REVIEW OF NUMERICAL ANALYSES FOR MAGMA 

DRIFT INTERACTION AT THE PROPOSED 

YUCCA MOUNTAIN REPOSITORY 

Prepared for 

U.S. Nuclear Regulatory Commission 

Contract NRC–02–07–006 

Prepared by 

Debashis Basu1 

Kaushik Das1 

1

Center for Nuclear Waste Regulatory Analyses 

San Antonio, Texas 

September 2011 
ii 

ABSTRACT 

The location for the proposed high-level nuclear waste repository at Yucca Mountain, Nevada, is 

in a small volume basaltic volcanic field in the western Great Basin. Based on the recent 

volcanic history of that field and region, if a future event occurred, it would begin with basaltic 

magma ascending through dikes 1 to 3 m [ 3.3 to 9.8 ft] in width. With continued ascent, a 

conduit up to 10 m [33 ft] in diameter might develop along the strike of the dike that reaches the 

surface, and eruptive activity, which includes effusion of lava flows and Strombolian–violent 

Strombolian eruptions, might ensue and construct a monogenetic, basaltic scoria cone. A range 

of models and data has been considered during the development of performance assessments 

conducted by the U.S. Department of Energy and as part of the U.S. Nuclear Regulatory 

Commission safety analysis for the proposed repository. A key component when abstracting 

these types of events is to understand how rising basaltic magma will interact with subsurface 

repository structures, such as tunnels (drifts), waste packages, and drip shields. Several past 

investigations have focused on numerically analyzing specific aspects of the intersection of a 

basaltic dike with the proposed repository drifts. Those analyses took into account the 

characteristics of the basalt lava (and hence magma) generally encountered in the Yucca 

Mountain region. Most of the analyses looked into the large uncertainties that existed in many 

key parameters, such as magma volatile contents, specific subsurface geometries of 

intersection between a basaltic dike and a repository drift, and the complex fluid dynamics 

nature of magma. Some of these analyses considered multiphase flow of fragmented magma 

into an open drift immediately after intersection, followed by rapid filling of the drift. Other 

analyses considered effusive flow of hot basaltic magma inside the drift neglecting gravity. 

However, most of the prior analyses (i) focused on the various aspects of dike–drift interactions 

that showed that a drift intersected by ascending basaltic magma will quickly fill with magma 

and (ii) concluded that the physical conditions, such as the velocity of the magma and the static 

and dynamic pressure inside the drift, will be significantly high. This report only considers 

analyses that have been published as technical papers, and it provides brief overviews of the 

different numerical analyses that have been carried out to simulate magma dynamics at the 

proposed Yucca Mountain repository. The report also summarizes one experimental study to 

analyze the potential interaction between rising magma and the proposed repository. 
iii 

CONTENTS 

Section Page 

ABSTRACT ................................................................................................................................... ii 

FIGURES ..................................................................................................................................... iv 

TABLE .......................................................................................................................................... v 

ACKNOWLEDGMENTS .............................................................................................................. vi 

1 INTRODUCTION ............................................................................................................ 1-1

1.1 Background ........................................................................................................ 1-1

1.2 Purpose and Scope ............................................................................................ 1-2

2 NUMERICAL SIMULATIONS: DISCUSSIONS AND OBSERVATIONS ....................... 2-1

2.1 Woods, et al. (2002) ........................................................................................... 2-1

2.2 Dartevelle and Valentine (2005) ......................................................................... 2-2

2.3 Dartevelle and Valentine (2008) ......................................................................... 2-4

2.4 Menand, et al. (2008) ......................................................................................... 2-5

2.5 Basu, et al. 2008 ................................................................................................ 2-6

3 CONCLUSIONS ............................................................................................................. 3-1

4 REFERENCES ............................................................................................................... 4-1
iv 

FIGURES 

Figure Page 

2-1 Volumetric Solid Fraction Shown in Colors .................................................................... 2-3 

2-2 Schematic Showing the Interaction of the Magma With Bubbles and 

 Gas Segregation ............................................................................................................ 2-7 

2-3 Effect of Distance Between Dike and Obstacles on the Flow Field ................................ 2-9 
v 

TABLE 

Table Page 

2-1 Geometry Configuration and Magma Dynamics ............................................................ 2-5 
vi 

ACKNOWLEDGMENTS 

This report describes work performed by the Center for Nuclear Waste Regulatory Analyses 

(CNWRA®) and its contractors for the U.S. Nuclear Regulatory Commission (USNRC) under 

Contract No. NRC–02–07–006. The activities reported here were performed on behalf of the 

USNRC Office of Nuclear Material Safety and Safeguards, Division of High-Level Waste 

Repository Safety. This report is an independent product of CNWRA and does not necessarily 

reflect the view or regulatory position of USNRC. 

The authors gratefully acknowledge D. Hooper for his technical review, E. Pearcy for 

his programmatic review, L. Mulverhill for her editorial review, and B. Street for her 

administrative support. 

QUALITY OF DATA, ANALYSES, AND CODE DEVELOPMENT 

DATA: No original data were generated for this report. 

ANALYSES AND CODES: No technical analyses or codes are presented or used in this report. 
1-1 

1 INTRODUCTION 

This report is part of the knowledge management activities for the U.S. Nuclear Regulatory 

Commission high-level waste repository safety program. It summarizes several numerical 

studies and one experimental study that have been carried out to analyze the magma dynamics 

and the possible interaction between magma and the proposed repository at Yucca Mountain. 

This report documents the different scenarios (extrusive and intrusive) that have been 

considered in the previous analyses, the numerical techniques that have been used, and the 

major findings of the investigations. 

1.1 Background 

Yucca Mountain is located in southern Nevada in a region that has experienced sporadic 

basaltic volcanism since the late Miocene (Crowe, 1986; Fleck, et al., 1996; Valentine and 

Perry, 2006; Dartevelle and Valentine, 2008). It lies within one of many small volume basaltic 

volcanic fields that typify the western Great Basin (e.g., Faulds and Varga, 1998), the Crater 

Flat Volcanic Field (Valentine et al. 2006, Connor, et al., 2000). In this field and the surrounding 

area, more than 40 basaltic vents have formed in the past 11 million years. There are 6 cinder 

(or scoria) cones within 20 km [12.5 mi] of Yucca Mountain that formed in the last million years 

(e.g., Fleck, et al., 1996) and some dikes that may have fed older eruptions. Volcanic hazard 

assessment has been a major focus of study since Yucca Mountain was first proposed as a 

repository for high-level nuclear waste. 

Most of the prior analysis of interaction between the proposed repository and rising basaltic 

magma (Dartevelle and Valentine, 2005, 2008; Woods, et al., 2002) accept a generalized 

conceptual model for basaltic volcanism near Yucca Mountain that would likely begin with an 

alkalic basalt melt ascending through the brittle crust in magma-filled cracks or dikes that are 

1 to 3 m [3.3 to 9.8 ft] thick and on the order of 1 to 5 km [0.6 to 3 mi] in length 

(Detournay, et al., 2003). Studies of the Crater Flat basaltic magmatic system (Valentine, et al., 

2005, 2006; Valentine and Perry, 2006) considered that if a future eruption occurred it would be 

similar to the most recent eruptions; the initial surface expression of the eruption would be a 

fissure, but within a few days, eruptive activity would quickly be focused into a central vent. The 

resulting volcano is likely to be a monogenetic cinder cone with a total volume on the order of 

0.01 to 1 km3 [1.3 × 103 to 1.3 × 109 yd3

] (Detournay, et al., 2003). Because the most likely 

composition of the magma is potassic trachybasalt with up to 4.6 wt% pre-eruptive volatiles 

(Nicholis and Rutherford, 2004), the eruption style will likely be Strombolian to violent 

Strombolian, characterized by both explosively emplaced tephra and effusively erupted lava 

flows, the former as evidenced by the presence of ballistic fragments in the cones (classic 

Strombolian style) and by scoria and ash-fall deposits representing fall-out material from the 

plume (violent Strombolian). 

The lack of direct physical evidence or analog cases for what might happen should magma 

intersect open drifts (sub-surface tunnels) makes it difficult to accurately quantify the impact of 

the magma dynamics on the proposed repository and its drifts (tunnels). The study by 

Dartevelle and Valentine (2007) of the explosive eruption of basaltic tephra through a 

geothermal borehole (Namafjall, Iceland) provides a unique perspective on the simulations of 

multiphase volcanic processes. The model results were consistent with observations, including 

development of complex compressible flow phenomena along with ejection of particles. 

Woods and Sparks (1998) performed initial scoping calculations to determine the potential 

behavior of magma flow inside a repository drift at Yucca Mountain. The work of Woods and 
1-2 

Sparks (1998) also led to a series of papers and reports that examined the potential 

consequences of basaltic magma intrusion into drifts (e.g., Lejeune, et al., 2002; Woods, et al., 

2002, Connor, et al., 2009 ). Collectively these papers show that the drifts will quickly fill with 

magma once the basaltic dike intersects the repository. These models considered effusive flow 

of hot basaltic magma inside the drift and neglected gravity. Dartevelle and Valentine (2005) 

considered multiphase flow of fragmented magma into an open drift immediately after 

intersection, followed by rapid filling of the drift. 

Additionally, in the last few years, a series of papers (Menand and Phillips, 2007a,b; Menand, 

et al., 2008; Phillips, et al., 2008; Woods, et al., 2002, Connor, et al., 2009) focusing on various 

aspects of dike–drift interactions have collectively shown that a drift intersected by ascending 

basaltic magma will quickly fill with magma and concluded that the physical conditions, such as 

the velocity of the magma and the static and dynamic pressure inside the drift, will significantly 

influence the integrity of a repository. These papers describe multiphase flow in a dike–drift 

configuration and experiments examining circulation patterns established in a drift after 

intersection under steady-state conditions. 

In this report, the Center for Nuclear Waste Regulatory Analyses (CNWRA®) has summarized 

and documented the various computational studies that have been carried out to date to 

analyze the predicted magma dynamics and the complex interaction between magma and the 

proposed repository at Yucca Mountain. 

1.2 Purpose and Scope 

This report documents the important technical aspects and results of computational analyses 

carried out to study the magma dynamics at the proposed Yucca Mountain repository. 

Modeling and analyses for two possible scenarios have been considered here. The scenarios 

have a spectrum from gas-poor to gas-rich magma entering repository tunnels, corresponding to 

the range of volcanic eruption behaviors that can be broadly classified as effusive to explosive. 

The explosive eruption involves the intersection of a dike with a drift, the dike then reaching the 

surface, forming a conduit, and feeding a cone- and tephra blanket-forming explosive eruption. 

The effusive eruption is much less violent and is, beneath the surface, intrusive in nature. The 

different cases considered in this report primarily deal with intrusive flow of gas-poor magma 

within the drift and some cases of invasion of a drift by gas-rich magma during an explosive 

eruption. The different numerical models in the various analyses are explained, and the 

conclusions from each of these analyses are also documented in this report. This report 

provides a brief literature review of the several numerical and experimental studies carried 

out in the past on the analysis of the magma dynamics and the possible scenarios of 

magma–repository interaction. All these past analyses were carried out from a fluid 

dynamics perspective. 
2-1 

2 NUMERICAL SIMULATIONS: DISCUSSIONS AND OBSERVATIONS 

This section details prior numerical simulations that several groups have carried out. Most of 

these studies deal with flow of magma in empty drifts (subsurface tunnels) and none of the 

analyses, except that by Basu, et al. (2008), have modeled drifts with waste containers. 

2.1 Woods, et al. (2002) 

The work by Woods, et al. (2002) was one of the first analyses carried out to evaluate 

the consequence of a rising basaltic dike intersecting a horizontal repository. It was a 

quasi-two-dimensional numerical analysis. Simulations were carried out for a homogeneous 

flow model with magma, gas, and particles all moving at the same speed. Woods, et al. (2002) 

assumed a one-dimensional flow of a homogeneous multiphase mixture where all the phases 

(magmatic melt, volatile water vapor, and exsolved gas) are in thermal and dynamical 

equilibrium. The simulations were carried out with a water content of 2 percent in the basaltic 

magma. Woods, et al. (2002) assumed a compressible flow inside the repository. The 

shock-capturing Lax scheme was used in conjunction with an essentially non-oscillatory 

scheme (Bokhove, et al., 2005). The simulations assume that the magma originated at a depth 

of 30 km [18.6 mi] at the base of the crust. Calculations show that the density difference 

between the magma and the crust result in a net buoyancy to drive the dense basaltic magma 

through the lower density rocks. The work also assumed that the dike remains open after 

breaking into the horizontal repository and magma continues to rise into and flow along the 

repository. In the simulations, the dike has a total pressure on the order of 10–20 MPa 

[210,000 lbf/ft2

–420,000 lbf/ft2], which is the total lithostatic pressure plus overpressure. 

The model results revealed that initially there is a rapid expansion of the magma mixture as 

a rarefaction wave propagates back into the dike with exsolved volatiles. The resulting mixture 

expands and accelerates along the repository length. A complex shockwave structure forms 

inside the repository with multiple shock reflections. The analysis focused on two situations: 

closed or open drift. The analysis found that if one end of the drift is closed, then on reaching 

the end of the drift, the shock is reflected and its amplitude increases by an order of magnitude. 

Subsequently, recompression of the magma-volatile mixture takes place, accompanied by 

shock waves. Woods, et al. (2002) also found that in this case, a region of high pressure 

and density develops between the end of the drift and the shock. On the other hand, for an 

open-ended drift, the calculations suggested that the explosively intruding magma will fill the 

repository within a few hours after intersection and the magma pressure in the repository drifts 

will increase steadily toward values comparable to the driving pressure. 

The analysis concluded that the precise nature of magma dynamics and magma pathways will 

depend on many factors, including any heterogeneity or fractures in the overlying rock strata, 

proximity of the repository to the surface, and any damage to the rock structure prior to the 

intersection of the dike with the repository drift(s). The analysis of Woods, et al. (2002) also 

found that once a flow path to the surface develops, a quasi-steady eruption would be 

established. However, their primary conclusion on the magma dynamics is that the intersected 

horizontal repository will be quickly filled by magma at an early stage of eruption and ascent. 

They further postulated that a steady flow system from the repository depth to the atmosphere 

would be established with three possible cases: (i) circular conduits that extend from the points 

of dike-repository intersection to the surface; (ii) magma flow through part of the repository and 

then eruption through secondary dikes; and (iii) magma flow through the intersected repository, 
2-2 

followed by further magma flow through access tunnels and then to the open 

atmospheric surface. 

The simulation by Woods, et al. (2002) assumed homogeneity within the gas-particle mixture, 

which may be a reasonable assumption for confined flow of a fragmented magma within a 

tunnel, but this assumption has not been rigorously tested. The analysis provided a starting 

point for simulating gas particle flows associated with interaction between rising basaltic magma 

and horizontal repository. 

2.2 Dartevelle and Valentine (2005) 

Dartevelle and Valentine (2005) carried out simulations to investigate the interaction between 

the horizontal repository emplacement tunnels and hawaiitic magma (alkaline basalt). They 

primarily investigated the intersection of a single feeder dike with the intersected repository 

tunnels and subsequent extension of the dike above the repository. Their results indicated that 

the dynamic pressure waves generated within the repository from the expansion of the rising 

magma and subsequent pyroclastic flows is on the order of 107

 Pa [210,000 lbf/ft2]. The 

analysis by Dartevelle and Valentine (2005) did not assume homogeneous multiphase flow 

(as assumed by Woods, et al., 2002). Instead Dartevelle and Valentine (2005) considered 

separated flow of the melt (in the form of pyroclasts) and gas. They carried out two-dimensional 

unsteady simulations using the multiphase code GMFIX (Dartevelle, 2004) that relies on the 

implicit multiphase formulation in which each phase is modeled as a continuum. GMFIX solved 

the Navier-Stokes equations as well as the partial differential equations of energy for each 

phase with appropriate turbulence models and interfacial coupling between phases. 

In the first set of simulations, the geometry consisted of a single opening above the main dike 

and at the inlet. A gas-dominated magmatic mixture (40 volume percent pyroclasts and 

60 volume percent of water vapor) is generated by the sudden decompression and 

fragmentation of an overpressurized rising magma into the repository that has an initial pressure 

of 0.1 MPa [2,100 lbf/ft2

]. The simulations revealed that about 60–65 percent of the 

gas-pyroclasts mixture flows vertically up the dike and that swift decompression of the 

mixture causes a gas shock that propagates through the repository drift with very high horizontal 

speed {~200 m/s [660 ft/s]} and a dynamic pressure of 7 × 104 Pa [1,500 lbf/ft2

]. The remaining 

30–35 percent of gas–pyroclasts mixture formed a hot, buoyant pyroclastic flow-like density 

current that propagated along the roof of the repository with a horizontal speed of 125 m/s 

[410 ft/s] and a dynamic pressure of 107

 Pa [210,000 lbf/ft2 ]. Reflection of the shock takes 

place from the end of the drifts toward the dike. The reflected gas shock was found to create a 

quasi “zero-dynamic pressure front” that moved upstream as pre-shock- and post-shockreflection gas velocities. The gas velocities change between pre-shock and post-shock. 

Simulations by Dartevelle and Valentine (2005) with a secondary dike found that some of the 

within-drift “pyroclastic flows” are diverted into the secondary dike. However, the horizontal 

speed and the dynamic pressure were identical to the case without the secondary dike 

(closed drift). Figure 2-1 shows the contours of the solid volume fraction for both cases. 

Dartevelle and Valentine (2005) concluded that the drift will eventually fill up through a process 

of recirculating flow with a continuous supply of new pyroclastic material. However, the analysis 

did not predict what happens in the adjacent drifts.They determined that flow will be inhibited 

when the concentration of pyroclasts becomes sufficiently high. 

In summary, the computational results by Dartevelle and Valentine (2005) showed that the initial 

interaction between the rising magma and the repository results in a complex transient, 
2-3 

Figure 2-1. The Dartevelle and Valentine (2005) Model of Pyroclastic Flow Inside the Drift. 

Volumetric Solid Fraction Shown in Colors. The Pyroclastic Flow Turns Downward and 

Forms a Dense Flow on the Drift Floor That Moves Backwards Towards the Main Dike (t = 

3.00 Seconds) 

(Reproduced With Permission From the American Geophysical Union) 
2-4 

explosive, multiphase flow (density current) where the speed of the pyroclastic (fragmented 

magma) mixture varies between subsonic and supersonic regimes. The simulations revealed 

that this gas–particle mixture enters a horizontal repository drift along the ceiling of the drift due 

to the upward momentum of the mixture at the dike–drift intersection. The mixture then flows 

along the roof for some considerable distance before it begins to settle downward, acting like a 

density current. If the current reaches the closed end of a drift before it settles to the floor, it 

turns and travels back toward the dike–drift intersection point along the drift floor, setting up a 

transient return flow. This sets up a circulation pattern within the repository drift. 

This work by Dartevelle and Valentine (2005) was one of the earliest simulations that 

considered multiphase magma dynamics for the proposed Yucca Mountain repository. Their 

simulation was the first for explosive violent eruption and subsequent interaction with drifts that 

considered a multiphase approach. Subsequently, Dartevelle and Valentine (2008), discussed 

in the next section, carried out more simulations and comparisons with, and incorporation of 

data derived from, analog sites. 

2.3 Dartevelle and Valentine (2008) 

Dartevelle and Valentine (2008) carried out numerical simulations to understand the range 

of processes and dynamic parameter values where a repository would be intersected by 

volatile-rich trachybasaltic magma as it ascends in a vertical dike. The analysis focused on a 

fragmented magmatic mixture (explosive disruption) under pressure interacting with an 

underground cavity, which forms a density current or flow. The simulations were two 

dimensional and time dependent and were carried out with the multiphase hydrodynamics code 

GMFIX. The numerical simulations indicated that when gas–particle mixtures rising from below 

interact with horizontal repository drifts, complex flow patterns involving varying degrees of 

recirculation develop in the density current, along with deposition of pyroclasts in the repository. 

The analysis was primarily based on three assumptions: (i) the geometry of the dike and the 

conduit was chosen based on studies from older volcanoes in the regions; (ii) the fragmented 

gas-pyroclastic flow (density current) is considered as an end-member for interaction between 

magma and repository (the other end-member is the flow of viscous, effusive (unfragmented) 

magma); and (iii) a multiphase approach is the most suitable where a continuous gas phase and 

a dispersed particle phase are treated as an overlapping continuum with each phase satisfying 

the mass, momentum, and energy equations. 

Initial conditions for most of the simulations had atmospheric pressure inside the repository drift 

and a temperature of 25 °C [77 °F]. The inlet pressure was taken as 12.5 MPa [261,000 lbf/ft2

]. 

This consists of an overpressure of 6 MPa [125,000 lbf/ft2

] and a lithostatic pressure of 6.5 MPa 

[136,000 lbf/ft2

]. Simulations were carried out for two values of water content for the gas–

particle mixture: 4.6 WT% (high water content) and 1.2 weight percent (low water 

content). Total mass flux at the inlet was 7.4 × 105

 kg/s [1,630,000 lbm/sec]. The average 

vertical inlet velocity for the gas–pyroclast mixture at the dike entrance was 3.9 m/s [12.8 ft/sec]. 

Temperature of the gas-pyroclast mixture at the inlet was 1,273 °K [1,832 °F]. 

Computed results demonstrated that the nature of the gas–pyroclast mixture flow inside the 

repository after intersection with the dike and the circulation pattern is strongly influenced by 

repository geometry. Simulations with a closed drift geometry (without any exit) generated the 
2-5 

highest absolute dynamic pressure and the flows are more dilute if there is an opening. Also, 

the dynamic pressure is higher for the high-water-content gas–pyroclast mixture compared to 

the low-water-content gas–pyroclast mixture. 

The dynamic pressure generated inside the repository is also found to be influenced by the 

diameter of pyroclastic particles considered in the simulations. Simulations showed that the 

least inertial particles with a diameter of 100 mm [0.33 ft] have the fastest motion and produce 

the highest dynamic pressure. On the other hand, the particles with the most inertia are those 

with a diameter of 1 cm [0.033 ft], which generated the least dynamic pressure. As the flow 

moves downstream in the horizontal direction within the repository drift, the 1-mm [0.0033-ft] 

and 1-cm [0.033-ft] particles settle rapidly on the floor to form a denser concentrated granular 

flow, while the finer particles maintain a diluted flow. 

Simulations reveal that apart from the geometric configuration, the water (vapor) content of the 

magma in dike is also important for the flow dynamics. Higher water (vapor) contents in the 

magma will lead to more dilute flows in terms of pyroclastic mixtures. A more dilute flow can 

maintain a slower flow on the roof of the drift and a more turbulent gas–particle mixture over the 

whole length of the repository drift. Hence the dilute flow is able to generate higher dynamic 

pressures because of the higher vapor content. 

Overall, magma dynamics and interaction of the ascending magma with the horizontal drift is 

found to be sensitive to the geometry of the interaction (closed or open repository), particle size 

of the pyroclasts, the volatile content of the pyroclasts, and the pressure boundary conditions. 

Table 2-1 provides a summary of the different geometrical configurations and magma dynamics. 

2.4 Menand, et al. (2008) 

All three previous simulations considered one end-member of the intrusive scenario; namely, 

fragmental (“explosive”) flow into the repository drifts. A study by Menand, et al. (2008) 

considered the other end member: effusive eruption and associated magma dynamics within the 

horizontal repository drifts. Many basaltic volcanoes that have Strombolian eruptions have 

phases during which a relatively stationary column of liquid magma remains in the volcanic 

conduit and sub-surface plumbing system for a period of time (Dartevelle and Valentine, 2008), 

so this could be a realistic scenario for a disruptive event at future repository drift. 

Under this situation, bubbles are formed by slow exsolution of volatiles from the magma. These 

bubbles tend to rise and set up circulation patterns in shallow magmatic systems. Many 

classical Strombolian eruptions are found to be caused by large bubbles bursting at the surface 

Table 2-1. Geometry Configuration and Magma Dynamics for Different Experiments 

Construct Value 

Closed repository drift Generated the highest absolute dynamic pressure 

Granular concentration increases with time because there is 

no exit 

Strong pyroclastic current generated in the recirculating zone 

Repository drift with one opening Less dynamic pressure compared to the closed repository 

More turbulence compared to closed repository drift 

Opening creates much more complex circulation pattern 

within the repository drift compared to the closed repository 

drift 

Repository drift with two openings Flow field is similar to the closed repository with one opening 
2-6 

of magma columns with exsolved volatiles. Menand, et al. (2008) studied the physics 

associated with gas segregation in a magma-filled drift through analogous experiments. This 

analysis deals with the effusive sustained magma (lava-like) flow in a repository drift intersected 

by a vertical dike. The experiments revealed how gas segregation is dominated by exchange 

flow between the vertical dike and the horizontal repository drift due to the presence of exsolved 

gas bubbles. Menand, et al. (2008) showed that circulation would develop in the tunnel, with 

the primary vortex closest to the entrance of the cavity being the strongest and the strength of 

the successive vortices decreasing down the tunnel. They also showed that foam, which 

developed from degassing (bubble growth), could change the flow style in the tunnel. 

The experiment shown in Figure 2-2 demonstrated that if a horizontal pipe or sill is connected to 

the vertical feeding conduit of such a volcano, a flow pattern can be set up in which some 

bubbly magma is diverted into the horizontal body (in this case the horizontal repository drift). 

As the magma flows horizontally away from the main conduit/dike, bubbles continue to rise and 

form a foam at the top of the horizontal repository drift, while the bottom of the horizontal 

repository drift becomes enriched in denser, degassed magma. The interaction of the foam and 

degassed magma sets up an exchange flow between the vertical conduit (or dike) and the 

horizontal repository drift. This constitutes the gas segregation mechanism. 

Experimental results determined that the time for gas segregation is controlled by the rate of 

rise of the bubbles in the drift. The time required for steady-state gas segregation in an effusive 

eruption will range from hours to hundreds of years depending on the average size of the 

exsolved gas bubbles and the viscosity of degassed magmas. The amount of degassing will be 

determined by the degree of water exsolution, cooling, and crystallization. 

The mass flux associated with gas segregation was found to be dependent on the viscosity of 

the magma. It is less for most viscous degassed magmas. The mass flux is also found to be 

strongly dependent on the average exsolved bubble diameter. If the magma supply rate is 

higher than the flux associated with gas segregation, then the eruption will be of a violent 

Strombolian nature. For a magma supply rate that is lower than the flux associated with gas 

segregation, the eruption characteristics will be those of milder episodic Strombolian explosions. 

These explosions are generated by the repeated collapse of the foam accumulated at the top 

of drifts. 

2.5 Basu, et al. 2008 

CNWRA staff carried out a computational analysis to investigate the flow of magma into a 

horizontal subsurface tunnel, including obstacles, after intersection during initial ascent in a dike 

(Basu, et al., 2008). These models were not designed to simulate the conditions of initial 

intersection or investigate possible changes to the properties of the first magma to arrive at the 

drift, but rather the conditions after intersection as the drift is effusively invaded and filled with 

magma. The numerical model provided some ideas about the flow patterns that might develop 

in a dry subsurface tunnel intruded and transected by a dike of degassed (single-phase) basaltic 

magma, where the tunnel contains obstacles. This showed that the tunnel will fill with magma 

and provides a glimpse of the complex flow patterns that might develop in the tunnel near the 

dike under various conditions of magma supply rate and obstacle position. The 

two-dimensional simulation results show that magma flow patterns that develop within 

the tunnel are affected by the location of the dike intersection, relative to obstacles present 

in the tunnel. Under the conditions modeled in this study, low viscosity, nonexpanding magma 

ascending along a dike that intersects a repository drift will fill the drift under the influence 
2-7 

Figure 2-2. Schematic Showing the Interaction of the Magma With Bubbles and Gas 

Segregation (Menand, T., J.C. Phillips, and R.S.J. Sparks. “Circulation of Bubbly Magma 

and Gas Segregation Within Tunnels of the Potential Yucca Mountain Repository.” 

Bulletin of Volcanology. Vol. 70, No. 8. pp. 947–960. 2008. Reproduced With Kind 

Permission of Springer Science+Business Media). 

 
2-8 

of gravity from the base to the top and then continue upwards along the dike. Counterrotating 

vortices in magma adjacent to the dike that extend into the tunnel are driven by viscous 

coupling between the magma rising in the connected dike and the magma in the tunnel. In the 

tunnel beyond these primary vortices, a larger, low velocity circulation cell is established with 

magma flowing away from the dike along the base of the tunnel and toward the dike along the 

tunnel ceiling. 

This same pattern develops in the presence of an obstacle in the tunnel. Flow patterns that 

develop in a magma-filled tunnel can be affected by the location of dike intersection, specifically 

relative to obstacles in the tunnel. Slight changes in the modeled distance between the dike 

and the obstacles produced additional vortices adjacent to the primary vortices (i.e., those 

located directly next to dike position) that extended higher velocity circulating magma further 

down the tunnel, as shown in Figure 2-3. In addition to the strength and size of the primary 

vortices, the shape and distribution of the vortices that develop are affected by the ascent rate 

of the magma in the dike. At higher ascent rates, vertically coupled counterrotating vortices 

develop in the space between the dike and the obstacles. In all cases, some pattern of 

circulation developed in the tunnel, and the pattern was largely influenced by the interplay 

between the ascending magma and location of the obstacles. 

 
2-9 

(a) 

Distance Between Dike and Obstacle: 4 m 

(b) 

Distance Between Dike and Obstacle: 7 m 

Figure 2-3. Effect of Distance Between Dike and Obstacles on the Flow Field. Color 

Contours Show Vorticity Superimposed With Velocity Vectors (Basu, et al., 2008). 

Magma Inlet Velocity = 1 m/sec [3.28 ft/sec]; Length Is in Meters. 
3-1 

3 CONCLUSIONS 

This report presents and summarizes the results of several numerical studies and one 

experimental study that analyze magma dynamics in the case where a rising dike may 

intersect the drifts at the proposed Yucca Mountain repository. The analyses focused on 

different scenarios of an ascending basaltic dike intersecting a horizontal repository drift and 

its significance. 

The analyses considered in this report have taken into account both end-member types of flow 

into (and out of) repository drifts: (i) flow of gas-poor magma as an incompressible viscous fluid 

and (ii) compressible flow of fragmented magma and a continuous gas phase (i.e., a pyroclastic 

flow-like density current). Basu, et al. (2008) considered the flow of gas-poor magma, while the 

analyses of Woods, et al. (2002) and Dartevelle and Valentine (2005, 2008) considered the 

compressible flow of fragmented magma and a continuous gas phase. In between these two 

end members are flows that are bubbly in nature; however, in these flows, the continuous phase 

is treated as incompressible basaltic melt. Menand, et al. (2008) and Phillips, et al. (2008) 

considered such flows and conducted experiments to study the role of a horizontal body on the 

mass transfer processes in a vertical conduit with bubbles. 

The analyses showed that the interaction of rising basaltic magma and the horizontal repository 

drift is controlled by the geometry of the repository drift, the conditions inside the drift, and the 

presence of obstacles (Basu, et al., 2008). Flow features encountered in compressible 

fragmented magma flow are different from the flow features observed in effusive incompressible 

magma flow inside the repository drift. For degassed magma, gas segregation may occur. 

However, that possibility is controlled by the rate of bubble formation in the magma and the 

magma viscosity. 
4-1 

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