varying depths have been drilled in the 

Yucca Mountain site vicinity. Coleman et al. (2004) conclude that it is unlikely that multiple dikes 

could exist in the repository footprint and escape detection in the site characterization. Drilling is 

an ineffective way to discover near-vertical dikes, but the deepest drill holes in the repository 

footprint were deep enough to locate basaltic sills if they were present. None were found. 

Aeromagnetic methods also can have difficulty locating basalts if dikes are small, because of 

interference with high amplitude, short-wavelength anomalies produced by faulted tuffs (Hill and 

Stamatakos, 2002). The best technique for finding basaltic dikes in the repository footprint was 

the detailed mapping of drift walls and the mapping of surface geology. In particular, the 

detailed mapping of fault expressions at the surface greatly enhanced the likelihood of locating 

dikes if they were present. 

No dikes have been found in the potential repository footprint at Yucca Mountain − this is 

a key observation. The northern part of the horst block that forms Yucca Mountain appears to 

represent a zone of relative volcanic quiescence during the last 10 Myr. Since that time 

volcanism has instead mainly focused within the alluvial basins to the east, west, and south, 

with no evidence of post-Miocene activity east of Yucca Mountain in Jackass Flats. If in the 

future the repository footprint were to be expanded westward, then one known dike would exist 

within that footprint, the Solitario Canyon dike, which intruded segments of the Solitario Canyon 

fault 10-12 Myr ago during Miocene time. Although changes in the areal footprint of the 

repository could affect probability calculations, the tendency for dikes to follow pre-existing faults 

or to be influenced by topographic effects could compensate for this by tending to divert dikes 

away from emplacement drifts. 

5.2.5. Change in Basaltic Volcanism with Time 

Rates of extension and volumes of basaltic volcanism have significantly declined in the 

four recognized episodes during the last 11 Myr (since late Miocene time) (Figure 33). There is 

compelling evidence that volcanism has waned in concert with this reduction in crustal strain. 

Fridrich et al. (1999) suggested that the ascent of basalt through the crust is structurally 

controlled in the Crater Flat basin because volcanic vents form a northwest-trending belt that 

coincides with the strongest transtensional (lateral and extensional) deformation in the basin. 

The approximate temporal correlation of volcanism and rates of extension suggest that they 

represent a single phenomenon—a tectonic system that may once have been among the most 

active zones in the Great Basin, comparable to tectonism in Death Valley today. Fridrich et al. 

(1999) interpret that the Crater Flat basin remains tectonically active, but is now in an advanced 

stage of decline. Although the overall pattern is declining, extensional faulting has been cyclical 

and has varied generally in parallel with episodic volcanism. 

The cumulative extension map of Fridrich et al. (1999) integrates the extension over the 

last 12 Myr in Crater Flat. It was previously known that the volumes of volcanic events 

significantly declined after Miocene time. Figure 34, developed by Frank Perry (2006), shows 

that volumes of Pliocene to Pleistocene volcanism have also declined, suggesting that 

magmatic systems near Yucca Mountain are dying. Further evidence lies in the declining 
68

maximum lava effusion rate and fissure length of Plio-Pleistocene basaltic activity in the Yucca 

Mountain region (Figure 35). 

Figure 33 Estimated extension rates in Crater Flat basin as a function of time and 

magma volume erupted as a function of time (From DOE, 2003). 

Figure 34 Age vs. volume of Plio-Pleistocene volcanic episodes in the Yucca 

Mountain region. Figure includes buried Pliocene basalts in the northern 

Amargosa Desert. The diameter of the circles is proportional to volume. 

The dot at far lower right represents Lathrop Wells. The dot to its left 

represents Sleeping Butte. The small circle at 1.1 Ma represents the five 

Pleistocene cones of Crater Flat (After Perry, 2006). 

Perry and Valentine (2007) discussed regional factors that may help explain long-term 

trends for volcanism in the Yucca Mountain region. Following the end of major caldera-forming 

silicic volcanism in the Southwestern Nevada Volcanic Field (SNVF), at least 10 episodes of 
69

alkalic basaltic volcanism occurred over the last ~11 Ma. A program of geophysics, drilling, 

radiometric dating, and geochemistry conducted since 2004 by Los Alamos National Laboratory 

and the U.S. Geological Survey, combined with previous and ongoing petrogenetic and physical 

volcanology studies, sheds more light on the early and middle evolution of the volcanic field, 

much of which has been buried in alluvial basins. Volumes of erupted basalt in this volcanic field 

greatly declined over time from as much as 50 km3 in the Miocene to about 0.5 km3

 in the 

Pleistocene. The volume decrease was accompanied by a dramatic decrease in extension rate, 

suggesting a close link between magmatism and tectonism. Neodymium and strontium isotopic 

analyses indicate that enriched lithospheric mantle has been the source of basalt throughout the 

history of the field. Decreasing eruption volumes were accompanied by a doubling of Ce/Yb 

ratios, indicating that the volume decrease reflects a decrease in degree of partial melting of the 

lithospheric source. Eruption style has also changed with time, reflecting an increase in magma 

volatile content consistent with decreased amounts of partial melting of a volatile-bearing 

source. These observations are consistent with a model in which the lithospheric mantle source 

was hottest during the period of major silicic volcanism (Miocene) and the presence of an active 

plate subduction system. After the breakdown of subduction, continued thermal input into the 

lithosphere ended and the lithosphere started to cool. Melt accumulation in non-convecting, 

static lithosphere is probably related to mantle heterogeneities enriched in hydrous minerals that 

are partially melted. During regional extension, these zones are relatively weak and 

preferentially deform, forming melt bands of increased porosity that concentrate melt and lead to 

dike generation. Decreasing regional extension results in less melt accumulation and 

decreasing eruption volumes. Without a new source of heat and limited lithospheric extension, it 

is likely that the next million years of volcanic activity in the field will likely be characterized by 

eruptions similar to those that have occurred in the past million years: infrequent eruptions of 

small-volume (<0.1 km3

), volatile-rich alkali basalt magmas within the most tectonically active 

southern and western margins of the volcanic field (Perry and Valentine, 2007). 

Figure 35 Plot of fissure length (lines) and lava effusion rate (dots) for PlioPleistocene volcanoes of the Southwestern Nevada Volcanic Field. Note 

that age determinations do not allow discrimination of relative ages 

amongst the five Pleistocene volcanoes in Crater Flat, therefore they are 

plotted in random order around 1 Ma. The eruptive products of SW and NE 

Little Cones are largely buried by alluvium and mapped by aeromagnetic 

anomalies (Valentine et al., 2006); their volumes are lumped together in this 

plot (After Valentine and Perry, 2006) (Permission to use this copyrighted 

material is granted by the American Geophysical Union). 
70

Valentine and Perry (2007) summarize physical volcanological, geochemical, and time–

volume characteristics of the Plio-Pleistocene part of the Southwestern Nevada Volcanic Field 

(SNVF) as an example of an extremely low volume-flux end member of basaltic fields. The 

SNVF has produced 17 volcanoes of dominantly trachybasaltic composition over the past 5 Myr 

with a total volume of slightly less than 6 km3

. Eruptive fissure lengths, volumes, and inferred 

lava effusion rates decreased between Pliocene- and Pleistocene-age volcanoes. Major 

element data suggest that most of the magmas underwent similar degrees of fractionation 

during ascent, and trace element compositions indicate a decrease in the degree of partial 

melting of the lithospheric mantle source since about 3 Ma ago. Isotopic data support an 

interpretation where magmas ascended quickly from their source regions with little if any 

interaction with crustal rocks. Relationships between age and cumulative erupted volume 

indicate that the repose interval between eruptive episodes is determined by the volumes of 

prior episodes and, since approximately 3 Ma, an average eruption rate of ~0.5 km3

/Myr, i.e., 

the field is time-predictable. These features support a model where magmatism is a passive 

result of regional tectonic strain. Partial melt resides in pockets of lithospheric mantle that are 

relatively enriched in hydrous minerals. Slow deformation focuses melt, occasionally resulting 

in sufficiently high melt pressure to drive dikes upward and feed eruptive episodes. Larger 

source volumes result in larger eruptive volumes and wider dikes that relieve relatively more 

strain in the crust than smaller volume events, and therefore are followed by longer repose 

intervals required for recovery of crustal stresses. Valentine and Perry (2007) suggest that 

time-predictability may be a fundamental property of tectonically controlled basaltic fields, where 

melt accumulation and ascent are controlled by tectonic strain rate. This behavior contrasts with 

magmatically controlled fields where magma flux is great enough to overwhelm local tectonic 

strain, eruptions are primarily caused by magmatic processes that build pressure in reservoirs, 

and the systems are more likely to be volume-predictable (Valentine and Perry, 2007). 

Valentine and Perry (2007) conclude that if basaltic volcanism in the SNVF continues to 

exhibit tectonically controlled, time-predictable behavior with a ~0.5 km3

/Myr eruptive volume 

flux, their linear regression model (time to next episode is dependent on previous episode's 

volume) suggests that the next episode of volcanic activity somewhere in the volcanic field will 

occur ~270 kyr after the Lathrop Wells episode (with a 90% prediction interval of ±290 kyr 

reflecting the small data set), or about 190 kyr in the future (Valentine and Perry, 2007). The 

interval to the next episode predicted by the time–volume relationship is consistent with SNVF 

recurrence intervals that have been estimated using probabilistic approaches. One caveat they 

offer is that it is possible that the ~77 ka eruption of Lathrop Wells volcano might be the start of 

an episode rather than comprising an entire episode. The lapsed time since the Lathrop Wells 

event suggests that it is likely to have been the sole event in its episode, but this cannot be 

proven. This highlights the value of probabilistic approaches that incorporate uncertainties into 

temporal recurrence models, rather than relying only on deterministic, empirical time-predictable 

behavior. Time-predictability in a tectonically controlled field does not constrain the size or 

location of potential future episodes, requiring the incorporation of additional information. The 

fact that most of the basaltic episodes (except the ~2.9 Ma Buckboard Mesa event) have 

occurred near existing clusters suggests that the magmatic footprints of future events will 

probably also occur near or within those clusters. General similarities in volcano size and 

eruptive styles during the past ~1.1 Myr suggest that the future events during the next 100s of 

kyr will have similar characteristics (Valentine and Perry, 2007). 

The 80-ka Lathrop Wells volcano (Heizler et al., 1999) represents the youngest event in 

the vicinity of the Crater Flat basin. Fridrich et al. (1999) report that it lies between the southern 

ends of the Windy Wash and Stagecoach Road faults, the most active site of late Pleistocene 

faulting in the Crater Flat basin. They also report a close spatial and temporal relationship 
71

between sites of extension and volcanism throughout this basin. The occurrence of the three 

episodes of post–Miocene volcanism in the southwestern part of Crater Flat basin suggests that 

volcanism is less likely to occur at Yucca Mountain, which lies outside the transtensional zone in 

an area where no post-Miocene volcanism has occurred. Fridrich et al. (1999) reported that 

other geologic and geophysical studies provide corroborative evidence that areas of maximum 

extension in the southwestern Crater Flat basin correspond closely to volcanic source zones. 

Alternatively, Smith et al. (2002) and Ho et al. (2006) suggest that the volcanism in the 

Yucca Mountain region is related to a common mantle zone of melt that extends from Death 

Valley through Crater Flat to the Lunar Crater volcanic field roughly 140 km north of Yucca 

Mountain (Figure 36). They hypothesize that the episodic volcanism of the Crater Flat-Lunar 

Crater trend shown in Figure 37 is related to varying strain accumulation in the lithosphere and 

“volcanism is not dead and another eruption peak is possible” (Smith et al.,2002, p. 9). The 

implication of their model is that the recurrence rate of volcanism in the Yucca Mountain region 

could increase dramatically in the future, perhaps by as much as an order of magnitude, to the 

rates observed in Lunar Crater volcanic field. However, as argued by Perry et al. (2005), there 

are major differences between volcanic activity in Lunar Crater and the Yucca Mountain region 

that indicate it is unlikely there is a connection between the volcanism in these regions. In 

addition to the significant differences in the recurrence rate and volume of volcanic activity, 

there are major variations in the trace element chemistry of the Pleistocene volcanic rocks of the 

two areas (Farmer et al., 1989) that indicate quite different source zones for magma in the 

mantle rocks. Accordingly, the Yucca Mountain region source may be unlikely to produce 

frequent or large volumes of basalt. 

Figure 36 Age and distribution of Pliocene-Pleistocene basaltic volcanoes in Crater 

Flat-Lunar Crater zone (CFLC) (After Smith and Keenan, 2005) (Permission 

to use this copyrighted material is granted by the American Geophysical 

Union). 
72

Figure 37 The number of volcanic events as a function of time in the Lunar CraterReveille Range and Yucca Mountain areas. Note that the scale for the time 

axis does not have equal intervals (After Smith et al., 2002) (Permission to 

use this copyrighted material is granted by the Geological Society of 

America. 

Although Figure 37 appears to support periodicity of volcanism, this view is distorted by 

the nonlinearity of the time scale. Furthermore, regional extension rates (Figure 33), magma 

volumes (Figure 34), and fissure lengths and lava effusion rates (Figure 35) show evidence of 

clustering (and declining) activity over time but do not provide evidence of periodicity. 

5.3. Time Period Used in Extrapolation of Igneous Activity 

The time period used to evaluate future igneous activity should be reasonably 

representative of present-day geologic and tectonic conditions. For example, there is no 

evidence that the extensive felsic pyroclastic eruptions that formed the surface rocks at Yucca 

Mountain ~13 Myr ago will recur. The dramatic decline in both tectonism and basaltic volcanism 

over the last 11 Myr indicates that crustal conditions during post-Miocene time (<5.3 Ma) are 

more representative of present-day conditions than of those that prevailed during the Miocene 

Epoch. The last tuff-forming eruptions occurred in the region ~7.7 Ma ago, depositing the 

Thirsty Canyon Tuff. There is also greater uncertainty about the actual numbers of Miocene 

events because of concealment by younger volcanics and the longer time available for physical 

erosion and burial by alluvium. In developing estimates of volcanism recurrence rates, more 

reliable counts can therefore be made of Pliocene, and especially of Pleistocene, events for 

extrapolation purposes (Coleman et al., 2004). 

5.4. Controls on Occurrence of Igneous Activity 

In developing a sound basis for estimating the probability of igneous events, it is 

necessary to identify the most likely areas of the Yucca Mountain region for the occurrence of 

igneous activity. An active magma chamber and crustal conditions favorable for the magma to 

rise to the surface are both needed for basaltic igneous activity to occur. 

Efforts have been made to isolate active magma chambers in the upper mantle of the 

Yucca Mountain region using tomographic methods to identify seismic velocity variations 
73

associated with the partial melts of the magma chambers (e.g., Evans and Smith, 1992 and 

1995; Connor and Sanders, 1994). Unfortunately, these studies have not led to definitive 

results. Evans and Smith (1995) find a weak low seismic velocity feature beneath Crater Flat 

that may represent crustal heating beneath the basin. Biasi (2005) reported to the PVHA-U 

panel that he has mapped variations in seismic velocity in the upper mantle in the Yucca 

Mountain region that he relates to surface features. He interprets the velocity variations within 

the mantle as a dehydrated root extending to depths of 300 km beneath the Timber 

Mountain/Silent Canyon caldera complex north of Yucca Mountain that is related to the caldera 

volcanism. Post-Miocene basaltic events occur on the margin of the dehydrated root. Beneath 

parts of Crater Flat basin, Biasi’s data indicate slow velocity mantle that is separate from the fast 

velocity root beneath the calderas. The position of the proposed repository is in the diffuse 

boundary between these two areas. Biasi suggests that the waning volcanism in this area is 

more indicative of the effect of the dehydrated root than cooling of the system. His investigations 

indicate that the Plio-Pleistocene volcanism has dehydrated the mantle underlying Crater Flat, 

thus somewhat cooling it and increasing its melting temperature, suggesting that the area may 

be less prone to volcanism in the future. Other remote sensing techniques of isolating the 

magma chambers are insufficiently sensitive to the minor effects of the magma reservoirs 

associated with the basaltic volcanism. 

O’Leary (2001) described possible tectonic controls on basaltic volcanism near Yucca 

Mountain. He noted that the Plio-Pleistocene basalts near Yucca Mountain are transitional 

alkaline-olivine basalts or trachybasalts, which are typical of other basalts of that age in the 

western Great Basin. Such basalts are generally thought to originate as partial melts of 

lithospheric mantle, uncontaminated by crustal components. Each volcano probably represents 

a batch of magma collected from a resident equilibrium melt, with upward pathways being 

provided by local tectonic conditions. Given the low rate of post-Miocene extension, O’Leary 

(2001) proposed that present-day melt generation near Yucca Mountain would not be influenced 

by decompression, and further stated that the small extrusive volumes are not likely to be 

influenced by buoyancy. 

Most of the volcanic centers originating over the past 5 Myr are located in Crater Flat 

basin or in the Amargosa Desert. Some of the cones show a NNE-oriented alignment. This 

alignment of small-volume eruptions, the relatively high volatile content of the erupted materials, 

and lack of crustal contamination or evidence of fractionation suggest that the magmas ascend 

directly from an upper mantle source along fractures influenced by right-lateral transtension 

(O’Leary, 2001). A tectonic model that treats Crater Flat basin and the Amargosa trough as a 

graben/rift feature modified by right-lateral shear, and accounts for extension effects and 

fracturing in the upper mantle melt zone, provides a mechanism for basalt rise through the crust 

as well as a structural association with observed tectonic features. Consistent with the apparent 

waning volcanism, activity should decrease over time as local magma reservoirs are depleted 

and the magma solidification temperature is pushed to greater mantle depths with a cooling 

lithosphere (O’Leary, 2001). 

O’Leary (2007b) described the Crater Flat basin as a half-graben controlled by 

subsidence along the Bare Mountain fault (Figure 13). The basin can be interpreted as a 

southward propagated rift within the older, shallower Amargosa trough. This trough is a seam 

between major crustal blocks: the Spring Mountains block and the Funeral Mountains-Bare 

Mountain blocks. The trough is probably pre-middle Miocene in age. Crater Flat basin 

originated about 12 Ma, during and following deposition of the Paintbrush and Timber Mountain 

Groups (tuffs). Basin subsidence, along with right-lateral transtension, produced the present 

structure and configuration of Yucca Mountain. O’Leary (2007b) proposed a rift propagation 

model for Crater Flat basin, based on stress history and on analysis of enhanced satellite image 
74

data and recently acquired high-resolution aeromagnetic data. Rift propagation of Crater Flat 

basin as a wedge-like opening under influence of dextral transtension explains problematic 

structures in the transition zone between Crater Flat basin and the Amargosa Desert, and also 

provides a context for the Miocene to Pleistocene basaltic volcanism in this area 

(O’Leary, 2007b). 

The DOE (2003) summarizes stress conditions near Yucca Mountain. Along with 

faulting, magma intrusion is an important component of worldwide crustal extension (Parsons 

and Thompson, 1991). Yucca Mountain lies in the southern Great Basin in the Basin and Range 

province, which is undergoing active ESE–WNW extension (Zoback and Zoback, 1989). The 

crustal stress in the Yucca Mountain region has been investigated using hydraulic-fracturing 

stress measurements, borehole breakouts, drilling-induced fractures, earthquake focal 

mechanisms and fault-slip orientations (Stock and Healy, 1988). Dikes tend to strike orthogonal 

to the direction of the least compressive horizontal stress (parallel to the direction of the greatest 

compressive horizontal stress; Pollard (1987)). The orientation of the greatest compressive 

horizontal stress in the Yucca Mountain region is approximately N30°E ±15 degrees. 

Uncertainty in this orientation results from both inaccuracies in measurement and real variations 

in stress with depth and location which vary by up to 40° in Yucca Mountain drillholes (Stock 

et al., 1985). 

The Crater Flat structural domain is a basin bounded on the west by the Bare Mountain 

fault (Figure 11) and on the east by structures beneath Jackass Flats. Seismic reflection 

surveys show that the Crater Flat basin is deepest on the western side (Brocher et al., 1998). It 

includes the Crater Flat topographic basin on the west and Yucca Mountain near the center of 

the structural domain. Because the potential repository lies within the Crater Flat structural 

basin, the structural and geophysical features of the domain, and the degree to which they 

influence the location of volcanism within the domain, have been key factors in conceptual 

models for assessing hazards to the repository (DOE, 2003). 

Connor et al. (2000) hypothesized that magmas ascending a steeply dipping fault may 

be diverted laterally by as much as 5 km depending on the depth of dike capture by the fault 

and the dip of the fault plane. Dikes also have a tendency to break out of the fault system and 

propagate vertically at shallow depth because of rapid changes in the magnitude and orientation 

of the stress field. Therefore cinder cones are often located beside faults in the hanging wall of 

the fault. The arcuate map pattern of the Pleistocene Crater Flat alignment may partly owe its 

origin to this mechanism. The dip of the Bare Mountain fault shallows progressively northward 

(Ferrill et al., 1996) and cinder cones along the alignment are displaced progressively eastward. 

Basin and Range normal faults commonly grow by formation, propagation, and amalgamation of 

smaller normal faults (Ferrill et al., 1999). This progressive fault growth commonly involves 

development of en echelon fault systems. Ferrill et al. (1999) identified the Solitario Canyon 

fault and related west-dipping faults on the western edge of Yucca Mountain as one such set of 

left-stepping en echelon faults produced by progressive deformation. The Pliocene vents 

immediately south and west of these fault segments reflect this trend, forming a left-stepping 

array of vent alignments. En echelon fault geometries may therefore provide preferential 

pathways to the surface for magmas ascending along fault segments. Linear, north-trending 

magnetic anomalies intersect Northern (Makani) Cone, located in the Crater Flat basin. These 

anomalies result from vertical offsets across faults that are arguably part of the same array of 

left-stepping normal faults. At the western edge of the proposed repository, a Miocene-aged 

dike intruded a segment of the Solitario Canyon fault. Such relationships indicate that the en 

echelon array of faults has hosted dikes at least three times in Miocene through Pleistocene 

time. 
75

Spatially, most of the Plio-Pleistocene basalts near Yucca Mountain erupted in basins 

rather than on topographically high ranges. Basalts in basins include the Pleistocene aged 

cones of Crater Flat, the Lathrop Wells cone, Pliocene Crater Flat, and buried basalts of 

Pliocene age located by drilling (Anomalies B and G, and by inference, Anomalies F and H). 

There is a clear preference for Plio-Pleistocene basalts to erupt in basins, the shortest path to 

the surface for dikes. Panelists of the ongoing PVHA-U have discussed this phenomenon and 

have requested that DOE develop a dataset of lithostatic (overburden) pressure variations to 

compare with areas where past volcanism has occurred. At Yucca Mountain itself intrusions 

may have been inhibited over the last 10-12 Myr by higher rock pressure compared to the 

Crater Flat basin area to the west. Lithostatic pressure data provide information on likely 

magma flow paths in the upper crust. In waning volcanic systems like the Crater Flat region, the 

driving energy of the magma systems is small enough that lithostatic pressure variations may be 

sufficient to help guide magma flow paths. Eruptions from such systems would hypothetically be 

favored to occur in basins where the pressure from the overlying rocks is lower rather than in 

adjacent topographically high areas like Yucca Mountain. This concept was investigated by 

Parsons et al. (2006) using three-dimensional finite-element modeling to determine the 

sensitivity of basalt intrusions and faulting to the magnitude and orientation of the least principal 

stress in extensional terranes such as the Yucca Mountain region. They found that in the 

absence of fault slip, lithostatic pressure variations favored intrusions into Crater Flat. However, 

when faults were allowed to slip, intrusions were not favored in either the Crater Flat basin or 

the central Yucca Mountain block, but rather near fault terminations. They find the latter 

situation is consistent with the Lathrop Wells volcano. 

There are exceptions, but most of the basaltic eruptions near Yucca Mountain occurred 

in the basins. More energetic magma systems of greater volume (e.g., Reveille Range-Lunar 

Crater) could be less sensitive to lateral lithostatic pressure variations and, therefore, show a 

lesser tendency to concentrate eruptions in topographic lows. 

Gaffney and Damjanac (2006) investigated topographic effects on dike propagation and 

conduit formation. They modeled magma flow in a dike rising in a fault whose strike extends 

from a highland to an adjacent lowland. Their results indicate that a dike rising from great depth 

near the transition from a lowland to a highland, and striking across that transition, will 

preferentially erupt toward the lowland and will avoid intrusion into the highland. The 

concentration of flow away from the ridge will focus advective heat flow in that region, 

maintaining low viscosities, which will in turn favor conduit localization in the lowland portion of 

the strike length of the dike (e.g., Wylie et al., 1999). Separation of the geometric effect of the 

topography from its effect on lateral confining stresses on the crack indicates that both 

contribute to the diversion effect but that the effect of stress is less important. The authors 

concluded that their analysis explains the tendency for eruptions to occur in lowlands, but does 

not preclude eruptions on highlands. Gaffney and Damjanac (2006) further concluded that the 

scenario they modeled mimics topography around the proposed repository at Yucca Mountain, 

so that their results may indicate some reduction in volcanic hazard to the repository site. Along 

with insights about locations of enhanced crustal extension, the topographic analysis by Gaffney 

and Damjanac (2006) helps to explain why Plio-Pleistocene volcanism near Yucca Mountain 

focused in lowlands rather than on topographic highs. The number of events in the basins is 

approximately an order of magnitude greater than in highlands. 

Gaffney et al. (2007) further investigated the effects of pre-existing geologic structures 

on the propagation of dikes. They examined the capture of vertically rising dikes by faults, using 

a combination of an analytic solution, numerical simulations, and field observations. One of the 

numerical solutions and the field observations also provide insights about the intrusion of sills 

into the hanging wall of faults that are reactivated when lubricated by magma. The approximate 
76

analytic solution indicates that dike capture by a fault will be limited primarily to steeply-dipping 

faults. Capture will become easier, meaning that it will be possible for faults with shallower dips, 

as the intersection of the dike with the fault occurs at smaller depths. Capture will also be easier 

as it is harder for a crack to grow in the hanging wall. Gaffney et al. (2007) interpreted this in 

terms of a higher tensile strength, shorter preexisting cracks, or higher fracture toughness. 

Numerical analysis using a discrete element code confirms this conclusion but also shows that 

the analytic solutions overestimate the difficulty of intruding a pre-existing fault, the maximum 

deviation occurring for faults dipping at 45°. This finding that dike capture by faults should be 

restricted to high-angle faults and shallow depths is supported by field observations of exhumed 

Miocene basaltic volcanics in central Nevada. Gaffney et al. (2007) attributed differences in 

style seen in other regions to the rock properties and the regional stress field. The numerical 

solutions also indicate that synintrusive fault slip is likely to lead to formation of sills in the 

hanging wall at depths of a few hundred meters or less: a finding that is also consistent with the 

field observations in Nevada. Gaffney et al. (2007) report that their results should be applicable 

to basaltic volcanic fields in tectonically neutral to extensional environments (on a local or 

regional scale) where dike injection is mostly vertical and where normal faults are abundant. 

This combination is most likely to occur in low magma flux systems such as the Southwestern 

Nevada Volcanic Field (Valentine and Perry, 2006). In higher flux basaltic fields, normal faults 

are less abundant because tectonic strain is taken up by magma injection instead of faulting. 

5.5. Calculation Methods 

Many methods have been used to predict future volcanism. Most are directed toward 

the near real-time eruption of existing volcanoes. These predictions are increasingly successful 

with increasing knowledge of the cause and mechanisms of volcanic activity. However, 

consideration of volcanic activity at Yucca Mountain involves the likelihood, location, and nature 

of new igneous activity that could intersect the repository over time frames of tens and hundreds 

of thousands of years. In this section the methods of prediction are described including the use 

of physical precursors, analysis of hypothetical linkages between volcanic fields, and various 

mathematical and statistical methods that can be used to analyze past spatial and temporal 

patterns of volcanism. The latter is the generally used method for studying Yucca Mountain 

region igneous activity and thus is the primary focus. 

5.5.1. Physical Precursors 

Many volcanoes repeatedly erupt in one place over geologic time (polycyclic volcanoes). 

Examples include Kilauea, Mount Suribachi, Mount Etna, Vesuvius, and the Cascade volcanoes 

(Mounts Rainier, St. Helens, Hood, and many others). The main eruption of Mount St. Helens in 

1980 was anticipated by real-time phenomena, such as an increase in seismic activity, changes 

in gaseous emissions from the summit crater, and changes in the volcano’s topography. Nine 

main pulses of activity have occurred at Mount St. Helens in the last 40,000 years, with multiple 

eruptions in each pulse (Tilling et al., 1990). In contrast, there is no evidence that the basaltic 

eruptions during the last 5 million years near Yucca Mountain were polycyclic (Valentine 

et al., 2006). They formed discrete cinder cones and associated lava flows. The most recent 

volcanic activity near Yucca Mountain formed the Lathrop Wells cone and basalt flows that have 

undergone extensive study (Zreda et al., 1993; Fleck et al., 1996; Heizler et al., 1999; Nicholis 

and Rutherford, 2004; Valentine et al., 2005, 2007). 
77

As reported by Fridrich et al (1999) there is an observed relationship in the Yucca 

Mountain region between strain rate and volcanism. Wernicke et al. (1998) suggested that the 

region is experiencing an epoch of anomalously rapid crustal strain accumulation, and that 

hazard analyses based only on the local record of magmatic and tectonic events would 

underestimate the probability of future events by an order of magnitude. The claim of 

anomalous strain was countered by Savage (1998) who reported a N65°W strain rate of 8 ± 20 

nanostrain/yr. He found that Wernicke et al. (1998) did not include monument instability in their 

error budget and did not give proper weight to the strain effects of the nearby 1992 Little Skull 

Mountain earthquake. Later work by Savage et al. (2001) continued to find that the principal 

extension rate averaged over their 50-km geodetic array is substantially less than reported by 

Wernicke et al. (1998) and is consistent with the low extension rate inferred from the geologic 

record. Likewise, Connor et al. (1998) noted that the lack of a known volcano younger than the 

Lathrop Wells event diminished the argument that volcanic recurrence rates have been 

underestimated by an order of magnitude. Therefore, present-day strain rates do not support an 

order of magnitude increase in hazard from tectonic or magmatic events. Furthermore, as 

discussed above, seismic tomographic methods have not provided definitive information on the 

presence of magma chambers within the mantle because of their great depth and limited size. 

5.5.2. Proposed Linkages to Other Volcanic Zones 

Smith et al. (2002) and Ho et al. (2006) propose that the volcanoes near Yucca 

Mountain are part of a larger zone of basaltic volcanism associated with a common area of hot 

mantle that extends from Death Valley northward to the Reveille Range-Lunar Crater (RLC) 

volcanic area (Figure 36). Within this zone, volcanism is of similar age with three peaks of 

volcanism: one between 9.5 and 6.5 Ma, the second from 4.5 to 3.5 Ma, and the most recent 

between 1.5 and 0.5 Ma (Figure 37). Smith et al. (2002) report that volcanism in this zone is 

relatively quiet at present, with only three eruptions in the last 80,000 years. Episodic volcanism 

in the Crater Flat-Lunar Crater zone may be related to episodes of rapid strain accumulation in 

the lithosphere. They concluded that a zone of hot, buoyant mantle exists beneath this zone 

and provides a common driving force for magmatism. Smith et al. (2002) propose that the 

magma that erupted in these volcanic zones had a common source. 

Volcanism recurrence rates in the RLC are approximately four times higher than in 

Crater Flat near Yucca Mountain. Smith and Keenan (2005) suggested that the higher 

recurrence rates in the RLC may occur in the future in the Yucca Mountain area. They 

concluded that the higher recurrence rates, along with data from future geophysical surveys, 

could result in a probability of volcanic disruption of a repository that is one to two orders of 

magnitude greater than the EPA guideline for consideration of disruptive events. Smith and 

Keenan (2005) suggested that the probability of repository disruption could be as high as 10-7/yr 

to 10-6/yr. A key implication of their model is that recurrence rates in the Yucca Mountain region 

could increase to rates typical of the Lunar Crater volcanic field in the future. Perry et al. (2005) 

commented that the hypothesis is inconsistent with the Quaternary volcanic history of the two 

volcanic fields, which for the past million years have differed significantly in recurrence rate and 

eruption volume. Compared to the eight Quaternary cones in the Yucca Mountain region (with a 

total eruption volume of <0.5 km3

), there are ~80 Quaternary cones in the Lunar Crater field, 

with a total eruption volume that is one to two orders of magnitude greater than in the Yucca 

Mountain region during the Quaternary. These major differences, plus major differences in 

neodymium and strontium isotopic composition (Farmer et al., 1989), are consistent with models 

of hotter asthenospheric mantle and colder lithospheric mantle sources for the Lunar Crater 

volcanic field and Yucca Mountain region, respectively. The contrasting eruptive histories and 

mantle sources with different magma production potentials, suggest the two volcanic fields 
78

should not be linked for purposes of assessing volcanic hazards at Yucca Mountain (Perry 

et al., 2005). Smith and Keenan (2005) have suggested that the isotopic differences between 

the volcanic fields could be explained by contamination of rising magma by lithosphere of 

different composition or age. 

Tynan et al. (2004) proposed that “mega-rings” surround the Timber Mountain caldera 

complex, defining a zone ~80-100 km in diameter centered on Timber Mountain. The megarings encompass known smaller rhyolitic nested Miocene calderas (~11-15 Ma, < 10 km circular 

to elliptical small "rings") and later stage basaltic features (< 11 Ma, small flows, cones, dikes) in 

the Southwest Nevada Volcanic Field. Miocene rhyolitic calderas cluster within the central area 

and on the outer margin of the interpreted larger mega-ring complex. Tynan et al. (2004) 

commented that the mega-ring interpretation is consistent with observations of regional 

physiography, tomographic images, seismicity patterns, and structural relationships. Mega-rings 

consist of arcuate faulted blocks with deformation patterns showing a genetic relationship to the 

Timber Mountain volcanic system; they appear to be spatially associated and temporally 

correlated with Miocene volcanism and two geophysically identified crustal/upper mantle 

features (Tynan et al., 2007). 

Carlson (2005) gave a presentation to the PVHA-U expert panel titled “Spatial 

Distribution: Why is Volcanism Where it is Around Yucca Mountain?” For Miocene and postMiocene basalts, he described the appearance of a nearly circular volcanic field centered 

around the Timber Mountain caldera complex with a more-or-less random distribution and some 

suggestion of spatial clustering. In Miocene time volcanism was active in Jackass Flats but not 

in post-Miocene time. Carlson (2005) described several plausible patterns for post-Miocene 

volcanism, depending on whether the basalts of Buckboard Mesa are included. In one case he 

described a shrinking circular volcanic field centered on the Timber Mountain caldera complex. 

In a second case (excluding Buckboard Mesa) the pattern suggests contraction of the original 

volcanic field to a linear vent alignment that reflects strong control by the local structure and 

stress field. He suggested it may be possible to decide between the two cases by investigating 

the causes of magnetic anomalies in the region through the drilling and dating of buried basalts. 

5.5.3. Expert Elicitation 

Although acquisition and analysis of physical data are the primary methods of 

determining the probability of an igneous event intersecting the proposed repository, the 

complexity of the igneous process and limitations in knowledge of the process and related 

parameters has led to a variety of professional opinions resulting in contrasting hazard 

evaluations. In an effort to evaluate the probability in the face of these contrasting views and the 

lack of a clear path to resolving them, the DOE implemented an expert elicitation of the volcanic 

hazard, the Probabilistic Volcanic Hazard Analysis (PVHA). Expert elicitation is a formal, highly 

structured, and well-documented process whereby the judgment of a range of experts in the 

discipline is determined and combined to provide a composite evaluation and the range of 

uncertainty associated with that evaluation. The experts do not create knowledge, rather they 

synthesize disparate and often conflicting sources of information to produce an integrated 

picture (Hora, 1993). The use of expert elicitation is accepted in the licensing arena providing 

that a series of protocols are faithfully followed in organizing, conducting, documenting, and 

evaluating the process (Kotra et al., 1996). 

The goal of the DOE’s expert elicitation was “To represent the center, the body, and the 

range of the technical interpretations (regarding volcanic hazards) that the larger informed 

technical community would have if they were to conduct the study.” (Coppersmith, 2007). The 

results of this evaluation of the views of ten experts are described by Geomatrix Consultants 
79

(1996) and are referred to as PVHA-96. The Geomatrix Consultants report describes the 

organization, process, and the results of the elicitation. Kevin Coppersmith, the Technical 

Facilitator Integrator for the PVHA-96 as well as the current PVHA-Update, has described 

specific aspects of the process. His description of the expert elicitation process with minor 

editing is provided below. 

With regard to spatial distributions of future events, there was a range of assessments 

across the expert panel and for any given expert (i.e., the experts were free to exercise multiple 

conceptual models). Spatial PVHA models define the spatial variation in the relative intensity of 

future events and, when combined with a temporal model define the rate of future events for any 

location within the region of interest. One spatial model used by some experts called for a 

homogeneous spatial distribution (“random”) within expert-defined zones. Uncertainties 

associated with this model were quantified, including alternative zone configurations and 

uncertainty in the zone boundary locations. Additional spatial models used by some experts 

result in a future spatial distribution defined by proximity to past events (e.g., spatial smoothing 

models) or proximity to groups of past events (e.g., field shape models). 

In PVHA-96, there were no assumptions made regarding either the temporal or spatial 

distribution of volcanic events in time. The assessment of future distributions varied with the 

individual expert and, in some cases, individual experts used more than one model. Across all 

experts, three temporal models were used: a homogenous Poisson model (commonly thought 

of as “random”), non-homogenous Poisson models (allowing for a time-dependent rate that can 

be either increasing or decreasing), and a time-volume model that considers the change in 

cumulative magma volume and volume-per-event over time in estimating the current and future 

rate. For all three approaches the rate was estimated based on the number of expert-identified 

volcanic events over a time period identified by the expert as relevant (e.g., over Quaternary 

time). 

Several temporal models were considered by the experts, including models with timedependent rates and models that focus on the change in magma volume over time. An 

interpretation of “waning” volcanism over the past several million years has been made primarily 

on the basis of observed decreases in cumulative volume and volume-per-event, but not 

necessarily on the basis of observed decreases in rate. For example, it is well documented that 

the rate of events in the Yucca Mountain region was low during the 3.7 to 1 Ma timeframe, but 

this was followed by a period of higher rate about 1 Ma ago (Figure 37). The time-volume 

models used by some experts were developed explicitly to capture these changes and generally 

led to estimates of decreases in the volumes over time. 

The PVHA process concentrated on quantifying uncertainties and arriving at a full 

probability distribution. Subsequent to the study, the focus has been on the mean value of 

probability as a summary measure for the results. The mean value exceeds the limit for 

screening out events, and the mean level of seven of the ten experts was at or above the 

screening level (i.e., 10-8/yr). However, the entire probability distribution of the annual 

probability of dike intersection is passed to the DOE’s TSPA, obviating confusion about the 

PVHA results. For convenience and discussion, the mean or median (or some percentile) of the 

distribution may be cited, but the risk analysis incorporates the entire distribution. As a 

probabilistic analysis designed to capture uncertainties, the PVHA process discouraged 

invoking conservatisms or optimisms to deal with uncertainty. Rather, experts were encouraged 

to identify and to quantify their uncertainties in conceptual models and parameters. 
80

With respect to volcanic source zones, the experts considered that any part of the 

Southern Basin and Range would have a finite likelihood of hosting a basaltic igneous event, 

albeit at a low recurrence rates. This is due to the extensional tectonic environment and the 

observations throughout the region of basaltic igneous events as a response to crustal 

extension. Generally, the experts used the rates of events over larger regions (e.g., the 

Southern Basin and Range region) to estimate the rates for these zones. The experts also used 

comparisons with other zones in the Yucca Mountain region and assessments of the relative 

rates of volcanism. However, in other evaluations where the Yucca Mountain block was within a 

zone with no known past events, they used the approaches described above to estimate a rate 

for that zone. However, in some cases, the Yucca Mountain block was within a zone that 

included past events (such as the Crater Flat basin or events to the north at Thirsty Mountain 

and Buckboard Mesa). The relative distribution of recurrence rate was defined by the spatial 

model and temporal model for that zone. 

With regard to rates of volcanic activity, there is an important distinction between “event 

frequencies” and “intersection frequencies.” The first is an expression of recurrence rate and is 

given as a rate density (i.e., number of events per year per square kilometer) and varies with 

location according to a spatial model. Intersection frequencies are the rates of events that 

intersect with the repository. The latter is developed considering both event frequencies and 

dike geometries (azimuth and length), considering both those events (points) that are located 

within the repository footprint and those events whose dike would extend into the repository 

footprint. Volcanic event frequency is illustrated in Figure 38, where the variation in rate is 

aggregated across the PVHA assessments displayed as mean frequency per year per square 

kilometer. The location of the repository is shown as the black rectangle on the figure. 

The PVHA-type elicitation process involves a number of attributes (e.g., multiple experts, 

dissemination of databases, interactions of experts, vetting of proponent views, feedback) that 

are all designed to improve the precision of the assessments. This is much more complex and 

requires greater engagement and learning on the part of the experts than merely eliciting 

experts on a particular technical topic. 

Figure 38 Spatial distribution of expected volcanic event frequency defined by the 

Probabilistic Volcanic Hazard Analysis Expert Panel. The map represents the 

mean results averaged over 10 experts and over each expert’s logic tree. The 

black area in the center of the map is the location of the proposed repository (From 

Figure 6-11 of BSC, 2004b). 
81

5.5.4. Mathematical and Statistical Techniques 

Various methods can be used to analyze spatial and temporal patterns of past volcanism 

to gain insights about where future events might occur (e.g., Connor and Hill, 1994). Most 

volcanic fields are only partially characterized. The Crater Flat volcanic field is relatively wellstudied both in terms of surface exposures and buried basalts that have been identified with 

geophysical studies and subsequently drilled and dated. Extensive field geology and 

petrographic work also have been performed on basalts near Yucca Mountain. 

5.5.4.1. Data-Based Approach 

Estimates of the probability of an igneous event intersecting the proposed repository 

have employed a general methodology used for predicting events in existing volcanic fields. The 

critical variables in this methodology are the spatial and temporal models developed from the 

intensive studies of the volcanoes in the Yucca Mountain region. However, interpretation of the 

results of these studies has led to differing input parameters to the methodology, resulting in a 

range of probabilities covering roughly two to three orders of magnitude. 

The general method used in determining the probability of a future intersecting event is the 

product of two quantities: (1) the estimated recurrence rate, N(R,T)/T, the recurrence rate, 

which is the number of igneous events within a specified volcanic zone adjacent to or including 

the site of the repository over a specified time period [N(R,T)] divided by the specified time 

period (T), and (2) the conditional probability of disruption within the footprint of the repository 

(ar), given the occurrence of an igneous event, ar/A which is the area of the footprint of the 

repository divided by the area of the volcanic zone (A) used in establishing the number of 

igneous events. The conditional probability of disruption relates the recurrence rate to the 

footprint of the repository and the area over which the recurrence rate is calculated. Thus, the 

probability of a future igneous event intersecting the repository per year. 

P = [N(R,t)/T] x [ar/A], 

where the time duration (T) is given in years. 

A variation on this methodology has been considered by Ho et al. (2006) that 

incorporates procedures prescribed by the US Federal Aviation Administration for licensing 

commercial space launches and reentry to limit risks to public health and safety. 

The recurrence interval is based on the spatial and temporal distribution of events which 

in turn is determined from the volcanic, geologic, and tectonic history of the Yucca Mountain 

region. It requires consideration of numerous components as illustrated in the logic chart (Figure 

4) including definition of the following: 

• an igneous event, 

• the volcanic zone model which specifies the area and geographic location of the 

region of similar volcanic features adjacent to or including the proposed repository, 

• the temporal model which specifies the number of igneous events in the volcanic 

model zone mapped from surface exposures and geophysical exploration and the 

number of events that are assumed to occur without being detected, 

• the interval of time extending into the past which is representative of future igneous 

events at the proposed repository, and 
82

• the location and area of the repository. 

There is considerable uncertainty in most of these components except for the location 

and area of the repository and the number of igneous events mapped by surface exposures, 

geophysical studies, and drilling and dating. As a result the evaluation of probability is treated 

statistically by including the potential range of uncertainty assigned to each component of the 

probability equation. The result is a range of probabilities of intersection of the proposed 

repository which is incorporated in the performance assessment analysis. The uncertainty in P 

can be constrained by incorporating distribution functions specified by assumed controls on the 

occurrence of events in the equation for P (e.g., Connor et al., 2000). This is sometimes referred 

to as a Bayesian approach. 

The recurrence rate term dominates the estimate of the probability of intersection and is 

the main source of uncertainty. Most estimates of the recurrence rate (events per year) range 

from 10-6 to 10-5 and conditional distribution probability values vary from 10-3 to 10-2. Thus, in the 

simplest case the probability of intersection ranges from 10-9 to 10-7 per year. 

5.5.4.2. Locally Homogeneous Spatial and Temporal Models 

Temporal models that describe the frequency of occurrence of an event include both 

homogeneous and non-homogeneous models. Homogeneous models are based on a uniform 

rate of volcanism over the specified duration of time over the area of the volcanic zone model. In 

contrast nonhomogeneous models assume a non-uniform rate of igneous activity. Spatial 

models employ identified spatial source zones which reflect the presence and nature of igneous 

events and assumed geologic controls (e.g., faults and topography) on future igneous events in 

the zone. These source zones may consider nonhomogeneous, nonparametric models based 

on the location of existing events and their limits may be smoothed using various functions to 

describe the change in recurrence rate over the source zone. 

Homogeneous Poisson models are commonly used to represent hazards from rare 

events. A key assumption is that one can identify a region where the rate of occurrence of 

volcanic events can be considered uniform in space and time over the period of interest. The 

Poisson model provides a reasonable representation for the combined effects of multiple 

independent processes, even when the individual processes may be non-Poissonian 

(Geomatrix Consultants, 1996). Areas of interest are divided into non-overlapping zones within 

which the frequency of intersection of volcanic events is estimated. One zone might be a large 

region with diffuse (background rate) volcanic activity, while another zone might display more 

concentrated volcanic activity. The rate of occurrence is estimated from data from a zone. The 

maximum likelihood estimate is given by the number of observed events in a time interval, 

divided by that interval. 

5.5.4.3. Nonhomogeneous Spatial Models 

5.5.4.3.1. Parametric Spatial Density Function 

Parametric methods are mathematical procedures for hypothesis testing that assume 

that the distributions of the variables being assessed belong to known families of probability 

distributions. For example, analysis of variance assumes that the underlying distributions are 

normally distributed and that the variances of the distributions being compared are similar. 

While parametric techniques are robust (statistically powerful), some distributions violate the 

underlying assumptions so much that non-parametric methods are more likely to detect 

differences or similarities. 
83

Sheridan (1990) developed a model for volcanic fields that represents the spatial density 

of events using a bivariate Gaussian distribution. The resulting mathematical representation 

has an elliptical shape defined by five parameters: coordinates of the field center, lengths of the 

major and minor axes, and the orientation (azimuth) of the major axis. Members of the PVHA 

(Geomatrix Consultants, 1996) used this method and others, estimating the parameters of 

Gaussian volcanic fields using data from the Yucca Mountain area. 

5.5.4.3.2. Nonparametric Spatial Density Function 

Non-parametric methods differ from parametric methods because the model structure is 

determined entirely from data. No assumptions are made about the frequency (or other) 

distributions of the variables being assessed. A histogram is an example of a simple 

nonparametric estimate of a probability distribution. The Chi-square test is one of the most 

frequently used non-parametric statistical tests. 

Stochastic kernels are commonly used in parameter density estimation. Connor and Hill 

(1995) presented three nonhomogeneous spatial models for evaluating volcanic hazards. 

These three models included kernel density estimation, spatial-temporal nearest neighbor 

density estimation, and nearest neighbor kernel density estimation. Connor and Hill (1995) and 

Connor et al. (2000) presented a geologic and statistical basis for probabilistic hazard 

assessment at Yucca Mountain. Connor et et al. (2000) and Connor et al. (2002) developed 

software and accompanying data sets that use kernel density estimators to calculate probability 

surfaces using the location and timing of past, discrete volcanic events. They used both 

Gaussian and Epanechnikov kernels. The software by Connor et al. (2002) added several 

features, including the ability to represent the length and orientation of dikes and vent 

alignments. Also, isostatic gravity anomaly data could be incorporated into the analysis using a 

weighting factor determined by the user. 

Coleman et al. (2004) used the software and data sets of Connor et al. (2002) to 

evaluate numbers of volcanic events in the region that should have been expected if recurrence 

rates were as large as claimed by some researchers. For example, some have claimed that the 

probability of volcanic intersection at Yucca Mountain could be as high as 10-6/yr. The model 

and data sets of Connor et al. (2002) suggest that 40 to 192 eruptions should have been 

expected in the region in the last million years if the probability is as high as 10-6/yr. However, 

only 8 events are known in all of the Pleistocene (1.8 Ma). 

5.5.4.4. Nonhomogeneous Temporal Models 

Several investigators have used nonhomogeneous models. Ho (1991, 1992) suggested 

that the rate of volcanic activity in the Yucca Mountain Region was not stationary in time and 

that the rate of activity could be modeled as a nonhomogeneous Poisson process using a 

Weibull function. Crowe (1995) applied a model in which the event rate of igneous activity 

intersecting the proposed repository was estimated by dividing the instantaneous rate of magma 

production by the time-varying volume per volcanic event. One PVHA expert used this method 

in his analysis (Geomatrix Consultants, 1996). 

5.6. Treatment of Probability in Performance Assessments 

The NRC, the DOE, and EPRI have performed detailed performance assessments of the 

proposed repository at Yucca Mountain using varying ranges and point values of the probability 

of an igneous event intersecting the proposed repository. 
84

5.6.1. DOE Analysis 

The DOE used the probability range developed by expert elicitation in the 1990’s 

(Geomatrix Consultants, 1996). That probability range was recalculated (BSC, 2003a, p. 113) 

using PVHA outputs to account for the proposed license application (LA) repository footprint 

(the outline of the waste emplacement area) and extended to include the probability of an 

eruption within the proposed LA repository footprint, conditional on dike intersection (5th

percentile = 7.4 × 10-10/yr; mean = 1.7 × 10-8/yr; 95th percentile = 5.5 × 10-8/yr; median = 

9 x10-9/yr). It is expected that if the repository layout is changed or expanded, that would be 

considered in the documentation for a license application. An update of the PVHA is now being 

conducted that includes new information gathered since 1996, including the results of a 

magnetic anomaly exploratory drilling program. 

The DOE had agreed to resolve the probability issue with NRC by 

providing in the Site Recommendation and License Application, in addition to DOE’s 

licensing case, the results of a single point sensitivity analysis for extrusive and 

intrusive igneous processes at an annual probability of 10-7. By agreeing to provide 

these analyses, [the NRC] staff consider the probability subissue closed-pending, 

because the 10-7 analyses provide a reasonably conservative approach for 

evaluating risks from igneous activity (Hill and Connor, 2000, p. 74). 

5.6.2. EPRI Analysis 

EPRI (2005) has adopted the PVHA (Geomatrix Consultants, 1996) mean probability 

value (i.e., 1.7 × 10-8 /yr) and an approximate intersection probability range of 10-9 to 10-7 per 

year. 

5.6.3. NRC Analysis 

The NRC performance assessments do not use a range of values for volcanism 

probability, but instead use the single-point value of 10-7/yr as the probability that a volcanic 

conduit (extrusive scenario) could intersect a repository drift (Mohanty et al., 2004). The 

ACNW&M has commented (ACNW&M, 2005) that instead of using a single value of probability 

in performance assessments, the NRC should consider a range of estimates on the order 10-8/yr 

to 10-7/yr based on studies published by NRC (Connor et al., 2000) and previous ACNW&M 

views. If the staff decides to use a single-point value approach, the staff should document how 

this decision would support a risk-informed review of the consequences of an igneous event in a 

potential license application. The NRC (Reyes, 2006) responded that: 

the significance of alternative conceptual probability models can be evaluated as 

single values in performance calculations. By using a representative probability 

value as a baseline in calculations, staff can evaluate the risk significance of any 

available probability value by simple comparison to the baseline value. Staff 

continues to evaluate new data and conceptual models for igneous event 

probabilities developed by DOE and other scientists, as well as DOE's ongoing 

expert elicitation on Probabilistic Volcanic Hazard Assessment and associated field 

and laboratory investigations. The potential risk significance of this new information 

can be determined and communicated by using a combination of review methods. 

The NRC’s use of a constant intersection probability value of 10-7/yr appears to be overly 

conservative – it does not represent a mean estimate but instead lies near the upper limit of 

most calculated probability ranges. This deterministic and bounding approach by the staff is 
85

inconsistent with the risk-informed approach used elsewhere in their Total-System Performance 

Assessment (TPA) for Yucca Mountain and does not provide a basis for directly reviewing the 

probabilistic analysis expected from DOE. 

For the extrusive scenario, dose consequences are largest for events that occur soon 

after repository closure, while the relatively short-lived radionuclides are present in significant 

quantities (see Figure 39, derived from Figures 3-44 and 3-45 of Mohanty et al., 2004). Igneous 

events after the first 1000 years would involve reduced dose. 

Figure 39 Conditional dose and expected dose from extrusive igneous activity. Top 

frame - mean dose arising from extrusive igneous activity shown with 

various times for the volcanic event in 350 realizations. Lower frame - 

contribution of extrusive igneous activity to the total dose, weighted by an 

annual probability for the volcanic event of 10-7/yr (After Mohanty 

et al., 2004, p. 3-84). 

5.7. Perspectives on Igneous Activity Probability 

Table 5 presents a summary of published views on the probability of an igneous event 

intersecting the proposed high-level waste repository at Yucca Mountain. 
86

Table 5 Summary of Published Perspectives on Probability of Igneous 

Activity. 

Source Probability range for 

volcanic disruption 

Notes 

Crowe et al. (1982) 10-10/yr to 10-8/yr Based on two estimation methods: 

one based on rate of magma 

production in the Nevada Test Site 

area and a second using the 

number of volcanic vents over a 

specified time period. 

Smith et al. (1990) Assigned the site of the 

Yucca Mountain repository 

to risk-category 3 

Based on a proposed qualitative 

index of volcanic risk for areas in 

the Yucca Mountain region. In this 

index, risk level 5 is highest and 1 

is lowest. 

Ho et al. (1991) Probability not specified – 

see notes 

Estimated the recurrence rate of 

volcanic eruption (not the 

probability of intersecting a 

repository). Values obtained: 

5 × 10-6/yr 

5.9 × 10-6/yr 

5 × 10-6/yr. 

Crowe et al. (1993) 2.6 × 10-8/yr Median value of probability 

distribution. 

Connor and Hill 

(1995) 

1-5 × 10-8/yr Range of 3 alternative models for 

probability of an eruption (volcanic 

conduit intersecting the repository). 

Crowe et al. (1995) 1.8 × 10-8/yr Median value of 22 alternative 

probability models. 

Geomatrix 

Consultants (1996) 

1.5 × 10-8/yr 

5.4 × 10-10/yr to 4.9 × 10-8 /yr 

Expected frequency of intersection. 

90% confidence interval 

Ho and Smith 

(1997) 

1.4 × 10-7/yr to 3.0 × 10-6 /yr Consideration of Bayesian 

methods. 

Ho and Smith 

(1998) 

(1) 1.5 × 10-8/yr 

(2) 1.09 × 10-8/yr to 

 2.83 × 10-8/yr 

(3) 3.14 × 10-7/yr 

Authors presented 3 alternative 

models. 
87

Source Probability range for 

volcanic disruption 

Notes 

Wernicke et al. 

(1998) 

Probability not specified – 

see notes 

Yucca Mountain area experiencing 

epoch of anomalously rapid strain 

accumulation. Hazard analyses 

based on local geologic record may 

underestimate volcanism probability by an order of magnitude. 

Lathrop Wells may represent onset 

of a cluster of volcanism that could 

continue over the next few tens of 

thousands of years.

Savage (1998) Reply to Wernicke et al. 

(1998) 

Savage (1998) countered the claim 

of anomalous strain reported by 

Wernicke et al. (1998), and 

reported a N65°W strain rate of 8 

±20 nanostrain yr-1. He concluded 

that Wernicke et al. (1998) had not 

included monument instability in 

their error budget and did not give 

proper weight to the effects of the 

1992 Little Skull Mountain 

earthquake. Later work by Savage 

et al. (2001) continued to find that 

the principal extension rate is 

substantially less than reported by 

Wernicke et al. (1998), consistent 

with the low extension rate inferred 

from the geologic record. 

BSC (2003a) 1.7 × 10-8/yr 

5th percentile = 7.4 × 10-10/yr 

95th percentile = 5.5 × 10-8/yr 

Revision of probability based on 

change in area of proposed 

repository footprint for License 

Application. 

CRWMS M&O 

(1998) 

2.5 × 10-8/yr Sensitivity analysis that 

conservatively assumes all 

magnetic anomalies in Amargosa 

Desert have Pleistocene age (less 

than 1.8 Ma). 

Connor et al. 

(2000) 

10-8/yr to 10-7/yr Use of diffusion-based model with 

gravity weighting, and use of data 

sets that assume most magnetic 

anomalies represent post-Miocene 

basalts. 
88

Source Probability range for 

volcanic disruption 

Notes 

Hill and Connor 

(2000) 

10-7/yr NRC staff considered the 

probability issue closed-pending 

based on DOE agreement to 

evaluate risk using this value. 

Hill and 

Stamatakos (2002) 

Up to an order of magnitude 

increase in the probability of 

volcanic disruption. 

Compared to Connor et al. 

(2000), this infers a 

probability up to 10-6/yr 

At least ten additional basaltic 

volcanoes may be represented by 

magnetic anomalies in the YMR. 

The first-order effect on probability 

models could range from negligible, 

to an order of magnitude increase 

in volcanic recurrence rates. 

Smith et al. (2002) No estimate provided, but 

this report cited Smith et al. 

(1990) and Ho and Smith 

(1997; 1998) 

Petrologic arguments suggest that 

recurrence rates of volcanism used 

by DOE and NRC may be underestimated. Higher rates typical of 

the Lunar Crater–Reveille Range 

volcanic zone may be applicable to 

Yucca Mountain. If models of hot 

mantle are correct, another 

eruption peak is possible. 

ACNW&M (2002) The range of estimated 

probabilities, ~10-9 to ~10-7

per year, of an intrusion into 

the repository used by DOE 

in its performance 

assessment is reasonable. 

New information from a 

recently completed 

aeromagnetic survey (2000) 

needs to be evaluated more 

fully to determine possible 

changes in the appropriate 

probability range. 

ACNW&M letter dated 

August 1, 2002. 

Detournay et et al. 

(2003) 

No estimate provided Analog evidence from recent 

(< 5 Ma) igneous events that were 

close to Yucca Mountain (Crater 

Flat and Lathrop Wells) should be 

given more weight than earlier or 

more distant events. 

ACNW&M (2004) 10-8/yr to 10-7/yr Letter to NRC Chairman dated 

November 3, 2004. 
89

Source Probability range for 

volcanic disruption 

Notes 

Coleman et al. 

(2004) 

Expected value 5 × 10-8/yr 

with a 95% upper bound of 

1 × 10-7/yr 

Claims of high intrusion frequency 

(i.e., 10-6/yr) fail tests of volcanic 

recurrence in the Yucca Mountain 

region; analyses conservatively 

assume 5-15 magnetic anomalies 

are post-Miocene buried basalts; 

model results also suggest Lathrop 

Wells event was not the start of a 

new volcanism cluster. 

Mohanty et al. 

(2004; 2005) 

1 × 10-7/yr Use of single value only – no 

probability range was used. 

ACNW&M (2005) 10-8/yr to 10-7/yr ACNW&M recommended that the 

NRC staff reevaluate the use of a 

single probability value for volcanic 

intersection and consider a range 

of estimates on the order 10-8/yr to 

10-7/yr based on published NRC 

studies and previous ACNW&M 

views. 

NRC (2005a) 1 × 10-7/yr Use of single value only – no 

probability range was used. 

EPRI (2005) 1.6 × 10-8 /yr EPRI (2005) adopts the PVHA 

1996 probability value (the 

expected frequency of intersection).

Smith and Keenan 

(2005) 

Up to 10-7/yr to 10-6/yr Range that may result by adding 

data from future geophysical 

surveys and higher recurrence 

rates.

Reyes (2006) No probability specified in 

letter – however, the 

baseline used in a recent 

NRC performance 

assessment (Mohanty 

et al., 2004) was a single 

value of 1 × 10-7/yr 

Response to ACNW&M (2005) 

letter: “As an alternative (to using a 

probability range), the significance 

of alternative conceptual probability 

models can be evaluated as single 

values in performance calculations. 

By using a representative 

probability value as a baseline in 

calculations, staff can evaluate the 

risk significance of any available 

probability value by simple 

comparison to the baseline value.” 
90

Source Probability range for 

volcanic disruption 

Notes 

Ho et al. (2006) No probability specified. The authors present a strategy to 

evaluate “hazards areas” based on 

a debris-fall model developed for 

the space transportation industry. 

Coleman and 

Marsh (2007) 

Estimated repository dike 

penetration frequency of 

4.2E-8/yr 

Result incorporates latest data from 

drilling and dating of basalts; NRC 

PVHA model was applied using an 

updated Plio-Quaternary dataset 

reduced to 22 basaltic events 

(CFB_plio-quat-Mag from Connor 

et al., 2002); the 95% upper 

confidence bound was not given in 

the GSA abstract but is reported 

here as 6.0 × 10-8 /yr (based on 

confidence limits for expectation of 

a Poisson variable, given that 

n = 22; Pearson and Hartley, 1970). 

Valentine and 

Perry (2007) 

Did not estimate a repository 

intersection frequency, but 

based on a regression model 

suggested the next episode 

of volcanic activity somewhere in the volcanic field 

will occur ~270 kyr after the 

Lathrop Wells event (with a 

90% prediction interval of 

±290 kyr in consideration of 

the small data set). 

Based on the assumption that 

basaltic volcanism in the SNVF will 

continue to exhibit tectonically 

controlled, time-predictable 

behavior with a ~0.5 km3/Myr 

eruptive volume flux, the authors 

applied a linear regression model 

(time to next episode is dependent 

on previous episode's volume). 

PVHA-Update 

(ongoing expert 

elicitation) 

----- Work by expert panel is in 

progress. Final report not expected 

until mid-2008. 

5.7.1. NRC Analysis 

The NRC has not adopted a preferred time period for extrapolating the future occurrence 

of volcanic events. However, Connor et al. (2000) state the following: 

The proposed high-level radioactive waste repository at Yucca Mountain, Nevada, is 

located within an active volcanic field. Probabilistic volcanic hazard models for future 

eruptions through the proposed repository depend heavily on our understanding of 

the spatial controls on volcano distribution at a variety of scales. On regional scales, 

Pliocene-Quaternary volcano clusters are located east of the Bare Mountain fault. 
91

Extension has resulted in large-scale crustal density contrast across the fault, and 

vents are restricted to low-density areas of the hanging wall. Finite element modeling 

indicates that this crustal density contrast can result in transient pressure changes of 

up to 7 MPa at 40 km depth, providing a mechanism to generate partial melts in 

areas where mantle rocks are already close to their solidus. On subregional scales, 

vent alignments, including one alignment newly recognized by ground magnetic 

mapping, parallel the trends of high–dilation tendency faults in the Yucca Mountain 

region (YMR). Forty percent of vents in the Yucca Mountain region are part of vent 

alignments that vary in length from 2 to 16 km. Locally, new geological and 

geophysical data show that individual vents and short vent alignments occur along 

and adjacent to faults, particularly at fault intersections, and leftstepping en echelon

fault segments adjacent to Yucca Mountain. Conditions which formed these 

structures persist in the YMR today, indicating that volcanism will likely continue in 

the region and that the proposed repository site is within an area where future 

volcanism may occur. On the basis of these data the probability of volcanic 

disruptions of the proposed repository is estimated between 10-8/yr and 10-7/yr. 

Hill and Connor (2000, p. 74) state the following: 

Prior to the August 2000 Technical Exchange with the DOE, staff had identified 12 

specific technical concerns regarding the probability subissue....To address these 

concerns, the DOE agreed to resolve the probability subissue by providing in the Site 

Recommendation and License Application, in addition to DOE’s licensing case, the 

results of a single point sensitivity analysis for extrusive and intrusive igneous 

processes at an annual probability of 10-7. By agreeing to provide these analyses, 

staff consider the probability subissue closed-pending, because the 10-7 analyses 

provide a reasonably conservative approach for evaluating risks from igneous 

activity. 

Hill and Stamatakos (2002, p. xi) state the following: 

The U.S. Geological Survey recently completed a large-scale aeromagnetic survey of 

the Yucca Mountain region. Interpretations of this survey and associated Center for 

Nuclear Waste Regulatory Analyses ground magnetic surveys indicates there may be 

twice as many basaltic volcanoes in the Yucca Mountain region than previously 

recognized. Additional volcanoes also may be present but undetected within 

approximately 20 km [12 mi] of the proposed repository site due to relatively low 

resolution of the aeromagnetic survey. Without direct information on the age and 

composition of these buried volcanoes, associated effects on probability models and 

risk calculations are highly uncertain. The potential risk significance of this 

uncertainty ranges from negligible to an order of magnitude increase in the probability 

of volcanic disruption of the proposed repository site. This uncertainty can be 

reduced through drilling of anomalies likely to be caused by buried basalt, and to a 

lesser extent by additional ground magnetic surveys. At present, the range of 

uncertainty in these interpretations and associated new information clearly exceeds 

uncertainties and information considered by the U.S. Department of Energy (DOE) 

during probability model development in 1995. An update to the DOE probability 

elicitation appears necessary for acceptable use in licensing. 

5.7.2. DOE Analysis 

The DOE has primarily adopted the Plio-Pleistocene time period for extrapolation of 

events, consistent with the approach by the majority of members of the 1996 PVHA expert 

panel. Several members of that panel considered the Pleistocene to be the preferred time 

period for extrapolation. BSC (2003a, p. 113) states the following: 
92

The result of the PVHA [Geomatrix Consultants, 1996] has been recalculated using 

PVHA outputs to account for the proposed LA repository footprint (the outline of the 

waste emplacement area) and extended to include the probability of an eruption 

within the proposed LA repository footprint, conditional on a dike intersection. A 

conceptual framework for the probability calculations, based on PVHA outputs and 

subsequent studies, accounts for deep (mantle) and shallow (structural control) 

processes that influence volcanic event distribution and recurrence rate in the YMR 

[Yucca Mountain region]. The framework presented here emphasizes the close 

correlation between the distribution of volcanic events and areas of crustal extension 

and faulting in the YMR, and within this context, the appropriateness of volcanic 

source zone boundaries defined in the PVHA. It also emphasizes the appropriate 

selection of parameter distributions that affect probability models and provides 

support for comparison of alternative scenarios and parameter selection, within the 

framework of the volcanic history of the YMR. Alternative models presented by 

Connor et al. (2000) that result in higher eruption probabilities (10-7 versus 1.3 × 10-8

per year) than those presented here are found to employ input parameters that either 

represent extreme values (e.g., event length) or assume a specific geologic control 

(i.e., crustal density) on spatial distribution while not considering more defensible and 

observable controls (i.e., crustal extension and structure). Spatial density models 

weighted by crustal density result in higher event frequencies at the proposed 

repository site, while the same models weighted by an alternative geologic control 

such as cumulative crustal extension across the Crater Flat structural domain would 

likely lead to decreased event frequencies at the site. Connor et al. (2000) state that 

the highest value (10-7 per year) in their range of calculated probability values (10-8

–

10-7 per year) cannot be considered more or less likely than any other value they 

have calculated using alternative probability models. The analysis in this report 

suggests that the choice of input parameters used by Connor et al. (2000) compared 

to those used in the PVHA logically places their highest probability value at the 

extreme upper tail of a probability distribution. 

The DOE (2003, p. 2-9) states the following: 

In summary, the areas of greatest likelihood for future volcanic activity in the region 

are those where previous volcanism has occurred, and where extensional 

deformation has been and continues to be greatest, (i.e., the southwestern part of the 

Crater Flat structural domain) (Figure 2-5) (Geomatrix Consultants, 1996, pp. RC-5, 

BC-12, AM-5, MS-2, GT-2, and expert zone maps). Analysis by the U.S. Nuclear 

Regulatory Commission (NRC) also indicates that the highest likelihood of future 

volcanic activity is in southwestern Crater Flat (Reamer, 1999 [Sections 4.1.5.4 and 

4.1.6.3.3; Figure 28]). The southern and southwestern part of the Crater Flat basin is 

the most extended (Ferrill et al., 1996; Stamatakos et al., 1997; Fridrich et al., 1999) 

and is the locus of post-Miocene volcanism (Fridrich et al. 1999; Reamer, 1999). 

Therefore, the volcanic source zones defined in the PVHA (Geomatrix Consultants, 

1996 [Figure 2-5]) are consistent with the tectonic history and structural features of 

the Crater Flat structural domain. 

5.7.3. Probabilistic Volcanic Hazard Analysis (PVHA) 

The Probabilistic Volcanic Hazard Analysis (Geomatrix Consultants, 1996, p. 4-14) 

states the following: 

The results of the PVHA analysis are that the aggregate expected annual frequency 

of intersection of the repository footprint by a volcanic event is 1.7 x 10-8, with a 90-

percent confidence interval of 7.4 x 10-10/yr to 5.5 x 10-8 after adjustment for the 

change in size of the repository footprint. The median value without adjustment for 

the footprint size is 9 x 10-9/yr. The major contributions to the uncertainty in the 

frequency of intersection are the statistical uncertainty in estimating the rate of 
93

volcanic events from small data sets and the uncertainty in modeling the spatial 

distribution of future events. Although there are significant differences between the 

interpretations of the 10 experts, most of the uncertainty in the computed frequency 

of intersection is due to the average uncertainty that an individual expert expressed 

in developing the appropriate PVHA model. 

5.7.4. DOE Igneous Consequence Peer Review (ICPR) Panel 

The ICPR panel did not evaluate the probability of future volcanism at Yucca Mountain. 

However, they did provide conclusions and recommendations that relate to evaluating 

probability. 

Detournay et al. (2003, p. 19-20) state the following: 

There are ten known unburied eruptive vents in the Yucca Mountain region younger 

than 5 Ma, and seven buried volcanoes were identified in aeromagnetic surveys up 

to 1995. This gives a sum of 17 volcanic events over the past 5 Ma, assuming, for 

illustrative purposes, each anomaly represents an independent volcanic event. If the 

magnetic anomalies recently identified (Blakely et al., 2000; O’Leary et al., 2002) 

represent buried basalt flows or tephra deposits that are less than 5-Myr old, then the 

total number of post-Miocene vents is ~30, roughly double previous estimates. If all 

of the most recently identified aeromagnetic anomalies are relatively young (e.g., ~ 

0.5 Ma to 1 Ma) with eruptive volumes ~ 0.05 km3

, then eruption probabilities would 

increase significantly. Alternatively, if the buried volcanics are at the opposite end of 

the age spectrum (e.g., 2 Ma to 4 Ma), the probability picture changes — although 

not dramatically, provided volumes associated with individual anomalies are ~ 

0.05 km3

 or less. Finally, if all buried volcanics (magnetic anomalies) are prePliocene, eruption probabilities change little. A preliminary conclusion is that until 

better information regarding the number, volume and the age distribution of buried 

basaltic lavas and tephra is available, it will be difficult to know how to adjust 

estimates of volcanism rate and recurrence interval most relevant to disruptive 

igneous activity at the proposed Yucca Mountain region. One of the 

recommendations of this Panel is that further attempts be made to define the ages 

and volumes of the buried magnetic anomalies. 

Detournay et al. (2003, p. 20) also state the following: 

High-precision geochronological information would enable better estimates of 

volcanic recurrence rates at Crater Flat relevant to igneous consequences at the 

proposed YMR at relatively modest cost. This issue could be clarified, or at least 

significantly better constrained, by an intensive high-resolution geochronological 

program. 

Detournay et al. (2003, p. 76) state the following: 

As far as the range of quantitative characteristics of the igneous event considered is 

concerned, we have reviewed all the literature available and conclude that the 

approach adopted so far — namely, that the analog evidence from recent (< 5 Ma) 

igneous events that have occurred close to [Yucca Mountain] (Crater Flats, Lathrop 

Wells) be given more weight than earlier events or those further afield — is entirely 

reasonable. We recommend that further high-resolution geochronological work be 

performed to better constrain the ages of exposed Pliocene and Quaternary basalts 

in Crater Flat as well as possible basaltic volcanic rocks identified by aeromagnetic 

studies. 

Detournay et al. (2003, p. 77) state the following: 
94

The probability that a violent erupting mixture could follow dogleg conduits, thus 

potentially entraining a larger number of waste packages, is, in our opinion, small and 

is more than offset by the level of conservatism built into the existing estimates ... 

The Panel has not been able to quantify the probability of a dogleg conduit in any 

rigorous fashion, nor its effect on waste packages. The opinion expressed ... above 

was arrived at by combining our separate independent views of where the upper 

limits would lie. 

5.7.5. EPRI Analysis 

EPRI (2005, p. vii) state the following: 

 There is evidence of volcanic centers near the proposed site at Yucca Mountain, 

Nevada for a geologic repository for the disposal of spent nuclear fuel (SNF) and 

high-level radioactive waste (HLW). This evidence indicates that potential future 

igneous activity (i.e., an “igneous event scenario”) may be a factor in the assessment 

of post-closure risk for the proposed repository. In 1996, a panel of independent 

technical experts for the Yucca Mountain Project’s Management and Operations 

(M&O) contractor ... conducted a study, the Probabilistic Volcanic Hazards Analysis 

(PVHA) study, that estimated a mean annual probability of an igneous event 

occurring at/near the Yucca Mountain site at 1.6 x 10-8/year [Geomatrix Consultants, 

1996]. This probability, though extremely low, fell just above the 1.0 x 10-8/year 

regulatory threshold that had been established for the dismissal of extremely low 

probability events. 

EPRI (2005, p. viii to ix) state the following: 

 The objectives of this report, which is a companion to EPRI (2004a), are to analyze 

the intrusive-release case and determine the potential impact on repository 

performance and safety, expressed as probability weighted mean annual dose rate, 

for the latter scenario. EPRI’s analyses contained in this report adopt the igneous 

event probability of 1.6 x 10-8/year previously derived by the Probabilistic Volcanic 

Hazards Analysis (PVHA) panel [Geomatrix Consultants, 1996]. The analyses also 

reflect recent data on basaltic eruptive centers in the Yucca Mountain region that 

support the conclusion that relatively low-temperature (~1010°C), high viscosity 

basaltic magmas, as opposed to the ~ 1200°C magmas postulated by the DOE, are 

the most representative characteristics of future igneous events. Lower temperature 

implies lower and less prolonged thermal-perturbation of the host rock and contacted 

waste packages, and magma of much higher viscosity. The high viscosity supports 

the contention that such magma will only partially penetrate into emplacement drifts 

intersected by the magmatic dike, thereby only impacting a limited number of waste 

packages. 

5.7.6. State of Nevada Contractors 

Smith et al. (1990) introduced a risk rectangle concept that suggests that future 

volcanism will occur either to the northeast or southwest of existing volcanoes in the Yucca 

Mountain region. This view relies heavily on the concept of volcanic chains and the northeast 

alignment of volcanoes. 

Smith et al. (1990) state the following: 

The proposed area of most recent volcanism (AMRV) includes all known post-6 Ma 

volcanic complexes in the Yucca Mountain area and encompasses the four volcanic 

centers in Crater Flat, the Lathrop Wells cone, several centers in southeast Crater 

flat, two centers at Sleeping Butte, and a center at Buckboard Mesa within the moat 

of the Timber Mountain Caldera. The delineation of high-risk zones for volcanism 
95

within the AMRV is an important goal in any risk assessment study. The dimensions 

and orientation of high-risk zones were based on structural and volcanic chain length 

data obtained by detailed studies of Plio-Pleistocene volcanic centers in the Yucca 

Mountain area. Analog studies of Pliocene volcanic centers in the Fortification Hill 

field (Lake Mead area, Arizona and Nevada) and the Reveille Range (south-central 

Nevada) were also used to establish the nature of structural control of volcanic vents 

and to determine the lengths of volcanic chains. Two high-risk rectangles were 

constructed at each cluster of Quaternary centers. The smaller-dimension rectangle 

is 12 km long and 1 km wide and is equivalent to the dimensions of the Crater Flat 

chain. The larger-dimension rectangle is 25 km long and 3 km wide and is equivalent 

to the dimensions of volcanic chains in the Fortification Hill field and the Reveille 

Range. Based on geologic studies and the high-risk rectangles, five risk levels were 

defined with risk level 5 representing the highest relative risk and 1 the lowest. 

Based on this risk scale, the site of the proposed high-level nuclear waste repository 

is assigned to risk-category 3. 

Bradshaw and Smith (1994) state the following: 

Alkali basalts erupted during the Quaternary at Crater Flat, Nevada, record a 

complex history of polycyclic and polygenetic volcanism. Magmas from the two main 

centers (Black Cone and Red Cone) are petrographically and geochemically similar, 

although field evidence suggests a number of separate emptive events. High 

incompatible element concentrations, low Nb/La and high Zr/Y indicate that the 

magmas were derived by small degrees of partial melting from the lithospheric 

mantle. At Red Cone, a significant range of Sr, La, Ce, Ba and Th concentrations is 

observed with time (e.g.. Sr range 1308-1848 ppm): the youngest samples having the 

more elevated values. However, there is only limited variation in the compatible trace 

elements (e.g., Sc and Ni). The array of compositions at Red Cone could not have 

been produced by changes in the degree of partial melting, or by fractional 

crystallization. Rather, a model of magma mixing is proposed between relatively 

enriched and depleted end-members. The cluster of Black Cone data falls 

consistently at the least-enriched end of the Red Cone sample arrays, suggesting 

that the Black Cone magma represents one of the mixing end-members. The 

modeling indicates that the magmatic plumbing systems of the two centers were 

linked, at least during the early stages of volcanism. Moreover, volcanic activity may 

have occurred at a number of sites along the length of the magmatic feeder zone 

during a single eruptive phase. This could have significant implications for volcanic 

hazard assessment’ in the region around Yucca Mountain, and the proposed nuclear 

waste repository. 

Ho et al. (1991, p. 56) state the following: 

At this preliminary stage of our work, all we can conclude is that the probabilistic 

results of Crowe et al. (1982) are based on idealized model assumptions, a 

premature data base, and inadequate estimates of the required parameters. For the 

reasons discussed, we think that Crowe et al. underestimate the risk of volcanism at 

the proposed Yucca Mountain repository site. 

Ho and Smith (1998, p. 508) state the following: 

The instantaneous temporal recurrence rate (at present time) estimated from a PLP 

[power-law process] is about 5.9 × 10-6/year. Thus, the combined temporal-spatial 

recurrence rate calculated for the 3-D NHPP [non-homogeneous Poisson process] is 

between 1.36 × 10-9 and 3.54 × 10-9/(year × km2

). The recurrence rate obtained 

based on a 3-D HPP [homogeneous Poisson process] (= 1.88 × 10-9) is in this 

interval. For this study, the estimated overall probability of at least one disruption of a 

repository at the Yucca Mountain site by basaltic volcanism for the next 10,000 years 

(= hazard) is: 1.5 × 10-4 for a 3-D HPP; 1.09 × 10-4 to 2.83 × 10-4 for a 3-D NHPP if λs
96

[recurrence rate] is estimated as 2.3 × 10-4 to 6.0 × 10-4; and 3.14 × 10-3 for a 

Bayesian approach. We also note that the hazard based on an HPP and an NHPP 

are very comparable as long as the area of the sample region A (was estimated as 

1953 km2

 for the 3-D HPP) is bounded between 1035 km2 and 2701 km2. 

Smith et al. (2002, p. 9) state the following: 

A knowledge of recurrence rates is crucial to the calculation of probability of 

magmatic disruption. We contend that there is more uncertainty in recurrence rate 

estimates than assumed by the DOE, the expert panel, and the NRC. Our petrologic 

data suggest that volcanic fields in the Crater Flat–Lunar Crater zone are linked to a 

common area of hot mantle. Also, we show that volcanism is episodic with a good 

possibility of a new peak of activity occurring in the future. These observations imply 

that volcanism is not dead in the Yucca Mountain area and that a future pulse of 

activity could have recurrence rates equivalent to those recorded in the Lunar Crater–

Reveille area of the Crater Flat–Lunar Crater zone. Specifically, the DOE and the 

NRC have used recurrence rates of from 3.7 to 12 events per m.y. to calculate 

probability of volcanic disruption (Connor and Hill, 1995; Crowe et al., 1998; Connor 

et al., 2000). Based on our arguments, recurrence rates of 11 to >15 events per m.y. 

are possible. Because higher recurrence rates raise the likelihood of magmatic 

disruption of the repository, we recommend that future probability studies factor these 

higher rates into probability models. 

Smith and Keenan (2005, p. 317-321) state the following: 

Perry et al. [2004] speculated that the 20 additional volcanic centers discovered by 

the aeromagnetic surveys would raise the probability of site disruption by about 40%. 

This number is a minimum figure because the surveys do not cover the entire area. 

Volcanic recurrence rates for the RLC (Reveille–Lunar Crater) are as high as 12 events 

per million years, four times the rate calculated for the Yucca Mountain area. These figures are 

minimum estimates because only 70% of the volcanic centers in the RLC are dated. 

A linkage between Yucca Mountain and RLC implies that higher recurrence rates may 

occur in the Yucca Mountain area. Adding data from future surveys of uncovered areas and 

higher recurrence rates may result in a probability of disruption 1–2 orders of magnitude greater 

than the EPA standard. A longer health standard, as ordered by the U.S. Court of Appeals, 

makes a disruptive event during the period of compliance even more likely.” In this article by 

Smith and Keenan (2005), they imply that using higher recurrence rates and adding data from 

future aeromagnetic surveys may result in a probability of disruption of up to 10-6/yr. 

5.7.7. Nuclear Energy Institute (NEI) 

The Nuclear Energy Institute issued a policy statement (NEI, 2006) titled “Common 

Objections to the Yucca Mountain Project, and What the Science Really Says.” This policy 

statement gave frequently cited objections to the Yucca Mountain project and the NEI response 

based on scientific analysis. For volcanoes (igneous activity), the cited concern is that “A 

volcano could erupt through the repository.” 

The NEI position is as follows: 

• A volcanic eruption that affects the repository is a highly improbable event. 

• There has not been a single volcanic eruption through Yucca Mountain in 10 million 

years. 
97

• Millions of years of history show that the region surrounding Yucca Mountain is 

becoming less volcanically active with time. 

• Nevertheless, NRC is requiring that DOE analyze the consequences of such an 

event and include this analysis in the repository performance assessment. 

• The volcano itself is likely to cause more harm than any radiation it might release. 

5.7.8. Other Estimates of Probability 

Crowe et al. (1982, p. 185) state the following: 

The calculated probabilities of volcanic disruption of a high-level radioactive waste 

repository buried within the Yucca Mountain site of the NTS area are exceedingly 

small (range calculated for a one year time period of 10-8 to 10-10). These values 

provide a numerical expression of the low past rates of volcanism in the region. 

However, there are several precautions that must accompany the calculations: First, 

they assume that volcanism is a random process although geologic studies on a 

global scale have shown that volcanism is commonly nonrandom in both space and 

time. We have attempted to compensate for this shortcoming by restricting the 

calculation parameters to a defined volcanic province and by developing a method 

for determining the area ratio (a/A) based on the distribution of volcanic centers. 

Second, calculated rates of volcanic activity (λ) are averaged over a time scale of 

millions of years. They are therefore relatively insensitive to short-term variations in 

rates of volcanism. Such short-term variations may be less than or on the order of 

the required containment period of waste elements. Third, the calculated rates of 

volcanism are based on the past record of volcanism and not on a complete 

understanding of the future controlling processes of magma generation. They were 

calculated from a limited number of data points and are projected into the future 

assuming future rates will be the same as in the past. Some degree of confidence 

can be placed in this projection however due to the relatively uniform rate of volcanic 

activity in the NTS region for the last 6 to 8 m.y. 

Coleman et al. (2004, p. 3) also state the following: 

Analysis indicates that a dike intersection rate of 10-6/yr (one expected per million 

years) is unrealistically high. If this rate prevailed in the last million yrs, an expected 

40 to 96 volcanoes would have erupted in the YMR (or 80–192 without gravity 

weighting). This far exceeds the 8 events known to have occurred in all of the 

Pleistocene (1.8 Myr), yielding a recurrence rate of only 4.4 per million years. 

Dividing these numbers by 10 reduces the time scale to 100,000 years. This time 

scale is especially interesting because we can test whether the youngest-known 

volcanic event in the region, Lathrop Wells, began a new pulse of volcanism, as 

suggested by Wernicke et al. (1998). For a dike penetration rate of 10-6/yr, the PVHA 

results indicate 4–10 (8–19 without gravity weighting) volcanic events would have 

been expected in the YMR in the last 100,000 yrs. Only one is known. We conclude 

that claims of high intrusion frequency fail tests of volcanic recurrence in the YMR at 

time scales of 106

 and 105 yrs. 

We consider that spatial and temporal patterns of Pleistocene volcanism provide the 

best available representation of trends in recent geologic time... If future volcanism 

follows this pattern, the expected frequency of dike intersection is 5.4 × 10-8/yr using 

the PVHA_YM code with zero gravity weighting, file ‘‘Quaternary_8events,’’ and a 

recurrence rate of 4.4 × 10-6/yr (8 events in 1.8 Myr). Considering the statistical 

uncertainty of the frequency based on eight events, a 95% upper confidence bound 

for the intersection frequency is 9.8 × 10-8/yr [Pearson and Hartley, 1970]. The 

recurrence rate would be even smaller if some of the Pleistocene events in Crater 

Flat represent fewer events. 
98

We agree with Connor et al. [2000] that rates of basaltic volcanism at Yucca Mtn. 

(i.e., ~2–12 events/Myr) have not been comparable to recurrence rates in more 

active zones, such as the Cima volcanic field, CA (i.e., ~30 events/Myr). Our 

analysis raises doubts about claims that a potential repository could be penetrated by 

a basaltic dike with a frequency as high as 10-6/yr (on average, one per million 

years). Such claims fail simple tests at four time scales. Furthermore, spatialtemporal models that predict future penetration frequencies >2 × 10-7/yr are overly 

pessimistic, based on nondetection of dikes in the potential repository footprint. 

Organization for Economic Cooperation and Development (OECD, 2002, p. 15), in its 

joint report by the NEA and the IAEA, states the following: 

3.3 Disruptive events and human intrusion Disruptive events — Volcanism at Yucca 

Mountain is a very low probability event. With regard to volcanism, more explosive 

rhyolitic eruptions can occur at the same time as basaltic eruptions (so-called 

“bimodal volcanism”). That was not discussed in the TSPA-SR. It is recommended 

that the probability of bimodal basaltic-rhyolitic volcanism be estimated and, if 

relevant, the consequences be analyzed. The IRT considers that the TSPA-SR 

adequately addresses seismological influences and finds the analysis in line with 

other international studies. 

Although this peer review made this recommendation, available evidence points to the 

fact that the silicic volcanism that spawned multiple calderas and formed the surface rocks at 

Yucca Mountain had already ended by late Miocene time. 

5.7.9. ACNW&M Observations of PVHA-U 

The panelists participating in PVHA-U are incorporating new information available since 

1996 in their estimates, including interpretations based on lithostatic pressure variations and 

geochemical analyses. Based on the ACNW&M’s observations of PVHA-U proceedings, most 

panelists appear to be placing greater emphasis on Pleistocene events rather than on older 

events. Eruption cycles are being discussed, and fewer hidden events are now being 

considered based on the results of drilling of anomalies. 

5.8 Summary (Igneous Event Probability) 

The rocks that comprise Yucca Mountain record an integrated tectonic-volcanic history 

since the ~13 Ma old surface rocks were deposited. No basaltic dikes have been found in the 

potential repository footprint at Yucca Mountain despite more than 25 years of intensive site 

characterization studies. It appears that the northern part of the fault-bounded block that forms 

Yucca Mountain has been a zone of relative volcanic quiescence during the last 10 Myr. Since 

that time volcanism has instead mainly focused within the alluvial basins to the east, west, and 

south, with no evidence of post-Miocene activity (younger than ~5 Ma) east of Yucca Mountain 

in Jackass Flats. 

The volume of basaltic volcanism near Yucca Mountain has dramatically declined during 

the last 10 Myr such that the Crater Flat basin volcanic field represents a zone of low activity 

compared to other volcanic fields in the region (e.g., Lunar Crater-Reveille Range, NV, Cima, 

CA, and Springerville, AZ). This decline suggests that magmatic systems near Yucca Mountain 

are waning. Further evidence of this lies in the declining maximum lava effusion rate and fissure 

length of Plio-Pleistocene basaltic activity in the Yucca Mountain region. There are no 

precursory indicators that volcanic activity is likely in the immediate future in the region. 
99

 Results of recent drilling on magnetic anomalies following completion of the 2004 

aeromagnetic survey have not yet been incorporated into published estimates of the probability 

of igneous activity intersection of the proposed repository. However, the information from the 

drilling will reduce some of the uncertainty about the number and age of buried basalts and will 

influence the statistical-mathematical models used in determining evaluating probability. 

 Both DOE and EPRI currently rely on probability estimates from the 1996 PVHA expert 

elicitation (i.e., ~2 × 10-8/yr). This PVHA is now being updated with new information but 

published results will not be available until 2008. In response to NRC concerns, the DOE has 

agreed to provide (along with their licensing case) the results of a single point sensitivity 

analysis for extrusive and intrusive igneous processes at a repository intersection probability of 

10-7/yr. The NRC considers that the 10-7/yr analyses will provide a reasonably conservative 

approach for evaluating risks from igneous activity. However, using a single point value fails to 

capture the impact of the uncertainty in probability estimates inherent to a performance 

assessment and could significantly limit the usefulness of the results and the risk-informed 

insights that can be gleaned from such an analysis. 

The State of Nevada contractors suggest that the probability of future volcanism may be 

at least an order of magnitude higher based on temporal clustering of volcanic activity, 

hypothetical linkages between volcanism in the Crater Flat basin and the Lunar Crater-Reveille 

Range area, and incorporation of new data that they recommend be acquired in regions beyond 

the latest aeromagnetic survey. However, claims of frequent recurrence of volcanism much 

higher than the PVHA results are inconsistent with the small number of events known to have 

occurred during the past 5 million years. If the probability of repository intersection were 

10-6/year, many (~40 to 192) eruptions should have occurred in the Yucca Mountain region in 

the last million years, and approximately four to 19 eruptions should have occurred in the last 

100,000 years (Coleman et al., 2004). However, only 8 events are known to have occurred 

over the past 1.8 million years and only one occurred in the last 100,000 years. No volcanism 

has occurred near Yucca Mountain since the eruption of the Lathrop Wells volcano 80,000 

years ago and no post-Miocene (< 5.3 Ma) volcanism is known to have occurred at the Yucca 

Mountain site or in Jackass Flats. 

A probability range for repository disruption of 10-9/yr to 10-7/yr is consistent with most 

previous studies (Figure 40), the observed rate of Pleistocene volcanic activity (8 events in the 

Yucca Mountain region in 1.8 Myr), and the latest drilling results which reduce the number of 

suspected buried basalts of post-Miocene age. It is significant that no post-Miocene basalt was 

found in drilling magnetic anomalies in Jackass Flats. If buried Pliocene basalts had been found 

there, that would suggest that the Plio-Pleistocene volcanic zone of Crater Flat basin extends 

through Yucca Mountain significantly affecting the spatial models of volcanism and increasing 

the modeled probability of future repository intersection. 
100

Figure 40 Comparison of selected estimates of the probability of future volcanic 

intersection of a repository at Yucca Mountain (from Perry et al., 2000). 
101

6. Consequences of Igneous Activity Intersecting the Repository 

6.1. Introduction 

 This chapter will discuss the final question of the risk triplet: If the repository is 

intersected, what are the consequences of the igneous activity to the repository and to the 

stored HLW, and what is the impact of its potential release to the environment upon humans? 

The consequences for future radiological exposures vary significantly among the hypothetical 

scenarios for volcanic interaction with the repository (described in previous sections). They 

include an intrusive event, an extrusive (volcanic) event, and secondary breakouts of magma 

from a repository at some distance from the point of initial intersection (the “dogleg” scenario). 

The logic flow charts, Figure 5 and Figure 6, show the components that enter into consideration 

of these scenarios. The dogleg scenario is a variation of the intrusion scenario which results in a 

secondary volcanic eruption. As mentioned already, the potentially critical effects of quenching 

and solidification on waste packages and drift walls have yet to be fully evaluated by the DOE 

and NRC. However, they do have the potential to limit the distance that magma can penetrate 

into drifts, making the “dogleg” scenario much less likely to occur than the other scenarios. 

6.2. Effects from an Intrusive Event (Magma/Drift/Waste Interaction) 

 Many quantitative studies have been published on the basaltic magma involved in 

igneous activity at Yucca Mountain. Discussed here are only those studies most pertinent to the 

present analysis of magma invading a repository drift. 

6.2.1. Critical Magmatic Aspects 

To evaluate the impact of a basaltic dike intersecting the proposed repository, the 

magma type, approximate composition, volatile content, and viscosity must be known or 

estimated. 

6.2.1.1. Magma Composition 

The composition of the magma likely to erupt at Yucca Mountain is best estimated from 

nearby eruptive examples that have occurred in this region over the past 10 Myr. Each 

interested party has used this approach in specifying the most likely future magma type, and 

has assumed that the most likely magma will be alkali basalt. For example, decisions made 

with regard to the magma type and composition state the following: 

The base case chemical composition of basalt...was derived...through analysis of 

45 samples taken from the Lathrop Wells Cone. The Lathrop Wells Cone is the 

youngest volcanic center in the Yucca Mountain region, and, therefore is considered 

an adequate analog for the composition of a possible igneous intrusion into Yucca 

Mountain. (BSC, 2004, p.4-6) 

and 

Magmas in the Yucca Mountain region are typically alkali basalts. (EPRI, 2003, 

p. 2-9) 

On the subject of magma volatile content, all parties have used petrologic indicators in 

the nearest erupted lavas (e.g., Lathrop Wells) to estimate indirectly the pre-eruptive volatile 
102

content of the magma. The presence of the mineral phase amphibole in lavas at Crater Flat 

indicates a magma temperature at or below 1050°C that, coupled with an overall low phenocryst 

content, suggests the magma was near its liquidus temperature. Magma water content had to 

have been in the range of about 1-4 wt.% for basaltic magma to have such a low liquidus 

temperature. Hence, the following assessments are made: 

No magmatic water has a zero probability of occurrence. This statement reflects our 

knowledge that very low volatile contents are rare. With 1 to 3 percent magmatic 

water, the probability should be uniform, reflecting that this is the most likely range of 

water contents. The probability should decrease linearly between 3 and 4 wt.%, so 

that it is zero at 4 wt.%, representing the expectation that at about 4 wt.%, basaltic 

magmas will crystallize before reaching the surface to erupt.” (DOE, 2000, p. 54) 

H2O concentrations in the range 2.5 wt to 4 wt.% with bulk mass H2O/CO2 ratios 

around 6-20 are representative.” (Detournay et al., 2003, p.16) 

These basalts may have water contents of 0-4 wt.% and a wide range of thermomechanical properties that reflect the water content and bubble (void) fraction.” 

(EPRI, 2003, p. 2-9). 

The context of the last quote from EPRI is that the magma involved may be understood 

as a range of processes to contain the stated amounts of water. That is, the original magma 

may contain 4 wt.% water, but upon degassing it may as a lava, for example, contain far less 

water. 

It is also important to note that, besides water, basaltic magmas typically contain 

significant amounts of CO2 and SO2 and lesser amounts of fluorine and chlorine. There are no 

reliable straightforward methods to estimate the pre-eruption concentrations of these volatile 

species, although enough is understood about CO2 in basalt to know that the ratio of H2O to 

CO2 is commonly in the range of about 6 to 20. Nicholis and Rutherford (2004) have 

investigated the range of estimates of water content through experimental phase equilibria 

studies using a sample of Lathrop Wells lava. 

In summary, the type of magma likely to erupt in the future at Yucca Mountain, and its 

chemical composition and volatile content are agreed upon. Of these three features, the exact 

basalt type and chemical composition are not of great importance, but the volatile content is 

important to know well for several reasons, including characterizing the style of the eruption and 

gauging the rheology of the lava that may enter the repository drifts.

6.2.1.2. Magma Viscosity 

In the present context, there is no other magma property more important to know than 

viscosity. To clarify, this is the usual viscosity characterizing viscous shear flows and is 

sometimes denoted as the shear viscosity, or Newtonian viscosity, as opposed to the bulk 

viscosity, which is associated with volumetric expansion of fluids as in the work associated with 

adiabatic expansion. 

There is no single value of viscosity that can be used to characterize the probable entire 

magmatic process at Yucca Mountain. There are at least four distinct phases of the magma, 

each of which will have a characteristic viscosity even though the viscosity will vary continuously 

from one phase to another. Because the solubility of water in magma increases strongly with 

pressure or depth, at depths greater than about 6 km the anticipated magma will be 

undersaturated in water and will be a single fluid phase with a viscosity of about 5 Pa·s 
103

(50 poise, see below). Bubbles will form as the magma ascends and becomes saturated in 

water, and this magma will be described by a second viscosity. The magma itself at this stage is 

still a basalt containing a dispersed collection of bubbles. With continued ascent, the bubble or 

gas phase becomes volumetrically the dominant or continuous phase with dispersed fragments 

of quenched magma, which is characterized by a third viscosity (see 

Figure 41 A). If the magma ascends under conditions conducive to allow extensive and 

continuous degassing, and it extrudes as lava, this lava will be characterized by a fourth 

viscosity (see Figure 41B). In addition, within each of these phases, temperature and 

crystallinity, particle content, or bubble content will have a significant effect on viscosity. 

The approach of all parties has been to estimate viscosity from the bulk chemical 

composition of the given basaltic magma at its liquidus temperature and the estimated amount 

of water. The most important factors governing magma viscosity are chemical composition 

(especially silica content), temperature, water content, and crystal content. Water and 

crystallinity have strong effects on viscosity. Water lowers viscosity, and crystals increase 

viscosity. Bubbles can raise or lower viscosity depending mainly on their size. The effects of 

other volatile species are mixed and, at the concentrations expected, are not likely to be major 

factors in affecting viscosity. The effect of crystals has generally been ignored in the Yucca 

Mountain studies primarily because the associated lavas (e.g., Lathrop Wells) contain only 

‘sparse’ amounts of phenocrysts, which are relatively large (~ 1 mm) conspicuous crystals that 

grew at depth long before eruption. In contrast to phenocrysts, groundmass crystals are very 

small and grow in response to the sudden cooling or quenching attending various aspects of 

eruption. 

The paucity of phenocrysts found in the lavas of the nearby basaltic magmas suggests 

the pre-eruptive state of these magmas was at a temperature near the liquidus (~1000°C) and 

the magma contained 2-4 wt.% water. Given these conditions, it is straightforward to estimate 

viscosity using a number of reliable models. The viscosity of this pre-eruptive magma is 

generally in the neighborhood of 5 Pa·s (50 poise), although there is significant disagreement. 

This issue should be evaluated further. 

Detournay et al. (2003 [Appendix A2.6.1]) give a detailed discussion of magma rheology 

at various stages in the eruption sequence, especially during the critical eruptive stages when 

the magma is saturated with vapor and contains bubbles. In terms of rheology, the central issue 

is the behavior of the bubbles and their size. Small bubbles act as rigid spheres and increase 

viscosity, sometimes to the point of introducing non-Newtonian behavior. Large bubbles are 

deformable and, in effect, act to lubricate the magma, thus reducing viscosity. The quantitative 

difference between small and large bubbles is measured by the capillary number (Ca), which is 

a relative measure of the energy (i.e., work) of viscous shear relative to the interfacial surface 

energy (σ) between vapor and magma. That is, viscous work is measured by the product of the 

local shear or strain rate (G), a characteristic length scale, which is given by bubble radius (rb), 

and magma viscosity (μ). The capillary number is then given by Ca = G rb μ/σ. The effect of 

bubble concentration as a function of Ca on the relative viscosity of the magma is given in 

Figure 42. Relative viscosity (μr) is the ratio of the viscosity of the mixture of melt and bubbles 

(often called the psuedofluid) relative to the viscosity of the melt itself (i.e., melt free of bubbles). 
104

Figure 41 Schematic depiction of cinder cone volcanism and the underlying 

magmatic eruptive column. 

Magma, rich in dissolved volatiles, saturates and vesiculates with approach to 

Earth’s surface and reduction in confining pressure. In essence, the magma gets 

the ‘Bends.’ Increased bubble formation eventually leads to fragmentation of the 

magma and the explosive production of tephra and ash. Also shown are the 

governing magma viscosities (left column) as estimated for each stage of the 

eruptive process. Notice the large contrast in viscosity between the gas rich 

tephra and the late stage lava flows. Observations suggest that the sequence of 

eruptive styles is variable and that explosive and effusive activity can be 

interspersed with other and probably coeval from a single eruptive center 

(Valentine et al., 2006, 2007; Valentine and Keating, 2007; and ANL-MGR-GS000002 Rev 03 now under review at DOE). 

(A) Cinder Cone formation and eruption, schematically depicting explosive tephra 

and ash production leading to formation of the volcanic cone and an ash plume. 

(B) Stage of Cinder Cone eruption where the ascending magma has 

progressively degassed with approach to the surface and the eruption is 

dominated by the extrusion of highly viscous, sluggishly moving lava flows 

emanating from the basal area of the cone. 
105

Figure 42 Relative viscosity as a function of capillary number (After Detournay 

et al., 2003). 

 The important result is that the overall effect of capillary number on viscosity is relatively 

small. For small Ca (i.e., Ca <1) the bubbles are ‘hard’ spheres and viscosity is increased at 

most by a factor of about 2.5 for a volume fraction of 0.5. At the other extreme for large Ca 

(i.e., Ca >>1), where the bubbles are easily deformable by the shear flow, viscosity is reduced 

by a factor of about four. This occurs because the high viscosity fluid (i.e., melt) still forms a 

continuum, which essentially controls the rheology. The overall effect, however, also depends 

on the bubble size distribution, which controls packing and, ultimately, the bubble concentration 

at the point of melt continuum breakdown and, eventually, the process of melt fragmentation. 

In light of these results, in the regime where the magma contains bubbles but is still a 

continuum of melt (i.e., the bubble concentration is below about 50 vol.%) containing isolated 

bubbles, the dominant viscosity is determined by the composition of the magma. The effects of 

the bubbles themselves are not large. There is another effect, however, that has caused some 

confusion in defining the dominant viscosity. 

Magma viscosity is not only highly sensitive to chemical composition, including the 

amount of dissolved water, but also to the concentration of solids or crystals in suspension. 

Crystal content increases systematically with cooling from the liquidus (0 vol.% crystals) to the 

solidus (100 vol.%). As the concentration of crystals reaches maximum packing at ~ 50 vol.%, 

the crystals interlock, and viscosity increases essentially without limit to that of an assemblage 

of solids. This effect is shown in Figure 43 where viscosity is measured against crystal fraction 

(Φ). There are many formulations available to calculate this effect and several are used here to 

show the range of estimates (Marsh, 1981). The most critical factor in each calculation is the 

point of maximum packing or critical crystallinity (Φc), which is well known for magmatic crystals 

to be Φc~0.55 (i.e., 55 vol.%). When the magma contains water, bubbles will eventually appear 

as crystallization proceeds, and these will also affect the viscosity as noted in Figure 42. 
106

 

Figure 43 Viscosity (μ) as a function of crystallinity (Φ) (After Mooney, 1951; Roscoe, 

1952; Gay et al., 1969; Marsh, 1981). 

It is important to realize that this effect occurs relative to the liquidus and solidus, which 

are each highly sensitive to the water content of the magma. As water is added to magma, the 

liquidus and solidus are systematically (to a point) reduced in temperature. And, because overall 

viscosity is a strong function of temperature (which includes the effect of crystal buildup), it is 

essential when estimating magma viscosity to do so relative to the liquidus, at whatever 

temperature it may be. Viscosity cannot be estimated from temperature alone. 

Groundmass volume fractions in pyroclastic materials at Lathrop Wells that have been 

quantified to date range from 20-30% (volume). Values of viscosity in ANL-MGR-GS-000002 

Rev03 (under review by the DOE) are reported clearly as values at the liquidus for appropriate 

temperatures and water contents and are consistent with the plot in Figure 43 in the range of 

log(viscosity,poise) = ~2.7-1.9 for water contents of 0-4 wt.%. 

Lore et al. (2000), in studying the effect of cooling on fracturing of basalt lava from the 

Snake River Plain, presented a figure showing the viscosity of anhydrous basalt covering an 

unusually wide temperature range from 1500°C to 100°C. These results are shown in Figure 44 

along with other information that has been used by EPRI (2005) to estimate the viscosity of 

possible Yucca Mountain magma. 

The approximate liquidus and solidus for a basalt of this type is indicated along with a 

curve, labeled basalt + crystals, showing the variation of viscosity for a magma of this 

composition undergoing crystallization as it solidifies. This variation is in accordance with the 

results presented above. Beginning at the liquidus, where the viscosity is about 100 poise (10 

Pa·s), the viscosity increases strongly midway through the crystallization interval as the crystal 

content approaches 50 vol.%. This is in contrast to the curves of Lore et al. (2000) that continue 

smoothly through the crystallization interval and only rise strongly below the glass transition 

temperature at about 700 °C, which is some 300°C below the solidus, where the magma is 
107

completely solid and its viscosity is effectively infinite. The reasoning behind the curve of Lore 

et al. is the assumption that the basalt does not crystallize but becomes a glass (solid curve) 

containing 20 vol.% crystals (dashed curve). Because they are interested in rapidly cooled lava, 

this is an appropriate approximation at sub-solidus temperatures. However, their curves are not 

accurate near the liquidus nor within the melting range in general. Because this is an anhydrous 

(i.e., water-free) basalt lava, these results do not directly pertain to the possible Yucca Mountain 

magma at depth where it is expected to contain 2-4 wt.% water. 

Figure 44 Magma phase diagram showing change in viscosity (μ) as a function of 

temperature. 

6.2.1.3. Perspectives on Magma Viscosity 

6.2.1.3.1. DOE Perspective 

 The DOE (DOE, 2004, p.6-29) summarized the flow regimes for basaltic magma: 

 • Homogeneous with small, low Reynolds number bubbles moving with the melt 

 • Bubbly flow with bubbles rising faster than the melt 

 • Slug flow with bubble sizes approaching the width of the dike (Vergniolle and Jaupart, 

1986). 

The DOE goes on to explain these regimes and the final choices for modeling as follows. 

The operative flow regime will be a function of many variables including, but not limited to 

moisture content, other gases present, pressure, melt viscosity, and surface tension. Figure 45 

shows the phase equilibria diagram for Lathrop Wells basalt, inverted from the normal 

presentation, together with the eruption column anticipated for these phases. As the magma 

first encounters a drift, it may do so under slug flow. As time progresses and the magma front 

continues up the dike, the flow entering the drift may become bubbly. The viscosity of the bubbly 

flow is very complicated and in certain cases will be non-Newtonian. This could include either 

shear thinning or shear thickening depending on the variables listed above (Detournay 

et al., 2003; Appendix 2, p. 1, Figure 2B). Therefore, it is not possible to determine the effect of 

this uncertainty. 
108

Figure 45 Phases in a volcanic eruption column showing the three regimes (wet 

magma, water saturated bubbly magma, and particulate-laden gas) and 

associated phase equilibria diagram for Lathrop Wells basalt under 

conditions of water free (denoted as Dry Magma) and containing about 

4 wt.% water (denoted as Wet Magma). The approximate depth of the 

repository is also marked. Notice the large effect of water in lowering the 

crystallization range of the magma to the extent that as the Wet magma 

approaches the surface it is at a temperature where it would be completely 

solid if it were on the surface. 

6.2.1.3.2. EPRI Perspective 

Using the experimental phase equilibria on basalts near Yucca Mountain, EPRI (2005, 

p.3-1) estimated magma viscosity as follows. Based on phase-equilibria stability diagrams 

(Nicholis and Rutherford, 2004), the magma ascended from depths >7km (>175 MPa) with 

temperatures <975°C for the Little Cone samples and 1000-1010°C for the Lathrop Wells 

samples. The corresponding viscosities for this range of temperatures at repository depths are 

105

-107 Pa·s (106-108 poise) (Lore et al., 2000); Delaney and Pollard, 1982) and a magma 

rheology characteristic of an aa flow (Soule et al., 2004). 

The problem with this approach in estimating viscosity is that these temperatures cannot 

be used directly with the above curves of Lore et al. because the liquidi of the hydrous Yucca 

Mountain magma and the dry Snake River Plain basalt are greatly different. With each magma 

at the respective liquidus temperature, the Yucca Mountain magma will actually have a viscosity 

lower than that of the Snake River Plain basalt because the Yucca Mountain magma contains 

water. That is, the Yucca Mountain magma at about 1000°C and containing water will have a 

viscosity about ten times smaller than the Snake River Plain magma at 1200°C and containing 

no water. 

In terms of estimating the viscosity of the degassed Yucca Mountain magma, which may 

form a glassy basalt through rapid cooling during ascent, the viscosity from the Lore et al. 
109

(2000) curves at a temperature of ~1000°C would be about 1010 poise (109

 Pa·s). Strictly 

speaking, under these conditions this value may be correct. 

6.2.1.3.3. Additional Comments on Magma Viscosity 

The various possible rheological regimes experienced by hydrous basaltic magma as it 

decompresses on approach to the surface are appreciated by all parties. But the application of 

this information is inconsistent. The central point of confusion concerns the rheology of basalt 

as it degasses with ascent under isothermal conditions. That is, the most sophisticated 

calculations show that basalt degassing under adiabatic conditions will ascend essentially 

isothermally due to crystallization (Mastin and Ghiorso, 2001). For hydrous basalt beginning its 

ascent at a temperature of about 1000°C, as has been suggested from experimental phase 

equilibria, an isothermal ascent will produce either rapid crystallization or quenching to a glass 

(vitrification) containing some crystals. In either case the viscosity increases enormously. Rapid 

crystallization or vitrification occurs because the hydrous basalt begins its final ascent at a 

temperature (~1000°C) that is at or below its low-pressure (i.e., near surface) solidus 

temperature. This is illustrated in Figure 46 (Marsh and Coleman, 2006; 2008). As the 

concentration of solids (i.e., crystals) approaches that of maximum packing, which for basaltic 

magma is at ~50-55vol.%, viscosity increases to ~1018 Pa·s with complete crystallization 

(Marsh, 1981; Pinkerton and Stevenson, 1992). If the basalt, instead, quenches to a glass, with 

a modest (~10-20 vol.%) amount of crystals, the viscosity will become ~1010 to 1012 Pa·s, 

depending on the exact temperature. The attainment of this condition is reflected in the lack of 

mobility of lavas from Lathrop Wells. 

Figure 46 Details of the near surface eruption thermal trajectory and the possible rheology if 

the magma quenches to a glass. Phase diagram (C on the RHS) for Lathrop Wells 

basalt under dry and wet conditions. Note the contrasting ascent trajectories of 

Dry versus Wet magma. The detailed temperature history for an adiabatic ascent (B 

above) for both basalt (lower temperature scale) and rhyolite (upper scale) as 

calculated by Mastin and Ghiorso (2001) where the effect of loss of gravitational 

potential energy has been included. The magma reaches the surface undergoing 

strong cooling. If the ascent is rapid enough the magma will quench to a glass the 

rheology of which is given by diagram A (LHS) as a function of strain rate. The 

probable range of viscosity is also indicated (After Webb and Dingwell, 1990; 

Marsh and Coleman, 2006; 2008). 
110

On the other hand, water-poor or anhydrous basaltic magma ascends along its high 

temperature liquidus and erupts at near liquidus temperatures. The viscosity is very low, about 

10 Pa·s, and the magma is highly mobile. The bottom line is that hydrous magmas are explosive 

as the gas exsolves and escapes, but the ensuing lavas are relatively immobile. Dry magmas 

are not explosive, but the lavas are highly mobile. This is emphasized more explicitly in Figure 

47 where the near surface ascent (last ~ 5 km) is shown in detail along with the associated 

variations in viscosity due to crystallinity alone without glass formation. 

Figure 47 The increase in viscosity in response to increasing crystallinity during the final 

stages of ascent for a water-saturated magma containing 4 wt.% water (left). The 

eruption window is noted within which the crystallinity is less than ~50 vol.%. The 

effect of latent heat due to crystallization, keeping the magma isothermal, has been 

taken into account. The general increase in crystallinity with decreasing temperature for Lathrop Wells basalt is shown in the center (upper) panel and the 

concomitant increase in viscosity is shown by the lower center panel. The increase 

in viscosity during the final stages of ascent for basaltic magma containing 4, 2, 

and 0 wt.% water is also shown (right) along with the position of the repository and 

the range of viscosity for silicate glasses. The largest increase in viscosity occurs 

for magma containing the most water, because at its liquidus it is the coolest prior 

to eruption. For magma free of water (i.e., dry magma) there is no (or minor) 

crystallization immediately prior to eruption and no significant increase in 

viscosity (After Hinze et al., 2008). 

There is confusion in all of the modeling over the viscosity of the basalt in the near 

surface regime. Either the magma is assumed to have its high-pressure, water-rich viscosity all 

the way to the surface (DOE, 2004, p. 6-30) or the magma is assumed to be unusually hot 

(~1200°C) and highly mobile. EPRI (2005) does assume a high viscosity magma, but for 

incorrect reasons. In particular, the DOE states (BSC, 2004, p. 6-30-31): 

Many of the calculations used in this model are for magma less dense than 

1300 kg/m3

, which consists of more than 50 percent by volume gas. The viscosity of 

such a mixture is uncertain, so a viscosity of range of 10 Pa·s to 40 Pa·s, equivalent 

to the pure silicate liquid is used. The range of viscosities used in this analysis is 

derived from Detournay et al. (2003, Figure 2-1e). Most of the results in this report 

are for a viscosity of 10 Pa·s, representing a fluid magma that would quickly fill the 

drifts and, therefore, a more conservative condition from the perspective of dike/drift 

interaction. 
111

The Detournay et al. (2003, Figure 2-1e) results referred to here are shown in Figure 48 

where the assumed conditions of the calculation are that the magma is at 1150°C, which is near 

the dry liquidus temperature, as opposed to about 1000°C for the potential Yucca Mountain wet 

magma. 

 

Figure 48 Magma viscosity calculated at 1150o

 C during near-surface ascent and 

degassing (After Detournay et al., 2003). 

Assuming this high temperature of 1150°C avoids having to consider the effects of 

crystallization and vitrification. This result is used by Detournay et al. (2003) as an illustrative 

assumption and should not be construed to represent the true rheology of the ascending 

basaltic magma. This can be seen by comparing this assumed temperature to the phase 

relations shown by Figure 46. A more meaningful calculation is to put the magma at a starting 

temperature at 1000°C and, as it ascends, follow it through the course of crystallization and/or 

vitrification, which is done schematically in Figure 47 and can also be done using Figure 44 from 

Lore et al. (2000). In this case, the magma viscosity reaches the much higher values mentioned 

earlier of 1010 to 1012 Pa·s. 

It is important to appreciate the individual processes involved in forming crystals and 

glass in magma due to heat loss as opposed to crystallization induced by rapid depressurization 

associated with ascent and extrusion. As mentioned already, crystallinity is absolutely critical to 

magma mobility, as no lava has ever been erupted carrying more than 55 vol.% phenocrysts 

(Marsh, 1981). In cooling from liquidus to solidus all magmas either crystallize to a network of 

solids, quench to a glass, or go to a combination of each. For crystallization, the increase in 

viscosity in cooling from the liquidus to the point of beyond 55% solids is by a factor of more 

than 1014; perhaps the largest change in any earth material physical property. The actual end 

product depends on the rate of cooling relative to the rates of crystal nucleation and growth. The 

rate at which any local region of magma can be cooled is limited by the thermal diffusivity 

(K~10-02 cm2

/s) and the spatial position (L) of the locale relative to the proximal cooling surface; 

from scaling the heat equation, cooling time is t~L2

/K. When L is small quenching to a glass is 

possible, but deeper in the magma interior crystallization will always occur, especially in basaltic 

magmas. Temperature-induced crystallization operates, in essence, as a surface force: It must 

propagate in from a surface. 

Pressure-induced crystallization is a much different process. Pressure-induced 

crystallization due to de-volatilization operates much as a body force. Like gravity, it can operate 

throughout the magma essentially instantaneously. (It can propagate at the rate of an acoustic 
112

wave.) The rate-limiting step is the rate of local diffusion of water into bubbles. This diffusion 

time (t~d2

/D, where D is H2O diffusivity ~10-6 cm2/s) is given by the same equation, but here the 

length scale (d) is a local length scale and can be made arbitrarily small due to increased 

bubble nucleation density. Quenching to a glass can happen throughout the body and is 

dependent on the rate of ascent, the amount of water present, and, perhaps most important, the 

form of the phase diagram. The degree of quenching or crystallization depends strongly on the 

amount of water present. For a dry magma, as seen in the above figure, there is no 

crystallization pressure effect in ascending along the (almost isothermal) liquidus. For a magma 

rich in water, rapid depressurization with attendant gas loss will quench the magma to a 

combination of crystals and glass. Motion is still possible, albeit as a highly viscous mass. 

There is a field example of what happens to basaltic magma when it tries to flow through 

a narrow tube in rock that is relatively cold (251-256oC) compared to magma. In Iceland, on 

September 8, 1977, magma reached the depth range of boreholes in the Námafjall geothermal 

field. Three tons of very fine volcanic ash erupted through an 1,138 m deep drillhole, forming a 

tephra sheet with a volume of 26 m3

 (Larsen et al., 1979). The drillhole was part of the 

infrastructure for a hydrothermal field. The eruption lasted ~20 minutes. The drillhole was cased 

to 625 m, had an uncased diameter of 0.16 m, and the main producing zones were reported at 

depths of 638 m and 1038 m (Larsen et al., 1979). Tephra composition indicated temperatures 

at the time of chilling of 1153-1158°C. Compared to lava at Yucca Mountain, this Icelandic 

magma was dry and relatively mobile, but lava never flowed out of this drillhole, which indicates 

limited vertical rise of magma due to quenching on drillhole walls and increasing flow resistance 

and viscosity during ascent. 

The short eruption time can be used to estimate a lower limit for the magma viscosity. It 

is assumed that, after the initial pyroclastic phase, degassed magma entered the drillhole via 

the deeper producing zone and began traveling up the uncased section. Using Poiseuille’s Law 

for pressure-driven flow, and given an overburden pressure of >2 ×107

 N/m2, viscosities for this 

mobile magma must nonetheless have exceeded 100 Pa·s, otherwise the velocity of the liquid 

magma front would have been great enough to reach and seal the cased part of the borehole in 

20 minutes. This did not happen because steam production continued from this borehole after 

the magmatic event. For comparison, previous workers (Woods et al., 2002 and 2006) assumed 

low viscosities of 10-100 Pa·s for relatively immobile, wet magmas at Yucca Mountain. 

Dartevelle and Valentine (2007) analyzed the Námafjall borehole eruption. They noted 

that the eruption provides a unique test case for multiphase processes because its vertical 

extent of ~1 km is similar to that of natural volcanic conduits and its geometry is well known. 

They modeled the eruption by solving time-dependent governing equations for conservation of 

mass, momentum, and energy of the gas and particle phases. Their analysis allowed for drag 

and heat transfer between the phases. The model results indicate the development of transient 

waves of high particle concentration that propagatee up the borehole, resulting in ejection of 

particles in pulses like those observed at Námafjall. Dartevelle and Valentine’s (2007) results 

indicate that transient multiphase behavior is probably common in volcanic conduit flows. They 

suggest that a key topic of future research is quantifying the time-dependent behaviors and their 

impacts on eruption column dynamics. 

In sum, researchers must be consistent in how they estimate the viscosity of Yucca 

Mountain basalt as it ascends and degasses near the surface. There has been a tendency to 

assume rheological properties pertaining to both wet, cool magmas and dry, hot magmas, 

leading incorrectly to the postulate of a highly explosive system with highly mobile lavas. The 

potential Yucca Mountain magma is likely a wet, cool magma. Wet basaltic magma is 
113

explosive, but relatively immobile as lava. Dry (e.g., Icelandic) magma is not explosive, but 

highly mobile as lava. 

6.2.2. DOE, EPRI, and NRC Perspectives on the Magma/Waste Package 

Interaction 

6.2.2.1. DOE Perspective 

The DOE (e.g., BSC, 2004) and EPRI (2004, 2005) have considered many aspects of 

the dynamics of dike propagation, magma flow into drifts, magma-waste package interactions, 

and subsequent waste package-water interaction. For magma flow into a drift the DOE uses 

various coupled models, analytical and numerical, of fluid flow from the dike to the drift. The 

magma is given a viscosity of 10-40 Pa·s, and the drift is filled in about 15 minutes. Effects of 

solidification on magma rheology are mentioned, but not explicitly used in flow modeling. This 

analysis suggests that waste packages may be softened, deformed, and corroded by the 

magma, but not be easily moved, and glassy waste forms are unlikely to be significantly altered 

by the magma. Yet because of the many uncertain facets of the process encountered in this 

investigation, the DOE concluded (BSC, 2004, p. 6-111) that “On balance, it would be proper to 

adopt the conservative position that all waste packages and associated drip shields that come in 

contact with basalt magma immediately fail.” 

6.2.2.2. EPRI Perspective 

 EPRI (2004) analyzed an extrusive release scenario for Yucca Mountain and concluded 

that the waste package, if intact and still strong, can provide a significant barrier to inhibit the 

volcanic release of radionuclides. EPRI analyzed several failure mechanisms, including a direct 

hit on a waste package from below, and found reasonable expectation that no waste packages 

would fail. EPRI (2004) therefore concluded that the expected consequence of an igneous 

extrusive event would be no release of radionuclides to the atmosphere. EPRI did note that 

waste packages located directly within a magmatic conduit could conceivably contribute 

radionuclides during the Strombolian stage of an eruption. 

Use of more reasonable (to them) assumptions in EPRI’s (2005) work lead them to deemphasize the importance of igneous scenarios in estimating probability-weighted peak doses. 

They suggest that the DOE and the NRC have used so many compounding conservatisms in 

their evaluations that igneous scenarios have taken on greater apparent risk importance than is 

justified. They conclude that present DOE and NRC assessments of repository performance are 

conservative, and state that reliance on more realistic scenarios and input data would 

demonstrate an even greater margin of compliance. Based on the results of two summary 

reports, EPRI (2004; 2005) reached the overall conclusion that there is reasonable expectation 

that an intrusive or extrusive igneous event at Yucca Mountain would not be expected to result 

in dose levels exceeding those levels anticipated for a base-case scenario with no igneous 

event, and that no further work need be pursued to address the igneous scenarios. 

A key aspect of the EPRI (2005) analysis concerns the realization that magmatic 

eruptive temperatures are apt to be significantly lower than they (and DOE) have previously 

assumed. This stems from experimental phase equilibrium studies on basalt from the nearby 

Crater Flat basin by Nicholis and Rutherford (2004). Their work suggests that, although the 

magma was at or near its liquidus temperature, because of the magma water content this 
114

temperature was much lower than previously assumed (i.e., ~1000°C vs 1150-1200°C). EPRI 

(2005) then used the viscosity-temperature relations of Lore et al. (2000) to find a much larger 

magma viscosity of 105

 to 107 Pa·s. The difficulty with this approach is that the relation shown 

by Lore et al. (2000) is based on experiments for water-free melts and glasses and cannot be 

used for hydrous magmas. Even though the new temperature is much lower, the fact that it is at 

the liquidus of a water-rich magma means that the intial viscosity at depth will be as low (or 

possibly lower) than that initially assumed by EPRI and DOE. The correlation and regression 

given by Lore et al. (2000) is useful as an overall indication of rheology from melt to glass in 

lava, but as discussed above it does not capture the detailed changes due to crystallinity, water 

content, and bulk composition within the liquidus-solidus range for magma in general. 

6.2.2.3. NRC Perspective 

As mentioned already, Woods et al. (2002) also analyzed the hypothetical case in which 

magma diverts along multiple emplacement drifts and into the main access drift, from which it 

vents to the surface. Intersected drifts could thus quickly fill with magma, and a large number of 

waste packages in the repository could be affected. Woods et al. suggested that prolonged 

magma flow through the repository, enveloping and bathing the waste packages for days to 

months results in failure of waste packages and provides a mechanism to transport waste to the 

surface. They did not consider the effects of solidification on rheology or of quenching on waste 

packages. 

Woods et al. (2002) also suggested the possibility of generation of a shock wave, which 

propagates through the drifts as the dike cuts the drift. The ideal experimental situation by 

which to produce a shock wave is to puncture a diaphragm separating a fluid under high 

pressure from a space at much lower pressure. Disruption of the diaphragm produces a 

pressure wave with a discontinuity in pressure at its leading edge. 

Shock waves have indeed been recorded in volcanic eruptions at well-established 

volcanoes associated with island arcs such as at Nguaruhoe in New Zealand (Nairn, 1976) and 

Mount St. Helens (Reed, 1980). Shock waves have not been observed during venting of a dike 

in establishing a fissure-style eruption. The basic structure of island arc stratocone volcanoes, 

however, makes them ripe locations for shock wave production. Stratocone volcanoes almost 

always emit magma from a central summit vent. Korovin volcano on the island of Atka in the 

Aleutian Islands, for example, has such a cylindrical vent about 300 m wide and 1 km deep that 

has been periodically observed to be empty and later brimming with magma (Marsh, 1990). 

Should the summit area become plugged with congealed magma, which is commonplace, rising 

magma along with the inevitable exsolution of volatiles will overpressure the volcano until it 

suddenly ruptures. Moreover, many highly explosive island arc volcanoes erupt high 

crystallinity magma that is near the point of critical crystallinity (~55 vol. %; Marsh, 1981) where 

the magma becomes a shear resistant dilatant solid, forming an effective plug at the summit. 

Merapi volcano in Indonesia is a clear example of this condition (e.g., del Marmol, 1989). Thus, 

large volcanoes repeatedly issuing magma from a central summit vent are, in essence, almost 

ideal shock wave generators. A dike entering a drift at Yucca Mountain would be distinctly 

different from this occurrence. 

A propagating dike is a magma-filled elastic crack. The leading edge of the dike is knifelike and the width of the dike increases slowly away from the tip. Although this is sometimes 

difficult to calculate in highly fractured country rock with complex elastic properties, examples 

are available from field occurrences. For example, in the north wall of the east end of Wright 

Valley in the McMurdo Dry Valleys, Antarctica, the leading edge of the dike associated with the 

emplacement of the 300 m thick Basement sill is fully exposed (Marsh, 2004). Over a distance 
115

of about 5 km the dike thickness increases progressively from 1 cm at the leading tip to 300 m. 

A dike intersecting a subsurface cavity or drift will gradually open to its full thickness. Rapid 

quenching of (most probably) low crystallinity magma along all margins will further impede the 

rate of opening so that the pressure release will not be catastrophic, as with a punctured 

diaphragm, but will ramp-up over a finite time and not allow development of a discontinuity in 

the pressure field. 

The scenario analyzed by Woods et al. (2002) creates a shock wave because of the way 

the problem and simulation is set up. The imposed initial conditions (both geometric and 

dynamic) essentially presuppose the solution. But it is the magma physics before the assumed 

initial conditions that actually determines the outcome. The proper portrayal of this part of the 

problem (e.g., the gradual opening of a leaky fracture into a cavity) precludes formation of a 

shock wave. BSC (2004) and EPRI (2004) also analyzed the possibility of generation of a 

shock wave and found magma-drift interactions to be far less severe than those hypothesized 

by Woods et al. (2002). 

6.2.2.4. Summary of Views 

A recent numerical analysis by Dartevelle and Valentine (2005) builds on the Woods 

et al. (2002) approach but includes full time dependence, 2-D geometry, and a multiphase flow 

of steam and pyroclastic particles. Although this work has attractive features in time 

dependence, spatial deposition of particles, and spatial dependence of flow speed and 

pressure, it also suffers in its fixed (i.e., non-time dependent) 2-D geometry. A shock wave 

forms at the outset in response to the fixed geometry and the initial conditions of the pressure 

contrast between the dike flow and the drift. 

Detournay et al. (2003) present an extensive discussion of igneous consequences at 

Yucca Mountain, including the potential interactions between a basaltic dike and a repository. In 

their opinion, the probability that a violent erupting mixture could follow dogleg conduits is small 

and more than offset by the degree of conservatism built into the existing estimates. They 

recommended that a number of new analyses be made, including development of a coupled 3D 

model for unsteady dike-drift flow for the scenario of a drift being intersected by a vertical dike, 

and that experimental studies be made on the chemical and mechanical effects of basaltic 

magma on waste packages in drift and conduit flows. 

Overall, it appears that significant conservatisms exist in the DOE and NRC analyses of 

igneous scenarios. These conservatisms exist, in a large part, because of major uncertainties 

in the understanding of the interaction of magma with the repository, and much of the 

uncertainty centers on the problem of the thermo-viscous state of magma as it undergoes 

solidification. For example, Woods et al. (2002) assume that magma moving through a 

repository drift remains isothermal with “water-like” flow characteristics. This is based on the 

assumption that magma flow rates will be rapid (10 to 100 m/s, or 22 to 220 mph) and the 

thermal inertia of the flow will be large as in flow in a lava tube. But repository drifts are small 

(~5.5 m diameter) and cool (100-300°C) and lava, being always within its crystallization interval 

(Figure 47), quenches and stagnates on all it touches. By not considering realistic scenarios for 

the thermal interaction of magma with tunnel openings, waste packages, and tunnel walls, there 

is a real possibility that important processes could be missed. This would not only have 

implications for understanding other processes (e.g., entrainment and eruption of waste) but 

also in correctly estimating the overall seriousness of the magma disruption process itself. A 

prime example in previous work is the serious omission of the exceedingly common 

phenomenon of magma solidification and quenching. An explanation for this view is given below 

after first describing the physical situation. 
116

6.2.3. Number of Waste Packages Potentially Affected by Dike Intrusion 

The extent to which a repository could be affected by a hypothetical dike intrusion 

depends on how far magma could penetrate drifts before it solidified. As discussed in the 

preceding section, this would be determined by the composition, rheology, and driving pressure 

of the magma if it should encounter tunnels. Both the DOE and EPRI have performed 

quantitative analyses of the number of waste packages that could be affected by hypothetical 

dike intrusion. 

6.2.3.1. DOE Analysis 

The DOE (2004) states that the rate of magma flow into drifts will be limited by the rate 

of magma supply, except probably when the supply is very large (velocity on the order to 

10 m/s) and the magma viscosity is on the order of 40 Pa·s. The time needed to fill 500 m of 

drift would be on the order of 15 minutes given a magma velocity of 1 m/s. The time needed 

depends on the supply rate, and the results can be linearly scaled to other drift lengths. 

The presence of the drift will have an impact on the rise of the magma inside the dike. In 

fact, the magma front may stop rising, and a steady state flow into the drift (total magma flow 

inside the dike diverted into the drift) may be reached before it is completely filled. However, the 

magma will rise several tens of meters above the drift before if fully invades it. Pressures in the 

drift will be minimal (a few kilopascals) while the magma is invading it. 

Uncertainty exists in the magmatic effects on waste package integrity. Flow of magma 

into drifts is likely to result in plastic deformation of waste packages, but it is unlikely to result in 

movement of waste packages over large distances. Exposure of packages to the high 

temperatures and corrosive gases of the magmatic environment are expected to enhance 

corrosion. 

The DOE assumes that commercial spent fuel will eventually be reduced to relatively 

small particles due to oxidation. Glassy waste forms are not expected to be significantly altered 

by interaction with magma. On balance, it would be proper to adopt the conservative position 

that all waste packages and associated drip shields that come in contact with basalt magma 

immediately fail (BSC, 2004, p. 6-111). 

DOE (2004) documents calculations of the number of waste packages that could be 

damaged in a potential future igneous event. The igneous intrusion scenario shows a range of 

consequences, extending from virtually no waste packages damaged to nearly all waste 

packages in the repository. The 50th percentile value indicates approximately 1,600 waste 

packages could be impacted, out of over 11,000 waste packages in the repository. DOE made 

the following assumptions in these analyses: 

1. For any drift intersected by a dike, all of the waste packages located in that drift will fail. 

In other words, they will provide no further protection for the waste. 

2. For any drift not intersected by a dike, none of the waste packages located in that drift 

will fail. 

The rationale for these assumptions is: 

1. Since the emplacement drifts will not be backfilled, there are no credible mechanisms to 

block or mitigate the resulting effects from the dike intrusion upon the waste packages. 
117

2. The presence of backfill in ventilation drifts, access drifts, and turnouts will serve as 

credible mechanisms, provided sufficient engineering is implemented, to protect waste 

packages in emplacement drifts which are not exposed directly to magma (i.e., drifts 

which are not intersected by a dike). 

6.2.3.2. EPRI Analysis 

The results of EPRI’s (2005) analysis of hypothetical magma intrusion are summarized 

in Table 6 Within the “red” zone they estimate that 0-6 waste packages could become engulfed 

by magma intrusion in a waste emplacement drift. They further estimate that in the “blue” zone 

14-24 waste packages could be significantly affected by heat and corrosive gases. 

Table 6 Summary of the impacts on waste packages and specifically containment 

and controlled-release functions of barriers, for each of the three zones for 

the expected intrusive-release variant case (After EPRI, 2005) (Permission 

to use this copyrighted material is granted by the Electric Power Research 

Institute). 

Zone Description 

of Zone 

Extent 

of Zone 

Total No. of 

Waste 

Packages 

(both 

directions) 

Condition of 

Cladding 

Condition of Alloy22 Waste Package 

Outer Barrier and 

Drip Shield 

Impact on 

Transport 

Properties

Red Waste 

packages 

engulfed by 

magma 

intrusion 

0-20 m 

from 

magmatic 

dike 

0-6 Failed Additional 

considerations: 

• WPs are unlikely to 

fail by overpressurization because 

of restraint by the 

external magmatic load. 

• Creep failure is 

considered unlikely as 

the magma will prevent 

sufficient strain of the 

WP. 

• Potential for DS 

displacement by 

magma intrusion. 

Fractured 

basalt 

- Flow 

diversion 

- sorption 

- fractured 

matrix 

Blue Waste 

packages 

experiencing 

significant 

thermal 

impacts 

37-66 m 

from end 

of Red 

zone 

(front of 

magma 

intrusion 

14-24 Failed All of the WPs in the 

‘Blue Zone’ are 

conservatively assumed 

to fail by creep. 

Additional 

considerations: 

• 1-2 WPs in the region 

immediately in front of 

an intruding magma 

plug, in addition a 

single WP that might be 

only partially engulfed 

by magma plug, are 

likely to fail by overOpen air 
118

Zone Description 

of Zone 

Extent 

of Zone 

Total No. of 

Waste 

Packages 

(both 

directions) 

Condition of 

Cladding 

Condition of Alloy22 Waste Package 

Outer Barrier and 

Drip Shield 

Impact on 

Transport 

Properties

pressurization. 

• The hottest WPs may 

become sensitized and 

subject to enhanced 

general corrosion and 

greater localized 

corrosion susceptibility. 

• Corrosion due to 

volatile gases will range 

from 0.1-1 mm for the 

10 hottest WPs. 

• Drip shield 

displacement unlikely. 

Green Waste 

packages 

contacted by 

magmatic 

gases 

The 

remainder 

of the 

intersected 

emplace

ment drift 

beyond 

the limit 

of the 

“Blue” 

zone 

All of the 

remaining WPs 

in the 

emplacement 

drift outside 

the “Red” and 

“Blue” zones 

Intact No WP failures are 

expected in the ‘Green 

Zone’. Additional 

considerations: 

• No WP failures due to 

overpressurization 

because of the 

relatively low 

temperatures. 

• No creep failures are 

predicted in the ‘Green 

Zone’. 

• WP temperatures are 

too low to cause 

thermal aging of the 

Alloy 22. 

• Extent of corrosion 

due to exposure of 

approximately 12 WPs 

to volatile magmatic 

gases is expected to be 

<0.1 mm. 

• DS displacement 

unlikely. 

Open air 

6.2.3.3. NRC Considerations 

In TPA 4.1 (Mohanty et al., 2004) the NRC estimated a mean value of 37 magmainduced mechanical failures from an intrusive event, based on a log uniform distribution from 1 

to 1402 waste package failures. Igneous activity causes the largest increase in dose 

conditionally from both groundwater and airborne pathways, but the risk is still small when the 

probability of the volcanic event is factored into the calculations. The probability-weighted dose 
119

from igneous activity is approximately 3.6 μSv/yr (0.36 mrem/yr), which is greater than the base 

case groundwater dose of 0.00021 mSv/yr (0.021 mrem/yr), but still small compared to the 

regulatory criterion of 0.15 mSv/yr (15 mrem/yr) (Mohanty et al., 2004). 

6.2.3.4. ACNW&M Comments on Magma Viscosity and Potential Dike Intrusion 

The question of the number of waste packages involved in an eruptive event involves, in 

part, the length of drift exposed to magma. This is dependent on the number of drifts intersected 

by the magmatic event and the extent to which magma flows into each drift. Magma viscosity 

and the pressure gradient driving the magma into the drift are key factors in evaluating the 

distance of magma penetration. The eruptive event can be separated into two periods or styles. 

In the earliest stages, the initial magma is characterized by a low viscosity, gas-rich, particleladen pyroclastic fluid. As the eruption proceeds, over days to weeks, the eruption will transition 

to the extrusion of high viscosity lava, which reflects the arrival of degassed magma into the 

near surface. This evolutionary sequence from pyroclasitcs to lava may not necessarily be a 

strict succession, but the eruption may, right from the beginning, change back and forth from 

pyroclastic to lava and vice versa (e.g., Sparks, 2007). Some examples of this behavior are 

Paricutin, Mexico (1943-1952) and Eldfell, Iceland (1973), although neither of these is 

particularly similar in magma composition or water content to what is expected at Yucca 

Mountain. Recent work by Valentine et al. (2007; see their Figure 3) also suggests a similar 

behavior at Lathrop Wells. 

6.2.3.4.1. Magma/drift Interaction Scenarios 

If the initial eruptive material breaching the repository is pyroclastic debris, given a 

delivery rate of ~1 m3

/s or more, a local small subsurface cinder cone, in effect, would quickly 

form near the entry point, plugging the drift through avalanching and welding. On the other 

hand, if the eruptive is low viscosity (e.g.~102

 Pa·s) lava, as has often been assumed for this 

process, the flow rate is rapid (10-100 m/s) and a significant distance of drift may become 

involved. If the flow rate is 10s of meters per second, the drifts would be filled with lava to 100s 

of meters in a very short time (minutes). The flow of lava through a drift can be estimated by 

assuming flow through a pipe whose radius shrinks in time due to magma solidification around 

the margins of the drift. A prime difficulty in performing such calculations is in the proper choice 

of the viscosity of the lava. Given the magma composition, temperature, volatile content, and 

crystallinity, the estimation of viscosity is straightforward (e.g., Marsh, 1981). Each of these 

characteristics can be estimated for magma similar to alkali basalt erupted nearby at Lathrop 

Wells, but there is a major problem in using this approach. As explained already in association 

with 

Figure 41, Figure 45, Figure 46, and Figure 47, because of the anticipated high volatile 

content, this magma will undergo volatile saturation at depth (~5 km, Figure 49) long before it 

reaches the surface and will begin devolatilizing and solidifying and/or vitrifying rapidly in 

approaching the surface. This huge loss of volatiles causes a commensurate large increase in 

magma viscosity. Moreover, when the degassed magma reaches the surface it will already be 

near its 1-atm solidus temperature and will be, in essence, a glassy paste-like material of 

enormous viscosity. This is strongly reflected in the limited extent of the lava flows at Lathrop 

Wells, which can be analyzed to yield an estimate of the effective viscosity controlling the 

extrusion of the lava. 
120

 

Figure 49 The solubility of volatiles in magmas is a function of temperature, pressure, and 

the compositions of the liquids and gases. This diagram shows the solubility of 

water, which is the major volatile species in most magmas, in basaltic and 

andesitic magmas as a function of total pressure at 1100° C. The dominant control 

on water solubility is pressure; the effect of temperature is relatively minor. The 

pressure of another gas, such as carbon dioxide, would decrease the solubility of 

water. At Earth surface conditions (pressure = 1 bar), the solubility of water is 

virtually zero (vertical axis of diagram is marked in kilobars) (After McBirney, 2007). 

For a basaltic magma containing 2-4 wt.% water, saturation will occur at depths of, 

respectively, about 2-5 km, and by the time it reaches the surface it will have lost 

all water. Notice that at the depth of the repository (300 m), the magma could still 

contain ~0.7 wt.% water. 

6.2.3.4.2. Estimating Viscosity using Lava Flows 

The radial extent of the flow field at Lathrop Wells is about 1 km, and the volume of the 

lava field is about 0.03 km3

 (e.g., Heizler et al., 1999; Valentine et al., 2007). Although the 

duration of the flow is not known with any certainty, because of the nature of the flow the 

viscosity controlling the flow can be estimated. The flow can be approximated as a gravity 

current of viscous fluid spreading on a nearly flat surface (e.g., Huppert, 1982). This method has 

also been used to examine lava dome and lava growth associated with the 1979 eruptive event 

on Soufriere on St. Vincent Island (Huppert et al., 1982). 

Approximating the radial spreading of lava as an isothermal viscous gravity flow is but 

one of several mechanisms suggested that govern lava spreading and lava dome growth 

(e.g., Fink and Griffiths, 1998; Griffiths, 2000; Lescinsky and Merle, 2005). The strength of the 

enveloping crust, the internal yield stress, and the role of damming at the toe of the flow may 

each also dominate the flow at certain stages of growth or stages of cooling. Although the rates 

of radial growth predicted by the various models are similar, lava dome height over time tends to 

favor growth controlled by the yield strength of the surficial crust. In terms of revealing an 

effective viscosity of the lava itself, however, the various models are mutually exclusive. That is, 

each model yields a set of physical properties not found in the other models, and additional, 

more detailed, physical features added to a model often yield a better fit to observation. The 

viscous model, for example, can be made to fit better if the effect of damming at the toe is larger 

or if the lava viscosity is significantly larger than that independently estimated from lava 

composition and temperature. In the latter respect due to the sudden loss of volatiles with 
121

approach to the surface, the Lathrop Wells alkali basalt underwent rapid quenching and may 

well have attained a viscosity much larger than otherwise anticipated. And this viscosity is 

remarkably consistent with that found from modeling the Lathrop Wells lavas as gravity flows. 

On these grounds and the fact that only through this model can an estimate of viscosity be 

found, preference is given to modeling the spread of lava as a viscous gravity flow. 

The radial extent (R) of the viscous flow of a fixed volume of released magma is given by 

(Huppert et al., 1982), where the radial extent of the flow is a function of gravity, initial flow 

volume, lava kinematic viscosity (= μ/ρ where μ is shear viscosity and ρ is density), and time. 

The flow can be modeled with this approach as the spreading of (1) a fixed volume of fluid 

deposited on a surface all at once and allowed to spread, as (2) the spreading of a fluid supplied 

at certain flux (e.g., m3

/sec), or as (3) a specific volume of fluid released by a flux rate applied 

over a specific period of time. Results from this equation for the first two cases, which perhaps 

bracket the volcanic situation, are shown by Figure 50 for a variety of viscosities, total lava 

volume, lava flow thickness, and effusive flux as a function of the duration of the event. The 

results are not highly dependent on the means of emplacement of the lava. 

From these results and with a maximum flow extent of ~1 km, the effective kinematic 

viscosity of the lava is unusually large, being in the vicinity of about 108

 to 109 Pa·s. The exact 

duration of this ~80,000 year old flow is not known, but flow events of this nature generally last 

about a month to a year. The aa character of these flows suggests a flux rate of about 12 m3

/s 

(Wood, 1980), which when used in concert with the observed volume suggests a duration of 

about 30 days. If on the other hand, the total volume of lava at Lathrop Wells is assumed to 

have been emplaced in the span of a single year, then the effective flux would have been about 

1 m3

/s. 

A significantly larger viscosity (2 x 1011 Pa·s) was similarly deduced by Huppert et al. 

(1982) for Soufriere volcano, which, apparently not believing the result, they ascribed to the 

influence of a high viscosity skin or quench rind enclosing the lava. Although this effect may be 

important, the fact that the Soufriere lava contains almost 50 vol.% crystals is also a major 

factor in greatly increasing the viscosity (Marsh, 1981), making the derived result clearly 

realistic. At Lathrop Wells, although the crystallinity was not large, there is evidence in the 

steep flow fronts, the rafted well-formed vent blocks supported by the flow, and the degassing 

sequence of extrusion (more below) that the viscosity was large. 

A last somewhat independent result (Figure 51) shows the relationship between the 

length of a single lava flow moving on an inclined surface (1 degree incline) as through a 

channel or other accommodating terrain. Results are shown for various flow viscosities and 

flow thicknesses. For flows of thicknesses of 5-10 m and extending 500 m over the period of 

about a month the governing viscosity is in the range of 107

 to 108 Pa·s. Flow thicknesses in 

some instances may be as much as 15 m at Lathrop Wells (Valentine et. al., 2007), which would 

further increase the estimated viscosity. Using a similar approach based on the Jefferys 

equation, which also describes flow down an inclined surface, Manley (1992) found similar 

results for blocky basaltic andesite and andesite flows. He noted that these values are some 1.8 

to 3.6 orders of magnitude above that predicted for the lava itself based simply on chemical 

composition (Manley, 1992). 
122

 

 

Figure 50 Radial extent of the Lathrop Wells, Nevada, lava field as a function of the duration 

of the flow event. The observed extent of the lava field is about 1 km, but this 

most likely is the culmination of a series of lavas The upper two panels describe 

the flow of a fixed volume of magma over time as a function of viscosity (upper 

left) and total lava volume (upper right). The lower panels describe the flow of lava 

at a given rate of effusion or flux. The lower left panel shows the relationship 

between lava viscosity and flow time to establish a flow 500 m long for flux rates of 

5, 1.5, and 0.5 m3

/s. The lower right panel shows the relationship between lava 

viscosity and radial extent as a function of eruptive flux and flow duration (in 

months). 

There is also direct evidence in the lavas from Lathrop Wells of the petrologic conditions 

favoring such large estimated values of effective viscosity. This evidence is in the form of the 

modal concentration of crystals, mainly plagioclase, and glass in the lavas and in the spatial 

variations in these quantities with distance outward from the central vent. Photomicrographs of 

three representative samples (from a larger suite collected by ACNW&M staff) are shown as 

Figure 52 (after ACNW&M, 2007b). The modal amount of crystals (i.e., degree of crystallinity) 

and the coarseness of the crystals increase with distance from the vent from about 40 vol.% to 

about 70 vol.% at ~1km from the vent. The presence of glass (quenched magma) is readily 

apparent (brown interstitial material) and this decreases in abundance with distance from the 

vent and increased cooling. Since viscosity effectively becomes infinite when crystallinity 
123

exceeds about 60 vol.%, the lava fragments into large blocks and moves more as a debris flow 

than a viscous fluid. This fragmentation increases the volume of the lava and when this occurs 

in a confined space, as in the subsurface or a repository drift, the lava dilates upon shear to plug 

the vent, stifling further flow. Dilatantcy of this nature is a common property of all granular 

material (e.g., Marsh, 1981). 

The overall sense of these results, together with the asymptotic character of some of 

these curves, suggests that the viscosity range noted above may well be reasonable for 

degassed magma and can be used in calculations of lava travel distance and for gaining insight 

on the flow of magma through the repository drifts. 

 

Figure 51 The extent of flow of a single lava flow on an inclined surface as a function 

of time, flow thickness and lava effective viscosity (After Marsh and 

Coleman, 2008). 

6.2.3.4.3. Magma Flow into Drifts 

In modeling the flow of magma into a Yucca Mountain repository, insight into the nature 

of the magma likely to be involved has been gathered from the nearby alkali basalt cinder 

cones. The almost universal tendency has been to use a volatile-rich basaltic magma as the 

characteristic magma involved in all interactions with the repository. This is the deep preeruptive magma containing 2-4 wt.% water and with a viscosity of 5-50 Pa·s, making it both 

explosive and highly mobile. Typical calculated flow velocities are 10-100 m/s (e.g., Woods 

et al. (2002) estimated steady magma flow speeds of 10 m/s through a tunnel by assuming 2 

wt.% water, isothermal flow without quenching, and a low viscosity of 10 Pa·s). This hypothetical 

lava would flow a distance of 1 km in 10-100 seconds. A similar flow, assuming availability of 

enough magma and a continuous downhill path, would reach the outskirts of Las Vegas (150 

km) in as short a time as 40 minutes. There is nothing in the character of the erupted lavas in 

the region of Yucca Mountain that would suggest any behavior of this nature. On the contrary, 

the flows from the cinder cones scattered throughout the region are exceedingly limited in 

spatial extent (~1 km in radius). This limited extent is also not merely due to the limited volume 
124

of these eruptions, although this is certainly partly the reason. If the Lathrop Wells governing 

viscosity is reduced to 10 Pa·s (e.g., as in Woods et al., 2002), keeping the volume at 0.03 km3

, 

the flow would have traveled 5 km in about 2 days. 

Figure 52 Photomicrographs of thin sections of samples of lava from Lathrop Wells. The 

field of view in each view is ~1 mm, and the upper row is under crossed Nicols and 

polarized light and the bottom row are the same sections in uncrossed Nicols. The 

white laths are plagioclase and the brown interstitial material is glass. The left pair 

of thin sections is nearest the vent and the others to the right are at successively 

greater distances from the vent, approximately evenly spaced out to a distance of 

approximately 1 km. The degree of crystallinity increases from left to right from 

about 40 vol.% to over 70 vol.% and the crystals coarsen in size, which reflects the 

overall cooling of the flow with distance from the vent. As the effective viscosity 

becomes very large, the flow moves more as a debris flow than as a viscous fluid. 

 

Altogether this suggests that, should alkali basalt of the general nature of that erupted at 

nearby Lathrop Wells intersect and enter repository drifts at Yucca Mountain, the extent of flow 

would be exceedingly limited. Even based simply on the nature of the flows at Crater Flat, the 

lava would be blocky and sluggish and advancement would be difficult in a cylindrical drift, 

especially one filled with waste packages. It certainly would not be a simple case of a viscous, 

non-solidifying fluid flowing along a pipe. And, contrary to the analysis of Woods et al. (2002), 

there is no chance that the lava would undergo any form of wholesale thermal convection 

(Marsh, 1989; Brandeis and Marsh, 1989 and 1990; Hort et al., 1999). 

Prior to the arrival of lava, however, the leading region of the ascending dike would be 

laden with gas and tephra. That is, should an ascending dike of water-saturated basaltic magma 

encounter the repository, the already rapidly quenching magma will undergo even stronger 

exsolution-induced quenching. Instead of fluid magma entering the drift and flowing along to 

eventually fill it, as in filling a bathtub, a small cinder cone would begin developing at the point of 

intersection. Cinders would avalanche into the drift, rapidly piling up and plugging the drift; the 

fragmental material will not flow far, especially given the presence of waste packages and other 
125

components of the engineered barrier. The insulating effect of the close rock wall will minimize 

air-fall and radiant heat loss, allowing the pile of cinders and tephra to tack or partially anneal 

together to form a mass of considerable strength. Magma will continue to quench on this mass 

of cinders and tephra. This process would form a plug in the drift, sealing the point of 

intersection, which would either force the magma to continue upward to erupt on the surface or 

simply seal off the dike locally, redirecting the flow to other portions of the dike that have already 

reached the surface. This sequence of events would also be expected for a scenario involving 

the intersection of multiple dikes with the repository. 

The initial ‘hole’ (at the point of tunnel intersection) in the wall of the ascending dike 

causes a local depressurization producing a perturbation in the pressure field driving the dike 

upward. This pressure perturbation will travel outward into the dike, informing, in effect, the 

broader flow of the presence of this vent. But because the vent into the repository is small 

relative to the surface area of the dike (for a typical dike length of 1 km, this ratio is ~10-5), this 

perturbation is relatively small and will not travel far in the thin (~1-10 m wide) dike before 

(<~1 s) the rapidly ascending dike (~km/s) reaches the nearby surface, short-circuiting the flow 

from the repository drift to the surface. 

The formation of a plug at the point of magma entry into the repository will also allow 

pressures on the dike side of the plug to return to the initial pressure. The initial magma 

pressure within a basaltic dike at Yucca Mountain would likely be in the range of 4.5 MPa to 8.0 

MPa (i.e., ~1 MPa larger than the horizontal far-field stress at repository depth) (BSC, 2004). 

The initial magma pressure can be approximated by the lithostatic pressure at repository depth 

(i.e., <7 MPa at 300 m, given a mean tuff density of <2400 kg m-3). The magnitude and 

temporal evolution of this governing pressure is of considerable uncertainty and is also central 

to understanding the dynamics and rate of magma penetration into the drifts. This will be 

returned to again below. But, for the present discussion, the above range is sufficient for 

consideration of the mentioned effects. This can be compared to the expected strength of the 

tephra plug. 

Schultz (1995) has measured the strength of the Cohassett basalt flow of the Columbia 

River Basalt Group. Intact basalt at 20°C and at < 9 MPa confining pressure has a compressive 

strength of 266 ± 98 MPa, a cohesive strength of 66 MPa, and a tensile strength of ~14 ± 3 

MPa. Basalt has shear strength in the range of 20-60 MPa. A welded tephra plug need only 

achieve ~3% of the compressive strength or 1/3 to 1/8 of the shear strength of intact basalt to 

withstand the full pressure that could be exerted by magma in an adjacent dike. A compressive 

strength of 7 MPa, for example, is more typical of clay soils than of rocks. Increasing 

temperature into the melting range, however, significantly reduces the strength of basalt. The 

strength of partially-molten basaltic magma under tension has been estimated from a summary 

of experimental and observational results by Marsh (2002). At ~50% crystals strength 

increases from about 0.03 MPa to about 30 MPa at ~ 100% crystals and about 1000°C. For 

compressive strength, these estimates increase by a factor of 10-20 (e.g., Jaeger and Cook, 

1979). Although these estimates hold only for massive, intact material, fragmental tephra will 

tend to tack together and form a continuum under these high temperature conditions. 

The tephra plug also could not readily be pushed along the drift by either later higher 

density tephra or magma. Tephra will tend to tack to the tunnel walls and waste packages/drip 

shields and also be obstructed by waste packages aligned in series. More important, perhaps, 

is that tephra, being fragmental material at maximum packing will, like any particulate medium at 

near maximum packing, dilate upon shear and form a stiff plug (e.g., Marsh, 1981). The net 

effect is that, after a brief local perturbation, magma is most likely to continue flowing to the 
126

surface in the original dike. The area of the drift affected by the invading magma may be 

minimal, and the number of waste packages affected may therefore be very limited. 

After the initial tephra phase, little magma would flow through the interstices of any 

welded tephra plug because of the high viscosity of the degassing magma, which would move 

as a high temperature glass. 

In light of these effects it is, nevertheless, essential to appreciate a full range of possible 

effects that will influence the distance that magma will penetrate a typical drift. Perhaps the 

most extreme case is where all the dynamics of flow, cooling, and solidification are ignored and 

assume that magma flows from the intersecting dike into the drift at ~ 1 m3

/sec, which is the rate 

estimated by assuming the full volume of Lathrop Wells lava (~0.03 km3

) erupted in one year 

from a single vent. Magma entering an 800 m long drift of 5.5 m diameter at 1 m3

/sec would fill 

the drift in about 5.5 hrs. It is clear from this example that the rate of flow into the drift is 

important to estimate. Another, more realistic, example is to assume that magma moves 

through the drift just as a lava flow moves on the surface as described above in estimating the 

viscosity of lava moving down a slightly inclined surface. For a flow of thickness 5 m with a 

viscosity of about 108

 Pa·s, the flow will travel about 100 m in a month. Here again all the effects 

of solidification, the presence of obstacles (waste packages), and drag due to the drift walls 

have been ignored. 

Next we consider viscous magma flowing in a cylindrical drift with an effective initial 

diameter of 3.5 m that reduces in time due to the effects of solidification. The rate of 

solidification is modeled to agree with all results from measured rates from Hawaiian lava lakes 

(e.g., Wright and Okamura, 1977) and lava flows (e.g., Hon et al., 1994). The flux of magma 

flow is calculated as a function of time, magma viscosity, and the magnitude of the driving 

pressure; the penetration distance is found by normalizing the time-integrated flux to the drift 

volume per meter. The flux (Q) is controlled by several variables that are best appreciated by 

considering the following simplified equation. 

 Q ~ (ΔP/L) a(t)4

/μ

Here, ΔP/L is the horizontal pressure gradient driving the flow, a(t) is the effective drift diameter 

which varies with time due to solidification, and μ is the effective viscosity of the magma. 

Methods of estimating magma viscosity have already been considered during the later stages of 

ascent and flow on the surface as lava. The possible effect on the overall drag of the gravity 

slump at the leading free surface of the magma flow as it enters the empty drift is ignored. This 

can be in some instances an important effect (Lejeune et al., 2002), but for the large viscosities 

anticipated here the front will be steep and will only further impede flow. There is also the 

possibility that, if the dike is under a large pressure gradient when it encounters the drift, the 

sudden pressure reduction in the dike flow with the transition to the atmospheric pressure of the 

drift may cause pinching or collapse of the dike locally and/or also fracturing and collapse of the 

wall/drift rock at the dike (Woods et al., 2002). 

Of these critical parameters, the driving pressure is perhaps the most difficult to 

estimate; ΔP is the pressure difference acting, in effect, over a distance L along the flow. At one 

extreme ΔP is the pressure difference (ΔP = ρg h) created by gravity acting on a standing (i.e., 

hydrostatic) column of magma (of density ρ) extending from the drift at a depth of h (=300 m) to 

the surface, which for a magma density of 2500 kg/m3

 amounts to about 7.35 MPa (=ΔP). If, 

once established, this standing column is suddenly allowed to flow into the drift, the governing 

driving pressure is that acting over the distance L (i.e., ΔP/L). If L is allowed to become 
127

exceedingly small, the local pressure gradient becomes enormous and the flow, over a short 

distance is exceedingly rapid. (Recall in the earlier discussion that if L is allowed to approach 

zero a shock wave can be generated.) As the flow develops, the length L increases and the 

pressure gradient systematically lessens. 

At another limit is the pressure gradient driving a lava flow down an inclined slope; here 

ΔP ~ ρg h sin(θ), where now h is the thickness of a lava flow (~10 m). This pressure difference, 

for ρ = 2500 kg/m3

, and a slope of 5°, amounts to about 2.5 x 10-2 MPa. This is 300 times 

smaller than the previous estimate based on a standing column of magma extending from the 

repository to the surface. That is, the two estimates of driving pressure gradients are equivalent 

when the length scale L in the first estimate is 300 m. Results for the penetration distance of 

magma into a drift are given in Figure 53 where the effects of solidification on the effective 

diameter of the drift are taken into account (the full formulation is given by Marsh and 

Coleman, 2008). 

 

Figure 53 The penetration distance of magma into a repository drift as a function of magma 

viscosity (left panel) and as a function of time (right panel). Each panel covers a 

range of pressure gradients, denoted by the effective length scale L, covering 

those possible for various styles of magma flow discussed in the text. The left 

panel (LHS) is for a flow period of 10 hours, and the right panel covers a range of 

specific viscosities. The initial effective drift diameter is 3.5 m in all cases. For 

magma flowing as a lava flow, the penetration distance is indicated on the lower 

part of the right panel (After Marsh and Coleman, 2008). 

The strong effect of the pressure gradient is clear in these results. As L decreases and 

the pressure gradient increases, penetration distance for any viscosity increases strongly. For a 

magma viscosity of 108

 Pa·s and L = 100, the penetration distance is about 35 m. If L is 

increased to 1000, penetration decreases to less than 5 m, and if L further increases to about 

3000, as for a lava flow, the penetration distance is only a few meters or less. If viscosity is 

decreased to 107

 Pa·s and L = 500, the magma penetrates about 70 m into the drift. In the 

actual process the driving pressure will decrease in response to the evolution of the flow. Others 

have also noted the difficulty in estimating this governing pressure gradient. Detournay et al., 

(2003) discuss this is some detail and mention the possibility that, because of the porous and 

permeable nature of the wall rock, the leading edge of the ascending magma-filled dike (after 

the dike has been established) may be at or near atmospheric pressure at the level of the drift. 

This would make the dynamics of inflow more akin to a lava flow. And they go on to estimate 

this driving pressure by relating it to the head (h) of magma above the drift that results from the 

interaction of the ongoing dike flow and magma loss into a series of drifts. 
128

The best estimate of the drift penetration distance comes from a full consideration of a 

specific eruption scenario and not simply from an isolated calculation detailing a specific 

physical part of the entire process. For example, any eruption is most likely to commence as a 

gas-rich tephra and agglutinate-laden Strombolian phase. This will deposit, and possibly plug as 

discussed already, a great deal of material in the drift at the intersection with the dike. As this 

Strombolian phase wanes and dense magma approaches the surface and reaches the level of 

the repository, the magma may well lack sufficient driving pressure to reach the surface all at 

once (as observed at Paricutin), and it may flow into the repository drift as a lava flow. The 

overlying dike to the surface, will be filled with porous tephra and agglutinate, the dike walls 

would suffer permanent (i.e., unrecoverable) deformation, and the overpressure may approach 

atmospheric pressure at the repository depth of 300 m. That is, the overlying dike may be 

structurally more like an open mineshaft than a fluid-filled column under hydrostatic pressure. 

The presence of pre-existing deposits of tephra will greatly subdue the effective pressure 

gradient driving the magma laterally and will also act as a granular plug to stifle progress of the 

magma. In addition, with approach to this depth the magma, still saturated with water (it will 

contain ~ 0.5-0.7 wt.% water), will be degassing through rapid vesiculation and crystal growth 

and/or glass formation. Degassing may be by rapid gas escape through tiny cracks throughout 

the basalt. If vesiculation occurs, it would cause a significant increase in magma volume that 

will go to further plugging of the drift, greatly decreasing the penetration distance. If the drift is 

sealed by plan or accident, there is also the possible effect of the inflow being resisted by 

progressive compression of the air by the advancing flow. Lejeune et al. (2002) show that this 

could be a major effect in retarding the inflow, regardless of fluid viscosity. Throughout this 

process, the driving pressure will change in concert with the motion of the magma itself. To 

properly estimate the penetration distance of magma flowing into the drift, each of these effects 

and factors must be simultaneously taken into account. With due care and insight into the 

physics of magmatic processes with consideration of the full eruptive scenario this can be done, 

but it has not been so far attempted by any group. 

In summary, these calculations suggest the high-velocity entry of magma into repository 

drifts is unlikely. Any flow of magma into drifts would be sluggish and of limited extent, perhaps 

reaching only a few tens of meters depending on the driving pressure. Alternatively, it is likely 

that a tephra plug could form at the point of dike intersection with a drift, potentially sealing off 

the drift from magma entry. 

6.2.3.4.4. Quenching Effects on Waste Packages 

Magma on and near the Earth’s surface is always experiencing crystallization. There is 

no natural way to arrest crystallization. All sudden local changes in temperature due to cooling 

of any kind will cause enhanced crystal nucleation and/or glass formation, if cooling is rapid 

enough. This is the process of quenching, and magma in this state quenches on all that it 

touches from water to trees to other cooler solid objects (Figure 54). Geologists at Hawaii, 

wanting a sample of an active lava flow, will throw a hammer on a long wire into the lava and 

immediately retrieve the hammer containing a grapefruit size mass of lava quenched on the cool 

hammer. Hawaiian magmas contain relatively little dissolved water (<~0.5 wt.%) and the lavas 

erupt at much higher temperatures than is anticipated for the magmas common to the Yucca 

Mountain region. As discussed earlier, the magmas anticipated for the Yucca Mountain area are 

likely to be much more water rich than Hawaiian magmas and will erupt at much lower 

temperatures, making them much more responsive to quenching. 
129

 

Figure 54 Photos of quenched magma. Examples of magma quenching on trees in Hawaii 

(left) and on a piece of wall rock from the upper mantle (right). Lava quenches 

against the trees that burn away to leave a cylindrical column of glassy basalt. 

Foreign pieces of rock (xenoliths) are common in many basalts and are commonly 

encased in a layer of quenched magma (left panel is from Takahashi and Griggs, 

1987). 

Quenching will occur on all surfaces with which the magma comes in contact, even on 

the waste packages at the their highest anticipated temperatures (~200°C). The rate of 

quenching is rapid and is given by an equation of the form: t = (C(κ)

0.5 )-2 d2

, where t is time 

(secs), C is a constant, κ is thermal diffusivity, and d is the thickness of the quenched rind. The 

form of this equation holds for a wide spectrum of situations involving solidification (e.g., 

Carslaw and Jaeger, 1959). The group C(κ )0.5 = 1.87 x 10-4 T- 6.58 x 10-2, where T is a 

particular isotherm in °C and the overall units are cm-sec0.5 (after Wright and Okamura, 1977; 

Mangan and Marsh, 1992; Hon et al., 1994; and Marsh and Coleman, 2008). Example 

calculations from this formulation are given by Figure 55. A quenched rind of a thickness of 

10 cm will form on a waste package and on the drift walls in about one minute. With time the 

rind will continue to thicken, although the rate of growth, as in any diffusively-controlled process, 

will systematically diminish. It is emphasized that the magma need not completely solidify to 

form a stagnant quenched rind, but only have its temperature reduced to near the solidus, which 

will render it stagnant as a crystal-bearing glass. Moreover, the proper thermal conditions 

leading to quenching are significantly enhanced by the anticipated nature of the magma, which 

is thought to be initially water rich and erupt at or near the solidus temperature. 

Once formed, there is also the question of the possible later reheating or ‘burning back’ 

of the quenched rind. Because of the anticipated nature of the magma, in terms of temperature 

and duration and style of eruption, this is highly unlikely. The high viscosity of the magma 

ensures that any flow will be sluggish and cooling will be by conduction with or without latent 

heat depending on the extent of crystallization and glass formation. There is no possibility of 

the magma undergoing thermal convection (Marsh, 1989; Hort et al., 1999). When magma 

touches a cooler surface the temperature at the interface or contact becomes approximately the 

average of the two initial temperatures. That is, the interface temperature T = 0.5 (T1+T2), where 

T1 and T2 are the initial temperatures of the magma and object contacted. This is a well known 

result (e.g., Jaeger, 1968; Turcotte and Schubert, 1982; Marsh, 1989). Strictly speaking, this 

result only holds if there is no latent heat of crystallization involved, and if latent heat is included 

the constant changes to 0.65. For magma at 1050°C and a waste package at 200°C, the 

interface temperature will be about 650°C, which is far below the magma solidus temperature, 

promoting massive quenching. In the cooling of two juxtaposed planar sheets of material, this 

temperature does not change until the cooling front has reached the center of the hotter body 
130

and then this contact temperature slowly decreases with time. This condition of planar sheets is 

not met for magma against a cylindrical waste package in a repository drift, but it is 

approximately met for a rind that is thin relative to the radius of curvature of the waste package. 

An estimate of the actual magma temperature necessary to reverse cooling can be determined 

by finding the conditions when cooling is arrested, which can be determined by employing the 

well known Schwarz solution (Carslaw and Jaeger, 1959). The most general result shows that 

for no quenching, the sum given above (i.e., T1+T2) must be twice the melting temperature of 

the wall material. If the quenched rind is taken as the wall material at a temperature of 650°C, 

which at the very least has a ‘melting’ temperature of 1050°C, then the magma temperature 

must be about 2100 - 650 = 1450°C, which is well beyond the eruption temperature of any 

known terrestrial basaltic magmas. 

 

Figure 55 The time to grow a quenched rind on a cool surface as a function of time 

for a basaltic magma or lava. A quenched rind about 10 cm thick will form 

on a waste package in about 1 minute (After Marsh and Coleman, 2008). 

Quenching on the walls of the drift will also occur and there is the question of the effect 

of earlier radiant heating by ash and tephra on quenching. The drift wall could, in effect, be 

possibly heated enough to become insulating. Although the problem needs to consider the full 

development of the eruptive scenario, surficial heating of the drift wall will produce a thin skin of 

high temperature (less than the magma temperature) that will dissipate quickly. In essence, 

upon contact with magma this skin thickness will, in a thermal sense, become part of the 

magma thermal anomaly, which will be quickly dissipated by the reservoir of underlying cooler 

wall rock. If magma were to enter a drift, the cool wall rock reservoir would produce a classic 

thermal entry effect, which is very much unlike the flow of magma in lava tubes. The much 

hotter wall rock of lava tubes on long-term active volcanoes like Etna and Kilauea cannot be 

used as analogs for flow in repository drifts. 

Although the effect of quenching has been considered in various earlier investigations, 

primarily by the DOE, the context under which it has been studied has generally been under the 

unrealistic assumptions that the inflowing magma will be of unusually low viscosity and will be 

much hotter than anticipated herein for hydrous basalt. Because of these assumed conditions, 

magma has been generally inferred to flow at 10 – 100 m/s (i.e., 22-220 mph). 
131

6.2.3.4.5. Secondary Venting and Magma Flow in Drifts 

It is useful to consider the potential paths that magma may take if it encounters the 

repository. Magma flow along a drift, filling and over-pressurizing or re-pressurizing the drift to 

the degree that a new fissure is forced to the surface forming a secondary vent has been 

described earlier (see Section 3.3.4) in connection with the so-called ‘dogleg’ scenario. But 

there is also the possibility that a secondary vent might develop as a natural consequence of the 

volcanic process itself (e.g., Fiske and Jackson, 1972; Ryan et al., 1981). That is, once the 

magma in the ascending dike breaches the surface the eruptive flow has the natural tendency to 

concentrate into a single vent, which gives rise to the common occurrence of cinder cones and 

the associated lava flows. But it is also not uncommon to find systems that form a secondary, 

commonly less powerful, vent along the initial fissure at some distance from the main central 

vent. This apparently occurs in response to, in effect, ‘capping’ of the initial vent by the 

volumetric weight of erupted materials. Sustained pressure in the ascending magma reopens 

the initial fissure and the eruption moves to a new location, although simultaneous eruption from 

both vents is also possible. Secondary vents could also form in response to further lateral 

propagation at depth of the magma-filled dike as it moves into areas of new topography that are 

conducive to venting. An example of this latter process has been modeled by Gaffney and 

Damjanac (2006). They show that for the topography characteristic of Yucca Mountain the flow 

to an initial vent at higher elevations might, in effect, be siphoned off by a vent at lower 

elevations at some distance from the repository. If the dike associated with the new vent 

transects the repository, a secondary conduit might form. Secondary vents are generally 

significantly weaker and shorter lived than primary vents. The possibility that magma would flow 

from the primary vent to the new vent, using repository drifts as an interconnecting conduit, is 

unlikely in the face of the constraints imposed by the highly viscous nature of the expected 

magma. This process, nevertheless, has been considered by the DOE (2004; Dike-Drift 

Interactions) and by NRC (2005a; e.g., p. 47) in response to the DOE and the wider implications 

of the possible ’dogleg’ scenario of Woods et al. (2002). The NRC has also discussed this 

possibility at length in letter IA.2.18 (10 January 2005) addressing an Igneous Activity Key 

Technical Issue (hereafter Kokajko, 2005b). 

The concept of a secondary vent is sometimes synonymous with a satellite or Bocca 

vent, stemming from the formation in 1968 in the central crater of Mt. Etna of a second eruptive 

pit or Bocca Nuova (i.e., New Mouth) accompanying the original Chasm pit (La Voragine), which 

was established in the 1950’s. Interest in the formation of a secondary eruptive vent at Yucca 

Mountain centers on the greatly increased exposure of waste packages to magma were it to 

flow a considerable distance along a drift (perhaps several hundred meters) and then vent to the 

surface at a secondary vent. The steady flow of magma, even at a slow rate along the drift, 

could possibly expose waste packages to unusually prolonged high temperatures. The 

dynamics of this process was treated in some detail by Detournay et al. (2003) and 

subsequently more extensively by DOE in their Dike/Drift Interactions report of 2004. Although 

each group found that a flow of this type was highly unlikely, the NRC (e.g., NRC, 2005a, p. 43-

57) discusses this issue in a way that suggests this process may indeed be possible and 

perhaps even likely. This is evidenced in the following NRC discussion of the DOE results. 

From NRC (2005a), page 43: 

In addition, some physical conditions could potentially result in horizontal flow of 

magma along a drift, with a conduit forming some lateral distance away from the 

point of initial intrusion intersection (Woods, et al., 2002). Although conditions for this 

horizontal flow pathway now appear less likely to occur (BSC, 2004), if this process 

occurred, it could affect a significantly larger number of waste packages than a 
132

simple vertical conduit. Damage to waste packages intersected by a subvolcanic 

conduit likely occurs from the high thermal and mechanical stresses created by a 

basaltic magma during an eruption (e.g., BSC, 2003d). Although detailed process 

models for these effects have not been developed, available information indicates the 

current waste package design would not provide the physical integrity necessary for 

waste isolation after direct entrainment in an erupting volcanic conduit (BSC, 2003d; 

NRC, 1999). [boldface added] 

And from page 54: 

An alternative conceptual model for magma ascent at a location away from the point 

of initial drift intersection is proposed by Woods, et al. (2002). This model is based on 

consideration that topographic variations above a drift could potentially result in 

stress conditions more favorable for magma ascent at a location away from the point 

of initial drift intersection. The significance of this alternative model is horizontal flow 

paths along a drift could be significantly longer than 150 m [492 ft], which is the 

maximum diameter of subvolcanic conduits, and thus entrain more waste packages 

than modeled by a simple vertical conduit. DOE provides extensive evaluation of this 

alternative conceptual model in BSC (2004). This evaluation uses the same 

hydrofracture model used to evaluate the initial ascent of magma. This model 

concludes that if a fracture were to occur at the distal end of a potentially intersected 

drift, magma could ascend through this fracture once the drift was filled. However, 

magma also would continue to simultaneously rise along the original plane of 

intersection. The rate of magma ascent along the distal fracture would be no more 

than half the ascent rate as modeled along the original plane of ascent because 

magma in the distal fracture is supported only by magma in the potentially intersected 

drift. In contrast, magma in the original vertical fracture is supported by magma from 

depth, which gives a larger effective fluid pressure to dilate the fracture. Thus, 

magma modeled along the distal fracture will likely cool more rapidly, and ascend 

much more slowly, than along the original plane of ascent. These effects will cause 

the magma along the original ascent fracture to reach the surface well before magma 

along the distal fracture can ascend far from the drift. The DOE model concludes 

magma ascent to the surface along a distal fracture appears highly unlikely, relative 

to continued ascent along the original vertical fracture. Based on the mechanical 

analysis presented in BSC (2004), conditions for this alternative conceptual 

model currently appear less likely to occur than conditions for the model of 

continued ascent along the original plane of ascent. [boldface added] 

Moreover, the key feature in the NRC perspective is that, although the ‘dogleg’ scenario 

as analyzed by the DOE and the ICPR may be highly unlikely during the initial eruptive phase 

(i.e., “initial minutes” KTI IA.2.18, p. 5), at any later time in the eruptive cycle, perhaps days to 

months later, a secondary eruptive center or vent may yet appear. They base this perspective 

on the occasional occurrence of this style of activity at other, perhaps comparable, volcanic 

centers, like Tolbachik and Paricutin and even nearby Lathrop Wells. In the latter case, more 

detailed recent work has not found evidence of secondary vents (Valentine et al., 2007). The 

physics behind this NRC perspective is that whereas in the initial phase of the eruption the 

driving pressures in the shallow dike system drop significantly once the ascending dike reaches 

the surface, later flow will fill breached drifts with magma to the point of producing sustained 

overpressures large enough to “dilate secondary fractures in the drift walls” (KTI IA.2.18, p.5). 

The sustaining of these over-pressurized drift conditions throughout the entire volcanic event, 

the NRC feels, provides the necessary conditions for secondary breakouts to appear at any time 

“throughout the duration of the volcanic eruption” (KTI IA.2.18, p.5). The NRC bases these 

findings on a series of research efforts by Woods et al. (2002; 2004; 2006), Bokhove et al. 

(2004) and Lejeune et al. (2002). 
133

The primary aspects of these works deal with two broad subjects: 1) the ascent of an 

isothermal, isoviscous fluid (e.g., 30 Pa·s; Bokhove et al., 2004) in elastic wall-rock or as in the 

filling of a drift; and 2) the ascent of bubble-rich, isothermal and isoviscous fluid in terms of 

acceleration of the fluid due to bubble expansion and coalescence. Although there are aspects 

of these works that are valuable to understanding magma ascent and eruption in a broad 

perspective, several fundamental features of this work may make it of limited usefulness to 

understanding the possible behavior of magma at Yucca Mountain. First the fluids used are 

isothermal, isoviscous, and of low viscosity. As discussed already, volatile-rich basaltic magma, 

which these cited studies are intended to simulate, will be undergoing severe pressure 

quenching (i.e., rapid solidification) as it ascends and de-volatilizes with approach to the surface 

in the vicinity of the drifts and its viscosity will be increasing exponentially. The magma will 

either fragment, if the gasses cannot escape, quench to a glass, if the gas escapes and ascent 

is rapid enough, or quench to a glass containing myriads of tiny acicular crystals 

(i.e., plagioclase microlites (Figure 52)). Second, elastic-walled dike work is premised on the 

assumption that the dike is connected to a deeper, large magma chamber feeding magma to 

the dike and also supplying overpressure to propagate the dike and, in some respects, act as a 

shock absorber in the system. The existence of a deep-seated, large volume magma chamber 

is highly unlikely in the small volume, cinder cone volcanisms characteristic of the Yucca 

Mountain region. Third, the longevity of magma residing in a drift as a molten material is very 

short. Taking an extreme conservative example, if Hawaiian lava were to quickly fill a drift it 

would solidify in about 25 days. Hawaiian lava is much hotter, of much lower viscosity, and 

further from solidification than the hydrous, low temperature basalt anticipated at Yucca 

Mountain. Because of the extreme rate of pressure quenching, this basalt will already be near 

solidification and its longevity in a drift as mobile magma will be hours to days (Figure 47 and 

Figure 53). Thus the time is severely limited over which a magma-filled drift can be sustained in 

a pressurized state to allow inception of a secondary fracture into which magma can flow to 

establish a secondary vent on the surface. More of the quantitative reasoning behind this 

conclusion can be gained from an appreciation of complementary work on this process by 

Detournay et al. (2003) and the DOE. And although the NRC relegates the relevance of some 

of these results mainly to the very early or initial phase of the magmatic event, they do, in fact, 

have a bearing on the full cycle of the event. In this context there are three critical processes to 

consider: (1) the flow of magma into and along the breached drift to fill and pressurize the drift, 

(2) the initiation of a new fracture in the drift roof or wall, and (3) the flow of magma to the 

surface in this new fissure. Each of these issues is considered in turn. 

6.2.3.4.5.1. Flow of Magma to Pressurize the Drift 

The rate of flow of magma into a breached drift will depend, as discussed above, on the 

pressure gradient driving the magma, the viscosity of the magma, and the rate at which magma 

is supplied from the parent dike. The first two of these parameters have been discussed at 

length above and here it is important to contrast them with the DOE model assumptions and 

results. First, almost without exception the DOE assumes a magma viscosity of 10 to 40 Pa·s 

(BSC, 2004a, Table 6-2), which follows from similar values assumed by Detournay et al. (2003). 

The DOE summarizes their findings (BSC, 2004a, p. 6-111): 

The rate of magma flow into drifts will be limited by the rate of magma supply, except 

probably when the supply is very large (v [deep velocity] on the order to [sic] 10 m/s) 

and the magma viscosity is high (on the order of 40 Pa·s). The time needed to fill 500 

m of drift will be on the order of 15 minutes for a magma velocity of 1 m/s. It obviously 

depends on the supply rate, and the results can be linearly scaled to other drift 

lengths. 
134

A central part of the calculation leading to this summary is that the flux supplied by the 

main dike is equated to the flux into the drift, with due care for the geometric transition as 

outlined by Detournay et al. (2003). And since in this calculation the viscosity of the magma is 

uniform (10-40 Pa·s) for all the magma, regardless of the rate of degassing and the effect of 

rapid quenching by depressurization, the supply rate essentially controls the entire process. For 

supply rates based on magma flow in the dike of 1-10 m/s, within 10 seconds of breaching the 

flux into the drift reaches, respectively, 50-1000 m3

/s, filling the drift to 10-50 m in this time 

(BSC, 2004a, Figures 6-50 and 6-51). At the same time the magma in the central dike rises to, 

respectively, 2 m to 300 m above the drift. The effect of the presence or absence of waste 

packages and whether the viscosity is 10 or 40 Pa·s has relatively little effect on the results. But 

this influence will change markedly if the viscosity of the dike magma increases strongly with 

loss of pressure and approach to the drift and surface. Repeating this calculation in this case, 

where the viscosity is changing strongly, will make the region with the largest viscosity, which is 

the drift, the rate-controlling region for flow. This was also emphasized by Detournay et al. 

(2003, p. 56): 

The sustained propagation of a secondary dike requires considerations beyond the 

simple condition that the magma pressure in the drift has to exceed the normal stress 

across the fracture. The supply of magma into the drifts and up to the primary dike 

above the repository is best characterized as flux-limited. 

In their brief analysis of the possible effects of increased viscosity due to cooling and 

crystallization in the primary ‘dogleg’ scenario, the DOE indeed came to a similar conclusion 

(BSC, 2004a, p. 6-144): 

The effect of only 10 to 20 percent of crystals on the rheology of the partially 

crystallized magma is dramatic. This increase in percent crystals results in an 

increase in viscosity of 1.5 to 2 orders of magnitude, a roughly indicated by the 

highlighted region in Figure 6-75. 

And on the same page: 

In light of the very rapid increase of apparent viscosity as temperatures drop, the 

temperature at which the apparent viscosity reaches 1000 Pa·s has been chosen as 

Ts [solidification temperature] in Table 6-11. 

That is, they consider that with an increase of viscosity to 1000 Pa·s, the magma can be 

taken as being solidified and thus no longer mobile. And from the earlier detailed discussion of 

magma viscosity during ascent (Figure 43, Figure 44, Figure 46, and Figure 47), the viscosity 

will certainly exceed 1000 Pa·s. Sparks (2007) also concludes that the viscosity at the drift 

depth will be beyond this limit. The rate of filling the drift is thus greatly reduced, and the 

movement of magma along the drift is similarly reduced (Figure 53). 

6.2.3.4.5.2. Initiation of a New Fracture in the Drift Roof or Wall 

If the magma in the drift is of high viscosity and in essentially a solid state, as suggested 

here, the drift cannot be properly pressurized to produce the conditions necessary for initiation 

of a new fracture and to transmit magma to the surface. In the DOE analysis of the conditions 

necessary for this process they investigated the rate of opening of new fractures relative to the 

arrival of the primary dike to the surface and thus short-circuiting magma from breached drifts to 

the surface. They explore the effects of several prime physical properties, including wall rock 

elasticity, initial crack width, and magma viscosity. They find (BSC, 2004a, Figure 6-61, and 

p. 6-129): 
135

Because a dimensional and scaling analysis was not carried out, simulations of 

Cases 116 through 120 were conducted to investigate the effect of an increase in 

magma viscosity from 10 Pa·s to 100 Pa·s. As expected, an increase in magma 

viscosity results in a proportional increase in time scale. For example, in Case 103 

(viscosity 10 Pa·s) it takes 13 s to reach a 10-mm thickness increase; whereas, in 

Case 117 (viscosity 100 Pa·s) the thickness increase is reached after 130 s. 

Even if the argument of magma freezing is not used, among all of the 20 analyzed 

cases, only in Cases 103 and 112 to 115 does a magma front inside the joint move 

faster than 0.5 m/s. That result implies that the magma front inside the original dike 

(which could also be 80 m or more above the repository level) will reach the ground 

surface much sooner than the magma injected into joints inside the drift. 

Raising the viscosity still higher to the range of > 104

 Pa s, as suggested earlier and by Sparks 

(2007), will proportionally reduce the potential crack propagation rate to rates of less than 5x10-3 m/s, 

making this process not competitive with the main dike flow. 

6.2.3.4.5.3. Flow of Magma to the Surface in the New Fissure 

If magma is going to reach the surface in a fracture newly generated from a drift roof or 

wall, it must be able to avoid solidification as it enters and traverses to the surface. This is 

exceedingly difficult in small cracks because the cooling time is vanishing small and the new 

dike immediately fills with quenched magma, stalling any further advance. Both the DOE 

(BSC, 2004a) and Detournay et al. (2003, p. 56) evaluate this effect and come to the same 

conclusion: 

An important consideration relevant to magmatic dog-legs is that it is very difficult to 

start a dike in cold rock. In order for a dike to escape an early thermal death, it must 

widen elastically (due to propagation of the tip) faster than it freezes shut. Flow of hot 

liquid through a cold channel can be divided into a thermal entrance region, where 

most of the heat still resides in the liquid, and a downstream region, where most of 

this heat has been lost to the surroundings. The thermal entrance length [this is the 

distance over which a fluid adjusts to a sudden change in wall temperature] is 

proportional to the product of the flow velocity and the cooling time, where the latter is 

proportional to the channel thickness squared. For a dike driven by a constantpressure source, both the flow velocity and dike thickness are proportional to length. 

Thus, the thermal entrance length is proportional to the dike length cubed, and 

sufficiently short dikes are always longer than the thermal entrance length and near 

the temperature of the host rock (Rubin, 1995). In Appendix 3.4, we estimate that 

basaltic dikes in cold rock would not widen elastically faster than they freeze shut 

until the dike length was tens of meters and the thickness several centimeters. As a 

concrete example, a typical dike thickness:length aspect ratio is ~ 1:1000, and a 

typical propagation velocity for a km-scale dike is 1 m/s. A reasonable estimate is 

that a 1-m long dike is ~ 1-mm wide, propagates at ~ 1 mm/s, and widens at ~10-3

mm/s. The chilled margin in the same dike would reach 1 mm (the dike thickness) in 

~ 1 s. Such a dike could not grow. This is not an argument that dikes cannot form — 

clearly, they do. However, those that survive thermally must satisfy conditions .... that 

cannot easily be met by dikes initiating from a drift. 

The DOE (BSC, 2004a, p. 6-145) finds that “Clearly, such cracks will not be able to grow 

to any appreciable width before they are halted by solidification.” 

And further on this same page in their overall synthesis: 

Comparing this growth history for a constant viscosity magma with the results of the 

chill-zone growth rate, it is seen that the dike will never be able to propagate more 

than a few meters from the drift because the magma will chill rapidly, blocking off the 
136

flow of fluid to drive the crack growth. Note, however, that the effect of advection on 

the heat balance has been neglected in deriving this result. 

Neglecting the thermal effect of advection, which is forced convection of magma within 

the growing dike, is clearly warranted by the large viscosity of the magma. 

In summary, although the analysis of DOE (BSC, 2004a) and Detournay et al. (2003) 

was primarily concerned with the formation of a secondary vent branching from a drift early in 

the eruptive episode, the basic physics and thermal considerations are, for the most part, 

applicable at all times during the volcanism. Drifts will be difficult to fill to a sustained 

overpressure state; new elastic cracks will be difficult to initiate in drift walls; and magma were it 

available, would quench and stall in new-forming cracks. The basic magma physics underlying 

this work is well founded. It is therefore unlikely that a secondary vent branching from a drift will 

form at any time in the style of volcanism expected at Yucca Mountain. The principal means of 

magma transfer in the near-surface region is expected to be through the main system of dikes. 

6.2.3.4.6. Overview 

There are two broad areas where almost all specific approaches to the evaluation of 

igneous consequences can be improved. The first is in appreciating the full implications of the 

phase equilibria of ascending hydrous basaltic magma. The strong effect of water on greatly 

lowering the temperature of the magma as it approaches Earth’s surface, beginning at depths of 

about 5 km, colors all further analysis regarding eruption scenarios, magma viscosity, and 

quenching. Aspects of magma flow, cooling, and general behavior from studies of Hawaiian 

and Etna lavas cannot be assumed to hold also for Yucca Mountain magmas. In prior studies, 

almost universally, the magnitude of magma viscosity has been underestimated by a factor of 

104

 to 105, depending on the specific process being considered, and the strong quenching 

character of the magma has been similarly underestimated. Second, it is important to place 

individual studies in as realistic a context as possible within likely eruption scenarios. For proper 

realistic quantitative analysis, most specific aspects of magma ascent, drift intersection, drift 

penetration, degassing, tephra formation, lava effusion, and other more detailed processes each 

depend on the full sequence of processes attending magma delivery, extrusion, and 

solidification. The initial conditions assumed in each simulation are critically important to the 

outcome. Yet in most quantitative studies the initial conditions have been assumed in isolation 

to the remainder of the eruptive scenario. In this context, the eruptive scenarios based on field 

geology proposed by Valentine and associates for the Crater Flat basin and Lathrop Wells 

cones are highly valuable. But there have been no similar detailed petrologic studies of the 

lavas themselves. All consequence scenarios rely heavily on the inferences of the experimental 

study by Nicholis and Rutherford (2004) that the Crater Flat magma may have contained 

2-4 wt.% water. This is based on the occurrence of amphibole in Crater Flat lavas. However, 

inspection of a suite of thin sections of lavas from Lathrop Wells found no amphibole, and the 

study often referenced by Vaniman et al. (1982) is primarily concerned with geochemistry. 

Sophisticated, detailed petrologic studies involving geothermometry, crystal size distribution 

analysis in concert with heat transfer, need to be carried out on these lava fields. Studies as 

described above would lead to further reduction of uncertainty in igneous consequences. 

6.3. Effects from an Extrusive (Volcanic) Event 

The extrusive scenario involves the intersection of a tephra-cone-forming volcanic vent 

(i.e., conduit) with the repository drift (see Figure 6). The transition from flow in dikes to vent 

flow occurs early in an eruptive sequence, and vents form under various conditions. In low-
137

viscosity basalts, the transition may occur when narrow parts of the dike freeze followed by 

mechanical and thermal erosion of wider sections as the flow is repartitioned (e.g., Bruce and 

Huppert, 1990). A key difference between a volcanic conduit and a dike is that the diameter of 

a vent is much smaller (generally <75 m) than the length of a dike (1-5 km or more). Given a 

repository drift spacing of >50 m, a vent could directly intersect only one drift and a relatively 

small number of waste packages in the cross-sectional area of the vent. New work to be 

reported in DOE’s ANL-MGR-GS-000002, rev. 03 (under review at DOE) supersedes the DOE 

range of conduit diameters at repository depth with a lower mean value based on recent analog 

studies (ACNW&M, 2007). 

Due to the perceived complexity of the processes involved, both NRC (Mohanty 

et al., 2004) and DOE (2003) assume that the small number of waste packages (approximately 

1-10) entrained within a conduit would be completely destroyed and the contents carried to the 

surface and ejected as tephra of varying sizes. DOE has commented (ACNW&M, 2007) that it 

is important to keep in mind the range of dynamics in a conduit and the period of time (months 

to years) during which magma in various forms could interact with waste packages. The degree 

to which ceramic or glass waste forms could be reduced to fine particulate materials in a 

volcanic conduit is uncertain, particularly during the first 1000 years when the waste packages 

and waste forms should still be relatively intact (see additional discussion in Section 6.3.3, 

Comments on Potential Fate of High-Level Waste in a Volcanic Conduit or Vent). The manner 

and degree to which the fragments would be incorporated in volcanic tephra is uncertain, but 

would involve the well-known phenomenon of magma quenching. 

6.3.1. DOE and NRC Approaches 

The DOE has estimated that the median number of waste packages that would be 

disrupted in a volcanic eruption scenario (i.e., intercepted by a conduit) is fewer than 10 

(DOE, 2004; Number of Waste Packages Hit by Igneous Intrusion). The NRC has determined 

that the number of waste packages affected by an extrusive volcanic event would have high 

significance to waste isolation because the consequences are directly proportional to how many 

waste packages would be intersected by an erupting volcanic conduit. Apparently due to the 

complexity of the processes involved, neither the NRC (Mohanty et al., 2004) nor DOE (2003) 

rely on evaluations of magma-drift-waste package interactions in any detail. They instead 

assume that a small number of waste packages are completely destroyed and the contents are 

carried to the surface via a volcanic conduit in a cone-forming event. Nevertheless, it is as yet 

unclear how or whether the Alloy-22 waste packages or the ceramic or glass waste forms 

themselves would be reduced to particles of respirable size, as is currently assumed by the 

DOE and NRC. 

The number of affected packages is estimated based on observed conduit size at analog 

volcanoes. Alternative models of how a volcano may interact with repository drifts and develop 

a conduit could increase the number of entrained waste packages and thus increase the 

concentration of radionuclides in erupted ash. The following material is from NRC (2004): 

Normally, in the absence of subsurface drifts, volcanoes form roughly cylindrical 

conduits along the vertical plane of magma ascent. Based on analogy with deposits 

at active or deeply eroded volcanoes, the NRC staff determined that conduit 

diameters from 5 to 50 m represent the most likely range of diameters for a potential 

future eruption at the potential repository site (NRC, 1999; Doubik and Hill, 1999). In 

contrast, DOE considers potential conduit diameters up to 150 m, albeit with very low 

likelihoods of occurrence (e.g., CRWMS M&O, 2000b; DOE, 2003). Actively erupting 

volcanic conduits have high temperatures and large physical stresses that most likely 

would completely disrupt any waste package directly intersected by the conduit 
138

(NRC, 1999; CRWMS M&O, 2000b). Thus, both NRC and DOE have concluded that 

any waste package entrained in an erupting volcanic conduit would reasonably fail to 

provide containment and release its contents into the rapidly flowing magma. 

Open drifts at depths of 300 m could potentially cause magma ascent and flow 

processes to behave differently than in undisturbed geologic settings, because rising 

magma is a fluid with an overpressure sufficient to fracture and dilate surrounding 

wall rock. Intersection with a subsurface drift at essentially atmospheric pressure 

provides a horizontal pathway out of the original plane of vertical magma ascent, 

allowing flow localization and nonequilibrium expansion of volatiles (NRC, 1999; 

Woods et al., 2002). Using the alternative conceptual model [dogleg scenario] from 

Woods et al. (2002), magma could potentially flow down an intersected drift and 

break out at some point away from the point of original intersection. For randomly 

located points of intersection and breakout and a single drift containing 155 waste 

packages, an estimated average of 51 waste packages would be located along the 

alternative flow path. In contrast, a normal, vertical conduit would intersect an 

estimated average of 4.5 waste packages using the TPA Version 4.1j code. There is 

a directly proportional relationship between the number of waste packages entrained 

and conditional dose (i.e., dose not weighted by the probability of scenario 

occurrence). This sensitivity appears reasonable, as the mass of high-level waste 

potentially entrained is relatively small compared to the mass of magma. It is 

assumed that high-level waste is uniformly distributed in the mass of a modeled 

eruption; thus, high-level waste behaves as a trace phase in the magma and does 

not appreciably affect the transport characteristics of a modeled eruption plume 

(NRC, 1999; CRWMS M&O, 2000b; DOE, 2003). 

In addition to alternative conceptual models for the magma-flow pathway, the number of volcanic 

conduits created during an igneous event also is uncertain. Using vent location information in Hill 

and Stamatakos (2002) and assuming medium-to-high confidence magnetic anomalies represent 

buried volcanoes, it is estimated that there are 17 paired and 13 nonpaired volcanoes in the 

Yucca Mountain region; most volcano pairs occur in alignments of three to five volcanoes. 

Volcano pairs have an average spacing of 2.0 ± 1.3 km. Assuming that there is a uniform 

probability of one, two, or three volcanoes intersecting the repository during a potential extrusive 

event, and that the overall eruption character remains unaffected by the number of volcanic 

conduits, dose increases by approximately a factor of two from this process. 

The expert panel of the ongoing PVHA-U has been asked to provide expert opinions 

about volcanic conduit size in the Yucca Mountain region. However, the final report of the 

PVHA-U proceedings is not expected to be available until sometime in 2008. 

The NRC approach to evaluating an extrusive event is documented in Mohanty et al. 

(2004), which is NRC’s “System-Level Performance Assessment of the Proposed Repository at 

Yucca Mountain Using the “System-level Performance Assessment of the Proposed Repository 

at Yucca Mountain Using the TPA Version 4.1 Code.” This NRC document outlines how the 

repository is described for the NRC calculations in TPA 4.1: 

A final design for a repository at Yucca Mountain has not yet been identified by 

DOE, but would be contained in a license application (now expected in 2008). The 

waste emplaced at Yucca Mountain is assumed to total 70,040 MTU in an area of 

5,400,000 m2

 {approximately 5,000 m long and 1,000 m wide}. Assuming an 

average of 7.89 MTU per waste package and an equivalence between the spent 

nuclear fuel and other types of wastes, such as DOE spent nuclear fuel and glass 

high-level waste, approximately 8,877 waste packages will be needed for waste 

disposal. The initial inventory activity is ~6.65 × 1020 Bq [1.8 × 1010 Ci]. Waste 

packages with a 5.3-m length and a 1.6-m diameter are emplaced in drifts 5.5 m in 

diameter, spaced 81.0 m apart. The average age of the spent nuclear fuel is 26 

years. 
139

The NRC currently assumes that volcanic conduits will have an average diameter of 

~50 m (Mohanty et al., 2004). If the center of a conduit were to coincide with the axis of a drift, 

then ~5 waste packages would be entrained within the cross-section of the conduit and 

potentially transported to the surface (the worst case situation). The NRC/CNWRA staff has also 

performed calculations assuming that up to 100 waste packages could be impacted by an 

extrusive event (Mohanty et al., 2005). In considering eruptions from satellite vents in the TPA 

4.1 analyses (Mohanty et al., 2004), the staff assumed that a mean value of 51 waste packages 

could be entrained by an extrusive event and contained in volcanic ejecta. 

Radiologic risks associated with volcanic eruptions are calculated in the TPA Version 4.1 

code by modeling airborne releases of radionuclides for simulated eruptions. The volcanism 

modules assume that a small number of waste packages become entrained in a developing 

volcanic conduit (vent). These waste packages are assumed to be destroyed within the conduit 

and their waste contents move upward with volcanic tephra to the land surface. At the surface 

the mixture of tephra and spent nuclear fuel is ejected into the atmosphere, from which it settles 

to form tephra deposits. 

Igneous activity contributes to waste package failures for both extrusive and intrusive 

events. As modeled, extrusive events result in the direct release and deposition of radionuclides 

on the ground surface, whereas intrusive events contribute to releases to groundwater. In the 

NRC performance assessment, an igneous event occurs between 100- and 10,000-years 

postclosure, with a recurrence rate of 1 × 10-7 per year. After the hypothetical volcanic event 

penetrates the repository and exhumes spent nuclear fuel, the areal density of deposited ash 

and radionuclides is computed at the compliance point. A new revision of the NRC TPA code is 

now being prepared that will incorporate fluvial and eolian remobilization of tephra. 

6.3.2. EPRI Approach 

EPRI has summarized their views regarding the potential consequences of future 

volcanism at Yucca Mountain, if it should occur, are clearly stated in the executive summary of 

their report on the intrusive release scenario (EPRI, 2005). In brief, EPRI has reached an 

overall conclusion that there is reasonable expectation that neither an intrusive nor extrusive 

igneous event in the Yucca Mountain region would result in doses exceeding those anticipated 

for the case of no igneous event. The summary from EPRI (2005) is quoted below: 

There is evidence of volcanic centers near the proposed site at Yucca Mountain, Nevada 

for a geologic repository for the disposal of spent nuclear fuel (SNF) and high-level radioactive 

waste (HLW). This evidence indicates that potential future igneous activity (i.e., an “igneous 

event scenario”) may be a factor in the assessment of post-closure risk for the proposed 

repository. In 1996, a panel of independent technical experts for the Yucca Mountain Project’s 

Management and Operations (M&O) contractor conducted a study, the Probabilistic Volcanic 

Hazards Analysis (PVHA) study that estimated a mean annual probability of an igneous event 

occurring at/near the Yucca Mountain site at 1.6 x 10–8/year (Geomatrix Consultants, 1996). 

This probability, though extremely low, fell just above the 1.0 x 10–8/year regulatory threshold 

that had been established for the dismissal of extremely low probability events. 

Based on the findings of the 1996 PVHA Panel, a number of speculative analyses of the 

possible consequences of a future igneous event at Yucca Mountain have been conducted by 

the Yucca Mountain Project (CRWMS M&O, 2000c; 2001), and the NRC, in conjunction with 

NRC’s contractor, the Center for Nuclear Waste Regulatory Analysis (CNWRA) (e.g., Woods 

et al., 2002). In brief, the igneous event itself is characterized as a rising dike of basaltic magma 

that intersects one or more emplacement drifts containing nuclear waste packages, shown 
140

schematically in Figure ES-1 (Figure 56). Based on an in-depth, independent scientific review 

conducted by an Igneous Consequences Peer Review (ICPR) panel of experts (Detournay 

et al., 2003), the dike is postulated to most likely progress directly to the surface, intercepting a 

minimal number of waste packages in the conduit of the eruptive vent. Limited lateral magma 

flow through unbackfilled emplacement drifts is a credible possibility according to Detournay 

et al. (2003). Such lateral flow would lead to contact, and possible envelopment, of a limited 

number of “satellite” waste packages by magma away from the main locus of the dike-drift 

intersection. 

Thus, two principal variant cases for a given igneous event can be specified: 

• The extrusive-release case in which magma rising vertically in the conduit contacts 

waste packages in its path causing them to fail and possibly release radionuclides 

that would subsequently be erupted with the magma at the surface with subsequent 

radionuclide transport controlled by atmospheric and surficial processes, and 

• The intrusive-release case in which waste packages, either directly contacted by the 

lateral flow of magma into the impacted drifts or indirectly affected by the elevated 

temperature and potential release of volatiles species from the intruding magma, 

would fail and release radionuclides via groundwater pathways at an earlier time 

than for waste packages unperturbed by these localized effects from an igneous 

event. 

Figure 56 Schematic of zones of intruding magma effects in a repository drift on the 

engineered barrier system (EBS). Magma is assumed to completely fill the 

spaces in the “Red Zone,” with significant thermal/chemical effects on 

Alloy 22 in adjacent “Blue Zones.” No effects on the EBS are assumed for 

the “Green Zones” (After Figure ES-1 of EPRI, 2005) (Permission to use this 

copyrighted material is granted by the Electric Power Research Institute). 

EPRI, as part of its efforts to provide an independent technical/scientific assessment of 

issues that are anticipated to be important to the licensing of the proposed Yucca Mountain 

repository, has previously evaluated the extrusive-release case (EPRI, 2003; 2004a). This 

analysis critiqued and cast considerable doubt on several of the more speculative 

consequences put forward by Woods et al. (2002) while indicating that the expected dose 

consequence for the extrusive-release variant case is at or near zero because of multiple 

factors including waste package durability, finite extent, duration and magnitude of likely future 
141

igneous events, and limitations imposed by realistic consideration of magma-waste package 

and magma-waste form interactions (EPRI, 2004a). 

The objectives of this report, which is a companion to EPRI (2004a), are to analyze the 

intrusive-release case and determine the potential impact on repository performance and safety, 

expressed as probability weighted mean annual dose rate, for the latter scenario. 

6.3.2.1. EPRI Analyses 

EPRI’s analyses contained in this report adopt the igneous event probability of 

1.6 x 10-8/year previously derived by the Probabilistic Volcanic Hazards Analysis (PVHA) panel 

(Geomatrix Consultants, 1996). The analyses also reflect recent data on basaltic eruptive 

centers in the Yucca Mountain region that support the conclusion that relatively low-temperature 

(~1010°C), high viscosity basaltic magmas, as opposed to the ~1200°C magmas postulated by 

the DOE, are the most representative characteristics of future igneous events. Lower 

temperature implies lower and less prolonged thermal-perturbation of the host rock and 

contacted waste packages, and magma of much higher viscosity. The high viscosity supports 

the contention that such magma will only partially penetrate into emplacement drifts intersected 

by the magmatic dike, thereby only impacting a limited number of waste packages. 

Partial intrusion of magma into emplacement drifts with controlled cooling and 

solidification of the magma implicitly leads to development of three “zones” within the 

emplacement drift (Figure 56): 

• The ‘Red Zone,’ the area immediately adjacent to the rising magmatic dike and 

where drip shields and waste packages are assumed to be fully engulfed by magma. 

The ‘Red Zone’ is characterized by displaced/ disrupted drip shields, thermally 

sensitized Alloy-22, and spent fuel cladding that fails at the time of the igneous 

event, 

• The ‘Blue Zone,’ the area just beyond the ‘Red Zone’ where drip shields and waste 

packages are not contacted directly by magma but experience significantly elevated, 

high temperatures. The ‘Blue Zone’ is characterized by intact drip shields, but failure 

of the Alloy-22 waste package outer barrier and spent fuel cladding within a relatively 

short time after the igneous intrusion event, 

• The ‘Green Zone,’ the area beyond the ‘Blue Zone’ where waste packages 

experience modest (<350°C) and transitory high temperatures, with possible 

deposition of reactive magmatic volatiles onto the waste package surface. The 

‘Green Zone’ is characterized by intact drip shields, Alloy-22 waste package outer 

barrier and spent fuel cladding that are unperturbed from their nominal corrosion 

behavior. 

The range of the spatial extent and the number of waste packages in each zone are also 

derived in this EPRI report. These analyses show that the number of waste packages in the 

‘Red Zone’ is extremely limited while those in the ‘Blue Zone,’ albeit more extensive, are still 

less than a majority of the waste packages in the impacted drifts. 

Modification of the existing near-field source-term and radionuclide transport sub-model 

in EPRI’s Yucca Mountain total system performance assessment (TSPA) model, IMARC 

(EPRI, 2005), is made to specifically model radionuclide releases for each of the three zones. 

The release rate behavior for waste packages in the ‘Green Zone’ exactly conforms to the 

nominal case following failure of the Alloy-22 waste package outer barrier. The potential for 
142

favorable water diversion by solidification of massive basalt around waste packages in the ‘Red 

Zone’ is shown through sensitivity analyses, but this potential contribution is also conservatively 

ignored in the presented analyses. Near-field sub-model calculations show that there is a delay 

in the release of radionuclides from the ‘Red Zone’ attributable to sorption properties of the 

encompassing basalt, but that the long-term release rates for key dose-contributing 

radionuclides (99Tc, 129I, 237Np, 229Th) from the ‘Red Zone’ and ‘Blue Zone’ eventually converge. 

The long-term release rates, on a per waste package basis, from both the ‘Red’ and ‘Blue’ 

zones are found to be higher (by a factor of ~40) than that for the nominal case (and ‘Green 

Zone’) because the time-dependent distribution of cladding failure would not be a factor in these 

cases. 

A set of IMARC analyses was conducted to investigate the total system performance 

implications of the observations and analyses in each component of the system. First, IMARC 

was used to explore conditional dose analyses (“conditional” in the sense that the probability of 

occurrence of a magma intrusive event is set to one), to evaluate the dose consequences of the 

magma intrusion. There is reasonable expectation that the magma will only affect some of the 

waste packages in a drift intersected by a rising dike, with the remaining waste packages in the 

impacted drifts functioning in the same way as in drifts not intersected by the dike. In this 

situation, the peak conditional dose from the affected part of the repository is smaller than that 

produced from the unaffected part of the repository due to the small percentage of the total 

repository waste packages that are impacted. If the probability of a magma intrusion is also 

factored in, the contribution to overall probability-weighted peak dose becomes minuscule. 

Even when a series of conservative, “bounding” assumptions are made (e.g., full penetration of 

the magma into the drifts, and 100% of the drifts affected), the probability-weighted estimated 

bounding dose rates from such a bounding event only rise to be on par with the peak dose rates 

from the nominal case. It is therefore concluded there is reasonable expectation that magma 

intrusion is inconsequential with respect to peak dose. 

Combining this conclusion with that of the earlier EPRI analysis of the extrusive igneous 

scenario (EPRI, 2004a) results in the overall EPRI conclusion that there is reasonable 

expectation that an igneous event in the Yucca Mountain region, either intrusive or extrusive, 

will not result in dose levels exceeding the levels anticipated for the nominal release (i.e., no 

igneous event) case. Given the above, robust conclusions regarding the relative lack of 

importance of the igneous scenarios to probability-weighted peak dose estimates, and the 

regulatory requirement that the DOE demonstrate that the probability-weighted peak doses for 

the repository will comply with applicable regulations, EPRI has concluded that no further 

activities need be pursued to address the igneous scenarios. 

6.3.2.2. EPRI Comments on Tephra Dispersal Models 

EPRI (2004) conducted additional analyses using three alternative computer codes for 

volcanic plume modeling (i.e., BENT, PUFF, ATHAM). Several assumptions in TEPHRA (or 

ASHPLUME) were identified as conservative. EPRI (2004) also reported that ASHPLUME, like 

other models based on comparable physics, tends to overestimate accumulation of tephra at 

the compliance point, since it tends to underestimate the dispersion of the plume. The DOE and 

NRC implementation of ASHPLUME accentuates this conservatism in potential deposition at the 

compliance point because of the fine grain size and rather large column height used as input 

parameters. 
143

6.3.3. ACNW&M Comments on Potential Fate of High-Level Waste in a Volcanic 

Conduit 

Available information provides practical insights about the plausible fate of high-level 

radioactive waste (HLW) if it should become entrained within a volcanic vent (conduit) and 

transported to the surface. The following points need to be considered in a realistic assessment 

of volcanic processes (also see discussion in Weiner and Coleman, 2008). 

Most of the waste planned for disposal at Yucca Mountain consists of spent nuclear fuel 

rods from PWR and BWR reactors. The physical form of the waste is ceramic pellets of UO2, 

about a centimeter in diameter, with a melting point of >2800°C. This is much higher than the 

magma temperatures of 1000-1200°C. Spent fuel would not dissolve in magma; therefore the 

size range of transported fragments would largely be determined by pre-existing particle sizes in 

fuel rods. This range would differ from that of volcanic ejecta. 

A volcanic conduit is not born full size. Its diameter increases as the eruption proceeds. 

This means that only one nuclear waste package could be initially entrained in the conduit, with 

others becoming entrained within the final radius of the conduit at depth. Therefore additional 

waste packages would be exposed to varying stages of the eruption sequence. It is also 

possible that a conduit intersecting a repository could form in the separation distance between 

drifts, and although an intrusive event could occur, no waste packages would be directly 

intersected by the conduit. Volcanic conduits would be significantly smaller 300 m below the 

surface at repository depth than at ground surface (Figure 57). This would minimize the number 

of waste packages that could be intersected by a conduit. Lithostatic pressure keeps the 

opening smaller at depth, whereas at the surface the vent periphery in the zone of 

fragmentation grows in diameter through active erosion by expelled tephra. The DOE reports 

they have now better constrained the conduit size at depth and agrees that the diameters are 

smaller than previously assumed (ACNW&M, 2007). 

 

Figure 57 Schematic cross-section through Shirtcollar Butte, Crater Flat, Nevada, a 

Pliocene (3.7 Ma) basalt volcano. The degree of fusing and welding of 

scoria increases up-section and grades into dense basalt on the top of the 

butte (After DOE, 2006). 
144

Present information shows that dikes are more likely to be injected into pre-existing 

faults. Conduits form along dikes, therefore if the DOE continues to use a “setback” strategy 

from major faults (places waste tunnels at a minimum distance from faults), this would reduce 

the likelihood of a hypothetical extrusive event impacting the repository. 

The expected time of travel in a conduit from repository depth to the surface would be 

approximately one minute or less. This allows little time for erosion of ceramic pellets, but does 

permit rapid quenching of magma onto the relatively cold waste packages and their contents. 

The formation of a quench rind on waste pellets would protect them during their rapid transit to 

the surface within a flowing column of frothy magma. This protective quenching effect in 

volcanic conduits has not been considered in the DOE and NRC performance assessments 

(Mohanty et al., 2004; Codell, 2004; DOE, 2003). 

 Since the time of TPA version 3.2 (Mohanty and McCartin, 1998; Mohanty, 1999), the 

NRC has used relatively consistent assumptions about the size range of spent fuel particles that 

would hypothetically be incorporated in volcanic ash. Fuel particle sizes using a triangular 

distribution from 1-100 microns (Figure 58) are sampled in the TPA. For comparison, a grain of 

table salt is about 100 microns across, and a grain of talcum powder is about 10 microns 

across. The low end of the NRC size range is at 1 micron, which happens to be the wavelength 

of light in the near infrared band (just above the wavelength of visible light). A CNWRA study 

for NRC (Jarzemba and LaPlante, 1996, their Figure 4), suggested a log triangular distribution 

from 0.01 to 1.0 cm (100 to 10,000 microns), based on the observed fracturing and crazing of 

irradiated fuel pellets, as shown in Figure 59. 

A variable range of spent fuel particle diameters is to be expected. However, in 

documenting the assumed distribution for the size range of spent fuel particle size, TPA 4.0, 

(Mohanty et al., 2002) cite an NRC handbook that evaluated the consequences of major 

accidents in nuclear fuel cycle facilities (NUREG-1320; Ayer et al., 1988). Review of this report 

shows that it does not support the use of a greatly reduced size range for particle sizes. It 

instead suggests that a larger size range should be used for ejected fuel particles. Ayer et al. 

(1988, pp. 4.87-4.103) present results of crush-impact experiments on glass, aggregates, and 

ceramics, including spent UO2 fuel pellets. 

Figure 60a is taken from this report, and shows results of crush-impacts on fuel pellets 

that had previously been irradiated. About 2% of the fuel (by weight) was reduced to particles 

smaller than 1000 microns. Reardon et al. (1992) reported results of crushing tests at energies 

of 10 to 1000 J/g using irradiated fuel (22 and 33 GWd/MTU KWO). At 10 J/g, <30% of the 

mass of irradiated fuel was reduced to particle sizes <100 microns, and <10% of the mass was 

reduced to <10 microns. At 1000 J/g, ~60% of the mass was reduced to less than 100 microns 

and <30% was reduced to under 10 microns. These size fractions do not consider the effects of 

fuel cladding or magma quenching on ejected waste particles in volcanism scenarios, which 

would significantly increase particle diameters (Weiner and Coleman, 2008). 
145

Figure 58 Median tephra diameter distribution plotted with spent fuel particle size 

distributions used in TPA versions 3.1 to 4.1. For comparison the size 

distribution suggested by Jarzemba and LaPlante (1996) is also shown. 

The Wentworth scale of particle sizes appears at top of figure for 

comparison. The intermediate size distribution used by Codell (2004) is not 

shown, but is a triangular distribution that ranges from 10 to 1000 microns. 

The distribution for median tephra particle diameter is a sampled parameter 

in the TPA code. The distribution of tephra particle sizes was postulated 

by Hill et al. (1998) based on data from the 1995 Cerro Negro eruption 

(Codell, 2004). The tephra “cutoff” identifies the maximum particle size 

that can be transported through convective dispersal (Mohanty et al., 2002, 

p. A-165). Particles larger than 10 cm would fall in close proximity to the 

volcanic vent. 
146

Figure 59 Cross-section of a fuel pellet after irradiation in a reactor core (After 

Jarzemba and LaPlante, 1996, Figure 3). 

Calculated doses are highly sensitive to assumptions about fuel particle size because of 

the strong dependence on respirability, which decreases sharply as particle diameters increase 

beyond 10 microns. The TPA code, version 4.1j, using several particle size distributions as 

input, was used by the ACNW&M staff to assess the sensitivity of dose estimates to fuel particle 

sizes assumed in the volcanism scenarios. Using a size range of 100-10,000 microns (also see 

test data set in Manteufel et al., 1997) results in approximately a 200-fold reduction in 

calculated dose as compared to the range of 1 to 100 microns, which indicates significantly 

reduced consequences from extrusive volcanism. Using an intermediate fuel size range of 

10-1000 microns reduces calculated dose by a factor of two (Codell, 2004). 
147

Figure 60 Crush-impact experimental results and photo of xenolith with basalt rind. 

(a) Crush-impact experimental results - size distribution of fragments from 

fuel pellets irradiated to 6000 MWd/MTU (After Ayer et al., 1988, Figure 

4.12). (b) Tuff xenolith with basalt rind, collected from the scoria cone at 

Lathrop Wells. Scale is in cm. 

The relative volume of ash deposits vs. volume of scoria cone and lava flows can be 

used to estimate practical limits on the fraction of ejected waste in the form of fallout that could 

be available for fluvial and eolian transport. The 80,000-year-old Lathrop Wells Cone is larger in 

volume than the older Pleistocene-aged Red Cone and Black Cone in Crater Flat (see Valentine 

et al., 2006). BSC (2003c) estimate the total volume of eruptive products at Lathrop Wells at 

~0.09 km3

 (cone, 0.02 km3; lavas, 0.03 km3; fallout, 0.04 km3). Valentine et al. (2007) estimated 

a larger fallout volume of 0.07 km3

. The fallout comprised approximately half of the eruptive 

products. The DOE agrees that fallout (inferred violent Strombolian eruptive style) accounts for 

a fraction of total products of an individual volcano. At Lathrop Wells the fallout volume is about 

1.4 times the cone plus lava volumes. Current modeling by the DOE is accounting for the 

relative fractions in terms of quantities of material available for violent Strombolian dispersal 

during a potential future eruption (ACNW, 2007). Waste incorporated in lava flows or scoria 

cones would be protected from erosion and transport for many hundreds of thousands of years, 

as demonstrated by the million-year-old cones and flows in Crater Flat near Yucca Mountain. 
148

Over this time scale the lava flows experienced very little erosion. The scoria cones have 

experienced erosion during the pluvial climates of the Quaternary, when the climate of Yucca 

Mountain was significantly wetter than today for most of the time. Valentine et al. (2006) 

document that these cones are highly eroded, and only remnants of the inward dipping beds of 

the inner cones are preserved at Red and Black cones. However, entrainment of waste in 

scoria cones would immobilize the waste far beyond the time of peak risk from extrusive 

volcanism. 

EPRI (2003b) also noted that waste could be entrained within lava, as well as in tephra. 

The solidified lava presents a mechanically durable matrix for entrained and dissolved 

radionuclides. Both erosion and aqueous dissolution are mechanisms that may lead to 

subsequent release, but Quaternary age and older lava flows are well preserved in the arid 

environment surrounding Yucca Mountain. 

At Lathrop Wells, lithic fragments of conduit wall rock (tuff) are commonly found 

embedded within the scoria that make up the cinder cone (Heizler et al., 1999). The nonwelded 

to partly welded tuff fragments were eroded from the walls of the volcanic conduit, vary in size 

from a fraction of a cm to 6 cm or larger, and have quenched rinds of basalt. 

Figure 60b shows a xenolith 9 cm long that was collected by ACNW&M staff at Lathrop 

Wells. These expelled wall rock fragments are so abundant that they have been used to 

estimate the eroded volume of the Lathrop Wells conduit (Valentine et al., 2007). The size of 

the lithic fragments suggests that spent nuclear fuel pellets and fragments could be expelled in 

similar fashion during the cone-building phase of an eruption, intact and with protective quench 

rinds. The result is that entrained HLW would be likely to remain in relatively large fragments 

that would be deposited in or near a tephra cone, rather than as far-strewn, fine-grained ash. A 

xenolith 30 cm in diameter has been found at the Lathrop Wells cone (Heizler et al., 1999). The 

existence of this and many other xenoliths is further evidence that UO2 pellets could be 

expected to survive relatively intact over the short conduit travel distance from repository depth 

to the surface (only ~300 m). This is especially true for the period of greatest hazard from a 

volcanic event (i.e., the first 1000 years; Figure 39) when waste packages and waste forms 

should still be relatively intact. 

Based on the available information about properties of UO2 fuel and volcanic processes, 

including consideration of magma quenching and observations of xenoliths, there is no evidence 

that most of the spent fuel contained in HLW packages intersected by a volcanic conduit woule 

be reduced to fine-grained material and subsequently erupted and transported as volcanic ash. 

A significant fraction of waste would likely be entombed in a scoria cone and lava flows. Use of 

a more realistic size range for spent fuel particle sizes leads to substantially lower doses, based 

on analysis using TPA 4.1j. NRC has now updated this code and its accompanying user’s 

guide. The revised code version is TPA 5.1 (NRC, 2007a). 

6.4. Remobilization of Contaminated Volcanic Ash 

6.4.1. Introduction 

Future basaltic volcanism intersecting the proposed repository at Yucca Mountain could 

lead to eruption of contaminated ash to the surrounding countryside during a violent 

Strombolian eruption phase. The contaminated ash would be derived from destruction of the 

waste packages within the volcanic conduit and entrainment of the fragmented waste into the 
149

erupting magma. It is unclear how much of the entrained radioactive waste could be ejected 

from the subsurface and to what degree the waste would be fractionated, thus there are 

differences in views about the resulting consequences of such an event. The discussion here 

pertains only to the fate of contaminated ash hypothetically ejected during a volcanic event and 

deposited in the drainage basin of Fortymile Wash where it would be subject to erosion and 

transport by both water (fluvial) and wind (eolian) processes into the immediate vicinity of the 

RMEI. Contaminated ash deposited elsewhere in the vicinity of Yucca Mountain would not reach 

the RMEI. 

Fluvial processes are limited in the Yucca Mountain region because the climate is arid to 

semi-arid with high rates of evapo-transpiration and low annual precipitation that averages 

about 165 mm/yr. Stream flow results from infrequent regional storms, mostly during the winter, 

and from localized but intense thunderstorms that occur primarily during summer months. 

There are no perennial streams in the Yucca Mountain area, and even the larger streams in the 

region are ephemeral. Throughout the Death Valley Basin, perennial flow only occurs 

downstream from springs and around the margins of low-lying playas (dry lake beds) where the 

water table intersects the land surface. 

6.4.2. Characteristics of the Fortymile Wash Drainage System 

Fortymile Wash is a fluvial system about 150 km long, that drains an area of 815 square 

km on the east and north of Yucca Mountain. It is an important fluvial system because it drains 

into the area near the RMEI where contaminated ash could be deposited from a volcanic vent 

intersecting the proposed repository. Surface water at Yucca Mountain drains mainly eastward 

toward Fortymile Wash, a tributary of the Amargosa River. The main tributaries to Fortymile 

Wash are Yucca Wash, located north of the proposed repository, Drill Hole Wash, which drains 

most of the potential repository area, and Busted Butte (Dune) Wash located south of the 

proposed repository. 

Fortymile Wash crosses Highway 95 immediately east of Lathrop Wells (Amargosa 

Desert) and continues southward, ultimately intersecting the Amargosa River. The Amargosa 

River drains an area of about 8,000 square km by the time it reaches Tecopa, California. The 

mostly-dry river bed extends another 100 km before ending in Death Valley. Fortymile Wash 

has four distinct segments (Figure 61) with different morphologies: (1) a broad northern area 

comprised of ephemeral streams (washes) that feed a central channel that is incised in bedrock; 

(2) a central reach that deeply incises an alluvial fan of Plio-Pleistocene age; (3) a segment near 

the intersection with Highway 95 that is referred to as the “active” fan (northernmost part of the 

depositional basin); and (4) the remainder of the depositional basin that consists of 

anastomosing channels that terminate at the juncture with the Amargosa River. 

The erosion, transport, and deposition of the sediments in Fortymile Wash are directly 

related to the flow characteristics of the ephemeral stream and particularly to its flood 

characteristics. Numerous continuous streamflow and peak-flow gauges have been operated 

and monitored in the Yucca Mountain area. However, as of September 30, 1995, all but three 

continuous and most of the peak-flow gauges were discontinued (DOE, 1997, p. 3-14). As of 

September 30, 1997, the only continuous streamflow gauges operating near Yucca Mountain 

were on Fortymile Wash near well UE-25 J-13 (“narrows” gauge) and near Amargosa Desert 

(Bonner et al., 1998). 
150

Figure 61 LANDSAT Thematic Mapper image showing the Fortymile Wash drainage 

system. The Pleistocene depositional basin has an Area of 136 km2

. Map 

Projection: Universal Transverse Mercator, Zone 11 North, in meters (After 

Hooper, 2005, Figure 3-1). 

The period of record for flooding in Fortymile Wash is less than 40 years. Waddell et al. 

(1984) reported that the U.S. Geological Survey has collected monthly crest-stage data in the 

Yucca Mountain region since the early 1960s, using flood data from 12 crest-stage sites to 

estimate flood characteristics in the region. Data from 1969 to 1993 from six gauging stations 

are shown in Table 7. 

The largest recorded flows occurred after a storm in February 1969, when the upper 

Amargosa River near Beatty, Nevada, carried a maximum flow of 450 m3

/s. Squires and Young 

(1984) estimated that in Fortymile Wash this flood had an estimated discharge of 93 m3

/s and 

that the peak discharge may have reached 560 m3

/s (Glancy and Beck,1998). The 100-yr peak 

discharge for Fortymile Wash has been estimated at 340 m3

/s (Squires and Young, 1984). 
151

Table 7 Peak discharges at stream gauges along Fortymile Wash (After Table 1-2 of 

Hooper, 2005, which was based on data from CRWMS M&O, 2000a, and 

Tanko and Glancy, 2001). 

Date Fortymile 

Wash at 

Narrows 

Yucca 

Wash 

Near 

Mouth 

(tributary)

Drillhole 

Wash at 

Mouth 

(tributary) 

Fortymile 

Wash 

Near Well 

J-13 

Dune Wash 

Near 

Busted 

Butte 

(tributary) 

Fortymile 

Wash Near 

Amargosa 

Valley 

Jan. 25, 1969 − − − − − 42.5 

Feb. 24-26, 

1969 

− − − 570 − 93.5 

Mar. 3, 1983 43.0 2.83 − 16.1 − 11.3 

Jul. 21-23, 

1984 

20.7 26.6 22.4 52.7 − 40.5 

Aug. 14-16, 

1984 

1.42 − − − − −

Aug. 18-20, 

1984 

19.3 0.88 1.22 24.4 0.40 10.5 

Jul. 19-20, 

1985 

0.33 0.0003 0.48 0.17 2.66 0.09 

Feb. 23, 1987 − − − − − 0.02 

May 7, 1987 − <0.003 − − − −

Nov. 6, 1987 − − − − − 0.02 

Sep. 23, 1990 − − − − − 0.02 

Aug. 12-13, 

1991 

− − − − − −

Sep. 7, 1991 − − − − 0.12 −

Feb. 12-15, 

1992 

0.68 0.42 − − 0.04 −

Mar. 30-31, 

1992 

− <0.03 − − 0.03 −

Jan. 17-19, 

1993 

1.50 2.26 − − − −

Feb. 9, 1993 − − − − − −

Feb. 23, 1993 − − − − − −

Jan. 25-27, 

1995 

0.20 5.24 − − 0.08 −

Mar. 11-13, 

1995 

85.0 − 0.003 85.0 0.08 34.0 

Feb. 23-24, 

1998 †

5.7 6.2 0.7 5.7 nd ‡ 9.6 

Sources: CRWMS M&O, 2000; Tanko and Glancy, 2001 

*Dash symbol means either no streamflow was recorded or stream gaging site was not operating during 

period of streamflow. 

†Cumulative streamflow volumes for the 1995 and 1998 storm runoffs were estimated differently because 

most of the streamflow gaging stations were discontinued prior to the 1998 flood. 

‡Site disturbed by road crews prior to measurements (nd = not determined).
152

The first documented case of a regional water-flow event during site characterization 

studies, in which Fortymile Wash and the Amargosa River flowed simultaneously throughout 

their reaches, took place on March 11, 1995 (Beck and Glancy, 1995). USGS and Nevada Test 

Site rain gauges showed that cumulative precipitation ranged from 5 to 15 cm during March 9 to 

11, with the largest amounts falling at higher altitude sites. High-altitude snowmelt also 

probably contributed to the 10- to 12-hour runoff event in Fortymile Wash. The peak flow near 

the location where the existing Yucca Mountain access road crosses Fortymile Wash was 

reported at ~100 m3

/s (Glancy and Beck, 1998, p. 7). This flow is much less than that 

calculated as a 100-year flood event for Fortymile Wash (i.e., 340 m3

/s). 

Squires and Young (1984) calculated discharge, area, width, mean velocity, and 

maximum depth of flood flows for 100-year and 500-year exceedence recurrence frequencies 

and maximum flood peak for various profiles across Fortymile Wash and its three major 

tributaries in the Yucca Mountain area. Estimated peak discharges are shown in Table 8. 

Table 8 Estimated peak discharges (m3/s) along stream channels of 

Fortymile Wash at Yucca Mountain. 

--------------------------------------------------------------------------------------------------------------------------- 

 Wash Drainage Area (sq km) 100-year 500-year Regional Maximum 

---------------------------------------------------------------------------------------------------------------------------- 

Fortymile 810 340 1,600 15,000 

Dune Wash 17 40 180 1,200 

(Busted Butte) 

Drill Hole 40 65 280 2,400 

Yucca 43 68 310 2,600 

---------------------------------------------------------------------------------------------------------------------------- 

Fortymile Wash apparently has not overflowed its banks near Yucca Mountain for 

thousands of years. In the vicinity of wells J-12 and J-13, the channel is deeply incised in 

alluvial fan deposits, and paleoindian artifacts are commonly seen on the surface adjacent to 

both channel banks. They have not been carried away or buried by overbank flows. 

6.4.3. Approaches to Fluvial Sediment Transport and Erosion Evaluation 

6.4.3.1. NRC Approach to Fluvial Volcanic Ash Redistribution 

Basaltic materials are common in the alluvial deposits along Fortymile Wash. Much of 

this material probably originated from the extensive basalts in Jackass Flats, but some cobbles 

and boulders have been rounded by abrasion during long-distance transport and may have 

originated from the basalt units in the northern part of the drainage basin (i.e., Buckboard Mesa 

and the basalts of Dome Mountain). 

The NRC has developed a sediment budget approach to model the long-term fluvial 

redistribution of basaltic tephra in Fortymile Wash (Hooper, 2005). In the event that extrusive 

volcanism intersects the repository and transports waste in the volcanic tephra plume, 

deposition of radionuclides may occur at the RMEI location from the remobilization of tephra by 

water after initial deposition. A sediment budget was estimated to demonstrate the quantitative 
153

relationship between components such as sediment yield, discharge to the depositional fan, 

balance of remaining tephra, dilution by mixing of contaminated sediment with ambient 

sediment, and associated changes in sediment storage over time. Using parameters specific to 

Fortymile Wash and a hypothetical eruption at Yucca Mountain, Hooper (2005) concluded that 

substantial tephra deposits can persist for more than 1,000 years in arid terrains, even with a 

period of accelerated erosion after the eruption. Hooper (2005) estimated that ~98 percent of 

the tephra deposit remains in the Fortymile Wash catchment basin after 100 years and 50 

percent remains after 1,800 years. These results suggest that the amount of remobilized tephra 

may be large—even when mixed with ambient sediment—and could significantly affect airborne 

radioactive particle concentrations for the RMEI. However, see the discussion in Section 6.3.3 

regarding the potential fate of spent fuel in a volcanic conduit. The physical and chemical 

properties of spent fuel suggest that this material could retain much of its integrity even if 

transported through a conduit to the surface. 

The amount and distribution of hypothetical tephra deposits were calculated using the 

TEPHRA code (visit http://www.cas.usf.edu/~cconnor/parallel/tephra/tephra.html; Connor 

et al., 2001). For each realization in performance assessment, the calculated tephra deposit is 

partitioned into (i) initial deposits (if any) at the receptor location, (ii) potential deposits in the 

Fortymile Wash drainage system that are subject to fluvial redistribution, and (iii) potential 

deposits in areas subject to wind erosion and transport (Benke et al., 2006). Areas of 

Fortymile Wash that lack tephra deposits are assumed to contribute uncontaminated sediment 

with the pre-eruption ambient sediment yield. A dilution factor is calculated as the ratio of 

contaminated sediment volume to the total (uncontaminated + contaminated) sediment volume 

assuming uniform mixing of sediments. The duration that Fortymile Wash yields contaminated 

sediment was estimated as the time for significant flow events to fully deplete the ash in the 

Fortymile Wash drainage system (Benke et al., 2006). 

The NRC approach to fluvial ash redistribution assumes that all contaminated ash that is 

fluvially remobilized is deposited in the “active” fan, outlined in red in Figure 3-2 of Hooper 

(2005) (Figure 62), but leaves the fan only by wind erosion. Wind then blows contaminated ash 

from the depositional fan toward the RMEI. However, wind is not permitted to remove 

contaminated ash from the drainage basin where ash was originally deposited. The entire 

tephra blanket in the drainage basin is assumed to ultimately be removed. 

These assumptions appear to be conservative, leading to overestimates of hypothetical 

dose, because all contaminated ash removed by flooding is assumed to be deposited and 

accumulated near the RMEI in a 24 km2

 area. The assumption that wind alone is permitted to 

move contaminated ash from the fan to the RMEI is inconsistent with the erosion model, in 

which the tephra blanket is eroded only by water - wind is not allowed to remove contaminated 

ash from the drainage basin. In reality, large floods would dominate the process of fluvial 

erosion and transport and would carry contaminated ash beyond the active fan to the Amargosa 

River and beyond. For example, in the short period of historical record, at least two large 

floods have reached Death Valley. The finer-grained materials that are potentially significant to 

the inhalation dose and could eventually be remobilized by wind would be the most likely 

components to stay in suspension during floods and to be deposited at and far beyond the 

active fan, the location of the RMEI. Moreover, major rain events can occur in parts of the 

system and not necessarily throughout the entire Fortymile Wash. 
154

Figure 62 Landsat Thematic Mapper image showing the hypothesized active part of 

the Fortymile Wash depositional (or alluvial) basin in red. Area of the 

active fan is 24 ± 2 km2

. Map projection: Universal Transverse Mercator 

Zone 11 North, in meters (After Hooper, 2005, Fig. 3-2). 

Figure 63 shows the estimated sediment yield following a hypothetical eruption at Yucca 

Mountain. This is much more protracted than the sediment yield seen at Paricutín volcano, 

where the sediment yield returned to ambient conditions after ~30 years (Segerstrom, 1950). 

Hooper (2005) suggests that the humid climate of Paricutin makes that volcano a poor analog 

for Yucca Mountain. Nonetheless, it is unclear why sediment yields after hypothetical volcanism 

at Yucca Mountain would remain elevated more than 800 times longer than at Paricutín 

volcano. Very large floods have been documented in Fortymile Wash. Large floods in this 

ephemeral dryland system (Coleman, 2007) have the potential to erode and move large 

quantities of sediment with high suspended sediment concentrations and high bedload transport 

efficiency (Rathburn, 2007). 
155

Figure 63 Plot of calculated accelerated erosion following potential tephra fall in the 

Fortymile Wash drainage system. After an eruption, there would be an 

increase in sediment yield due to accelerated erosion, followed by a 

gradual decrease in sediment yield from these elevated values until 

conditions return to preeruption conditions (represented by a relative yield 

of 1.0 in the figure) (After Hooper, 2005, Figure 4-4). 

Sara Rathburn (Colorado State University) provided comments (ACNW, 2007) regarding 

the report by Hooper (2005). She compared the relative importance of fluvial versus eolian 

transport of sediment in Fortymile Wash. In her view, fluvial transport will be much more 

important than wind in transporting the greatest volume of sediment. She considers that 

sediment production in the Fortymile Wash basin will always be relatively high, given the lack of 

vegetation and the constancy of weathering of substrate material. Every time Fortymile Wash 

receives flow there is a flood that will transport sediment downstream until transmission losses 

overwhelm transport capacity. The sediment transport will be episodic and punctuated by the 

large flows, some of which have been shown historically to deliver water and sediment to the 

Amargosa River. Dr. Rathburn also noted that Hooper (2005) has no discussion of uncertainty, 

or of an attempt to quantify the uncertainty related to sediment transport in Fortymile Wash. If 

limited or no field data are used, and if the physical characteristics of the sediment (ash) are 

unknown (e.g. clumps of ash crystals vs. individual crystals), then using empirical equations in 

the sediment budget involves major assumptions that will have a large bearing on the results 

and how they are to be used. It is imperative that an effort be made to bracket the estimates of 

sediment production, delivery to channels, and transport. Otherwise, the discussion by Hooper 

(2005) reads with an unjustified amount of confidence in its sediment budget numbers. 

Overall, the NRC approach appears to be a simplistic view of ephemeral stream 

dynamics. Fortymile Wash is not always dominated by erosion and the active fan is not always 

dominated by deposition. Small flow events would not even reach the fan and instead would 

produce deposits in the Wash that are flushed out by the largest flow events. Precipitation in 

this basin is not homogeneous in space or time because most of the Fortymile Wash drainage 

basin occurs to the north at higher elevations. It is possible to have isolated rain events to the 
156

north that cause major flooding in the wash (and erosion of the depositional fan) but no local 

sheet wash erosion of the tephra blanket. Also, in arid regions such as Yucca Mountain, most 

of the erosion and long-distance sediment transport takes place during the largest discharge 

events, which are infrequent. The sediments most likely to be suspended and transported long 

distances are the smallest particles 7

. The sediments of the Fortymile Wash fan are relatively 

coarse, consisting mainly of sand and gravel pavements that dropped out of suspension quickly 

following Stokes’ Law, while the finer materials have been winnowed out and carried 

downstream. The smallest particles of concern in health physics will not settle out of overland 

flows until the water infiltrates, evaporates, or ponds. Long-distance transport of contaminated 

ash would result in extensive dilution of this material by uncontaminated sediments along the 

Fortymile Wash-Amargosa River drainage system. As discussed in Section 6.3.3, less 

contaminated ash would be available for transport if a more realistic treatment of spent fuel 

particle sizes (i.e., a coarser particle distribution) were to be applied. 

6.4.3.2. EPRI Analysis of Fluvial Transport from Extrusive Volcanic Activity 

EPRI (2004) commented on various conservatisms used in the NRC and DOE analyses. 

EPRI’s model of ash transport modeling showed that particles smaller than 130 microns in 

diameter would not be deposited at the compliance point (the RMEI). Both DOE and NRC use 

a conservative assumption that all deposited material is in the respirable size range, although 

neither the NRC nor DOE discuss realistic mechanisms that would break down ash in this way. 

6.4.3.3. DOE Volcanic Ash Fluvial Redistribution Model 

The DOE (2003) has developed a model for fluvial redistribution of volcanic ash that 

initiates with tephra being transported by hillside erosion. Sediment then moves into drainages 

and is transported via drainages that coalesce into larger and larger channels. Water and 

sediment from different channels begin a mixing process that ultimately leads to a 

homogeneous sediment containing materials from all drainages in the basin (Folk,1980). This 

mixing of sediments occurs everywhere that sediment is transported by water, including 

intermittent streams. Mixing occurs at higher rates and involves larger clasts in larger drainages 

than smaller ones and on steeper hillslopes than on low-gradient land surfaces. Sediment 

mixing also occurs from wind transport across the landscape. Drainage channels that develop 

across newly deposited tephra sheets exhibit the same processes as observed in streams, and, 

produce well-mixed sediment loads. 

In the Yucca Mountain area, sediments in drainage channels are commonly clasts of 

welded tuff and wind-blown quartz sand, which are more durable than basaltic tephra. Mixing of 

sediments occurs very rapidly, and welded tuff clasts and quartz sand/silt deposits are more 

abundant in the larger channels, so that the ash component from the Lathrop Wells volcano has 

been progressively diluted during transport relative to the total sediment volume. Eolian 

processes also mix sand and silt with the fluvially transported materials. The ratio of basaltic 

ash to non-ash continues to decrease with the passage of time. 

The DOE (2003) has performed studies of ash redistribution near the Lathrop Wells 

volcano to evaluate the fraction of basaltic ash components as a function of transport distance. 

-- 

7

 The Wentworth scale classifies silt particles in the range from 4 - 62 microns. Clay particles are smaller than 

4 microns. In a motionless water column, all of the sand drops out in 40 seconds and silts drop out of 

suspension in 2 hours (re: Stokes Law). After 2 hours only clays would remain in suspension. 
157

These data indicate that the concentration of basaltic ash in sediments decreases to about 50 

percent within 1 km of the head of the tephra sheet drainage on the eastern side of Lathrop 

Wells, whereas the channel on the west side has less than 40 percent basaltic ash after 1 km of 

transport. The indicated dilution factor is 50 to 60 percent per kilometer. 

Fortymile Wash is a major 815-km2

 drainage basin that includes the entire eastern slope 

of Yucca Mountain and the Fortymile Wash alluvial fan. Understanding the redistribution 

processes along Fortymile Wash is important to volcanic-eruption consequence scenarios. The 

fan spreads out into the Amargosa Valley from the mouth of Fortymile Wash. In the upper or 

northern half of the fan, the channels are well defined and widely spaced, with sizable 

interstream area between all pairs of channels. These interstream divide tracts are more 

prominent on the upper fan. On the lower fan they are neither as topographically prominent nor 

as wide because the distributary channels become progressively closer on the lower fan. 

Previous worldwide above ground nuclear tests introduced radioactive 137Cs into the 

atmosphere. 137Cs forms a time-stratigraphic marker in alluvial or eolian deposits and can be 

used to assess the extent of local erosion and deposition. The depth to which 137Cs infiltrates 

into the soil can be used as a general proxy for the depth to which sorbing radionuclides may 

infiltrate after deposition with volcanic ash (DOE, 2003). To evaluate erosion rates on the upper 

Fortymile Wash fan, soil samples were taken for analysis of 137Cs concentrations (BSC, 2003b). 

The analyses show that the upper-fan inter stream divide areas have been eroding over the last 

50+ years and have lost 1 to 2 cm of the upper soil horizon, most likely as a result of wind 

erosion, rather than from removal by fluvial processes (BSC, 2003b). There is also evidence of 

some eolian deposition on these same surfaces. 

The majority of the fan surface is interstream divide area, from which 1 to 2 cm of 

material, on average, has been removed during the last 50 years. When large floods occur, the 

flood waters can carry large quantities of sediment rapidly southward across the fan to the 

Amargosa River and may overflow channel banks forming small patches of overbank deposits. 

As flood levels subside, the suspended and bedload materials in the channel flow are deposited 

within the channels and are stored in the channel until the next flood occurs (BSC, 2003b). In 

contrast to the inter stream divide areas, the amount of sediment deposited in channels varies 

greatly from location to location. In TSPA, the DOE models distributary channel areas as 

having a layer of contaminated ash of uncertain thickness that appears immediately following 

the eruption. This layer will be of variable thickness, ranging from zero to several tens of 

centimeters (represented by a uniform distribution from 0 to 15 cm) (DOE, 2003). Although 

sediment thickness may exceed 15 cm, it is likely that contributions to dose from radionuclides 

at greater depths will be negligible. Observations of 137Cs content also indicate that 

radionuclides are unlikely to migrate more than 9 cm into sediment below the ash layer due to 

the widespread presence of carbonate layers in soil (DOE, 2003). Within any portion of the fan 

contaminated ash will be removed and deposited continuously, and average values for layer 

thickness are used as input in TSPA. Dilution of contaminated tephra would occur during 

transport in distributary channels. However, field data are insufficient to quantify this reduction 

in concentrations for the Fortymile Wash drainage and fan (DOE, 2003). DOE’s TSPA 

conservatively assumes that the concentration of radionuclides in the contaminated sediment in 

the channel areas is the same as that derived from ASHPLUME for the mid-line of a plume 

about 18 km from the vent. The extent to which this assumption overestimates concentrations is 

not well known but may be large, especially for eruptive events in which the wind is blowing 

from the west or southwest and the ash deposition occurs upstream from the location of the 

RMEI. The DOE considers the use of a single concentration to represent a spatially variable 

parameter to be reasonable because exposures would be integrated over a region that is large 

compared to the scale of local variability (BSC, 2003b). 
158

The DOE reports that their approach to redistribution is being completely replaced with a 

process-based landscape model of redistribution and sediment mixing. This comment was 

made by the DOE in their review of the draft version of this report (see ACNW, 2007). 

The DOE reports, based on observations from the Lathrop Wells Cone, that volcanic ash 

would not remain indefinitely in the channel area. The time needed to remove most tephra from 

the basin is unknown but is substantially less than the age of the Lathrop Wells Cone 

(DOE, 2003). Given the limited amount of residual ash observed near Lathrop Wells, the time 

required to remove most ash from the basin may be very short, perhaps on the scale of 

centuries. The DOE’s TSPA approach applies a uniform removal rate to channel deposits such 

that the initial layer is entirely removed within an uncertain period of time that is sampled 

uniformly between 100 and 1,000 years. Some residual contamination will likely persist 

indefinitely after the tephra deposits are eroded (DOE, 2003). The latest results from Valentine 

et al. (2007) indicate that a significant portion of the proximal and medial tephra deposits from 

Lathrop Wells are buried by fluvial deposits, rather than eroded away. 

DOE’s current approach in modeling atmospheric dispersal and deposition of tephra 

from a potential volcanic eruption at Yucca Mountain is documented in the model report BSC 

(2005). The report documents the conceptual and mathematical model (ASHPLUME) for 

atmospheric dispersal and subsequent deposition of ash on the land surface from a potential 

volcanic eruption. The report also documents the conceptual model for ash (tephra) 

redistribution. The ASHPLUME conceptual model accounts for incorporation and entrainment 

of waste fuel particles associated with a hypothetical volcanic eruption through the repository 

and downwind transport of contaminated tephra. The ASHPLUME mathematical model 

describes the conceptual model in mathematical terms to allow for prediction of contaminated 

ash deposition on the ground. BSC (2005) also describes the conceptual model for tephra 

redistribution within Fortymile Wash and on its alluvial fan. Sensitivity analyses and model 

validation activities for the ash dispersal and redistribution models are presented. The DOE 

considered models for atmospheric dispersal of contaminated tephra during and after violent 

Strombolian eruptions of the type that could occur in the Yucca Mountain region and for 

redistribution of contaminated tephra after the volcanic eruption. If such an eruption were to 

intersect the repository, the possibility exists for wastes to become entrained in the eruptive 

mixture and be transported via the same mechanisms as the ash plume. Although other 

eruption types that include nonviolent as well as violent phases exist, the violent Strombolian 

eruption has the greatest potential to erupt ash and waste particles high into the atmosphere, 

thus increasing the potential distance of dispersal. The DOE’s ASHPLUME conceptual model 

includes only the eruptive ash plume, convective/dispersive transport of contaminated ash 

particles downwind, and deposition on the ground surface. The ASHPLUME mathematical 

model can be used to evaluate ash and waste concentration at any point or multiple points on 

the surface relative to the volcanic vent. The DOE’s ash redistribution conceptual model 

describes the erosion and subsequent deposition of contaminated ash. Recently acquired wind 

data collected at Desert Rock (near Mercury, Nevada) were used to calculate wind speed and 

direction up to a height of 13 km. This data set replaces the Nevada Test Site data that were 

used for the TSPA-SR. Parameterization for the atmospheric dispersal model used in all 

ASHPLUME versions was documented in Igneous Consequence Modeling for the TSPA-SR 

(BSC, 2001). Tephra deposit thicknesses were simulated using ASHPLUME 1.4LV and 

compared with actual tephra deposit thicknesses from the 1995 eruptive event at the Cerro 

Negro volcano in Nicaragua. The DOE’s ash redistribution conceptual model is new and was 

not used in the TSPA-SR. 

BSC (2005, Appendix I) also developed an alternative numerical model for ash and fuel 

redistribution that calculates near-surface and at-depth fuel (waste) concentrations through time 
159

in soil columns near the RMEI location. This alternative model was designed to provide a more 

complete representation of the redistribution mechanisms involved, and to eliminate the mass 

balance conservatism of the simplified ash redistribution conceptual model. This alternative 

model is still under development by the DOE (BSC, 2005, Appendix I). It uses a spatiallydistributed Geographic Information System (GIS) framework to calculate the ash and fuel 

transported to the RMEI location from the upper Fortymile Wash watershed by hillslope and 

fluvial processes. This redistributed ash and fuel is combined with any primary ash and fuel that 

was hypothetically deposited directly on the RMEI location. By explicitly modeling the primary 

ash fall and redistribution processes, the model directly computes how much volcanic ash and 

fuel would be transported to the RMEI location under any wind conditions. 

The DOE’s alternative redistribution model (BSC, 2005, Appendix I) further considers the 

fate of ash and fuel delivered to the RMEI location, distinguishing between channels and recent 

(< 10 kyr) depositional surfaces (i.e., “channels”), and older (> 10 kyr) interchannel divide 

surfaces on the RMEI location. In the model, ash and fuel delivered from the upper Fortymile 

Wash watershed are deposited only in channels. This treatment assumes that areas of the 

RMEI location that have not been subject to fluvial erosion or deposition over the last 10 kyr will 

not be subject to fluvial activity within the next 10 kyr. The model also distinguishes between 

channels and divides for the purposes of modeling fuel redistribution in the soil profile. Vertical 

redistribution within the soil profile is modeled as a diffusion process. The lower boundary of the 

soil layer represents the presence of impermeable soil horizons. The alternative redistribution 

model evaluates over time the surface and depth-averaged fuel concentration on channels and 

divides at the RMEI location after an eruption (BSC, 2005, Appendix I). 

The alternative model does not incorporate eolian erosion or deposition or the long-term 

geologic dynamics of fan interchannel divide and channel interactions (BSC, 2005, Appendix I). 

Several key assumptions are made under the alternate model. First, it is assumed the climate 

through much of the regulatory period will be similar to today’s climate and will have relatively 

little impact on the Fortymile Wash alluvial fan even with a projected increase in annual 

precipitation. The rationale for this is that the expected effects of increased precipitation would 

include more vegetation and this will result in less ash being derived from the hillslopes. Total 

precipitation during a pluvial climate would be greater, but increased storm intensities or peak 

channel discharges would not be expected. The precipitation increase would come primarily 

from more frequent rainfall events (BSC, 2005, Appendix I). 

The second assumption is that the model assumes distributary channels in the RMEI 

location do not migrate (BSC, 2005, Appendix I). Therefore, the areal fraction of channels and 

interchannel divides would not change with time. The rationale for this is that fans are dynamic 

landforms that can evolve topographically over both long and short time scales. A distinction 

can be made, however, between the evolution of alluvial fans over millions of years and the 

evolution of “entrenched” alluvial fans over shorter time scales. In tectonically-active areas and 

over millions of years, alluvial fans aggrade by sedimentation in channels and by channel 

migration. Over these long time scales, alluvial fans are best considered to be subject to 

redeposition across the entire fan area. The Quaternary period has caused cycles of channel 

aggradation and incision on alluvial fans in the western US. As a result, fluvial activity on many 

fans is restricted to a small fraction of the piedmont area near the modern channels. Older 

terraces are commonly preserved from previous episodes of aggradation and incision, but are 

no longer subject to fluvial activity even during extreme events based on evidence of pavement 

development. Surface characteristics observed in the field, including well-developed desert 

pavement and varnish, provide evidence for the stability of channels and the lack of significant, 

soil-disruptive floods on interchannel divides. Well-developed desert pavements and varnish 

have been observed on divides near the RMEI location, indicating that most of these 
160

interchannel divides are Pleistocene in age and have not been flooded for at least 10,000 years. 

As a result, they may be considered stable for treatment in performance assessment 

(BSC, 2005, Appendix I). 

The third assumption is that in the model eolian transport to the RMEI location can be 

neglected compared with fluvial transport processes (BSC, 2005, Appendix I). The rationale for 

this is that fluvial transport is considered the dominant redistribution process for ash and source 

material from the upper Fortymile Wash because (1) the prevailing wind is away from the RMEI 

location and towards the drainage basin (so eolian transport is most likely to redistribute ash 

into the drainage basin, away from the RMEI location), and (2) fluvial transport processes in a 

tributary drainage system focus transported material onto the RMEI location, while eolian 

processes disperse ash by repeated episodes of entrainment, turbulent dispersion in the 

atmosphere, and redeposition (BSC, 2005, Appendix I). 

6.4.3.4. NWTRB Comments on Potential Consequences of Igneous Activity 

The Nuclear Waste Technical Review Board (NWTRB) has commented (NWTRB, 2002) 

that performance assessment calculations appear to show that “igneous activity is the largest 

contributor by far to radioactive dose during the first 10,000 years,” an observation that was 

repeated in a report the following year (NWTRB, 2003). However, the NWTRB observed in its 

2002 report that the igneous activity model proposed by NRC may be a “conservative endmember” model. This particular report of the NWTRB predates many of the observations and 

analyses discussed in previous sections of the present report. 

At the September, 2002, meeting of the NWTRB, Dr. William Melson, a consultant on 

igneous activity issues to the NWTRB, commented that studies of the mama-waste package 

interaction should focus on identifying conditions that would lead to disruption of the waste 

package and release of radioactive material from the package, in particular the effects of 

temperatures up to 1200° C and the effects of corrosive gases on the package welds. 

Dr. Melson also commented on the “dogleg” scenario, in which magma moves down the drift 

and then out through a secondary vent. This scenario would involve the largest number of waste 

packages with magma entering the drift. Dr. Melson noted that this was a worst-case scenario, 

and its probability of occurrence was small (Melson, 2003). 

In 2003, the NWTRB made three recommendations regarding igneous activity: 

• that the DOE conduct modeling studies of compressible fluids 

• that the DOE study the waste package-magma interaction, including both chemical 

and mechanical interactions and 

• that the DOE study aeromagnetic anomalies near the Yucca Mountain site. 

These recommendations were repeated in the NWTRB’s 2004 report to Congress 

(NWTRB, 2004). 

6.4.4. Effects of Transport of Contaminated Ash on Dose to the RMEI 

6.4.4.1. How Transport Can Result in a Dose 

6.4.4.1.1. Potential Dose from an Extrusive Scenario 

According to some stakeholders, a number of waste packages would be completely 

destroyed in the extrusive scenario, and at least some of the spent fuel contents would be 
161

reduced to small particles that are dispersed over the surrounding region by the eruption plume. 

The extrusive scenario accounts for this phenomenon by analyzing the fate of the fraction of the 

ejected radioactively contaminated ash particles that will be deposited on the ground. This 

deposited particulate matter can be remobilized and thereby moved into the vicinity of the RMEI 

by surface water (fluvial remobilization) or wind (eolian remobilization). Moreover, any 

remobilized material can be resuspended by wind or mechanical action. Thus transport of 

radioactive particulate matter could result in a radiation dose to the RMEI. Although 

radionuclides can persist in the environment and can cause exposure hundreds to thousands of 

years after the event, erosion and mixing with uncontaminated soil will decrease the 

concentration of radionuclides and thus the exposure of the RMEI. The emphasis in this 

section is on eolian remobilization and resuspension. Fluvial remobilization is discussed in the 

preceding section. 

 In eolian transport, deposited ash is resuspended by wind, and the resuspended ash is 

carried predominantly downwind. The plume shape of the resuspended ash depends on 

particle size and density and on meteorological conditions. A review of atmospheric dispersion, 

including the dispersion of the initial plume from the eruption, is presented in Section 3.4. The 

present section expands on that initial discussion and on the relationship between the dispersed 

ash plume and radiation dose to the RMEI. 

Radioactively contaminated ash to which the RMEI is exposed can potentially deliver the 

following types of radiation doses: an external dose from groundshine (direct radiation from 

radioactive material on the ground), an external dose from cloudshine (direct radiation from 

radioactive material in the air), an ingestion dose, and an inhalation dose. A groundshine dose 

would be significant only at the time of the eruption and is not considered for this analysis 

because direct hazards during an eruption would involve more serious risks. Cloudshine doses 

are rarely significant under any circumstances (Neuhauser et al., 2000) and are therefore not 

considered in this analysis. 

An ingestion dose to the RMEI would depend on uptake of radionuclides by food crops 

and the ingestion of these crops. Anspaugh et al. (2002) reviewed measurements of vegetation 

uptake of deposited radionuclides at the Nevada Test Site following atmospheric nuclear tests. 

Table 9 shows the computed fractions of fallout particles that were intercepted by vegetation. 

Table 9 Summary of computed mass interception fractions of fallout from 

nuclear tests at the Nevada Test Site (After Anspaugh et al., 2002). 

Computed values of mass interception fractions 

m2 of contaminated surface/kg vegetation dry weight 

Native desert vegetation Pasture-type vegetation 

Parameter 

Total fallout ≤44 μm Total fallout ≤44 μm 

Arithmetic mean 0.18 0.81 0.20 1.9 

Standard deviation 0.25 1.3 0.29 4.29 

Geometric mean 0.062 0.37 0.081 0.82 

Standard deviation 6.3 3.7 4.8 3.2 
162

Smaller particles are more likely to be taken up by vegetation than larger particles, and 

dissolved material is the most likely to be absorbed. Lee et al. (2005) have observed that 

rainfall would have to increase about ten fold to provide enough water for locally grown crops or 

enough water for families to grow a significant fraction of their own food. Most water used for 

irrigation in the Amargosa Valley is groundwater rather than surface water (Fenelon and 

Moreno, 2002), and groundwater would not be affected by surface remobilization of 

contaminated ash. Virtually no agricultural products intended for human consumption are 

produced in the area occupied by the RMEI and any ingestion dose would probably be limited to 

meat and milk for this scenario. Some immediate fallout could be absorbed by pasture-type 

vegetation, since alfalfa is grown in the Amargosa Valley, but there is not enough locally grown 

alfalfa to maintain either beef or dairy cattle8

. Therefore, any ingestion dose would be a minor, 

probably negligible contributor to a radiation dose to the RMEI. 

An inhalation dose would be the only significant dose to the RMEI. The inhalation dose 

is the dose delivered by an inhaled radionuclide to the organ of the body in which it is lodged. 

This Committed Effective Dose Equivalent (CEDE) is summed over 50 years and assigned to 

the year the intake occurs (Schleien et al., 1998). The dose delivered by an inhaled and 

absorbed radionuclide also depends on metabolism and particle size; the most penetrating 

particles are about 0.3 microns (AMAD). The energy absorbed by various organs and the type 

of radiation are reflected in the dose conversion factors (DCFs) for each radionuclide (Eckerman 

and Ryman, 1993; Eckerman et al., 1999; Leggett and Eckerman, 2003). These DCFs are 

specific to the pathway by which the RMEI is exposed (ingestion, inhalation), and to the organ 

absorbing the radionuclide, and take into account both radioactive decay and physiological 

elimination from the body. 

6.4.4.1.2. Potential Dose from an Intrusive Scenario 

An intrusive scenario could result in a dose to the RMEI only through ingestion of 

groundwater or crops that absorbed radionuclides from the groundwater. The only radionuclides 

significant to dose in the intrusive scenario are those that would travel in the groundwater: 129I, 

99Tc, and 237Np. The contribution to the RMEI dose of 129I is the subject of a recent study by 

Moeller et al. (2005), which provides an insight into the role of stable (non-radioactive) iodine in 

calculating doses from 129I (also see Killough and Rohwer, 2005). Moeller and Ryan (2005) 

noted: 

The science of internal dosimetry has undergone significant progress and dramatic 

change during the years [since 1960].... It is essential, therefore, that the analysts 

and regulators acknowledge that these changes have occurred, that the dose 

estimates will differ depending on the basis on which they are made, and that caution 

must be exercised to ensure that these factors are taken into consideration in 

interpreting the outcomes .... Differences in dose coefficients can result in changes in 

dose estimates by an order of magnitude depending on the source from which [the 

dose coefficients] were obtained. 

For example, the dose conversion factor for 129I is strongly influenced by the intake of 

stable iodine in food and water in the diet (Moeller and Ryan, 2004). Another example is from a 

recent paper on dose conversion factors for tritium and 14C (Richardson and Dunford, 2001). 

This paper notes: 

-- 

8

 As was observed in the 2004 ACNW&M tour of the Amargosa Valley, the one commercial farm, a dairy farm, 

imports most of its alfalfa. 
163

It is shown how the dose coefficients for intakes of tritium and 14C compounds are 

affected by different interpretations of the methods recommended by the ICRP for 

two of the three classes of vapors and gases. Some aspects of the ICRP models, 

such as the percent oxidized, would benefit from reconsideration so as to produce 

tritium and 14C biokinetics that are less dependent on the radionuclide. 

6.4.4.2. NRC Analysis 

Jarzemba et al. (1997) modified the Suzuki ash transport model and incorporated it into 

the TPA code to calculate the distribution of the released radionuclides during a hypothetical 

eruption through the repository. The composition of the radionuclide layer on the ground takes 

into account the thickness of the ash deposit, leaching and erosion rates, and radionuclide 

decay. In the TPA analysis the wind direction during an eruption was assumed to always be in 

the general direction of the RMEI. A more realistic treatment of wind is now being incorporated 

in TPA. This is especially important given that the two parameters most influential to eolian 

dispersion are the mass of soil in the air above a fresh volcanic ash blanket (mass loading) and 

the wind speed (Table 4-5 of Mohanty et al., 2004). 

The calculated risk from volcanism appears to be small within the 10,000-year simulation 

period (Mohanty et al., 2004). Results from a range of alternative conceptual models for waste 

form dissolution, waste package lifetime, and radionuclide transport resulted in calculated doses 

to the RMEI that were well within the EPA standard. 

The most recent NRC simulations of extrusive volcanism at Yucca Mountain are 

documented in Mohanty et al. (2005, p. iii), where the NRC summarized the following overall 

results: 

Analyses to assist staff in understanding the significance of features, events, and 

processes associated with extrusive volcanism include estimates of the impact of 

(i) wind-field variability assumptions, (ii) ash deposition and remobilization, (iii) ash 

mass loading, (iv) assumptions regarding spent nuclear fuel incorporation and initial 

plume velocity, and (v) drift degradation on magma-waste package interactions. 

Results of these analyses for 10,000 years indicate (i) current assumptions for ash 

mass loading and wind-field speed and direction are reasonable; the assumptions 

have the potential to affect the dose estimate by approximately one order of 

magnitude, (ii) alternative mass loading reduces dose estimates by approximately a 

factor of two, (iii) current and alternative models for spent nuclear fuel incorporation 

and initial plume velocity cause only small differences in dose estimates, and (iv) no 

effects on the peak eruptive risk are estimated from coupling drift degradation with 

the number of entrained waste packages. Ash remobilization and wind variations are 

implemented in an alternative model. 

Mohanty et al. (2005) present the following conclusions related to the volcanic extrusion 

scenario and ash deposition/remobilization: 

• Redistribution of contaminated ash appears unlikely to increase significantly the 

estimated peak dose arising from a volcanic eruption over the case in which the ash 

is directly deposited at the RMEI location. Although not a likely bounding approach, 

fixing the wind direction to the south appears reasonable to account for the effect of 

remobilization of the contaminated ash.

• Overall, results suggest variability in the wind field does not significantly alter the 

estimated peak dose at the RMEI location. Fixing the wind direction to the south 

appears a reasonably conservative approach to account for the effect of a variable 

wind field. 
164

• Analysis estimates composite daily mass loading varies by approximately a factor of 

two for a wide range of duration for the peak values (i.e., 5 to 50 percent of the time). 

Using the medium value for the composite mass loading for fresh ash conditions 

(i.e., 1.12 mg/m3 (7.0 × 10-8 lbm/ft3

)) and soil conditions (i.e., 0.1 mg/m3

(6.2 × 10-9 lbm/ft3)) in the TPA code resulted in approximately a factor of two 

reduction in the overall dose estimate. The results from this analysis were 

considered in developing mass loading parameters in the latest version of the TPA 

code. 

The groundwater dose from an intrusive event is similar to the dose in the base case 

with faulting events (see Mohanty et al., 2004, Figure 3-14). The increase in groundwater dose 

from igneous activity is smaller than that for faulting events because only 53 waste packages 

fail by intrusive igneous activity as compared to 208 waste packages by the faulting event in the 

mean value, single-realization case. 

Dose conversion factors (rem per curie) are computed in the TPA Version 4.1 code by 

using GENTPA, a modification of the GENII computer code (Napier et al., 1988). Subsequent 

versions of the TPA code use the dose conversion factors tabulated in Federal Guidance Report 

13 (Eckerman et al., 1999). 

6.4.4.3. DOE Analysis 

The 50-year record of deposition and remobilization of 137Cs on the Nevada Test Site 

suggests that eolian removal of material has been the major process causing erosion 

(DOE, 2003). In the interstream divides, erosion removes sediment at a relatively rapid rate of 1 

to 2 cm per 50 years. The DOE’s TSPA model calculates doses using the initial ash-layer 

thicknesses and radionuclide concentrations from ASHPLUME, modified by a time dependent 

soil removal factor, estimated to range from 0.02 to 0.04 cm/yr (DOE, 2003). Given these 

erosion rates, ash layers will be removed within a few centuries, depending on initial thickness. 

Based on field observations, it is likely some fine-grained ash and radionuclides will persist in 

the soil below the surface ash layer, and some additional radionuclides may be brought into the 

interstream divide areas by infrequent flooding events that cover the entire fan. Residual 

contamination after erosion removal of the tephra deposits is estimated to be on the order of 

0.01 of the initial ASHPLUME radionuclide concentration (BSC, 2003b). 

Like the NRC, the DOE uses the generally accepted convention that airborne 

resuspended material is dispersed in the same way as any airborne material. The DOE has 

recently validated both its dispersion and inhalation models by using measurements of total 

suspended particulates raised both by resuspension and by mechanical disturbance of the soil 

surface, as in farming (BSC, 2006). The DOE’s literature review suggest that ash from basaltic 

volcanoes has a somewhat smaller concentration of very fine particles than ash from other 

volcanoes (like Mt. St. Helens), but that these are the particles that are carried farthest from the 

eruption site to the vicinity of the RMEI. In addition, BSC (2006) cites extensive literature 

reports of measurements of particle sizes that can contribute to inhalation dose, concentrating 

on particles of 10 microns diameter or less (particles designated as PM10 by EPA). The DOE 

biosphere model assumes that particles of 1 micron AMAD play the greatest role in inhalation 

dose (BSC 2006, p. 6-23) and, like Jarzemba and LaPlante (1996) assumes a triangular 

distribution. 

DOE has validated its ASHPLUME modeling by examining the distribution of ash from 

the Lathrop Wells volcanic cone as well as from Cerro Negro volcano (DOE, 2004). Hill et al. 

(1998) have also verified the use of the Suzuki (1983) formulation in modeling ash distribution 
165

from Cerro Negro. Apparently, the DOE does not use the Anspaugh model for eolian 

redistribution, but depends on its own validation. 

6.4.5. Remobilization Summary 

The consequences to the RMEI associated with an extrusive igneous event depend on 

estimation of the following parameters: 

• particle size and density of spent fuel and radionuclides released in the event 

• particle size and density of ash into which radioactive material is incorporated 

• power of the eruption and total mass of material from an igneous event 

• areal extent and thickness of ash layer in Fortymile Wash drainage basin 

• wind direction 

• meteorologic parameters used in the Suzuki and atmospheric dispersion models 

• areal extent of vegetation exposed to deposited material 

• elapsed time between the igneous event and exposure of the RMEI 

• DCF reference document used to calculate dose 

• RMEI breathing rate. 

The consequences associated with an intrusive igneous event depend on: 

• agricultural crops and livestock exposed to potentially contaminated groundwater 

• elapsed time between the igneous event and exposure of the RMEI. 

Both the NRC and DOE favor using Federal Guidance Report (FGR) 13 (Eckerman et al, 1999) 

because the uptake models of FGR 13 are a considerable refinement over earlier clearance 

models. 

The potential dose to the RMEI is the compliance criterion, and is also the culmination of 

all the assumptions that have gone into the analysis of an igneous event. Both the NRC and the 

DOE consider the inhalation dose (including inhalation of resuspended material) much more 

significant than an external dose. Neither agency has considered the possibility of an ingestion 

dose. 

The NRC employed several alternative models, varied the degree to which SNF was 

incorporated in ash, varied the wind direction and other dispersion parameters, considered a 

range of remobilizations, and notes that the differences result in variations of the inhalation dose 

to the RMEI by factors between two and ten. This appears to be a useful approach to 

generating performance assessment inputs (inputs to the TPA) and results in a risk-informed 

analysis. The NRC considers that the maximum contribution to inhalation dose is from particles 

of approximately one micron AMAD (Compton, 2004) or less. 

The DOE (2004) uses the same assumptions as the NRC about the range of size and 

density of spent nuclear fuel particles that can be incorporated into ash particles, and also cites 

Jarzemba and La Plante (1996). The DOE defines the particle density as a function of the 

fraction of magma incorporated into the ash particle. The resulting range of contaminated ash 

particle densities is similar to that postulated by the NRC. The DOE does make the point that 

the frequency of wind blowing toward the RMEI location is considerably smaller than for wind 

blowing away from the RMEI, so that the probability of an inhalation dose from resuspended 
166

material is relatively small. The DOE further postulates that the high winds in the vicinity of the 

RMEI make persistence of a thick remobilizable layer of undiluted contaminated ash unlikely. 

The DOE considers two scenarios for RMEI exposure: (1) exposure to contaminated ash due 

primarily to eolian dispersion, and (2) exposure due to fluvially remobilized resuspended ash. 

The DOE postulated the first as less likely because of the relatively infrequent high winds in the 

direction of the RMEI. 

6.5. Summary 

The consequences for future radiological exposures vary significantly among the 

hypothetical scenarios for volcanic interaction with the repository. These scenarios are an 

extrusive (volcanic) event and an intrusive event. The latter includes hypothesized secondary 

breakouts of magma from a repository at some distance from the point of initial intersection (socalled “dogleg” scenario). 

Extrusive event – The number of waste packages that could be damaged or destroyed 

by extrusive volcanism depends on the diameter of a volcanic conduit at the depth that it 

intersects a repository drift. The DOE has estimated that the median number of waste 

packages that would be disrupted in an eruption scenario is fewer than 10. The NRC currently 

assumes that volcanic conduits would have an average diameter of ~50 m. If the center of a 

conduit were to coincide with the axis of a drift, then ~5 waste packages could be entrained 

within the cross-section of the conduit and their contents potentially transported to the surface. 

The ongoing PVHA-U expert elicitation is evaluating the potential size range of volcanic 

conduits based on analog studies. Final results of that elicitation will not be available until 2008, 

but are expected to provide the best available estimate of conduit diameter at repository depth. 

Magma/drift/waste interactions in the extrusive scenario are incompletely understood. 

Due to the perceived complexity of the processes involved, neither the NRC nor DOE evaluate 

magma/drift/waste package interactions in any detail. In the DOE and NRC performance 

assessment codes the assumption is made that all spent fuel entrained in a volcanic conduit in 

the extrusive scenario would be reduced to a very fine powder, incorporated in tephra, erupted 

into the atmosphere, and distributed across the countryside by prevailing winds. This appears to 

be a conservative assumption because the ceramic pellets that comprise spent nuclear fuel 

have great strength and a melting point of 2600o

 C, much higher than magma temperatures of 

about 1100o

 C. Also, the ejected fuel pellets and fragments may be encased in a protective 

layer of quenched magma, consistent with natural volcanic analogs of wall rock materials that 

have been caught up in the magma and brought to the surface in volcanic conduits (i.e., 

xenoliths). The result is larger fragments that are unlikely to be inhaled. It is unclear how or 

whether the Alloy-22 waste packages or the ceramic or glass waste forms themselves would be 

reduced to particles of respirable size, as currently assumed by the DOE and NRC. EPRI has 

concluded, based on multiple lines of evidence, that it is unlikely that waste packages would be 

breached by magma during an active eruption period. EPRI found that the expected 

consequence of an igneous extrusive event would be zero releases of radioactive matter from 

the repository to the atmosphere. 

Slightly more than half of the eruptive products of basaltic volcanoes in the Yucca 

Mountain region consists of ash that was dispersed from the eruption plumes. The remainder 

occurs as volcanic cone fragments and lavas, which are resistant to erosion. Radioactive waste 
167

incorporated in the cone and lava flows would contribute little to the RMEI dose because of this 

resistance to erosion. 

Intrusive event – the DOE has estimated the number of waste packages that could be 

damaged in a potential future igneous event. The igneous intrusion scenario shows a range of 

consequences, extending from virtually no waste packages damaged to nearly all waste 

packages in the repository. The 50th percentile value indicates approximately 1600 waste 

packages could be impacted, out of over 11,000 waste packages in the repository. In TPA 4.1 

the NRC estimated a mean value of 37 magma-induced mechanical failures from an intrusive 

event, based on a log uniform distribution from 1 to 1402 waste package failures. Igneous 

activity causes the largest increase in dose conditionally from both groundwater and airborne 

pathways, but the risk is still small when the probability of the volcanic event is factored into the 

calculations. EPRI concluded that magma viscosity would be larger than previously assumed. 

They estimate that only 0-6 waste packages could become engulfed by magma intrusion in a 

waste emplacement drift. They further estimate that 14-24 waste packages could be 

significantly affected by heat and corrosive gases (but not engulfed by magma). 

Viscosity is the most important magma property to understand because it controls the 

flow behavior and the distance that magma could penetrate a repository in the unlikely event of 

volcanic intersection. ACNW&M observes that previous researchers have not been consistent 

in their approach to estimating the viscosity of the Yucca Mountain basalt as it ascends and 

degasses with approach to the surface. There has been a tendency to assume rheological 

properties pertaining to both wet, cool magmas and dry, hot magmas, leading incorrectly to the 

postulate of a highly explosive system with highly mobile lavas. Therefore, previous claims of 

severe consequences of igneous intersection appear to be poorly founded. The potential Yucca 

Mountain magma is likely a wet, cool explosive magma with relatively immobile lavas. The 

Pleistocene lava flows in the Crater Flat basin and at Lathrop Wells demonstrate that the lavas 

had high viscosities and were relatively immobile. Characteristics of these lava flows indicate 

viscosities orders of magnitude larger than had been assumed in analyses of igneous 

interaction with a repository. These high viscosities, along with magma solidification effects, 

would significantly reduce the distance that magma could penetrate into tunnels and thereby 

reduce the number of impacted waste packages. 

The so-called “dogleg” scenario (Woods et al., 2002) refers to a hypothetical scenario 

proposed by the NRC in which magma might rapidly fill a drift and create enough pressure to 

generate (at a distance from the entry point) a secondary dike to the surface. This “dogleg” 

model was analyzed by the Igneous Consequences Peer Review (ICPR) Panel (Detournay 

et al., 2003), by EPRI, and by the DOE. In TPA 4.1 analyses the NRC assumed that a mean 

value of 51 waste packages could be entrained by an extrusive event and contained in volcanic 

ejecta. The ICPR considered the propagation of either a magmatic or pyroclastic “dogleg” 

scenario to be quite improbable, found that the initial and boundary conditions in the model are 

unrealistic, but recommended further analyses to assess the impacts of a partially coupled 

pyroclastic flow scenario on repository performance. EPRI concluded that their independent 

modeling results show that pressure conditions in a repository intersected by magma would be 

significantly less forceful than postulated by the NRC. The DOE concluded that the “dogleg” 

model overestimates the violence of magma-repository interaction. Use of realistic boundary 

conditions (including compressible walls and backfill, permeable country rock and backfill, 

phase separation in the magma-volatile mixture, partial blockage of the drift by waste packages 

and other engineering features, and the axial spacing of the waste packages) would greatly 

reduce the amplitude of any shock wave that might form. Use of realistic initial conditions such 

as a dike tip would preclude shock waves for all but the most rapid magma ascent rates. 
168

Overall, the “dogleg” intrusion/extrusion scenario is not credible. Increased magma 

viscosity, quenching of magma on waste packages and drift walls, and reduction of magma 

pressure at a distance from the drift entry point, would inhibit magma from moving from the main 

conduit, through the repository, and to the surface at a secondary vent at any time during the 

eruptive cycle. 

The presence of backfill, either intentionally placed or as a result of drift-roof collapse, 

could be beneficial from the standpoint of intrusive volcanism because it would minimize contact 

of magma with waste packages. Backfill would not significantly alter the extrusive scenario 

because in the unlikely event that a volcanic conduit were to intersect a waste drift it would likely 

entrain both waste packages and the backfill itself. 

Remobilization – Assuming a hypothetical volcanic eruption through a repository, the 

DOE has performed studies of ash redistribution near the Lathrop Wells cone to evaluate the 

fraction of basaltic ash components as a function of distance from the tephra sheet. These data 

indicate that the concentration of basaltic ash in sediments would decrease to about 50 percent 

within 1 km of the head of the tephra sheet drainage on the eastern side of Lathrop Wells, 

whereas the channel on the west side has less than 40 percent basaltic ash after 1 km of 

transport. The DOE’s TSPA model calculates doses using the initial ash-layer thicknesses and 

radionuclide concentrations from ASHPLUME, modified by a time dependent soil removal 

factor, estimated to range from 0.02 to 0.04 cm/yr. Given these erosion rates, ash layers would 

be removed within a few centuries, depending on initial thickness. 

The NRC has developed a sediment budget approach to model the long-term fluvial 

redistribution of basaltic tephra in Fortymile Wash. Using parameters specific to Fortymile 

Wash and a hypothetical eruption at Yucca Mountain, they concluded that substantial tephra 

deposits can persist for more than 1,000 years in arid terrains, even with a period of accelerated 

erosion after the eruption. It is estimated that ~98 percent of the tephra deposit remains in the 

Fortymile Wash catchment basin after 100 years and 50 percent remains after 1,800 years. 

The NRC suggests that the amount of remobilized tephra may be large—even when mixed with 

ambient sediment—and could significantly affect airborne radioactive particle concentrations for 

the RMEI. The NRC assumes that all contaminated ash that is fluvially remobilized would be 

deposited in an “active” fan located west of the RMEI, but once it gets there, no ash is permitted 

to leave this fan area except by wind erosion. 

The ACNW&M has observed that large floods would dominate the process of fluvial 

erosion and transport and would carry contaminated ash beyond the active fan and all the way 

to the Amargosa River and beyond. In the short period of historical record, at least two (and 

probably three) large floods in the Fortymile Wash/Amargosa River system have reached Death 

Valley. The sediments most likely to be suspended and transported long distances are the 

smallest particles – the same particles of concern for respiration or ingestion. Long-distance 

transport of contaminated ash would result in extensive dilution of this material by 

uncontaminated sediments along the Fortymile Wash-Amargosa River drainage system. 

EPRI has commented on various conservatisms used in the NRC and the DOE 

analyses. EPRI’s model of ash transport modeling showed that particles smaller than 130 

microns in diameter would not be deposited at the compliance point. Both the DOE and NRC 

use a conservative assumption that all deposited material is in the respirable size range, 

although neither NRC nor the DOE discuss realistic mechanisms that would break down tephra 

in this way. 
169

Eolian (wind) transport could result in an inhalation dose to the RMEI in the extrusive 

scenario. Eolian transport can move radioactively contaminated ash from fluvial deposits as 

well as from material deposited on the surface of the ground as a result of the eruption itself. 

The mechanism of eolian transport is the same in both cases: ash is remobilized by wind, and 

the remobilized ash is carried and dispersed predominantly downwind. The shape of the 

remobilized plume depends on particle mass and density and on meteorological conditions. 

Both the DOE and the NRC have estimated triangular particle size distribution of ash 

particles, with the mean and mode at 1 micron aerodynamic diameter. Both agencies have 

estimated the dimensions and density of spent fuel particles that could be incorporated into and 

dispersed with the ash. The code ASHPLUME has been used to model this dispersion. The 

NRC has designed a new module, REMOB, for estimating resuspension and remobilization, but 

ACNW&M has not seen the equations or results for that model. If there is an igneous event, the 

peak dose to the RMEI would occur earlier in the postclosure period than in the absence of an 

igneous event, and the dose to the RMEI would probably be larger. The difference between 

doses calculated using these scenarios gradually decreases with time, and is approximately an 

order of magnitude at 10,000 years. 

Like the NRC, the DOE uses ASHPLUME to model the initial eolian dispersion of 

contaminated ash, as well as the generally accepted convention that airborne resuspended 

material is dispersed in the same way as any airborne material. The DOE appears to have 

accepted the Anspaugh formulation of both long-term and short-term resuspension. The DOE 

makes the point that the frequency of wind blowing toward the RMEI location is considerably 

smaller than wind blowing away from the RMEI, so that the probability of an inhalation dose 

from resuspended material is relatively small. The DOE further postulates that the high winds in 

the vicinity of the RMEI make persistence of a thick remobilizable layer of undiluted 

contaminated tephra unlikely. The NRC does not appear to have accepted the Anspaugh 

formulation, but has postulated a larger fraction of resuspended material considering the longer 

times during which resuspension of contaminated ash can take place. The NRC also assumes 

that all resuspended material, resuspended at any time after the eruption, is ash (i.e., none of it 

is overburden). The DOE has validated its ASHPLUME modeling by examining the distribution 

of ash from the Lathrop Wells cone as well as from the Cerro Negro volcano. Both the NRC 

and the DOE favor using Federal Guidance Report (FGR 13) (Eckerman et al, 1999) rather than 

FGR 11 and 12 as a source of dose conversion factors. Since the uptake models of FGR 13 

are a considerable refinement when compared to earlier clearance models, FGR 13 dose 

conversion factors are widely accepted and agreed to. 
170

This page intentionally blank. 
171

7. SUMMARY/CONCLUSIONS 

7.1. Introduction 

As the studies on the impact of igneous activity on the proposed high-level waste 

repository at Yucca Mountain mature, it is appropriate to review and analyze the current state of 

knowledge regarding igneous activity that provides the technical bases for decisionmaking. 

Due to inherent uncertainties in the igneous processes that have occurred and may 

occur in the future in the Yucca Mountain region, and limitations in knowledge of controlling 

parameters, there is a range of professional views regarding the features, events, and 

processes associated with igneous activity and their impact on risk. These views involve the 

nature of anticipated igneous activity during the compliance period of the repository, the 

likelihood that igneous activity will occur, and the consequences of igneous activity due to 

potential release of waste to the environment. This report summarizes these views and 

analyzes them based on professional judgment and quantitative considerations within the scope 

of resources available to the ACNW&M. 

Taking into account the different role and responsibilities of the stakeholders in license 

preparation and review, the views of the DOE, NRC, and others have been abstracted from the 

published literature and public agency reports and presentations. In addition, a draft of this 

report was distributed for review to the aforementioned stakeholders and to an international 

group of experts in igneous activity and high-temperature processes. The response to the 

ACNW&M’s request was generally excellent. Also, written reviews and oral presentations at an 

ACNW&M Working Group meeting held in early 2007 have been used to revise this report by 

taking into account the latest and best available information. 

Several alternative models describe potential future extrusive (volcanic) and intrusive 

igneous scenarios at Yucca Mountain. Although many of these models are relatively mature, 

others, particularly those involved in consequence modeling, are undergoing continuing 

improvement. As a result, this report, which serves as a benchmark for evaluating the technical 

bases for igneous activity decisionmaking, is a snapshot based on current understanding of the 

views on igneous activity. Ongoing studies by the DOE, NRC, and others may modify the results 

presented in this report. 

Based on current views regarding potential igneous activity at Yucca Mountain, 

performance assessment calculations by stakeholders (including the NRC, DOE, and EPRI), 

indicate that dose consequences are largest for events that occur soon after repository closure, 

while the relatively short-lived radionuclides are present in significant quantities. The 

probability-weighted dose associated with risk from extrusive volcanism, according to present 

assessments, is smaller than the 10,000-year dose standard of 15 millirem/yr and decreases 

gradually after 1,000 years in proportion to the rate of decay of radionuclides in the waste. The 

risk from an intrusive event, based on current calculations, reaches a maximum after several 

tens of thousands of years, but the maximum probability-weighted dose is only a fraction of the 

current 10,000-year standard. 

In determining risk, both the probability and consequence of the igneous event are 

considered. Factors important to the extrusive event scenario are probability of the event, 

including both spatial and temporal considerations, the number of waste packages entrained 

(volcanic conduit diameter), the eruption volume and dispersal of the contaminated ash, the size 

distribution range of the spent fuel particles and ash, surface remobilization of contaminated ash 
172

by water and wind, and inhalation of contaminated ash by humans. In the intrusive scenario, the 

major factors in determining risk, in addition to probability of the event, are the number of waste 

packages affected by the intruding magma, the distance magma can flow into the drifts (which is 

determined by the viscosity of the intruding magma and the magnitude and duration of the 

driving pressure upon entry into the drifts), the degree of dissolution of waste released from 

damaged waste packages into the ground water, the transport of the waste contaminated 

ground water to the RMEI, and the ingestion of released radionuclides by the RMEI. 

The views of the NRC, DOE, and others pertaining to igneous activity at Yucca Mountain 

are summarized in the final sections of Chapters 4, 5, and 6. In addition, the accompanying 

table (Table 10) presents a brief, simplified summary of the current views on significant igneous 

activity topics abstracted from the published literature and public presentations. A fuller 

explanation of these views is in the text and the original documents referenced in this report. 

The germane sections of this report that pertain to these items and that reference original 

literature are cited in each cell for reference by the reader. This table shows that there is general 

agreement on many of the topics, particularly those dealing with the nature and probability of 

igneous events. However, there is considerable difference in the views pertaining to the 

consequences of igneous activity, especially those involving the intrusive scenario. 

In the following sections of this chapter, the views on the nature of anticipated igneous 

activity affecting the proposed repository, the likelihood of igneous activity, and its 

consequences are summarized and commented on. Additionally, conclusions are given in 

sections that summarize uncertainties in igneous activity and the role of alternative models in 

evaluating risk due to igneous activity. 

7.2. Nature of Anticipated Igneous Activity 

1. Two possible scenarios that involve intersection of the repository by igneous activity 

include different processes and risk consequences. The extrusive (volcanic) scenario 

involves intersection of a volcanic-cone-forming conduit through the repository to the 

surface causing waste in the conduit to contaminate the ash and be dispersed over the 

Yucca Mountain vicinity. The greatest risk from such an event will occur during the first 

thousand years due to the presence of significant quantities of short-lived radionuclides. 

The intrusive scenario involves intrusion of an igneous dike into the repository leading to 

damage or destruction of the waste packages and premature release of the waste to 

infiltrating waters passing through the repository, but does not involve a volcanic conduit 

directly to the surface. 

2. One volcano has erupted near Yucca Mountain during the time of modern humans. The 

Lathrop Wells volcano, which erupted 80,000 years ago, is generally agreed to represent 

the type of igneous activity possible in the region during the compliance period of the 

repository. This is a small-volume, single-episode basaltic volcanic event, lasting 

perhaps a year, with the largest volume of material in the form of ash and other ejecta 

and lesser amounts in lava flows and the volcanic (scoria) cone. Other volcanoes that 

occurred during the past few million years in the Yucca Mountain region are of a similar 

nature. 

3. There is general agreement regarding the nature of any future igneous event (i.e., power 

and approximate duration of event, volume and types of erupted products, general 

magma type and its volatile content, and the characteristics of the crustal pathways 

(dikes) for the magma). There is also agreement that dikes (which can locally evolve 

into volcanoes) tend to follow pre-existing fault zones where faults exist in proximity to 
173

an ascending dike. Thus, current DOE plans to avoid existing faults in constructing the 

repository (setback strategy) will minimize the likelihood of an extrusive event 

intersecting the repository. 

4. The current 50-75 m width assumed for volcanic conduits beneath volcanoes appears to 

be a reasonable upper bound based on regional analogs. This width is important 

because it constrains the number of waste packages that could become entrained and 

ejected in a volcanic eruption (i.e., ≤5 waste packages). Recent studies indicate that 

conduit widths at repository depth are likely to be significantly smaller, perhaps a few 

tens of meters, and could therefore intercept fewer waste packages. 

5. The majority of past volcanic activity occurred within a basin, e.g., Crater Flat basin, the 

northern Amargosa Desert, and Jackass Flats, not on ridges like Yucca Mountain. 

Although one ancient (>10 million year old) basaltic dike exists on the western flank of 

Yucca Mountain, no volcanic activity is known to have intersected the repository footprint 

since the surface rocks were deposited 13 million years ago. 

6. Igneous event definitions have evolved during site characterization and analysis. Prior to 

the mid-1990s, the definition of event was largely restricted to volcanic eruptions. 

Subsequently, the importance of dike intersection with the repository has been 

emphasized as well as volcanic events. Even more recently, studies of similar smallvolume basaltic igneous events dating back to 10 million years ago in the nearby 

Nevada Test Site suggest that igneous sills, which are near-horizontal tabular igneous 

intrusions, should be considered in event definition. This evolution in event definition 

may be important in evaluating published igneous event probabilities because of the 

change in definition from point events to long (dikes), and perhaps broad igneous 

features (sills). 

7. Recent detailed studies of nearby basaltic volcanoes in the Yucca Mountain region have 

provided an improved understanding of nominal eruptive behavior, including the style of 

lava effusion, that place controls on the nature of the possible igneous event scenarios. 

For example, the conditions necessary for explosive phreatic eruptions (maar volcanism, 

involving heating and expansion of groundwater) do not exist at Yucca Mountain. There 

is also no evidence that maar volcanoes formed near Yucca Mountain during the last 

10 million years and they are not expected in the future. 

In conclusion, there is general agreement that igneous activity may occur either in 

an extrusive or intrusive scenario. The nature of igneous activity that could occur over 

the compliance period of the repository will probably be similar in composition, 

structure, and style to the 80,000-year-old Lathrop Wells volcano, the most recent 

volcanism in the area. 

7.3. Probability of an Igneous Event Intersecting the Repository 

1. Published estimates of the probability of an igneous event intersecting the proposed 

repository range from 10-10/yr to 3×10-6/yr (see Table 5 for the full range of probability 

estimates). The 1996 DOE expert elicitation (Probabilistic Volcanic Hazard Analysis 

(PVHA)) estimated a range after adjustment for the size of the repository footprint 

(90-percent confidence interval) of 7.4 × 10-10/yr to 5.5 × 10-8/yr with a mean value of 

1.7 x 10-8/yr, which exceeds the 10-8/yr limit for screening out events. The mean value of 

seven of the ten experts was at or above the screening level. The highest estimated 

probabilities, as reported by the State of Nevada contractors, were obtained by 
174

assuming a new cluster of volcanism is about to occur, although there is no evidence of 

impending igneous activity. 

2. Claims of frequent recurrence of volcanism much higher than the PVHA results are 

inconsistent with the events known to occur during the past 1.8 million years. If the 

probability of repository intersection were 10-6/year, many (~40 to 192) eruptions should 

have occurred in the Yucca Mountain region in the last million years. Approximately four 

to 19 eruptions should have occurred in the last 100,000 years. However, only 8 events 

are known to have occurred over the past 1.8 million years and only one occurred in the 

last 100,000 years. No volcanism has occurred near Yucca Mountain since the eruption 

of the Lathrop Wells volcano 80,000 years ago and no post-Miocene (< 5.3 Ma) 

volcanism is known to have occurred at the Yucca Mountain site or in Jackass Flats. 

3. Trends in rates of crustal extension and volume of basaltic volcanism within the Yucca 

Mountain region suggest that the deep source of the igneous activity is waning, although 

the frequency of eruption has not notably decreased over the past 5 million years. 

Waning of igneous activity is consistent with the observed significant reduction in crustal 

extension rates over the last 10 million years. These changes suggest that the 

volcanism recurrence rate of the last few million years is most important to use in 

projections of future volcanic activity. Although there is some indication of a crude 

periodicity in the occurrence of igneous activity in the Yucca Mountain region, the 

existence of a periodic relationship remains a matter of differing opinions. 

4. Magnetic anomalies that were interpreted to be caused by buried basalts near Yucca 

Mountain were recently investigated by exploratory drilling. This investigation reduced 

uncertainty because it showed that most of the anomalies are either not due to basalts 

or are caused by 8- to 13-million-year-old basalts that would have limited influence on 

recurrence models based on rates of activity during the last 5 million years. These new 

results have not yet been considered in published estimates of the probability of future 

igneous intersection of the repository. Probability estimates that assumed the existence 

of numerous buried (“hidden”) basalts less than 5 million years old will now need to be 

reconsidered. 

5. Based on review of available information, the probability of intersection of the repository 

during the compliance period is believed to be in the range of 10-9/yr to 10-7/yr. An 

updated estimate is now being developed by the expert panelists of the ongoing DOE 

PVHA-U, which will incorporate the latest geophysical and drilling data and a wide range 

of views on alternative models for estimating probability. Results will include appraisal of 

the probability over one million years as well as 10,000 years. The final report of the 

PVHA update is not expected until 2008, but will provide the most up to date, credible 

estimate of the probability of igneous activity intersection with the proposed repository. 

6. The NRC has asked that the DOE provide (along with their licensing case) the results of 

a single point sensitivity analysis for extrusive and intrusive igneous processes at a 

repository intersection probability of 10-7/yr. The NRC considers that the 10-7/yr analyses 

will provide a reasonably conservative approach for evaluating risks from igneous 

activity. However, the use of a single point value fails to capture the impact of the 

uncertainty in probability estimates and could significantly limit the usefulness of the 

results and the risk insights that can be gleaned from such an analysis. 

In conclusion, the anticipated nature of future igneous events in the Yucca 

Mountain region and the record of volcanism, particularly during the past 5 million years, 

suggest a variety of alternative models for evaluating the probability of future igneous 

activity. Considering the technical bases of these views, the range of probability of an 
175

igneous event intersecting the proposed repository is believed to be between 10-9 and 

10-7/yr. The results of the ongoing PVHA-U will incorporate the latest geophysical and 

drilling data and will provide the most up-to-date, credible estimate of the probability of 

an igneous event intersecting the proposed Yucca Mountain repository. 

7.4. Consequences of an Igneous Event 

1. Consequence modeling for the intrusion scenario is evolving. This is particularly true of 

modeling the movement of magma into the drifts and of the interaction of magma with 

the waste packages and with radioactive material from breached packages in the 

intrusive scenario. The movement of magma into drifts depends on the viscosity of the 

magma and the magnitude and duration of the magma driving pressure on entry into the 

drifts. Previous studies and current views of the NRC and DOE appear to have 

underestimated the magnitude of the viscosity by as much as 105

. The magma driving 

pressure is uncertain by a factor of about 102

. Nevertheless, within these bounds 

consideration of magma physics shows that the flow of magma into the drifts would be 

sluggish, significantly slower than estimated by the DOE and NRC. The beneficial 

effects of quenching and progressive solidification of invading magma on the movement 

of magma in repository drifts and on the waste packages may also have been 

underestimated and damage to and releases from waste packages consequently 

overestimated. Likewise, the possible formation of tephra plugs in intersected drifts 

would limit the inflow of magma to drifts. This phenomenon has not been considered by 

either the DOE or NRC. Ongoing studies are clarifying these issues, but full technical 

resolution and agreement among the DOE, NRC, and other interested parties is unlikely 

before the presently planned license application date (mid-2008). 

2. The so-called “dogleg” intrusion scenario of Woods et al. (2002) is not credible. In this 

scenario, highly fluid, low-viscosity magma is assumed to enter and flow rapidly 

throughout the repository drifts, possibly breaking out to the surface at a significant 

distance from the drift entry point. But this is not the expected behavior of magma in the 

drift. Increased magma viscosity, quenching of magma on waste packages and drift 

walls, and reduction of magma pressure at a distance from the drift entry point, would 

inhibit magma from moving from the main conduit, through the repository, and to the 

surface at a secondary vent at any time during the eruptive cycle. 

3. Slightly more than half of the eruptive products of basaltic volcanoes in the Yucca 

Mountain region consists of ash that is dispersed from the eruption plume. The 

remainder occurs as volcanic cone fragments and lavas, which are resistant to erosion. 

Radioactive waste incorporated in the cone and lava flows would contribute little to dose 

to the RMEI because of this resistance to erosion. 

4. Based on the estimated size of volcanic conduits, approximately one to ten waste 

packages could be entrained within a conduit during extrusive volcanism. 

Magma/drift/waste interactions in the extrusive scenario are incompletely understood. 

Accordingly, both the DOE and NRC assume that entrained packages would be 

destroyed and the contents incorporated into volcanic ash that would be distributed 

across the surrounding countryside by prevailing winds. 

5. In the DOE and NRC performance assessment codes, the assumption is made that all 

spent fuel entrained in a volcanic conduit in the extrusive scenario would be reduced to a 

very fine powder, incorporated in tephra, and erupted into the atmosphere. However, the 

ceramic pellets that comprise spent nuclear fuel have great strength and a melting point 

of 2600o

 C, much higher than magma temperatures of about 1100o C. Also, the ejected 
176

fuel pellets and fragments may be encased in a protective layer of quenched magma, 

consistent with natural volcanic analogs of wall rock materials that have been caught up 

in the magma and brought to the surface in volcanic conduits (i.e., xenoliths). The result 

is larger fragments that are unlikely to be inhaled. 

6. The presence of backfill, either intentionally placed or as a result of drift-roof collapse, 

could be beneficial from the standpoint of intrusive volcanism because it would minimize 

contact of magma with waste packages. Backfill would not significantly alter the 

extrusive scenario because in the unlikely event that a volcanic conduit were to intersect 

a waste drift it would likely entrain both waste packages and the backfill itself. 

7. Modeling the redistribution of deposited ash by water needs to account for the 

preferential removal of the smaller-sized fraction of the ash and other volcanic ejecta 

from both the catchment and depositional areas of drainage systems. Remobilization 

models need to consider the effects of large floods in Fortymile Wash (adjacent to Yucca 

Mountain) that have historically transported sediments as far as the Amargosa River and 

beyond. Long-distance transport of contaminated ash would result in extensive dilution 

of this material by uncontaminated sediments along the Fortymile Wash-Amargosa River 

drainage system that would result in a significantly lower calculated dose to the RMEI 

than if these effects are ignored. 

In conclusion, a clear understanding of the processes involved in interaction 

between magma and drifts, waste packages, and waste is evolving and providing new 

insights, especially with regard to magma/drift/waste package interaction. As a result, 

there is limited consensus regarding the consequences of igneous activity in either the 

extrusive or intrusive scenario. The proposed alternative models differ significantly from 

each other. The application of magma physics will reduce differences and 

conservatisms particularly in the intrusive scenario. 

7.5. Uncertainties in Igneous Activity 

1. Limitations and differing interpretations of field and laboratory data cause significant 

model and parameter uncertainty in the analysis of the potential risk from igneous 

activity at the proposed Yucca Mountain repository. 

2. As a result of more than a quarter of a century of investigations of igneous activity in the 

Yucca Mountain region, uncertainties in the general nature of anticipated volcanism in 

this region are relatively small. The 80,000-year-old Lathrop Wells cone and lava flows 

provide useful analogs of possible future volcanism in the vicinity of Yucca Mountain. 

Uncertainties remain regarding the volcanic conduit size at repository depth, range of 

water content of the intruding magma, dike characteristics, etc. These parameters are 

important to probabilistic performance assessment. Uncertainties in defining conceptual 

models appear to exceed parameter uncertainty in the evaluation of probability of 

intersection with the proposed repository. 

3. Estimates of the probability of an igneous event intersecting the proposed repository 

include significant uncertainties because of difficulties in predicting the temporal 

recurrence rate as a result of limited volcanic activity over the past 5 million years and in 

identifying the spatial distribution of events due to the few igneous events that have 

occurred in the region over the last few million years. Additional uncertainties are 

caused by the failure to identify magma sources within subcrustal rocks that are the 

source of the magma, and the location of the proposed repository in the spatiallysensitive region near the boundary of the geologic/topographic Crater Flat basin 
177

structure, which has been the center of volcanic activity in the Yucca Mountain region 

over the past 5 million years.

4. Consequence models are evolving and being improved. Recent detailed geologic 

investigations of basaltic volcanoes in the Yucca Mountain region are adding significant 

new insights into processes and parameters. Improved models incorporating magma 

solidification effects on magma flow, quenching around waste packages, and the 

formation of tephra plugs in drifts are providing new information for consideration in the 

intrusive scenario. Significant uncertainties in evaluating igneous consequences due to 

model and parameter uncertainty can be reduced by proper consideration of magma 

physics. 

In conclusion, variability and uncertainty exist in evaluating conceptual models in 

estimating the probability of an igneous event intersecting the repository, and in 

estimating the consequences of such an event, particularly in the intrusive scenario. 

7.6. Alternative Models and Risk from the Proposed Repository 

1. Determining the validity of the differing professional opinions regarding igneous activity 

at Yucca Mountain and its consequences with certitude is not possible, but it is possible 

and useful to determine the bases and impact of credible alternative models and 

parameters through consideration of magma physics and geological evidence. 

2. Quantitative evaluation of the impact of specific alternative models can determine their 

significance to risk and the importance of further studies of the models and 

understanding and constraining their uncertainties. 

3. Available analyses of differing models of igneous activity processes and scenarios have 

generally not captured the importance of each model to risk. This is particularly true of 

consequence models. 

In conclusion, assessment of the performance of the proposed repository as a 

result of igneous activity requires evaluation of a range of credible views on both the 

extrusive and intrusive scenarios and the range of parameter uncertainty. These 

analyses will be useful in determining the risk from the repository as well as those 

aspects of igneous activity that are important to risk and thus worthy of further 

investigation to reduce uncertainties. Presentation of the full range of results of each 

analysis will be useful in evaluating the model and the parameters to which the analysis 

is most sensitive. 
178

 

This page intentionally blank. 
179

Table 10 Summary of views on significant igneous activity topics (organized 

by the risk triplet). This table is a simplification and generalization of 

views that are reviewed in the report. The reader is encouraged to 

read the text on each topic in the section of the report specified with 

each view. Cells in the table that are marked by dashes indicate that 

published or publicly-presented views on the topics are unavailable. 

 

TOPIC NRC DOE EPRI OTHER 

WHAT IS THE NATURE OF POTENTIAL IGNEOUS EVENTS IN THE YUCCA MOUNTAIN 

REGION? 

Igneous 

scenarios Extrusive 

(volcanic) and 

intrusive igneous 

scenarios 

(Sec. 6.2.2.3; 

6.3.2) 

Extrusive 

(volcanic) and 

intrusive igneous 

scenarios 

(Sec. 6.2.2.1; 

6.3.1 ) 

Extrusive (volcanic) 

and intrusive igneous 

scenarios 

(Sec. 6.2.2.2; 6.3.3; 

Appendix C) 

------ 

 Volcanic event Small-volume, 

single-episode 

basaltic volcano 

similar to Lathrop 

Wells volcano (< 

0.1 km3

). Multiple 

vents possible; 

possible flank 

eruptions via 

dogleg through 

the drifts of 

repository 

(Sec. 3.3.4; 4.3.3; 

4.4) 

Small-volume, 

single-episode 

basaltic volcano 

similar to Lathrop 

Wells volcano 

(< 0.1 km 3

). 

Multiple vents 

possible on single 

principal dike 

(Sec. 4.3.2; 4.4) 

Small-volume, singleepisode volcano 

similar to Lathrop 

Wells volcano 

(< 0.1 km3

 ). Multiple 

vents possible; 

vent(s) are all located 

along one dike 

(Sec. 4.3.4; 

Appendix C)

------- 

Volcanic 

conduit diameter 

 

25 to 78 m 

(average of ~51 

m) 

(Sec. 4.3.3)

Lathrop Wells 

average 8-9 m, 

with maximum 

average diameter 

of 21 m 

(Sec. 4.3.2) 

Conduit diameters 

>10 m; not expected 

below 100-150 m. 

 (Sec. 4.3.4) 

------ 
180

TOPIC NRC DOE EPRI OTHER 

Dike length 6 km (2-11 km) 

 (Sec. 4.3.3; 4.4) 

2 km (0.4-8 km); 

(Sec. 4.4) 

2.0 km (0.5-5 km) 

(Sec. 4.3.4) 

------- 

Dike width 5 m (1-10 m) 

 (Sec. 4.3.3) 

8 m (1-12 m) 

(Sec. 4.3.2) 

1.5 m (0.3-4 m) 

(Sec. 4.3.4) 

------ 

Number of dikes --------- Multiple dikes, 

spacing from 100 

to 1000 m 

(Sec. 4.3.2) 

3 dikes (1-10 dikes), 

spacing from 100 to 

690 m 

(Sec. 4.3.4) 

------ 

Controls on 

occurrence of 

igneous activity 

Nature and 

orientation of 

crustal stress, 

gravity anomalies 

(lithostatic 

pressure), faults 

(Sec. 5.4) 

Nature and 

orientation of 

crustal stress, 

faults, 

topographic 

effects 

(Sec. 5.4) 

Local stress field, 

surface topography, 

existing fractures, 

heterogeneous rock 

strength, thermally 

induced stresses 

(Sec. 5.4) 

Lithostatic 

pressure 

(Parsons et al. 

(2006)) 

(Sec. 5.4) 

WHAT IS THE PROBABILITY OF POTENTIAL IGNEOUS ACTIVITY INTERSECTING THE 

REPOSITORY? 

Time period used 

in extrapolating 

igneous activity 

------- Emphasis on last 

5 million years 

and the last 2 

million years in 

particular 

(Sec. 5.7.2) 

Adopted PVHA 

probability which 

suggests emphasis 

on last 5 million years 

(Sec. 5.7.5) 

Last 5 million 

years with 

emphasis on 

last 2 million 

years (Coleman 

et al.(2004)); 

Emphasis on 

last 5 million 

years 

(Detournay 

et al. (2003)) 

(Sec. 5.78; 

5.74) 
181

TOPIC NRC DOE EPRI OTHER 

Probability of IA 

in regulatory 

period 

(Table 5-3) 

10-7/yr for TPA 

purposes and 

license application 

review; 10-8 to 

10-7/yr with 

possibility of 

increase by an 

order of 

magnitude 

(Sec. 5.6.3; 

5.7.2)

10-9-10-7/yr; mean 

of 1.7 x 10-8/yr 

(Geomatrix 

Consultants, 

1996; now being 

updated) 

(Sec. 4.3.2; 5.6.1; 

5.7.1) 

Adopted PVHA-1996 

results; 10-9-10-7/yr, 

mean of 

1.7 x 10-8/yr 

(Sec. 5.6.2; 5.7; 

5.7.5) 

Up to 

~3 x 10-6/yr (Ho 

and Smith 

(1997)) 

(Sec. 5.7.6)

Temporal trend 

in igneous 

activity 

(waxing/waning) 

------ Waning 

(Sec. 5.2.5) 

Waning 

(Sec. 5.2.5) 

Possible waxing 

based on 

conceptual 

model [Smith 

and Keenan 

(2005)] 

(Sec. 5.2.5; 

5.7.6) 

Possible waning 

from seismic 

studies of 

mantle (Biasi, 

2005) 

(Sec. 5.4) 

WHAT ARE CONSEQUENCES OF IGNEOUS ACTIVITY INTERSECTING THE REPOSITORY? 

Magma viscosity 

upon entering 

repository 

Remains liquid for 

significant time; 

no rapid 

solidification 

(Sec. 6.2.2.4) 

Homogeneous 

flow; small 

bubbles; no rapid 

solidification; 

10-40 Pa·s 

(Sec. 6.2.1.3.1; 

6.2.2.1) 

105

-107 Pa·s for lava 

at its eruption T of 

975-1010°C; magma 

crystallizes rapidly 

and terminates flow 

(Sec. 6.2.1.3.2) 

107

 to 108 Pa·s 

(Marsh and 

Coleman 

(2008)) 

(Sec. 6.2.1.2) 

Up to 104 to 105

Pa·s (Sparks 

(2007)) 

(Sec. 6.2.1.3.3) 
182

TOPIC NRC DOE EPRI OTHER 

Magma eruption 

temperature 

------ 1150°C 

[Detournay et al. 

(2003)] 

(Sec. 6.2.1.3.3) 

975-1010°C 

(Sec. 6.2.1.3.2); 

~1000°C (Marsh 

and Coleman 

(2008)) 

(Sec. 6.2.1.1) 

1030-1055°C 

(Sparks (2007)) 

(Sec. 3.2.3) 

975-1010°C 

(Nicholis and 

Rutherford 

(2004)) 

Magma drift 

inflow rate 

10 to 100 m/s (22 

to 220 mph) 

(Sec. 6.2.2.4, 

6.2.3.4) 

10 m/s (22 mph) 

(Sec. 6.2.3.1) 

0.04 to 10 m/s 

(Appendix C, where 

EPRI cites Nicholis 

and Rutherford, 

2004) 

Number of waste 

packages 

affected: 

extrusive event 

<10 packages 

completely 

destroyed & all 

waste reduced to 

fine powder 

(Sec. 6.2.2.3)

<10 packages 

completely 

destroyed & all 

waste reduced to 

fine powder 

(Sec. 6.2.2.1) 

No mechanical 

failure, but possible 

failure by 

ovepressurization 

near conduit 

(Sec. 6.2.2.2; 6.3.3)

------ 

Number of waste 

packages 

affected: 

intrusive event 

37 packages 

(1-1402 

packageslognormal 

distribution) 

(Sec. 6.2.2.3, 

6.2.3.3) 

1600 packages 

(0-11000 

packages) 

(Sec. 6.2.2.1; 

6.2.3.1) 

0-6 packages 

engulfed by magma; 

14-24 packages 

failed by hightemperature creep 

 (Sec. 6.2.2.2; 

6.2.3.2) 

-------- 

Dogleg scenario 

with secondary 

eruption 

Possible with 50 

packages 

destroyed and 

contents entrained 

into ejects 

(Sec. 6.2.2.3; 

6.3.1) 

Dogleg model 

improbable 

(Sec. 6.2.2.4) 

Dogleg model highly 

unlikely 

(Sec. 6.3.3) 

Dogleg model 

improbable 

(Marsh and 

Coleman 

(2008)) 

(Sec. 6.2.1.3.3; 

6.2.2.3) 

Ash 

redistribution by 

wind 

Effects of 

redistribution of 

ash by wind 

transport currently 

Effects of 

redistribution of 

ash by wind 

transport 

------- ------- 
183

TOPIC NRC DOE EPRI OTHER 

being 

incorporated into 

performance 

assessment 

analysis 

(Sec. 6.4.4.1) 

incorporated into 

dose calculations 

(Sec. 6.4.4.2) 

Ash 

redistribution by 

water 

All contaminated 

ash eroded and 

transported with 

dilution to vicinity 

of compliance 

point, neglects 

transport in 

largest floods 

beyond this point 

(Sec. 6.4.3.1)

Water erosion 

and transport of 

ash with dilution 

to vicinity of 

compliance point 

and beyond 

(Sec. 6.4.3.3) 

Particles < 130 

microns would not be 

deposited at the 

compliance point 

(Sec. 6.4.3.2)

------- 

Inhaled particle 

size at RMEI 

All deposited, 

remobilized, and 

resuspended 

particles < 10 

microns contribute 

to inhalation dose 

(Sec. 6.4.3.1; 

6.4.4.1) 

All deposited, 

remobilized, and 

resuspended 

particles < 10 

microns 

contribute to 

inhalation dose 

(Sec. 6.4.3.3; 

6.4.4.2) 

Deposited material 

> 130 microns; not 

respirable 

(Sec. 6.4.3.2) 

------ 

Conversion 

factors for 

inhalation dose 

FGR and 13 

(Sec. 6.4.5) 

FGR 13 

(Sec. 6.4.5) 

ICRP 72 (equivalent 

to FGR 13) 

(Sec. 6.4.5) 

-------- 
184

This page intentionally blank. 
185

8. References 

ACNW&M, 2002, Letter to NRC Chairman R. Meserve from ACNW&M Chairman 

G. Hornberger dated August 1, 2002,”Igneous Activity Issues at the Proposed Yucca Mountain 

Repository,” NRC Accession No. ML022270114. 

ACNW&M, 2004, Letter to NRC Chairman N. Diaz from ACNW&M Chairman M. Ryan dated 

November 3, 2004, “Working Group on the Evaluation of Igneous Activity and its Consequences 

for a Geologic Repository at Yucca Mountain, Nevada,” NRC Accession No. ML043100350. 

ACNW&M, 2005, Letter to NRC Chairman N. Diaz from ACNW&M Chairman M. Ryan dated 

December 9, 2005. “Review of the NRC Program on the Risk from Igneous Activity at the 

Proposed Yucca Mountain Repository,” NRC Accession No. ML0534900650. 

ACNW&M, 2007, Review comments received on Draft ACNW&M White Paper - Igneous Activity 

at Yucca Mountain: Technical Basis for Decisionmaking, April 2007. 

ACNW&M, 2007b, “Igneous Activity at Yucca Mountain: Technical Basis for Decisionmaking,” 

Prepared by the Advisory Committee on Nuclear Waste and Materials, U.S. Nuclear Regulatory 

Commission (June 2007), Available online at: http://www.nrc.gov/reading-rm/doccollections/acnw/letters/2007/. 

Anspaugh, L. R., S. L. Simon, K. I. Gordeev, I. A. Likhtarev, R. M. Maxwell, and S. M. 

Shinkarev, 2002, “Movement of Radionuclides in Terrestrial Systems by Physical Processes,” 

Health Physics, 82, 669-678. 

Anspaugh. L. R., 2004, “Perspectives on Resuspension Modeling,” Presentation at the 153rd

ACNW&M meeting, Las Vegas, NV, September, 2004. 

Ayer, J. E., A. T. Clark, P. Loysen, M. Y. Ballinger, J. Mishima, P. C. Owczarski, W. S. Gregory, 

and B. D. Nichols, 1988, “Nuclear Fuel Cycle Facility Accident Analysis Handbook,” NUREG1320, U.S. Nuclear Regulatory Commission, Office of Nuclear Material Safety and Safeguards, 

Washington, DC. 

Benke, R. R., B. E. Hill, and D. M. Hooper, 2006, “Fluvial redistribution of contaminated tephra: 

Description of an abstracted model,” International High-Level Radioactive Waste Management 

Conference, HLRWM 2006, Las Vegas, NV, April 30-May 4, 2006. 

Biasi, G., 2005, “Tomographic imaging of the crust and upper mantle in the southern Great 

Basin – Interpretation,” Narrative to accompany the DOE PVHA – Working Group Meeting, 

Update II, February 15, 2005. 

Blakely, R. J., V. E. Langenheim, D. A. Ponce, and G. L. Dixon, 2000, “Aeromagnetic survey of 

the Amargosa Desert, Nevada and California: A tool for understanding near-surface geology 

and hydrology,” U.S. Geol. Surv. Open-File Rept. 00-188. 

Bokhove, O., A. W. Woods, and A. de Boer, 2004, “Magma flow through elastic-walled dikes,” 

CNWRA Report, NRC Accession No. ML042110072. 

Bonner, L. J., P. E. Elliott, L. P. Etchemendy, and J.R. Swartwood, 1998, “Water resources 

data, Nevada, Water Year 1997,” U.S. U.S. Geol. Surv. Water Data Rpt. NV-97-1, 636 p. 

Bradshaw, T. K., and E. I. Smith, 1994, “Polygenetic Quaternary volcanism in Crater Flat, 

Nevada,” Jour. of Volcanology and Geothermal Res., 63, 165-182. 
186

Brandeis, G., and B. D. Marsh, 1989, “The convective liquidus in a solidifying magma chamber: 

A fluid dynamical investigation,” Nature, 339, 613-616. 

Brandeis, G. and B. D. Marsh, 1990, “Transient magmatic convection prolonged by 

solidification,“ Geophys. Res. Lett., 17, 1125-1128. 

Brocher, T. M., W. C. Hunter, and V. E. Langenheim, 1998, ”Implications of seismic reflection 

and potential field geophysical data on the structural framework of the Yucca Mountain-Crater 

Flat Region, Nevada,” Geol. Soc. of Am. Bull., 105, 947-971. 

Bruce, P. M., and H. E. Huppert, 1990, “Solidification and melting along dykes by the laminar 

flow of basaltic magma,” In M.P. Ryan (ed.) Magma Transport and Storage, Wiley and Sons, 

New York, NY, 87-101. 

BSC, 2003a, “Characterize framework for igneous activity at Yucca Mountain, Nevada,” ANLMGR-GS-000001 Rev. 01C, Las Vegas, Nevada, MOL.20030711.0103. 

BSC, 2003b. “Atmospheric dispersal and deposition of tephra from a potential volcanic eruption 

at Yucca Mountain, Nevada,” Las Vegas, Nevada, MDL-MGR-GS-000002 Rev. 00D, 

MOL.20030922.0197. 

BSC, 2003c, “Characterize eruptive processes at Yucca Mountain, Nevada,” ANL-MGR-GS000002, Rev. 01.

BSC, 2003d, “Igneous intrusion impacts on waste packages and waste forms.” ANL–EBS–GS–

000002, Rev. 0, Las Vegas, Nevada.

BSC, 2004, “Dike/drift interactions,” MDL-MGR-GS-000005 Rev. 01, Las Vegas, Nevada. 

BSC, 2004b, “Characterize framework for igneous activity at Yucca Mountain, Nevada,” ANLMGR-GS-000001, Rev. 2, Las Vegas, Nevada. 

BSC, 2005, “Atmospheric dispersal and deposition of tephra from a potential volcanic eruption 

at Yucca Mountain, Nevada,” MDL-MGR-GS-000002 Rev. 02, Las Vegas, Nevada. 

BSC, 2006, “Inhalation exposure input parameters for the biosphere mode,” ANL-MGRMD000001, Rev. 4, Las Vegas, Nevada. 

Beck, D. A., and P.A. Glancy, 1995, “Overview of runoff of March 11, 1995 in Fortymile Wash 

and Amargosa River, Southern Nevada,” U.S. Geol. Surv. Fact Sheet FS-210-95.

Byers, F. M., Jr., W. J. Carr, and P. P. Orkild, 1989, “Volcanic centers of southwestern Nevada: 

Evolution of understanding, 1960-1988,” Jour. Geophys. Res., 94, 5,908-5,924. 

Carlson, R. W., 2005, “Spatial distribution: Why is volcanism where it is around Yucca 

Mountain?” Presentation at PVHA - Update Workshop, August 31, 2005.

Carr, W. J., and L. D. Parrish, 1985, ”Geology of drill hole USW VH-2, and structure of Crater 

Flat, southwestern Nevada,” U.S. Geol. Surv. Open File Rep. 85-475, 41 p. 

Calabrese, E. J. and Kenyon, E. M., 1991, “Air Toxics and Risk Assessment,” Lewis Publishers, 

Inc., Chelsea, MI., 688 p. 

Carslaw, H. S. and J. C. Jaeger, 1959, “Conduction of heat in solids, 2nd ed.,” Oxford Univ. 

Press, London, 510 p. 

CNWRA, 2004, “System-level performance assessment of the proposed repository at Yucca 

Mountain using the TPA Version 4.1 code,” CNWRA 2002-05, Rev. 2, Revised March 2004, 

NRC Accession No. ML041350316. 
187

Christiansen, R. L., P. W. Lipman, W. J. Carr, F. M. Byers, Jr., P. P. Orkild, and K. A. Sargent, 

1977, “The Timber Mountain-Oasis Caldera complex of southern Nevada,” Bull. Geol. Soc. of 

Am., 88, 943-959. 

Codell, R. B., 2004, “Alternative igneous source term model for tephra dispersal at the Yucca 

Mountain repository,” Nuclear Tech., 48, 205-212. 

Coleman, N. M., 2007, “Morphology and flood history of Fortymile Wash – Importance to 

volcanism at Yucca Mountain,” Presentation at 176th ACNW&M meeting, February 14, 2007. 

Coleman, N. and B. Marsh, 2007, “Reduced likelihood of volcanic disruption of a geologic 

repository at Yucca Mountain,“ Paper No. 3-1, Geological Society of America Abstracts with 

Programs, Vol. 39, No. 6, p. 18. 

Coleman, N. M., B. D. Marsh, and L. R. Abramson, 2004, “Testing claims about volcanic 

disruption of a potential geologic repository at Yucca Mountain, NV,” Geophys. Res. Lett., 

doi:10.1029/2004GL021032. 

Compton, K. C., 2004, “NRC staff perspective on modeling doses due to igneous events,” 

Presentation at the 153rd ACNW&M meeting, September 23rd 2004, Las Vegas, NV. 

Connor, C. B. and B. H. Hill, 1994, “Strategy for the evaluation and use of probability models for 

volcanic disruptive scenarios,” CNWRA Report 94-015, ML040160535. 

Connor, C. B., and B. H. Hill, 1995, “Three nonhomogeneous Poisson models for the probability 

of basaltic volcanism: Application to the Yucca Mountain region, NV,” Jour. Geophys. Res., 100, 

10,107– 10,125. 

Connor, C. B. and C. O. Sanders, 1994, “Geophysics review topical report: Application of 

seismic tomographic and magnetic methods to issues in basaltic volcanism,” CNWRA Report 

94-013, ML040160528.

Connor, C. B., J. A. Stamatakos, D. A. Ferrill, and B. E. Hill, 1998, “Detecting strain in the Yucca 

Mountain area (comment),” Science, 282, 1007b. 

Connor, C. B., J. Stamatakos, D. Ferrill, B. Hill, G. Ofoegbu, F. Conway, B. Sagar, and J. 

Trapp, 2000, “Geologic factors controlling patterns of small-volume basaltic volcanism: 

Application to a volcanic hazards assessment at Yucca Mountain, NV,” Jour. Geophys. Res., 

105, 417– 432. 

Connor, C. B., B. E. Hill, B. Winfrey, N. Franklin, and P. C. La Femina, 2001, “Estimation of 

volcanic hazards from tephra fallout,” Natural Hazards Review, 2, 33–42. 

Connor, L., C. Connor, and B. Hill, 2002, “PVHA_YM Ver. 2.0 – Probabilistic volcanic hazards 

assessment methods for a proposed high-level radioactive waste repository at Yucca Mtn., NV,” 

CNWRA Report, NRC Accession No. ML030240079. 

Coppersmith, K. J., 2007, “The use of expert elicitation in predicting the probability of volcanic 

events at the proposed Yucca Mountain repository – objectives, methodology, implications of 

the PVHA and PVHA-U,” Presentation at the 176th ACNW&M meeting, February 13, 2007. 

Crowe, B. M., 2005, “Revisiting temporal models: Uncertainty perspectives,” Proceedings of 

PVHA – Update Workshop #2A, August 31, 2005. 

Crowe, B. M., M. E. Johnson, and R. J. Beckman, 1982, “Calculation of the probability of 

volcanic disruption of a high-level radioactive waste repository within southern Nevada, USA,” 

Radioactive Waste Management & Nuclear Fuel Cycle, 3, 167–190. 
188

Crowe, B.M., S. Self, D. Vaniman, R. Amos, and F. Perry, 1983, “Aspects of potential magmatic 

disruption of a high-level radioactive waste repository in southern Nevada,” Jour. of Geol., 91, 

259-276. 

Crowe, B. M., F. V. Perry, G. A. Valentine, P. C. Wallmann, and R. Kossik, 1993, “Simulation 

modeling of the probability of magmatic disruption of the potential Yucca Mountain Site,” In 

Proceedings of the Topical Meeting on Site Characterization and Model Validation, FOCUS '93, 

September 26-29, 1993, Las Vegas, Nevada, 182-191, La Grange Park, Illinois, American 

Nuclear Society. 

Crowe, B. and nine others, 1995, “Status of volcanism studies for the Yucca Mountain site 

characterization project,” Report of the Las Alamos National Laboratory LA-12908-MS.

Crowe, B. M., P. Wallmann, and L. M. Bowker, 1998, “Probabilistic modeling of volcanism data: 

Final volcanic hazard studies for the Yucca Mountain site,” in Perry, F.V., et al. (eds.), 

Volcanism studies: Final report for the Yucca Mountain project: Los Alamos National Laboratory 

Report, LA-13478, 415 p. 

Crowe, B. M., G. A. Valentine, F. V. Perry, and P. K. Black, 2006, “Volcanism: The continuing 

saga,” In A. Macfalane and R. Ewing (eds.), Uncertainty Underground – Yucca Mountain and 

the Nation’s High-Level Nuclear Waste, MIT Press, Cambridge, MA, 131-148. 

CRWMS M&O, 1998, “Synthesis of volcanism studies for the Yucca Mountain site 

characterization project,” Deliverable 3781MR1, Las Vegas, Nevada, MOL.19990511.0400. 

CRWMS M&O, 2000a, “Yucca Mountain site description document, Section 7—Surface Water 

Hydrology,” TDR–CRW–GS–000001, Rev. 01 ICN 01, Las Vegas, Nevada. 

CRWMS M&O, 2000b, “Total system performance assessment for the site recommendation,” 

TDR–WIS–PA–000001. Rev. 00 ICN 01, Las Vegas, Nevada. 

CRWMS M&O, 2000c, “Features, events, and processes in UZ flow and transport,” ANL-NBSMD-000001 Rev. 00, Las Vegas Nevada. 

CRWMS M&O, 2001, “Geochemical and isotopic constraints on groundwater flow directions, 

mixing, and recharge at Yucca Mountain, Nevada,” ANL-NBS-HS-000021, Las Vegas, Nevada. 

Dartevelle, S., and G.A . Valentine, 2005, “Early-time multiphase interactions between basaltic 

magma and underground openings at the proposed Yucca Mountain radioactive waste 

repository,” Geophys. Res. Lett., doi:1029/2005GL0241172. 

Dartevelle, S. and G.A. Valentine, 2007, “Transient multiphase processes during the explosive 

eruption of basalt through a geothermal borehole (Namafjall, Iceland, 1977) and implications for 

natural volcanic flows,” Earth and Planetary Science Lett., Vol. 262, Issues 3-4, 363-384. 

Decker, R. and B. Decker, 1997, “Volcanoes,” Freeman, San Francisco, CA, 321 pp. 

Delaney, P. T., and D. D. Pollard, 1981, “Deformation of host rocks and flow of magma during 

growth of minette dikes and breccia-bearing intrusions near Ship Rock, New Mexico,” U.S. 

Geol. Surv. Prof. Paper 1201, Washington, D.C., 61 pp. 

Delaney, P. T., and D. D. Pollard, 1982, “Solidification of basaltic magma during flow in a dike,” 

Am. Jour. of Sc., 282, 856-885. 

Delaney, P. T., and A. E. Gartner, 1997, “Physical processes of shallow mafic dike 

emplacement near the San Rafael Swell, Utah,” Bull. Geol. Soc. of Am., 109, 1172-1192. 

Del Marmol, M., 1989, “The petrology and geochemistry of Merapi volcano, central Java, 

Indonesia,” Ph.D., Dissertation, Johns Hopkins University, 384 p. 
189

Detournay, E., L. G. Mastin, J.R. Anthony Pearson, A. M. Rubin, and F. J. Spera, 2003, “Final 

report [April 2003] of the [Yucca Mountain] Igneous Consequences Peer Review Panel,” 86 p. 

Dickinson, W. R., 2006, “Geotectonic evolution of the Great Basin,” Geosphere, 2, 353-368; doi: 

10.1130/GES00054.1. 

DOE, 1997, “Site characterization progress report: Yucca Mountain, Nevada,” Number 15, 

DOE/RW-0498, Washington, DC, Office of Civilian Radioactive Waste Management. 

DOE, 1999, “MGR external events hazards analysis,” ANL-MGR-SE-000004, Rev. 00, CRWMS 

M&O, Las Vegas, Nevada. 

DOE, 2000. “ASHPLUME: Characterize eruptive processes at Yucca Mountain, Nevada,” ANLMGR-GS-000002, Las Vegas, Nevada. 

DOE, 2002a, “Final environmental impact statement for a geologic repository at Yucca 

Mountain, Nye County, Nevada,” DOE/FEIS-0250.

DOE, 2002, “Yucca Mountain science and engineering report: Technical Information supporting 

site recommendation consideration,” Rev. 1, U. S. Dept. of Energy, DOE/RW-0539-1, available 

online at http://www.ocrwm.doe.gov/documents/ser_b/index.htm. 

DOE, 2003, “Volcanic events, technical basis document 13, Bechtel SAIC Co., LLC, Las 

Vegas, Nevada, Available at: http://www.ocrwm.doe.gov/documents/38453_tbd/index.htm. 

DOE, 2006, “Probabilistic volcanic hazard analysis update field guide, May 1-4, 2006,” Handout 

at PVHA-U meeting prior to field trip. 

Doubik, P., and B. Hill, 1999, “Magmatic and hydromagmatic conduit development during the 

1975 Tolbachik eruption, Kamchatka, with implications for hazards assessment at Yucca 

Mountain, NV,” Jour. of Volcanology and Geothermal Res., 91, 43-64. 

Eckerman, K. F. and J. C. Ryman, 1993, “External exposure to radionuclides in air, water, and 

soil,” U.S. EPA, Washington, DC. 

Eckerman, K. F., R. W. Leggett, C. B. Nelson, J. S. Puskin, and A. C. B. Richardson, 1999, 

“Cancer risk coefficients for environmental exposure to radionuclides,” U.S. EPA, Washington, 

DC. 

EPA, 1993, “40 CFR Part 191, Environmental radiation protection standards for the 

management and disposal of spent nuclear fuel, high-level and transuranic radioactive wastes,” 

Federal Register 58 FR 66398, December 20, 1993, Washington, D.C. 

EPA, 2001, “40 CFR Part 197: Public health and environmental radiation protection standards 

for Yucca Mountain Nevada, Final Rule,” Federal Register 66, 32074-32135, Washington, DC. 

EPA, 2005, “40 CFR 197 Public health and environmental radiation protection standards for 

Yucca Mountain Nevada, proposed rule,” Federal Register 70, 49014-49065, Washington, DC. 

EPRI (Electric Power Research Institute), 2003a, “Igneous event scenario,” Tech. Update Rept. 

1007898, December, 2003. 

EPRI, 2003b, “Scientific and technical priorities at Yucca Mountain,” Tech. Rept. 1003335, 

December, 2003. 

EPRI, 2004, “Potential igneous processes relevant to the Yucca Mountain repository: Extrusiverelease scenario, analysis and implications,” Tech. Rept. 1008169. 

EPRI, 2005, “Program on technology innovation: Potential igneous processes relevant to the 

Yucca Mountain repository: Intrusive-release scenario,” Tech. Rept. 1011165. 
190

EPRI, 2007, “Program on technology innovation: EPRI Yucca Mountain spent fuel repository 

evaluation, 2007 progress report,” Electric Power Research Institute, Palo Alto, CA. 

Evans, J.R., and M. Smith, III, 1992, “Teleseismic tomography of the Yucca Mountain region: 

volcanism and tectonism,” American Nuclear Society, Proceedings of the Third Annual 

International Conference on High-Level Radioactive Waste Management, 2, 2372-2380. 

Evans, J.R., and M. Smith, III, 1995, “Teleseismic investigations, Chapter 7, Major results of 

geophysical investigations at Yucca Mountain and vicinity, southern Nevada,” In Oliver, H.W., D. 

A. Ponce, and W. C. Hunter (eds.), U.S. Geol. Surv. Open-File Report 95-74, 135-156. 

Farmer, G. L., F. V. Perry, S. Semken, B. Crowe, D. Curtis, and D. J. DePaolo, 1989, “Isotopic 

evidence on the structure and origin of subcontinental lithospheric mantle in Southern Nevada,” 

Jour. Geophys. Res., 94, 7885-7898. 

Faulds, J.E., J. W. Bell, D. Feuerbach, and A. R. Ramelli, 1994, “Geologic map of part of Crater 

Flat, southern Nevada,” Nevada Bureau of Mines and Geology Map 101, 1:24,000. 

Fenelon, J. M. and M. T. Moreo, 2002, “Trend analysis of ground-water levels and spring 

discharge in the Yucca Mountain region, Nevada and California, 1960-2000,” U.S. Geol. Surv. 

Water-Resources Investigations Report 02-4178, 97 p, Available at: 

http://pubs.usgs.gov/wri/wrir024178/wrir024178.pdf. 

Ferrill, D. A., J. A. Stamatakos, S. M. Jones, B. Rahe, H. L. McKague, R. H. Martin, and A. P. 

Morris, 1996, “Quaternary slip history of the Bare Mountain fault (Nevada) from the morphology 

and distribution of alluvial fan deposits,” Geology, 24, 559-562. 

Ferrill, D. A., J. A. Stamatakos, and D. Sims, 1999, “Normal fault corrugation: Implications for 

growth and seismicity of active normal faults,” Jour. Struct. Geol., 21, 1027-1038. 

Fink, J. H., and R. W. Griffiths, 1998, “Morphology, eruption rate and rheology of lava domes: 

Insights from laboratory models,” Jour. Geophys. Res., 103, 527-545. 

Fisher, R. V., G. Heiken, and J. B. Hulen, 1997, “Volcanoes: Crucible of Change,” Princeton 

University Press, Princeton, NJ, 317 p. 

Fiske, R. and E. Jackson, 1972, “Orientation and growth of Hawaiian volcanic rifts: the effect of 

regional structure and gravitational stresses,” Proc. R. Soc. London A, 329, 299-326. 

Fleck, R. J., B. D. Turrin, D. A. Sawyer, R. G. Warren, D. E. Champion, M. R. Hudson, and S. A. 

Minor, 1996, “Age and character of basaltic rocks of the Yucca Mountain region, southern 

Nevada,” Jour. Geophys. Res., 101, 8205-8227. 

Folk, R. L., 1980, “Petrology of Sedimentary Rocks,” Hemphill Publishing Company, Austin, 

Texas, 182 p. 

Forrester, Y., 2005, “The quality of expert judgment: An interdisciplinary investigation, “ Ph.D. 

dissertation, Univ. of Maryland, Available at: http://hdl.handle.net/1903/3267. 

Fridrich, C., J. Whitney, M. Hudson, and B. Crowe, 1999, “Space-time patterns of L. Cenozoic 

extension, vertical axis rotation, and volcanism in the Crater Flat Basin, SW Nevada,” In 

Cenozoic Basins of the Death Valley Region, Geol. Soc. of Am. Spec. Pap. 333, 197–212. 

Gaffney, E. S. and B. Damjanac, 2006, “Localization of volcanic activity: Topographic effects on 

dike propagation, eruption and conduit formation,” Geophys. Res. Lett., 33, L14313, 

doi:10.1029/2006GL026852. 

Gaffney, E. S., B. Damjanac, and G. A. Valentine, 2007, “Localization of volcanic activity: 2. 

Effects of pre-existing structure,” Earth and Planetary Sc. Lett., v. 263, 323-338. 
191

Garrick, B. J., and S. Kaplan, 1995, “Radioactive and mixed waste: Risk as a basis for waste 

classification,” National Council of Radiation Protection and Measurements Symposium 

Proceedings No. 2, Bethesda, MD, NCRP, 59-73. 

Gay, E. C., P. A. Nelson, and W. P. Armstrong, 1969, “Flow properties of suspensions with high 

solid concentrations,” Am. Inst. of Chem. Eng. Jour., 15, 815-822. 

Geomatrix Consultants, 1996, “Probabilistic volcanic hazard analysis for Yucca Mountain, NV,” 

Rep. BA0000000-1717-2200-00082, Rev. 0, San Francisco, CA. 

Glancy, P. A., and D. A. Beck, 1998, “Modern flooding and runoff of the Amargosa River, 

Nevada-California, emphasizing contributions of Fortymile Wash,” In E.M. Taylor (ed.), 

Quaternary Geology of the Yucca Mountain Area, Southern Nevada, Friends of the Pleistocene, 

Pacific Cell, October 1998, Field Trip Guide, 51-62. 

Grauch, V. J. S., D. A. Sawyer, and C. J. Fridrich, 1999, “Southwestern Nevada volcanic field 

and hydrogeologic implications,” U.S. Geol. Surv. Prof. Paper 1608, 39 pp. 

Griffiths, R. W., 2000, “The dynamics of lava flow,” Annu. Rev. Fluid Mech., 32, 477-518. 

Hallett, R. B., 1992, “Volcanic geology of the Rio Puerco Necks,” In S.G. Lucas, B.S. Kues, T.E. 

Williamson, and A.P. Hunt (eds.), San Juan Basin IV: New Mexico Geological Society, 43rd 

Annual Field Conference, September 30-October 3, 1992, 135-144, New Mexico Geological 

Society. 

Hardy, M. P., and S. J. Bauer, 1991, “Rock mechanics considerations in designing a nuclear 

waste repository in hard rock,” U.S. Symposium on Rock Mechanics, Rept. SAND-91-2853C,

Sandia National Laboratories, Albuquerque, NM, 19 pp. 

Heizler, M. T., F. V. Perry, B. M. Crowe, L. Peters, and R. Appelt, 1999, “The age of the Lathrop 

Wells volcanic center: An 40Ar/39Ar dating investigation,” Jour. Geophys. Res. 104, 767-804. 

Hill, B. E.,1995, “Expert–panel review of CNWRA volcanism research programs,” CNWRA Rept. 

95–002, NRC Accession No. ML040160679. 

Hill, B. E., C. B. Connor, M. S. Jarzemba, P. C. La Femina, M. Navarro, and W. Strauch, 1998, 

“1995 eruptions on Cerro Negro volcano, Nicaragua, and risk assessment for future eruptions,” 

Bull. Geol. Soc. of Am., 110, 1231-1241. 

Hill, B. E., 2007, “NRC perspective on the risk significance of potential consequences from 

igneous activity,” Presentation at the 176th ACNW&M meeting, February 14, 2007. 

Hill, B. E. and C. B. Connor, 2000, “Technical basis for resolution of the igneous activity key 

technical issue,” CNWRA Rept., NRC Accession No. ML011930254. 

Hill, B. E., and J. A. Stamatakos, 2002, “Evaluation of geophysical information used to detect 

and characterize buried volcanic features in the Yucca Mountain region,” CNWRA Rept., 

Washington, D. C. 

Hinze, W. J., B. D. Marsh, R. F. Weiner, and N. M. Coleman, 2008, “Evaluating Igneous Activity 

at Yucca Mountain,” Eos, Transactions, Vol. 89, No. 4, Amer. Geophys. Union (22 Jan. 2008). 

Ho, C.-H., 1992, “Risk assessment for the Yucca Mountain high-level nuclear waste repository 

site: Estimation of volcanic disruption,” Math. Geol., 24, 347-364. 

Ho, C.-H., E. I. Smith, D. L. Feuerbach, and T. R. Naumann, 1991, “Eruptive probability 

calculation for the Yucca Mountain site, USA: Statistical estimation of recurrence rates,” Bull. of 

Volcanology, 54, 50-56. 
192

Ho, C.-H., and E. I. Smith, 1997, “Volcanic hazard assessment incorporating expert knowledge: 

Application to the Yucca Mountain region, NV, USA,” Math. Geol., 29, 615–627. 

Ho, C.-H., and E. I. Smith, 1998, “A spatial-temporal/3-D model for volcanic hazard assessment: 

Application to the Yucca Mountain region, NV,” Math. Geol., 30, 497–510. 

Ho, C.-H., E.I. Smith, and D.L. Keenan, 2006, “Hazard area and probability of volcanic 

disruption of the proposed high-level radioactive waste repository at Yucca Mountain, Nevada, 

USA,” Bull. of Volcanology, DOI 10.1007/s00445-006-0058-5. 

Hon, K., J. Kauahikaua, J. Denlinger, and K. Mackay, 1994, “Emplacement and inflation of 

pahoehoe sheet flows: Observations and measurements of active lava flows on Kilauea 

Volcano, Hawaii,” Geol. Soc. of Amer. Bull., 106, 351-370. 

Hooper, D. M., 2005, “Modeling the long-term fluvial redistribution of tephra in Fortymile Wash, 

Yucca Mountain, Nevada,” CNWRA Rept. 

Hort, M., B. D. Marsh, R. G. Resmini, and M. K. Smith, 1999, “Convection and crystallization in 

a liquid cooled from above: An experimental and theoretical study,” Jour. Petrology, 40, 1,271-

1,300. 

Huppert, H. E., 1982, “Flow and instability of a viscous current down a slope,” Nature, 300, 427-

429. 

Huppert, H. E., J. B. Shepherd, H. Sigurdsson, and S. Sparks, 1982, “On lava dome growth, 

with application to the 1979 Lava extrusion of the Soufriere of St. Vincent,” Journal of 

Volcanology and Geothermal Res., 14, 199-222. 

International Commission on Stratigraphy, 2005, International Stratigraphic Chart, Available at: 

http://www.stratigraphy.org/chus.pdf. 

Jaeger, J.C.,1968, “Cooling and solidification of igneous rocks,” In H. H. Hess and A. 

Poldervardt (eds.), Basalts: the Poldervaart Treatise on Rocks of Basaltic Composition, v. 2, 

503-536, Interscience, 1968. 

Jaeger, J. C., and N. G. W. Cook, 1979, “Fundamentals of rock mechanics,” Chapman and Hall, 

New York, NY, 539 pp. 

Jarzemba, M. S., and P. A. LaPlante, 1996, “Preliminary calculations of expected dose from 

extrusive volcanic events at Yucca Mountain,” CNWRA Rept., NRC Accession No. 

ML040220041. 

Jarzemba, M. S., 1997, “Stochastic Radionuclide Distributions after a Basaltic Eruption for 

Performance Assessments of Yucca Mountain,” Nuclear Technology, v. 118, 132–141, 

American Nuclear Society, La Grange Park, Illinois. 

Kaplan, S., and B. J. Garrick, 1981, “On the quantitative definition of risk,” Risk Analysis, v. 1, 

11-27. 

Keating, G. N., and G. A. Valentine, 1998, “Proximal stratigraphy and syn-eruption faulting in 

rhyolitic Grants Ridge Tuff, New Mexico, USA,” Jour. of Volcanology and Geothermal Res., 81, 

37-49. 

Killough, G. G., and P. S. Rohwer, 2005, “Comment (and reply) on Moeller et al. (2005), 

Impacts of stable element intake on 14C and 129I dose estimates,” Health Physics, v. 90, 273-

276. 
193

Kokajko, L. E., 2005, “Staff Review of U.S. Department of Energy Response to Igneous Activity 

Agreement Item IA.2.17,” Letter with Enclosures (January 10) to J.D. Ziegler, DOE, Washington, 

DC, U.S. Nuclear Regulatory Commission, Washington, DC. 

Kokajko, L. E., 2005b, “Letter dated January 10, 2005 to J. D. Ziegler (U.S. DOE) titled Staff 

Review of US Department of Energy Response to Igneous Activity Agreement item IA 2.18,” 

NRC Accession No. ML043500588. 

Kotra, J. P., Lee, M. P., Eisenberg, N. A., De Wispelare, A. R., 1996, “Branch Technical Position 

on the Use of Expert Elicitation in the High-Level Radioactive Waste Program,” NUREG-1563, 

U.S. Nuclear Regulatory Commission, Washington, DC. 

Krier, D., G. A. Valentine, F. V. Perry, and G. Heiken, 2006, “Eruptive and geomorphic 

processes at Lathrop Wells scoria cone volcano,” EOS Trans. Am. Geophys. Un., 87, Fall Meet. 

Suppl., Abstract V51 A-1663. 

Larsen, G., K.. Grönvold, and S. Thorarinsson, 1979, “Volcanic eruption through a geothermal 

borehole at Námafjall, Iceland,” Nature, 278, 707-710, DOI:10.1038/278707a0. 

Lee, M.P., N. M. Coleman, and T. J. Nicholson, 2005, “History of water development in the 

Amargosa Desert area: A literature review,” U.S. Nuclear Regulatory Commission, NUREG1710, Vol. 1, February 2005. 

Leggett, R. W., and K. F. Eckerman, 2003, “Dosimetric significance of the ICRP’s updated 

guidance and models, 1989-2003, and Implications for U.S. Federal Guidance,” ORNL/TM2003/207, Oak Ridge National Laboratory, Oak Ridge, TN. 

Lejeune, A. M., A. W. Woods, R. S. J. Sparks, B. E. Hill, and C. B. Connor, 2002, “The 

decompression of volatile-poor basaltic magma from a dike into a horizontal subsurface tunnel,” 

CNWRA Rept., NRC Accession No. ML033640075. 

Lescinsky, D. T., and O. Merle, 2005, “Extensional and compressional strain in lava flows and 

the formation of fractures in surface crust,” In M. Manga and G. Ventura (eds.), Geol. Soc. of 

Am., Spec. Pap. 396, 163-179. 

Lewis, R. J. 1993, Hawley’s Condensed Chemical Dictionary, Twelfth Edition. Van Nostrand 

Reinhold, New York, NY,1200 p. 

Lipman, P. W., 2007, “Incremental assembly and prolonged consolidation of Cordilleran magma 

chambers: Evidence from the Southern Rocky Mountain volcanic field,” Geosphere, 3, 42-70; 

doi:10.1130/GES00061.1. 

Lore, J., H. Gao, and A. Aydin, 2000, “Viscoelastic thermal stress in cooling basalt flows,“ Jour. 

Geophys. Res., v. 105, 23695-23709. 

Mangan, M., and B. D. Marsh, 1992, “Solidification front fractionation in phenocryst-free sheetlike magma bodies,” Jour. of Geology, v. 100, 605-620. 

Manley, C. R., 1992, “Extended Cooling and viscous flow of large, hot rhyolite lavas: 

implications of numerical modeling results,” Jour. of Volcanology and Geothermeral Res., 53, 

27-56. 

Manteufel, R. D., R. G. Baca, S. Mohanty, M. S. Jarzemba, R. W. Janetzke, S. A. Stothoff, C. B. 

Connor, G. A. Cragnolino, A. H. Chowdhury, T. J. McCartin, and T. M. Ahn, 1997, “Total-System 

Performance Assessment (TPA) Version 3.0 Code: Module Descriptions and User’s Guide,” 

CNWRA Rept., NRC Accession No. ML040200150. 

Marsh, B. D., 1981, “On the crystallinity, probability of occurrence, and rheology of lava and 

magma,” Contr. Min. Pet., v. 78, 85-98. 
194

Marsh, B. D., 1989, “Convective style and vigour in magma chambers,” Jour. Petrology, 30, 

479-530. 

Marsh, B. D., 1990, “Atka, Central Aleutian Islands,” In C.A. Wood and J. Kienle (eds.) 

Volcanoes of North America, United States and Canada, Cambridge University Press, New 

York, NY. 

Marsh, B. D., 2000, “Magma Chambers,” Encyclopedia of Volcanoes, Academic Press, 191-

206. 

Marsh, B. D., 2002, “On bimodal differentiation by solidification front instability in basaltic 

magmas, part I: basic mechanics,” Geochimica et Cosmochimica Acta, v. 66, 2211-2229. 

Marsh, B. D., 2004, “A magmatic mush column rosetta stone: The McMurdo Dry Valleys of 

Antarctica,” EOS, Trans. Am. Geophys. Un., v. 85,. 497-502. 

Marsh, B. D., 2006, “Dynamics of Magma Chambers,” Elements, v. 2, 287-292. 

Marsh, B. and N. Coleman, 2006, “Near-surface eruptive state of wet versus dry magma.” 

Paper No. 183-1, Geol. Soc. of Am. Abstr. with Programs, v. 38, 445. 

Marsh, B.D. and N. M. Coleman, 2008, “Magma Flow and Interaction with Waste Packages in a 

Geologic Repository at Yucca Mountain, Nevada,” Paper submitted (January) to Journal of 

Volcanology and Geothermal Research. 

Mastin, L. G. and M. S. Ghiorso, 2001, “Adiabatic temperature changes on magma–gas 

mixtures during ascent and eruption,” Contr. Min. Pet., v. 141, 307-321. 

McBirney, A. R., 2005, “Hazards of phreato-magmatic eruptions,” Presentation at the PVHA – 

Update Workshop 2A, August 30-31, 2005. 

McBirney, A. R., 2007, “Igneous Petrology (3rd Edition),” Jones and Bartlett Publishers, Boston, 

MA, 550 p. 

McKague, H. L., 1998, “Transmittal of Administrative Item, Summary of CNWRA Workshop on 

the Consequences of Volcanic Activity (AI 20-1402-461-831),” Letter from H. L. McKague 

(CNWRA) to J. Trapp (NRC), August 17, 1998, NRC-02-97-009, with enclosures, NRC 

Accession No. ML033600146. 

McKague, H. L., D. Ferrill, K. Smart, J. Stamatakos, D. Waiting, and B. Hill, 2006, “Tectonic 

Model Synthesis Report for the Yucca Mountain Region,” CNWRA Rept., San Antonio, TX. 

Melson, W., 2002. Memo to Leon Reiter, "Report on Meeting of the Volcanic Consequences 

Peer Review: Presentation of Interim Report, September 8, 2002, Las Vegas, NV," September 

23, 2002, Available at http://www.nwtrb/meetings/melson.pdf. 

Melson, W., 2003, Memo to Leon Reiter, “Comments on "Final Report of the Igneous 

Consequences Peer Review Panel", Presented in Las Vegas, February 26, 2002. 

Merriam-Webster, 1988. Webster’s Ninth Collegiate Dictionary, Merriam-Webster, Springfield, 

MA.. 

Moeller, D.W. and M.T. Ryan, 2004, ”Limitations on upper bound dose to adults due to intake of 

129I in drinking water and a total diet – Implications relative to the proposed Yucca Mountain high 

level radioactive waste repository,” Health Physics, v. 86, 586-589. 

Moeller, D. W. and M. T. Ryan, 2005, “Sensitivity analyses of the standards for the proposed 

Yucca Mountain repository – A review, evaluation, and commentary,” Health Physics, v. 88, 

459-468. 
195

Moeller, D. W., M. T. Ryan, L-S C. Sun, and R. N. Cherry, Jr., 2005, “Impacts of stable element 

intake on 14C and 129I dose estimates,” Health Physics, v. 89, 349-354. 

Mohanty, S., 1999, “Change pages to the Total-System Performance Assessment (TPA) 

Version 3.2 code: Module descriptions and user’s guide, January 11, 1999,” CNWRA Rept., 

NRC Accession No. ML033630530. 

Mohanty, S. and T. McCartin, 1998, “Total-System Performance Assessment (TPA) version 3.2 

code: Module description and user’s guide,” CNWRA Rept., NRC Accession No. ML040260387. 

Mohanty, S., T. J. McCartin, and D. W. Esh, 2002, “Total-System Performance Assessment 

(TPA) version 4.0 code: Module descriptions and user’s guide,” CNWRA Rept., NRC Accession 

No. ML031680620. 

Mohanty, S., R. Codell, J.M. Menchaca, R. Janetzke, M. Smith, P. LaPlante, M. Rahimi, and A. 

Lozano, 2004, “System-Level Performance Assessment of the proposed repository at Yucca 

Mountain using the TPA version 4.1 code,” CNWRA Rept. 2002–05, Rev. 2, San Antonio, 

Texas, NRC Accession No. ML041350316. 

Mohanty, S., R. Benke, R. Codell, K. Compton, D. Esh, D. Gute, L. Howard, T. McCartin, O. 

Pensado, M. Smith, G. Adams, T. Ahn, P. Bertetti, L. Browning, G. Cragnolino, D. Dunn, R. 

Fedors, B. Hill, D. Hooper, P. LaPlante, B. Leslie, R. Nes, G. Ofoegbu, R. Pabalan, R. Rice, J. 

Rubenstone, J. Trapp, B. Winfrey, and L. Yang, 2005, “Risk analysis for risk insights progress 

report,” CNWRA Rept., San Antonio, TX. 

Molecke, M. A., J. E. Brockmann, D. E. Lucero, M. Steyskal, M. W. Gregson, M. C. Nillone, T. 

Burtseva, W. Koch, O. Nolte, G. G. Pretzsch, W. Bruecher, B. A. Autrusson, and O. Loiseau, 

2006, “Spent fuel sabotage aerosol test program: FY2005-2006 testing and aerosol data 

summary,” SAND2006-56, Sandia National Laboratories, Albuquerque, NM. 

Mooney, M., 1951, “The viscosity of a concentrated suspension of spherical particles,” Jour. of 

Colloid and Interface Sc., v. 6, 162-170. 

Morrissey, M., 2006, “Natural analogs for future volcanism in the Yucca Mountain region,” 

Proceedings of the 11th International High-Level Radioactive Waste Management Conference, 

Las Vegas, NV, May 2006. 

Nairn, I.A., 1976, “Atmospheric shock waves and condensation clouds from Nguaruhoe 

explosive eruptions,” Nature, v. 259, 190-192. 

Napier, B. A.., R. A.. Peloquin, D. L. Strenge, and J. V. Ramsdell, 1988, ”GENII: The Hanford 

environmental radiation dosimetry software system,” Vols. 1, 2, and 3, Conceptual 

Representation, User’s Manual, and Code Maintenance Manual, PNL Rept.-6584, Pacific 

Northwest National Laboratory, Richland, WA. 

National Research Council, 1995, “Technical Bases for Yucca Mountain Standards, “ National 

Academy Press, Washington, D.C, 205 pp. 

Neuendorf, K. K. E., J. P. Mehl, Jr., and J. A. Jackson, 2005, “Glossary of Geology (5th Ed.),” 

American Geological Institute, Alexandria, VA, 779 pp. 

NEI (Nuclear Energy Institute), 2006, “Common objections to the Yucca Mountain Project, and 

what the science really says,” Available at http://www.nei.org/doc.asp? catnum=2&catid=197. 

Neuhauser, K.. S., F. L. Kanipe, and R. F. Weiner, 2000, “RADTRAN5: Technical Manual,” 

Rept. no. SAND2000-1256, Transportation Safety and Security Analysis Department, Sandia 

National Laboratory, Albuquerque, NM, 148 pp., Available at: https://radtran.sandia.gov/docs/ 

SAND2000-1256.pdf. 
196

Nicholis, M. G. and M. J. Rutherford, 2004, “Experimental constraints on magma ascent rate for 

the Crater Flat volcanic zone hawaiite,” Geology, v. 32, 489-492. 

NRC (U.S. Nuclear Regulatory Commission), 1999, “Issue Resolution Status Report, Key 

Technical Issue: Igneous Activity, Rev. 2,” Division of Waste Management, Washington, DC. 

NRC, 2004, “Risk insights baseline report,” NRC Accession no. ML040560162, Division of 

Waste Management, Washington, DC, Available at: http://www.nrc.gov/waste/hlw-disposal/reginitiatives/ml040560162.pdf. 

NRC, 2005a, “Integrated issue resolution status report,” NUREG-1762, Vol. 1 and 2, Rev. 1, 

Office of Nuclear Material Safety and Safeguards, Washington, D.C., Available at: 

http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1762. 

NRC, 2005b, ”Rulemaking issue SECY-05-0144, proposed rule; 10 CFR 63 Implementation of a 

Dose Standard after 10,000 Years,” Washington, DC. 

NRC, 2007, “U. S. Nuclear Regulatory Commission staff perspectives on ACNW draft white 

paper on igneous activity at Yucca Mountain,” NRC Accession No. ML070600793. 

NRC, 2007a, “Total-System Performance Assessment (TPA) Version 5.1 Module Descriptions 

and User Guide,” NRC Accession No. ML072710060025. 

NWTRB (Nuclear Waste Technical Review Board), 2001, “Letter of Jared L. Cohon to the Hon. 

Dennis J. Hastert,” April, 2001. 

NWTRB (Nuclear Waste Technical Review Board), 2002, “Report to the U.S. Congress and 

Secretary of Energy, January 1, 2001 to January 31, 2002.” 

NWTRB (Nuclear Waste Technical Review Board), 2003, “Letter of Michael L. Corradini to Dr. 

Margaret S. Y. Chu, December 16, 2003.” 

NWTRB (Nuclear Waste Technical Review Board), 2004, “Enclosure in letter of B. John 

Garrick to the Hon. Dennis J. Hastert, December 30, 2004”. 

OECD [Organization for Economic Co-operation and Development], 2002. “An international 

peer review of the Yucca Mountain project TSPA-SR Total System Performance Assessment 

for the site recommendation (TSPA-SR) - A joint report by the OECD Nuclear Energy Agency 

and the International Atomic Energy Agency,” Available at: http://www.nea.fr/html/rwm/reports/ 

2002/nea3682-yucca.pdf. 

Office of Technology Assessment (OTA), 1985, “Managing the Nation’s Commercial High-Level 

Radioactive Waste,” U.S. Congress, Washington, DC 

O’Leary, D. W., 1996, “Synthesis of tectonic models for the Yucca Mountain area,” Chapter 8 in 

Seismotectonic Framework and Characterization of Faulting at Yucca Mountain, Nevada (J.W. 

Whitney, Coordinator), U.S Geol. Surv. Rept. to the U.S. Department of Energy, WBS Number 

1.2.3.2.8.3.6, 153 pp. 

O’Leary, D. W., 2001, “Tectonic controls on basaltic volcanism near Yucca Mountain, Nevada,” 

Geol. Soc. of Am. Annual Meeting, November 2001, Abst. No. 162-0, Available at: 

http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_20245.htm. 

O’Leary, D. W., 2007a, “Tectonic models for Yucca Mountain, Nevada,” in J.S. Stuckless and 

R.A. Levich (eds.), The Geology and Climatology of Yucca Mountain and Vicinity, Southern 

Nevada and California, Geol. Soc. of Am., Memoir 199, 105-153, doi: 10.1130/2007.1199(04). 
197

O’Leary, D. W., 2007b, “Crater Flat basin as a propagating rift in the Amargosa Trough, 

Nevada,” Abst. and Presentation at the 2007 Devils Hole Workshop, Furnace Creek, California, 

May 2-3, 2007. 

O’Leary, D. W., E. A. Mankinen, R. J. Blakely, V. E. Langenheim, and D. A. Ponce, 2002, 

“Aeromagnetic expression of buried basaltic volcanoes near Yucca Mountain, NV,” U.S. Geol. 

Surv. Open File Rept. 02-020, 26 pp., Available at: http://geopubs.wr.usgs.gov/open-file/of02-

020/of02-020nav.pdf. 

Parsons, T., and G. A. Thompson, 1991, “The role of magma overpressure in suppressing 

earthquakes and topography: Worldwide examples,” Science, v. 253, 1399-1402. 

Parsons, T., 1995, “The Basin and Range Province,” In K.H. Olsen (ed.), Continental Rifts: 

Evolution, Structure, and Tectonics , Elsevier, Amsterdam, 277-324. 

Parsons, T., G. A. Thompson, A..H. Cogbill, 2006, “Earthquake and volcano clustering via 

stress transfer at Yucca Mountain, Nevada,” Geology, v. 34, 785–788. 

Pearson, E. S., and H. O. Hartley (eds.), 1970, “Table 40: Confidence limits for expectation of a 

Poisson variable,” In Biometrika Tables for Statisticians, Vol. 1, Cambridge Univ. Press, New 

York, NY. 

Perry, F. V., 2002, “Overview of volcanism in the Yucca Mountain region: the geologic basis for 

probability estimates,” Presentation at the Igneous Consequences Peer Review Panel, May 

21, 2002. 

Perry, F. V. and Valentine, G. A., 2007, “Twilight of a volcanic field: 11 million years of basaltic 

volcanism in the Southwestern Nevada Volcanic Field, USA,” Eos Trans. AGU, 88 (52), Fall 

Meet. Suppl., Abstract V13C-1492. 

Perry, F. V., B.M. Crowe, G. A. Valentine, and L. M. Bowker (eds.), 1998, “Volcanism studies,” 

Final Rept. for Yucca Mountain Project, LA-13478, Los Alamos National Laboratories, Los 

Alamos, NM. 

Perry, F. V., B. Crowe, and G. Valentine, 2000, “Analyzing volcanic hazards at Yucca 

Mountain,” Los Alamos Science, 492-493. 

Perry, F. V., A. H. Cogbill, and R. E. Kelley, 2005, “Uncovering buried volcanoes at Yucca 

Mountain,” EOS, Trans. Amer. Geophys. Union, v. 86, 485-488. 

Perry, F., A. Cogbill, R. Kelly, M. Cline, C. Lewis, and R. Fleck, 2006, “Status and Interpretation 

of Aeromagnetic Survey and Drilling Program to Support Probabilistic Volcanic Hazard Analysis 

– Update,” Presentation at 172nd ACNW&M meeting, July 17, 2006, Rockville, MD. 

Pinkerton, H., and R. J. Stevenson, 1992, “Methods of determining the rheological properties of 

magma at sub-liquidus temperatures,” Jour. of Volcanology and Geothermal Res., v. 53, 47-66. 

Pollard, D. D., 1987, “Elementary fracture mechanics applied to the structural interpretation of 

dykes,” In H.C. Halls and W.F. Fahrig (eds.) Mafic Dyke Swarms; A Collection of Papers Based 

on the Proceedings of an International Conference, Geol. Assoc. of Canada, Toronto, 5-24. 

Rathburn, S., 2007, “Fluvial processes in dryland rivers,” Presentation at the 176th ACNW&M 

meeting, February 14, 2007. 

Reardon, P. C., Y. R. Rashid, and G. S. Brown, 1992, “On the particle size distribution of 

crushed spent fuel,” Proceedings of the 3rd Intl. Conference on High Level Radioactive Waste 

Management, 137-142, Las Vegas, NV, April 12-16. 
198

Reed, J. W., 1980, “Air pressure waves from Mount St. Helens eruptions,” EOS, Trans. Amer., 

Geophys. Un., v. 61, 1136. 

Reyes, L., 2006, Letter to Michael T. Ryan (ACNW&M Chairman), dated February 7, 2006, titled 

“Review of the NRC program on the risk from igneous activity at the proposed Yucca Mountain 

repository,” NRC Accession No. ML060040264. 

Richardson, R. B., and D. W. Dunford, 2001, “Review of the ICRP tritium and 14C internal 

dosimetry models and their implementation in the Genmod-PC code,” Health Physics, v. 81, 

289-301. 

Roscoe, R., 1952, “The viscosity of suspensions of rigid spheres,” British Jour. Appl. Phys., v. 3, 

267-269. 

Rubin, A., 1995, “Propagation of magma-filled cracks,” Annual Review of Earth and Planetary 

Science, v. 23, 287. 

Ryan, M., Y. Koyanagi, and R. Fiske, 1981, “Modeling the three-dimensional structure of 

macroscopic magma transport systems: Applications to Kilauea volcano, Hawaii,” Jour. 

Geophys. Res., v. 86, 7111-7129. 

Savage, J. C., 1998, “Detecting strain in the Yucca Mountain area, NV (comment),” Science, v. 

282, 1007b. 

Savage, J. C., J. Svarc, and W. Prescott, 2001, “Strain accumulation at Yucca Mountain, NV, 

1993–1998,” Jour. Geophys. Res., v. 106, 16483–16488. 

Savage, J.C., J. L. Svarc, and W. H. Prescott, 1999, “Strain accumulation at Yucca Mountain, 

Nevada,” Jour. Geophys. Res., v. 104, 17627-17631. 

Schmincke, H-U., 2004, “Volcanism,“ Springer, Berlin, Germany, 324 pp. 

Schultz, R. A., 1995, “Limits on strength and deformation properties of jointed basaltic rock 

masses,” Rock Mech. and Rock Eng., v. 28, 1-15. 

Segerstrom, K., 1950, “Erosion studies at Parícutin, State of Michoacán, Mexico,” U.S. Geol. 

Surv. Bull. 965–A, 164 pp. 

Sheridan, M. F., 1990, “Volcano occurrences,” in Demonstration of a Risk-Based Approach to 

High-Level Waste Repository Evaluation,” EPRI Report NP-7057, Palo Alto, CA. 

Shleien, B., L. A. Slaback, and B. K. Birky, 1998, ”Handbook of Health Physics and Radiological 

Health, Third Edition,” Williams and Wilkins, Baltimore, MD, 700 pp. 

Siebert L. and T. Simkin, (2002-present). Volcanoes of the World: an Illustrated Catalog of 

Holocene Volcanoes and their Eruptions. Smithsonian Institution, Global Volcanism Program 

Digital Information Series, GVP-3, (http://www.volcano.si.edu/world/). 

Sisson, T. W. and T. L. Grove, 1993, “Experimental investigations of the role of H2O in calcalkaline differentiation and subduction zone magmatism,” Contr. Min. Pet., v. 113, 143-166. 

Smith, E.I., D. L. Feuerbach, T. R. Naumann, and J. E. Faulds, 1990, “The area of most recent 

volcanism near Yucca Mountain, Nevada: Implications for volcanic risk assessment,” High-Level 

Radioactive Waste Management, Proceedings International Topical Meeting, Las Vegas, 

Nevada, April 8-12, 1990, American Nuclear Society, La Grange Park, Illinois, 81–90. 

Smith, E. I., D. L. Keenan, and T. Plank, 2002, “Episodic volcanism and hot mantle: 

Implications for volcanic hazard studies at the proposed nuclear waste repository at Yucca 

Mountain, Nevada,” GSA Today, April 2002, 4-10. 
199

Smith, E. I., and D. L. Keenan, 2005, “Yucca Mountain could face greater volcanic threat,” EOS, 

Trans. Amer. Geophys. Un., v. 86, August 30, 2005, 317-321. 

Soule, S. A., K. V. Cashman, and J. P. Kauahikaua, 2004, ”Examining flow emplacement 

through the surface morphology of three rapidly emplaced, solidified lava flows, Kilauea 

Volcano, Hawaii,” Bull. of Volcanology, v. 66, 1-14. 

Sparks, S., 2007, “Volcanology: State of the Science – Eruption analogues for Yucca 

Mountain,” Presentation at 176th ACNW&M meeting, February 13, 2007 [see meeting transcript 

at: http://www.nrc.gov/reading-rm/doc-collections/acnw/tr/2007/ nw021307.pdf]. 

Sparks, R. S. J., and A. W. Woods, 1998, “Review of the potential processes and 

consequences of volcanic activity at the proposed nuclear waste repository at Yucca Mountain, 

Nevada,” NRC Accession No. ML033600149, 13 pp. 

Squires, R. R., and R. L. Young, 1984, “Flood Potential of Fortymile Wash and its Principal 

Southwestern Tributaries, Nevada Test Site, Southern Nevada,” U.S. Geol. Surv. WaterResources Investigations Rept. 83-4001, 33 pp. 

Stamatakos, J. A., C. B. Connor, and R.H. Martin, 1997, “Quaternary basin evolution and 

basaltic volcanism of Crater Flat, Nevada from detailed ground magnetic surveys of the Little 

Cones,” Jour. of Geol., v. 105, 319-330. 

Stamatakos, J.A., S. Biswas, and M. Silver, 2007, “Supplemental evaluation of geophysical 

information used to detect and characterize buried volcanic features in the Yucca Mountain 

region,” prepared for NRC by Center for Nuclear Waste Regulatory Analyses. 

Stock, J. M., and J. H. Healy, S. H. Hickman, and M. D. Zoback, 1985, “Hydraulic fracturing 

stress measurements at Yucca Mountain, Nevada and relationship to the regional stress field,” 

Jour. Geophys. Res., v. 90, 8691-8706. 

Stock, J. M., and J. H. Healy, 1988, “Continuation of a deep borehole stress measurement 

profile near the San Andreas Fault 2. Hydraulic fracturing stress measurements at Black Butte, 

Mojave Desert, California,” Jour. Geophys. Res., v. 93, 15196-15206. 

Stuckless, J. S. and D. W. O’Leary, 2007, “Geology of the Yucca Mountain region,” In J.S. 

Stuckless and R.A. Levich (eds.), The Geology and Climatology of Yucca Mountain and Vicinity, 

Southern Nevada and California, 9-52, doi:10.1130/2007.1199(02). 

Suzuki, T. 1983. “A theoretical model for dispersion of tephra,” Arc Volcanism: Physics and 

Tectonics., Terra Scientific Publishing, Tokyo, 95-113. 

Takahashi, T. J. and J. D. Griggs, 1987, “Hawaiian Volcanic Features: A Photoglossary.” In 

Decker, R. W., T. L. Wright, and P. H. Stauffer, Volcanism in Hawaii, Vol. 2, USGS Prof. Paper 

1350, U.S. Govt. Printing Office, pp. 845-902. 

Tanko, D. J., and P. A. Glancy, 2001, “Flooding in the Amargosa River Drainage Basin, 

February 23–24, 1998, Southern Nevada and Eastern California, Including the Nevada Test 

Site,” U.S. Geol. Surv. Fact Sheet 036–01. 

Tilling, R. I., L. Topinka, and D. A. Swanson, 1990, “Eruptions of Mount St. Helens: Past, 

Present, and Future ,” U.S. Geol. Surv. Special Interest Pub., 56 pp., Available at: 

http://pubs.usgs.gov/gip/msh//title.html.

Turcotte, D.L. and G. Schubert, 1982, “Geodynamics: Applications of Continuum Physics to 

Geological Problems,” J. Wiley and Sons, New York, 450 pp. 

Tynan, M. C., K D. Smith, J. M. Savino, T. J. Vogt, 2004, “Mega-rings surrounding Timber 

Mountain nested calderas, geophysical anomalies: Rethinking structure and volcanism near 
200

Yucca Mountain (YM), Nevada,” EOS, Trans. Am. Geophys. Un., v. 85, Fall Meet. Suppl., 

Abstract T31A-1256. 

Tynan, M., C., J. M. Savino, and T. Vogt, 2007, “An alternative conceptual model for reassessing spatial and temporal distribution of basaltic volcanism near Yucca Mountain, Nevada: 

Interpreted mega-rings, banded basalt distribution, and geophysical anomalies encompassing 

the Timber Mountain nested calderas – Draft White Paper,” prepared for U.S. Department of 

Energy, Office of Yucca Mountain Site Operations, MOL.20060731.0216.

Valentine, G. A., and K. R. Groves, 1996, “Entrainment of country rock during basaltic eruptions 

of the Lucero Volcanic Field, New Mexico,” Jour. of Geology, v. 104, 71-90. 

Valentine, G. A., D. Krier, F. V. Perry, and G. Heiken, 2005, “Scoria cone construction 

mechanisms, Lathrop Wells volcano, southern Nevada, USA,” Geology, v. 33, 629-632. 

Valentine, G. A., 2006, “Igneous scenarios,” Presented at DOE/NRC Technical Exchange on 

Total System Performance Assessment (TSPA) for Yucca Mountain, Las Vegas, NV. 

Valentine, G. A. and F. V. Perry, 2006, “Decreasing magmatic footprints of individual volcanoes 

in a waning basaltic field,” Geophys. Res. Lett., v. 33, L14305, doi:10.1029/2006GL026743. 

Valentine, G. A. and F. V. Perry, 2007, “Tectonically controlled, time-predictable basaltic 

volcanism from a lithospheric mantle source (central Basin and Range Province, USA), Earth 

and Planetary Sc. Lett., v. 261, 201-216. 

Valentine, G. A. and K. E. C. Krogh, 2006, “Emplacement of shallow dikes and sills beneath a 

small basaltic volcanic center – The role of pre-exisiting structure (Paiute Ridge, southern 

Nevada, USA),” Earth and Planetary Sc. Lett., v. 246, 217-230. 

Valentine, G. A., F. V. Perry, D. Krier, G. N. Keating, R. E. Kelley, and A. H. Cogbill, 2006, 

“Small-volume basaltic volcanoes: Eruptive products and processes, and posteruptive 

geomorphic evolution in Crater Flat (Pleistocene), southern Nevada,” Geol. Soc. of Am. Bull., v. 

118, 1313-1330, doi:10.1130/B25956.1. 

Valentine, G. A. and G. N. Keating, 2007, “Eruptive styles and inferences about plumbing 

systems at Hidden Cone and Little Black Peak scoria cone volcanoes (Nevada, USA),” Bull. of 

Volcanology, doi:10.1007/s00445-007-0123-8. 

Valentine, G. A., D. J. Krier, F. V. Perry, and G. Heiken, 2007, “Eruptive and geomorphic 

processes at the Lathrop Wells scoria cone volcano,” Jour. Volcanology and Geothermal Res.,

v. 161, 57–80. 

Vaniman, D. T., B. M. Crowe, and E. S. Gladney, 1982, “Petrology and geochemistry of 

Hawaiite lavas from Crater Flat, Nevada,” Contr. Min. Pet., v. 80, 341–357. 

Vergniolle, S., and C. Jaupart, 1986, “Separated two-phase flow and basaltic eruptions,” Jour. 

Geophys. Res., v. 91, 12842-12860. 

Waddell, R. K., J. H. Robison, and R. K. Blankennagel, 1984, “Hydrology of Yucca mountain 

and Vicinity, Nevada-California – Investigative Results Through Mid-1983,” U.S. Geol. Surv. 

Water-Resources Investigations Rept. 84-4267, 72 pp. 

Wark, K.., C. F. Warner, and W. T. Davis, 1998, “Air Pollution: Its Origin and Control, third 

edition,” Harper & Row, New York, NY, 560 pp. 

Webb, S.L. and Dingwell, D.B., 1990, “Non-Newtonian rheology of igneous melts at high 

stresses and strain rates: experimental results for rhyolite, andesite, basalt, and nephelinite.” 

Jour. of Geophysical Research, 95, 15695-15701. 
201

Weigel, F., 1986, “Uranium,” In J.J. Katz, G. T. Seaborg, and L. R. Morse (eds.), “The Chemistry 

of the Actinide Elements,” New York, NY, 169-442. 

Weiner, R. and N. Coleman, 2008, “Factors affecting radiation dose from a hypothetical 

extrusive volcanic event at Yucca Mountain, Nevada,” Proceedings of the Waste Management 

2008 Conference, Feb. 24-28, Phoenix, AZ. 

Wernicke, B., J. L. Davis, R. A. Bennett, P. Elosegui, M. J. Abolins, R. J. Brady, M. A. House, N. 

A. Niemi, and J. K. Snow, 1998, “Anomalous strain accumulation in the Yucca Mtn. area, NV,” 

Science, v. 279, 2096–2100. 

Wernicke, B., J. L. Davis, R. A. Bennett, J. E. Normandeau, A. M. Friedrich, and N. A. 

Niemi, 2004, “Tectonic implications of dense continuous GPS velocity field at Yucca Mountain, 

Nevada,” Jour. of Geophys. Res., v. 109, doi:10.1029/2003JB002832. 

WoldeGabriel, G., G. N. Keating, and G. A. Valentine, 1999, “Effects of shallow basaltic 

intrusion into pyroclastic deposits, Grants Ridge, New Mexico, USA,” Jour. of Volcanology and 

Geothermal Res., v. 92, 389-411. 

Wood, C. A., 1980, “Morphometric evolution of cinder cones,” Jour. of Volcanology and 

Geothermal Res., v. 7, 387-413. 

Woods, A. W., S. Sparks, O. Bokhove, A.-M. LeJeune, C. B. Connor, and B. E. Hill, 2002, 

“Modeling magma-drift interaction at the proposed high-level radioactive waste repository at 

Yucca Mountain, Nevada, USA,” Geophys. Res. Lett., v. 29, doi:10.1029/2002GL014665. 

Woods A. W., O. Bokhove, A. de Boer, and B. E. Hill, 2006, “Compressible magma flow in a 

two-dimensional elastic-walled dike,” Earth and Planetary Sc. Lett., v. 246, 241-250. 

Wright, T. L.., and R. T. Okamura, 1977, “Cooling and crystallization of tholeiitic basalt, 1965 

Makaopuhi lava lake, Hawaii,” U.S. Geol. Survey Prof. Paper, 1004, 78 pp. 

Wylie, J. J., K. R. Helfrich, B. Dade, J. R. Lister, and J. F. Salzig, 1999, “Flow localization in 

fissure eruptions,” Bull. of Volcanology, v. 60, 432–440. 

Yogodzinski, G. M., T. R. Naumann, E. I. Smith, T. K. Bradshaw, and J. D. Walker, 1996, 

“Evolution of a mafic volcanic field in the central Great Basin, south central Nevada,” Jour. 

Geophys. Res., v. 101, 17425-17445. 

Ziegler, J. D., 2003, “Letter to NRC re: Igneous activity agreement 1.02,” NRC Accession No. 

ML033110050, U.S. Nuclear Regulatory Commission, Washington, DC. 

Zoback, M. L. and M. D. Zoback, 1989, “Tectonic stress field of the continental United States,” 

In L.C. Pakiser and W.D. Mooney (eds.), Geophysical Framework of the Continental United 

States, Geol. Soc. of Am., Memoir 172, 523-540. 

Zreda, M. G., F. M. Phillips, P. W. Kubik, P. Sharma, and D. Elmore, 1993, “Cosmogenic 36Cl 

dating of a young basaltic eruption complex, Lathrop Wells, Nevada,” Geology, v. 21, 57-60. 
202

This page intentionally blank. 
APPENDIX A. STATUS OF NRC IGNEOUS ACTIVITY KEY TECHNICAL 

ISSUE RESPONSES (2006) 

The current status of differences between the DOE and the NRC is given by the status 

of the Igneous Activity Key Technical Issues (KTI) as identified by the NRC. The following table 

which is based on a 2006 compilation gives a brief description of each KTI the DOE response 

date and the status of the agreement between the DOE and NRC. The significance of each KTI 

to overall performance of the repository is also given. Of the 20 KTIs, fourteen have been 

satisfactorily agreed to by both agencies, while six await further information from the DOE and 

evaluation by the NRC. Four of the KTIs are ranked as having high importance to risk and three 

of these remain open (IA. 1.02.2.07, 2.17, and 2.18). 

NRC KTI Responses 

KTI Response 

Date Description Status Risk 

IA.1.01 4/30/2001 

In addition to DOE's licensing case, include for Site 

Recommendation and License Application, for information 

purposes, the results of a single point sensitivity analysis 

for extrusive and intrusive igneous processes at 10E-7. 

CompleteMedium

IA.1.02 11/5/2004 

Examine new aeromagnetic data for potential buried 

igneous features (see U.S. Geological Survey, Open-File 

Report 00-188, Online Version 1.0), and evaluate the 

effect on the probability estimate. 

NAI High 

IA.2.01 4/30/2001 

Re-examine the ASHPLUME Code to confirm that particle 

density is appropriately changed when waste particles are 

incorporated into the ash. 

Complete Low 

IA.2.02 4/14/2003 

Document results of sensitivity studies for particle size, 

consistent with (1) above. (Eruptive AC-4) DOE agreed 

and will document the waste particle size sensitivity study 

in a calculation document. 

Complete Low 

IA.2.03 3/31/2005 

Document how the tephra volumes from analog volcanoes 

represent the likely range of tephra volumes from Yucca 

Mountain region (YMR) volcanoes. 

CompleteMedium

IA.2.04 4/30/2001 

Document that the ASHPLUME model, as used in the 

DOE performance assessment, has been compared with 

an analog igneous system. 

Complete Low 

IA.2.05 6/6/2001 

Document how current approach to calculating the number 

of waste packages intersected by conduits addresses 

potential effects of conduit elongation along a drift. 

CompleteMedium

A-1
KTI Response 

Date Description Status Risk 

IA.2.06 6/6/2001 

Develop a linkage between soil removal rate used in TSPA 

and surface remobilization processes characteristics of the 

Yucca Mountain region (which includes additions and 

deletions to the system). 

CompleteMedium

IA.2.07 6/6/2001 

Document the basis for airborne particle concentrations 

used in TSPA in Rev. 1 to the Input Values for External 

and Inhalation Radiation Exposure AMR. 

Complete High 

IA.2.08 4/30/2001 

Provide additional justification on the reasonableness of 

the assumption that the inhalation of particles in the 10-

100 micron range is treated as additional soil ingestion, or 

change the BDCFs to reflect ICRP-30. 

Complete Low 

IA.2.09 3/31/2005 

Use the appropriate wind speeds for the various heights of 

eruption columns being modeled. (Eruptive AC-5) DOE 

agreed and will evaluate the wind speed data appropriate 

for the height of the eruptive columns being modeled. 

CompleteMedium

IA.2.10 2/13/2003 

Document the ICNs to the Igneous Consequences AMR 

and the Dike Propagation AMR regarding the calculation ofComplete

the number of waste packages hit by the intrusion. 

Medium

IA.2.11 6/14/2004 

Provide an analysis that shows the relationship between 

any static measurements used in the TSPA and expected 

types and durations of surface disturbing activities 

associated with the habits and lifestyles of the critical 

group. 

NAI Medium

IA.2.12 8/2/2002 

Provide clarifying information on how PM10 

measurements have been extrapolated to TSP 

concentrations. This should include consideration of the 

difference in behavior between PM10 and TSP particulates 

under both static and disturbed conditions. 

Complete Low 

IA.2.13 4/25/2002 

Provide the justification that sampling of range of transition 

period BDCFs is necessarily conservative in evaluating 

long-term remobilization processes. 

Complete Low 

IA.2.14 6/14/2004 

Provide information clarifying the method used in TSPA to 

calculate how deposit thickness effects the average mass 

load over the transition period. 

Complete Low 

IA.2.15 2/4/2004 

Clarify that external exposure from HLW-contaminated 

ash, in addition to inhalation and ingestion, was 

considered in the TSPA. 

Complete Low 

A-2
KTI Response 

Date Description Status Risk 

IA.2.16 8/20/2002 

Document that neglecting the effects of climate change on 

disruptive event BDCFs is conservative. DOE will 

document that neglecting effects of climate change on 

disruptive event BDCFs is conservative in a subsequent 

revision to AMRs. 

Complete Low 

IA.2.17 1/10/2005 

DOE will evaluate conclusions that the risk effects (i.e., 

effective annual dose) of eolian and fluvial remobilization 

are bounded by conservative modeling assumptions in the 

TSPA-SR, Rev 00, ICN1. 

NAI High 

IA.2.18 1/10/2005 

DOE will evaluate how the presence of repository 

structures may affect magma ascent, conduit localization, 

and evolution of the conduit and flow system. 

NAI High 

IA.2.19 11/07/2006 

DOE will evaluate waste package response to stresses 

from thermal and mechanical effects associated with 

exposure to basaltic magma, considering the results of 

evaluations attendant to IA Agreement 2.18. 

CompleteMedium

IA.2.20 11/07/2006 

DOE will evaluate how ascent and flow of basaltic magma 

through repository structures could result in processes that 

might incorporate HLW, considering the results of 

evaluations attendant to IA Agreements 2.18 and 2.19. 

NAI Medium

A-3
This page intentionally blank. 

A-4
APPENDIX B. THE PROGRAMMATIC AND TECHNICAL ACTIVITIES 

OF THE NRC STAFF IN REVIEWING IGNEOUS ACTIVITY 

ASSOCIATED WITH THE YUCCA MOUNTAIN PROJECT 

This appendix is largely based on NRC (2007), which provided comments on the 

ACNW&M’s Draft White Paper on Igneous Activity at Yucca Mountain. 

No single document presents the technical and programmatic activities of the staff of the 

U.S. Nuclear Regulatory Commission (NRC) regarding igneous activity at Yucca Mountain or 

the staff’s history of prelicensing interaction with the U.S. Department of Energy (DOE). 

Instead, numerous documents and publications available through the NRC’s public record 

system (the Agencywide Documents Access and Management System (ADAMS)) and the 

Licensing Support Network (http://www.lsnnet.gov/) provide that history. Two key licensingrelated documents do give important summaries of the relevant technical background and 

criteria for a future review of a license application. These are the Integrated Issue Resolution 

Status Report (NRC, 2005) and the Yucca Mountain Review Plan (NRC, 2003). The NRC has 

posted the staff’s approach to resolution of key technical issues (KTIs) on the agency’s public 

Web site at http://www.nrc.gov/waste/hlw-disposal/reg-initiatives/resolve-key-tech-issues.html. 

Since the early 1980s, the NRC staff has systematically developed focused technical 

investigations to enhance review capabilities in areas of potential risk significance, probe risksignificant areas of DOE information, gain risk insights for alternative conceptual models, and 

integrate technical information into an independent total system performance assessment. 

The purpose of these investigations has been to develop an independent and neutral 

expertise on igneous features, events, and processes in preparation for reviewing the 

anticipated DOE construction license application. In response to questions and concerns with 

the DOE program for igneous activity, the NRC developed technical investigation programs to 

provide an independent assessment and review capability for igneous activity issues. Early 

results from these programs provided a technical basis for evaluating uncertainties in, for 

example, probability models (e.g., Connor and Hill, 1993; Connor and Hill, 1995; Condit and 

Connor, 1996); use of historically active volcanoes to help interpret characteristics of past 

activity in the Yucca Mountain region (e.g., Connor, 1993; Connor and Hill, 1994; Hill, et al., 

1995); and modeling airborne transport from basaltic volcanoes (e.g., Jarzemba et al., 1997; 

Hill, et al., 1996). 

The NRC staff has produced many reports and interacted with DOE. This information 

provides a detailed record of how the available information, including the NRC staff’s 

independent information, was synthesized and applied to understanding and resolving technical 

uncertainties in the DOE information. The staff used available information to understand risksignificant uncertainties in the DOE program and provide early identification of potentially 

significant issues. For example, external review of the Center for Nuclear Waste Regulatory 

Analysis (CNWRA) program (McKague, 1998) identified the potential risk significance of 

magma-drift interaction processes, which supported the identification of this issue as significant 

in NRC staff comments on the DOE Viability Assessment (Travers, 1999) and Site 

Recommendation (Meserve, 2001). Initial results from first-order models for gas-bearing 

(Bokhove and Woods, 2000; Woods, et al., 2002) and gas-absent (Lejeune et al., 2002) flows 

supported numerous technical exchanges with DOE, which resulted in a DOE agreement to 

provide additional support for the information used in the site recommendation (Reamer, 2001). 

The independent NRC staff information provided a technical basis for determining the high 

significance of this issue in terms of repository performance (Mohanty, et al., 2004; NRC, 2004) 

B-1
and for resolving technical concerns with DOE information (Kokajko, 2005a; NRC, 2005). This 

information was developed to probe the DOE program and respond to NRC staff and other 

stakeholder concerns with the DOE program. 

Independent external reviews of the CNWRA igneous activity program were conducted 

in 1994 (Hill, 1995) and 1997 (McKague, 1998; Sparks and Woods, 1998). These reviews 

evaluated many of the risk-significant areas associated with potential igneous events and 

assessed planned and ongoing NRC/CNWRA technical investigations in these areas. The NRC 

staff has developed an independent understanding of the tectonic and magmatic framework for 

basaltic volcanism in the Yucca Mountain region, which is the foundation for evaluating the 

likelihood of future igneous activity in this region. Part of the technical basis the NRC staff has 

developed in this area appears in Connor and Hill (1994); Stirewalt et al. (1995); Hill and Connor 

(1996); Stamatakos and Ferrill (1998); Stamatakos et al. (1998); and Waiting et al. (2001). 

Staff work to understand methods to evaluate probability model utility in forecasting 

future igneous events, effects of potential buried volcanoes, and uncertainties in recurrence rate 

estimates for basaltic volcanic fields appears in such papers as Condit and Connor (1996); 

Connor and Sanders (1994); Connor et al. (1997, 2000); Magsino et al. (1998); Connor and Hill 

(1994b, 1995a); Hill et al. (1994); Conway et al. (1997; 1998); and Connor and Conway (2000). 

Probability models prepared by the staff have emphasized the development of review 

capabilities for probability issues. In the area of igneous event consequences, Bokhove and 

Woods (2000), Lejeune et al. (2002), Bokhove et al. (2005), Woods et al. (2006), and Menand 

and Philips (2005) have performed work to support staff understanding of potential magmarepository interactions. Analyses presented by Smart (2004) are relevant to understanding 

thermo-mechanical response of drift walls and the potential for magma-drift interactions. In 

addition to the above papers, NRC (2005) presents important information on waste package 

response to potential igneous events, which supports the models used in Mohanty et al. (2004). 

Information provided in NRC (1999), Jarzemba et al. (1997), and Codell (2004) supports the 

consideration of waste form response to potential intrusive igneous events. The KTI resolution 

process (e.g., Schlueter, 2003; Kokajko, 2005b) has presented additional discussion about 

igneous event consequences. 

Hill (1996), Doubik and Hill (1999), NRC (2005), and Woods et al. (2005) provide 

information relevant to understanding NRC staff perspectives on subvolcanic conduit 

development and the hypothetical formation of secondary breakouts (i.e., the “dogleg scenario”) 

beyond that discussed in Woods et al. (2002). Kokajko (2005a) discusses the KTI resolution 

process in relation to the extrusive event. Information relevant to understanding the modeling of 

airborne transport of radionuclides appears in Jarzemba et al. (1997); Jarzemba (1997); Hill 

et al. (1998); Connor et al. (2001); and Mohanty et al. (2004). Hill and Connor (2000); Mohanty 

et al. (2004); and Hill (2004) present the development of associated parameters. 

Codell (2004) and Spradley (2006) present NRC staff information relevant to 

understanding significance or limitations in alternative conceptual models. Hill and Connor 

(1995); Hill et al. (1995, 1996, 2001); Jarzemba (1997); and McKague (1998) discuss 

characteristics of volcanic deposits and associated airborne mass loads. Information developed 

for NRC staff perspectives on postvolcanic redistribution effects includes analyses in Hill and 

Connor (2000) and NRC (2004). Initial models and associated information relevant to 

understanding long-term redistribution processes also are discussed by Hooper (2004) and 

Mohanty et al. (2005), with additional information presented in Hooper and Benke (2006) and 

Benke et al. (2006). 

B-2
The NRC staff recognizes that limited data for difficult-to-observe igneous processes can 

lead to alternative views on the probability and consequences of potential igneous events. The 

NRC staff has developed an integrated program that uses quantitative modeling and 

professional judgment to evaluate the risk significance of technical issues and associated 

uncertainties. Examples of these risk insights appear in NRC (2004, 2005) and Mohanty et al. 

(2004, 2005). In addition, the NRC staff has used risk information to focus, and at times 

resolve, key technical uncertainties using DOE information. For example, igneous activity KTI 

Agreement 2.02 used a DOE sensitivity analysis to conclude that existing uncertainties in 

particle size distributions were not significant to risk (Schlueter, 2003). The influence of risk 

insights on the evolution of many other uncertainties can also be determined by consideration of 

the information in the Risk Insights Baseline Report (NRC, 2004). 

References 

Basu, D., N.K. Adams, J.A. Stamatakos, S. Sparks, and A. Woods. 2007. “Review of Two 

Electric Power Research Institute Technical Reports on the Potential Igneous Processes 

Relevant to the Yucca Mountain Repository.” ML0701202800. 

Benke, R., B. Hill, and D. Hooper. 2006. “Fluvial Redistribution of Contaminated Tephra: 

Description of an Abstracted Model.” International High-Level Radioactive Waste Management 

Meeting, May 2006, Las Vegas, Nevada. pp. 958–962. ML061030107. 

Bokhove, O., and A.W. Woods. 2000. “Explosive Magma-Air Interactions by Volatile-Rich 

Basaltic Melts in a Dike-Drift Geometry.” ML013370008. 

Bokhove, O., A.W. Woods, and A. de Boer. 2005. “Magma Flow through Elastic-Walled Dikes.” 

Theoretical and Computational Fluid Dynamics, 22: 261–286. 

Codell, R.B. 2004. “Alternative Igneous Source Term Model for Tephra Dispersal at the Yucca 

Mountain Repository.” Nuclear Technology, 148: 1–8. 

Condit, C.D., and C.B. Connor. 1996. “Recurrence Rate of Basaltic Volcanism in Volcanic 

Fields: An Example from the Springerville Volcanic Field, AZ, USA.” Geological Society of 

America, Bulletin, 108: 1225–1241. 

Connor, C.B. 1993. “Technical and Regulatory Basis for the Study of Recently Active Cinder 

Cones.” ML033630413. 

Connor, C.B., and F.M. Conway. 2000. “Basaltic Volcanic Fields.” Chapter in: Encyclopedia 

of Volcanology, Academic Press, pp. 331–343. 

Connor, C.B., and B.E. Hill. 1995a. Chapter 7, “Volcanic Systems of the Basin and Range,” of 

“NRC High-Level Radioactive Waste Research at CNWRA, July–December 1994.” CNWRA 

94-02S. pp. 99–119. ML040210615. 

Connor, C.B., and B.E. Hill. 1995b. “Three Nonhomogeneous Poisson Models for the 

Probability of Basaltic Volcanism: Application to the Yucca Mountain Region, Nevada, U.S.A.” 

Journal of Geophysical Research 100(B6): 10107–10125. 

Connor, C.B., and B.E. Hill. 1994. “Strategy for the Evaluation and Use of Probability Models 

for Volcanic Disruptive Scenarios.” CNWRA 94-015. ML040160535. 

Connor, C.B., and B.E. Hill. 1993. Chapter 10, “Volcanism Research,” of “NRC High-Level 

Radioactive Waste Research at CNWRA, January through June 1993.” CNWRA 93-01S. 

pp. 10-1–10-30. ML033650178. 

B-3
Connor, C.B., B.E. Hill, B. Winfrey, N. Franklin, and P.C. La Femina. 2001. “Estimation of 

Volcanic Hazards from Tephra Fallout.” Natural Hazards Review 2(1): 33–42. 

Connor, C.B., S. Lane-Magsino, J.A. Stamatakos, R.H. Martin, P.C. La Femina, B.E. Hill, and S. 

Lieber. 1997. “Magnetic Surveys Help Reassess Volcanic Hazards at Yucca Mountain, 

Nevada.” EOS, Trans. of the American Geophysical Union 78(7): 73–78. 

Connor, C. B., J. Stamatakos, D. Ferrill, B. Hill, G. Ofoegbu, F. Conway, B. Sagar, and J. 

Trapp. 2000. “Geologic factors controlling patterns of small-volume basaltic volcanism: 

Application to a volcanic hazards assessment at Yucca Mountain, NV.” Jour. Geophys. Res., 

105, 417– 432. 

Connor, C.B., and C.O. Sanders. 1994. “Geophysics Review Topical Report: Application of 

Seismic Tomographic and Magnetic Methods to Issues in Basaltic Volcanism.” CNWRA 94-

013. ML040160528. 

Conway, F.M., C.B. Connor, B.E. Hill, C.D. Condit, K. Mullaney, and C.M. Hall. 1998. 

“Recurrence Rates of Basaltic Volcanism in SP Cluster, San Francisco Volcanic Field, Arizona.” 

Geology 26: 655–658. 

Conway, F.M., D.A. Ferrill, C.M. Hall, A.P. Morris, J.A. Stamatakos, C.B. Connor, A.N. Halliday, 

and C. Condit. 1997. “Timing of Basaltic Volcanism along the Mesa Butte Fault Zone in the 

San Francisco Volcanic Field, Arizona, from 40Ar/39Ar Ages: Implications for Longevity of Cinder 

Cone Alignments,” Journal of Geophysical Research, 102: 815–824. 

Doubik, P., and B.E. Hill. 1999. Magmatic and hydromagmatic conduit development during the 

1975 Tolbachik eruption, Kamchatka, with implications for hazards assessment at Yucca 

Mountain, Nevada. Journal of Volcanology and Geothermal Research, 91: 43–64. 

Electric Power Research Institute. 2005. “Program on Technology Innovation: Potential 

Igneous Processes Relevant to the Yucca Mountain Repository: Intrusive-Release Scenario.” 

EPRI TR–1011165. Palo Alto, CA: Electric Power Research Institute. 

Electric Power Research Institute. 2004. “Potential Igneous Processes Relevant to the Yucca 

Mountain Repository: Extrusive-Release Scenario.” EPRI TR–1008169. Palo Alto, CA: 

Electric Power Research Institute. 

Hill, B.E. 2004. “Formation of Basaltic Tephra-Fall Deposits at Either Agglutinated or 

Fragmented Scoria Cones.” International Association of Volcanology and Chemistry of the 

Earth’s Interior, General Assembly 2004 Abstracts. ML041140066. 

Hill, B.E. 1996. “Constraints on the Potential Subsurface Area of Disruption Associated with 

Yucca Mountain Region Basaltic Volcanoes.” ML040160855. 

Hill, B.E. 1995. “Expert-Panel Review of CNWRA Volcanism Research Programs.” CNWRA 

95-002. ML040160679. 

Hill, B.E., and C.B. Connor. 2000. “Technical Basis for Resolution of the Igneous Activity Key 

Technical Issue.” ML011930254 and ML011930261. 

Hill, B.E., and C.B. Connor. 1996. Chapter 5, “Volcanic Systems of the Basin and Range,” of 

“NRC High-Level Radioactive Waste Research at CNWRA, July–December 1995.” CNWRA 

95-02S. pp. 5-1–5-21. ML040230584. 

Hill, B.E., and C.B. Connor. 1995. Chapter 9, “Field Volcanism,“ of “NRC High-Level 

Radioactive Waste Research at CNWRA, July–December 1994.” CNWRA 94-02S. pp. 141–

154. ML003745756. 

B-4
Hill, B.E., and C.B. Connor. 1994a. “Review of: DOE Study Plan 8.3.1.8.1.2 Physical 

Processes of Magmatism and Effects on the Potential Repository (Revision 0), Dated August, 

1993.” ML033640255. 

Hill, B.E., and C.B. Connor. 1994b. Chapter 8, “Volcanism Research,” of “NRC High-Level 

Radioactive Waste Research at CNWRA, July–December 1993.” CNWRA 93-02S. pp. 8-1–8-

26. ML033650211. 

Hill, B.E., C.B. Connor, M.S. Jarzemba, P.C. La Femina, M. Navarro, and W. Strauch. 1998. 

“1995 Eruptions of Cerro Negro Volcano, Nicaragua, and Risk Assessment for Future 

Eruptions.” Geological Society of America Bulletin, 10: 1231–1241. 

Hill, B.E., C.B. Connor, J. Weldy, and N. Franklin. 2001. “Quantifying Hazards from Basaltic 

Tephra-Fall Eruptions.” C. Stewart, ed., Proceedings of the Cities on Volcanoes 2 Conference, 

Auckland, New Zealand, 12–14 February 2001. Institute of Geological and Nuclear Sciences 

Information Series 49. Institute of Geological and Nuclear Sciences Limited: Lower Hutt, New 

Zealand. p. 50. 

Hill, B.E., F.M. Conway, C.B. Connor, and P. LaFemina. 1995. Chapter 7, “Field Volcanism,” of 

“NRC High-Level Radioactive Waste Research at CNWRA, January–June 1995.” CNWRA 95-

01S. pp. 7-1–7-22. ML040220368. 

Hooper, D.M. 2004. “First-Order Conceptual Model for Fluvial Remobilization of Tephra along 

Fortymile Wash, Yucca Mountain, Nevada.” ML041320668. 

Hooper, D., and R. Benke. 2006. “Fluvial Redistribution of Contaminated Tephra: ProcessLevel Modeling and Parameter Estimation.” International High-Level Radioactive Waste 

Management Meeting, May 2006, Las Vegas, Nevada. pp. 963–966. ML061070325. 

Jarzemba, M.S. 1997. “Stochastic Radionuclide Distributions after a Basaltic Eruption for 

Performance Assessments of Yucca Mountain.” Nuclear Technology 118(2): 132–141. 

Jarzemba, M.S., P.A. LaPlante, and K.J. Poor. 1997. “ASHPLUME Version 1.0—A Code for 

Contaminated Ash Dispersal and Deposition, Technical Description and User’s Guide.” 

CNWRA 97-004. ML040200038. 

Kokajko, L.E. 2005a. “Staff Review of U.S. Department of Energy Response to Igneous Activity 

Agreement Item IA.2.18.” Letter (January 10) to J.D. Ziegler (DOE). ML0435006641. 

Kokajko, L.E. 2005b. “Pre-licensing Evaluation of Key Technical Issue Agreements: Igneous 

Activity 2.03 Additional Information Needed, 2.09 Additional Information Needed, 2.19, and 

2.20.” Letter (March 31) to J.D. Ziegler (DOE). ML021840173. 

Kokajko, L.E., 2006, “Review of Additional Information Provided by the US DOE, Associated 

with Key Technical Issue Agreements – Igneous Activity Agreements 2.19 and 2.20,” Letter 

(November 7) to M. H. Williams (DOE). ML062890342. 

Lejeune, A.-M., A.W. Woods, R.S.J. Sparks, B.E. Hill, and C.B. Connor. 2002. “The 

Decompression of Volatile-Poor Basaltic Magma from a Dike into a Horizontal Subsurface 

Tunnel.” ML0336400750. 

Magsino, S.L., C.B. Connor, B.E. Hill, J.A. Stamatakos, P.C. La Femina, D.A. Sims, and 

R.H. Martin. 1998. “CNWRA Ground Magnetic Surveys in the Yucca Mountain Region, Nevada 

(1996–1997).” CNWRA 98-001. ML032890330. 

McKague, H.L. 1998. Summary of CNWRA Workshop on the Consequences of Volcanic 

Activity. ML033600146. 

Menand, T., and J.C. Phillips. 2005. “Gas Segregation in Dykes and Sills.” ML053610176. 

B-5
Meserve, R.A. 2001. Letter (November 13) to R. Card (DOE) Regarding Yucca Mountain 

Sufficiency Comments. ML012110116. 

Mohanty, S., et al. 2005. “Risk Analysis for Risk Insights Progress Report.” ML051580323. 

Mohanty, S., et al. 2004. “System-Level Performance Assessment of the Proposed Repository 

at Yucca Mountain Using the TPA Version 4.1 Code.” Revision 2. ML041350316. 

NRC. 1999. “Issue Resolution Status Report, Key Technical Issue: Igneous Activity.” 

Revision 2. Washington, DC: U.S. Nuclear Regulatory Commission. 

NRC. 2003. “Yucca Mountain Review Plan—Final Report.” NUREG-1804, Revision 2. 

Washington, DC: U.S. Nuclear Regulatory Commission (report available at 

http://www.nrc.gov/waste/hlw-disposal/reg-initiatives/ml032030389.pdf). 

NRC. 2004. “Risk Insights Baseline Report.” Washington, DC: U.S. Nuclear Regulatory 

Commission. ML040560162. 

NRC. 2005. “Integrated Issue Resolution Status Report.” NUREG-1762, Revision 1. 

Washington, DC: U.S. Nuclear Regulatory Commission. ML051360159. 

NRC (US Nuclear Regulatory Commission), 2007, “U.S. Nuclear Regulatory Commission Staff 

perspectives on ACNW Draft White Paper on Igneous Activity at Yucca Mountain,” 

ML070600793. 

Reamer, C.W. 2001. “U.S. Nuclear Regulatory Commission/U.S. Department of Energy 

Technical Exchange and Management Meeting on Igneous Activity (September 5, 2001).” 

Letter (September 12) to S. Brocoum (DOE). ML012560423. 

Travers, W.D. 1999. “Staff Review of the U.S. Department of Energy Viability Assessment for a 

High-Level Radioactive Waste Repository at Yucca Mountain, Nevada.” SECY-99-074. 

Washington, DC: U.S. Nuclear Regulatory Commission. ML992810072. 

Schlueter, J.R. 2003. “Igneous Activity Agreement Item 2.02; Status: Complete.” Letter 

(April 14) to J. Ziegler (DOE). ML031050240. 

Smart, K.J. 2004. “Examination of Effects of Geologic Features on Thermally Induced Stress at 

Yucca Mountain, NV.” ML041670370. 

Sparks, R.S.J., and A.W. Woods. 1998. “Summary of CNWRA Workshop on Consequences of 

Volcanic Activity.” ML033600149. 

Spradley, L, and R. Codell. 2006. “Alternative Lagrangian Model for Volcanic Plume Dispersion 

at Yucca Mountain.” International High-Level Radioactive Waste Management Meeting, 

May 2006, Las Vegas, NV. 

Stamatakos, J.A., and D.A. Ferrill. 1998. “Strike-Slip Fault System in Amargosa Valley and 

Yucca Mountain, Nevada—Comment.” Tectonophysics 294: 151–160. 

Stamatakos, J.A., D.A. Ferrill, and K.H. Spivey. 1998. “Paleomagnetic constraints on the 

tectonic evolution of Bare Mountain, Nevada.” Geological Society of America Bulletin 110(12): 

1530–1546. 

Stirewalt, G.L., B.E. Hill, C.B. Connor, and C. Lin. 1995. “A Critical Review of Data in the 

CNWRA Volcanism Geographic Information System (GIS) Database.” CNWRA 95-003. 

ML040160675. 

Waiting, D.L., R. Chen, J.G. Crider, W.M. Dunne, R.W. Fedors, D.A. Ferrill, M.B. Gray, B.E. Hill, 

P.C. La Femina, H.L. McKague, A.P. Morris, D.W. Sims, and J.A. Stamatakos. 2001. 

B-6
“Technical Assessment of Structural Deformation and Seismicity at Yucca Mountain, Nevada.” 

ML033630629. 

Woods, A.W., O. Bokhove, A. deBoer, and B. Hill. 2006. “Compressible Magma Flow in a TwoDimensional Elastic-Walled Conduit.” Earth and Planetary Science Letters 246 (3–4): 241–250.

Woods, A.W., C.A. Gladstone, and B.E. Hill. 2005. “Dynamic Controls on Summit and Flank 

Eruptions of Basalt.” In Review, Bulletin of Volcanology. ML051180483. 

Woods, A.W., S. Sparks, O. Bokhove, A.-M. Lejeune, C.B. Connor, and B.E. Hill. 2002. 

“Modeling Magma-Drift Interaction at the Proposed High-Level Radioactive Waste Repository at 

Yucca Mountain, Nevada, U.S.A.” Geophysical Research Letters 29(13): 19-1–19-4. 

[10.1029/2002GL014665]. 

B-7
This page intentionally blank.

B-8
APPENDIX C. CONCEPTUAL MODEL FOR DEFINING NATURAL 

ANALOGS FOR FUTURE YUCCA MOUNTAIN VOLCANISM AND 

EXPECTED CONSEQUENCES 

Addendum to EPRI 2006 Internal Report on Igneous Events (by Meghan M. Morrissey, 

Colorado School of Mines, 2007)

As part of their comments on a draft of this report, EPRI provided a concise description 

of their conceptual model for natural analogs of future volcanism in the Yucca Mountain region 

(YMR). This material is an addendum to EPRI’s internal report on igneous events. Because 

this addendum may not be readily available in the public record, we provide it here as an 

appendix (with minor editing) along with its own figures, table, and list of references. 

Introduction 

This report presents an updated version of EPRI's conceptual model for a possible future 

(< 106 yr) igneous event at Yucca Mountain from which natural analogs are defined. The most 

credible and defensible basis for assigning characteristics to a postulate future volcanic eruption 

at Yucca Mountain is the geological evidence from recent volcanic events in the region. Field 

observations and petrologic data (Crowe et al., 1988; Perry et al., 1998; Nicholis and 

Rutherford, 2002; OCRWM, 2003; BSC, 2004; Valentine et al., 2005) made at basalt centers 

found in the Yucca Mountain region (YMR) that include Thirsty Mesa, Amargosa Valley, 

southeast Crater Flat, Buckboard Mesa, Quaternary basalts of Crater Flat, Sleeping Butte, and 

Lathrop Wells, suggest that a future eruption in YMR will likely be a typical basaltic fissure 

eruption in which < 0.1 km3 of magma could reach the surface. The Lathrop Wells basalt center 

is considered the best example of a natural analog of a future eruption in the YMR. EPRI 

continues to support the hypothesis that any magma that erupts in the Yucca Mountain region 

within the next 106 year will be a low volume (< 0.1 km3

) water bearing, crystallizing basaltic 

magma with an eruption temperature between 975-1010oC. The expected series of eruptive 

events for a future igneous event in Yucca Mountain within the next 106 yr would be comparable 

to that at the Lathrop Wells basalt center. Recent data published by DOE and professional 

journals (i.e., Nicholis and Rutherford, 2002; BSC, 2004; Valentine et al., 2005) on Lathrop 

Wells basalt center have provided new insight on the interpretation of the eruption history at the 

center. This report is divided into two sections: summary of Lathrop Wells volcanology and 

inferred eruption history, and expected scenarios for a future eruption in the Yucca Mountain 

region. 

Summary of Lathrop Wells Physical Volcanology and Eruption History 

Physical Volcanology 

The Lathrop Wells basalt center (0.09 km3

; Fig. 1) consists of a large scoria cone and 

three or four sets of fissures marked by accumulations of spatter, bombs and scoria deposits 

that represent eroded smaller cones (possibly 3-10 small scoria cones (Crowe et al., 1988)). 

Multiple eruptive events occurred along two sets of fissures that extend 0.2-2 km. The main 

scoria cone (Lathrop Wells cone) is 140 m high, has a base of 875 m by 525 m, and is roughly 

0.018 km3 in volume. Based on data from a recent petrologic and field study of deposits at 

Lathrop Wells (Valentine et al., 2005), it has been suggested that the cone may have been built 

from several distinguishable eruptive events occurring essentially in two phases. The first phase 

(Fig. 2A) produced the lower portion of the cone (0.006 km3

) comprised of lapilli and bomb sized 

scoria, ribbon and spindle shaped bombs meter in length (Valentine et al., 2005). This phase 

began with a fire fountain event that produced a thin (1 m) scoria deposit at the base on the 

C-1
cone containing mostly sideromelane clasts (quenched reddish-brown glass). Overlying this 

sideromelane rich layer are 4-5 layers of coarsening upward tachylite (crystalline clasts) rich 

layers (lower portion of the cone) suggesting pulsating eruptive events. The south (0.015 km3

) 

aa lava flow (Fig. 2B) is thought to have occurred contemporaneously with the initial cone 

building stage. The second phase was the upper cone-building stage that was accompanied by 

a sustained eruption column from which 0.04 km3 of mostly tachylite tephra was produced (Fig. 

2C). As noted in Valentine et al. (2005), the contact between the upper and lower cone deposits 

is sharp suggesting a dramatic change in emplacement and eruption mechanisms. The lower 

cone deposits appear to dip both inward and outward and have characteristic features of grain 

avalanches (Valentine et al., 2005). The upper cone deposits appear to mantle the lower 

deposits characteristic of emplacement from fallout and are finer grain then the lower cone 

deposits (Valentine et al., 2005). The upper cone-building stage also emitted the northeastern 

(0.015 km3

) lava flow (Fig. 2D). The last eruptive event was a small hydrovolcanic event. The 

hydrovolcanic event is thought to involve a shallow groundwater source, in particular, water 

stored in the alluvium or sand ramp deposits or pre-volcanic surficial deposits (BSC, 2004). 

Figure 1: Geologic setting of the Lathrop Wells basalt center (Fig. 2.8 in Perry et al., 1998). 

Lathrop Wells main cone (denoted by Qbs within the dark grey area) is located along two sets of 

fissure (cross-hatched lines). Stars mark sites where distal fall deposits have been found (Perry 

et al., 1998). Mt and Pb identify locations where Miocene tuff and Pliocene basalt are exposed. 

C-2
Figure 2: Schematic of (A-D) four possible eruptive events for the main cone at Lathrop Wells 

basalt center (Valentine et al., 2005). 

Clast Analysis 

Clast component analyses of scoria deposits from the two phases provide a method for 

assessing the magma ascent history. For instance, magma that was transported to the Earth’s 

surface rapidly, then fragmented and quenched while airborne, produces reddish-brown basaltic 

glassy clasts known as sideromelane. Sideromelane droplets are thought to be products of 

energetic lava fountains or Hawaiian eruptions (Heiken and Wohletz, 1985; BSC, 2004). Magma 

that was transported to the Earth’s surface slower and/or stopping along its way will crystallize 

producing crystalline clasts known as tachylite. Tachylites pyroclasts are microcrystalline 

textured fragments of basalt that have been described as “quenched crystal” textures (Heiken, 

1978). A significant number of samples from scoria deposits at Lathrop Wells were collected 

and analyzed for clast components by DOE (BSC, 2004). Six different clast types were 

identified in each sample (BSC, 2004): tachylite, glassy tachylite, sideromelane and crystals 

(broken olivine, amphibole and/or feldspar phenocrysts) or lithics (tuff or carbonate). Results 

from this study (BSC, 2004) show that the earliest material erupted produced mostly 

sideromelane clasts whereas material erupted during the lower and upper cone building phases 

produced mostly tachylite clasts. 

Crystal size measurements of both phenocrysts (> 1 mm) and microlites (< 0.01 mm) 

can be used to determine ascent rates from results from decompression petrologic experiments 

(Cashman, 1992; Geschwind and Rutherford, 1995). Isothermal decompression experiments 

C-3
can determine the pressure and temperature conditions of crystal phase equilibrium observed in 

tephra and lava samples. A study of this type was conducted on tephra and lava samples 

collected at Lathrop Wells (Nicholis and Rutherford, 2004). According to Nicholis and Rutherford 

(2004), most of the Lathrop Wells samples contain < 2-4 vol.% phenocrysts of olivine and 

amphibole. The phenocrysts assemblage along with the known water content of < 4.6 wt.% from 

previous experiments (Luhr and Housh, 2002) suggested a phenocryst-melt equilibrium 

pressure and temperature of < 175 MPa and 1010o-975 oC, respectively (Nicholis and 

Rutherford, 2004). Plagioclase (An69) is found rarely as microphenocrysts (>0.1 mm) in a 

crystalline groundmass (microlites) of plagioclase (Nicholis and Rutherford, 2004). The 

experiments determined that to achieve the crystal size range of the plagioclase microlites 

observed in the samples, an ascent rate of > 0.04 m/s is required for magma with < 4.6 wt % 

H2O (Nicholis and Rutherford, 2004). Equilibrium conditions can also be determined from 

reactions rims of amphibole (water-bearing mineral) crystals that are very reactive with the liquid 

phase of magma (melt). The rims of amphiboles in Lathrop Wells’ samples suggest a short-lived 

residence time at a depth roughly 800 m below the surface. At this depth, amphiboles react with 

the liquid phase of magma to produce the reactions rims visible on amphibole phenocrysts 

(Nicholis and Rutherford, 2004). 

Lathrop Wells Eruption History 

The above mentioned petrologic and field data are used by EPRI to derive an eruption 

history and a magma plumbing system for the Lathrop Wells basalt center. EPRI’s eruption 

history is divided into two phases as recognized by DOE from field deposits (Valentine 

et al., 2005). Within each phase, a series of eruption styles are described that correspond to 

eruption products at Lathrop Wells basalt center described by DOE (BSC, 2004; Valentine 

et al., 2005). The first eruptive phase begins with a series of fissure eruptions that lasted only a 

few days that transitioned to focused eruptions where the main cone is located. This phase 

includes the lower cone building deposits and aa lava found to the south of the cone. The lower 

cone building eruption is thought to have formed from Strombolian eruptive events whereas the 

aa lava was eruptive effusively (non-explosive, less energetic than the Strombolian events). 

As noted by Valentine et al. (2005), the lower cone deposits have characteristic features 

related to an emplacement and eruption mechanism modeled by McGetchin et al. (1974) as 

ballistic trajectories of hot fluid fragments of magma. The travel distance is not sufficient to 

solidify large fragments (bomb size) such that partially welding of ejected material occurs. The 

model (McGetchen et al., 1974) also considers the accumulation of scoria as rim deposits that 

may develop into grain avalanches. This model appears to be applicable to the lower cone 

deposits and is commonly used to describe scoria cone formation. The second phase includes 

the northern lava flow and the final cone-building event that produced a sustained ash column 

(Valentine et al., 2005). As noted by Valentine et al. (2005), the upper cone deposits have 

characteristic features unrelated to the ballistic emplacement model (McGetchin et al., 1974). 

They propose that the magma in the later stages was likely more viscous and fragment similarly 

to more silicic magmas thus producing the sustained column of finer grain tephra (Valentine 

et al., 2005). 

EPRI’s Interpretation of the Magma Plumbing System at Lathrop Wells 

 The magma plumbing system (Figs. 3A-3B) during the first phase is inferred from the 

relative amount of sideromelane and tachylite clasts found in the respective pyroclastic deposits 

and crystal content of lavas following a similar approach taken by Corsaro and Pompilio (2004) 

at Mt. Etna. Lathrop Wells basalts are thought to have originated from 7-8 km depth and 

C-4
transported through the crust in a system of dikes (ICRP, 2002; Nicholis and Rutherford, 2004). 

Magma that reached the surface first and erupted along the fissures was essentially crystal poor 

associated with lava fountains. Magma erupted at this time (Fig. 4) is characterized as 

fragments of molten magma carried by exsolved gases as an annular flow or dispersed flow 

(Verniolle and Manga, 2000) and was likely partially depleted in volatiles (< 1 wt.% H2O; 

Holloway and Blank, 1994). This interpretation is based on the presence of sideromelane clasts 

(quenched glass basalt) found in deposits at the base of the lower portion of the cone 

(BSC, 2004). To form quenched glass, magma ascended rapidly through the dike to inhibit the 

formation of microlites then cooled rapidly as it erupted at the surface during the lava fountain 

phase. The later part of the lower cone building event erupted more crystalline magma based on 

the predominate appearance of tachylite in the samples from deposits from the lower portion of 

the cone (BSC, 2004). Magma that reached the surface during the later part of the lower cone 

building event may have ascended slower allowing crystals to begin nucleating and growing in 

magma. Tachylite pyroclasts are also thought to form from quench crystallization of fragmented 

basalt that becomes clogged in the vent during a Strombolian eruptive event (Heiken, 1978). 

Unlike magma that erupted along the length of the fissure, magma associated with lower cone 

building Strombolian events erupted from a point source along the fissure. Strombolian style of 

eruption (characterized by ballistic spatter bombs) is thought to be produced by the expansion 

and bursting of gas slugs (Fig. 4) at the surface or vent produces the (Verniolle and 

Manga, 2000). Gas slugs form in rising magma from exsolved volatiles that form bubbles and 

rise through magma and coalesce to form larger bubbles (slugs) when the bubble fraction 

reaches at least 70% (Verniolle and Manga, 2000). Slugs are thought to be separated by 

regions of magma containing bubbles (Verniolle and Manga, 2000). 

The transition from a fissure eruption (lava fountains) to a point source or conduit 

eruption (Strombolian) is thought to occur when magma cools to near its solidus temperature 

along the dike where the thickness is < 2 m (ICRP, 2003; Delaney and Pollard, 1982). Magma 

erupted at the surface from the thicker or wider portion of the dike would produce Strombolian 

activity (Fig. 3A). The contemporaneous occurrence of Strombolian activity and aa lava 

extrusion suggest a lateral variation in crystallization and bubble content along the length of the 

dike at depth. These two processes are controlled in part by cooling rates. Lava likely extruded 

from a thinner portion of the dike adjacent to where the conduit developed (Fig. 3A). The thinner 

regions of the dike (< 2 m) conductive heat loss at the wall rock will induce crystallization of 

magma (Delaney and Pollard, 1982; Carrigan, 2002) and as magma crystallize it will become 

more viscous eventually reaching a critical crystal content at which it freezes (Delaney and 

Pollard, 1982). Exsolved volatiles (bubbles) in magma in the thinner regions of the dike may 

either move into less viscous magma located in the thicker, hotter, less viscous part of the dike 

or be released into permeable wall rock. 

C-5
Figure 3: Schematic drawing of EPRI’s conceptual model of the magma plumbing related to the 

Lathrop Wells basalt center (not to scale).

The second phase includes the northern lava flow and the final cone-building 

event that produced a sustained ash column (Valentine et al., 2005). From the observed 

reaction rims on amphiboles from Lathrop Wells samples (Nicholis and 

Rutherford, 2004), magma erupted during this time may have resided at depths of 800 m 

for a few days. At this depth, basaltic magma moving up from depth containing 

< 4.6 wt.% H2O would exsolve at least half of its H2O (Holloway and Bank, 1984). The 

slow ascent or stalling of magma in the lower portion of the conduit (Fig. 4) would allow 

for the formation of microlites as suggested by the tachylite textures in eruptive products 

associated with this phase. The presence of crystals in magma would increase the 

viscosity. The ascent from 800 m would exsolve volatiles that would rise at the same 

rate as the magma (more viscous then earlier magma) thus forming a bubbly or 

homogenous fluid (Fig. 4; Sparks et al., 1997). As this magma approaches the surface 

volatiles will continue to exsolve and the magma will begin to fragment into an ash-gas 

mixture when the bubble fraction reaches roughly 75% (Wilson et al., 1980). The 

formation and behavior of bubbles in this later more crystalline magma would be similar 

to that in a silicic magma (Valentine et al., 2005). This process would explain the 

sustained eruption column (Valentine et al., 2005). During this phase of the eruption, 

more crystalline degassed magma (< 1 wt.% H2O; Holloway and Blank, 1994) is brought 

up to the surface at the northern end of the cone producing the later lavas. 

C-6
Figure 4: Conceptual model of the change in bubble content with depth in the magma column 

for Lathrop Wells. Not to scale. 

EPRI’s interpretation of the magma ascent history at Lathrop Wells becomes important 

when developing a conceptual model for possible eruptions in the Yucca Mountain region and 

analysis of dike-drift interaction. Previous models for dike-drift interaction assume magma 

entering a drift would have a viscosity of the order 1-10 Pa·s capable of filling all drifts and 

access drifts eventually creating secondary dikes from which magma will erupt at the surface 

(Woods et al., 2002). Such a model requires that all magma associated with a future eruption at 

Yucca Mountain remain essentially crystal-free throughout its ascent. As noted in the clast 

analysis of Lathrop Wells basalt samples, crystallinity of erupted material varies from quenched 

glass products (sideromelane) that is essentially crystal free to tachylite and crystalline lava that 

contain abundant microlites. Therefore, a crystal-free magma does not accurately represent 

Lathrop Wells magma. 

C-7
Viscosity 

EPRI (2006) estimated viscosities for magma in EPRI’s conceptual model for the active 

part of the dike connected to the conduit (Fig. 4). Viscosity values (Fig. 5) for initial crystal-free 

basalt are available from experimental data for crystal-free, alkali basalt containing up to 5 wt. % 

H2O (Murase, 1962; Cas and Wright, 1987) at four temperatures 800oC, 100000°CC, 1200oC, 

and 1400oC (denoted in Fig. 5 by vertical columns of respective symbols) and for H2O depleted 

alkali basalt at temperatures between 1100oC to 1500oC (Murase and McBirney, 1973; solid 

black line in Fig. 5). As demonstrated in Fig. 5, the exsolution of H2O (due to decompression) 

from basalt increases the viscosity by 1-2 orders of magnitude depending on temperature. For 

example, in Fig. 3 at 1000oC and 5 wt. % H2O, the viscosity is approximately 40 Pa·s and at 0 

wt. % H2O the viscosity is 800 Pa·s. 

EPRI (2006) estimated viscosity for basalt as a function of crystal content using the 

Einstein-Roscoe equation (McBirney and Murase, 1984). The Einstein-Roscoe equation 

estimates an apparent viscosity (η) of magma containing crystals of any size by the following 

expression: 

η = ηo

(1-Rφ)

-2.5

Where ηo is the initial crystal free viscosity, φ is the crystal fraction, and R is a constant 

with a value 1.67 (Griffiths, 2000). The apparent viscosity for Lathrop Wells basalt just below 

repository depths is estimated at 110 Pa·s (arrow in Fig. 5) using an initial crystal free magma 

contains 2 wt.% H2O at 1000oC. Results from this calculation are shown in the inset of Fig. 3. 

For basalt containing 2 wt. % H2O, the presence of crystals in basalt increases the viscosity by 

up to 5 orders of magnitude; 1.1 x102 Pa·s to ~6.0 x 106 Pa·s for a crystal content increasing 

from 0 to 0.6. Lava flows tend to terminate their advancement when the crystal content reaches 

a critical value of 0.55-0.6, which corresponds to a viscosity on the order of 107 Pa·s (Marsh, 

1981; Griffiths, 2000). 

For the range of magma rheologies interpreted for the main magma plumbing system 

(Fig. 4) at Lathrop Wells, Fig. 5 is used to assign a viscosity to each magma rheology. EPRI 

considers ~40 Pa·s to be a reasonable viscosity for magma ascending from source depth (7-8 

km) at Lathrop Wells (magma at this depth is essentially crystal free and contains up to 4.6 wt.% 

H2O (Luhr and Housh, 2002; Nicholis and Rutherford, 2004). As magma ascends through the 

crust it will exsolve volatiles and as it does its viscosity will increase as shown in the black 

crosses in Fig. 5 assuming magma remains crystal free (Lathrop Wells basalts do contain a 

negligible amount of phenocrysts, 3-4 vol.%). Magma erupting in the first phase as lava 

fountains (annular flow) and Strombolian events (slugs and bubble flow alternating) will likely 

have a viscosity on the order of 102 Pa·s. Magma erupting as lava may contain some volatiles 

(< 1 wt.% H2O; Holloway and Blank, 1994) and will be crystallizing therefore the viscosity will 

range from 103

-105 Pa·s. Upon decompression, a portion of the remaining H2O will exsolve 

forming bubbles that will increase the viscosity by up to an order of magnitude (Pinkerton and 

Sparks, 1978; Detournay et al., 2003). Decompression induces exsolution of H2O to the lower 

pressure that in turn induces undercooling of the magma resulting in quenched crystallization 

(Sparks and Pinkerton, 1978). EPRI considers 103

-106 Pa·s to be a reasonable range of 

viscosities for lava at its eruption temperature of 975-1010oC. Viscosities will rapidly increase 

several orders of magnitude 107

-108 Pa·s as the lava cools a few 10oC below its solidus 

(Griffiths, 2000; Lore et al., 2000) that it is very close to when it erupts. During the second phase 

of expected eruptive events, a reasonable viscosity for magma before it erupts as a sustained 

eruption column may be at least 103

-104 Pa·s accounting for microlites and bubbles in the 

magma. 

C-8
Figure 5: Viscosity as a function of temperature and H2O content for crystal free basaltic 

magma (after Murase, 1962; Cas and Wright, 1987). Inset is viscosity as a function of crystal 

content calculated using Einstein-Roscoe equation with a crystal free starting viscosity denoted 

by the arrow. 

Expected Igneous Consequences Scenarios 

The expected extrusive igneous consequences are described in 5 stages. The expected 

consequences are based on the interpreted eruption history for the Lathrop Wells basalt center. 

Extrusive Release Scenarios 

Stage 1: Intersection of dike with drift 

The first stage of the model considers the ascent of magma through the crust to depths 

of the proposed repository (300-400 m). The expected sequence of events during magma 

ascent is based on linear elastic fracture mechanic models for dike propagation (Lister, 1999; 

Rubin 1995). As discussed by the Igneous Consequence Review Panel (ICRP, 2003), the 

expected interaction of an ascending sheet dike with a repository drift would involve a < 0.2 m 

width and 100-200 m long crack tip propagating ahead of the magma filled dike (Fig. 6). Table 1 

lists the range of values of characteristic parameters for dikes in the YMR. The ascent rate or 

propagation rate of a dike has been estimated from decompression experiment to be > 0.04 m/s 

(Nicholis and Rutherford, 2004). The maximum ascent rate observed at fissure systems in 

Hawaii and Iceland is 10 m/s (Lister, 1999; Rubin 1995) that provides the upper bound in 

Table 1. 

C-9
The width of a future dike in the YMR is expected to be < 4 m at depths below 100 to 

125 m from the surface (BSC, 2004). Dike width with respect to depth is constrained from recent 

field observations of dikes and conduits at monogenetic volcanoes in Nevada and New Mexico 

(BSC, 2004). Dikes are believed to reach the surface with widths < 4.0 m. As flow activity along 

a dike (fissure) concentrates at points along the fissure, conduits develop. Magma rising through 

a conduit will begin to erode the walls by several mechanisms (e.g., thermal erosion, spallation 

(Valentine and Groves, 1995)) to diameters as large as 125 m, however these diameters 

develop only in the upper 100-150 m of the surface (BSC, 2004). In EPRI’s model, conduit 

diameters on the order of >10s m are not expected below 100-150 m. 

An important part of the conceptual model is the geometry of the crack tip and dike 

because it provides initial conditions for modeling dike-drift interaction. According to linear 

elastic models for dikes expected in YMR (ICRP, 2003), the width of a crack tip is expected to 

be < 0.2 m and when magma reaches the drift, the dike will expand to 1.5 m, the mode width of 

dike found in YMR (OCRWM, 2003). The number of drifts that will be intersected by the dike will 

depend on the lateral extent of the dike that is expected to be 0.5-5.0 km (Crowe et al., 1983). 

Following the initial intersection of the dike with a drift, the ascending dike tip can be expected to 

reach the ground surface above a repository in a matter of minutes (ICRP, 2003; BSC, 2004). 

Stage 2: Initial stage magma-drift interaction 

Magma that first reaches the repository (Fig. 6) is expected to be similar to that 

interpreted for the first eruptive phase at Lathrop Wells. EPRI’s model suggests that a dike in 

the Yucca Mountain region is expected to be nonuniform both laterally and vertically with 

respect to rheology. Magma with the lowest viscosity is expected in the center or the widest part 

the dike and more crystalline viscous magma is expected along the outer regions or the thinner 

parts of the dike. The lateral variation in magma properties will produce in general two different 

styles of expected activity upon entering a drift. Magma may be either a mixture of fragmented 

magma and gas characteristic of a lava fountain phase or crystallizing magma relatively 

depleted in volatiles characteristic of aa lava. The former type of magma would produce a spray 

of pyroclastics (scoria, spatter and ribbon bombs) into a drift thereby potentially bombarding and 

coating waste packages with magma (d1 in Fig. 7A-7B). Spray of magma onto waste packages 

is not expected to damage waste packages (EPRI, 2005). The latter type of magma would 

produce a slow moving crystallizing lava flow inside the drift (d2 in Fig. 7A-7B). The lava flow 

will have a viscosity of 103

-106 Pa·s and will likely flow over or around waste packages forming a 

chilled margin upon contact with a waste package. Waste packages would be entombed in 

crystallizing magma (d3 in Fig. 7A-7B). 

C-10
Figure 6: Conceptual model of the change in bubble content with depth in the magma column 

prior to intersecting a drift. Not to scale. White areas denote gas phase and grey denotes liquid 

magma. (adapted from Sparks, 1978; Vergniolle and Manga, 2000) 

Stage 3: Initial fissure eruption 

Magma that is not diverted into the drift will follow the crack tip and make its way to the 

surface. Magma will erupt at the surface along the fissure as a curtain of lava fountains. The 

initial width of the dike will be that of the crack tip (< 10 cm) and will gradually increase to 4.0 m 

the maximum width of fissures in the YMR (OCRWM, 2003). This phase will last hours to 

several days (ICRP, 2003; Delaney and Pollard, 1982), then eruption activity will localize to 1-3 

locations along the fissure. 

Magma in the dike will be laterally and vertically gradational with respect to volume 

fraction of exsolved volatiles, crystallinity and liquid magma as interpreted for Lathrop Wells 

basalt (Figs. 3A-3B). Aa lava that erupted contemporaneous with the initial cone-building phase 

at Lathrop Wells suggests that part of the magma in the fissure-conduit system was crystallizing 

and volatile depleted. Therefore, a lateral temperature gradient is expected from the margin of 

the dike to the center. Assuming that the width of the dike varies laterally, then it is expected 

that the conduit or cone building part of the eruption would develop at the widest part of the dike 

where cooling rates are lowest. Lava is expected to erupt along thinner parts of the dike where 

temperatures are lower due to high rates of heat loss by contact with the wall rock. Volcanic 

activity is expected to cease along the thinnest (< 1 m wide) parts of the dike within 10 days 

when temperatures are at or below the solidus temperature due to conductive cooling for alkali 

basalts similar to Lathrop Wells basalts (ICRP, 2003). 

C-11
Figure 7: Conceptual model for magma-drift interaction during the (A-B) first three stages and 

(C-D) and last 2 stages. Not to scale. d1, d2, d3 denote three drifts located along different 

region of the drift. This model will be updated as new data are made available by DOE and 

other agencies. 

C-12
Stage 4: Formation of conduits and central vents 

Within hours to 10s of days from onset, the fissure eruption at the surface will cease and 

activity will be focused at 1 to 3 conduits (ICRP, 2003). At the repository, drifts that contain 

spatter and other pyroclastic deposits from an earlier stage and are connected to the center or 

the widest part the dike may be inundated by a bubble-magma mixture (Fig. 6 and d3 in Fig.7C7D). In other drifts that contain spatter or pyroclastic material or lava and located within the 

narrow regions of the dike crystallizing magma may move into drifts filling space not occupied 

by volcanic materials (d2 in Fig.7C-7D). 

At the surface, material not diverted into the drift will likely produce an ash plume 

capable of transporting ash > 20 km from the vent to the regulatory compliance boundary. The 

expected volume of scoria deposited from this phase is 0.01-0.048 km3 (this includes the 

fraction of ash size material transported in the plume away from the cone, violent Strombolian 

event). 

During this stage of the eruption, erupted magma may contain radioactive material, 

either as entrained UO2 or as radionuclides dissolved into the magma, from the waste packages 

damaged by the initial interaction with the dike (EPRI, 2004). The mechanical processes that 

would result in the most damage to the waste packages include the impact of fragments of wall 

rock and magma from the initial intrusion of the dike into a drift. Thermal erosion of a waste 

package may arise if a package becomes caught in the upward flow of magma. This process 

may affect at least one waste package (1.8 m diameter, 5.0 m length) and possibly two, 

depending on the dike width (0.3 - 4 m) and the location of the dike intersection relative to it. 

The amount of radioactive material that may contaminate the magma depends, in part, 

on the size of the conduit and how magma interacts with waste packages during this prolonged 

stage (EPRI, 2004). The expected conduit width at future YMR basaltic eruptions is < 4 m at the 

repository depth (BSC, 2005) and at depths < 100 m the conduit is expected to flare to 

diameters > 10-50 m (e.g., Paiute Ridge and Basalt Ridge (BSC, 2005)). Waste packages 

cannot be transported to the surface if the conduit widths are < 2 m. The size of an intact waste 

package (1.8 m diameter, 5.0 m length), assuming it could be lifted by the flow of magma, will 

restrict magma transport through a fissure. This constriction in the fissure and sluggish flow of 

magma will lead to rapid solidification of the dike in this constricted region. Thus, it may be 

C-13
reasonable to suggest that waste packages would only be transported to the surface in dikes 

with widths at the upper end of the range of YMR dikes (2-4 m). 

Stage 5: Final stage magma-drift interaction 

The final magma-drift interaction scenarios involve relatively degassed, crystallizing 

magma. Magma diverted into a drift may overlap earlier aa lava that entombed or covered 

waste packages if there is space, otherwise the drift will be sealed off from additional magma 

(d2 in Fig.7C-7D). If additional magma does enter, this later lava flow is not expected to 

completely fill the drift. Another scenario is a drift that already is closed off to the conduit by a 

chilled lava plug (d1 in Fig.7C-7D). No additional lava is expected to enter these drifts. 

C-14
REFERENCES 

BSC, “Characterize Eruptive Processes at Yucca Mountain, Nevada”, MDL-MGR-GS-000005

Las Vegas. Nevada: Bechtel SAIC Company (2004). 

BSC (Bechtel SAIC Company), “Magma Dynamics at Yucca Mountain, Nevada”, ANL-MGRGS-000005 REV 00 (2005). 

Cas and Wright, 1987. Volcanic Successions: Modern and ancient. Allen and Unwin Co. 

London, p. 528. 

Cashman, K.V., 1992. Groundmass crystallization of Mount St. Helens dacite, 1980-1986. A tool 

for interpreting shallow magmatic processes: Contributions to Mineralogy and Petrology. 61: 

292-305. 

Cashman, K.V., C. Thornber, J.P. Kauahikaua, “Cooling and crystallization of lava in open 

channels and the transition of pahoehoe lava to ‘A’a”, Bulletin of Volcanology, 61, 3, (1999). 

Cosaro, R.A. and M. Pompilio, 2004. Magma dynamics in the shallow plumbing system of Mt. 

Etna as recorded by compositional variations in volcanics of recent summit activity (1995-1999), 

J. Volcanol. Geotherm Res. 137, p. 55-71. 

Crowe, B. S. Self, D. Vaniman, R. Amos, and F. Perry, “Aspects of potential magmatic 

disruption of a high level radioactive waste repository in southern Nevada”, Journal of Geology, 

91, 259, (1983). 

Crowe, B. C. Harrington, L. McFadden, F. Perry, S. Wells, B. Turrin and D. Champion, 

“Preliminary geological map of the Lathrop Wells volcanic center”, LA-UR-88-4155, (1988). 

Delaney, P., D. D. Pollard, “Solidification of basaltic magma during flow in a dike,” American 

Journal of Science, 282, 856, (1982). 

EPRI, “Potential Igneous Processes Relevant to the Yucca Mountain Repository: ExtrusiveRelease Scenario, Analysis and Implication”, EPRI Report 1008169 (2004). 

EPRI, “Potential Igneous Processes Relevant to the Yucca Mountain Repository: IntrusiveRelease Scenario”, EPRI Report 1011165 (2005). 

Gerschwind J.E. and MJ Rutherford, 1995. Crystallization of microlites during magma ascent: 

the fluid mechanics of the 1980-86 eruptions at Mt. St. Helens. Bulletin of Volcanology. 57:356-

370. 

Griffiths, R.W., 2000. The Dynamics of Lava Flows. Annual Reviews of Fluid Mechanics. 32: 

477-518. 

Heiken, G. 1978. Characteristics of tephra frm Cinder Cone, Lassen Volcanic National Park 

California. Bulletin of Volcanology. 41: 119-130. 

Heiken G, and Wohletz, K (1985) Volcanic Ash. University of California. Press, 258. 

Holloway J. and J. Bank, 1994. Applications of experimental results to C-O-H species in natural 

melts, in Carroll, MR and Holloway, J. eds. Volatiles in magmas: Mineralogical Society of 

America Reviews in Mineralogy. 30: 187-230. 

ICRP, “Final report of the igneous consequences peer review panel”, Bechtel SAIC Company 

LLC, pp. 86 (2003). 

Lister, J.R., 1990. “Buoyancy driven fluid fracture: the effects of material toughness and of lowviscosity precursors”, Journal of Fluid Mechanics, 210, 263-280. 

C-15
Lore, J., H. Gao, A. Aydin, (2000). Viscoelastic thermal stress in cooling basalt flows. Journal of 

Geophysical Research, vol. 105, p. 23,695-23,709. 

Luhr, J.F. and TB Housh, 2002. Melt volatile contents in basalts from Lathrop Wells and Red 

Cone, Yucca Mountain Region: Insights from glass inclusions: Eos (Transactions, American 

Geophysical Union), 83: V22A-1221. 

Marsh, B. D., (1981). On the crystallinity, probability of occurrence, and rheology of lava and 

magma. Contrib. Mineral. Petrol. 78: 85-98. 

McBirney A. and Murase T, 1984. Rheological properties of magma. A Rev. Earth Planet. Sci. 

12:337-357. 

McGetchin, T.R.; Settle, M.; and Chouet, B.A. 1974. Cinder Cone Growth Modeled after 

Northeast Crater, Mount Etna, Sicily. Journal of Geophysical Research, 79:3257-3272. 

McBirney A. and Murase T., (1984). Rheological properties of magma. A Rev. Earth Planet. Sci.

12:337-357. 

Murase, T., (1962), Viscosity and related properties of volcanic rocks at 800° to 1400°C. 

Hokkaido Univ. Fac. Sci. J, Ser. 71: 487-584. 

Murase T and A. McBirney, 1973. Properties of some common igneous rocks and their melts at 

high temperatures. Geological Society of America Bulletin. 84:3563-3592. 

Nicholis, M. and M. Rutherford, “Experimental constraints on magma ascent rate for the Crater 

Flat volcanic zone hawaiite”, Geology, 32, 489 (2004). 

OCRWM, “Characterize eruptive processes at Yucca Mountain, Nevada”, ANL-MGR-GS000002 REV 00.1 (2003). 

Perry, F. V., B. M. Crowe, G. A. Valentine, and L. M. Bowker, editors, Volcanism Studies: Final 

Report for Yucca Mountain Project, Los Alamos National Laboratories, LA-13478, Tables 1.2, 

2.A and 2.B, December 1998. 

Rubin, A., “Propagation of magma-filled cracks”, Annual Review of Earth and Planetary 

Science, 23, 287, (1995). 

Sparks, R.S.J.; Bursik, M.I.; Carey, S.N.; Gilbert, J.S.; Glaze, L.S.; Sigurdsson, H.; and Woods, 

A.W. 1997. Volcanic Plumes. New York, New York: John Wiley and Sons. TIC: 247134. 

Sparks, R.S.J. and H. Pinkerton, (1978). Effect of degassing on rheology of basaltic lava. 

Nature. 276: 385-386. 

Valentine, G. A., and K. R. Groves 1995. Entrainment of country rock during basaltic eruptions 

of the Lucero Volcanic Field, New Mexico. Journal of Geology 104: 71-90. 

Valentine, G., D. Krier, F. Perry, and G. Heiken 2005. Scoria cone construction mechanism, 

Lathrop Wells volcano southern Nevada, USA. Geology 33: 629-632. 

Vergniolle, S. and M. Mangan 2000. Hawaiian and Strombolian eruptions. In: Encyclopedia of 

Volcanoes. Ed. H. Sigurdsson. Academic Press. p. 447. 

Wilson, L., Sparks, R.S.J. and Walker, G.P.L., 1980. Explosive volcanic eruptions. IV. The 

control of magma properties and conduit geometry on eruption column behavior. Geophys. J. R. 

Astron. Soc. 63, p. 117-148. 

Woods, A.W, S. Sparks, O. Bokhove, A. LeJeune, C. Connor, and B. Hill. Modeling magma-drift 

interaction at the proposed high-level radioactive waste repository at Yucca Mountain, Nevada, 

USA, Geophysical Research Letters, 13, (2002). 

C-16
APPENDIX D. LIST OF AGENCIES, ORGANIZATIONS, AND 

INDIVIDUALS RECEIVING PRELIMINARY DRAFT OF THIS REPORT 

FOR THEIR REVIEW AND COMMENT 

A. Kalt, Churchill County, NV A. Elzeftawy, Las Vegas Paiute Tribe 

R. Massey, Churchill/Lander County, NV J. Treichel, Nuclear Waste Task Force 

I. Navis, Clark County, NV W. Briggs, Ross, Dixon & Bell 

E. von Tiesenhausen, Clark County, NV R. Murray, DOE/OCRWM 

G. McCorkell, Esmeralda County, NV G. Runkle, DOE/Washington, D.C. 

R. Damele, Eureka County, NV C. Einberg, DOE/Washington, D.C. 

L. Marshall, Eureka County, NV S. Gomberg, DOE/Washington, D.C. 

A. Johnson, Eureka County, NV W. J. Arthur, III , DOE/OCRWM 

S. Schubert, Sen. Reid=s Office R. Dyer, DOE/OCRWM 

M. Yarbro, Lander County, NV J. Espinoza, GAO 

J. Donnell, DOE/OCRWM A. Gil, DOE/OCRWM 

M. Baughman, Lincoln County, NV W. Boyle, DOE/OCRWM 

L. Mathias, Mineral County, NV M. Ulshafer, DOE/OCRWM 

J. Saldarini, BSC S.A. Wade, DOE/OCRWM 

M. Henderson, Cong. J. Gibbon=s Office C. Hanlon, DOE/OCRWM 

D. Swanson, Nye County, NV T. Gunter, DOE/OCRWM 

M. Simon, White Pine County, NV A. Benson, DOE/OCRWM 

E. Sproat, DOE/OCRWM N. Hunemuller, DOE/OCRWM 

D. Cornwall, NV Congressional Delegation P. Harrington, OPM&E 

T. Story, NV Congressional Delegation M. Mason, BSC 

R. Herbert, NV Sen. Reid=s Office S. Cereghino, BSC 

M. Murphy, Nye County, NV B. Gattoni, Burns & Roe 

R. Lambe, NV Congressional Delegation E. Mueller, BSC 

D-1
K. Kirkeby, NV Congressional Delegation J. Gervers, Clark County, NV 

R. Loux, State of NV D. Beckman, BSC/B&A 

S. Frishman, State of NV L. Rasura-Alfano, Lincoln County, NV 

S. Lynch, State of NV J. Kennedy, Timbisha Shoshone Tribe 

P. Guinan, Legislative Counsel Bureau B. Durham, Timbisha Shoshone Tribe 

R. Clark, EPA R. Arnold, Pahrump Paiute Tribe 

R. Anderson, NEI J. Birchim, Yomba Shoshone Tribe 

R. McCullum, NEI R. Holden, NCAI 

S. Kraft, NEI C. Meyers, Moapa Paiute Indian Tribe 

J. Kessler, EPRI C. Dahlberg, Fort Independence Indian Tribe 

D. Duncan, USGS D. Vega, Bishop Paiute Indian Tribe 

K. Skipper, USGS Egan, Fitzpatrick, Malsch, PLLC 

W. Booth, Engineering Svcs, LTD J. Leeds, Las Vegas Indian Center 

C. Marden, BNFL Inc. J. C. Saulque, Benton Paiute Indian Tribe 

J. Bacoch, Big Pine Paiute Tribe of the 

Owens Valley 

C. Bradley, Kaibab Band of Southern Paiutes 

P. Thompson, Duckwater Shoshone Tribe R. Joseph, Lone Pine Paiute-Shoshone Tribe 

T. Kingham, GAO L. Tom, Paiute Indian Tribes of Utah 

D. Feehan, GAO E. Smith, Chemehuevi Indian Tribe 

E. Hiruo, Platts Nuclear Publications D. Buckner, Ely Shoshone Tribe 

G. Hernandez, Las Vegas Paiute Tribe V. Guzman, Walker River Paiute 

K. Finfrock, NV Congressional Delegation D. Eddy, Jr., Colorado River Indian Tribes 

P. Johnson, Citizen Alert M. Boyd, Public Citizen 

M. Williams, DOE/OCRWM J. Wells, Western Shoshone National Council 

J. Williams, DOE/Washington, DC D. Crawford, Inter-Tribal Council of NV 

D-2
A. Robinson, Robinson-Seidler I. Zabarte, Western Shoshone National 

Council 

M. Plaster, City of Las Vegas S. Devlin 

S. Rayborn, Sen. Reid=s Office G. Hudlow 

L. Lehman, T-REG, Inc. D. Irwin, Hunton & Williams 

B.J. Garrick, NWTRB P. Golan, DOE 

T. Feigenbaum, BSC M. Rice, Lincoln County, NV 

M. Urie, DOE G. Hellstrom, DOE 

J. Brandt, Lander County S. Joya, Sen. Ensign=s Office 

R. Holland, Inyo County M. Gaffney, Inyo County 

B. Sagar, CNWRA L. Desell, RW/DOE 

V. Trebules, RW/DOE R. List, Esmeralda County 

R. Warther, DOE/OCRWM D. Curran, Harmon, Curran, Spielberg & 

Eisenberg, L.L.P. 

B. Neuman, Carter Ledyard & Milburn L.L.P. 

 Charles Connor, University of South Florida 

 Bruce Crowe, Battelle Memorial Institute 

 George Hornberger, University of Virginia 

 Eric Smistad, DOE (Las Vegas) 

 William Melson, Smithsonian Institution 

 Art Montana, University of City of Los Angeles 

 Eugene Smith, University of Nevada, Las Vegas 

 Steve Sparks, University of Bristol 

D-3
This page intentionally blank.

D-4
APPENDIX E. MEETING AGENDA FOR FEBRUARY 2007 ACNW&M 

WORKING GROUP ON THE IGNEOUS ACTIVITY WHITE PAPER 

AGENDA 

176th ACNW&M MEETING 

FEBRUARY 13-15, 2007 

TUESDAY, FEBRUARY 13, 2007, CONFERENCE ROOM T-2B3, TWO WHITE FLINT 

NORTH, ROCKVILLE, MARYLAND

ACNW&M WORKING GROUP ON THE IGNEOUS ACTIVITY WHITE PAPER (OPEN)

DAY 1: DISCUSSION OF THE NATURE AND PROBABILITY OF IGNEOUS ACTIVITY

1) 8:30 - 8:45 A.M. Opening Remarks and Introductions (MTR/WJH/NMC) 

The ACNW&M Chairman will make opening remarks regarding 

the conduct of today’s sessions. ACNW&M Member Dr. Bill Hinze 

will provide an overview of the first day of the Working Group 

Meeting, including the meeting purpose, scope, anticipated 

results, and introduce invited subject matter experts. 

2) 8:45 - 9:15 A.M. Dr. Steve Sparks (University of Bristol, England) will discuss the 

state of Volcanology science and eruption analogs for Yucca 

Mountain. 

3) 9:15 - 9:45 A.M. Dr. Bruce Crowe (Battelle Corporation) will discuss the volcanic 

history of the Yucca Mountain region and implications for the risk 

triplet. 

4) 9:45 - 10:00 A.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the two topics just presented. 

10:00 - 10:15 A.M. ***BREAK***

5) 10:15 - 10:45 A.M. Prof. Charles Connor (University of South Florida) will provide an 

overview of methodologies in probabilistic volcanic hazard 

assessment and application at Yucca Mountain. 

6) 10:45 -11:15 A.M. Prof. Eugene Smith (University of Nevada – Las Vegas; Clark 

County, Nevada contractor) will discuss the importance of 

understanding the process of magma generation for volcanic 

hazard studies about the proposed Yucca Mountain repository. 

7) 11:15 -11:45 A.M. Dr. Kevin Coppersmith (DOE – YMPO; contractor, leader of PVHA 

& PVHA-U) will discuss the use of expert elicitation in predicting 

the probability of volcanic events at the proposed Yucca Mountain 

repository – objectives, methodology, implications of the PVHA 

and PVHA-U. 

E-1
8) 11:45 - 12:15 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the three topics just presented. 

12:15 - 1:15 P.M. ***LUNCH*** 

9) 1:15 - 2:00 P.M. NRC staff representative will brief the Committee on the staff’s 

regulatory role and responsibilities with respect to volcanism. 

10) 2:00 - 2:15 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the topic just presented. 

11) 2:15 - 3:00 P.M. A representative from the US Department of Energy (DOE/YMPO) 

will brief the Committee about DOE’s views on the ACNW&M draft 

White Paper in relation to the nature and prediction of igneous 

activity. 

12) 3:00 - 3:15 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the topic just presented. 

3:15 - 3:30 P.M. ***BREAK***

13) 3:30 - 4:00 P.M. A representative from Clark County, Nevada will brief the 

Committee on the County’s views on the ACNW&M draft White 

Paper in relation to the nature and prediction of igneous activity. 

14) 4:00 - 4:15 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the topic just presented. 

15) 4:15 - 4:45 P.M. A representative from the Electric Power Research Institute 

(EPRI) will brief the Committee about their views on the ACNW&M 

draft White Paper in relation to the nature and prediction of 

igneous activity. 

16) 4:45 - 5:00 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the topic just presented. 

17) 5:00 - 5:30 P.M. Wrap Up

Committee Member Hinze will lead a panel discussion, including a 

summary of the Working Group Meeting. 

 5:30 P.M. Adjourn 

E-2
WEDNESDAY, FEBRUARY 14, 2007, CONFERENCE ROOM T-2B3, TWO WHITE FLINT 

NORTH, ROCKVILLE, MARYLAND

ACNW&M WORKING GROUP ON THE IGNEOUS ACTIVITY WHITE PAPER (OPEN) 

DAY 2: DISCUSSION OF CONSEQUENCES OF IGNEOUS ACTIVITY

18) 8:30 - 8:45 A.M. Opening Remarks and Introductions (MTR/WJH/NMC) 

The ACNW&M Chairman will make opening remarks regarding 

the conduct of today’s sessions. ACNW&M Member Hinze will 

provide an overview of the second day of the Working Group 

Meeting, including the meeting purpose, scope, anticipated 

results, and introduce invited subject matter experts. 

19) 8:45 - 9:30 A.M. Prof. Bruce Marsh (Johns Hopkins University; ACNW&M 

consultant) will discuss the magma/repository/waste package 

processes in both eruptive and intrusive scenarios and implication 

for risk from igneous activity at the proposed Yucca Mountain 

repository. 

20) 9:30 - 10:00 A.M. Prof. Art Montana (University of California – Los Angeles) will 

discuss the thermal and mechanical magma/waste package 

interactions associated with the intrusion scenario at the proposed 

Yucca Mountain Repository. 

10:00 - 10:15 A.M. ***BREAK***

21) 10:15 - 10:45 A.M. Neil Coleman (ACNW&M staff) will brief the Committee about the 

flooding history and geomorphology of Fortymile Wash near 

Yucca Mountain. 

22) 10:45 -11:30 A.M. Dr. Sara Rathburn (Colorado State University) will brief the 

Committee on processes of importance in fluvial and eolian 

transport of sediments. 

23) 11:30 - 11:45 A.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the four topics just presented. 

11:45 - 12:45 P.M. ***LUNCH*** 

24) 12:45 - 1:15 P.M. Prof. Lynn Anspaugh (University of Utah) will discuss the 

resuspension of ash and implications to risk from igneous activity. 

25) 1:15 - 1:30 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the topic just presented. 

26) 1:30 - 2:15 P.M. A representative from the US Department of Energy (DOE/YMPO) 

will brief the Committee on DOE’s views on the ACNW&M draft 

White Paper in relation to the consequences of igneous activity. 

27) 2:15 - 2:30 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the topic just presented. 

E-3
28) 2:30 - 3:00 P.M. A representative from Clark County, Nevada, will brief the 

Committee on the County’s views on the ACNW&M draft White 

Paper in relation to the consequences of igneous activity. 

29) 3:00 - 3:15 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the topic just presented. 

3:15 - 3:30 P.M. ***BREAK***

 

30) 3:30 - 4:00 P.M. A representative from the Electric Power Research Institute 

(EPRI) will brief the Committee about their views on the ACNW&M 

draft White Paper in relation to Consequences of Igneous Activity. 

31) 4:00 - 4:15 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the topic just presented. 

32) 4:15 - 4:45 P.M. NRC staff representative will brief the Committee on the staff’s 

views of the White Paper in relation to the Consequences of 

Igneous Activity. 

33) 4:45 - 5:00 P.M. Questions and Round Table Discussion (All) 

Committee Member Hinze will lead a panel discussion with the 

invited subject matter experts on the topic just presented. 

34) 5:00 - 5:45 P.M. Wrap Up (All) 

Committee Member Hinze will lead a panel discussion including a 

summary of the Working Group Meeting. Some of the issues to 

be addressed include: 

 • Has an effective and accurate understanding of the various 

views on volcanism been identified and documented in the 

ACNW&M draft White Paper? 

 • Have the risk-significant topics regarding igneous activity been 

identified? 

 • Are the technical bases for positions taken for determining risk 

from igneous activity at Yucca Mountain scientifically sound? 

 • Are there risk-significant topics regarding igneous activity that 

have not been adequately addressed considering the current 

state of the science? If so, how can they be addressed? 

 5:45 P.M. Adjourn

E-4
APPENDIX F. MINUTES OF THE ACNW&M’S FEBRUARY 13 AND 

14, 2007 WORKING GROUP ON IGNEOUS ACTIVITY 

During February 13-14, 2007 the ACNW convened a working group meeting to solicit comments 

on the draft White Paper on volcanism that was published in December, 2006. At the 

Commission’s request [SRM M060111B, February 9, 2006], the Committee has reviewed and 

analyzed the current state of knowledge regarding igneous activity, including the range of 

technical views by experts and stakeholders. A draft White Paper was developed that 

summarizes current knowledge of potential igneous activity at the proposed repository site, 

including igneous activity scenarios and their potential impacts on the repository performance. 

The White Paper also provides an assessment of differing professional views, including the 

views of experts representing DOE, NRC, the State of Nevada, and other organizations and 

stakeholders. 

Dr. William Hinze provided opening remarks that set the stage for the working group meeting. 

The Committee has invited scientifically-based criticism and recommendations for improving the 

draft White Paper. The bottom line is to prepare the best possible report for the Commission. 

Dr. Hinze noted that Day 1 of the working group would focus on the nature and probability of 

igneous activity at Yucca Mountain. Day 2 would focus on discussions of the consequences of 

igneous activity. Round table discussions would be held at various times during the meeting to 

gain additional insights from the invited experts. Invited experts for ACNW included Bruce 

Marsh (Johns Hopkins University), William Melson (Smithsonian Institution), Charles Connor 

(University of South Florida), and Sara Rathburn (Colorado State University). 

Day 1 - Discussion of the Nature and Probability of Igneous Activity 

The working group meeting began with a series of invited talks by recognized experts in 

volcanism, and including experts with extensive experience studying volcanism in the 

southwestern USA. The first of these invited talks was given by Steven Sparks (University of 

Bristol, England), who discussed the state of volcanology science and eruption analogs for 

Yucca Mountain. Professor Sparks described advances in volcanology studies and prediction, 

including specific discussion of the Soufrière Hills volcano, monitoring techniques, and modeling 

and prediction. Soufrière Hills is on the Caribbean island of Montserrat. A total of 0.7 cubic km 

of lava have been erupted so far at this volcano. 

Professor Sparks reported an extrusion viscosity of ~1010 to 1012 Pa·s, based on analysis of the 

rheology of the lava dome, which he says is 6 to 7 orders of magnitude higher than would be 

expected for extrusion viscosities at the Lathrop Wells volcano near Yucca Mountain. One 

reason for the high viscosity at Soufrière Hills is that the lava has a minimum crystal content of 

65% and sometimes extrudes with a crystal content of 90%. This volcano displays episodic 

activity over time. During the latest eruption the volcano has been active since 1995. Professor 

Sparks described one of the proposed models for the Soufrière Hills volcano, which explains 

much of what is observed and monitored. The volcano is theorized to experience strong 

overpressure at depth due to resistance to outflow near the surface as a result of high viscosity. 

This overpressure provides an explanation for shallow earthquakes, ground deformation, and 

explosive activity. 

Professor Sparks then discussed possible volcanic analogs for volcanism at Yucca Mountain, 

and provided extensive information about Eldfell eruption on Heimaey Island, Iceland, in 1973. 

This was a typical monogenetic (one time) basaltic eruption that was remarkably similar to what 

likely happened at Lathrop Wells, in many respects. The 6-month eruption began on January 

22, 1973 with earthquakes and the opening of a fissure, with a classic “curtain of fire” eruption. 

F-1
Interestingly, degassed lava was observed to be flowing as early as January 24th at a time when 

the activity was at its most intense stage, with eruption columns 8 to 9 km high. By January 31st

a scoria cone had already accumulated to a height of 180 m. During the month of March lava 

flowed into the nearby town and measures were taken to halt this flow using high-volume sprays 

of seawater. This succeeded in limiting the distance that lava flowed into the town, and caused 

the flow to focus in another direction. The eruption was declared over in July, 1973. One of the 

most important observations was that explosive activity and extrusion of degassed lava can be 

simultaneous, involving gas segregation mechanisms. 

Professor Sparks compared the petrology and geochemistry at Eldfell, Lathrop Wells, and Etna. 

He noted that the ACNW draft White Paper comments that the Lathrop Wells eruption occurred 

at temperatures around 1000°C, but he observed that this estimate does not account for the 

latent heat of crystallization, so magma that rises up and crystallizes will erupt at higher 

temperatures of 1030-1055°C. These volcanoes typically display an exponential decrease in 

extrusion rate. Other similarities of these volcanoes is relatively high water pressure (~4% 

water) and the presence of microphenocrysts (small crystals in lava) up to 40% consisting of 

plagioclase-olivine-oxides. An important difference was noted between Heimaey and Lathrop 

Wells. At the Icelandic volcano the tephra volume was small (0.02 km3

) compared to the lava 

volume (0.23 km3

), whereas at Lathrop Wells these volumes were roughly equal. One possible 

explanation is that the Icelandic study that reported these results may have underestimated the 

tephra volume because much fell into the sea. 

Professor Sparks showed how shearing experiments were conducted at Etna in 1975, to 

estimate the lava viscosity. These experiments using a field rheometer yielded an upper bound 

for degassed trachy-basalt magma around 105

 Pa·s. Representing a rather crystal-rich magma 

at Etna, this should approximate an upper bound for magmas like those that erupted at Lathrop 

Wells. Sparks then described viscosity estimates from a long lava flow at Lonquimay, Chile, in 

1989. This was a mafic andesitic magma, which has a higher silica content and should 

therefore be more viscous than the Lathrop Wells magma. Viscosities were calculated using 

open channel flow equations. It took a year of flow time over a distance of 10 km for the 

viscosity to reach a level of 109

 Pa·s. 

Professor Sparks then described volcanic blast effects from the Soufrière Hills volcano. And 

although this kind of event is not exactly analogous to Lathrop Wells, the flow density at 

Soufrière Hills would be about the same as the flow density of a Strombolian jet coming out the 

vent at Lathrop Wells. He summarized his interpretations of phenomena that could potentially 

be applied to Yucca Mountain: intense explosive eruptions dominate for ~ 1 week, but with lava 

effusion; discharge of explosive jet at hundreds of m3

/s and up to 200 m/s speed; wet magma 

starts out at <1000°C, then erupts at 1030-1055°C with latent heat of crystallization; wet trachybasalt lava extrudes with a viscosity of ~104

-105 Pa·s; flow front evolves to aa flow (viscosity 

< 107

 Pa·s) and blocky lava (viscosity = 107 to 1010 Pa·s); the lava viscosity evolves; buildings 

destroyed by aa flows; and high-speed gas-particle flows can be highly destructive. 

Bruce Crowe (Battelle Corporation) described the volcanic history of the Yucca Mountain region 

and implications for the risk triplet (what can go wrong?; how likely is it?; what would the 

consequences be?). He presented background information about the evolution of volcanic 

hazard models, the setting and volcanic history of the Yucca Mountain region, and provided a 

discussion of risk-informed perspectives from modeling for environmental problems. Dr. Crowe 

was formerly a participant in the Yucca Mountain project; he is now a “distant and interested 

observer.” He presented a flow chart that outlined the elements of an event probability 

calculation (i.e., the conditional probability of repository disruption by igneous activity). There 

has been a multi-decade progression in probabilistic modeling, from development of a 

probabilistic volcanic hazard model in the early 1980's leading to probabilistic modeling for 

F-2
complex environmental problems in the 2000's. A current opinion is that volcanic hazard 

models are now relatively mature but that consequence modeling is still evolving. A remaining 

challenge is to quantify and reach agreement on uncertainty components. 

Dr. Crowe described the regional geologic and tectonic setting for the southwest Nevada 

volcanic field, where Crater Flat and Yucca Mountain are located. There is a long history of 

studies in the Nevada Test Site region, including multiple decades of geologic mapping and 

geophysical studies (1950's to 1990's); drilling of a large number of boreholes for the 

underground testing of weapons (1950's to 1992); geologic and hydrologic studies for Yucca 

Mountain (late 1970's and continuing); specific boreholes for volcanic hazard studies (VH-1 and 

VH-2, plus seven new holes drilled in 2006 to explore aeromagnetic anomalies); and geologic 

and hydrologic studies for Environmental Management programs. There is an unprecedented 

level of knowledge of the geology and hydrology of a complex geologic and hydrologic setting 

that has been partly incorporated in a 3-D Earth Vision model of the Yucca Mountain site. 

Dr. Crowe then gave general descriptions of various phases of volcanism in the region, starting 

with locations of the silicic volcanism that deposited the surface rocks at Yucca Mountain. He 

then described four cycles of basaltic volcanism, starting with the volcanism associated with the 

waning phase of the silicic pyroclastic Timber Mountain-Oasis Valley caldera complex. This 

basaltic episode occurred in Miocene time from ~10 to 12 Ma and produced a large volume of 

basalts (>3 km3

). Basalts also were produced during basin development following the eruptions 

of the Black Mountain Caldera (Frenchman and Yucca Flats) during 10 to 8 Ma. These postcaldera basalts had volumes of <3 to <1 km3

. Additional basalts were produced from 8.6 to 

7.3 Ma showing an apparent decline in volume. Dr. Crowe then described a Pliocene volcanic 

cycle in the Amargosa Trough. Apparent ages range from ~4.9 to 3.0 Ma ago, with a cycle 

duration of about 2 Ma. The volume of basalt declined through the cycle. Finally, he discussed 

the Quaternary volcanic cycle of the Amargosa Trough. The eruptions occurred from about 1.1 

to 0.08 Ma with volume decline through the cycle. The volume produced around 1 Ma was 

~0.15 km3

, whereas the combined volume from Sleeping Butte and Lathrop Wells was 0.09 km3. 

The question remains whether this Pleistocene cycle is over. Dr. Crowe noted the possibility of 

a 2 million-year time gap between volcanic cycles with a mean cycle duration of ~1.5 Ma. He 

illustrated various possibilities, one being that the next event in the Yucca Mountain region could 

have a recurrence interval somewhere around the range of 300,000 years. He emphasized the 

use of multiple permissive models as providing multiple ways to look at the probability data to try 

to forecast what might happen. 

Dr. Crowe then described a new type of modeling approach being explored in fluid and 

contaminant transport models. This approach is called Bayesian Model Averaging (BMA). This 

methodology had previously been presented to the ACNW and is documented in the 2003 NRC 

report NUREG/CR-6805. This kind of approach may have applicability to volcanism models. 

The Bayesian perspective provides a way to integrate data to both quantify the uncertainty and 

to try to assemble good predictions. Dr. Crowe has shown the Yucca Mountain scenario and 

associated probability distributions to other decision analysts who work with environmental 

modeling problems. Compared to dealing with remediation and decision options for Superfund 

sites, those analysts found the roughly order of magnitude uncertainty in volcanic intersection at 

Yucca Mountain to be relatively minor by comparison. 

In closing, Dr. Crowe commented that it will be difficult to be able to further reduce the 

uncertainty, and that limits may have been approached for the data sets available for the Yucca 

Mountain region. The key thing to do is to quantify the uncertainty using a variety of techniques 

using multiple permissive models. 

F-3
Charles Connor (University of South Florida) gave an overview of methodologies in probabilistic 

volcanic hazard assessment and their application at Yucca Mountain. His talk was titled 

“Probabilistic Assessments of Volcanic Hazards at Yucca Mountain, Nevada.” He addressed 

the question, “What is the probability of igneous disruption of the proposed repository at Yucca 

Mountain?” Key factors to estimate are the spatial intensity and recurrence rate of volcanism. It 

is important to define the igneous event (dikes, volcanic vents and related vent structures, and 

sills and related intrusive structures). 

Professor Connor described a model approach using maps in probability assessment scenarios, 

and development of a Monte Carlo event simulator that considers volcanic event types and 

geometries, based on analogous events. The simulator is based on a library of dike, vent, and 

sill geometries derived from geologic mapping at the well-exposed San Rafael volcanic field. 

The library includes 94 dikes, 34 vents, and 3 mapped sills. Mapping reveals basic features of 

dike injection associated with igneous events in basaltic volcanic fields. Dikes segment and 

rotate as they rise in the shallow crust. Dike trends in the shallow crust may be oblique to 

regional maximum horizontal compressional stress. Vents are the surface expression of 

conduits through which magma flows. Worldwide mapping indicates the following features of 

vents that are associated with basaltic volcanic fields: multiple vents are normally associated 

with individual events; these vents are usually distributed along one or more dikes; vents are 

most common at offsets in dikes; not all vents build scoria cones at the surface; and vents 

develop complex zones of interaction with adjacent wall rock, often involving areas >100 m in 

diameter. Sills occasionally form in basaltic volcanic fields. The frequency of sills in the Yucca 

Mountain region is not known, but sills are present at the Miocene Paiute Ridge, east of Yucca 

Flat on the Nevada Test Site. New drilling data indicates that magnetic anomaly A is likely a sill 

[age is Miocene], and other sills may be present. It is uncertain if sills accompanied Quaternary 

activity in the Yucca Mountain region. 

Professor Connor presented several examples of event simulator output. He then described 

techniques used to estimate the spatial intensity of volcanism. These include homogeneous 

and spatially-nonhomogeneous methods (e.g., non-parametric kernel functions), Bayesian 

methods, and deterministic methods (such as a model that suggests there is a structural feature 

that dramatically lowers probability east of the Solitario Canyon fault). Non-parametric models 

of spatial intensity have the following advantages: (1) being based on the distribution of past 

volcanic events; (2) accounting for the spatial scale of volcano clustering in the Yucca Mountain 

region; (3) being consistent with large scale geophysical structures in the region (e.g., 

volcanoes in the AmargosaTrough, consistent with low velocity zones derived from sparse 

tomographic data; (4) avoiding discontinuities in spatial intensity that are geologically unrealistic; 

(5) having a physical basis – Gaussian kernel functions reflect the spatial scales of partial 

melting in the mantle in a manner consistent with heat and mass diffusion. 

Professor Connor described how a spatial probability model must consider the uncertainty in the 

estimate of spatial intensity. For non-parametric models (and most other estimates of spatial 

intensity), a major source of uncertainty is related to the relatively few events (older volcanoes) 

that are used to model the probability density function (pdf) of spatial intensity. It is possible to 

estimate the uncertainty spatial intensity using bootstrap methods. Essentially, the pdf derived 

from older volcano locations is sampled to find a set of new “hypothetical”volcano locations. 

These new locations are used to estimate the spatial intensity at a grid point. This procedure is 

repeated and the range of spatial intensity reflects the uncertainty in the model due to data 

(aleatoric uncertainty), assuming that the statistical model is correct. The fewer events (older 

volcanic events) available to create the model, the greater the uncertainty. 

Professor Connor then discussed the task of estimating temporal recurrence rates. He 

described apparent temporal clusters near Yucca Mountain (0.08 to 1 Ma; Pliocene 3.6 to 

F-4
4.2 Ma; and Miocene 9.0 to 11.2 Ma). He presented a series of probability calculations. Given 

a temporal recurrence rate of λ = 2 x 10-6 events/yr: 

Probability of dike intrusion within repository boundary is: (0.05)(2 x 10-6) = 1 x 10-7/yr 

Probability of vent or vent structure within repository boundary is: (0.01)(2 x 10-6) = 2 x 10-8/yr 

Probability of sill intrusion within repository boundary is: (0.002)(2 x 10-6) = 4 x 10-9 /yr 

Uncertainty in temporal recurrence rate was estimated using the likelihood ratio to be 6 x 10-6 

events/yr > λ > 2 x 10-7 events/yr (95% confidence), then: 

Probability of dike intrusion within repository boundary is: 1 x10-8 to 3 x 10-7/yr 

Probability of vent or vent structure within repository boundary is: 2 x 10-9 to 6 x 10-8 /yr 

Probability of sill intrusion within repository boundary is: 4 x10-10 to 1 x 10-8 /year 

Uncertainty in spatial intensity for bandwidth = 7 km is at least a factor of five (~ 95% 

confidence), then: 

Probability of dike intrusion within repository boundary is less than: 1 x 10-6/yr 

Probability of vent or vent structure within repository boundary is less than: 3 x 10-7/yr 

Probability of sill intrusion within repository boundary is less than 5 x 10-8 /yr ~95% confidence, 

accounting for uncertainty in temporal recurrence rate and spatial intensity. 

Professor Connor provided additional comments about the above calculations. The expected 

values of the probability of igneous disruption of the repository reported above are higher than 

most previous estimates. For example, the original PVHA estimates for volcanic disruption of 

the repository had expected values for this probability of 9 x 10-9 per year (revised to 1.2 x 10-8

/yr), this is roughly the same as calculated here for the expected value of probability of 

disruption by vents and vent structures (2 x 10-8/yr), but significantly less than the expected 

value of the probability of dike intersection (1 x 10-7 /yr). These differences in expected values 

arise because previous treatments of the geometry of igneous events were overly simplistic. In 

this analysis, igneous events are treated as geologically complex features, consistent with 

observations in basaltic volcanic fields. Uncertainties in temporal recurrence rate (because of 

few Quaternary events) and spatial intensity (because of few events) result in uncertainty in 

probability estimates. Cumulatively, this uncertainty is more than one order of magnitude at the 

95% confidence level. No assumptions are made in this analysis about the interaction between 

igneous features and the repository. Rather, this analysis assumes an undisturbed setting. For 

example, the probability of vents and vent structures forming within the repository boundaries 

may be higher than indicated by this analysis. The analysis presented is not complete. For 

example, consideration of the geophysical setting (isostatic gravity anomalies, seismic 

tomographic anomalies) is not included. These factors likely increase the probability of events 

centered SW of the repository in easternmost Crater Flat. Based on the event simulator results, 

an increase in probabilities at this location tends to increase probabilities of igneous disruption 

of the proposed repository. The PVHA process will consider a much wider range of scenarios, 

such as alternative models of igneous event recurrence rates and the roles of geophysical 

information. 

Eugene Smith (University of Nevada – Las Vegas; Clark County, Nevada contractor) discussed 

the importance of understanding the process of magma generation for volcanic hazard studies 

related to Yucca Mountain. Professor Smith commented on the influence of the mantle on 

magma source zones. He considers it very important to understand the process of volcanism 

before calculating the probability of future events. There is debate as to the depth of the 

F-5
boundary between the lithospheric mantle and the asthenospheric mantle under Yucca 

Mountain. The traditional model assumes melting in the lithosphere and implies that volcanism 

is waning. There is a very limited amount of material to melt in this area. If you assume the 

traditional model is correct and volcanism is waning, the probability of a future eruption is 

actually very small. Professor Smith previously proposed a model of deep melting in the 

asthenosphere at depths greater than about 100 kilometers. This model has broader 

perspective, focusing on an area extending from Death Valley all the way to Lunar Crater, 

including the Yucca Mountain area. The implication of this model is that a new peak of 

volcanism is possible, that volcanism is not dead and in the future there might have an upsurge 

of volcanism. 

Professor Smith briefly discussed several different models of volcanism, and then compared the 

traditional model (assumes lithospheric mantle melting and implies waning volcanism) with a 

deep melting model that assumes a Lunar Crater-Death Valley belt of volcanism (and implies a 

new peak of volcanism is possible). He described various patterns of petrology and trace 

element chemistry. The deep melting model involves melting of asthenospheric mantle - 

lithospheric mantle does not melt. The deep melting model is supported by similar episodic 

patterns of volcanism and depth of melting calculations. Professor Smith showed a figure that 

displays an alignment of volcanoes of various ages extending from Lunar Crater to Crater Flat 

and then to Death Valley. He then showed a plot of the number of events versus age, 

comparing Crater Flat to Lunar Crater-Reveille. After about four million years, there is a 

synchronous pattern between Crater Flat and Lunar Crater. Prior to that, the activities were 

disconnected. Now one of the questions that arises is whether this pattern is common 

throughout the Great Basin or whether it is focused just on this belt of volcanism. There is very 

little correspondence between southwestern Utah and the Crater Flat/Lunar Crater Belt. But 

there is good correspondence with the Coso-Lone Pine volcanic field. 

Professor Smith then discussed melting depth. Melting is really deep in the Crater 

Flat/Reveille/Lunar Crater area and becomes shallower as you go to the west or to the east. In 

general, most of the melting is occurring in the asthenospheric mantle and very little in the 

lithospheric mantle. The deep melting model must explain several things. Temperatures have 

to be about 200 degrees higher in the mantle in this particular area, and there must be an 

explanation for the very narrow belt of volcanism and the episodic pattern with basaltic 

volcanism occurring in the same belt for as long as 11 million years. It is important to take a step 

back and take a look at the history of Nevada for the past 400 to 500 million years. There have 

been a lot of mountain-building episodes in Nevada over the past 400 million years. The most 

recent of those are the Sevier Belt just to the east of the Lunar Crater/Crater Flat Belt and the 

Central Nevada Thrust Belt which actually goes right through the area of the Lunar 

Crater/Crater Flat Belt. There was ample opportunity for thickening of the lithosphere during 

Paleozoic and Mesozoic tectonic events and thinning of the lithosphere beneath the Sierra 

Nevada. Over time this has developed a keel in the mantle lithosphere. The mantle of 

lithosphere moves and kicks up mantle eddies. There is an edge effect where asthenospheric 

material is moving up along the boundary from high pressure to low pressure. And if magma 

moves from high pressure to low pressure, we can melt magma adiabatically (with no additional 

input of heat). The eddies in the very simplistic view are moving with the plate, so any time an 

area of hot mantle is intersected, there is the potential of producing volcanic activity. Once we 

reach an area of colder mantle, we get a period of quiescence and won’t get another peak of 

volcanic activity until another area of hot mantle is reached. Seismic tomography suggests the 

asthenospheric mantle is thermally very inhomogenous. There are a lot of areas that are hotter 

than others. The volume of material produced at any one time depends on the lengths of the 

melting so it is theoretically possible to get another episode of high volume material erupted 

F-6
within this belt if a hot spot is intersected that has a three-dimensional geometry that might be 

suitable. 

Professor Smith presented two conclusions. It is important to know “why” in order to determine 

“when.” And probability studies are dependent on the petrologic model. 

Kevin Coppersmith (DOE – YMPO; contractor, leader of PVHA & PVHA-U) discussed the use of 

expert elicitation in predicting the probability of volcanic events at the proposed Yucca Mountain 

repository – objectives, methodology, implications of the PVHA and PVHA-U. The objectives of 

his presentation were to summarize the evolution of formal expert elicitation methodologies for 

hazard analysis at US NRC-regulated facilities (lessons learned and solutions to identified 

problems); to define the essential steps in an expert elicitation; to describe the basic elements of 

a Probabilistic Volcanic Hazard Analysis (PVHA); to summarize the methodology used in PVHA96; and to review the methodology being used in the PVHA-Update (PVHA-U). Issues being 

addressed in PVHA-U include spatial evaluation (region of interest and spatial model); source 

zones (alternative zonations and nature of zone boundaries); spatial smoothing (smoothing 

operator and distance); and other conceptual models. 

Dr. Coppersmith described the historical context of formal expert elicitations, elements of the 

methodology, the various steps and criteria for a formal expert elicitation, and the expert 

selection criteria for the 1996 elicitation. He also showed various examples of temporal and 

spatial probability models. He then presented the following conclusions: (1) methods for 

conducting formal expert elicitations for probabilistic hazard analyses have evolved over the 

past 20+ years; (2) methodology guidance provides for essential steps that should be followed 

within NRC regulatory environment; (3) PVHA-96 and PVHA-U take advantage of the lessons 

learned; (4) each expert elicitation provides an opportunity for refinement. 

Jack Davis and John Trapp (both with the Office of NMSS) gave a talk titled “NRC Staff 

Perspective on Igneous Activity Issues: Overview of the Licensing Process, Development of NR 

Review Capabilities, and Probability of Igneous Activity.” This talk presented the roles and 

responsibilities of the NRC, the staff’s expectations for a DOE license application, risk 

information, development of NRC staff review capabilities, and also gave the status of igneous 

activity issues. DOE’s role is to characterize the Yucca Mountain site, develop a basis for 

meeting performance objectives, prepare and defend the license application, and construct and 

operate the repository, if it is licensed. The NRC staff have developed a technical 

understanding and process to review a license application, have conducted prelicensing 

interactions on site characterization and early identification of issues, will review a license 

application and develop a Safety Evaluation Report and also review an Environmental Impact 

Statement for adoption. NRC will also oversee and inspect DOE operations if the site is 

licensed. 

The NRC staff expectations for igneous activity in a license application were described. A 

transparent and traceable technical basis is needed for inclusion of site characteristics and 

appropriate features, events, and processes. DOE needs to provide an assessment of events 

with at least 1 chance in 10,000 of occurring in 10,000 years, plus evaluation of uncertainty, 

variability, and risk significance and consideration of alternative conceptual models. There is 

also an expectation of demonstrable model support. DOE is not required to “predict” igneous 

events. Stochastic methods are used to forecast a range of outcomes. An appropriate range of 

uncertainties and alternative models must be considered. DOE’s performance assessment is to 

consider features, events, and processes that significantly change the timing or magnitude of 

dose. The NRC staff will review DOE’s performance assessment, along with other relevant 

information, to determine if there is reasonable expectation that the site can meet the 

F-7
performance objectives. The NRC presenters also stated that the NRC staff has not developed 

a “position” on igneous activity. 

Both the NRC staff and DOE hold similar views on the relative risk ranking of igneous activity. 

The volcanism scenario has a low probability of occurrence but has potentially large 

consequences, and has high risk significance within the total system analysis. The estimated 

risk significance of different aspects of the igneous activity scenario are given in the Risk 

Insights Baseline Report. Through the successful key technical issue process, the NRC staff 

anticipates that DOE will have sufficient information in the license application to support NRC 

review. 

The NRC staff presenters commented that in their opinion the key concept of event definition 

was not clearly discussed in the draft ACNW white paper on volcanism. The NRC staff has 

concerns with event definition, that there many ways to define an event such as single 

mappable unit, vent alignment, etc. Such definitions require adjustment in number of events, 

size of events, recurrence rate, and other parameters. For example, is the Quaternary activity 

in Crater Flat one event, a vent alignment about 12 km long, or four or more individual events on 

the order of 1 km long? 

The NRC staff considers there is high risk significance associated with the probability of igneous 

activity, airborne transport of radionuclides, and magma-drift interactions. A summary was 

provided of staff work in each of these areas and the current issue resolution status. DOE has 

completed drilling of 7 new boreholes to investigate aeromagnetic anomalies in support of an 

ongoing update of their probabilistic volcanic hazard analysis (expert elicitation). DOE is also 

updating several analysis model reports to address the issues of airborne transport and magmarepository interactions. The NRC staff state that they have a transparent technical approach for 

use in evaluating the potential significance of data and model uncertainties, and that they have 

the necessary tools and information to conduct a licensing review. The NRC staff states that 

they are ready to review DOE products as they become available. 

Day 2 - Discussion of the Consequences of Igneous Activity

Several briefings that had been scheduled for Day 1 were postponed until the morning of Day 2 

due to an early dismissal of NRC personnel in response to inclement winter weather. These 

briefings included a talk by a representative from the US Department of Energy (DOE/Yucca 

Mountain Project Office), who provided DOE’s views on the ACNW draft White Paper in relation 

to the nature and prediction of igneous activity. 

Eric Smistad (DOE) gave a talk titled “Review of DOE’s Positions in the White Paper - Nature 

and Prediction of Igneous Activity.” He noted that the ACNW report reasonably captures much 

of the DOE technical work and approach. The ACNW report is a snapshot in time using 

available information; it cannot fully capture the technical basis for the License Application. 

Mr. Smistad’s presentation gave a high-level summary of observations regarding the white 

paper. He noted that more detailed comments and suggestions would be provided later. Mr. 

Smistad noted that the ACNW report includes some speculative comments about probabilistic 

volcanic hazard analysis-update (PVHA-U) outcomes (e.g., suggestion of lowering of 

probability); the PVHA-U work is underway and no hazard calculations have been done. This 

work will not be complete until after submission of a license application. The report cites some 

“areas of disagreement” between DOE and NRC—possibility of multiple vents, dike length, and 

dike width 

Mr. Smistad commented that the ACNW report does not include explicit discussion of DOE’s 

conceptual model of magma generation. This conceptual model provides important context for 

understanding waning volcanism, low eruption volumes, low eruption frequency, volatile-rich 

F-8
magmas, and the inappropriateness of proposed links between Yucca Mountain volcanism and 

other, more active, basalt fields originating from a more active magma source. Although 

Plio-Pleistocene basalts are heavily emphasized in DOE and PVHA models, Miocene episodes 

are still included with low weighting. 

Mr. Smistad provided the following conclusions: (1) The ACNW report reasonably captures 

much of the DOE technical work and approach; (2) the report is a snapshot in time using 

available information; it cannot fully capture the technical basis for a license application; (3) this 

presentation is a high-level summary of observations regarding the ACNW report - more 

detailed comments and suggestions will be provided (examples: detectability of anomalies; and 

age intervals of basalt episodes - in contrast to ACNW’s report, there was no volcanism 

between 5 and 7 Ma, and Miocene volcanism ended at approximately 7 Ma, not 8 Ma as stated. 

A representative for the Electric Power Research Institute (EPRI) provided feedback to the 

Committee regarding the draft White Paper. Professor Meghan Morrissey (Colorado School of 

Mines) gave a talk titled “Preliminary comments on ACNW “Igneous Activity at Yucca Mountain: 

Technical Basis for Decisionmaking:” Event Probability and Nature and Characteristics.” Her 

talk outlined key points documented in the ACNW report and provided additional comments for 

consideration. With respect to the probability of volcanism at Yucca Mountain, EPRI plans to 

review the report from the PVHA-U, to be released in 2008. Additional comments provided for 

ACNW consideration include: waning of basaltic volcanism in the region; dike evolution 

(geometry), and magma genesis in the Yucca Mountain region. With respect to the nature and 

characteristics of potential igneous activity, EPRI has developed three major reports. EPRI 

considers a “reasonably expected” volcanic scenario for the Yucca Mountain region to be based 

on the Lathrop Wells basalt center. EPRI considers this volcano to be the best analog for future 

volcanism, involving fissure eruption with fire fountains and aa lava, Strombolian eruptions 

(cone-building phase and tephra ejection), and additional aa lava flows. 

Professor Morrissey discussed characteristics of magma ascent and magma properties. DOE 

previously assumed that the magma in the Yucca Mountain region would be low viscosity, 

slowly crystallizing, with magma temperatures of 1150-1200°C. However, Nicholis and 

Rutherford (2004) showed the magma temperature would actually be 975-1010°C with higher 

viscosity and faster crystallizing magma. Viscosities would now be expected in the range of 

105

-107 Pa·s (106-108 poise). With regard to styles of volcanism, EPRI provides the following 

comments for ACNW consideration: (1) clast component analysis of pyroclastic deposits from 

Lathrop Wells and reaction rims of amphibole phenocrysts provide additional information on 

magma ascent history at shallow depths; (2) rheology of magma in a dike will vary in 3 

dimensions. Magma-drift interaction will vary along the length of a dike from a thick, tacky 

magma to a bubbly magma or fragmented magma; (3) if a dike should be counted as a single 

event, then a series of conduits (vents) located along a fissure should not be counted as 

separate events in PVHA-U calculations. 

Professor Morrissey noted a series of volcanoes that represent “uncertain” analogs for Yucca 

Mountain. These include Cerro Negro, Grants Ridge, Longuimay, Paricutin, and Tolbachik. In 

EPRI’s view, good analogs for Yucca Mountain include Basalt ridge, Boulder Dam, Paiute 

Ridge, and Red Cones, CA. In conclusion, EPRI has provided additional items for ACNW to 

consider but is in broad agreement with the technical analyses and implications made by ACNW 

(although ACNW has not yet completed a formal conclusions section for the white paper). EPRI 

will provide a set of more detailed comments as requested by the ACNW. 

On Day 2, the first talk related to consequences of igneous activity was given by Bruce Marsh 

(Johns Hopkins University; ACNW consultant). He gave a presentation about potential 

magma/repository/canister processes in both eruptive and intrusive scenarios and implications 

F-9
for risk from igneous activity at the proposed Yucca Mountain repository. Professor Marsh 

described pressure-temperature phase relations for basalts, including the specific case of 

Lathrop Wells basalt, and how they evolve during ascent through the crust. He described the 

processes of convection and solidification, using paraffin as an analog medium. 

Professor Marsh then described the effects of percentage of crystals on the mobility and 

viscosity of magma. He showed how the radial flow distance of lavas at Lathrop Wells can be 

used to estimate the effective viscosity of the flows during emplacement. The result obtained is 

an effective kinematic viscosity of 109 cm2

/s. Preliminary calculations of magma flow in 

repository drifts are being performed. A key conclusion reached is that eruptions of the type 

that occurred at Lathrop Wells involved relatively explosive “wet” magma that produced 

relatively viscous, immobile lavas. This would restrict the extent to which magma could 

penetrate repository drifts. 

Art Montana (University of California – Los Angeles [retired]) discussed potential thermal and 

mechanical magma/canister interactions associated with the intrusion scenario at the proposed 

Yucca Mountain Repository. His presentation considers the potential interaction between the 

alloys and the containment vessels and the volcanic fluids, magmas and vapors. Professor 

Montana stated that we simply cannot afford to design a repository for high-level nuclear waste 

without assuming that an igneous event will occur and that it will impact the canisters. Serious 

consideration must be given to designing the drifts so that they can be backfilled which would 

provide for safety and predictability, rather than adhering to preconceived concepts of 

accessibility. 

Professor Montana discussed the susceptibility of the containment vessels to corrosion and 

failure resulting from magmatic activity. He has worked with steels and other alloys under 

extreme conditions and has firsthand experience with non-ferrous alloys similar to that being 

considered as a protective envelope around the stainless steel containers. Considering the 

potential chemical interaction between magma and the canisters at elevated temperatures, the 

2004 EPRI report used several sources of information to assess the extent of corrosion of the 

Alloy-22 shelves surrounding the stainless steel waste canister when contacted by magma, 

supplementing the scarcity of available data with the information on corrosion in hightemperature glasses and molten salts. Alloy-22 is largely a nickel alloy with lesser amounts of 

chromium and molybdenum and even lesser yet amounts of iron and cobalt. Because data for 

Alloy-22 are limited, EPRI used Alloy-X and Inconel 625, for which more data were available. 

Alloy-X is similar to Alloy-22 except that the iron to nickel ratio is higher. The chromium content 

of these three alloys is quite similar and that is an important feature. EPRI took the data from 

those three alloys at the top primarily and drew a best fit curve and concluded that the corrosion 

rates at magmatic temperatures range up to about 30 microns per day. This corrosion is similar 

for all of the chromium-containing alloys, suggesting to the investigators that it's primarily the 

oxidation of chromium itself to chromium oxide, providing a protective coating. Other 

mechanisms are possible. 

Tests had been done on the corrosion of various stainless steels and high-temperature alloys in 

the presence of oxygen, sulfur dioxide, carbon, monoxide, methane, chlorine gas, hydrochloric 

acid, and others. The results also revealed that the formation of a coating of Cr (203), 

chromium oxide, in chromium-bearing alloys provided protection from attack by other 

components. However, an important point was that at temperatures above 1,000 Celsius, the 

chromium oxide became volatile. This might be worth looking into. 

Perhaps one of the studies most relevant to Yucca Mountain is that of a Douglas and Healey in 

1981, who investigated the oxidation sulfidization of unalloyed chromium and unalloyed nickel in 

basaltic liquid at 1150°C for as long as 96 hours. The combined effects of oxidation and 

F-10
sulfidization reached about 20 microns per day, with chromium again performing better than 

nickel. And then more recently Findlan and Peterson in 2004 conducted experiments for EPRI 

using Alloy-22 immersed in molten Hawaiian basalts at 1,200 degrees Celsius for periods from 

one hour to two weeks. Maximum penetration of a corrosion front in the longest experiments 

was about 300 microns, which would average about 20 to 30 microns per day, which is 

consistent with the previous data. A crucible removed from the magma shows the quenched 

basaltic liquid and either the chromium or the nickel ring inside. It looks pretty good after being 

at 1,200 degrees for 1 to 2 weeks, but closer examination showed that it was corroded and 

pitted. Then EPRI in 2004 presented the results of modeling, and concluded that an important 

parameter is the temperature difference between solidus and liquidus, that is, the temperature 

interval over which the canisters would be at contact with molten material. EPRI concluded that 

most of the corrosion would occur in the temperature range of 1,150 Celsius to 800 Celsius. 

EPRI's conclusion from these studies was that no waste package would fail during an igneous 

event at Yucca Mountain. 

Assuming that basaltic magma penetrates the drifts at a liquidus temperature of 1,100 Celsius—

it could be less, it could be more—the DOE report of November 2004 concludes—and here I'm 

going to quote, "Even if magma were to penetrate a waste package, the magma outside of the 

waste package is expected to stagnate once the drift is filled on the order of 1,000 seconds, 

approximately 17 minutes, so that there are not likely to be driving forces that would flow in 

through a waste package. Magma is likely to fill the drifts before the waste packages heat up to 

a point of failure." Then they conclude that "In view of these results, it is safe to conclude that in 

the absence of major cracking of waste packages, a significant amount of magma will not flow 

into or through waste packages and that the waste forms will remain in place." While that may 

be so, flow might continue through a dike up to the surface, resulting in a more prolonged flow 

of magma through at least one or more of the canisters. Professor Montana remains 

unconvinced that there are adequate experimental studies to support the claims that Alloy-22 

shells will be inert to failure when exposed to magma and attendant vapors. Possibly there is 

no alloy that would provide the desired assurances. 

Professor Montana then discussed the effects of corrosion on the tangential tensile strength in 

the containment vessels and the surrounding shield. He first assumed that magma contacted a 

canister or canisters and destroyed the outer 25 percent of the Alloy-22 shield, a value that's 

consistent with the maximum value in the EPRI model. This is the outer 5 millimeters of the 

20-millimeter-thick outer shell of Alloy-22. Professor Montana showed a slide with a crosssection of a waste package, illustrating the internal tensile tangential stress (σt). The skin along 

the long axis is the weakest part in any cylinder. The inside surface being pulled apart by 

tension is where things always fail. For an uncorroded alloy shell, 20-millimeter wall thickness, 

the tangential stress will amount to 40 times the internal pressure. If the outer 5 millimeters is 

corroded, the outer 25 percent of that alloy shell, then the tangential stress is 53 times the 

internal pressure, an increase of about 30 percent. If we lose 75 percent of that 20-millimeterthick shell with leaving a thickness of 5 millimeters, then the tangential stress becomes 160 

times the internal pressure. For the 316 stainless steel vessel with a wall thickness of 

50.8 millimeters, the tangential stress is only 15 times the internal pressure. Professor Montana 

described additional examples of waste package thermal response to magma. 

Professor Montana presented several conclusions. The repository should either be backfilled or 

give serious consideration to abandoning the Yucca Mountain site. Also, he sees nothing to be 

gained by speculating about the probability of an igneous event at Yucca Mountain. We should 

accept that it will happen and enter the repository accordingly assuming the worst case scenario 

for temperature, corrosiveness, duration, and momentum of the magma. 

F-11
Timothy McCartin (NRC staff) briefed the Committee about NRC’s Regulatory Perspective on 

the Use of Alternative Conceptual Models. Under 10 CFR Part 63.114, there are regulatory 

requirements to consider alternative models consistent with available data and to account for 

uncertainties (e.g., number of waste packages included in an extrusive event). NRC’s 

performance assessment (TPA) considers alternative models as parameters (examples: 

damage to waste packages; secondary break-outs; variation in probability) and uncertainties 

(examples: variation in conduit diameter and mass loading). Computational demands are 

minimized by linear effects. Analyses of consequences of an extrusive igneous event are 

primarily affected by: number of waste packages; damage to waste package; entrainment of fuel 

in magma; and mass loading. Mr. McCartin concluded that quantitative analysis of the 

significance of alternative views will assist dialogue among groups and will support review of a 

potential license application. 

Neil Coleman (ACNW Senior Staff Scientist) briefed the Committee about the flooding history 

and geomorphology of Fortymile Wash near Yucca Mountain. Flooding would provide one of 

the key processes for eroding and transporting any contaminated volcanic ash that may be 

deposited by extrusive volcanism through a repository at Yucca Mountain. Mr. Coleman 

described how Fortymile Wash is important to volcanic extrusion scenarios, summarized key 

processes and the flooding history, reviewed the significance of large floods to dose scenarios, 

and provided comments on the potential integrity of spent UO2 fuel in a conduit. 

Mr. Coleman emphasized there is no evidence that a vent or dike has penetrated the repository 

footprint in the last 13 Myr. One 10-12 Myr old dike came close, on the northwest flank of 

Yucca Mountain, but is not known to have entered the footprint. Also, the volume of regional 

basaltic volcanism has greatly diminished since that time. If a volcanic vent were to intersect a 

waste tunnel, expelled materials could contain contamination from spent fuel. These materials 

would be deposited on surrounding hillslopes and flats in the adjacent drainage basins. 

Subsequent erosion and fluvial transport in Fortymile Wash would carry some contaminated ash 

toward the RMEI (reasonably maximally exposed individual). Mr. Coleman described the 

general characteristics of Fortymile Wash in relation to a satellite image of the region. The NRC 

staff assume in their fluvial redistribution model that all transported contaminants would be 

deposited on the distributary fan that begins just north of the intersection with highway 95 and 

extends southward. The Fortymile Wash channels continue south across the Amargosa Desert 

where they intersect the Amargosa River. 

Mr. Coleman showed the inferred fallout distribution of Lathrop Wells volcanic ash, overlain on a 

digital elevation model, to show the kind of areal pattern associated with a past eruption in the 

Yucca Mountain region. In the unlikely event a future eruption were to occur through a 

repository at Yucca Mountain, any contaminated ash that would fall outside the Fortymile Wash 

drainage, such as in Crater Flat, could contribute little or no dose to the RMEI. Also, any 

contaminants that would become entrained in scoria cones or lava flows would not contribute to 

dose because these features resist erosion for hundreds of thousands of years. As Professor 

Sparks pointed out from the Icelandic eruption, you can have this combination of fairly quiescent 

lava flows along with the explosive eruption phase. It makes sense therefore to consider a 

fraction of any extruded waste will become entrained in lava flows. It would be a significant 

amount. The NRC model assumes that all extruded contaminants come out as tephra, not as 

lava. Mr. Coleman also showed a slide illustrating that the peak risk from igneous activity would 

occur in the first 1500 years. After that time the shorter lived radionuclides, such as 241Am 

(half-life = 432 yrs), would have decayed significantly. 

Mr. Coleman showed photographs of Fortymile Wash and its banks to give perspective to its 

size. He then showed a plot of elevations along the floor of the wash and also along the 

western bank of the channel. The figure shows how to the north the channel is incised 20 m, 

F-12
but grades into the alluvial fan further to the south. The energy slope of the channel floor is 

0.011, which is quite significant. This is not a lazy eastern stream - this slope is capable of 

producing quite powerful floods. Mr. Coleman presented a table of flood data from the relatively 

short period of record. In March 1995 and February 1998, Fortymile Wash and the Amargosa 

River flowed simultaneously through their primary channels to Death Valley. These were the 

first documented cases of this conditions. The extreme 1969 flooding must also have reached 

the Amargosa River but this was not documented. These largest floods dominate sediment 

transport processes in Fortymile Wash. The smallest sediments (<62 microns in diameter) have 

the greatest potential to remain suspended and travel the greatest distances in big floods, 

especially those less than 10 microns that are the primary concern for inhalation doses. 

To show that long-distance travel of floodwaters does indeed happen in the region, Mr. 

Coleman showed photos from the wet spring of 2005 when a large lake formed in Death Valley 

in response to regional precipitation and surface water flows, including flow in the Amargosa 

River which is one of the main channels that lead into the eastern end of Death Valley. 

Assessments for Yucca Mountain that neglect long-distance transport of silt and clay-sized 

particles by large floods will overpredict the mass of small-diameter contaminated ash that 

would be deposited near the RMEI. 

Mr. Coleman then noted that insights about the transport of small sediments led to a 

reexamination of the potential integrity of UO2 fuel in a volcanic conduit. He showed a slide that 

illustrated the fuel particle sizes assumed in the user’s guides for NRC’s version 3.0 and 4.0 

codes. NRC currently uses a fuel particle size distribution of 1 to 100 microns (0.0001 to 

0.01 cm), very different from a TPA 3.0 distribution of 100 to 10,000 microns. The NRC staff 

cite NUREG-1320 as a basis for using the smaller size distribution in 4.0. However, crushing 

experiments on irradiated fuel, as documented in that NUREG, produced only a small fraction of 

fine-grained material. Only a few percent of the material was reduced to a particle diameter 

<1000 microns. Available information suggests that the ceramic pellets that comprise spent fuel 

would retain much of their integrity in a volcanic conduit, given the short travel time and distance 

through a conduit and a melting point for the pellets (i.e., >2800°C) that greatly exceeds magma 

temperatures of ~1200°C. Magma quenching on pellets could provide a protective layer, and 

xenoliths provide natural analogs of large objects that survive travel through conduits. A more 

realistic size distribution for spent fuel would reduce calculated doses to the RMEI. This can 

easily be evaluated using performance assessment. 

Sara Rathburn (Colorado State University) briefed the Committee about processes of 

importance in fluvial and eolian transport of sediments. Dr. Rathburn’s talk was titled “Fluvial 

Processes in Dryland Rivers.” Arid-region rivers are unique because they tend to be 

ephemeral, flood-dominated, discontinuous in time and space, and illustrate the importance of 

riparian vegetation and subsurface and upstream hydrology. One thing arid regions have in 

common is that evapo-transpiration exceeds the precipitation. Complex response describes 

how a channel can actually undergo two different states, erosion and deposition, as a result of 

the same triggering event. 

Dr. Rathburn then described aspects of the fluvial system, from the drainage basin to the zone 

of transfer, and then to the depositional area. In arid drainage basins there are locally high 

rates of overland flow runoff, hillslope erosion by wash processes, or runoff infiltrates before 

reaching the channels. There tend to be high sediment yields in arid fluvial systems. Little 

subsurface flow is available for the removal of solutes. Soils tend to be thin and shallow, 

develop slowly, and tend to form calcretes. Mechanical weathering is dominant and clay 

production low. Channels tend to be wide and shallow with low sinuosity, low bank stability, are 

frequently braided, and may terminate in a fan in the manner of Fortymile Wash. Arid region 

streamflow tends to be flood-driven transient flow that produces “flashy” hydrographs (i.e., high 

F-13
intensity flows of short duration). As a result the flows are hard to measure. Transmission 

(seepage) losses through the channel bed tend to be high. 

The role of floods is supreme. Floods in arid regions have the potential to move large quantities 

of sediment, can dramatically alter channel morphology, and disrupt in-channel vegetation. Of 

the 12 largest floods ever measured in the US, all occurred in semi-arid to arid regions, with 10 

occurring in regions with less than 16 in (400 mm) of rainfall. Floods carry high suspended 

sediment concentrations with a greater size range than in other rivers. The sediment tends to 

move in step-wise sediment “waves.” Bedload transport efficiency is high. Erosion and 

deposition are discontinuous. Dr. Rathburn showed a curve developed by Langbein and 

Schumm which shows that the highest sediment yields are produced at a combination of 

effective precipitation of around 300 millimeters per year (about 12 inches per year). In areas 

with more precipitation, there's greater vegetation to stabilize the slopes. Where there's less 

precipitation there is less vegetation, but there’s not as much overland flow to carry sediments 

into the channels. 

Dr. Rathburn also commented on eolian transport, noting that sand-sized material and smaller is 

transported. Eolian processes can create desert pavements. In the Lahontan basin of Nevada, 

soil-forming intervals were caused by eolian sediment pulses. In closing, Dr. Rathburn 

mentioned some of the challenges in analyzing arid region fluvial systems. It is important to 

understand the connectivity between these systems from the hill slopes to the channels, the 

tributaries down to the trunk streams. Another challenge is understanding dry land river 

behavior over long time scales. 

Brittain Hill (NRC staff) gave a talk titled “NRC Perspective on the Risk Significance of Potential 

Consequences from Igneous Activity.” He noted that NRC has conducted a range of 

independent investigations to develop review capabilities. NRC has not developed a “position” 

on igneous activity. Independent information sometimes questioned DOE models in risk 

significant areas. DOE has often modified models or approaches in response to staff questions. 

Staff will consider a full range of information during review of a license application. The review 

will focus on the risk significant aspects of the DOE safety analysis report. 

Dr. Hill discussed the potential for magma to flow into drifts. This has been rated as moderate 

risk with respect to waste isolation. Information from numerical and experimental models shows 

that if magma intersects drifts, it will depressurize, flow rapidly, and fill intersected drifts with 

molten magma approximately 1-5 minutes after intersection. Dr. Hill stated that the draft white 

paper does not cite or discuss important NRC information on magma-drift interactions, including 

aspects of degassed magma flow, 2-phase flow in dikes, and magma ascent. Dr. Hill then 

discussed possible waste package response to magma, which has been rated as high risk with 

respect to waste isolation. Will a package fail if exposed to magma? Available information 

shows combined thermal and mechanical effects from sustained (days) magmatic exposure 

exceed design capacity of waste packages. Alternative information does not increase dose 

significantly. Dr. Hill stated that the draft white paper does not cite or discuss important NRC 

information on waste package response to magma conditions, including materials properties 

and coupled igneous processes. 

Dr. Hill discussed the number of waste packages that could become entrained in an eruption, 

which has been rated as high risk with respect to waste isolation. He stated that there is 

information from analog volcanoes that shows conduits widen progressively during eruptions 

and would intersect hot, breached waste packages. Effective conduit diameters appear to be 

5-50 m [16-164 ft]. The draft ACNW white paper does not cite or discuss important NRC 

information on conduit development. Another topic rated as high risk is whether secondary 

breakouts of magma could release more waste than a single conduit? The NRC staff consider 

F-14
that secondary breakouts may occur because of repressurization effects during eruption, not 

shock effects from initial flow. Dr. Hill considers that the draft white paper does not cite or 

discuss important NRC information on the formation of secondary breakouts. 

Airborne transport processes to the RMEI location has been rated moderate with respect to risk. 

Dr. Hill stated that there is available information from models and analog deposits, and good 

support for model performance. He considers that the white paper does not cite or discuss 

important NRC information on the airborne transport of radionuclides. The concentration of 

resuspended particles gives inhalation dose to RMEI. This topic is rated high with respect to 

risk by the NRC staff. Measured airborne particle concentrations are independent of particle 

sizes in the deposit. Dr. Hill considers that the draft white paper does not cite or discuss 

important NRC information on the tephra and waste particle-size distributions. The movement 

of tephra down Fortymile Wash after a potential eruption has been rated moderate with respect 

to risk. Analog information has been abstracted for a site-specific model using a sediment 

mass-balance approach to capture average long-term redistribution processes using sitespecific information. Dr. Hill considers that the draft white paper does not cite or discuss 

important NRC information on the long-term redistribution of potential tephra deposits. 

Dr. Hill presented the following conclusions: Sufficient information currently is available to 

support staff review of the potential DOE license application for igneous activity consequences. 

The ACNW draft white paper does not address relevant information developed by NRC in each 

area discussed. The ACNW draft white paper does not include consideration of risk insights 

and model sensitivities. ACNW’s draft white paper does not address limitations in alternative 

conceptual models. 

Dr. Mick Apted (Monitor Scientific, representing EPRI) gave a talk titled “Preliminary Comments 

on ACNW “Igneous Activity at Yucca Mountain: Technical Basis for Decisionmaking”: 

Consequence Analysis.” He outlined the performance assessment approach for an igneous 

event scenario at Yucca Mountain. It is a risk-informed approach based on a system analysis. 

Dr. Apted’s talk outlined key points documented in the ACNW report and provided additional 

comments for ACNW’s consideration. One such comment was that extending the areal 

repository footprint may not affect the probability of dike intrusion, if the structure or topography 

control dike location. Another point to consider is the possible mitigation of igneous 

consequences by natural backfilling, as has been suggested by the CNWRA. In addition, 

thermo-mechanical simulations and corrosion tests with Alloy-22 and 1200̊C basaltic magma 

suggest the waste package is robust. And will overpressurization and buckling of waste 

packages occur in waste packages exposed to magma? Another comment for ACNW 

consideration - are there credible mechanisms for waste mobilization into erupting magma from 

waste packages that are not entrained in a conduit? 

Dr. Apted summarized the EPRI views regarding the white paper and volcanism. EPRI broadly 

concurs with ACNW’s sequential, structured approach regarding igneous activity at Yucca 

Mountain, and placing ‘reasonable assurance’ in context with ‘conservative’ analyses. Riskinformed performance assessment is essential to: (1) Identify processes, assumptions, and 

uncertainties that are important to safety; (2) set Performance Confirmation priorities; (3) 

examine design options; and (4) determine sufficiency of data. Lathrop Wells is a reasonably 

representative analog for future volcanism. If further study is warranted regarding regulatory 

compliance with EPA’s proposed probability-weighted, mean annual peak dose-rate criterion, 

greater assurance of safety is more likely to be gained by examining event ‘consequences’ 

rather than by further refinement of event ‘probability’ (after completion of PVHA-U report). 

Mr. Eric Smistad (DOE) presented views on the ACNW draft White Paper in relation to the 

consequences of igneous activity. The ACNW report does not include enough quantitative 

F-15
discussion or detailed comparison to field data to support conclusions of conservatism in 

representation of magma–drift interactions and magma flow in drifts. The ACNW report also 

does not include results of detailed DOE analysis of topography and thermal stress perturbation 

(during thermal period) with respect to the impact on dike propagation. 

Mr. Smistad noted that DOE will provide updates for the license application regarding various 

parameters based on analog work. These include dike length and width, the number of dikes in 

an event, the number of potential eruptive conduits in an event, conduit diameter at repository 

depth, and fractions of eruptive products in lava, cone, and tephra. A new process-based model 

is being developed for post-eruptive tephra redistribution that accounts for hill slope erosion, 

fluvial transport, sediment mixing, and radionuclide diffusion into soils at the site of 

final deposition. 

Also for an update in the license application, more detailed analyses of magma–repository 

interactions are being prepared to examine compressible fluid and interaction with pre-existing 

structure and topography, potential pressure and flow transients during the igneous event, 

multiphase interaction between rising magma and drifts, and detailed analysis of coupled 

magma flow/heat transfer/solidification in repository openings. Mr. Smistad then presented a 

series of conclusions. The ACNW report reasonably captures much of the DOE technical work 

and approach. The ACNW report is a snapshot in time using available information; it cannot 

fully capture the technical basis for a license application. More detailed comments and 

suggestions will be provided later to ACNW. 

A wrap-up round table discussion was held at the end of the day address any topics that may 

not have been adequately covered elsewhere in the meeting. Dr. Hinze also invited Working 

Group participants to provide additional written comments for consideration by the Committee 

within two weeks of the meeting, by March 1, 2007. Along with the proceedings of the working 

group meeting, these written comments would be used to further enhance and finalize the White 

Paper. The working group briefing materials, discussions, transcripts, and any follow-up written 

comments will assist ACNW in preparing a final version of the White Paper that will provide an 

analysis of the current state of knowledge of igneous activity which the Commission can use as 

a technical basis for decisionmaking.

F-16