C.726 

Assessment of 

Geothermal Resources 

of the United States-1975 

GEOLOGICAL SURVEY CIRCULAR 726 

Prepared in cooperation with the 

Energy Research and Development Administration 

Assessment of 

Geothermal Resources 

of the United States-1975 

D. E. White and D. l. Williams, Editors 

G E 0 L 0 G I C A L S U R V E Y C I R C U L A R 726 

Prepared in cooperation with the 

Energy Research and Development Administration 

1975 
United States Department of the Interior 

CECIL D. ANDRUS, Secretary 

Geological Survey 

H. William Menard, Director 

Library of Congress catalog-card No. 75-600076 

First printing 1975 

Second printing 1975 

Third printing 1976 

Fourth printing 1979 

Free on application to Branch of Distribution, U.S. Geological Survey 

1200 South Eads Street, Arlington, Va. 22202 
FIGURE 1. 

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CONTENTS 

Page 

Introduction, by D. E. White and D. L. Williams ------------------------------- 1 

Hydrothermal convection systems, by J. L. Renner, D. E. White, and D. L. Williams 5 

Igneous-related geothermal systems, by R. L. Smith and H. R. Shaw ------------ 58 

Temperatures 'and heat contents based on conductive transport of heat, by W. H. 

Diment, T. C. Urban, J. H. Sass, B. V. Marshall, R. J. Munroe, and A. H. 

Lachenbruch -------------------------------------------------------------- 84 

Geothermal resources in hydrothermal convection systems and conduction-dominated areas, by Manuel Nathenson and L. J. P. Muffler --------------------- 104 

Recoverability of geothermal energy directly from molten igneous systems, by 

D. L. Peck ---------------------------------------------------------------- 122 

Assessment of onshore geopressured-geothermal resources in the northern Gulf 

of Mexico basin, by S. S. Papadopulos, R. H. Wallace, -Jr., .J. B. Wesselman, 

and R. E. Taylor --------------------------------------------------------- 125 

Appendix, discussion of data used -------------------------------------- 141 

Summary and conclusions, by D. E. White and D. L. Williams ------------------- 147 

ILLUSTRATIONS 

Map showing 1ocation of hydrothermal convection systems in the conterminous United SU3 tes 

Page 

~ith indicated subsurface telllpe~tures above 150°0 -------------------------------------- 22 

Map showing location of hydrothermal conve~tion systems in Alaska and Hawaii· with indicated 

subsurface temperatures above 150°0 and between 90° and 150°0 ------------------------- 23 

Map shoping location of hydrothermal conve~tion systems in the conterminous United Stztes 

·with indicated subsurface temperatures between 90°0 and 150°0 --------------------------- 50 

Graph of theoretical cooling time versus volume for magma bodies -------------------------- 74 

Map showing identified volcanic systems in the conterminous United States ------------------- 77 

Map showing identified volcanic systems and basaltic lava fields known to be less than 10,000 

years old in Alaska and Hawaii ----------·------------------------------------------------- 79 

Map showing basaltic lava fields known to be less than 10,000 years old in the contermin')US 

United States -----------------------------------------------~----------------------------- 80 

Histogram of heat-generation values obtained in connection with q-A ------------------------ 89 

Map of observed heat-flow (q) measurements in the United States -------------------------- 94 

Map of reduced heat-flow ( q*) measurements in the United Sta.tes --------------------------- 96 

Map showing probable extent of hot, normal, and cold crustal regions ------------------------ 98 

Graph of temperature profiles for various types of provinces --------------------------------- 101 

Maps showing locations of hydrothermal convection systems with temperatures above 90°0 and 

stored heat greater than or equal to 0.3 X 1018 cal ------------------------------------- 111 

A, Graph showing electric power per well as a function of mass flow for various temperatrres 

of hot-water and vapor-dominated systems; B, Graph showing electric power per well as 

a function of value needed to pay for the well for v·arions well costs --------------------- 116 

Location map showing the extent of the assessed geopressured zones and ·their division into 

subareas -------------------------------------------------------------------------------- 126 

Graphs showing variation of well spacing with the ratio of flow rate to the 20-year formation 

drawdown for each of the conceptual reservoirs ----------------------------------------- 135 

iii 
TABLE 1. 

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TABLES 

Page 

Categories of geothermal resource base ------------------------------------------------------- 3 

Metric units used in this volume ------------------------------------------------------------- 4 

Identified v·apor-dominated systems of the United States with probable subsurface temperatures 

exceeding 200°0 -----------------------·------------------------------------------------- 8 

Identified hot-water convection systems with indicated subsurface temperatures above 150°0 __ 10 

Identified hot-water convection systems with indicated subsurface temperatures from 90° to 150°0 24 

Summary of identified hydrothermal convection systems ------------------------------------ 55 

Magnitudes and heat co~tents of identified volcanic systems ----------------------------------- 59 

Basic volcanic fields probably less than 10,000 years old -------------------------------------- 81 

Excess temperature below a low-conductivity layer ------------------------------------------ 87 

Deficit of temperature below a high-conductivity layer ---------------------------------------- 88 

Basic calculations: temperatures Tz at depths z for various assumed v-alues of q* and A. ------- 90 

Heat stored in the depth intervals ~ km and 3-10 km -------------------------------------- 91 

Heat stored beneath provinces in the depth intervals ~ km and 3-10 km --------------------- 92 

Heat content above mean annual surface temperature CYf the continental crust ------------------ 93 

Recovery factors ( er) for electrical power generation ---------------------------------------- 107 

Estimated potential electric energy from identified high-temperature hydrothermal convection systems ----------------------------------------------------------------------------------- 108 

Typical values for electric energy produced per kilogram of reservoir fluid ( Wact) as a fpu.ction of 

source temperatures --------------------------------------------------------------------- 114 

Drilling cost model -------------------------·------------------------------------------------- 114 

Resources of hydrothermal convection systems for the generation of electrical power in megawatt 

centuries ------------------------------------------------------------------------------- 118 

Intermediate-temperature hydrothermal convection systems wi-th stored heat greater thar or equal 

to 0.3 X lif8 cal -----------------------·------------------------------------------------- 119 

21. Areal extent and average pressure, temperature, and salinity conditions in each subareB -------- 128 

22. Assumed thickness ·and properties of sand and shale beds in idealized "conceptual :rese~oirs" -- 129 

23 .• Calculated aquifer parameters and water properties used in this study ------------------------- 131 

24. Assessment of the "fluid resource base" -----·------------------------------------------------- 132 

25. Assessment of "recoverable energy" under the assumed basic development plan, Plan 1 --------- 137 

26. Estimated heat content of geothermal resource base of the United States ------------------------ 148 

27. Geothermal resources of hydrothermal convection systems ------------------------------------ 150 

28. Geothermal resources of geopressured sedimentary environments ----------------------------- 151 

jy 
Assessment of Geothef'imal Resources of the United States-1975 

Introduction 

By D. E. White and D. L. Williams 

Over the past 10 years, various individuals 

and organizations have made estimates of the 

geotherm·al resources of the United States (White, 

t965; Grossling, 1972; Rex and Howell, 1973; 

Hickel, 1973 ; N atl. Petrol. Council, 1973). These 

estimates have differed by several orders of magnitude. This wide variation has been due in part 

to lack of or differing assumptions regarding 

technology and economic conditions, but much of 

the uncertainty has been caused by an inadequate 

understanding of the nature and extent of the 

resources themselves. 

Although future technology and economic conditions continue to be difficult to predict, considerable progress has been made during the past 

few years toward ·a better understanding of the 

resources--enough to improve significantly the 

basis for a comprehensive assessment of the magnitude, distribution, and recoverability of various 

categories of geothermal resources within the 

United States. The new assessment presented here 

is appropriate in light of this improved understanding and is designed to help Government and 

private industry to evaluate the present and future significance of these resources during their 

consideration of problems and opportunities for 

the development of geothermal energy. 

Although these new resources estimates rest on 

a much improved scientific base, they should not 

be taken as final appraisals that are valid indefinitely into the future. They are limited by the 

data available to us early in 1975 and will need 

to be revised at appropriate times as more data 

and better methods of evaluation become available. A format has been chosen that is an;lenable 

to revision. 

1 

This assessment of geothermal resources differs 

from previous resource statements in that it tabulates each identified system or subdivision of the 

major resource categories of table 1, listing the 

paran1eters assumed in calculating volumes, heat 

contents, and recoverabilities. As technology, economic conditions, and our know ledge of specific 

systems change, any of the variables nay be 

changed to arrive at updated assessments, 

Resource-related terms used in this circular are 

defined as follows : 

Geothermal resource base includes all of tho stored 

heat above 15°C to 10 km depth in all 50 

states. 

Geothermal resources are defined as storei heat, 

both identified ·and undiscovered, that is recoverable using current or near-currert.. technology, regardless of cost. Geothennal resources are further divided into thre~ categories based on· cost of recovery : 

(1) Submarginal geothermal resources, recovable only at a cost that is more th".n two 

times the current price of competitive energy systems ; 

(2) Paramarginal geothermal resouroes, recoverable at a cost between one and two 

tiines the current price of competitive energy; and 

(3) Geothermal reserves, consisting of those 

identified resources recoverable ·at a cost 

that is competitive now with other commercial energy sources. 

Undiscovered resources that are economically 

recoverable are not differentiated in this report 

but would be the economic equivalent of reserves. 

The first sections of this assessment of geo-
thern1al resources include our estimates of the 

total resource base, subdivided into categories _of 

geothermal systems (table 1). The different categories are relate.d to the fact that, although temperature generally increases with depth below the 

surface of the Earth, the relative rates of increase 

differ fron1 place to place, depending on the local 

subsurface geology and hydrology. Depth below 

ground surface is an important factor in determining the cost of utilization, so we have arbitrarily limited our calculations of the resource 

base to two depth ranges : surface to 3 km 

(roughly the maximmn depth yet drilled for geothennal energy) and frmn 3 to 10 km (roughly 

the maximum depth yet drilled in search for oil 

and gas). 

The hydrothermal convection systems of cate,-

gories 1~ and 1b ( 1) (table 1) include all areas 

that are presently being utilized or explored for 

generation of electricity; the systems of category 

1b(2) are. attractive for nonelectrical space and 

proeess heating. The relatively high favorability 

of these systems is clue to the faet that convection 

of water (or steam) transfers heat from the hot 

deep parts of a system to its near-surface parts. 

Thus, higher temperatures are attainable in shallower wells at lower costs than in nortnal ten1-

pe.rature-graclient areas where heat is transferred 

dmuinantly, if not entirely, by conduction through 

solid roek. The presenee of steam or water as a 

natural working fluid is an additional tnajor advantage of the convection systems, but the locally 

available quantity may not be adequate for production on a commercial scale. Systems with assumed maximum temperatures below 90°C are 

omitted from our tabulations because adequate 

data are generally lacking, but many are listed 

by Waring (1965). 

The hot igneous systems of category 2 provide 

challenges for major future utilization. Of all 

categories, those with molten magn1a at temperatures ·above 650° C (and in part as high as 

,_,1~200°C, depending on type of n1agma) contain 

the most stored heat per unit of volume or mass; 

however, the technological problems of utilizing 

this heat are the most difficult for all categories. 

These large young magma systems are especially 

attractive targets for exploration, and their existenee aecounts for many of the known highly 

favorable hyclrother1nal convection systen1s. The 

hot llry rocks of category 2b may not always be 

2 

as hot or as dry at shallow and intennediate 

depths as generally envisioned be~ause hydrothermal convection in natural fractures may be 

more comn1on than is indicated from surface 

eviclPnce. 

Category 3 ineludes the conduction-dominated 

regions that underlie n1ost of the TJnited States 

and that constitute by far the largest part of the 

total resource base. The volumes of rock involved 

are huge, but average temperatures are low. Convection of natural fluids is a tninor faotor in many 

of these conduction-dominated -areas. Of special 

note in this category is the ge.opress11red environment of the gulf coast; the tenn "1uid resource 

base" denotes only the fluid part of the total 

geothermal resouroe base of the gulf coast. 

The later sections of this assessrnent consider 

the parts of the resource base that may be available for recovery and utilization, depending on 

various physical, econmnic, and technological constraints. Reliable estirnates of recoverability are 

n1ore difficult to derive than are the. estimates of 

the resource base because of the gr"'f.at unoertainties of :future prices, technologies, and .govenlmental and environmental eonsiclerations and the 

natural physieal properties of the deep subsurface. 

National parks have been given special status 

in this geothermal assessment. Some national 

parks and national monuments were created because of their young or active volcanism or be 

cause of their spectacular geysers and hot springs, 

which are the surface evidence of high-tenlperature convection systems (Yellowstone, Lassen, 

Crater Lake, Mount Rainier, Hawaii Volcanoes, 

and J{atmai). The parks are included in estimates of the resource base (they are in the United 

States, and they do have much heat in the 

around), but they have been excluded frotn all 

~onsiderations of recoverability and utilization. 

Geothermal exploitation of W airakei, New Zealand, and Beowawe Geysers, Nevada, has diverted 

the natural water supply into wells and has destroyed the hot springs and geyser~ These hotwater systems clearly cannot sustain both natural 

activity and exploitation. The vap'lr-dominated 

systems (Larderello, Italy, and The Geysers, 

California) are not so immediately sensitive, but 

long-range destruction of the natural activity by 

e.xploitation is equally cert·ain. 

Con version factors from the metric system of 

units to English units and explanations of some 
Table 1.-categories of geothermal resource base (heat in the ground at temperatures above 15° C to specified 

depths and without regard for recoverability) 

1. Hydrothermal convection systems 

(relatively high temperatures 

at shallow depths; heat content 

estimated only to 3 km depth; 

see Renner and others, this 

volume). 

a. Vapor-dominated systems 

b. Hot water systems 

Temperature 

Characteristics 

Natural fluid 

supply 

Available; not 

always adequate. 

(1) High-temperature systems >150oc Available; not 

always adequate. 

(2) Intermediate-temperature systems 150°C to ~gooc Available; not 

always adequate. 

(3) Low-temperature systems <90°C Available; not 

always adequate. (not tabulated; many in 

Waring, 1965) 

2. Hot igneous systems (excluding 

hydrothermal convection systems 

in (1) above; heat content estimated from 0 to 10 km depth; see 

Smith and Shaw, this volume). 

a. Assumed part still molten 

b. Assumed not molten but very hot ( 11 hot dry rocks 11

) 

3. Conduction-dominated areas (by heatflow provinces, utilizing available 

data on heat flowsl radiogenic heat 

production, and thermal conductivity 

of rocks; heat contents estimated for 

0 and 3 and 3 to 10 km depth; see 

Diment and others, this volume. This 

category includes the Gulf Coast geopressured environment with its fluid 

fraction specially considered by Papadopulos and others, this volume). 

terms in this report are shown in table 2. 

ACKNOWLEDGMENT 

The work of this assessment was carried out 

by the U.S. Geological Survey's Geothermal Research Program with encouragement and funding 

from the Energy Research and Development Administration. Its support made it possible to accomplish this assessment at an ac~lerated pace. 

REFERENCFS CITED 

Grossling, B. F., 1972, An appraisal of the prospects of 

geothermal energy in the United States, in U.S. 

energy outlook: Natl. Petroleum Council, Washington, D.C., Chap. 2, p. 15-26. 

3 

Inadequate. 

Generally 

inadequate. 

Adequate in parts 

of sedimentary basins, generally 

inadequate elsewhere.· 

Hickel, W. J., 1972, Geothermal energy; Geothermal RPsources Research Conference Final rept., Univ. of 

Alaska Press, 95 p. 

National Petroleum Council, 1973, U.S. energy <'ntlooknew energy forms: Washington, D.C., U.S. Govt. 

Printing Office, 9 p. 

Rex, R. W., and Howell, D. J., 1973, Assessment of U.S. 

geothermal resources, in Kruger, Paul, and Otte, 

Carel, Geothermal energy, resources, production, 

stimulation: Stanford, Calif., Stanford Uni'7, Press, 

p. 59-60. 

Waring, G. A., 1965, Thermal springs of the United States 

and other countries of the World-A summary, U.S. 

Geol. Survey Prof. Paper 492, 383 p. 

White, D. E., 1965, Geothermal energy: U.S. Gool. Survey Circ. 519, 17 p. 
Table 2.-Metric units used in this volume, conversion factors to other units, and some assumed values for physical 

parameters. 

Length: 

Area: 

meter (m) = 3.281 ft; 1 kilometer (km) = 3,231 ft 0.6214 mi; 

centimeter (em)= 0.3937 in. = 6.214 x 10- 6 mi. 

km2 = 106

m2 = 0.3861 mi 2 247.1 acres. 

Volume: 1 km3 = 0.239 mi 3 = 10 12 ~; 1 liter (Q) = 0.2642 gal; 1 ~/ min = 5.886 x 10- 4 ft 3/sec. 

Temperature: oc = 5/9 (°F- 32); ooc = 235.l5°K. 

Temperature gradient: l°C/km = lo- 3oc;m rate of increase in temperature with 

depth: conductive gradient is directly proportional to heat 

flow and inversely proportional to thermal conductivity of the 

rocks. 

Pressure: 

Heat/power: 

Heat flow: 

1 bar= 0.9869 atm = 1.020 kg/cm2 = 14.50 psi = 106 dynes/cm2 = 0.1 meganewtons/m2 . All pressures absolute, with 1.01 bar added 

to gage pressure at sea level and geothermal areas at low altitudes. 

1 cal = 4.186 joules= 3.9685 x 10-3 BTU= 0.001 kcal = 0.00116 

watt h; 1 cal/g = 1.80 BTU/lb. 1 MW (electric)·century = 7.53 x 10 14 cal (therma1¥ec, where ec is conversion efficiency. 

Coal assumed to have a potential heat content of 7.2 x 103 cal/~. A barrel of petroleum (42 gal) assumed to have potential heat 

of combustion of 1.45 x 109 cal = 5.8 x lOh BTU= 0.223 short tc~s 

coal. In this volume, heat contents stated in units of 1018 cal, 

with each unit equivalent in heat content of 690 million barrels 

of petroleum or 154 million short tons of coal. 

l x 10-6 cal/cm2 sec= 4.19 x 10-2 W/m2 (watts per sq. meter); 

the world-wide average conductive heat flow is approximately 

1.5 x 10- 6 cal/cm2 sec 

Thermal ctnductivity: 1 X 10-3 ca1/cm SPC or = 0.41R Wfm~K. 

M~ss: 1 q = 10-3 kg 10-6 metric ton= 2.20 x 10-3 1b 1.103 x 10-6 

short ton. 

Vo1umetrl~ specific hPat of pure water at standard temperature and pressure is 1.0 

ca1/cm3 oC and of average rocks, assumed 0.6 cal/cml/"C. Heat in 

granite magma at 900"C, crystallizing and cooling to ''·15"C assurred 

to release ''·300 cal/q or ,,,7 x 10 17 cal/krn ~ equivalent heat in 

molten basalt at 1,100°( is ~375 ca1/q. 

4 
Assessment of Geothermal 'Resources of the United States-1975 

Hydrothermal Convection Systems 

By J. L. Renner, D. E. White, and D. L Williams 

In hydrothermal convection systems, most of 

the heat is transferred by the convective circulation of water or steam rathe,r than by thennal 

conduction through solid rocks. Convection occurs in rocks of adequate permeability because 

of the buoyancy effect of heating and consequent 

thermal expansion of fluids in a gravity field. The 

heated fluid tends to rise, and the more dense, 

cooler fluid tends to descend elsewhere in the 

system. Convection, by its nature, tends to increase temperatures at higher levels as temperatures at lower levels decrease below those that 

would otherwise exist. 

Worldwide experience gained from geothermal 

exploration of hydrothermal convection systems 

indicates that most systems contain liquid water 

as the dominant pressure-controlling fluid in fractures and pores. Wells drilled into such systems 

normally deliver at the wellhead a mixture of 

liquid water and 10 to 30 percent of steam, which 

forms in the well bore as pressures decrease upward. In a few systems, however, such as Larderello, Italy, and The Geysers, California, wells 

produce saturated or even superheated steam, 

typically with no associated liquid. Moreover, inhole pressures measured in shut-in wells of these 

systems normally increase only slightly with 

depth within the reservoir; the increase in pressure is equivalent to that of a column of steam 

and associated gases and is much less than the 

pressure gradient in a oolumn of water. Pressures 

in these relatively rare systems evidently are controlled by vapor rather than by liquid, and thus 

the systems are called vapor-dominated systems. 

VAPOR-DOMINATED SYSTEMS 

There is still divided opinion on the origin and 

fundamental characteristics of vapor-dominated 

geothermal systems and on why they differ so 

much in their production characteristicf from 

the more abundant hot-water systems (Truesdell 

and 'Vhite, 1973). All successful wells in tre Geysers field, the outstanding example of this type 

of systen1 in the United States, produce saturated 

or slightly superheated steam containing little or 

no liquid water and only a small percentage of 

other gases. Some succesSful wells initially discharge some water that dries up to pure vapor 

with time. In-hole temperatures prior to much 

production tend to be close to 240°C if re.~ervoir 

depths are greater than about 400 n1; initid wellhead pressures are close to 34 bars (James, .,1968; 

Ramey, 1970; White. and others, 1971). These 

characteristics are generally accepted as typical 

of the deeper "virgin" parts of The Geyse~, Larderello, Italy, and Matsukawa, Japan.1 

5 

The stored heat of the reservoir rocks is probably 85 percent or more of the total heat in the 

vapor-dominated systems (Truesdell and White, 

1973). Production of steam frmn a reservoir results in a decline in pressures; consequently, water 

in the pores boils to steam, utilizing heat stored 

in the reservoir rocks. 

Many aspects of vapor-dominated systems are 

1 Other types of vapor-dominated systems exist, such as those near Monte Amiata, Italy (lower in temperature a'l'd much 

higher in gases other than steam; White, 1973, p. 87, 88; 

Truesdell and White, 1973), and those found in sh"llow re- gimes between ground surface and the water table under local 

topographic highs of hot-water systems. But in this r£port, the term "vapor dominated" refers to high-temperature low-gas 

systems such as The Geysers and Larderello. 
not well understood, and critical obseiW:ations 

within and below the reservoirs either have not 

boon made, or the .data have not yet been released 

by the operating con1panies. Our interpretations, 

however, favor steam as the continuous pressurecontrolling fluid in the reservoir, but with liquid 

water being locally available in small pore spaces 

and on fracture surfaces. Because of surface tension, this water cannot be drained completely by 

gravity. Below the vapor-dominated reservoir, 

we envision a deep water table with underlying 

rocks saturated with water, probably a highchloride brine (Truesdell and White, 1973)~ EstiInates of reserves and resources of vapor-dominated systems (N athenson and Muffler, this circular) are based on this model. 

Vapor-dominated systems are considered to 

develop initially frmn hot-water systems that 

have a very large supply of heat but a very low 

rate of recharge of new water. If the heat supply 

of a developing system becomes gre3!t enough to 

boil off more water than can be replaced by re-

'charge, a vapor-dominated syste.m starts to form. 

The fraction of discharged fluid that exceeds recharge is supplied from water previously stored 

in large fractures and pore spaces. Heat, supplied by condensation of rising steam, is conducted outward from the near-surface, nearly 

impermeable margins of the reservoir and thus 

accounts for the high conductive heat flows of 

these systen1s. The liquid condensate is in excess 

of the liquid that can be retained by surface tension; the excess drains down ward under gravity 

to the hypothesized deep water table where it 

is available for recycling along with newly recharged water. 

Our model requires that fluid in excess of that 

provided by reeharging water must be diseharged 

fron1 the systen1. This feature has important consequenees, if true, in that it requires identifiable 

vent areas. A small vapor-dominated system perhaps could discharge some stean1 and other gases 

into surrounding liquid-saturated ground with no 

conspicuous surface evidence for its existence, but 

we are skeptical that a large system with high 

total heat flow and high rate of diseharge of 

steam and other gases can remain concealed without developing the prominent vent areas that 

characterize all known vapor-dominated systems 

of this type. The low-temperature, high-gas sys6 

terns similar to Monte An1iata, Italy (White, 1973, 

p. 86-87), probably have. impermewHP. cap rocks 

and little or no surface evidence. ~uch systems 

can be eonsidered as thermal natural-gas fields 

that are high in C02 and H2S, relatively low in 

temperature, and at least in part characterized by 

water drive. 

Identified systems 

The Geysers, California, is the c'l.ly example 

of 1t large vapor-dominated system extensively 

drilled in the United States (table 3). The extent 

of the field is not yet known, but the drilling pattern established by more than 100 vrells suggests 

that the commercial limits may have been attained a little northwest of the Sulphur Bank 

seetion (about 2 km northwest of the first producing wells at The Geyse.rs). S.tep-O'lt wells have 

shown the field .to extend at least 31h km north 

and 21h km southwest of the first wells. Drilling 

is not yet con1plete to the southeast, but ·a belt 

2 to 5 km wide, 15 kn1 long, and ~.bout 70 km2 

in total area is our present estimate of the extent of the field. Most com,mercial wells are 11,4 

to 2112 km deep, ranging from about 0.2 km in 

s9me of the early wells to a prese"l:t maximum 

near 3 km. The hoot reservoir is assumed to be 

continuous between 1 and 3 km in depth; thus, 

its assumed volume is 140 km~.. If the average 

temperature is 240°C, as we assmne, then the 

estimated total heat content is 18.9 X 1018 cal. 

The Mud Volcano system in Yellowstone Park 

was first recognized by its surface c,.aracteristics 

and geochemistry as a probable vap'lr-domina~d 

system and later confirmed by .a single research 

drill hole (White and others, 1971). The area of 

surface activity is about 5 km2. Re.,istivity data 

(Zohdy and others, 1973) suggest thq,t the vapordominated part extends to a depth of 1 to !'lh km 

and is underlain by a better electric~1 conductor, 

presmnably a deep water table. The vapor-dominated part is assumed to extend from 0.2 to 1.5 

km in depth, and its calculated volume is 6.5 

km3 • If its average temperature is 230°0, then 

its estimated heat content is --0.8 >~ 1018 cal. 

Outlook for new discoveries 

All recognized vapor-dominated s:rstems of the 

Larderello type are characterized l:;" prominent 

vent areas with bleached rocks, scanty vegetation, 

acid-sulfate springs, and no closely associated 

chloride waters. If these systems do require such 
vent areas, then few similar unrecognized systems 

exist for future discovery. The principal possibilities known to us are in Yellowstone National 

Park and Mount Lassen Volcanic National Park. 

Yellowstone Park includes several possible systems other than the Mud Volcano system. The 

rather young sinter of the Mud Volcano system 

(White and others, 1971) indieates evolution 

from a hot-water syste,m soon after the last 

glacial stage (about 10,000 years ago). This evidence, combined with the resistivity data that 

suggest a relatively small system saturated with 

water at depths below about 11h kn1, implies a 

still-evolving systen1. During the last glacial 

stage, thick glacial ice and consequent deep Ineltwater lakes over the thermal areas 1nay have 

provided high water p1~sures that resulted in 

much recharge clown the present cliseharge channels, thereby insuring a water-saturated system. 

Thus, a vapor-dominated system n1ay beeome a 

hot-water system during glaeiation. If this is so, 

then other systems in Yellowstone Park may also 

have shallow vapor-dominated reservoirs that are 

still developing. 

The thermal activity within the boundaries of 

Mount Lassen V oleanic National Park has the 

characteristies of vapor-dominated systems, with 

chloride waters being eompletely absent. However, the Morgan Spring group, just outside of 

the park and about 8 km south of the thermal 

activity in the park, is a high-temperature 

chloricle-wa;ter system that discharges at an altitude of lh to 1 km below the surface springs in 

the park. Morgan Springs may be draining the 

deep ehloride part of a large vapor-dominated 

system within the park. 

HOT-WATER SYSTEMS 

General characteristics 

Hot-water systems (White, 1973) are dominated by eireulating liquid, whieh transfers 1nost 

of the heat and largely eontrols subsurface pressures (in contrast to vapor-dominated syste.ms). 

However, some vapor may be present, generally 

as bubbles dispersed in the wruter of the shallow 

low-pressure parts of these systen1s. 

Most known hot-water systmns are eharaeterizecl by hot springs that discharge at the surfaee. 

These springs, through their ehemical composition, areal distribution, and associa,ted hydro7 

thermal alteration, have provided very useful evidence on probable subsurface temperatures, volmnes, and heat eontents. However, springs eannot 

discharge fron1 eonvootion systems that are 

capped by in1perme,able rocks or that exist where 

the local water table is below the ground surface. 

Both of these exceptions exist, and many other 

examples are likely to be discovered. 

The tern peratures of hot-water systems range 

fron1 slightly above. ambient to about 361°0 in 

the Salton Sea syste1n and the nearby Cerro 

Prieto systen1 of Mexico. For convenience in this 

assessment, hot-water convection systen1s are divided into three temperature ranges: ( 1) ·rubove 

150°0 (table 4 and figs. 1 and 2) ; these Eystems 

may be considered for gene.ration of electricity; 

(2) fron1 90°C to 150°C (ta,ble 5 and figs. 2 and 

3) ; these systems are attractive for space and 

process heating; and (3) below 90°0(not tabulated) ; these systems are likely to be utilized for 

heat only in loeally favorable cireumstancef" in the 

United States. 

Direct ten1perature measurements are made 

either in surface springs or in wells. The teTUperatures of springs generally do not exceed tl'o, boiling temperature at existing air pressure (100°0 

at sea level to 93°0 for pure water at an altitude of .--2,200 m), although some springs in 

Yellowstone Park and elsewhere are superheated 

by 1 o to 2°0. At depth in wells, where pressures 

are much higher, the boiling temperature is also 

much higher. Wells that tap water initially at 

temperatures above surface boiling yield a nlixture of water and steam ("flash" steam) , with 

proportimis depending mainly on the initial water temperature and the pressure in the steamwater separator. For example, water flashei from 

300°0 to a se.parator pressure of 4.46 btr.rs (50 

lb/in2 ), near a emnmon operating pressure, yields 

33 pereent steam; 200°0 yields 11 perce:'lt, but 

150°0 (just at boiling for the pressure) yields 

none (Muffler, 1973, p. 255, fig. 28). Obviously 

the favorability of a hot-water system for generation of eleetrieity frmn flashed steam in~reases 

rapidly above 150°0. Binary systems may allow 

utilization of somewhrut lower ten1peratures for 

generation of electricity. 

The waters of these systen1s range frol'l very 

low salinity to brines of extreme salinity. The 

most co.mmon range is fron1 0.1 to 1 l'ercent 

(Text resumes on p. 51) 
Table 3.-Identified vapor-dominated systems of the United StatesLocation Temperatures oc 

Name Lati- Longi- Sur- Geochemical Subtude tude face sur- 0 0 face 

N w 

2/ 2/ 

l! ST02 Na-K-Ca 'Y 

The Geysers, CA 38 48 122 48 101 (not applicable) 'V240 

Mt. Lassen Nat'l 40 26 121 26 95!- (not applicable) 'V240 

Park, CA 

Mud Volcano system 44 37.5 110 26 'V90 (not applicable) 'V230 

Yellowstone Nat'l 

Park, Wyoming 

Totals for 3 systems 

Note: Yellowstone and Mt. Lassen National Parks permanently withdrawn from 

exploitation. 

lfMaximum surface temperature reported from a spring or well. 

2/Predicted using geothermometers, assuming last equilibration in the 

reservoir. 

3/Average reservoir temperature based on geothermometry unless ot1erwise - noted in comments. 

8 
with probable subsurface temperatures exceeding 200 ° C 

Reservoir Assumptions Comments 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 1Ql8 

cal 

km2 ~ km §_/ km3 6/ Z! 

70 2.0 140 18.9 2 

Area may range from 50 to 100 km ; bottom 

of reservoir may extend below assuw~d -3 km. 

>100 well's drilled by early 1975. Present 

heat production ~so times estimated natural 

heat flow. 

~47 1. 0 47 6.3 Likely to be a vapor-dominated system but 

not confirmed. 

5 1. 3 6.5 0.8 Reservoir assumed ~.2 to 1.5 km thickness 

underlain by hot-water system indicated 

by resistivity survey. 

~ 122 ~194 ~26 

i/From surface manifestations, geophysical data, well records and geologic inference. Assume ~1.5 km2 if no data pertinent to size is available. 

5/Top assumed at 1.5 km of no data on depth available. Bottom assume1 to - be-3 km for all systems. 

6/Calculated from area and thickness. 

]/Calculated as product of assumed volume, volumetric specific heat of - 0.6 cal/cm3oc, and temperature in degrees above mean annual surface 

temperature (assumed to be l5°C). 

9 
Table 4.-Identified hot-water convect~on systems 

Location Temperatures oc 

Name Lati- Longi- Sur- Geochemical Subtude tude face sur- 0 0 face N w 

2/ 2/ 

ll ST02 Na-K-Ca ~ 

ALASKA 

Geyser Bight 53 13 168 28 100 210 236 210 

Hot Springs Cove 53 14 168 21 89 131 154 155 

Shakes Springs 56 43 132 02 52 142 175 155 

Hot Springs Bay 54 10 165 50 83 152 179 180 

ARIZONA 

Power Ranch Wells 33 17. 1 111 41.2 180 

l/ Maximum surface temperature reported from a spring or fumarole. 

Y Predicted using chemica 1 geothermometers, assuming 1 ast equilibration in the reservoir; assumes saturation of Si02 with respect to quartz, and no loss of Ca from calcite deposition. 

3/ Assumed average reservoir temperature based on data presently available. 

4! From surface manifestations, geophysical data, well records and geologic inference. Assumes 1.5 km2 if no data pertinent to size is available. S/ Top assumed at depth of 1.5 km if no data available. Bottom assumed at 3 km depth for all convection systems. 6/ Calculated from assumed area and thickness. 

ij Calculated as product of assumed volume, volumetric specific heat of 0.6 cal/cm3 °C, and temperature in degrees C above l5°C. 

10 
with indicated subsurface temperatures above 150 °C 

Reservoir Assumptions 

Sub- Thick- Volsur- ness ume 

face 

area 

km2 y km §.! km3 §! 

4 2 8 

2 2 4 

1. 5 1.5 2.25 

1.5 1. 5 2.25 

2.5(?) 1 2.5 

Heat 

content 

1Ql8 

cal 

?! 

.9 

.3 

.2 

.2 

Comments 

22 springs and geysers in 3 thermal areas in 

2 km long zone, near Okmok Caldera; siliceous 

sinter deposit. 

Hot springs and geysers in area abo,Jt 1 km2 

near Okmok caldera. 

Several springs discharging ~380 lpm; chemical 

data not reliable. 

Hot springs and fumaroles on active Akutan 

volcano. 

.2 No natural springs; two wells ~1 km apart drilled to 3 km deP.th with bottom-hole temperatures of 163°C and 184°C; discharge estimated 19,000 1/min. from below 2 km. 

11 
Table 4.-Identified hot-water convection systems with 

Location 

Name Latitude 

0 I 

N 

CALIFORNIA 

Surprise Va 11 ey 41 40 

Morgan Springs 40 23 

Sulphur Bank mine 39 01 

Caiistoga 

Skagg's H.S. 

Long Valley 

Red's Meadow 

Coso H.S. 

Sespe H.S. 

Salton Sea 

Brawley 

Heber 

East Mesa 

Border 

38 34.9 

38 41.6 

37 40 

37 37 

36 03 

34 35.7 

33 12 

33 01 

32 43 

32 47 

32 44 

Longi- Surtude face 0 

w 

lJ 

120 12 97 

121 31 95 

122 39 80 

122:34.4 

123 01.5 57 

118 52 94 

119 04.5 49 

117 47 95 

118 59.9 90 

115 36 101 

115 31 

11531.7 

115 15 

115 07.6 

12 

Temperatures oc 

Geochemical 

2/ 

ST02 

174 

190 

181 

157 

150 

219 

161 

161 

133 

2/ 

Na-K-Ca 

1S9 

229 

157 

155 

153 

238 

130 

238 

155 

Sub .. surface 

~ 

175 

210 

185 

160 

155 

220 

165 

220 

155 

340 

200 

190 

180 

160 
indicated subsurface temperatures above 150 ° c-continued 

Reservoir Assumptions 

Sub- Thick- Vol- Heat 

sur- ness ume con- Conments 

face tent 

area lQlB 

cal 

km2 y km §! km ~ ?J 

125 2 250 24 7 spring grpups, in area of hydrothermal explosion, 1951; minor sinter, 4 wells drilled; 

maximum reported 160°C, mixing models as hiq·h 

as 225°C. 

5 2 10 1.2 25 springs flowing 350 lpm; and considerablE 

sinter; system may be much larger, if connected to Lassen. 

2.5 1.5 3.75 .4 Springs discharging into water-filled open rit 

of large mercury deposit; 4 wells drilled, 

reported maximum 182°C. 

4.5 2 9 .8 4 hot springs and several flowing wells; 

spring discharge about 30 lpm. 

2 1.5 3 .3 3 springs, flowing 57 lpm. 

225 2 450 55 Springs and fumaroles in area of about 10 kw2 • 

Recent caldera; about 10 wells drilled, reported to 18l°C, extensive geology and geo- physics. 

1.5 1.5 2.25 . 2 5 springs flowing 38 lpm . 

168 2 336 41 1 group of hot springs; weak fumarole areas; 

geophysics indicates may be a very large 

system. 

1.5 1.5 2.25 .2 4 hot springs flowing 470 lpm. 

54 2 108 21 Many low-temperature seeps; 1 group to 101°C, 

now under Salton Sea; numerous drill holes 

to 2~00 m and temperatures to 360°C in hyper- saline brine. 

18 1.5 27 3 No surface discharge, reported high tempera~ 

ture based on old oil test; size based on 

temperature-gradient survey. 

50 2 100 11 No surface discharge; much active exploration but no data released; estimated us~ng 

temperature gradient data and exploration activity. 

28 2 56 5.5 No surface discharge; temperature estimated 

using drilling data, volume from temperature 

gradient data and drill-hole data. 

3 .6 1.8 0.2 No surface discharge; estimated from temperrture gradient data and extrapolation of East 

Mesa geology. 

13 
Table 4.-Identified hot-water convection systems with 

Name 

IDAHO 

Big Creek H.S. 

Sharkey H.S. 

Weiser area 

Crane Creek 

Near Cambridge 

Wardrop H.S. 

r~urphy H.S. 

NEVADA 

Location 

Latitude 

0 I 

N 

45 18.8 

45 00.9 

44 17.9 

44 18.3 

44 34.4 

43 23.0 

42 02.2 

Baltazor H.S. 41 55.3 

Pinto H.S. 41 21 

Great Boiling 40 39.7 

(Gerlach) Springs 

Hot Sulphur Springs 41 28.2 

Near Wells 41 10.9 

Sulphur H.S. 40 35.2 

Longitude 

0 

w 

114 19.2 

113 51.1 

117 02.9 

116 44.7 

116 40.7 

114 55.9 

115 32. L~ 

118 42. i' 

118 47 

119 21.7 

116 09.0 

114 59.4 

115 17.1 

14 

Surface 

l/ 

93 

52 

77 

92 

26 

66 

51 

80 

93 

86 

90 

61 

93 

Temperatures oc 

Geochemical 

2/ 

sro2 

160 

135 

157 

173 

119 

120 

127 

165 

162 

167 

167 

140 

183 

2/ 

Na-K-Ca 

175 

175 

142 

166 

180 

155 

160 

152 

176 

205 

184 

181 

181 

Subsurface 

3/ 

175 

175 

160 

180 

180 

155 

160 

170 

165 

170 

185 

180 

190 
indicated subsurface temperatures above 150 ° C-Continued 

Reservoir Assumptions 

Sub- Thick- Volsur- ness ume 

face 

area 

2 1.5 

2 1.5 

35 2 

30 2 

1.5 1.5 

1.5 1.5 

1.5 1.5 

1.5 2 

5 1.5 

10 2.5 

1.5 1.5 

1.5 1.5 

4 2.5 

3 

3 

70 

60 

2.25 

2.25 

2.25 

3 

7.5 

25 

2.25 

2.25 

10 

Heat 

content 

1018 

Comments 

cal 

71 

.3 15 springs discharging ~280 lpm and depositing travertine and sinter; mixing model suggests 220°C; few wells . 

. 3 Spring discharging ~30 lpm; travertine and 

sinter(?) reported; Na-K-Ca may be inaccurate; mixing temperature 220°C. 

6.1 Numerous hot springs and wells; at depth 

may be connected to Crane Creek. Mixing 

model indicates possible 228°C. 

!5.9 Springs discharging ~200 lpm; extensive 

sinter, in area of mercury mineralization; 

Crane Creek and Weiser may be separate in a 

zone from Midvale, ID to Vale, OR. Mixing 

model indicates possible 239°C. 

.2 Flowing well; Na-K-Ca may be inaccurate. 

.2 Numerous springs discharging ~730 lpm; 

may be part of a larger system in Camas 

Prairie; mixing model suggests l60°C. 

.2 2 springs discharging ~260 lpm; mixing 

model suggests 200°C. 

.3 Springs discharging 100 lpm; flowing well 

90°C, discharging 25 lpm; the area may be 

large southern extension of Alvord Desert, 

OR. area . 

. 7 Two areas, probably interconnected; 2 springs 

of eastern area depositing travertine and 

and discharging 500 lpm; 1 well,western area, 

flowing 100 lpm. Na-K-Ca may be inaccurate. 

2.3 2 major groups of springs and 4 others; ~urface discharge ~1,000 lpm, calculated total 

discharge (from heat flow) ~2040 lpm; well ~150m deep, ll0°C. 

.2 Springs with abundant sulfur. 

.2 3 springs discharging 45 lpm; may be part of 

a more extensive system extending for 4.P km 

along the west edge of the Snake Mountairs. 

1.1 Many springs and pools in an area of about 

.5 km2 ; abundant sinter. 

15 
Table 4.-Identified hot-water convection systems with --1 

Location Temperatures oc 

Name Lati- Lonoi- Sur- Geochemical Subtude tude face sur- 0 0 face N w 

2/ 2/ 

ll ST02 Na-K-Ca ~~ 

NEVADA Con. 

Beowawe H.S. 40 34.2 116 34.8 226 242 ,240 

Kyle H.S. 40 24.5 117 52.9 77 161 211 180 

Leach H.S. 40 36.2 117 38.7 96 155 176 170 

Hot Springs Ranch 40 45.7 117 29.5 85 150 180 180 

Jersey Valley H.S. 4Q 10.7 117 29.4 29 143 182 185 

Stillwater area 39 31.3 118 33.1 96 159 140 160 

Soda Lake 39 34 118 49 90 165 161 165 

Brady H.S. 39 47.~ 119 00 98 179 214 

Steamboat Springs 39 23. 119 45 96 207 226 210 

Wabuska H.S. 39 09.7 119 11 97 145 152 155 

Lee H.S. 39 12.6 118 43.4 88 173 162 175 

Smith Creek Valley 39 21.4 117 32.8 86 143 157 160 

16 
indicated subsurface temperatures above 150 ° c-continued 

Reservoir Assumptions 

Sub- Thicksur- ness 

face 

area 

km2 ~/ km?} 

21 2 

1.5 1.5 

4 2.5 

1.5 1.5 

1.5 1.5 

10 2.5 

5 2.5 

12 2.5 

6 2.7 

1.5 1.5 

1.5 1.5 

1. 5 1.5 

Vol- Heat 

ume 

km 3 §_/ 

42 

2.25 

10 

2.25 

2.25 

25 

12.5 

30 

16 

2.25 

2.25 

2.25 

content 

1Ql8 

Comments 

cal 

7/ 

5.7 Prior to exploration, about 50 springs and 

small qeysers discharqing about 400 lpm from 

extensive area of sinter deposits; G wells 

drilled up to 600m depth, temperatures to 

2l2°C, 1 deep well but no data available. 

.2 Several springs, largest flowing ~20 lpm 

depositinq travertine. Na-K-Ca thermometry may be to high. 

.9 Several hot sprinqs discharging ~760 lpm; 

calculated total flow ~goo lpm. 

.2 Several springs, largest discharging ~100 

lpm and depositing travertine so Na-K-Ca 

may be inaccurate . 

. 2 One (3) spring discharging only 20 lpm in 

area of sinter and travertine; surface tewperature low because of low discharge. 

2.2 No surface springs,but hot wells at least 

to ll5°C; calculated total discharge (frow 

heat flow) ~6,000 lpm. 

1.1 No surface discharge,but small area altered 

by gases, and 21 km2 of anomalous heat flew. 

Shallow wells show 100°C near surface; between 2 recent basaltic eruptive centers. 

3.6 Several former srrings discharged ~200 lpw 

from small area of sinter; several wells; 

214°C reported in 1500 m well; calculated 

discharge ~2;00 lpm. 

1.9 About 70 springs discharging ~250 lpm frow 

extensive sinter deposits with ages at least 

as much as 1 million years, calculated total 

discharge ~4~00 lpm; more than 20 wells fr~ 

research, exploration,and spa supply . 

. 2 Several hot springs of low natural dischar~e 

discharge; three wells drilled to maximum of ~70 m, up to 106°C; sma 11 area of traver--

tine; area may be larger . 

. 2 Several springs dischar~ing ~130 lpm from 

area of sinter . 

. 2 Several springs, minor travertine. 

17 
Table 4.-Identified hot-water convection systems with 

Location 

Name Latitude 

0 

N 

NEW MEXICO 

Va 11 es ca 1 dera 35 43 

Lightning Dock area 32 08.5 

OREGON 

Mickey H.S. 

Alvord H.S. 

Hot Lake 

Vale H.S. 

Neal H.S. 

Lakeview 

Crumps Spring 

Weberg H.S. 

42 40.5 

42 32.6 

42 20.1 

43 59.4 

44 01.4 

42 12.0 

42 15.0 

44 00 

Longi- Surtude face 0 

w 

l/ 

106 32 87 

108 50 99 

118 20.7 73 

118 31.6 76 

118 36.0 96 

117 14.1 73 

117 27.6 87 

120 21.6 96 

119 53.0 78 

119 38.8 46 

18 

Temperatures oc 

Geochemical 

2/ 2/ 

S102 Na-K-Ca 

156 

180 

148 

"165 

153 

173 

157 

173 

125 

169 

207 

199 

176 

158 

181 

143 

144 

170 

Subsurface 

ll 

240 

170 

210 

200 

180 

160 

180 

160 

180 

170 
indicated subsurface temperatures above 150 ° c-continued 

Reservoir Assumptions 

Sub- Thick- Volsur- ness ume 

face 

area 

km2 4/ km 5/ km3 6/ 

65 2 130 

1.5 1.5 2.25 

6 2 12 

3 1.5 4.5 

6 2 12 

50 2 100 

2 2 4 

8 2 16 

4 2 8 

1.5 1.5 2.25 

Heat 

content 

1Ql8 

cal 

7/ 

18 

Comments 

Pleistocene caldera with 1 group acid-sulfate 

springs (Sulphur Springs} and very extensiv~ 

hydrothermal alteration; more than 6 geothe~­

mal wells drilled, but no detailed data available; suspected as having small vapor-domin- ated cap underlain by high-chloride hot-water 

system with temperatures over 240°C. 

.2 No surface springs; shallow water wells at 

boiling. The area may be much more extensive. 

Drill hole 3 km to north showed 12l°C at 2 km 

depth. B~tter estimate may be avg T = 130°C, 

area 4 km2 , thickness 2 km, heat content .5 x 

1018 ca 1. 

1.4 Several springs discharging ~100 lpm and depositing sinter; surface manifestations over 

0.1 km2. 

.5 Several springs in area of .5 km2 discharging ~sao lpm. If Hot Lake, Mickey, and 

Alvord H.S. are one large system with tempe~ature as at Mickey, the heat content would b~ 

30 x 101 8 cal; three separate systems is pr~-

ferred model. 

1.2 Thermal springs and 1 very large pool ( 1 ake) 

discharging surface manifestations over 0.1 

km2. Small spring N.of Hot Lake, 98°C. 

8.7 Hot springs discharging ~75 lpm; large area 

indicated. 

.4 1 spring discharging ~go lpm. 

1.4 About 16 springs including Hunter's and Bar~y 

Ranch discharging ~zsoo lpm in an area of ~s 

km2; several wells at Hunter's for heating spa. 

.8 Spring and well (121°Cat 505 m) that ~as er·•pted as a geyser; discharging 0 to 50 lpm; in 

small area of sinter. 

. 2 Hot sprfng discharging 40 lpm . 

19 
Table 4.-Identified hot-water convection systems witl' 

Location 

Name Latitude 

0 

N 

UTAH 

Roosevelt 38 30 

(McKean) H.S. 

Cove Fort-Sulphur- 38 36 

dale 

Thermo H.S. 38 11 

\~ASH I NGTON 

Baker H.S. 48 45.9 

Gamma H.S. 48 10 

Kennedy H.S. 48 07 

Longmire H.S. 46 45.1 

Summit Creek (Soda) 46 42.2 

WYOMING 

Yellowstone 

National Park 

Totals (63 systems) 

44 36 

Temperatures oc 

Longi- Sur- Geochemical Subtude face sur- 0 face w 

2/ 2/ 

l/ ST02 Na-K-Ca ll 

112 50 88 213 283 230 

112 33 200 

113 12.2 90 ltl4 200 200 

121 40.2 42 151 162 165 

121 02 60 161 220 165 

121 ll. 7 43 155 199 160 

121 48.7 21 169 168 170 

121 29.0 13 169 161 170 

110 30 250 270 250 

20 
indicated subsurface temperatures above 150 °C-continued 

Reservoir Assumptions 

Sub- Th1ck- Volsur- ness ume 

face 

area 

km2 4/ km 5/ km3 6/ 

4 

15 

1.5 

1.5 

1.5 

1.5 

1.5 

1.5 

375 

---

'1·1414 

2 

1.5 

1.5 

1.5 

1.5 

1.5 

1.5 

1.5 

2.5 

8 

22.5 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

940 

'\.2995 

Heat 

content 

1018 

Conments 

cal. 

71 

1.0 Hot springs decreasing from 88°C (1908) to 

55°C (1957), then ceased discharging from 

Si02 sealing; extensive siliceous sinter; ar~~a 

and volume may be much larger. 

2.5 No springs but active gas seeps; altered areas 

mined for sulfur; no reliable chemical data; 

possibly a vapor-dominated system. 

133 

.2 16 springs in 2 groups; travertine deposits. 

.2 1 (?) spring discharging 26 lpm and possibly 

depositing calcite. 

.2 

.2 4 springs discharging ~110 lpm, in extensive 

travertine deposits. 

.2 Spring deposits, not identified; in Mt. Ranier 

National Park; chemical temperatures not 

reliable. 

.2 Chemical temperatures not reliable. 

Numerous thermal phenomena, largely in Yellowstone caldera; individual areas not itemized; 

total discharge .,.185,000 lpm; 13 research 

drill holes with maximum T 237.5°C at 332m; 

other geochemical and mixing-model r•s indicate 330°C. 

'1·371 

21 
\ 

\ 

. . 

\ 

\ 

0 

0 

\ \ 

....................... --...,... 

--...,._ i j·-. 

,' ; 

i i 

! \ I • 

I ! -------------··- --~-------

I '· : \ 

---------.J '-, 

) 

/ 

,. 

i • ., . " 

; 

i 

i 

; 

j 

j 

i 

i 

I 

;-·-·-·--

1 

i •• I 

i I .. • ., . .,.. __ l \; ·-·-·-·-·-·-·-·---- i 

i •• i 

• ! .... ___ --1. ____ -.... 

\ 

\ 

\ 

\\ 

\ \ 

\ 

'. 

200 

200 400 

i 

j 

; 

i 

i 

i 

; ---~?-·-·-·-·-·- ; ·-; ; i 

i ,f ; ! ---·-

! 

I 

; 

; 

! 

I 

I 

! 

- ·-·t·-·-·-·-·----- 1 

i 

i 

i 

i 

400 MILES 

600 Kl LOMETRES 

I 

i 

i 

I 

i 

i 

i-·-·-·-·---

i 

; 

i 

I 

! ·-. .! ________ , 

I 

i 

j 

; 

i 

j 

; 

i 

; 

·--·-·-·-·:-·.1 ___ ·-·--

f--·-·-·-·--· -· i 

! 

I 

i 

; 

; 

i 

i 

i 

I 

i 

; ________ j 

'""''· 

--·----·r··-··i \ . 

; 

i 

\ 

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i 

I 

i 

·-·-·-·-·-·---~ ' 

' ., 

-... """.-. '-,_,.._,_':./ ... ~., ... 

FIGURE 1.-I..ocation of hydrothermal convection systems in the conterminous United States with indicated subsurface temperatures above 150 o C. 

22 
1:-0 

C/:1 

~ 

~?0 C) 

Principal Islands of 

HAWAII 

0 100 200MI. 

1Eio• 0 IOQ 200 300 KM. 

/..-- - I 

I - I ..--;~ I ,_.,- / 

............ - / / 

- / ~ / . ~ ./ 'V 

';l 

// - I ;1o•E :. I . \~I 

I 

: j··.' ~eod>JI". '~ ""'•···~~0 

\ I~ 

·,~ ~ 

1!:15" 

ALASKA 

100 zoo 300 

zoo •oo 

l7CJ•w 

FIGURE 2.-Loeation of·hydrothermal convection systems in Alaska and Hawaii with indicated subsurface temperatures above 

150°0 <+> and between 90° and 150°0 (dots). 
Table 5.-Identified hot-water convection systems with 

Name 

ALASKA 

Okmok ca 1 dera 

Great Sitkin Is. 

Pilgrim H. S. 

Serpentine Sprs. 

Near Lava Creek 

Clear Creek 

Granite Mtn. 

(Sweepstakes) 

South 

Melozi H.S. 

Little Melozitna 

Kanuti 

Location 

Lat;-

tude 

0 

N 

53 29 

52 04 

65 06 

65 51 

65 13 

64 51 

65 22 

66 09 

65 08 

65 28 

66 20 

Manley (Baker) H.S. 65 00 

Tolovana 

Chen a 

Circle 

E. Cold Bay 

Near Tenakee 

Inlet 

Hooniah H.S. 

Tenakee H.S. 

65 16 

65 03 

65 29 

55 13 

58 13 

57 48 

57 47 

ll Maximum surface temperature reported from a spring or fumarole. 

Longitude 

0 

w 

163 06 

176 05 

164 55 

164 42 

162 54 

162 18 

161 15 

157 07 

154 40 

153 19 

150 43 

150 38 

148 50 

146 03 

144 39 

162 29 

135 55 

136 20 

135 13 

Temperatures oc 

Sur- Geochemical 

far'" 

1/ 

100 

99 

88 

77 

65 

67 

49 

50 

55 

38 

66 

59 

60 

57 

54 

54 

82 

44 

43 

110 

137 

132 

128 

119 

122 

115 

124 

126 

115 

122 

129 

135 

117 

147 

136 

111 

2/ 

Na-K-Ca 

75 

146 

161 

91 

83 

I 

72 

136 

137 

162 

137 

143 

144 

72 

63 

Subsurface 

3/ 

125 

125 

150 

140 

130 

125 

130 

120 

130 

130 

140 

140 

130 

140 

145 

145 

150 

140 

115 

21 Predicted using chemical geothermometers, assuming last equilibration in the reservoir; assumes saturation of Si02 with respect to quartz, and no 

loss of Ca from calcite deposition. 

ll Assumed average reservoir temperature based on data presently available. 

4j From surface manifestations, geophysical data, well records, and geologic inference. Assumes 1.5 km2 if no data pertinent to size is available. 

?! Top assumed at depth of 1.5 km if no data available. Bottom assumed at 3 km depth for all convection systems. 

W Calculated from assumed area and thickness. 

7_/ Calculated as product of assumed volume, volumetric specific heat of 0.6 cal/cm3oc, and temperature in degrees C above 15°C. 

24 
indicated subsurface temperatures from 90 ° to 150 ° C 

Reservoir Assumptions C011111ents 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 1018 

cal 

km2 4/ km 5/ km3 6/ 7/ 

3 2 6 .4 About 18 springs near 1945 eruption in 

Okmok caldera; may be more extensive and 

higher in temperatures; sinter reported. 

1.5 1.5 2.25 .2 12 springs and fumaroles near recent 

volcanism. 

1.5 1.5 2.25 .2 Several hot springs in permanently thawed 

area of .25 km2. 

1.5 1.5 2.25 .2 2 spring areas 1.3 km apart discharging ~100 lpm and depositing travertine; Na-K-Ca 

may be too high. 

1.5 1.5 2.25 .2 One main spring. 

1.5 1.5 2.25 . 2 2 springs discharging ~1,000 lpm . 

1.5 1.5 2.25 .2 Several springs. 

1.5 1.5 2.25 . 1 Several springs. 

1.5 1.5 2.25 .2 One main spring discharging ~500 lpm; 

chemical data not reliable. 

1.5 1.5 2.25 .2 Hot springs discharging ~230 lpm. 

1.5 1.5 2.25 .2 Several hot springs. 

1.5 1.5 2.25 .2 Hot spring discharging ~560 lpm. 

1.5 1.5 2.25 .2 Several hot springs, 11 Small 11 discharge, possibly depositing travertine. 

1.5 1.5 2.25 .2 Hot springs discharging ~40 lpm, depositing sulfur 

1.5 1.5 2.25 .2 11 hot springs discharging ~500 lpm, 

depositing travertine. 

1.5 1.5 2.25 .2 In recent volcanic rocks. 

1.5 1.5 2.25 .2 Discharging ~40 lpm; chemical data not 

reliable. 

1.5 1.5 2.25 .2 3 hot springs discharging ~110 lpm; 

chemical data not reliable. 

1.5 1.5 2.25 . 1 About 12 hot springs discharging ~so lpm. 

25 
Table 5.-Identified hot-water convection systems with indicate(' 

Location Temperatures oc 

Name Lati- Longi- Sur- Geochemical Subtude tude face sur- 0 I 0 face 

N w 

2/ 2/ 

!! S102 Na-K-Ca '}} 

ALASKA Con. 

Near Fish Bay 57 22 135 23 47 143 150 

Baranof H.S. 57 05 134 50 50 119 68 125 

Goddard H.S. 56 50 135 22 67 148 147 150 

Bailey H. S. 55 59 131 40 88 158 150 

Be 11 Is 1 and H. S. 55 56 131 34 72 140 145 

ARIZONA 

Verde H.S. 34 21.5 111 42.5 36 118 1146 150 

Castle H.S. 33 59. 1 112 21.6 50 109 71 110 

North of Clifton 33 04.7 109 18.2 59 138 174 140 

Clifton H.S. 33 03.2 109 17.8 75 107 161 110 

Eagle Creek Spring 33 02.8 109 28.6 36 114 104 115 

G i 11 a rd H . S . 32 58.5 109 21.0 82 135 138 140 

Mt. Graham 32 51.4 109 44.9 42 106 102 110 

CALIFORNIA 

Kelley H.S. 41 27.5 120 50 96 144 85 130 

Hunt H.S. 41 02.1 122 55.1 58 101 75 105 

Big Bend H.S. 41 01.3 122 55. 1 82 121 137 140 

Sa 1 t Springs ( 1) 40 40.2 122 38.7 20 107 55 110 

Wende1-Amedee area 40 18 120 11 95 135 129 140 

26 
subsurface temperatures from 90 ° to 150 ° c-continued 

Reservoir Assumptions Comments 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 1Ql8 

cal 

km2 4/ km 5/ km 3 6/ 71 

1.5 1.5 2.25 .2 Springs discharging ~95 lpm; chemical data 

not reliable. 

1.5 1.5 2.25 .2 Springs discharging ~300 lpm. 

1.5 1.5 2.25 .2 3 hot springs discharging ~so lpm. 

1.5 1.5 2.25 .2 9 hot springs discharging ~315 lpm; chemical data not reliable. 

1.5 1.5 2.25 . 1 5 hot springs discharging ~40 lpm; chemical data not reliable. 

1.5 1.5 2.25 .2 Several springs; indicated temperatures may 

be too high. 

1.5 1.5 2.25 . 1 Two springs. 

1.5 1.5 2.25 .2 Two springs; may be depositing calcite 

1.5 1.5 2.25 . 1 Several springs; may be depositing calcite . 

1.5 1.5 2.25 • 1 Two springs; indicated geochemical temperature may be too high. 

1.5 1.5 2.25 .2 5 springs 

1.5 1.5 2.25 . 1 1 hot mineral well; geochemical temperatures may be too high. 

1.5 2 3 .2 1 spring flowing ~\200 lpm; 1,000 m well 

drilled in 1969, reported ll0°C. 

1.5 1.5 2.25 • 1 2 hot springs flowing 8 lpm 

1.5 1.5 2.25 . 2 6 hot springs, flowing 38 lpm . 

1.5 1.5 2.25 • 1 Spring from travertfne cone, flowing '20 lpm 

7 2 14 1.1 Many flowing ~00 lpm; 4 wells, deepest 

338 m, T=l07°C; possibly separate systems 

at Wendel and Amedee. 

27 
Table 5.-Identi:fied hot-water convection systems with indicated 

Location Temperatures °C 

Name Lati- Longi- Sur- Geochemical Subtude tude face sur- 0 I 0 face 

N w 

2/ 2/ 

l! ST02 Na-K-Ca 'Y 

CAL I FORN lA Con. 

Tuscan (Lick) s. 40 14.5 122 08.4 30 137 112 140 

Soda Spring 39 24.8 122 58.6 17 148 158 150 

Salt Spring(2) 39 25.8 122 32.3 25 157 123 150 

Crabtree H.S. 39 17.4 122 49.3 41 163 133 150 

Fouts (Redeye) S. 39 21.0 122 40.1 26 150 126 150 

Fouts (Champagne} S.39 20.5 122 39.4 18 117 128 130 

Orr's H.S. 39 13.8 123 21.9 40 112 67 115 

Vichy Springs 39 09.9 123 09.4 32 132 145 13f 

Cooks Springs 39 15.2 122 31.4 17 133 187 140 

Saratoga Springs 39 10.5 122 58.7 16 137 46 140 

Wilbur H.S. area 39 02.2 122 25.2 60 180 240 145 

Deadshot Spring 39 05.1 122 27.4 26 135 204 13!7 

Point Arena H.·s. 38 52.6 123 30.6 44 105 62 lOF 

Ornbaun Springs 38 54.7 123 18.4 16 126 122 12~ 

Seigler Springs 38 52.5 l22 41.3 52 169 188 150 

Baker Soda Spring 38 53.6 122 31.9 24 124 202 130 

One-Shot Mining Co. 38 50.0 122 21.4 22 135 153 150 

Aetna Springs 38 39.5 122 28.7 33 135 94 13!7 

Walter Springs 38 39.2 122 21.4 19 135 82 135 

Mark West Springs 38 32.9 122 43.2 31 140 48 140 

28 
subsurface temperatures from 90 ° to 150 ° c--continued 

Reservoir Assumptions Corm1ents 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 1018 

cal 

km2 1/ km §.! km 3 §.! ?J 

1.5 1.5 2.25 .2 20 Springs flowing 190 lpm. 

1.5 1.5 2.25 ,.2 High bicarbonate spring; geothermometry 

doubtful. 

1.5 1.5 2.25 .2 Note: distinct from Salt Springs, above; 

geothermometry doubtful. 

1.5 1.5 2.25 .2 4 springs, flowing 57 lpm; geothermometry 

doubtful. 

1.5 1.5 2.25 .2 4 springs, flow 7.5 lpm; geothermometry 

doubtful. 

1.5 1.5 2.25 .2 4 springs, geothermometry doubtful. 

1.5 1.5 2.25 . 1 7 springs flowing 95 lpm. 

1.5 1.5 2.25 .2 7 springs flowing 113 lpm; Na-K-Ca may be 

inaccurate due to travertine deposition. 

1.5 1.5 2.25 .2 Geothermometry doubtful. 

1.5 1.5 2.25 .2 5 springs, flow 9 lpm; geothermometry 

doubtful.-

16 2 32 2.5 12 springs, flow 80 lpm; well drilled to 

1,100 m, 141°t; should be in table 4? 

1.5 1.5 2.25 .2 4 springs flowing 4 lpm; geothermometry 

doubtful. 

1.5 1.5 2.25 . 1 2 springs flowing 19 lpm. 

1.5 1.5 2.25 .2 1 spring flowing less than 1 lpm. 

2 1.5 3 .2 13 springs flowing 132 1 pm; geothermometr." 

doubtful. 

1.5 1.5 2.25 .2 Numerous springs; geothermometry doubtful. 

1.5 1.5 2.25 .2 Flow 189 lpm; sinter and travertine 

reported. 

1.5 1.5 2.25 .2 6 springs flowing 75 lpm; geothermometry doubtful. 

1.5 1.5 2.25 .2 Flow 6 lpm; geothermometry doubtful. 

1.5 1.5 2.25 .2 "'9 hot springs in a group flowing 113 lpm. 

29 
Table 5.-Identified hot-water convection systems with indicated 

Location Temperatures oc 

Name Lati- Longi- Sur~ Geochemical Su'""":" 

tude tude face sur- 0 I 0 fa~e N w 

2/ 2/ 

!I sro2 Na-K-Ca 'H 

CAL I FORN lA Con. 

Napa Soda S. Rock 38 31.1 122 15.6 26 143 81 145 

(Priest) 

Los Guilicos W.S. 38 23.7 122 33.0 Jl 129 184 13~ 

(Jackson's) Napa 38 23.4 122 16.7 16 149 60 15'l 

Soda Springs 

Brockway (Corne- 39 13.5 120 0.4 60 119 94 121 

1ian) H.S. 

Grover:> H.S. 38 41.9 119 51.6 63 135 126 140 

Fales H.S. 38 20 119 24 62 147 165 15'l 

Buckeye H.S. 38 ·14. 3 119 19.6 64 122 1.38 140 

Benton H.S. 37 48 11831.8 57 113 79 115 

Travertine H.S. 38 14.8 119 12.1 70 114 172 121 

Near Black Pt. 38 2.4 119 5 63 122 124 12: 

Paoha Island 37 59.8 119 01.2 83 186 12:: 

Mono H.S. 37 19.5 11901.0 44 110 80 115 

Blayney Meadows H.S.37 14.1 118 53 43 102 57 10:: 

Mercey H.S. 36 42.2 120 51.6 46 122 94 125 

RandsDurg area 35 23.0 117 32.2 115 12: 

Arrowhead H.S. area 34 08.6 117.15.2 94 132 147 15'l 

Pilger Estates H.S. 33 26.0 115 41.1 82 125 145 145 

Warner H.S. 33 17.0 116 38.4 64 141 100 145 

Glamis (E. Brawley) 32 58 115 11 135 

Glamis (East) 33 59 115 04 1J5 

Dunes 32 49 115 01 125 

30 
subsurface temperatures from 90 ° to 150 ° c-continued 

Reservoir Assumptions C011111ents 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 101e 

cal 

km2 4/ km 5/ km3 6/ 7/ 

1.5 1.5 2.25 .2 2 springs flowing 60-85 lpm; geothermometry doubtful. 

1.5 1.5 2.25 .2 3 springs flowing 75 lpm; Na-K-Ca may be 

inaccurate due to travertine deposition. 

1.5 1.5 2.25 .2 27 springs; geothermometry doubtful. 

1.5 1.5 2.25 . 1 6 springs flowing 570 lpm. 

1.5 1.5 2.25 .2 12 springs flowing 378 lpm. 

1.5 1.5 2.25 .2 20 springs flowing 95 lpm, possibly depositing travertine. 

1.5 1.5 2.25 .2 1 spring flowing 75 lpm. 

1.5 1.5 2.25 . 1 2 springs flowing 1~00 lpm. 

1.5 1.5 2.25 . 1 3 main springs flowing 38 lpm; extensive 

travertine. 

1.5 1.5 2.25 . 1 

1.5 1.5 2.25 . 1 Several springs flowing 370 lpm; non-quartz equilibration of Si02 likely. 

1.5 1.5 2.25 . 1 Four springs flowing 95 lpm. 

1.5 1.5 2.25 . 1 Eight springs flowing 150 lpm . 

1.5 1.5 2.25 .2 3 hot springs flowing 23 lpm. 

1.5 2.5 3.75 .3 1 well reported ll5°C at 235m. 

2 1.5 3 . 2 2 groups of hot springs flowing 190 lpm . 

1.5 1.5 2.25 .2 Near Salton Sea; possibly more extensive. 

1.5 1.5 2.25 . 2 6 springs flowing 570 lpm . 

2 1.5 3 .2 Estimated using temperature gradient ~ata; 

a part above 150°C? 

4 1.5 6 .4 Temperature gradient data; a part above 

150°C? 

6 1.5 9 .6 Temperature gradient data: a part above 

150°C? 

31 
Table 5.-Identified hot-water convection systems with indicated 

Location Temperatures oc 

Name Lat1- Long1- Sur- Geochemical Subtude tude face sur- 0 I 0 face 

N w 

2/ 2/ 

1J ST02 Na-K-Ca 3/ 

COLORADO 

Routt H.S. 40 33.6 106 51 64 131 168 135 

Steamboat Springs 40 29. 1 106 50.3 66 129 195 135 

Idaho Springs 39 44.2 105 30.2 50 109 208 115 

Glenwood Springs 39 33 107 19.3 66 137 190 140 

Avalanche Springs 39 13.9 107 13.5 57 136 125 140 

Cottonwood Springs 38 48.7 106 13.5 62 107 83 110 

Mt. Princeton S. 38 43.9 106 10.2 66 112 52 115 

Poncha H.S. 38 29.9 106 04.5 76 129 143 145 

Minera 1 H. S. 38 10. 1 105 55.0 63 103 91 105 

Waunita H.S. 38 31.0 106 29.1 71 129 87 130 

Cebolla H.S. 38 16.5 107 05.9 46 125 233 130 

Orvis H.S. 38 08 107 44 58 109 231 110 

Wagon Wheel Gap 37 45 106 49.2 66 129 188 135 

Pagosa H.S. 37 15.5 107 00.5 70 165 278 150? 

32 
subsurface temperatures from 90 ° to 150 ° c-continued 

Reservoir Assumptions Conments 

Sub- th;ck- Vol- Heat 

sur- ness ume conface tent 

area 1018 

cal 

km2 4/ km 5/ km 3 6/ 7/ 

l.E 1.5 2.25 .2 Three hot springs; Chemical data not 

reliable. 

1.5 1.5 2.25 .2 Many hot springs; chemical data not 

reliable; some travertine. 

1.5 1.5 2.25 . 1 8 springs, total discharge 190 lpm 

depositing travertine; probably faultcontrolled; chemical data not reliable. 

1.5 1.5 2.25 .2 11 springs discharging about 11,400 lpm; chemical data not reliable; some travertine. 

1.5 1. 5 2.25 .2 5 springs discharging ~54 lpm; chemical 

data not reliable. 

4 1.5 6 .3 5 springs discharging ~570 lpm; extensive 

zeolitization. 

5 1.5 7.5 .5 4 main springs, 30 others; extensive zeolitization, present depositton of opal, calcite, and phillipsite reported. 

1.5 1.5 2.25 .2 3 springs depositing travertine and 

discharging ~1~00 lpm; associated with 

flourite deposits; Na-K-Ca temperature may be too high. 

1.5 1.5 2.25 . 1 30 springs discharging ~190 lpm, reported with travertine and sinter (?); wells to 

354 m depth and 60°C. 

1.5 1.5 2.25 .2 2 groups, more than 100 springs discharging 3,785 lpm. 

1.5 1.5 2.25 .2 20 springs discharging ~380 lpm; travertine 

reported; chemical data not reliable. 

1.5 1.5 2.25 . 1 1 spring discharging ~1,140 lpm; chemical 

data not reliable. 

1.5 1.5 2.25 .2 3 springs depositing travertine and 

associated with flourite deposits; 

Na-K-Ca temperature probably too high. 

1.5 1.5 2.25 .2 Springs discharging ~380 lpm and depositing 

travertine; 1 well for space heating; chemical data not reliable. 

33 
Table 5.-Identified hot-water convection systems with indicated 

Location Temperatures oc 

Name Lati- Longi- Sur- fieochemical Subtude tude face sur- 0 I 0 face 

N w 

2/ 2/ 

l! ST02 Na-K-Ca 'Y 

HA~JAI I 

Steaming Flats 19 26.5 155 16 97 --No Data-- "'150'i' 

(Sulphur Bank area) 

Upper Kau area 19 23.7 155 17.3 "'22 100 

1955 eruption area, 19 26.5 154 57 hot --No Data-- "'150? 

East Rift 

Puulena area, East 19 28.3 154 53 ? --No Data-- "'150? 

Rift 

IDAHO 

Red River H.S. 45 47.3 115 08.8 55 123 80 125 

Riggins H.S. 45 24.7 116 28.5 47 120 95 125 

Burgdorf H.S. 45 16.7 115 55.2 45 121 57 125 

Zim's (Yoghann) U.S.45 02.6 116 17.0 65 115 85 120 

Krigbaum H.S. 44 58. 1 116 11.4 43 121 96 125 

Starkey U.S 44 51.2 116 25.8 56 108 70 115 

Wh i te Li c k s H .S. 44 40.9 116 13.8 65 143 145 150 

Near Cove School 44 35.0 116 37.7 70 120 78 125 

Near Deer Creek 44 32.4 116 45.0 50 107 63 110 

Near Midvale 44 28.3 116 43.9 28 128 243 135 

Near Midvale Airprt.44 28.2 116 45.9 28 121 51 12'5 

Hot Creek Springs 44 38.5 116 02.7 34 111 62 115 

34 
subsurface temperatures from 90° to 150°c-continued 

Reservoir Assumptions 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 1018 

cal 

km2 ~ km ?) km3 §! ij 

1.5 1.5 2.25 

5 0.7 3.5 

2 2 4 

2 2 4 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

.2 

.2 

.3 

.3 

.2 

.2 

. 2 

. 1 

.2 

• 1 

.2 

.2 

• 1 

.2 

.2 

• 1 

Cornnents 

Nearly constant fumarolic activity, no 

water discharge; area may be larger. 

Resistivity anomally drilled by N.S.F. 

grant to G. V. Keller, 1973; low-temperature convection system identified top at 

water table, ~ooc at -490 m; bottom of 

convection near -\150 m, ~100°C, then steep 

gradient to basaltic magma chamber (?). 

Steaming area; three wells drilled 1961, 

deepest ~210m, ~ll3°C; NSF grant 1975 to 

University of Hawaii for deep test. 

No surface manifestations; geophysical anomalies identified. 

9 springs discharging ~130 lpm; mixing 

model T=l90°C. 

4 springs discharging ~190 lpm; mixing 

model T=220°C. 

2 spr~ngs discharging ~10 lpm . 

Discharging hot well . 

2 springs discharging 150 lpm; mixing model 

T=200°C. 

7 hot springs discharging 490 lpm . 

Numerous springs discharging 113 lpm; may be part of larger system including hot 

springs near Cove School; mixing model 

T=220°C. 

Numerous springs discharging 1,630 lpm. 

Hot springs discharging 219 lpm. 

Flowing well; may be part of single 

system including Deer Creek and Midvale. 

Flowing well; geochemical temperatures unreliable. 

Springs discharging ~3,000 lpm; mixing model suggests 195°C. 

35 
Table 5.-Identified hot-water convection systems with indicat£.ri 

Location 

Name Lat1-

tude 

0 

N 

IDAHO Con. 

Molly • s H. S. 44 38.3 

Vulcan H.S. 44 34.1 

Cabarton H. S. 44 25 

Boiling Springs 44 21.9 

Near Payette River 44 05.1 

Near Grimes Pass 44 02.8 

Kirkham H.S. 44 04.3 

Bonneville H.S. 44 09.5 

Stanley H.S. 44 13.5 

Sunbeam H.S. 44 16. 1 

Slate Creek H.S. 44 10.1 

Roystone H.S. 43 57.2 

N.E. Boise Thermal 43 36.1 

area 

Neinmeyer .. H.S. 43 45.5 

Dutch Frank Springs 43 47.7 

Paradise H.S. 43 33.2 

Worswick H.S. 43 33.5 

Long1-

tude 

0 

w 

11541.6 

11541.5 

116 01.7 

115 51.4 

116 03 

115 51.1 

115 32.6 

115 18.4 

114 55.6 

114 44.9 

114 37.5 

116 18 

116 09.9 

115 34.7 

115 25.5 

1"15 16.3 

114 47.2 

36 

Temperatures oc 

Sur- Geochemical 

face 

2/ 2/ 

1/ sro~ Na-K-Ca 

59 130 

87 148 

71 124 

86 134 

80 148 

55 110 

65 118 

85 138 

41 107 

76 133 

50 129 

55 148 

75 124 

76 138 

65 120 

56 118 

81 135 

83 

135 

99 

89 

139 

74 

79 

142 

47 

130 

91 

150 

79 

126 

72 

72 

93 

Subsurface 

3/ 

135 

150 

130 

140 

150 

115 

120 

145 

110 

140 

130 

150 

125 

140 

125 

120 

140 
subsurface temperatures from 90 ° to 150 ° c-continued 

Reservoir Assumptions Comnents 

Sub- Th;ck- Vol- Heat 

sur- ness ume conface tent 

area 1018 

cal 

km2 4/ km 5/ km 3 6/ 71 

1.5 1.5 2.25 .2 7 springs discharging 76 lpm; mixing model 

suggests 195°C. 

1.5 1.5 2.25 .2 13 springs discharging ~1~00 lpm; sinter 

reported. 

1.5 1.5 2.25 .2 Numerous springs discharing ~265 lpm; 

mixing model T = 165°C. 

1.5 1.5 2.25 .2 Numerous vents discharging ~600 lpm and 

depositing minor zeolites, calcites, and 

mercury minerals. 

1. 5 1.5 2.25 .2 One spring discharging ~75 lpm; mixing model suggests 200°C. 

1.5 1.5 2.25 . 1 Spring(s?) discharging ~260 lpm. 

1.5 1.5 2.25 . 1 Numerous springs discharging ~950 lpm. 

1.5 1.5 2.25 .2 8 springs and seeps discharging ~\900 

lpm; mixing model suggests 175°C. 

4 1.5 6 .3 6 springs discharging ~20 lpm; southwestern of a possible 10-km line extending NE to Sunbeam; mixing T = 180°C. 

1.5 1.5 2.25 .2 Numerous vents discharging ~1,700 lpm. 

1.5 1.5 2.25 .2 8 springs and seeps discharging ~100 lpm; 

mixing T = 2l0°C. 

2 1.5 3 .2 5 springs di scha·rgi ng ~75 1 pm. 

4 2 8 .5 Linear zone of springs and associated 

thermal wells on the ~edge of Boise; 

used for space heating. 

1.5 1.5 2.25 .2 13 springs discharging ~\300 lpm with gas, mixing model suggests 190°C. 

1.5 1.5 2.25 .2 Numerous springs, gassy, discharging ~1,150 lpm. 

1.5 1.5 2.25 . 1 Several springs. 

1.5 1.5 2.25 .2 Numerous springs discharging ~\750 lpm. 

37 
T;;lble 5.-Identified hot-water convection systems with indicate-:\ 

Location 

Name Latitude 

0 

N 

IDAHO Con. 

Guyer H.S. 43 40.5 

Clarendon H.S. 43 33.6 

Hailey H. S. 43 30.3 

Near Brockie Airpt 43 32.4 

Elk Creek H.S. 43 25.4 

Near Punkin Corner 43 18.1 

Barron's H.S. 

Near Magic Reservoir 

43 18.1 

43 19.7 

Near Bennett Creek 43 06.9 

Latty H.S. 43 07.0 

Near Ryegrass 43 05.8 

Creek 

Near Radio Towers 43 02.2 

White Arrow H.S. 43 02.9 

Near Chalk Mine 43 02.9 

Near Clover Creek 43 01.4 

Near Gravel Pits 42 54.3 

Bruneau-Grandview 42 56 

Near Banbury 42 41.4 

Longitude 

0 

w 

114 24.6 

114 24.9 

114 22.2 

113 30.1 

114 37.6 

114 54.4 

114 54.4 

114 23.2 

115 27.9 

115 18.3 

115 24.6 

115 27.5 

114 57.2 

114 55 

115 00.6 

115 29.5 

115 56 

114 50 

38 

Temperatures oc 

Sur- Geochemical 

face 

2/ 2/ 

ll sTo2 Na-K-Ca 

71 129 

47 125 

63 129 

41 107 

54 113 

35 123 

71 124 

71 138 

68 129 

55 138 

62 129 

38 129 

'65 136 

47 133 

43 113 

34 109 

84 138 

59 136 

88 

114 

83 

91 

80 

71 

91 

163 

71 

137 

81 

125 

113 

98 

70 

144 

93 

108 

Sub--

surfac€ 

'lJ 

135 

130 

135 

110 

120 

125 

130 

140 

135 

140 

135 

130 

140 

140 

120 

145 

145 

140 
subsurface temperatures from 90 ° to 150 ° c--continued 

Reservoir Assumptions 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area lQlB 

cal 

km2 ~ km ~ km3 §! ]_I 

1.5 1.5 2.25 

1.5 1.5 2.25 

1~5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1..5 2.2'5 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

1.5 1.5 2.25 

Conments 

.2 Numerous springs discharging ~~oo lpm. 

.2 Numerous springs discharging ~380 lpm; mixing model suggest 215°C. 

.2 Numerous springs discharging ~265 lpm; 

mixing model suggests 190°C. 

.1 1 well flowing ~45 lpm. 

.1 5 springs discharging ~ss lpm. 

.1 Flowing well discharging 15 lpm; may be 

part of extensive system underlying a 

large portion of the Carnes Prairie, and 

including Elk Creek, Barrons, and Waldrop. 

.2 Numerous springs discharging ~120 lpm. 

.2 One well flowing 51 lpm; mixing models 

indicate temperatures as high as 275°C . 

. 2 flowing ~11 discharging ~ZPOO lpm. 

.2 One spring; may be part of extensive syst~m 

that includes Bennett Creek and 

Ryegrass Creek; Si02 temperature of all may be too high because of equi llbration with 

diatomite.· 

.2 Flowing well . 

• 2 1 flowing well discharging 30 lpm. 

.2 4 springs discharging ~~100 l~; mixing 

model indicates 200°C . 

. 2 flowing well. 

.1 flowing well. 

.2 1 flowing well discharging ~a lpm. 

Na-K-Ca temperature may be inaccurate 

carbonate deposition reported. May,be diatomaceous earth at depth. 

2~50 l.S 3375 263 An extensive area with Qany warm and hot 

artesian wells; mixing model t~peratures 

up tb 275°C . 

8 1.5 12.0 • 9 1 flowJng well discharging ~225 1~; mixing T ~215°C; includes Miracle and 1 othe~ 

sprin~. 

39 
Table 5.-Identified hot-water convection systems with indicated 

Location Temperatures oc 

Name Lati- Longi- Sur- Geochemical Subtude tude face sur- 0 I 0 face N w 

2/ 2/ 

1/ ST02 Na-1<-Ca 3/ 

IDAHO Con. 

Near Cedar Uill 42 24.9 114 18. 1 38 116 65 120 

Near Bridger 42 28.7 113 37.5 60 111 89 115 

Springs 

Oakley Warm 42 10.4 11351.7 47 119 92 120 

Springs 

Raft River thennal 42 06.1 113 22.8 96 136 139 140 

arE!a 

Maple Grove H.S. 42 18.2 111 42.2 76 107 236 110 

Near Riverdale 42 09.9 111 50.4 45 126 170 125 

Wayland H.S. 42 08.2 111 56.9 77 126 270 130 

Near Newdale 43 53.2 111 35.4 36 122 84 125 

Ashton Warm 44 05.7 111 27.5 41 143 91 145 

Springs 

t10NTANA 

Helena (Broadwater) 46 36.5 112 05 65 136 135 140 

Hot Spring 

White Sulphur 46 32.8 110 54.2 57 103 148 150 

Springs 

Alhambra H.S. 46 27 111 59 59 115 111 120 

Boulder H.S. 46 12 112 05.6 76 143 135 145 

Gregson (Fairmont) 46 02.6 112 48.4 74 128 126 130 

H.S. 

Pipestone U.S. 45 53.8 112 13.9 61 115 113 120 

Barkels (Silver 45 41.5 112 17.2 72 143 139 145 

Star) H.S. 

Norris (Hapgood) 45 34.6 111 41 52 130 153 150 

H.S. 

Jardine (Big Hole 45 21.8 113 24.7 58 104 148 150 

or Jackson) H.S. 

40 
subsurface temperatures from 90 ° to 150 ° c-continued 

Reservoir Assumptions 

Sub- Thicksur- ness 

face 

area 

km2 4/ km 5/ 

6 1.5 

1.5 1.5 

1.5 1.5 

20 1.5 

2 1. 5 

1.5 1.5 

5 1.5 

1.5 1.5 

1.5 1.5 

1.5 1.5 

1.5 1.5 

1.5 1.5 

1.5 1.5 

1.5 1.5 

1.5 1.5 

1.5 1.5 

1.5 1.5 

1.5 1.5 

Volume 

km3 6/ 

9 

2.25 

2.25 

30 

3 

2.25 

7.5 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

Heat 

content 

1018 

cal 

7/ 

• 6 

• 1 

• 1 

2.3 

.2 

.2 

.5 

.2 

.2 

.2 

.2 

• 1 

.2 

.2 

. 1 

.2 

.2 

.2 

Conments 

1 flowing well discharging ~2P50 lpm . 

1 flowing well discharging 7~00 lpm; 

mixing T = 150°C • 

1 spring discharging 38 lpm; mixing 

T = 195°C. 

Area of flowing hot we 11 s recent 1 y exp 1 or,~d 

by ERDA; 140°C measured at depth of 1poo m 

in well flowing ~~oo lpm. 

Numerous springs discharging ~1)00 lpm; Na-k-Ca possibly inaccurate due to 

deposition of carbonate. 

1 flowing well; Na-K-Ca possibly inaccurate 

from deposition of carbonate. 

Numerous springs discharging ~3~00 lpm an1 

depositing travertine; Na-K-Ca thermometr.'f 

may be inaccurate. 

Flowing well. 

Springs discharging ~ lpm from Pleistoce1e 

basalt. 

2 hot springs discharging 110 lpm. 

About 9 springs discharging ~2POO lpm; 

mixing model suggests 150°C. 

About 22 springs 

Many springs in two groups; siliceous 

sinter; large discharge. 

Several springs 

Several springs. 

4 springs discharging 200 lpm. 

5 springs discharging 200 lpm. 

About 100 springs ~5100 lpm; mixing model 

indicates 150°C. 

41 
Table 5.-Identified hot-water convection systems with indicate.~ 

location 

Name latitude 

0 I 

N 

NEVADA 

Bog H.S. 41 55.5 

Howard H.S. 41 43.3 

Dyke H.S. 41 34.0 

Near Soldier Meadow 41 21.5 

Double H.S. 

Near Black Rock 

Fly Ranch H.S. 

Butte Sprs. 

41 03.0 

40 57 

40 52.0 

40 46 

Mineral H.S. 41 47.3 

Hot Hole (Elko) 40 49.1 

Near Carlin 40 42.0 

Hot Sulphur Sprs. 41 9.4 

Hot Springs Point 40 24.2 

Wa1ti H.S. 39 54.1 

Spencer H.S. 39 19 

Hot Pot 40 55.3 

longi- Surtude face 0 

w 

!I 

118 48.1 88 

118 30.3 56 

118 33.7 66 

119 13.2 54 

119 02.8 80 

118 58 90 

119 20.9 80 

119 07 86 

114 43.3 60 

115 46.5 89 

116 08.0 79 

114 59.1 90 

116 31.0 54 

116 35.2 72 

116 51 72 

117 06.5 58 

42 

Temperatures oc 

Geochemical 

2/ 

sTo2 

108 

128 

129 

113 

140 

148 

127 

129 

127 

115 

119 

128 

116 

117 

123 

125 

2/ 

Na-K-Ca 

109 

81 

137 

65 

127 

116 

154 

120 

129 

127 

81 

191 

233 

78 

210 

195 

Subsurface 

'# 

115 

130 

140 

115 

145 

150 

130 

130 

130 

115 

120 

140 

125 

120 

125 

125 
subsurface temperatures from 90 ° to 150 ° c-continued 

Reservoir Assumptions CoiTiflents 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 1Ql8 

cal 

km2 y km?} km 3 §! ?J 

2 2 4 .2 2 springs discharging ~,000 lpm at 54°C. 

1.5 1.5 2.25 . 2 Several springs . 

1.5 1.5 2.25 . 2 1 (?} spring discharging ~100 lpm . 

6 2 12 .7 Several springs in area of ~ km2 discharging ~so lpm. 

10 2 20 1.6 Several springs along linear zone 20 km 

north from Black Rock Point; largest 

group discharging ~175 lpm; minor travertine. 

1.5 1.5 2.25 .2 

8 2 16 1.1 Area of large spring pools and two abandoned wells discharging ~soo lpm and depo~-

iting travertine, so Na-K-Ca may be too 

high. 

1.5 1. 5 2.25 .2 

1.5 1.5 2.25 .2 Several springs and shallow wells. 

2 1.5 3 .2 Several springs depositing travertine, so 

Na-K-Ca temperature may be high. 

1.5 1.5 2.25 . 1 

1.5 1.5 2.25 .2 3 springs discharging ~190 lpm; paleozoic 

limestone at depth; Na-K-Ca geothermometer 

may be inaccurate; may be part of more 

extensive area extending 4.8 km along west 

edge of Snake Mtns. 

5 1.5 7.5 .5 Hot springs, discharging ~125 lpm; depositing travertine; Na-K-Ca may be inaccurate. 

2 1.5 3 .2 6 springs discharging 300 lpm and depos- iting travertine. 

1.5 1.5 2.25 .2 Several hot springs discharging 50 lpm and 

depositing travertine so Na-K-Ca thermometry may be inaccurate. 

1.5 1.5 2.25 .2 One spring discharging ~270 lpm; depositing 

travertine; Na-K-Ca may be inaccurate. 

43 
Table 5.-Identified hot-water convection systems with indicated 

Location 

Name Latitude 

0 t 

N 

NEVADA Con. 

Buffalo Valley H.S. 40 22.1 

Hot Springs 41 25.4 

Golconda H.S. 40 57.7 

Sou (Gilberts) H.S. 40 05.4 

Dixie H.S. 

The Needles 

Wa1leys H.S. 

Nevada H.S. 

Darrough H.S. 

Warm Springs 

Bartho1omae H.S. 

NEW MEXICO 

39 47.9 

40 08.8 

38 58.9 

38 54.0 

38 49.3 

38 11.3 

39 24.3 

Jemez (Ojos Ca1ien- 35 47 

tes) H.S. 

Radium H.S. 32 30 

Lower Frisco 33 15 

Gila H.S. 33 12 

Longi- Surtude face 0 

w 

11 

117 19.5 79 

117 23.0 58 

117 29.6 74 

117 43.5 93 

118 04.0 72 

119 40.5 98 

119 49.9 71 

119 24.7 61 

117 10.8 97 

116 22.5 61 

116 20.8 54 

106 41 73 

106 55.5 52 

108 47 37 

108 12 68 

44 

Temperatures oc 

Geochemical 

sfo2 

125 

107 

116 

115 

143 

137 

109 

104 

136 

111 

129 

134 

124 

128 

121 

y Na-K-Ca 

140 

209 

201 

99 

143 

214 

85 

86 

127 

192 

72 

197 

222 

150 

114 

Subsurface 

'lJ 

130 

110 

125 

115 

150 

145 

110 

105 

140 

125 

130 

135 

130 

150 

125 
subsurface temperatures from 90 ° to 150 ° c-continued 

Reservoir Assumptions Conments 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 1018 

cal km ~kmW km3 §} y 

4 2.5 10 .7 More than 200 hot springs with largest discharging 61 lpm; in travertine area so 

Na-K-Ca thermometry may be inaccurate. 

1.5 1.5 2.25 . 1 Discharging from travertine so Na-K-Ca 

thermometry may be inaccurate. 

1.5 1.5 2.25 .2 About 12 springs discharging 750 lpm and 

depositing manganiferous travertine; area 

may be considerably larger. 

1.5 1.5 2.25 • 1 Several hot springs depositi09 travertine. 

2 1.5 3 .2 Several hot springs discharging ~200 lpm. 

2 1.5 3 .2 Two lines of springs that have deposited travertine cones in Pyramid Lake; two wells 

on eastern line, ll6°C at 450 and 1$00 m 

depth; may be considerably larger system. 

1.5 1.5 2.25 . 1 Many hot springs discharging ~75 lpm along 

base of recent faultscarp. 

1.5 1.5 2.25 • 1 Several springs in travertine area discharging ~200 lpm. 

1.5 1.5 2.25 .2 Several springs and well discharging ~350 

lpm; one well 129°C at 230 m depth discharging ~,000 lpm; area may be considerably 

larger. 

1.5 1.5 2.25 .2 2 springs. 

1.5 1.5 2.25 .2 Spring discharging ~400 lpm. 

1.5 1.5 2.25 .2 About 10 springs depositing travertine and 

discharging ~750 lpm; Na-K-Ca probably not 

reliable; 9.7 km SSW of Valles Caldera. 

1.5 1.5 2.25 .2 

1.5 1.5 2.25 .2 Discharge ~75 lpm; Na-K-Ca probably not 

reliable. 

1.5 1.5 2.25 .2 Four hot springs discharging ~3~00 lpm; 

area may be somewhat larger. 

45 
Table 5.-Identified hot-water convection systems with indicated 

Location 

Name Latitude 

0 I 

N 

OREGON 

Mt. Hood 45 22.5 

Carey (Austin) H.S. 45 01.2 

Kahneetah H.S. 

Breitenbush H.S. 

Belknap H.S. 

Klamath Falls 

Summer Lake H.S. 

Radium H.S. 

Hot Lake (2) 

f·1ed i ca 1 H .S . 

Ritter H.S. 

Fisher H.S. 

Blue ~~untain H.S. 

Near Little Valley 

Beulah H.S. 

Near Riverside 

Crane H.S. 

Near Harney Lake 

Near Trout Creek 

Near McDermitt 

44 51.9 

44 46.9 

44 11.6 

42 15 

42 43.5 

44 55.8 

45 14.6 

45 01.1 

44 53.7 

42 17.9 

44 21.3 

43 53.5 

43 56.7 

43 28.0 

43 26.4 

43 10.9 

42 11.3 

42 04.1 

Longi- Surtude face 0 

w 

JJ 

121 42.5 90 

122 00.6 86 

121 12.9 52 

121 58.5 92 

122 03.2 71 

121 45 74 

120 38.7 43 

117 56.4 58 

117 57.6 80 

117 37.5 60 

119 08.6 41 

119 46.5 68 

118 34.4 58 

117 30.0 70 

118 08.2 60 

118 11.3 63 

118 38.4 78 

119 06.2 68 

118 09.2 52 

117 30.0 52 

46 

Temperatures oc 

Geochemical 

2/ 2/ 

ST02 Na-K-Ca 

--No Data--

126 

140 

127 

135 

136 

134 

124 

100 

125 

119 

123 

99 

145 

169 

143 

127 

133 

140 

120 

118 

103 

149 

114 

130 

112 

108 

115 

125 

92 

165 

126 

119 

86 

138 

124 

130 

144 

100 

Subsurface 

11 

125 

125 

140 

150 

140 

120 

140 

130 

120 

130 

125 

130 

130 

150 

130 

150 

130 

135 

145 

120 
subsurface temperatures from 90 ° to 150 ° c--continued 

Reservoir Assumptions CorTITients 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 101s 

cal 

km2 4/ km 5/ km 3 6/ 7/ 

2 2 4 .3 Many fumaroles but not water discharge; 

semiactive volcano; temperatures may be 

higher; area may be larger. 

1.5 1.5 2.25 . 1 Several hot springs in 0.1 km discharging 

"'950 lpm. 

1.5 1.5 2.25 .2 Hot spring discharging "'200 lpm. 

1.5 1.5 2.25 .2 40 to 60 springs in 0.1 km ~rea discharging 

3,400 lpm. 

1.5 1.5 2.25 . 2 3 springs discharging "'300 lpm . 

240 2 480 30 Numerous springs and shallow wells discharging from fault zones; largest spring "'2CO 

lpm; well temperatures 60° to ll5°C used 

for domestic heating; large area indicated. 

4 1.5 6.0 . 4 3 springs discharging "'75 lpm . 

1.5 1.5 2.25 .2 2 flowing wells discharging "'lJOO lpm. 

1.5 1.5 2.25 . 1 large spring pool discharging "'1,500 lpn· . 

1.5 1.5 2.25 .2 2 springs discharging "'200 lpm. 

1.5 1.5 2.25 • 1 hot spring discharging "'130 lpm. 

3 1.5 4.5 • 3 Hot spring discharging "'70 lpm; some H2S . 

1..5 1.5 2.25 .2 Several springs discharging "'250 lpm. 

1.5 1.5 2.25 .2 Several springs discharging "'550 lpm. 

1.5 1.5 2.25 .2 1 (?) spring discharging "'50 lpm from 

vitric tuff so Si02 temperature may not t~ 

reliable; sinter and travertine reported. 

l. 5 1.5 2.25 • 2 Several springs discharging "'200 lpm . 

1.5 1.5 2.25 .2 2 springs discharging "'550 lpm. 

3 1.5 4.5 .3 Spring discharging "'550 lpm. 

1.5 1.5 2.25 .2 Several springs discharging "'200 lpm. 

2 1.5 3.0 .2 Hot spring discharging "'750 lpm. 

47 
Table 5.-Identified hot-water convection systems with indicate~ 

Location Temperatures °C 

Name Lati- Longi- Sur- Geochemical Subtude tude face sur- 0 I 0 face 

N w 

2/ 2/ 

lJ ST02 Na-K-Ca '}./ 

UTAH 

Hooper H.S. 41 08 112 11.3 60 101 223 105 

Crystal H.S. 40 29 111 54 58 103 135 135 

Baker (Abraham, 39 36.8 112 43.9 87 118 122 125 

Crater) H.S. 

Meadow H.S. 38 51.8 112 30 41 100 68 105 

Monroe(Cooper) H.S. 38 38.2 112 06.4 76 110 118 120 

Joseph H.S. 38 36.7 112 11.2 64 l33 141 140 

WASHINGTON 

Sol Due H.S. 47 58.1 123 52.1 56 148 92 150 

Olympic H.S. 47 58.9 123 41.2 52 126 87 130 

Sulphur Creek H.S. 48 15.3 121 10.8 37 122 113 125 

Garland (San Juan) 47 20.5 121 53.4 38 148 185 150 

Ohanapecosh H.S. 46 44.2 121 33.6 49 126 164 130 

WYOMING 

Huckleberry H.S. 44 07 110 41 71 150 141 150 

Auburn H.S. 42 49.5 111 0 62 143 209 150 

Totals (224 Systems) 

48 
subsurface temperatures from 90 ° to 150 ° c-continued 

Reservoir Assumptions CorTITients 

Sub- Thick- Vol- Heat 

sur- ness ume conface tent 

area 1018 

cal 

km2 ~ km ?J km 3 §.1 ?J 

1.5 1.5 2.25 • 1 4 saline hot springs in 2 groups 0.6 km 

apart; geothermometry may not be reliable. 

1.5 1.5 2.25 . 2 4 hot springs discharging ~230 lpm • 

1.5 1.5 2.25 • 1 4 hot springs depositing travertine and M~ 

oxides at edge of young basalt flows. 

1.5 1.5 2.25 . 1 3 springs on 1.6 km trend; includes Hatton 

Hot Springs (Black Rock or Wiwepa) Hot 

Springs; analyzed spring discharges 226 lpm 

5 1. 5 7.5 .5 9 springs in 3 groups on 48 km trend along Sevier fault; includes Red Hill and Johnson 

Hot Springs; depositing travertine. 

1.5 1.5 2.25 .2 Springs depositing travertine and discharg i ng ~ 11 0 1 pm. 

1.5 1.5 2.25 .2 11 springs discharging ~500 lpm. 

1.5 1.5 2.25 .2 17 springs discharging ~500 lpm along fault 

zone. 

1.5 1.5 2.25 . 1 Springs discharginj 15 lpm; minor precipi- tation (carbonate? . 

1.5 1.5 2.25 .2 3 springs discharging ~95 lpm; extensive 

travertine; chemical temperatures not 

reliable. 

1.5 1.5 2.25 .2 5 springs discharging ~225 lpm; extensivr: 

precipitation (carbonate?). 

1.5 1.5 2.25 .2 2 small groups of hot springs discharginr ~380 lpm. 

1.5 1.5 2.25 .2 More than 100 vents; discharging ~140 lpm 

"'2938 '\i4564 'V345 and depositing travertine. 

49 
\. 

\ 

:.\ 

'\ ., \ .. ' 

0 

J.' .. ' I I 

0 

\ 

\ 

---...--. ... ~ 

--!--,...._ 

! ! ·--- / I --...._ ________ _ 

i i -

! \ 

I I " <.., 

i \ 

---------------- ---r------

--------. __ J\. • • • • • 

; 

; 

i 

I 

i 

i .2 .I 

• 

• 

\ 

\ 

' \ 

\\ 

\ 

• 

200 I ,• I 

"'· 

• • • 

I -' . .,. . .,. ..... _~ v 

•• j. I 

i 

i 

i 

,. • f ·-·--..!*.!.._-/ 

i 

• i 

----~-

! 

I 

i 

i 

I 

i 

I 

I 

j 

~- .. ---.. ----... _ .. ___ _ 

.. .. 

i 

i 

I 

j 

; 

i 

i 

i 

;-·-·-·--·-·--·----· 

I 

; 

~----------·-·- ; 

i 

; 

I 

! --• .L ________ , 

; 

i 

I 

i 

i 

i 

; 

--·+--·--------~---------

i 

i 

j 

i ----------,_ __ j _______ _ 

i 

i 

; 

i 

i ' 

i 

i 

! 

• •lj '· 

I 

i 

i 

• 

• 

-L __ r-··-----...t-·-----

400 MILES I t 

i (-------------- ; 

j 

i 

! 

I 

; 

j 

i 

I 

I 

i 

i ________ j 

r· .. ''··--··\ 

'·· \ 

\ 

200 400 600 KILOMETRES \. 

', __ 

), 

' \ 

------,---· \ 

i 

i 

\ .I 

i 

I 

i 

\ 

-------·-----~ \ 

-, 

-,~ 

FIGURE 3.-Location of hydrothermal convection systems in the conterminous United States with indicated sul:)f;urface temperatures between 90° and 1500C. 

50 
dissolved salts (1,000 to 10,000 mgjkg), but a fe.w 

contain 2 to 3 percent. The Salton Sea geothermal 

system is especially saline, having about 26 percent dissolved salts at reservoir temperatures exceeding 340°C. 

Much attention has been given re.oently to constituents whose contents are strongly dependent 

on temperature. A few of these are useful in predicting subsurface temperatures from che1nical 

·analyses of water samples from springs or shallow wells. Si02 (Fournier and Rowe, 1966) and 

Na-K-Ca relations (Fournier and Truesdell, 

1973) have been especially useful in providing 

most of the predicted temperatures in this report. 

The basic assumptions involved in chemical 

geothermon1eters need to be emphasized. The n1ost 

important (Fournier and others, 1974) are: (1) 

temperature-dependent reactions exist between 

constitutents in the water and the rocks of a reservoir; (2) all constituents involved in the reactions are sufficiently abundant so that supply is 

not a limiting factor; ( 3) che1nical equilibrium 

is attained at the reservoir temperature; ( 4) little 

or no equilibration or change in eomposition 

occurs at lower temperatures as the water flows 

from the reservoir to the surface ; and ( 5) the 

water from the reservoir does not n1ix with any 

other water at intermediate levels. Assumptions 1, 

2, and 3 commonly seem to be valid for the Si02 

and N:a-K -Ca geothermon1eters. Nearly all reservoir rocks contain quartz, and residence times of a 

few clays or weeks are sufficient to saturate the 

W31ter in Si02 with respect to quartz at temperatures much above 150°C. Also, 1nost waters 

seem to attain equilibriun1 in N a, K, and Ca with 

respect to the common clay minerals and feldspars. However, some indicated temperatures of 

our tabulated data are not reliable, at least in part 

because waters high in free C02 may not have 

attained equilibrium with the rocks or because 

they attained equilibrium with mineral asseinblages other-than those assumed for the geothem1-

ometers. In order to gain internal consistency, 

the Si02 temperatures reported in the tables are 

based on equilibrium with quartz rather than 

ehalcedony or an1orphous forms of silica. However, some reported systems, especially those of 

low temperature, may have equilibrated with one 

of these more soluble forms of silica. The predicted temperatures of such systems will be too high. 

Assumption 4, that water flows to the surface 

without chemical change, is prob81bly nevf~ striotly true, but useful minimum temperatures can be 

predieted. Assumption 5, that no mixing occurs 

with cool shallow waters, n1ay frequently be invalid. Mixing, formerly considered to be a major 

obstacle in predicting subsurface temperatures, 

has recently been utilized to advantage by Fournier 9 .. nd Truesdell (1974). In favorable circumstances, tempe.rRAtures higher than those indicated 

by the Si02 on Na-K-Ca geothermometers can 

be predicted at deeper levels in a stackrd series 

of reservoirs (Truesdell and Fournier, 1975). 

These mixing models are still so new tl'at they 

have been applied only to a few systems. Other 

chemical and isotopic methods of tem:oerature 

prediction are also being developed by T':'uesdell 

and others. 

Experience has shown that natural gey;;'ers and 

active deposition of siliceous sinter are reliable 

indicators of subsurface ten1peratures at least 

as high as 180°C. On the other hand, travertine 

deposits ( OaC03 ) and opaline residues r~duced 

by sulfuric acid leaching ( frmn oxidP,tion of 

H2S) are comn1only ident.ifioo incorrectl~r as siliceous sinter but actually have no reliable relation 

to reservoir temperature. 

The origin of the heat has major im:oortance 

in predicting the geothermal resources of individual convection systems. Two principal origins 

are considered here : ( 1) heat directly rdated to 

volcanic sources localized as "hotspots'' in the 

shallow crust of the Earth (Smith and Shaw, 

this circular) and ( 2) heat related to geothermal 

gradient, or the general increase in temperature 

with depth as a "consequence of conductive heat 

flow (Diment and others, this circular). For both 

types, the ultimate source of most of the heat 

is fro1m deep within •the Earth, prob31bly resulting 

in large part from natural radioactivity. As indicated by Smith and Shaw, the basalts and andesites that form most volcanoes have probably 

risen rapidly fron1 the mantle to the surface in 

volcanic eruption. As a result, their heat is dispersed rather than stored and does not provide 

useful geothermal concentrations. However, the 

high-silica varieties of volcanic rocks, perhaps 

because of their very high viscl>sities, commonly 

are associated with magma chambers at shallow 

levels in the crust (perhaps 2 to 10 km but most 

commonly rubout 4 kin; Smith and Shaw, this cir--

cular) and can sustain high-tempe-rature~ convec51 
tion systems for many thousands of years. Many 

large geothermal systems appear to be associated 

with young silicic volcanic rocks. Son1e hotspring systems that have no direct association 

with young silicic volcanic systems n1ay derive 

their heat froQl older volcanic systems or from 

very young igneous systems with no surface expression. 

Other hot-spring systems are probably not 

related to silicic volcanic rocks. The heat of their 

systems is related to the regional geotherm.al 

gradient, which is higher in some regions such 

as the Great Basin than in others ( Diment and 

others, this circular). Many hot springs of the 

Great Basin emerge from steeply dipping faults 

that 1nay extend to depths of at least a few 

kilometres (Hose and Taylor, 1974; Olmsted 

and others, 1975). The water may be entirely of 

surface origin, circulating downward, being 

heated by thermal conduction with consequent 

decrease in density, and then rising and discharging from surface springs. In such systems, the 

normal conducted heat is being removed; temperatures immediately adjacent to the deep recharge channels are lower than those at similar 

depths not affected by convective heat losses. 

Temperatures should decline with tin1e as rocks 

adjacent to channels are cooled and as new heat 

is supplied by conduction through increasing 

distances from channel walls. In our opinion, the 

abundant fault-controlled spring systems of low 

temperature throughout the Great Basin are likely to be. of this origin. We suspeet, however, that 

systems such as Beowawe, Leach, and Bradys in 

Nevada require volcanic heat and are not supplied 

only by geothermal gradient, even though located 

within the Battle Mountain high where conductive heat flow is considerably higher than the 

normal heat flow of the Great Basin ( Diment 

and others, this circular). 1V e, with .R. L. Smith 

(oral commun. 1975), are skeptical that geothermal gradient alone can sustain high temperatures for the long durations of time indicated 

for these systems. 

Identified systems 

The accom•panying tables are based on the 

scanty data available to us early in 1975. Sixtythree systems have indicated temperatures above 

150°C (table 4 and figs. 1 and 2), and 224 have 

indicated temperatures between 90°C and 150°C 

( ta;ble 5 and figs. 2 and 3) . Numerous hot springs 

in the range of 50° to 90°C (Waring, 1965) have 

not been included because geochmnical and other 

evidence is lacking to suggest reserYoir tenlperatures greater than 90°C. As additional data become. a vailable,some of these will no doubt qualify 

for higher temperature categories. 

The more prominent systems have wellestablished names from local usage and literature. 

In most instances the name appearing on the topographic ma;p of the area or the name given by 

Waring ( 1965) is used. If more tlJ an one name 

is available locally or in the literature for a 

particular spring, the additional na1nes are shown 

in parentheses in the tables. Other springs or 

wells without established names r.re identified 

by son1e nearby geographic feature on available 

maps, which also provide latitude and longitude. 

Measured surface temperatures provide minimunl reservoir ten1peratures. Where the chemical 

temperatures T Sio2 and T Na-K-ca both indicate 

temperatures above about 125°C, we are confident 

that most subsurface temperatures will equal or 

exceed the predicted temperature. The user of 

these tables, however, should be especially skeptical of temperatures that are below 125°C, as 

well as temperatures that differ between the two 

chen1ical methods by more than about 20°C. Other 

systems whose predicted temperat11res warrant 

skepticism are those of moderately high discharge 

(more than about 50 lpm from a single spring 

or obout 200 lpn1 from a system) ·that also have 

surface temperatures nn1Ch below l'"liling (70°C 

or less). An indicated high subsurface temperature is credible for ·a cool spring of low discharge 

where excess heat can be lost by ccnduction but 

is much less credible for a system combining a 

low surface temperature and a higl' rate of discharge. Geochemical temperatures in most but 

not all cases provide minimal estinates of subsurface temperatures. Note that we have predicted 

some reservoir temperatures that are near the 

average rather than the maximum geochemical 

temperature. In most cases, our predicted temperature is at least as high as the preferred 

geochemical temperature (generally T8102); however, in some systems where subsurface temperature projections have been made (mcst notably by 

Olmsted and others, 1975), the assumed reservoir 

volume includes a substantial part that may be 

less than the indicated geochemical temperature. 

52 
The subsurfac-e area assumed to be underlain 

by a reservoir of the indicated average, temperature is derived from all available data. These 

include, as 1nininnun~ the surface a1·ea containing springs, spring deposits~ and bleaching from 

attack by sulfuric acid derived from oxidation of 

H2S. Geophysical data ( Cmnbs and Muffier·, 

1973), where available, provided the principal 

means for estimating the area and, in a fe.w 

cases, the indicated depth of the rese.rvoir, even 

though sufficient drilling has not yet been clone 

to docmne,nt carefully the relation between a 

geophysical anomaly ,and geothermal potential. 

Parts or all of some electrical resistivity anomalies may he caused hy hydrothennal alteration, 

rocks rieh in clay minerals, or saline ground waters, particularly in many areas of the Basin and 

Range province. Other types of geophysical surveys 'may also indicate anomalies that are not 

closely related to geothennal reservoirs. In most. 

instanees where surface expression and geology 

were used to indicate reservoir dimensions and 

geophysical data were then examined, the reservoir dimensions either remained the same or, n1ore 

oonunonly, were significantly increased. 

Although the pattern of industry exploration 

and drilling activity is viewed as highly significant in indicating the extent of a reservoir in 

several areas, in general only scanty data are 

available now from private industry. The lack 

of reliable data concerning areal extent is a serious constraint in this· assessment because many 

estimates of the subsurface areas shown in tables 

3 to 5 differ by more than three orders of Inagnitude ; in contrast, all other parameters vary by 

less than one order of magnitude. Thus, the areal 

extent is the most critical single parameter in estimating the heat content o.f a system. Tmnperruture, 

however, is of critical importance in detennining 

how a systen1 may ibe utilized. Systen1s with miniIna! surface evidence, sueh as a single spring, a 

restricted group of springs, or a single thennal 

well without other evidenee, and systems for 

whieh geology or geophysics do not suggest a 

larger subsurface area are arbitrarily assigned a 

subsurface area of 1.5 k1n2 ( assun1ed to be 11/2 km 

long on the. dominant structural trend, even if unknown in direction, and 0.5 km on each side of this 

trend). ~fany of the separ8ite systems we have 

indicated may be interconnected at depths greater 

than 2 or 3 km. 

The heat re.gervoir of all convection systems 

is arbitrarily assun1ed to extend to 3 km in depth, 

which is the current limit of geothermal drilling. 

Heat at greater depths in volcanic systems is 

induded in the volcanic syste1n resources (Smith 

and Shaw, this circul,ar); heat below 3 km in 

de.pth in other areas is included in the resource 

base calculations for conduction-dominated regions (Diment and others, this circular). A convection system in the latter environment has 

re.moved heat, relative to surrounding ground, 

as previously noted. 

The top of a convective rese.rvoir is go,nerally 

not well defined but is generally assumed to have 

an average de.pth of 1, 1 lh, or 2 km, depending 

on assumed shape, of the convection system and 

inferred similarities to drilled areas. l lthough 

the, differences among our various depth esti1nates 

(tables a to 5) dearly -affect drilling costs, the 

tables show that assumed thickness introduces 

much less variation in calculated volumes and 

heat contents than the. assun1ed areas. 

The tabulated volumes are simple multiplications of the assumed areas and thicknerqes. Estimated stored heat is then calculated from 

reservoir temperatures (less l5°C, ambient surface temperature; for simplicity, assured constant for all of the United States), volume, and 

volumetric specific heat assumed as 0.6 cal/ 

cm3 °C. Volumetric specific heats are known to 

differ slightly by rock type, poros1ty, ar(l water 

content (Diment and others, this circu)ar), but 

the assumption of a single volumetric specific 

heat introduces only slight errors relative to the 

great uncertainties of other paramete ... s. 

Little. is known about the specific inter:'llediatetemperature systems of table 5 and figur~s 2 and 

3. Most of these systems are included in this category because of their chemically indicated temperatures but are listed with n1inin1al reservoir 

areas, volumes, and heat contents. One notable 

exception is the Bruneau-Grandview ar~a of 

Id8iho, shown on table 5 as having an area of 

2,250 kn12 and 263 X 1018 cal of stored hrat. This 

·large area in the southwestern part of the Snake 

River Plain is characterized by hot springs of 

modest ten1perature ( com,monly 35° to 45°0; 

Waring, 1965) and n1any shallow thermal wells 

that discharge at temperatures as high as 84°0. 

In addition to this broad distribution of thermal 

springs and wells, the regional heat flow is prob53 
ably high to very high (Diment and others, this 

circular) , and geophysical surveys show no sharp 

boundaries for the area known to be anomalous. 

This geothermal area is likely to be huge, and it 

may even extend under a large part of the Snake 

River Plain. 

Even less is known about our low-ten1perature 

hydrothermal resources ( <90°C). Many spring 

systen1s tabulated by Waring ( 1965) are probably in this category, and the warmer ones may 

be useful in space heating. For example, Iceland 

and Hungary make e::\..1:-ensive use of wateT at temperatures below 100°C, and 80°C is actually the 

preferred distribution ten1perature in Reykjavik, 

Iceland (Einarsson, 1970). 

Pattern of distribution of identified convection systems 

Figures 1 and 3 oonfirm the well-known abundance of thermal systems in the Western United 

States and their scarcity elsewhere. Most of the 

high-temperature systems occur in the areas of 

anomalously high conductive heat flow (Diment 

and others, this circular, figs. 9 to 11); many of 

these systems also occur in or near areas of young 

volcanic rocks (Smith and Shaw, this circular, 

figs. 5 to 7). 

The numerical data of tables 4 and 5 are sun1-

marized in table 6, which also divides the systems 

into two categories, depending on whether the 

predicted magnitude of their heat reservoirs exceeds the mininn1m assumed value. 

Note that the heat contained in identified hotwater systems is about 30 times that in vapordominated systems, and total heat contained in 

systems with indicated temperatures above 150°C 

is about the same as that in systems between 90°C 

and 150°C. Such con1parisons of systems of different types n1ust be tempered by the extent of 

our know ledge of each type. ; for obvious reasons, 

much more attention has been given to the more 

attractive large high-temperature systems. Six 

of the high-temperature systems (Surprise Valley, Long Valley, Coso Hot Springs, Salton Sea, 

and Heber, California, and Yellowstone National 

Park, Wyoming) are each predicted to contain 

more than 10 X 1018 cal of stored heat; they total 

about 75 percent of the total ·estimated heat of 

all of the identified high-temperature systems. 

Even more striking is the dominance of a few 

large systems in the intermediate-temperature 

range. Only two identified syste·ms are predicted 

to contain ·more than 10 X 1018 cal e~ch, and only 

seven contain more than 1 X 1018 cr.l. The dominance of the Bruneau-Grandview H.rea of Idaho 

is especially startling; this may be more a reflection of a lack of adequate dat3 and reliable 

predictive technique than of fact. Ifowever, geothermal convection systems may have the same 

log-normal relation between grade and frequency that metalliferous deposits r.nd hydrocarbon reservoirs have. If this is so, relatively few 

systems contain n1ost of the resourees. 

Undiscovered convective systems 

Good reasons exist for optimism that abundant 

geothermal resources in hot-water C'lnvective systems are available for future discovery. Our use 

of the term "discovery," however, must be defined; a geothermal discovery is corsidered to result from any of the following: 

1. New knowledge ·of the extent of an already 

- identified systen1 that incre~.ses its tabulated volume a·ppreciably; the difference 

is considered to ·be the newly discovered 

part (but this may be offs·~t in part by 

decreased estimates for inrlividual systems). 

2. The temperature of ~n identif~d system is 

found to be higher than firrt estimatedenough for the system to qualify for a 

higher ten1perature category and more 

valued potential utilization (but increases 

may also be offset, probably in small part, 

by decreases) . 

3. A previously unknown system is discovered, 

con1monly with no obvious surface evidence for its existence. 

Most of the tabulated convection s~rstems of this 

report (tables 4 and 5) should be Yiewed as targets for future exploration and discovery. 

Our reasons for being optimistic that many exploitable hot-water sJ!Stems exist for future discovery are: 

1. Many of the young silicic vol~anic systems 

tabluated by Smith and Sr~w (this circular) have no recognized convection syst$ls. 

2. Other young silicic systems may still be developing, with no direct evidence for their 

existence in the shallow cru1t. 

3. \Vith few exceptions, old, deepl;T eroded volcanic systems are associated with exten54 
Table 6.-Sumrnary of identified hydrothermal convection systems 

Number Subsurface Volume, Heat Content, 

area, km 3 1018 cal 

km2 

Vapor-dominated systems (~240°C) 3 122 194 26 -- Hot-water systems, identified 

High-temperature systems (<150°C) 

Systems each with heat content 

>0.2 x 1018 cal 38 1374 2939 366 

c:1t Systems each with heat content 

01 <0.~ x 1018 cal 25 40 56 5 -- -- --

Total high-temperature systems 63 1414 2995 371 -- -- --

Intermediate-temperature systems (90°-150°C) 

Systems each with heat content 

>0.2 x 101 8 cal 28 2638 4112 311 

Systems each with heat content 

<0.2 x 1018 cal 196 300 452 34 

Total intermediate-temperature system 224 2938 4564 345 

Total identified hot-water systems 287 4352 7559 714 -- -

Total hydrothermal convection systems 290 4474 7753 740 
sive hydrothermal alteration. Until recently~ such alteration was interpreted as 

the effect of n1agmatic fluids, perhaps 

much different from the large convection 

systems of Larderello, The Geysers, \V airakei, and the Imperial Valley fields. !-lowever, extensive isotope studies of waters 

and rocks of both the old and the pre~sently active systems have shown that local waters of surface origin are generally 

the dominant fluid (Taylor, 1974; White, 

197 4) ; the active systems are probably 

the present-day equivalents of old oreforming systmns. The volumes of altered 

rooks of the ore-forming systems are conlmonly many tens or hundreds of cubic 

kilometres. Furthermore~ the isotope studies also demonstrate that each vohune of 

altered rock com1nonly required the flow 

of 1 to 10 volumes of water through the 

system. The isotopic and other data also 

indicate that temperatures of the.se old 

systems n1ost frequently ranged from 

200° to 400° C at probable depths of 1 to 

4 km below the ground surface of the 

time. If this analogy is correct, many active systems should have similar volun1es 

and temperatures in their deeper parts. 

4. Many old voleanic systems probably still sustain moderate- to high-temperature. convection syste.ms that may not have surface 

expression. Most of these volcanic systems ·are too old or poorly known to be 

evaluated in detail (Smith and Shaw, 

this circular) . 

5. Recent major progress has been made in applying several kinds of chemical, isotopic, 

and thermodynamic mixing n1odels to 

convection systems that differ from the 

si1nple model (Fournier and Truesdell, 

1974; Truesdell and Fournier, 1975). Different levels of mixing with dilute, cool 

meteoric waters are probably involved. 

"\Vith proper sa1npling of springs and 

shallow wells, evidence for high temperatures at deeper levels can be obtained; 

such evidence is norinally lost by re-equilibration in a hot reservoir of a simple 

systen1. Reassessment of data from n1any 

of the systems of tables 4 and 5 and from 

other inconspicuous systems of low surface temperature is likely to result in 

many new discoveries, as Wt; have defined 

the tern1. 

\Ve are fully aware that some eYtensively explored areas are better known to some. others 

than to us, ·especially in light of the recent rapid 

rate of accumulation of proprietary data by industry. In thne, some of these data will becOine 

available, and our techniques, estimates, and assumptions will improve enough to justify a new 

assessment. 

\V e estimate that five. times the volume and heat 

eontents of the high- temperature ( > 150°0) systems of table. 4 (excluding Yellowstone Park) are 

not presently recognized and exist as targets for 

future discovery. We ca1mot specifically justify 

this number other than to en1phasize our previously stated reasons for optimism; a factor of 2 

is ahnoE,i certainly too s1nall, and :30 is likely to 

be too large. We estimate that about three times 

the volume and heat eontent of the intermediatetemperature resources of table 5 are unrecognized, 

but this may be conservative.. 

ACKNOWLEDGMENTS 

Many predicted reservoir tem]leratures are 

based on chemical data from R. H. Mariner, 

Theresa S. Presser, John Rap~, and I van 

Barnes of the U.S. Geological Sur,rey. Essential 

assistance was provided by F. H. Olmstead, 

H. W. Young, T. P. Miller, A. H. ':':'ruesdell, and 

geophysicists familiar with specific systems. 

C. A. Brook, J. P. Calzia, J. A. G~·owley, G. L. 

Galyardt, E. A. Johnson, Peter C'lerlindacher, 

E. D. Patterson, G. B. Shearer, F. W. Smith, 

and K. E. Telleen assisted in assE.mbling all of 

the data for our use. 

REFERENCES CITEI' 

Combs, Jim, and Muffier, L. J. P., 1973, Explorati<>n for 

geothermal resources, in Kruger, Paul, and Otte, 

Carel, eds., Geothermal energy-resources, production, 

stimul,ation : Stanford, Calif., Stanford Univ. Press, 

p. 95-128. 

Einarsson, S. S., 1970, Utilization <>f low enthalpy water 

for space heating, industrial, agricultural and other 

uses: (Jeothermics, Specioal Issue 2, v. 1, p. 112-121. 

Fournier, R. 0., and Rowe, J. J., 196f, Estimation of 

undergrom1d temperatures from the silica content of 

water from hot springs and wet-str:-am wells: Am. 

Jour. Sci., v. 264, p. 685-697. 

56 
~.,ournier, R. 0., and Truesdell, A. H., 1973, An empirical 

Na-K-Ca geothermometer for natural waters: Geochim. et Cosmochim. Acta, v. 37, p. 1255-1275. 

--- 197 4, Geochemical indicators of subsurface tempe:ratures, Pt. 2, Estimation of temperature and 

fraction of hot water mixed with cold water: U.S. 

Geol. Survey Jour. Research, v. 2, no. 3, p. 263-270. 

Fournier, R. 0., White, D. E., and Truesdell, A. H .. , 1974, 

Geochemical indicators of subsurface temperatures, 

Pt. 1, Basic assumptions: U.S. Geol. Survey Jour. 

Research, v. 2, no. 3, p. 259-262. 

Hose, R. K., and Taylor, B. F., 1974, Geothermal systems 

of northern Nevada: U.S. Geol. Survey open-file 

rept. 7 4-271, 27 p. 

James, Russell, 1968, Wairakei and Larderello; geothermal power systems compared: New Zealand 

Jour. Sci. and Technology, v. 11, p. 706-719. 

MufHer, L. J. P., 1973, Geothermal resources, in United 

States mineral resources : U.S. Geol. Survey Prof. 

Paper 820, p. 251-261. 

Olmsted, F. H., Glancy, P. A., Harrill, J. R., Rush, F. E., 

and Van Denburgh, A. S., 1975, Preliminary hydrogeologic appraisal of selected hydrothermal systems 

in northern and central Nevada: U.S. Geol. Survey 

open-tUe rept. 75-56, 267 p. 

Ramey, H. J., Jr., 1970, A reservoir engineering study of 

The Geysers geothermal field : Evidence Reich and 

Reich, petitioners vs. commissioner of Internal Revenue, 1969 Tax Court of the United States·, 52, T.C. 

No. 74, 36p. 

Taylor, H. P., Jr., 1974, The application of oxy~en and 

hydrogen isotope studies to problems of'. hydrothermal alteration and ore deposition : Econ. Geology., v. 69, p. 843-883. 

Truesdell, A. H., and Fournier, R. 0., 1975, Cal~uJ.atioos 

of deep temperatures in geothermal systmes from the 

chemistry of boiling spring waters of mixei origin: 

United Nations Symposium on Geothermal B~urces, 

2d, Proc. (in press). 

Truesdell, A. H., and White, D. E., 1973, Prod·•ction of 

superheated steam from vapor-dominated r~rvoirs : 

Geothermics, v. 2, p. 145-164. 

Waring, G. A., 1965, Thermal springs of tb~ United 

States and other countries of the world-A summary: U.S. Gool. Survey Prof. Paper 492, 383 p. 

White, D. E., 1973, Characteristics of geothermal resources and pr~blems of utiUzation, in Kruger, Paul 

and Otte, Carel, eds., Geotherma·l energy-~esources, 

production, stimulation : Stanford, Ca., Stanford 

Univ. Press, p. 69-94. 

--- 1974, Diverse origins of hydrothermal ore fluids: 

Econ. Geology, v. 69, p. 954-973. 

White, D. E., MufHer, L. J. P., and Truesde,l. A. H., 

1971, Vapor-dominated hydrothermal systems compared with hot-water systems : Econ. GE:-9logy·., v. 

66, no. 1, p. 75-97. 

Zohdy, A. A. R., Anderson, L. A., and MufHer, L. J. P., 

1973, Resistivity, self-potential, and induced polarization surveys of a V·apor-dominated goothermaJ. system : Geophysics, v. 38, p. 113()-1144. 

57 
Assessment of Geothermal Resources of the United.States-1975 

Igneous-Related Geothermal Systems 

By R. L. Smith and H. R. Shaw 

This preliminary survey of the geothermal resource base associated with igneous-derived 

thermal anomalies in the upper 10 km of the 

crust is a tentative first approach to an extremely 

complex problem. Our results are unavoidably 

speculative, and they mnphasize the paucity of 

quantitative knowledge in the field of geothermal 

energy. Many of the data gaps are the same 

ones that exist in the fields of igneous petrology 

and volcanology and, to some extent, in the field 

of igneous-related ore deposits. Relevant research 

in these fields can go far toward solving many 

geothermal problems and vice versa. 

Our approach to numerical estimates of 

igne,ous-related heat contents rests on estimates 

of the probable volumes of high-level magma 

chambers 2 and determinations of the radiometric ages of the youngest volcanism fron1 those 

chambers combined with simple thermal calculations based on these values. In the following discussion these quantities are symbolized VB (best 

volume) and Ty (last eruption), respectively, and 

are listed with the corresponding heat content 

estimates in table 7. This list contains the most 

important volcanic systems for which we were 

able to obtain data as well as many that may be 

of interest but for which data are lacking. 

Mathematically, our thermal calculations contain two major assumptions: (1) heat transfer 

in rocks surrounding the magma chamber is by 

solid-state conduction and (2) effects of magInatic preheating and gains of magma after the 

time Ty are ignored. 

The first assumption means that we neglect 

heat losses cau_sed by mass-transfer mechanisms 

in surrounding rocks; specifically, we have not 

attempted to account for heat losses by hydrothernlal convection systems. The second assumption 

• We use the term "magma chamber" in the most general sense. ln our thermal calculations, howP.ver, we specifically refer to the region of the crust that, at the time Ty (time- zero of our ealculatir ns), is inferred to contain molten &r 

partly molten rock (magma). 

means that, within the accuracy of VB and Ty, 

our calculations of total magmatic heat yield 

minimal estimates because both magmatic preheating and gains of magma are a9-ditive. 

Whereas the present rates of hydrothermal heat 

transfer are known for a few syri;ems such as 

those of Long Valley, California, Steamboat 

Springs, Nevada, and Yellowstone National 

Park, Wyoming, we defend the fir;;ot assumption 

from the standpoint that there ar~ no uniform 

quantitative criteria for adjustmerts. The same 

is true of the second assumption. The net effects 

of the two assumptions relative to the present 

igneous-related resource tend to. compensate one 

another, but the proportional amounts are not 

known with any confidence. Therefore, our calculations can only be used as a ref~.rence scale of 

heat contents on the "dry" basis that must be 

modified as data accrue on both the hydrothermal 

and magmatic histories of specific rystems. 

The calculations presented in tl'is report are 

based almost entirely on a series of working hypotheses and a general model for volcano evolution 

developed by us over a period of years, which is 

still incomplete (Smith and Shaw, 1973, and 

unpub. data). In its simplest form, the rationale 

for our model holds that basic r'lcks (basalts, 

andesite, and comparable magmas) are formed in 

the mantle and/or lower crust ard rise to the 

surface through narrow pipes anc1 fissures; the 

individual magma pulses are volumetrically 

small, and such systems contribute little stored 

heat to the upper crust until magma chambers 

begin to form at high levels. With the exception 

of the large oceanic volcapoes, basi.c magmas do 

not form large high-level storage chambers out 

of context with derivative 3 silicic magmas ( dacites rhyolites, and comparable df'~vative mag- ' . . . mas). On the other hand, we think that sihcic 

a 'l'he term "derivative" carries 'no specific connotation as· to the ultimate origin of the silicic end of the magma series; 

that is, crustal melting is not ruled out. 

58 (Text resu:zrf!s on p. 73) 
Table 7 .-Magnitudes and heat contents of identified volcanic systems1 

EXPLANATION OF SYMBOLS 

AGE = T 

Ty - Last eruption 

Tys - Youngest silicic eruption 

Tyb - Youngest basic eruption 

Ts - Age (silicic) 

Tc - Age caldera eruption 

The assumed 11 time-zero 11 for 

calculating the present distribution 

of heat is underlined in the table; 

Tys is used wherever data exist. 

Tg - Greatest known age (composition unspecified) 

Tgs - Greatest age (silicic) 

Tgb - Greatest age (basic) 

Tb - Age (basic) 

AREA = A 

Ac - From caldera 

Av - From vent distribution 

As - From shadow 

Af - From fractures 

Au - From uplift 

Ag - From geophysical anomaly (unspecified) 

Agg - Gravity 

Agm - Magnetic 

Ags - Seismic 

Ago - Other, see remarks 

Ao - Other, see remarks 

Yvolcanic systems marked by an asterisk in column 1 are known to ha\'e some 

associated hydrothermal activity (see Renner, White, and Williams, this 

volume). Heat content calculations in columns 11-13 ignore hydroth~rmal 

losses. Methods of calculation are outlined below. 

59 
Table 7.- Magnitudes and heat contents of identified volcanic systems-continuec\ 

VOLUME = V 

Vc - From caldera 

Vv - From vent distribution 

Vs - From shadow 

Vf - From fractures 

Vu - From uplift 

Vg - From geophysical tlnomaly 

Vgg - Gravity 

Vgm - Magnetic 

Vgs - Seismic 

Vgo - Other, see remarks 

Vo - Other, see remarks 

Vee - From extrapolation of silicic ejecta volume. 

Vb - Best estimate 

NOTES ON THERMAL CALCULATIONS IN TABLE 7 

COLUMN 11, ~Q, total calories x 1ol8 

Assumptions: Initial temperature = 850°C 

Latent heat of crystallization = 65 cal/g 

Heat capacity = 0.3 cal/g /°C 

Mean density of magma = 2.5 g /cm3 

The above values are approximate averages for the composition and 

temperature ranges of table 7. From these values the heat liberated 

between 850°C and 650°C is 125 ca1/g. The total heat liberated 

between 850°C and 300°C is 230 cal/g. 

One cubic kilometre of magma represents 2.5 x 1015 g. The total 

heat liberated per cubic kilometre is 0.575 x 1018 calories. This number 

multiplied by the volume VB in column 9 gives the ~Q Total of column 11. 

60 
Table 7 .-Magnitudes and heat contents of identified volcanic systems--continued 

Estimates of heat content in the tables are given in units of 1ol8 

calories. 

COLUMN 12, ~Q now, calories x 1ol8 

The time required for a change of the original gradient at the fartt''s 

surface to a steady-state gradient between the surface temperature and tt'~ 

magma chamber temperature is given approximately by relations discussed t~y 

Jaeger (1964). For the assumed depth of cover of 4 km and a thermal diffusivity of 0.007 cm2/sec, this time is about 360,000 years. Where Ty is much 

younger than this time, the total heat remaining in the system now 

(column 12) is assumed to be about the same as the total value in column 11. 

Estimates of losses for older systems require detailed calculations of the 

disturbance of the geothermal gradient. 

The value of thermal diffusivity used is an average estimate for crustal 

rocks. Roof rocks above large caldera systems such as Yellowstone, IdahoWyoming (IW-2}, Valles, New Mexico (NM-1) and Long Valley, California (C-3} 

may have smaller values of conductive thermal diffusivity. Hydrothermal 

convection systems, however, can increase the effective value of thermal 

diffusivity by a significant amount, depending on average permeabilities of 

roof rocks. 

COLUMN 13, ~Q out, calories x 1ol8 

The total amount of heat transfer per square centimetre from a magm=l 

chamber into roof rocks is given by Carslaw and Jaeger (1959, p.61} and 

also is discussed by Shaw (1974). Using these relations the total heat 

transfer (~Q t) in column 13 is given by ou 

61 
Table 7 .-Magnitudes and heat contents of identified volcanic systems-continued 

~Qout = 51.6At1'

2 (cal) 

where A is contact area {from column 7 converted to square centimeters) 

and t is the time in seconds since Ty. Calculations in column 13 ar~ 

approximately valid only if the time of solidification is greater tt'~n Ty 

in column 6. The time of solidification is approximated by lines 3 and 4 

in figure 4. 

If Ty is much greater than 360,000 years and the time for solidification, 

the calculation of heat content is ambiguous because of the increasing importance of hydrothermal losses. On the basis of conduction models, however, 

the total time for decay of igneous-related thermal anomalies may bP- very 

long. As an example, the time required for the central temperature in a 

magma chamber of horizontal slab like geometry to decay from the initial 

magma temperature to nearly ambient temperature is about 2 m.y. for a magma 

chamber 5 km thick and about 10 m.y. for a 10-km-thick chamber. EvP-n a 

liberal allowance for hydrothermal losses means that the igneous-related 

thermal anomalies for the largest systems of table 7 probably are preserved 

for times of the order 10 m.y. or longer. 

Queries in columns 11-13 mean that even though data exist, we are not 

confident that they pertain even approximately to the assumptions of the 

calculations. Blank spaces in the table mean that more geological and geochronological study is needed before we are willing to provide estimates. 

62 
0') 

~ 

I I 

S-S 

NO. NAME OF AREA 

* 

A·/ 8vLPIR 

A-2 KtsKA 

A·.3 S£GVLA 

A-4 !JAVIPOF 

A-S LITTLE SITK/N 

A-6 SEMISOPOCHNO/ 

(CERBERUS) 

A-7 StJGARLOAF 

A-8 GAR£LOI 

A-9 7ANA6A 

A-10 lAKAWANGIIA 

A-ll BoBROF 

A-12 XANAGA 

A-/3 /'10FF£T 

A-11 AOAGPAK 

A-15 GREAT S!Tif~N 

* 

A-16 lf'ASATOCH/ 

~fi:WIUJI S£RGI£F 

Table 7 .-Magnitudes and heat contents of identified volcanic systems-continued 

ALASKA I 4 5 ' , c.wfeER G.J.a 10 II II .. ... CotftsrriON AGE I 

CHAMBER SoliD- fOT<it. AQ AQ 

LAT. LONG. LAST DATA AREA VoLUME VOLUM£ IFICATION Now OUT REMARKS 

! 

ERUPTION KM' RANGE v. S~TE CALORIES CALORIES CAultlfS KM' K~ •Jo• lll0'1 I f0 

sz•zJ'N 171./JI'£ IJfJIC <Zxto•? >to KH .IJEPrll 

32.06it' 17~'£ 8A.SIC Acrtv£ >10 1(111 P£PTH 

J"n71iY 17e•tJar /)ASIC <to#? Nccp SETTER PATA tJN 

SILICIC? CDMPO.SIT/0/V ANP A6E 

.fi"SB'N 178.Z/)'£ AloiMTA <to4 ? s A, l.l.S.SO If /2.$ >6so• 7 7 

.JI-.J'7'N /78.J2'£ BASIC ACTIV£ 17.3 Ac <f5·180lt 75 >sso· -13 43 

51".f6'N /llo.JS'£ 8ASIC Acnv£ <fZ.fAc I06d24lf /50 >850. 86 86 

.51"5-f'N 11rJB'E BA.JIC </0+., > 10 Kl'f /)EPT/1 

sr-fB'N 178"f8'W BASIC ACTIVE >10 lfH lJ£PTH I 

5/".f'J'N 178()1'JV BASIC? ACTIVE 8S.9 Ac l/5-860Vc 400 >sso• 230 ZJO 

sr5Z'N 11roo'w BASIC? </04 89Ac 2Z.S-90Vc >Zl5 >6SO" IJ /3 

S/"55/Y 177"ll'W' BASIC l </04 ? ~/0/(N IJEPT/1 ? 

.51"55'/V 177"/0'W BASIC? ACTIV£ ZJOAc S7S-230Vc 75 >850° 43 13 

I 

5!0S6'N 17o"IS'W BASIC </0~? >/OKM IJ£PTII 

• 

..fl".f9'N 17o"36'W BAJIC ~1o"? >/0 Kl"' PEPTH 

Sl"OI'N 176°0/'W BASIC ACTIVE !.BAc -!.S-18 W: >5 >850" 3 3 

st•trN 17.r.J()'W 8A3/C? AcnvE? > /0 Kl'f /)EPTH ? 

·..;!' 1 :"·1 ·;,s· 'J'·) BAs::: ; · .-ic ·1~·;- ; · . > i.) • I /)£PTH J 

Sl"/9/V 171 • .!3';/ NoPATA No /JATA N£EP COHPOSITION AND 

AGE DATA 
en 

~ 

I 

s-s 

Nil 

* A·/9 

A-2() 

A-21 

A-22 

A..Z3 

A-2-1 

A.ZI 

A-26 

A-ll 

A-i~8 

A-19 

A-30 

A-31 

A-32 

A-3J 

A-_; 

* AM 

A-.M 

I 

NAM[(EAREA 

!<OROV/N 

KLIVCHEF 

JAR/CHEF 

SEGUAM 

A HUHTA 

CHA6VlAK 

YUNAJKA 

HERBERT 

CARLIJL£ 

CLEVELAND 

ULtA6A 

TANA 

XAGA/'1/L 

V.s£VIDOF 

R£CHESCHNOI 

JKMOI< 

TvuK 

8060SLOF 

Table 7 .-Magnitudes and heat contents of identified volcanic systems-continued 

ALASKA J 4 

... • 7 

C~R ~ .. II II .. .. AGE CtfN«R 5oLJI)- ~'i Mv &:1 LAT. LONG ~~ DATA AREA \t)LUH[ *'K IFICATIOI REMARKS 

KM' RANGE v. 

KM' KH' STATE -c CALous •JO• ~s ~ sz•tJ'N 171./()'JI 8A.SIC ACT IV£ > /0 Kif DEPTH 

sz•t9'N t?f-•onv No/M~ No!H.TA 28.6Ac lt)-280Yc >/00 58 N«D C~POS/TION ..4'\0 A6£ DATA 

sz•19'N 17-1•oJ'W ~SIC? ACTIVE? > 10 lfH DEPTH 

sz•tJ'N 11F2J'W Ab/MTA ACTIVE .21J(Z)Ac ,00-fOO"t; too >8SO /IS liS APPEARJ TD /JE A IJOU6t.E 

~Af:~RA. Nor REPORTeD 

n•JO'N 11rto'W fJASIC! ACTIVE > /0 /(H /)EPTN f 

sz•Js'N t7t•o9'W !J.fJIC? </0~? >IOKN DEPTH ? 

sz•J9W 170.J9W NoO.TA 

li93/C? 

ACTIVE 12.1 Ac J0-120Vc .f() >85() ZJ 23 

sz·.,.sw 170°0l'W aASIC? <to+? > /0 KH DEPTH ? 

sz•sf'N 170.()1.'11 IJASIC ~ ACTIVE > 10 /W DEPTH ? 

.f2•f9'N 169-.Rl'W BASIC.' AcriYE >10 KH /JEPTH ? 

S.JOOI'/11 169.-ll'lv BASIC? -4/0'"? >/OI<N DEPTH? 

S.t~W 169.16'1Y 8AJIC.' NOPATA > /0 KH DEPTH ? 

sz·SBw 169.H'W BASIC? .ACTIVE > 10 KH IJEPTH ? I 

s.roaw 168W'W SILICIC ACTIVE NE£0 MORE OATA I 

sJ•o9'N 168".JJ'W BASIC? '10~ NEED 1'10RE DATA 

.;, • ./.:..) ,~" ,_JJ :)j j ._44SIC ACTIVE ,f.) .1c /.i.i·_;uJ' .:.jJ >.J.jJ -// /)} 

axto' Tc 

sJ•2J'N 168.aJ'W /!JAJIC M1PA1it > 10 KIY PePrH 

S3"56'N 168"0.ZMI fJASIC ACTIVE > /0 KH DEPTH 
~ 

en 

I 

S-S 

Nil 

b.·* 

~·lt-37 

A-.l9 

A-19 

* A-1{1 

A-fi 

A-ll 

A-fJ 

A-11 

A-f.f 

A-16 

A--#7 

A--18 

A-19 

A·SO 

A-S/ 

A·JZ 

/1-~ 

A-.51-

I 

~(EMEA 

MAKVSHIN 

TA8LE ToP 

AKUTAN 

Mr. 61L8£!1T 

(AKVN) 

P06ROMIVI 

WEJTDAHL 

NSH£R 

SHt.SNALDIN 

/SANOTSKI 

RovNDTOP 

AMAK 

FROSTY 

WALRV.S 

( 1'10RZHOVOI) 

DUTTON 

£MHON.S 

HA6V£ 

'>01-:JL..: CR.ATII!i:/t. 

PAVLOF 

Table 7 .-Magnitudes and heat contents of identified volcanic systems-continued 

ALASKA J .. ~- ' , • ~ II II II II , .. AGE CtweER CtW18ER SoliD- far~ ~Q 

LAT. LONG. LAST DATA AREA VouK: VouK IFICATIOIII NoW ~ REMARKS 

UUPTIIIN KH' RANGE v. ST~TE CALORIES CAloRIES CAulllfS Kw KM' ••o• 11011 •10 

S3•.Jt'N !68-s6'W Sti.ICIC? ACTIVE ..l6Ac 9-36 Vc >/0 >850 6 6 

sJ•f8'N !o6.NJ'W !JASIC /Yo PAm >/0/(11 PEPTH 

s~·oa·N /66.()()'W !JASIC l AcTIV£ 3.S Ac 9-36"" >10 >850 6 6 

ff./6'/Y 16.r.J9'W BAste? /Yo.LJAl)l > 10 I<H DEPTH ? 

H-.Jf'N l61.1l'W BASIC AcTIVE >/() KH IJEPTH 

SI.31'N IH-.,.9'/V No .tHTA AcTtYE /VEEP NORE PATA 

S'f • .J8'/I 16f"Z5'# BASIC ACTIYE! 1216 Ac 

f<Zr/03 Ty 

JOIJ-1200 tic 600 >850 31S 315 

S-1-.<IS'N 16J • .JB'W 8AJIC AcTIVE > 10 KH DEPTH 

Sf.-1-S'N I6J·1-nv !JAstc? AcTIVE > /0 /(/11 DEPTH ! 

s-~•ta'N 16J~'W NoPATA ACTIVE, 

<21/fY? 

ss·zrN /63"tJ9'W /3ASIC '? Ab/JATA > /() KH DePTH l 

ss•04'N /6Z"SI'W SILICIC.' NoPATA 

BASIC! 

ss•oo·N t6z~o·w 13AStc No DATA >/0 K/11 PEPTH 

>to•? 

ss·I!'N 162.16'/V BASIC AbPATA > /() /(1'1 /JEPTH 

S"S"20'N /62"0f.'W /JASIC ACTIVE lllJ Ac ~00-IZOOI{; 600 >650 31f 315 

ss•zz'N 16/ 0

S9'W BASIC AcTtVE 

.SS'2.3"N t""':7"o' ::JASIC At:TIVC? 

s.r.ts'N /6/o.l"f'J.I /3ASIC ACTIVE > /0 /(M /JEPTH 
~ 

~ 

I 

S-S 

NO. 

~ 

A-55 

A-~ 

A-Sl 

A.SB 

A-59 

A-60 

A-61 

A-62 

A-63 

A-6f 

A-6S 

A-66 

A-67 

A-68 

A-69 

/1-71? 

A-71 

A-12 

z 

NAME OF AREA 

PAvLoF SISTER 

/}ANA 

/(vPR£ANOF 

J/ENIA/'1/NOF 

.BLACX 

(PvRPL£) 

ANIA.KCHAK 

CHIGIN/GAI( 

111ALAGVIK 

P.:vuK 

MARTIN 

MAG£/ X 

NovARVPTA 

/11T. 6RIG6S 

( liNIFF: PEAX) 

'li:l1P£NT 

/1ATMAI 

ONOWY 

/)EN/SON 

STELLER 

Table 7 .-Magnitudes and heat contents of identified volcanic systems--Continued 

ALASKA J 4 5 ' , a h , 10 II IZ 1.1 , .. CoHPosiTKW AGE CHAMBER CHAMBER ~v~ SoLID- .1Q AQ .6Q 

LAT LONG. LAST DATA AREA VOLUME IFICATION TOTAL NOW OUT REMARKS 

fRUPTIOff I(M' RANGE Ve STATE CALORIES CALORIES CAloRIES I KM' KM1 ·c X 1018 xro•• •to• 

sr21'!Y 16/"SI'W f:JAJIC AcnY£ >/OKM DEPTH 

55.37'N /61" IZ'W SILICIC No PArA </0#? 1.6 A, 4-16 Vc >.5 >J #££/) MORE PATA I 

56.01'/v' 159"18'# A0.?7ATA AcTIVE N££P /'10R£ OATA 

BASIC' 

,f6"!0/V !S9"23'JV BASIC Acrw£ S04Ac !ZS·SOOt1; zoo >8SO 115 115 

3.7x!01 Tc 

56.32'/V !S8'J7W' SILICIC <;o·o 

-- 69 A, 17S-70 tic >20 12 12 6 !V££0 !'tOR£ PATA I 

I 

S6.S3iV 1ss•;o·w SILICIC ACTIV£ 5S6 Ac 110·S60Yc us >850 /29 !29 I 

3.6X/0 3 Tc 

sr&'N !3700'W BASIC' ACT/V£ /V££0 1'10R£ OATA ' 

SILICIC 1 

J"?"IZ'N !S6'fl'W !Yo LJATA !Yo i?AT/1 No OATA 

..:7•4siV IS6.Z!'Jtl BASIC 7 ACTIVE,? IO.S A, ~:S-/00 VC >JO 17 17 SILICIC IN FOCI/.J 01' BOTH Cl'oL.DERA ~ HT PEIILIK; PERHAP!J YOUN& lM31C 

SILICIC ERIIPTION ON N FLANX PE:I/1-IK. 

NEEO AGE PATA 

.58.09'N !SSO.C1-'IV f3ASIC? ACT/II£ > 10 Kl'f j}£PTI{ ~? 

.5ir!Z/Y /.fS0/S'W ? AcTIVE SILICIC OOM£S ' 

#E£.P 1'10/i'.f .PATA 

59°17'# !S.f"IO'W SILICIC ,A.crw£ 8.1 A, 1.0-80 L{ so :::>8SO 29 29 

S/3.20/V 1Sf.08'W BASIC? ACT Ill£ > /0 /{H /J.:PT!t ? 

St9.!f-IV ;s.ron.; BASIC Acrw£ > /0 Kl'1 /).oPTH ? 

Sc5'.16/V !S1.S9W BASIC Acnvc 8.1 Ac Z.?-80 Vc >20 >8SO 12 IZ 

S8.20'N 1.51°1/'N ;1/o I'ATA /.0 I'ATA !Vo o~rA 

S8"25'N ;srz7'W No t'ATA ,.% !JATA No LJArll 

sa·z6AI !Sf-.Z-!'W Alo /)JtTA NOPATA No OAT.A 
~ 

...;J 

I 

S-S 

NO. 

* 

A-11 

A-71 

A-lS 

A-76 

A-77 

A-78 

A-19 

A-80 

A-81 

A-82 

A-83 

A-81-

A-85 

A-86 

A-87 

A-88 

z 

NAME Of AREA 

!1UKAK 

0£VILS /JESK 

KA6UYAK 

FovRP£AKE:O 

fJOU6LAS 

AucusnN£ 

fLIAI'fNA 

REDOUBT 

[JoUBLE 

BLACX 

SPuRR 

JJRt/1'1 

SANFORD 

WRANGELL 

WHIT£ RIVER 

£DG£Cut1BE 

Table 7 .-Magnitudes and heat contents of identified volcanic systems--Continued 

ALASKA 3 4 5 ' 7 8 , 10 II IZ 13 I. 

CoMPOSITION AGE CHAMBER CHAMBER CHAMBER SOLID- f!Q AQ ACI 

LAT LONG LAST DATA AREA VOLUME VOLUME IFICATION TOTAL Now OUT REMARKS fRUPTION KM1 RANGE v, 5Tfc!E CALORIES CALORIES CAloRIES Kw KMJ X 10 11 }( 1011 X 10• 

58'27'# 151"2/'W No PATA ACTIVE? /Vo DATA 

S8"29'!V lf·nnv !Vo ~ATA /VoiJATA /Vo Dl'lTA 

S8'J7'N 15-1-'05'#' S;uc;c '-10?-? 41 Ac ;o-4o v(: >/5 9 9 3 N££0 AGE OA TA 

58'47'N 153'12/.1 !1/oiJATA < 10~? /Vb OATA 

58"52/)1 153'33'J./ /Vo 0ATA ACTIVE? !1/o OATA 

59'22/V 153'2fW SILICIC AcnvE /V££0 6£0P.'IYSlCIIL £)AT/I ' 

60'02'/V !53"06 'W BASIC Acnv£ > /(1 I{M 0£PTH 

60'2.8'/V 152'1-S'N' BASIC ACTIVE >/0 liM DEPTH 

60'14'N 152'3SN' !1/oiJATA 1~-'o JAT/1 ;l--o IJATA 

60~1'/V 152'25W /Vo llATA #oiJATA ho 1/ATA i 

61"18'N !.5"2'!5W f3ASIC ACT!V£ CALDERA, 

NEED MOR£ DATA 

6Z"071V 11-f'.JcJ'N' SILICIC <;ax;o?rs 140 Av ~so-1100 v~ 400 230 ~zoo >/00 

1.8~10 Ts sx;osrs 

6Z'/3 IV 11-t'Ol'w ,# OATA <JSX/Os"TtJ /11££0 DATA ON PARASITIC VENTS 

1i16H ON FLANX.S OF SANFOI'IP 

(INACCESSIBLE:?) 

6Z'OO 'tV 144'0/'W !JA51C 1 ACT! !I£ 

>I 7xi03Tc IS Ac 375-ISO Vc so >850 29 29 

6!'27'/V /4/"Z8'W' SILICIC IS 1/05 80 ~£ 80 >850 4-6 46 

57'01'/V /35"46'/.v' BASIC' Acnv£? N Av 185·710Vj, zso 111 111 60 SILICIC IN FOCVS 

SILICIC < 9;<10 3 8ASIC 0/V FLANKS 

J__xjp5 Ts 
00 = 

Table 7 .-Magnitudes and heat contents of identified volcanic systems..!.-...Continued 

ARIZONA I I I .. ~-- ' , cHNfeER ~ .. II II II .. S-5 AGE CHAI'eER Souo- .6Q AQ AQ 

NO. NAME OF AREA LAT. LONG. LAST DATA AREA VoLUM£ VOUK IFICATION TOTAL Now our REMARKS 

[RUPTION KM' RANGE v. S]~TE CALORifS CALORIES CALMIES 

* K~ KM' X 1011 "10'1 X JO" 

~I SAN r/PAN<!tsC'o &.s.t .. r 8X#Tyl • .z.s-- .S,I/ADOWAHAANO IA'-li/N£.S ~0 

#ovNnftNS 35"ZIN /1/.-fi'W h'/l)la.H& fz~$2': -tSOAI .2.S"t:JO ~ /25"() >~.~· 7/'f 719 J/6 ~.f".II"£P~41".t'"t"v..c.,.fnV'£ I 

~ ,P/.1"~ ~ :.~.1~""" 

AZ·Z /rENPRg If' /1::-Air' ..!i.r2f',.Y 1/1~5-''W' .f/~I&'IC /.~K~~/'i <~5o• 

#.II"IP #1?~1" L:/.,fnt 

I 

AZ·J ~tTa=,f'OYES ..PEAif' j.u"'"..ti 1

N 1//l.POW /ily)lf?.u/".£ I·UXQ~ 1-::~42'· yot.IN6'Esr AtfE a.v ~"""~AW-

~7X~ #£Nr Hov...vnvN 

Lt.sx. i..-

AZ·-1 16'/..tL W!.l-4/A.I'IS tYTN w•;z'N j.5; .ucu: 1-JS)(.tO•/.i A/F.F.P ~..,.£ LlArA 

v.a-;.z'w j..r.tx#fi f<:~.So• -P,ft'?.8ABLY ~ O..I.P .ro.RS/ZE 

-- ---- --·---

----- 1--- 1.....- - ..___ - L....-. -1---

CALIFORNIA I I I .. • ' , C .. R ~ .. II II • ,. S-5 ~- AGE ow.£1 Souo- for'k NAMEfEAR£A LAT. LONG. 

.6Q ~ ~ DATA AREA \\)UK \UK Nil IFtr.ATIOif NOW REMARKS 

KH' RANG£ v. S~TE II K .... KM' 

CALORES •10" ~ ~ 

e; LA.SSENPK ~'"NN V.V-'h ~~Pa -2L)'KS 6b_., ~6:10· ~ ;?1.50 .. 230 2.~0 2 

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&s;c'! ~7~;.:: 25~A ... ~.,v, B'-~ 

f'!'~r CII!Mit'riiAP~ WII'Enr'"n_, 

C'L£Aif iAk'E ~~~At v.zz·~ /.slJO ";76,SZJ. e•3 ..,.,0 iO' .sfAIN'W(A.-J ~z. ~Z_ ${,.#~ ~?f)- AH(- ,s 41HAI~Ctvt~) * ~~ 

VIRW' - ~ ,.. /.100-

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~,;: /~.S"-

.eoo ,.,........,. AN'III6'FnT.(I A~ PAnl 

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Ct'J50#TS ~#OZtY f3X/o~;;. ~7S- MO 37-f. 374 6Y i-32 A"#,;tJ.t.;.rc- O!JnE.s 

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~--~ Ae /~0-

t'7 tf/E#JrttVE L.l'f.rE ..fi".J'S'N V.Q'"'J?"W' !n'H)'~//F ~/P, 7p ~"'"" $()0 ?'~SJ· /7.3 17S 7 7"1 Av ~-'"f~ 1"¥ 

ea ..5/'I'A..SrA 'f/"2.5' /II l.t2'"12'11" P~/.fF 

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..$l70YNC 'f'f,~ 1"/IVO L.AA'fiE t:'.f71fy/rr 

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* ~F/s.r.~ 

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#"-15N ~fi'.I/IF 7-1)'~/js ~PYFS.fi'd'llli'"W ~)'IF t! II ~Y~fPr.t"k'-...:r~ ',tt?•;t'W if.?Xt4?•,1; 'A"'~4Nr SUI.?'1141Wrl"'tv?'IW' 

* A- L2. A- .h l 
= t,C) 

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S-S 

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* 

CIZ 

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(!13 

.. t!l-1 

C/5 

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Ct7 

* 

I 

s-s 

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tf 

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H-f 

I 

NAME(FAREA 

~/AfEPP.If'T-LfOPI.£ 

~~~~~~£X :/FLAYA ff4!>UNTI'f/N.S 

&trr"/N'E 

OLANeHA /J()#E.s 

ci"A"..t'.iON Bv.nF..s 

PAOIIA /JL.ANP, 

I'?ONO LAK£ 

I 

NAMEtEAREA 

KILAUEA 

MAUNA LOA 

HuALALAI 

MAUNA /(£A 

HALEAKALA 

Table 7 .-Magnitudes and heat contents of identified volcanic systems-continued 

CALIFORNIA-CON. J .. ~-- ' , C~8ER ~~ .. II ll II ... I 

AG£ CHAMBER SOLID- .c1Q AQ ~Q 

LAT. LONG. LAST DATA AREA VoLUME VolUI'1[ IFICATION TOTAL Now OUT REMARKS 

[RUPTICNf KM' RANGE v. ST.fE CALORIES CAloR I£$ CALDR•a KM' KM1 X IO• •1011 ••o• ! 

'3e•ISN v.trta::~V 

~-S"X,ql Wrr,s .r Nll'£sr/,Ar"~ /YAY' 

.&f.s!C V.tKm'r. ~.UR~F.t.PW~~APE ' ~...,- ~/t!J' 12.syAP•n .. I 

~&'N ~.£Jint #//Ps J""A'YfSr/~,fT/d/V ;fS 

I 

111':1'",, W" ...5/~/C/~ ~£;sr..' /2ov..e >;z,-c < ~!IIJ· 7~1 .t.~w u~4P£ &-sD~If' .. F. ~£ 

10· hi'J4Aii Y ~.(I£_,T~"ie .qv:~I'O f-.1'"1 

~ .. p~';V ~;q" '-IXFqs 

/C.S- #N/Jl)".S",~V"-'(hl'~(~) ~ 

1//B~W 4.! As -120 ~ /a!' 4( ".so· .58 <10 .}0'! ~~ .S/If!CF.tA.Sr,£,VI"ri'A'V ~ 

~'!.'"~~1-.-s n N"A I 

.31-'"/f"AI V/?.SZ'w' RJYyat;Q? ~PAnt HIP AtU PAr" I 

.,,~'AI /.(p--f.JIY PAC17Fr MArA .N'....-.rp A.fE PAM R.IO"f 

J8WIV JII.IC/C 

8S YM! ACED /'!ME DAT.1. ACTIYE FVHARI 

1/JI-o.J'II' I~TA "FJNITIIC MJT ffof~ 'ft:i:f£,':!:0 ~~~"!RATE -

HAWAII J • ~- ' , C-R ~ • II ll .. .. AG£ CHN"ER Souo- .c1Q 6Q &:1 LAT. LONG. LAST DATA AREA VoLUME IIDUK IF !CATION TOTAL 

- REMARKS 

fWTION I<M' RANG£ v. S~T£ Kw KM' 

CAI.oRis 

••o• 

CAl.oRIES .rro- ~ 

19'l6'N lf.l/8'1( &.sALT AcTJY£ 12.fAu Jl!-/d l'w, <10 >8f0 23 Z3 ~ 1'111/MT A IWVJ I JIILJ IIIIKEJ 

7;. /ll11i ... .~,, (Jf"""' A«lf ~ JI(JtT/11 

AT MY IJitiE 71116 

/9°l9'N /Jf":Jl'JY OUYINC HYRJ >J KN PEPTH !JAJN.T AcTIVE r,... 

19.12'N IIJJ/'W' 0uYIN.! /.1/rlo' PoTENTIAI.LY ACTIYE. > f Kit IJEPJN /JA3AI.T TN 

PoJT- PoTENTIALLY ACTIVE ? No 19.-f9'N /fP.t8'/Y /IAWAIIT£ 6LACIAL HISTORIC ERVPTION.J. 

T,-. > J .I(H DEPTH 

20.-IJ'N lfl.!f'w' /1AFI&0L Z.Zfx/IJ'.? fl1r£NTIALLY ACTIVE. > f KN PEPTH 6iSAJ.T ,,. 
~ 

0 

I 

S-5 

Na 

* 

£Wf 

jZW.<' 

* 

~W3 

~w-f 

t 

S-S 

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* 

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s;s 

f'«). 

* 

1'111-1 

* 

/IN~! 

MV-J 

z 

NAME« AREA 

£5L.ANt7 P-1/?r.'-

1rff:JE%1~ 

)!.F,t,LOW$Tt:J/VE" 

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i,.&:'AC/.Ft'O/ .t)ONES 

,1!!?/c;:. SOvT/1E,.f'/li 

8VTTE 

z 

NAME« AREA 

..5/2'l1;1{~0Ar S.P'~N~.S 

5/LVE.f' ,P6(;t" 

-------~ 

I 

NAME«AREA 

#(LiE.S CALPEA'If 

/YT TAy'ftJA" 

..1;t' AG-VA OOHES 

Table 7 .-Magnitudes and heat contents of identified volcanic systems--Continued 

IDAHO- WYOMING 5 4 5 • T a ' 10 II ll IJ ,. ~SIT Of AGE CHAMBER CHAMBER ~v:R SoLID- llQ AQ M LAT LONG. LAST DATA AREA VOL LIM( IFICATION TOTAL NOW REMARKS 

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7XIp6h' ;> -fOOt:X'v" t1f/;fw, ·~ £ A5 SIN~L~ ff::;~:!~~;~~::; 

fH•#'A-' ~.f)l.tO~lp ~.<!SO8625 1900 YE.LI..OW.STCWE ~J.PERA 

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/f,{!r-Ep C::-t'-IW/'f .5V.if'YEY 

,1/tJ ,/VEEP ~;-+'-1nry .SV.if'YEV ANP 

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-- -

NEVADA J .. s ' T a G..J.u 10 II II IJ ... CotftsiTOf AGE CHAMBER CHAMBER SoliD- llQ AQ AQ 

LAT LONG. LAST DATA AREA VoL LIM( VoltK IF !CATION TOTAL NoW our REMARKS 

fRUPTION KM1 RANGE v. STATE CALORIES CALORIES CAl.M!fS K~ KM' X 10* X 1011 •10 

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18 A11 <rPSV. .5Z RELIIT£/J To CHAMI!J£1l flfVCH 

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-~.ext"'~ lOti/- /f'EC'ENT B'f.s.+..:..r C/.+""t--£ 

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NEW MEXICO 5 4 • ' T a ~.JaR 10 II II il , .. ~IT II* AGE CHHER CHAMBER SoliD- llQ AQ M LAT LONG. LAST DATA AREA VoLUHE VOlUMt IF !CATION TOTAL Now RtMARKS 

[RUPTION I(~ RANGE v. SJ:TE CALOR~S CALORIES CALMIES K~ KM' • to• X 10 .. •10· 

/01".7-f'JV /?J'IYOUIE 76.~".rp /«71!7- >~1!7·11' 

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0-6 ~ JEFFERS(JN /hHEJ 

* 'BR£1T£NBVSH .') 

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Burres 

()-8 CAPPY-BvM !JuTT£ 

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D-IJ QuARTZ MOUNTAIN 

04~ 6.£.Ass BurrEs 

0-IJ Cou6AR t10UNTAIN 

0-16 CburzAR PEAK AREA 

I 0;11 fHARNEY-MALHEVR 

Table 7.-Magnitudes and heat contents of identified volcanic systems-continued 

OREGON I • ~- • T 

C~R ~ • II .. &:1 .. ~GE I CHN"8EA Soul>- for 'it. AQ 

LAT. LONG. ~ ATA AREA \t)UK *" IFICATIOfil NoW REMARKS 

Kw RANGE v. 5T4:TE Kw CAL.oMs ~ ~ I I<H' •10• 

ll'li'N /tt•OP'Jt' JluCIC? I~:' 7C JIJAc ifH·.fl.rJJ6 >JiO >6SO >1/61- >/81- ., I 

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I 

>UI. 7C 100 

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'lrll'N ltr-IZ'W AliPrJIT£ ACTIVE >10 lfN 0£PTH ? 

J 

-lt•tl'N 122'19'1¥ ANIJ£J/Tl Acnv£.' > vo K, P.rPrH i 

H•lf'N 12/.#'lt SiliCIC No DATA .A.F£0 A6£ PATA PJ.Et.fT. I 

H·o?'N 12/,S'W' /)ACITE llbPA7:4 N££P ME PATA 

I 

PLEIJT. 

n•t9'N 121-s9'1t' IJACIT£ NDAfTA NEEP A6E tHTA I 

P/.{/JT. 

f.J-zB'N 11/.SlN' /)ACIT£ NoPATA NEEP A6£ tHTA I'LI!Sl 

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e•JJ'N 122£/'JI /JACIT£? NoJHrA AI£EP AU£ PATA P/.E!Jl 

4J.ItN ttroz·w fiHYOLIT£ l6r/o'Trs 

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46.()11/(}. "-6SO ? ~ "lEJ)J HR PlTAILDJ MJfQT/tJN EJ/1£· 

/J./J/V? VllrJB'JY? RHYOLITE? 91110' !.fOO ~£ !.jOO 11}8 I CIALLY l'llfl£ ACCURATE /.{)(AT/IN I &JM/f NR MEA. ~r l.filltfiiC iWUWAJl 
-l 

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Ut. 

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NAME OF AREA 

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WlllrE ...YiiY. RllfCJ'-!ff 

7(/..5/fA,f' /%1vNTAIIV5 

,TlJ,PAZ ~VA/??1//Y 

.S#ELTER ,f"Aia..t. --

z 

NAME OF AREA 

1'1T 8Ar.'Eif' 

GL.A~IEI( ?EAI( 

/"'T /i'AIIV!ER 

1"/T 5/JIELE/115 

)f/A.OA#5 

Table 7 .-Magnitudes and heat contents of identified volcanic systems-continued 

UTAH I 4 5 ' 7 a ~~ 10 II ll Ll , .. CoPftosrr~ AGE CHAMBER CtW18ER SoliD- .6Q .6Q 6Q 

LAT. LONG. LAST DATA AREA VOLUME VOLUr-1: IFICATION TOTAL Now OUT REMARKS 

ERUPTION KM' RANGE v, S~TE CALORIES CALORIES CAloRIES K..., KM" X 1011 111011 •1o• 

.3~;·~(,/V /12':11''# /f'.#YO.UIE .P~EtST" >to ? #EE.P ,Ye>..,.£ L/ArA ";7.50 >~'f 

~~~r ~'!~$c - Pu-t~r.r, .e3S- #.....-~ Ai$F .L/ArA 

I 3~'.-M'tV w.e·-Hw &!5At.r ~It/. 7; 9~A .. Ho 11., 400 .Z30 ? 

13.6'~/Y' ~SA"'-r <./O#T'YII -~ ' hEEP A<FE L7Anf I 

l/12~oW <:tO•?;$ PAni 

.M> ',YEEO #tJ,PE PE/A!.LEO 

~~·-...e5/V /12·L~w' /P#Y.t:lt/TE .ZX/Q"/S Plfr.-1 DA/It ~8-16-if'A ~-f.f'th: 

? ... - 'A,._ ,.,,... S'ISTEN 

l39•4...t'# ~XItrTys Alii' ~F.P /'J'bR.E L/,( TA 

/IYt:JBJV' R/Ty'OVI'F V.-'x~~>" Ts PAr.lf 

~#yt!~Ur& 3-.,x,~~~•~ ....v., Alr£o /Y&~>f?F OArA 

3'1'',(S'IV 1/12 • .531¥ .t?lfnrt 

~-- ...___ -'--· ------ -'-- -- -

WASHINGTON I 4 5 • 7 a ' 10 II ll Ll . .. CotftsiT~ AGE CHAMSER CHAMBER ~v~ SoliD- .6Q .6Q 6Q 

LAT. LONG. LAST DATA AREA VOLUME IFICATION TOTAL HOW OUT REMARKS 

ERUPTION KM' RANGE v. SJpE CALORIES CALORIES CAuMIIES K..., KM" X 1011 xro'' ••o• 

48.-IJ'IV 12/.,_fHI ~P£strE ACTIV'f > /0 J-'177 0F.Prh' 

~TyJ /.t'.S'·· 12..5 8? 8? 4? ;/(1-c'ti/YE 8)'AN..f.LtJtfy' To 

..,07'/V 1Vt:J7'W ,FJ'/~4 5J.3A,. ~J>6 .$/2.S' $f"/IFZc-/YS ,.<!HP OTHER f47..¢S'J# ~j,.~~P£ ~HilES 

ff' .. 5'/' ,.y 1z;-~w ~N'PESti"E ,1/C!nv£ > 10 ,r-'m PE.tdrh' 

f-K'i.Z' AI /-l2';1'W V4A'PESI/2?" 

At!nv4 

~,.,.x,.,;.z~ 5 Av /.Z.:r· 

ftJYv ?1-f.S ~850 >8 >8 

f1t•;_z IN 12/'.t'f'# ~Nt¥"51TE? iAcnvE r ,.W-Ep ,YPA'E 0-trA 

> /P ,f".?? L/EPr# ? 

---·-" 
magmas are always erupted from high-level stor- silicic extrusive rocks (Tys in table 7). n:re also 

age chambers, probably in the upper 10 km of give estimates for heat contents of systens lackthe crust. ing known silicic extrusive rocks, but it sl'··~mld be 

This reasoning suggests to us that purely basic recognized that the controlling concepts and asvolcanic systems (most common on a world sumptions are less applicable for those systems. 

basis) rarely form thermal anomalies of econ- Our scheme for evaluating volcanic areas for 

omic interest, whereas silicic volcanic systems their geothermal potential was conceived and deprobably always do if they are large enough. In veloped as a guide for exploration rather than as 

making this statement we are specifically ex- a rigorous method for quantitative estimation of 

eluding possible economic development of certain resources. As more and better data on geotheroceanic volcanic systems. In some oceanic sys- mal areas become available, we hope that the 

terns there is the admitted possibility of the scheme might ultimately evolve into a quantitaexistence of high-level basic magma chambers. tive method for characterizing both deyo,loping 

The estimates given in table 7 are based on and declining thermal anomalies associated with 

those volcanic systems showing evidence from high-level igneous systems. The method as apthe presence of silicic eruptives that a high-level plied in this summary of igneous-related goomagma chamber formed in the recent past or is thermal resources does not permit discuRsion of 

forming at the present time. In table 7 we have the many qualifiers that should accompr.ny any 

t?~~ to giv~ conservative estima~s for those detailed consideration of a given geothermal area. 

sihmc volcanic systems that we think have con- The estimates in table 7 should be viewed as first 

tributed the greatest original and present heat , ani~- incomplete approximations of an igneousto the upper 10 km of crust. . . related resource about which little is known with 

The problem of the thermal estimates IS many d f rt · t If thi·n else }'qwever . . . . . any egree o ce ain y. no g , . , faeeted, but our maJor concern Is In estimat.tng the table gives a list of areas that may be of 

the v~l~e of the magma cha~ber for a time geothermal interest and gives some idefl of the 

when It IS known to have contamed magma. The 1 t" •t d f ·gn 0 s related h,a,at con · · · be f re a I ve magru u es o I e u - .. - ~nge of volumes of silicic magm~ cham rs o tents that may exist in these areas. Figure 4 

Interest spans four orders of magnitude or more, .

11 t t th •t · th t u d to cage the 

h I f .

1

. . 1 . I us ra es e cri ena a we se ~' 

and t e vo umes o most SIICIC vo caniC systems t b bl th 1 t te f a m-ogmati·c 

be · ted · h" d f . presen pro a e erma s a o ... can approxima Wit In an or er o magni- te 

tude by inspection of a geologi~ map or by anal- sys m. 

ogy with kindred volcanoes that are better known. Some of the fundamental data, from ~hich all 

For well-documented volcanic areas, other con- estimates are made, are shown in table 7. The 

straints allow estimates of chamber volumes that basis of specific numbers in columns 6-f is indiare probably within a factor of 2 or 3 of their cated by symbols as explained in the legend of 

true volumes. The age of the last known erup- table 7. Column 7 is based on variouF surface 

tion of magma is taken as evidence for a magma manifestations of volcanism, volcano-tectonics, 

chamber that was then at least partly molten; geophysics, and silicic ejecta volumes. Tha. volume 

cooling from the time of that eruption is as- range (column 8) is calculated by assUII'ing that 

sumed to take place in a closed system. Because the thickness of the magma chamber ranges from 

many silicic volcanic systems are not closed but 2.5 to 10 km. This volume range is reiuced in 

continue to receive subchamber heating, this pro- column 9 to a single best estimate to simnlify tfie 

cedure gives minimum <1QOling times and heat thermal calculations for columns 11-13. In gencontents for most systems. Cooling by hydrother- eral we assume that the smaller the area, the 

mal convection tends to offset continued heating, smaller the thickness of the chamber. On an order 

but in our opinion the rate of supply of magma of magnitude basis, this assumption IPist genfrom deep crustal or mantle sources ia the domin- erally be correct. 

ant heat supply for both high-level magmatic Column 10 indicates our best guess on the presand hydrothe1"11l,Q,l systems. ent thermal state of a magma chamber and, thus, 

For most systems the value of Ty used for whether or not we think that magma exists jn the 

thermal calculations is the age of the youngest system now. Many entries are shown as greater 

73 
7 LITTLE GEOTHERMAL POTENTIAL 

i>l5 

6 

C9 Nt• 013. '.C14 

~12 

(f) 5 

a:: 

<( 

LIJ 

>-

z 

a.J" 

c.!J 

<( 

c.!J 

g 

3 

A5 A43 W'\, f63 • A6 e 2 A86 • 

AlO :A66 

• A60 A37. • A2j • :12 • 

e A69 C 1 A58• eA34 

POSSIBLE GEOTHERMAL POTEr'TIAL 

7 

FIGURE 4.-Graph of theoretical cooling time versus volume for magma bodies. Points represent yourgest ages (Ty) 

and estimated volumes ( r B) for the best known magmatic systems of table 7. See text for explanation of 

lines 1--6. 

than or less than 650°C, which is the approximate minim.um temperature of solidification of 

granitic melts. The assumed approximate liquidus 

(all liquid, no crystals) temperature :for most 

silicic magmatic systen1s is about 850°C. "There 

the value >850°C is given, as in Inany of the 

active Alaskan systems, present ejecta compositions indicate that the chan1bers contain andesites 

or dacites of higher liquidus teml'peratures than 

rhyolites. 

Column 11, designated .:lQtota1, is computed 

directly from column 9 and assumes that the 

entire heat content of the high -level storage chamher is contained in a fixed volume of magma. 

This assumption is clearly incorrect if a continuous convective supply of magma from deeper 

sources has been important in tha. origin and 

present state of high-level systems, as we maintain. The assumption leads to a minimum value 

for the total heat transfer in the upper crust derived from any given volcanic system. However, 

aQ total is the only quantity tlt31t can be defended 

as having existed in the chamber at one time. 

All of these systems have histories involving preheating, and evaluat,ion of the trne total will 

require much more data on volumes, compositions, 

depths, shapes, rates of magma convection, differentiation, etc., than are availabl~. today; geochronological data are imperative in this context. 

The total heat content of column 11 is the 

"initial" heat content of the magma chamber of 

74 
volume VB at the time Ty assumed in the calculations and is based on the total heat that would 

be liberated if the total chamber volume, assumed 

to be closed to additional inputs of magma, cooled 

from an initial average temperature of 850°C to 

a final average temperature of 300°C. The calculation includes the latent heat of crystallization 

and the heat capacity integrated over the temperature interval (see table 7, footnote) . The 

lower cutoft is an arbitrary approximation of 

the average preexisting ambient temperature 

within the depth zone occupied by magma. In 

some cases, 850°C is either too low or too high 

an initial temperature. This uncertainty and the 

uncertainties of thermal properties mean that 

some of the listed values may be as much as 50 

percent too high or too low. These uncertainties, 

however, tend to compensate because of the 

ranges of magma types and also because of the 

uncertainties of magmatic preheating and continued additions of magma. On this basis we believe that column 11 generally represents minimal estimates of the total igneous-related heat 

source. Hydrothermal convection does not affect 

this number because it is determined solely by 

the data on magma volumes and temperatures. 

Column 12 is our estimate of that part of the 

heat content of column 11 that still remains in the 

ground, both within and around the original 

magma chamber. The estimate is based on a calculation of the time that would be required for 

the geothermal gradient at the Earth's surface 

to be significantly increased by conductive heat 

transfer in dry rocks over its original value if 

a magma chamber was suddenly emplaced with 

its top at a depth of 4 km. The calculation is 

sensitive to the assumed depth of the roof and 

the properties of roof rocks. If the time since the 

last eruption, Ty, when the total heat content existed mainly in the environs of the magma chamber, is much less than 300,000 years, then little 

of that initial heat has been lost at the Earth's 

surface unless. there has been active hydrothermal convection in roof rocks for much of that 

time. In most places there is no way to evaluate 

this possibility so we have reported heat contents 

only on the basis of conductive models. Yellowstone is an obvious exception, but the magmatichydrothermaJ heat balances there are not discussed in this brief report. 

In detail, the calculation leading to column 

12 is very complicated and is strongly subject to 

all factors influencing heat-transfer mechanisms. 

More important uncertainties, however, are 

caused by the longevity of magmatic injection 

in the same vicinity both before and after the 

assumed value Ty. Again, we believe this to imply 

that the estimates of magma-related heat remaining in the ground are underestimates, probably 

grossly low, for systems with long histories of 

magmatic injection that have not had comparable 

hydrothermal losses. 

Column 13 (.:lQout) gives the heat trr.nsferred 

from the magma chamber into the roof rocks between Ty and the present, calculated by the usual 

1nethods of conduction theory. This he1Jt flow is 

a minimal estimate of the total amount of magmatic heat available throughout the life of the 

igneous event for the support of past and present 

hydrothermal systems within the assurr.~d 4 km 

of roof rock. Numerous complications attend this 

calculation : magmatic heating prior to Ty will 

greatly increase the estimates, wherea~ hydrothermal convection losses decrease the E'l'ltimates. 

Systems that have been volcanologically active 

over a significant time span and are still active 

clearly do not fit the primary assumption of the 

calculation, namely, that a single pulse of magma 

was emplaced instantaneously. Accordingly, we 

are unable to make any estimates of AQout for 

volcanoes labeled "active" in column 6. Generally 

speaking, the realistic magnitudes of h£,at transfer into roof rocks must be far greater than we 

can calculate from our simple assumptions. 

Column 11, .:lQtotal is the sum of the heat now 

in the intrusion, the anomalous heat new in the 

roof rocks, and the anomalous heat lost to 

the atmosphere through the life of tho igneous 

anomaly. Column 12 ( .:lQnow) is the su"ll of the 

heat now in the intrusion and the heat now in 

the roof rocks, whereas column 13 (6.Qout) is the 

sum of the heat in the roof rocks and the heat 

lost to the atmosphere. For igneous systems 

younger than about 300,000 years, the heat lost 

to the atmosphere is assumed to be small from 

the standpoint of conduction models, and AQout 

is equal tQ the anomalous heat now in the roof 

rocks. For systems older than 300,000 ye1l.rs, there 

has been significant escape of heat to tl~ atmosphere, so that .:lQnow is less than .6.Qtotah f.nd AQout 

is greater than the heat now stored in the roof 

rocks. It should be noted that table 7 includes 

only a few of the many existing volcanic systems 

old enough for atmospheric losses to b" signifi75 
cant. The amount of residual heat in these additional systems and the longevity of igneous 

intrusion and subchamber heating in all systems 

could increase our estimates of igneous-related 

heat contents by at least 2 and possibly up to 10 

times. This problem, however, converges with 

the more general problems of regional heat flow 

that are not considered here ( see Diment, this 

circular). 

The total for the llQnow of all magma-related 

systems of column 12 in the conterminous United 

States is roughly 23,000 X 1018 cal or about 30 

times the total estimated heat content of all tabulated hydrothermal systems (Renner and others, 

this volume). Of this total, about half (or 

11,000X1018 cal) probably exists as molten or 

partially molten magma. The total for molten 

magma in Alaska represents about 2,000 X 1018 

cal, which is nearly equal to its total "present 

heat content" of column 12. The total magmatic 

heat released to and presumably still contained 

by roof rocks in the conterminous United States 

is more than 6,000 X 1018 cal (column 13 adjusted 

for surface losses). In some systems, part of this 

heat has been dissipated by hydrothermal activity. The real total, because of the residual effects 

of preheating, probably exceeds the estimates of 

hydrothermal systems by at least an order of 

magnitude. 

The estimates given in table 7 include nearly 

all of the high -level systems in the United States 

known or inferred to contain magma, plus a few 

postmagmatic systems for which we have enough 

data to make a tentative estimate. The data on 

igneous-related heat contents presented in this 

tentative assessment, however, cannot be considered exhaustive. In table 7, for many of the 

silicic systems, column 12 indicates that virtually 

all of the original heat content remains in the 

ground on the basis of the simplified conduction 

models for dry rocks. The reason for this is that 

our reconnaissance was aimed at discovering the 

youngest silicic systems that may still contain 

magma, and usually these systems have the best 

surface exposures and are the most completely 

documented. Calculations of present heat content ( llQnow) for post magmatic systems are 

fewer because of the paucity of data. An exception, for example, is Sutter Buttes, California, 

for which good volcanological data exist but 

which is probably too old to represent an important thermal resource, as is indicated by the 

low present heat content of column 12. 

There are undoubtedly systems in the transitional range between those that still retain nearly 

all of their original heat and thm·e that retain 

virtually none. These are the systems that also 

would plot somewhere within the transitional 

band between lines 1 and 6 in figure 4, between 

subsolidus systems that are inferred to have pluton temperatures near 300° C and systems that 

are inferred to have chambers still entirely molten. Some of the transitional systems are represented in table 7 among the entries lacking sufficient data for heat- content calc·dations, but 

others may be added as data beco~e available. 

Inclusion of these systems would probably in· 

crease the total heat-content estimate by several 

times. 

Additionally, there are several b~oad areas in 

and peripheral to the Basin and Rr.nge province 

where fault-controlled warm and hot springs 

seem clustered near former silicic volcanic loci. 

The data neoossary to confirm or deny a relation 

between the thermal water and subjacent igneous 

bodies are inadequate. We think, how~ver, that estimates of the low-grade geothermal resources 

found to be related to silicic ign~us systems 

eventually will be revised upward and that old 

and very large silicic plutons may retain some 

heat not accounted for by currently proposed 

thermal models. Deep faulting supp,rimposed on 

these older plutons allows deep per~tration and 

circulation of ground waters. Three of these 

areas are listed in table 7 as examples of the kind 

of systems we have in mind (017, Harney-Malheur basin, Oregon; C12, Bridgeport-Bodie area, 

California; 016-C11, Cougar Peak-Purprise V·alley area, Oregon -California). 

Infigure4theage-volume (Ty, VB) data for 

54 volcanic systems are plotted to show the approximate present position of each system in relation to its probable solidification state and to the 

300°C isotherm. This plot is the eF~ence of our 

scheme for reconnaissance evaluati'ln of silicic 

volcanic areas (Smith and Shaw, 1973). 

Pairs of lines in figure 4 are drawr. to represent 

a spectrum of cooling models that identify igneous systems that are now approacl'ing ambient 

temperatures (points above lines 5 or 6), systems that may now just be approaching the postmagmatic stage (points between lin(\s 3 and 4), 

and systems that probably still 1'<:\,ve magma 

chambers with a large molten fraction (points 

below lines 1 or 2). The pairs of lines represent 

76 
-----... ---,-...,.... __ I i . -.. ........... _____ ~-

; ; ------- ; \ ----... ---------·- i ·, I • 

I '· ; \ 

-------·-·-... ~ 

..,. 

I 

') 

l 

i 

I 

i 

i 

) 

./ 

"'• ·-·- .., . .,.. __ f~·2· 

1•· I 

I 

·-·-·---------·-·---· 

1 oo(l 

--,-----

i 

i 

j 

l 

i 

j 

i 

j 

i 

;---·-·-·-·-·--·-·--

; 

i 

I 

--·----·r··-·· 

i ' 

I 

\ 

i 

i 

\ 

I 

\ 

·-·--·-·----~ .; 

., 

-----._ --1.. _____ _ i 

I .3f 

i 

j 

i 

I 

i 

j 

~--·-·-·----·-·-· 

I 

I 

I 

\I 

0 200 

I,',,.,. 

0 200 400 

1-·-·-·-·-----f 

; 

f ..... __ 

I 

j 

i 

i 

; 

i 

I 

' ! 

i 

j ' 

I 

i ·-. .L·-·-·-·-, 

i 

i 

I 

i 

i 

i 

j 

i 

-·-···--. ., .,J_.,_,! ~ \. 

~ 

. -t--·-·--·---·-----· 

I 

j 

i 

I ·--·--·--,--.J ___ ·-·-- i 

; 

; 

! 

i 

j 

i 

; 

i 

; 

; 

i 

i 

1. 

i r----..1-·-·-·- -..L... __ j 

400 Ml LES 

I I 

600 KILOMETRES 

j 

(--·-·-·-·--·-· 

j 

j 

i 

i 

; 

j 

; 

; 

I 

I 

i 

i ________ j 

'-~ 

\ 

\ -._ 

FIGURE 5.-ldentified volcanic systems in the conterminous United States. Numbers are the same as in table 7. 

77 
the effect of shapes ranging from slablike to 

equant for each of the different cooling models. 

Lines 1 and 2 assume that cooling takes place 

by internal convection of the magma chamber 

until solidification is nearly complete. Lines 3 

and 4 assume that cooling is entirely by conduction, both inside and outside the magma chamber, 

until solidification is complete. Even in the presence of convection inside the magma chamber, 

however, lines 3 and 4 come closest to representing the range of true solidification times -for n1ost 

chambers because magmatic convection tends to 

stagnate long before solidification is complete 

(Shaw, 1974). Lines 5 and 6 represent an estimate of the time required before the central temperature of the solidified pluton has fallen to 

about 300°0. Hydrothermal activity will cause 

these lines to shift toward lines 3 and 4, respectively, but it is our opinion that in most cases the 

shift is not large and the positions are fairly 

realistic. 

The points plotted in figure 4 can be compared with the lines only on the assumption that 

the plotted volume T7 R was instantaneously emplaced and cooled fron1 the time represented by 

the youngest age Ty. This assumption is usually questionable, so that the. relation of each point 

to the cooling 1nodels n1ust be individually examined in detail. The effects of magmatic preheating and continued supply of magma, of 

course, tend to shift points lower on the diagram 

relative to models of instantaneous emplacement 

of magma chambers that cool as closed systems. 

Basic (or basaltic) volcanic systems, except for 

the special case of Kilauea, Hawaii, are given 

little en1phasis in this resource estimate because 

they probably do not contain a significant highlevel thermal anomaly and because we do not yet 

have the data necessary to evaluate the1n even 

if they did. 

Young basic volcanoes, however, are indicators 

of magn1a source regions in the n1antle and under son1e conditions are potential indicators of 

buried high-level silicic bodies with no obvious 

surface manifestations. Future investigations may 

reveal these hidden silicic bodies by geophysical 

~tudies, studies of xenoliths in the basic rocks, 

or by other means. The common association of 

silicic domes and lavas with basaltic lava fields 

shows that basaltic systems should not be automatically rejected for geothermal exploration. 

However, completely hidden silicic m·agm'a bodies 

associated with basaltic lava fields at the present __./ 

time probably are few and small. Exceptions to 

this generalization may exist, such as the "Lassen-Shasta rectangle" of table 8, but in those the 

possibility is also indicated by abundant volcanological evidence. Figures 5, 6, and 7 illustrate the 

geographic distributions of the silicic and basaltic 

systems of tables 7 and 8 for the lTnited States.· 

Table 8 contains a partial list of known basic 

lava fields and cinder cones known or inferred 

to be less than about 10,000 years old. Whereas 

table 7 identifies systems by principal eruptive 

centers, table 8 identifies broader rejions of distributed basaltic volcanism. Ultimately these distributed basaltic systems, and perha:us older ones 

not listed in table 8, may form some small part 

of the resource base, but they cn.nnot be evaluated 

in the present context. 

A similar line of reasoning applies to a large 

number of simple andesitic stratovolcanoes of 

Alaska and the Cascade Mountains- that is, the 

ones for whicl}. no volume estimat~~s are given 

in table 7. These are listed because they are active or potentially active volcanoes and clearly 

reflect viable thermal sources. In our opinion, 

however, the significant thermal anomaly for 

most of these volcanoes lies below l 0 km and is 

so indicated in the table. Future studies may 

show that some of these volcanoes have evolved 

or are evolving higher level storage chambers, 

but we think that few of them will contribute 

greatly to the total resource base above the 10-

km level, though they may be important locally. 

We wish to thank R. G. Luedke for help in the 

final drafting of table 7 and figure 4 and Manuel 

N athenson for preparations of figure.s 5, 6, and 7. 

'Ve also thank T. P. Miller for reviewing table 

7 for errors of fact for the Alaskan volcanic 

systems. Time and space do not permit listing 

source references for tables 7 and 8. 

REFERENCES CITED 

Carslaw, H. S., ·and Jaeger, J. C., 1959, Conduction of 

beat in solids : Oxford, Clarendon Prl'~s. 510 p. 

Jaeger, J. C., 1964, Thermal effects of intrusions: Rev./ .. 

Geophysics, v. 2, p. 443-466. · 

Shaw, H. R., 1974, Diffusion of JI20 in granitic liquids: 

Part I Experimental data; Part II Mass transfer in 

magma chambers, in Hofmann, A. W"' Giletti, B. J., 

Yoder, H. S., and Yund, R. A., eds, Geochemical 

transport and kinetics: Carnegie Inst. Washington 

Pub. 634, p. 139-170. 

Smith, R. L., and Sbaw, H. R., 1973, Vol~anic rocks as 

geologic guides to geothermal exploration and evalu-

·ation : EffiS, Amer. Geophys. Union Trans., v. 54, 

p. 1213. 

78 
-l 

~ 

~ C::::::::7 

<u~ 

Principal Islands of 

HAWAII 

a 

0 100 200MI. 

160° 0 100 200 300 KM· _/---- I 

---:; I 

--- // ~ I II ' ~ I 

' '~':;!~ 

... •/ 

';)

/.. 20 

·•'/..Je~~ ·~ at 

~' 

ISs• 

40 

_...,._;,g.l._ra...-~· 

11a•w 

i 

\ ----------_/ __ C.!_f!S~E__-- -------~-

·~ 

ALASKA 

100 300 

zoo .oo 

ISO• 

FIGURE 6~-Identifled volcanic systems (small dots) and basaltic lava fields ( +) known to be less than 10,000 years old in Alask·a and Hawaii. 
.....__ ......... ........._ 

--7--r---. I i .... --... ---. ... -... ; i -- ! \ I • 

I ! 

I '· ; \ 

-----·-. __ j 

• 

,. 

I 

.} 

i 

i •' I 

i 

.... 

j 

'". 

I ..,. . .,.. __ ,v . • 

j 

• 

-------------··- --.,. ____ _ 

-... _____ _ 

j 

i 

j 

; 

i 

j 

j 

i 

j 

;-·-·-·--·-·--·-·--

; 

; 

I 

i 

; 

------. __ _j_ ______ _ 

; 

; 

; 

i 

i 

i 

I 

j 

j 

~--·-·-------·-·-·-· 

.\ 

0 

\ 

\ 

\ \ 

I,·,/;' 

0 

., \ 

\ 

\ 

\ \ 

200 

\ 

'. 

200 

I I 

400 

,---·-·-------1 

; 

....... f __ _ 

• ! 

I 

; 

i 

I 

; 

I ' j 

; 

; 

i 

I 

! 

--.J.·-------, 

i 

i 

. -·+·-·-·--·---·-----. 

I 

j 

i 

j 

; 

j 

i 

; 

j -----.----=--j _______ _ ; ' 

i 

; 

! 

i 

; 

; 

i 

I 

; 

i 

i 

i 

• 

·- --l.. __ r--·---..1-------

400 MILES 

I I 

600 Kl LOMETRES 

('------·-·----- ' 

; 

j 

; 

! 

i 

i 

i 

j 

I 

, 

j 

i ________ j 

·...., ... ~ 

_..__·----·r··-· \ I ; 

i 

' \ 

I 

\ 

I 

\ 

·---·---,·-----~ \ 

., 

-... -""' .. -... 

"'-'"''"'J"'""-.,.· 

FIGURE 7.-Basaltic lava fields known to be less than 10,000 years old in the conterminous United States. 

80 
Table 8.-Basic volcanic fields probably less than 10,000 years old 

ALASKA 

Devil Mountain field 

Imuruk Lake field 

Kookooligit Mountains (St. Lawrence I) 

St. Michaels 

Ingakslugwat Hills 

Nunivak Island 

St. Paul Island 

WASHINGTON 

II 

II 

II 

II 

Red Mountain-Big Lava Bed area 

OREGON 

North Cinder Peak 

Nash Crater 

Sand Crater 

Belknap Craters 

North Sisters area 

Leconte Crater 

Cayuse Cone 

Bachelor Butte 

Lava Butte 

Newberry Shield (lower flank) 

Davis Lake to Black Rock Butte 

Brown Mountain 

Diamond Craters 

Jordan Craters 

81 

Lat N 

66°18' 

65°32' 

63°36' 

63°28' 

61°23' 

60°05' 

57°11' 

44°37' 

44°25' 

44°23' 

44°17' 

44°11' 

44°03' 

44°04' 

43°59' 

43°55' 

43°43' 

43°33' 

42°22' 

43°06' 

43°02' 

Long W 

165"31' 

163"30' 

170°24' 

162°10' 

164°00' 

166°30' 

170°18' 

121°48' 

121°57' 

121°56 

121°50' 

121°47' 

121°48' 

121°40' 

121°41' 

121°21' 

121°14' 

121°49' 

122°16' 

118()42' 

117°25' 
Table 8.-Basic volcanic fields probably less than 10,000 years old-continued 

IDAHO 

Craters of the Moon 

NEVADA 

Lunar Crater field (?) 

ARIZONA 

UTAH 

Unikaret 

Sunset 

Ice Springs field 

Crescent, Miter, Terrace 

Santa Clara 

Crater Hill 

Markagunt field 

NEW MEXICO 

Carrizozo 

McCartys 

Capulin 

COLORADO 

Dotsero 

CAL I FOR'N I A 

Copco Lake ij rea 

Goosene.st 

lass·er.t-Shasta rectangle· 

Lat N 

37°15' 

37°13' 

37°34' 

33°47' 

34°48' 

36°47' 

39°40' 

tc"lg W 

1"' 3°38' 

113°06' 

112°42 1 

105°56' 

108°00 1 

103°58' 

122°20' 

122()'13 I 

An area a.p.proxi-mately corne·red by lassen-Shasta-Medicine iaf'e~ 

Eagl& late is about 40 x 80 miles (3.200. sq. mi.). This area 

8~ 
j 

Table 8.-Basie volcanic fields probably less than 10~000 years old-continued 

contains many Holocene cones and basic lava flows and must represent a profound thermal anomaly in the mantle. Future volcanic 

activity may be expected in any part of this area at any time. 

The possibility of hidden shallow silicic reservoirs should be 

considered, and the entire area should be investigated iP detail. 

Cinder Cone (1851), Hat Creek Lava flow, Burnt Lava flow and 

many other recent events are located in this area. 

Ubehebe Craters 

Cima field 

Amboy-Pisgah field 

88 
Assessment of Geother-mal Resources of the United States-1975 

Temperatures and Heat Contents Based on Conductive Transpo4: of Heat 

By W. H. niment, T. C. Urban, J. H. Sass, B. V. Marshall, R. J. Munroe, and A. H. Lachenbruch 

Our objectives here are (1) to describe the heatflow provinces of the United States as they are 

presently known, ( 2) to present estimates of 

temperatur·es to a depth of 10 km in these provinces and of the range of temperature that 1night 

be expected within each province, (3) to sunlmarize the physical data and assumptions that 

constrain these estimates, and ( 4:) to integrate 

the. temperature distributions with area and depth 

so as to give an estimate of the sensible heat 

stored in the Earth to a depth of 10 km. This 

quantity 1~presents an upper (and quite unapproachable) Emit to the thennal energy that can 

be extracted from the top 10 km of the solid earth. 

Various facets of these objectives have been addressed before, often with a rigor beyond the 

scope of this summary. IIowever, a new summary 

seems warranted because ( 1) additional data are 

available and notions regarding their interpretation are evolving, (2) existing data occasionally 

have been distorted to achieve an unrealistically 

favorable view of the potential of geothermal 

energy, and (3) the data base upon which all 

estimates are based reu1ains poor, and a sumn1ary 

of this sort is an opportunity to point out how it 

could be improved. 

In the petroleum-producing provinces, temperatures are reasonably well known from measurements of temperature along, or at the bottom of, 

holes drilled for petroleun1. In some provinces, 

such as the gulf coast, the information extends 

to depths of 7 km or more. A principal source 

for this information is the ''Geothermal Survey 

of North Ameriea" (for example, J(ehle and 

others, 1970), a project recently completed under 

the aegis of the American Association of Petrole.nm Geologists. The products of tl'is survey include: (1) A data bank (tape or cards) eontaining bottom-hole temperatures for n1ore than 25,-

000 wells along with appropriate mean annual 

surface temperatures; (2) two nu~.ps of North 

America at a seale of 1: 5,000,000; the first is the 

Geothermal Gradient ~fa p of North America 

(Am. Assoc. Petroleum Geologists-U.S. Geol. 

Survey, 1975); the second shows the depths to the 

70°, 100°, and 150°C isotherms in those areas 

where sufficient infonnation is available; and ( 3) 

a series of computer-drawn ten1perature gradient 

maps at ·a scale of 1:1,000,000. Reports of compilation .proc-edures and interpretation are available now only in abstract form (Gould, 197 4; 

J(ehle and Schoepel, 197 4; Shelton and others, 

1974:). 

Deep holes are scarce outside of the petroleumproducing provinces. However, ter1peratures at 

depth may be estimated from a know ledge. of the 

near-surface heat flow and the thennal properties 

of rocks. 

Bireh, Roy, and Deeker ( 1968) Fleasured heat 

flow q in holes drilled into plutonic roeks at various sites in the northeastern United States. They 

also measured the radioactive heat generation A 

of the rooks at each site and found a linear relation between q and A : 

q=q*+DA. 

In a general way the term DA is the component 

of heat flow clue to the 1~aclioactive heat .production of the upper ernst, and the q~'< or "reduced 

84 
heat flow" is the component that originates from 

the lower crust and mantle. Subsequent measurements in plutonic rocks of the Basin and Range 

(Roy and others, 1968b) and the Sierva Nevada 

(Lachenbruch, 1968; Roy and others~ 1968b) also 

showed a linear relation. The parameters for the 

three provinces, in which extensive q-A studies 

have been Inade, are shown in the. following table: 

Region q* D DA.max (HFU) (km) (HFU) 

Eastern United States 0.8 7.5 .-1.5 

Basin and Range province 1.4 10 .-1 

Sierra Nevada section --- .4 10 .-1 

1 heat·tlow unit 1 HFU) = 1 X 106 cal/cm2 s. 

The slope. (D) varies little among the regions, 

but differences among the intercept values (q*) 

are large. 

These observations lead to the notion that continents can be divided into he.at-flow provinces~ 

each typified mainly by its own q*, and that the 

variation of heat flow within a province is a consequence of the variation of the heat generation 

of upper crustal rocks. Indeed, q-A points from 

Australia (Jaeger, 1970) and the Precambrian 

shield areas of the world (see summary by R·ao 

and Jessup, 1975) seem to fall close to either the 

X ortheastern United States or the Basin and 

Range lines. ~foreovPr, the regions of high q* 

are those of recent tectonism, and those of low q* 

are tho:;e of either ancient tectonism (Northeastern United States and the Precan1brian shields) 

or l\'gions where a cold slab subducted into the 

mantle appears to give rise to anomalously low 

q*, as in the Sierr·a Nevada (Lachenbruch, 1968; 

Roy and others, 1968b, 1972; Blackwell, 1971). 

These observations have also been taken to 

mean (Roy and others, 1968b~ 1972; Blackwell, 

1971) that: (1) q* for the Eastern United States 

mny be. typical of all stable continental regions 

olde.r than a few hundred n1illion years, and ( 2) 

q* for the Basin and Range province is close to 

the maximum that might be found over broad 

regions of the continental crust, the rationale being that the base of the crust is near melting and 

further increase of temperature 'vould lead to 

melting that would buffer additional heat input 

into the crust. Both of these generalizations are 

attractive. They form a framework from which to 

view the many anomalies that are now becoming 

apparent. 

It is also evident from the preceding table that 

the second term D A in the equation cr.n be a 

large fraction of the observed heat flow. Consequently, a detailed Inap of heat flow ( ¥Tere the 

data available) within a heat-flow province would 

be both highly variable and highly intri~ate because of rapid lateral variations in heat production. This is be.st illustrated by the studies in New 

England (Birch and others, 1968; Roy and others, 

1968b; Roy and others, 1972), where a comparatively large number of heat-flow measurements 

have been made in a variety of basen1rnt rock 

types and a large amount of heat production information is .available both from 1neasurer1ents on 

eores and from surveys of gamma acti_vity. It is 

also evident from_ the relatively detailed investigations in the Sierra Nevada (Lachenbruch, 1968). 

TEMPERATURE CALCULA TIOl'TS 

Types of models 

The q-A relation provides a basis for calculation of temperature T at depth z, assuming that 

the variation with depth of heat proclu~tion A 

and thermal conductivity /( are reasonably well 

known. The hvo most commonly used n1odels for 

the deerease in A with depth are: (1) A is constant to the depth H, and (2) A decre~,ses exponentially with depth A=A0 exp-(z/D)where 

D is a c.onstant and Ao is the radioactive heat generation at the surface. 

Assuming the eonductivity is constant, the temperatures at depth for the two n1odels are (for 

example, Jaeger, 1965; Lachenbruch, 1968) : 

A/12

T=To+--[ 2z ( z2 )] q*_ z -- - +- · 2l{ H 11 J{ 

{ D2 .::..!.... q_*z T=T +-~--(1-e 0 

) +- • 0 /{ [{ 

where To is the mean surface temperature and 

here.after is taken as zero because we are interested primarily in temperature ahoY~ Inean 

surface temperature. 

If the two n1oclels are to yield equal ll eat flow 

at the surface~ D llUISt equal n·. If D is about 10 

km. as suggested by the q-A relation, A will aecrease to Au/ e or 0.37 Ao at 10 km and to 0.05Ao 

at 30 km (roughly the thickness of the crust). 

In a general way, then, the first model (constant 

A) represents the case where crustal radioactivity 

85 
is concentrated near the surface, and the second 

model (exponential .A.) represents the case where 

it decreases with depth throughout the crust. Consequently, g_* can be thought of as the heat coming from the lower crust and mantle in the first 

case and as the heat con1ing from the mantle 

in the second. 

For the same g_ the temperatures at depth for 

the exponential model are somewhat higher 

than for the constant .A. n1odel. However, at 3 

km the difference is about 1°, and at 10 km it 

does not exceed a few tens of degrees even for 

the highest values of heat generation. For purposes of the present discussion, the difference 

between the n1odels is unimportant. 

Thermal conductivity 

A constant conductivity of 6 meal/em s°C was 

chosen for the models because it is appropriate 

for igneous rock of felsic to intermediate composition, gneisses, and schists, which typify the 

major part of the metamorphosed and plutonized 

basement. Because the thermal conductivity of 

typical basement rocks decreases with temperature, a value of 6.5 to 7.5 meal/em s°C might be 

more appropriate for the lower temperature region and 5 to 6 for the higher temperature regions. 

The conductivities of most igneous and metamorphic rocks are reasonably well known (Birch 

and Clark, 1940; Clark, 1966) , as are the conductivities of their constituent minerals (see also 

Horai and Simmons, 1969). 

The dependence of conductivity upon temperature is also generally known for igneous and 

metamorphic rocks and some of the rock-forming 

minerals (Birch and Clark, 1940). It is important 

to recognize that, although the conductivities of 

most rock-forming minerals decrease with temperature, the conductivity of the feldspars (the 

principal constituents of rocks within the crust) 

increases slightly with temperature. Consequently, 

it is difficult to envision an average conductivity 

of a large volume of rock much less than 5 (see, 

for example, Birch and Clark, 1940, figs. 4 and 

5) even at the higher temperature levels. 

Conductivities of individual rock types may 

differ widely fron1 the average value assumed. 

Some of these types may occur in sufficient thickness that they result in temperature distributiom.s 

significantly different than the ones given. On the 

high-conductivity side we have dolomite ( --12), 

quartzose sandstone (10--16, depend~ng on porosity), salt {12), and dunite-peridotite-pyroxeniteeclogite (10--14}, and, on the low side, anorthosite ( 4""5), gabbro-basalt-diabase ( ,_,5), serpentinite ( ,_,5), and shale (2.5--4, depending on water 

content). 

Water (K ,_,1.5 at 30°C) is an inportant constituent of many sediments. Thus, recently deposited n1uds may have conductivitjes less than 2 

that increase on compaction to 3-4 as the mud is 

transformed into a shale. Some volcanic rocks, 

such as ash-flow tuffs, may have porosities approaching 50 percent and conductivities less than 

3. Bituminous materials such as corl, oil, and oil 

shale (Clark, 1966) have very low conductivities 

but rarely are thick enough to cause large distortions in the thermal regime. 

Clearly, if a region is blanketec1

. by low-conductivity sediments, the temperatrres at depth 

will be higher than those in our nodels, which 

assume a uniform· conductivity of 6. Let us assume a conductivity of 3 for the "thermal 

blanket," which is about the minimun1 permissible conductivity for a substantial thickness of 

sediment. The difference in temperature aT below the blanket as compared with the K = 6 model 

will be: 

~T=q[ {6-3)/ (6 X3) ]z 

where the numerical values are the conductivities 

and z is thickness of the low-conductivity blanket. 

The excess temperatures are given in table 9. 

The effect of the "blanket" is evidently small 

for low heat flow and thin blankds. It is substantial, however, for a thick blanket and a high 

heat flow. The upper limit (z=~ km, q=3.0, 

aT= 100) is difficult to envision but might be 

possible in some localities. 

If the conductivities are significantly higher 

than the 6 assumed in the models, the gradients 

will be lower and the temperatur~s below the 

higher conductivity zone will be lower. Following the table above, and aBSuming 1', conductivity 

of 9, we have: 

AT=q[ (6-9) /.{6X9) ]z 

and the effect of the high-conductivity layer is 

given in table 10. 

Evidently, the assumption of a high-conductivity layer, such as might be represented by a 

thick section of dolomite and qu~.rtzose sandstone along with accompanying interbeds of 

shale, produces a small distortion of the tempera86 
Table 9.-Excess temperature below a low-conductivity layer 

~T{°C) relative to K=6 models 

Thickness {z) of 

Low conductivity 

Layer (km) 

0.5 

1.0 

2.0 

q=-0.5 q=l.O 

4 8 

8 16 

16 33 

ture distribution as represented by K = 6, except 

for the highest q's and the greatest thicknesses. 

Radioactive heat generation 

The n1ean value of radioactive heat generation 

due to radioactive decay of uraniun1, thorium, 

and potassium for upper crustal rocks is probably 

close to 5.0 HGU (heat-generation units; see for 

an example Birch, 1954; Clark, 1966; Roy and 

others, 1968b; Blackwell, 1971). The range for 

rocks exposed at the surface is considerable: 

much less than 1 HGU for most ultramafic rocks 

and anorthosites, about 1 HGU for mafic rocks, 

and from 2 to 20 HGU for felsic and intermediate plutonic rocks, gneisses, and schists. The 

last group comprises the bulk of the basement 

rock of the upper cn1st and is the one that is of 

primary interest here. 

In figure 8 all A values obtained in connection with q-A studies in the United States are 

plotted as a histogran1. The range of A is large, 

and it is real. The lowest values represent such 

rocks as the Precambrian anorthosites of the 

Adirondack Mountains of New York, and the 

highest represent the rocks of the Mesozoic White 

Mountain Plutonic Series of New Han1pshire. 

The large number of relatively low values for 

the Basin and Range, northern Rocky Mountain, 

and San Andreas provinces represent Mesozoic 

87 

q=l.5 q=2.0 q=2.5 q=3.0 

13 17 21 25 

2.5 33 42 50 

50 67 84 100 

plutonic rocks of intermediate composid-<>n such 

as granodiorite, quartz diorite, and dior~i;e. 

This histogran1 reveals little about the average 

distribution of heat generation of near-surface 

crustal rocks ; metasedimentary rocks, an ~l gneisses are poorly known and are not represented. 

However, it indicates the extren1es to be expected, 

and it suggests that large volumes of rock of 

A> 10 are probably rare, at least in some geologic 

provinces. 

Average temperature distributions and heat contents by 

province 

In order to estimate the heat stored in the crust, 

we resort to some rather sweeping assmnptions: 

1. Three provinces are selected as "tyr~cal" of 

all provinces in the United States. Each 

physiographic province is assigned a parameter set (q*, A, D, ·and/{) of one of 

the. three "typical" prol"inces. For son1e 

provinces there is sufficient information 

for such assignment; for others it is based 

upon son1ewhat arbitrary judgements~ 

Moreover, we do not know wheth~r provinces having characteristics inte:rmediate 

between the "typical" provinces ?.re present, or whether extremes are rer: ..... esented 

by the "typical" provinces. 
Table 10.-Deficit of temperature below a high-conductivity layer 

6T(°C) relative to K=6 models 

Thickness of 

high~conductivity 

layer (km) 

0.5 

1. 0 

2.0 

3.0 

4.0 

5.0 

q=0.5 q=l.O 

-1 -3 

-3 -6 

-6 -11 

-9 -18 

-12 -22 

-15 -30 

2. An average A of 5 HGU has been assumed 

for all provinces, although regions of 

large lateral extent are known for which 

significantly higher or lower values would 

be appropriate. The significance of this 

assumption can be judged from tables 11 

and 12 and figure 8. 

3. An exponential n1odel for decreases of heat 

generation has been adopted. This model 

gives somewhat higher temperatures than 

the constant A model at depth (see tables 

11-14). 

The heat contents per unit area ( Q) of the 

two depth intervals (0-3 and 3-10 km) are calculated for the typical provinces (table 12) . The 

total heat content of the intervals in each province (table 13) is then obtained by multiplying 

by the appropriate area (S). The sum (table 

13) for the two intervals (over the whole of 

the conterminous United States) is designated 

q=l.5 q=2.0 q=2.5 q=3.0 

-4 -6 -7 -8 

-8 -11 -14 -17 

-17 -22 -28 -33 

-24 -33 -28 -54 

-34 -44 -56 -66 

-40 -55 -70 -85 

the basic calculation. In table 14 we show the 

effect of varying smne of the paraneters used to 

construct the models from the basic calculations. 

One of these (increase all q*'s by 0.2 HFU) 

requires an explanatory note. Birch ( 1948) 

showed that a gradient correction for Pleistocene 

climatic effects of about 3°C/km might be appropriate for holes of shallow depths ( .-.300 m). 

Diment, Urban, and Revetta ( 1972) suggested 

that application of such a correction would help 

reduce differences of heat-flow measurements 

made in high- and low-conductivit~? rocks in the 

Eastern United States and that q* in the Eastern 

United States might be raised by ahout 0.2 HFU. 

This view is not universally held (for example, 

Sass, Lachenbruch, and Jessop, 1971; Slack, 

1974), particularly with respect to its applicability to all regions. This detail illustrates the type 

of uncertainty that may arise in the measurement 

of heat flow in shallow holes. 

88 
(X) 

~ 

30-

en 

~2()-

~ 

--.., 

u 

_, 0 

... 

0 

s... 

cu 

i 

::::s 

:z 

10--

CA 

NY 

NY 

NY 

0 1 

CA 

CA 

CA 

CA 

CA 

CA 

CA 

CA 

CA 

CA CA 

CA CA CA 

CA CA CA 

CA CA CA 

CA CA CA UT 

CA CA CA NV 

CA NV CA NV 

CA NV CA NV CA CA 

CA NV WY NV CA CA 

CA NV NV NV CA OK 

CA I D NV MT CA NM 

CA CO NV MT NM NV 

OR AZ NV MT NV NV 

CA OR AZ NV MO NV NV CA 

CA NV AZ NV AZ AZ NV CA CA UT 

MN ID AZ NV AZ AZ AZ CA CA NV NY NH 

AZ AZ NH NV NY AZ NH MT NH AZ MA ME NH NH 

2-- -r-- -~ -~5 - 0~ 8 9 ---ur - -1.--.r- u--.. ,~------y-o- 16 17 18 19 £0 -------z1 

Radioactive heat generation (HGU) 

~!mr~E S.-'9i9t~~~~ !>! h~at---:ene~ation T:·ftlu~ !>'btftin"'!l in ~!>nn~ion "l"itn '1- 4. i'1"!AI:3tig'l.tiono:J. n'l.t'l. '!.!'~ g!v~n b-y St'l.t~. "F!.'"!)YTI "H~ny~'Y {1Q~), r ~q!!n~nl)!'~l!!n 

( 1968), Lachenbruch and Bunker (1971), Roy and others ( 1968b, 1972), Blackwell ( 1969, 1971, 197 4b), and U.S. Geological Survey unpublished data. 
Table 11.-Basic calculations: temperatures Tz (above mean annual surface temperature) at depths z of 3, 10, and 

30 km for various assumed values of q* and A 

Exponential A Constant A 

A=O A=5 A=10 A=15 A=20 A=O A=5 A=10 A=T5 A=20 

q*=0.4 HFU 

0=10 km 

T = 3 20 42 63 85 106 20 41 63 811 105 

T1o= 67 119 172 225 277 67 108 1.50 192 233 

T3o= 200 279 358 438 517 200 241 283 325 366 

q*=0.8 HFU 

0=7.5 km 

T = 3 40 55 71 86 102 40 55 70 85 100 

T1o= 133 168 202 237 271 133 154 175 196 217 

T3o= 400 446 492 538 584 400 421 442 463 484 

q*=1.4 HFU 

0=10 km 

T = 3 70 92 113 135 156 70 91 112 134 155 

T1o= 233 286 339 391 444 233 275 317 358 400 

T3o= 700 779 858 937 1017 700 742 784 825 867 

90 
u:> 

....... 

Table 12.-Heat storedl (Q in megacal/cm2) in the depth intervals 0-3 krh and 3-10 km for various assumed values of q* and A 

q*=0.4 HFU 

0=10 km 

Q0-3 

Q3-10 

q*=0.8 HFU 

0=7.5 km 

A=O 

1. 8 

18.2 

Q0-3 3.6 

Q3-10 36.4 

q*=l.4 HFU 

0=10 km 

Q0-3 6.3 

Q3-10 63.7 

Exponential A 

A=5 

3.8 

34.6 

5.1 

47.5 

8.3 

80.5 

A=lO 

5.9 

50.9 

6.6 

58.6 

10.4 

96.4 

A=l5 

7.9 

67.3 

8.1 

69.7 

12.4 

112.8 

A=20 

10.0 

83.6 

9.5 

80.8 

14.5 

129.1 

A=O 

1. 8 

18.2 

3.6 

36.4 

6.3 

63.7 

A=5 

3.8 

32.8 

5.1 

45.4 

8.3 

78.3 

Constant A 

A=lO 

5.9 

47.5 

6.5 

54.3 

10.4 

93.0 

A=l5 

7.9 

62.1 

8.0 

63.3 

12.4 

107.6 

A=20 

9.9 

76.8 

9.5 

72.2 

14.4 

122.3 

3 10 

1/ Q0_3=c ~ T dz, Q3_

10=c ~ Tdz, where the volumetric specific heat (c) is assumed 

0 3 

constant and equal to 0.6 cal/cm3 °C, and z is in units of km, and T is temperature above 0°C. 
Table 13.-Heat stored beneath provinces in depth intervals 0-3 km and 3-10 km 

Model Province Area (S) S(%) sQ0-3 sQ3-10 SQ0-10 

km2 x 106 cal x 1022 cal x 1022 cal x 1022 

q*=0.4 HFU Sierra Nevada 0.081 0.87 0.31 2.80 3.11 

D =10 km 

A =5 HGU 

q*=0.8 HFU Eastern 3.375 36.08 17.2 160.4 177.6 

D =7.5 km 

A =5 HGU Coastal Plain l. 313 14.03 6.70 62.4 69.1 

Great Plains 1.633 17.45 8.30 77.6 85.9 

Wyoming Basin 0.123 1.31 0.625 5.84 6.47 

Peninsular Ranges 0.009 0.10 0.046 0.428 0.474 

Pacific Northwest 0.092 0.98 0.468 4.37 4.84 

Klamath Mountains 0.050 0.53 0.254 2.38 2.63 

Great Valley 0.058 0.62 0.295 2.76 3.06 

Colorado Plateau 0.392 4.19 1.99 18.6 20.6 

Subtotal 7.046 75.29 35.9 334.8 370.7 

q*=l.4 HFU Basin and Range 1.045 11.16 8.72 83.7 92.4 

D =10 km 

A =5 HGU Northern Rocky Mountains 0.298 3.18 2.49 23.9 26.4 

Central Rocky Mountains 0.151 1.61 1.26 l2.1 13.4 

Southern Rocky Mountains 0.136 1.45 1.13 10.9 12.0 

Columbia Plateaus 0.324 3.46 2.70 25.9 28.6 

Cascade Range 0.128 1.37 1.07 10.3 11.4 

San Andreas fault zone 0.151 1.61 1.26 1-2.1 13.4 

Subtotal 2.233 23.84 18.6 178.9 197.5 

TOTAL (Conterminous United 9.360 100.00 54.8 516.9 571.3 

States) 

Alaska 1. 519 10.2 97.2 107.4 

Hawaii 0.017 0.141 1.37 1.5 

TOTAL {United States) 10.896 65. 141 615.47 680.2 

92 
Table 14.-Heat content above mean annual surface temperature of the continental crust of the conterminO''S 

United States in the depth intervals 0-3 km and 3-10 km 

Model Heat content (lo24 calories) - SQ0-3 SQ3-10 SQO .. lO 

1. Basic calculation (assume sets of q*, 0.55 5.17 5.72 

D, K=6, A=5 as in tab-1 e 13, fig. 1 o) 

2. Basic calculation (except K=5) 0.66 6.20 6.86 

3. Basic calculation (except K=7) 0.47 4.43 4.90 

4. Basic calculation (except all q*•s 0.63 6.01 6.64 

increased by 0.2 HFU) 

5. Basic calculation (except A=2.5 HGU) 0.48 4.60 5.08 

6. Basic calculation (except A=7.5 HGU) 0.63 5.74 6.37 

Best estimate (conterminous United 

States) 

Best estimate (United States) 

The heat content of the crust as represented 

by the basic calculation (table 14) is probably 

too low for several reasons : 

1. The thermal blanket of low-conductivity sediments of the coastal plain and other areas 

of recent sedimentation have not been 

taken into account. However, depression 

of the thermal gradient by subsidence 

would tend to offset the effect of the lowconductivity sediments ( Grossling, 1956; 

Jaeger, 1965). 

2. The geopressured region of the gulf coast 

(Papadopulos and others, this circular) 

e~hibits anQIInalously high temperatures. 

3. Several provinces have rather arbitrarily 

been assigned to the normal or eastern 

category. The Great Plains, Colorado 

Plateau, and Cascades (Smith and Shaw, 

this circular) may well exhibit temperatures intermediate between the eastern 

and Basin and Range types. 

4. Much of the observed high heat flow in the 

California Coast Ranges may be due to 

93 

0.7 + 0.1 6 + 1 7 + 1 

0.8 + 0.1 7 + 1 8 + 1 

mechanical generation of heat in tl1~ upper 10 to 15 km of the crust (L~chenbruch and Sass, 1973) also resultjng in 

temperatures intermediate betwee"l the 

eastern and Basin and Range typr~. 

5. The hot spots discussed in other rep<J rts in 

this circular have not been added. However, their volumes, as presently estimated, are so small that their cor~ribution to the value represented by the basic 

calculation is not significant. 

6. The possible existence of regions of anomalously high heat flow (with respect to the 

Basin and Range models) has no~ been 

taken into account (see subsequent discussion). 

Hawaii and Alaska have been listed sepr.rately 

in table 13 because so little is known of their 

thermal regimes. We have rather arbitrar~ly assigned Hawaii and half of Alaska to the Basin 

and Range (hot) type and the other half of 

Alaska to the eastern (normal) type. 
30° 

0 

I 

0 

120° 

200 

I I 

200 400 

IJOO J(X)O 

---o·------

+ ----------r~---6------·-y 

I ~ • 

4 i '',,, \ 

400 MILES I I 

600 KILOMETRES 

. I 

I ' ~---------~----· 

------t I 

~ I A' __ A t-- ----------, i . 

I 

- -- --L--. ., 

• i 

r---------- - I 

' I 

FIGURE 9.-()bserved heat-fiow (q) measurements in the United States. Measurements obtained in holes less than 

150 m deep (indicated by dots) are not considered reliable as a group and therefore are not codert as to value. 

References to earlier data may be found in a compilation by Lee and Uyeda (1965). References for later data 

are the same as those in figure 8 plus those cited in references and U.S. Geological Survey unpub1ished data. 

94 
90° 80° 70° 

~--~----~\--~\----~\--- \ 

:"'\ ---.J ~ 

I 

\ 

~ \.._ 

i 

,..... 

• 

..... _,, .. _ 

':' .... """"-' 

+ 

. , 

, 

l 0 .l 

-, 

., --+---~"--~1 

+ 

10 0 _/ 

0., 0 

--------.r' 

( 

'" ') 

-~ 

0 (..._ 

+<1.10 HFU 

0 1.10-1.49 HFU 

• 1-. 5-I. 9 9 HFU 

• 

\ 

r:------~'--------

A 2.0-2.49 ~l 

A 2.5-2.99 HFU ~~~ D 

c > 3.0 HFU ··'-~ 

~ ~ ~ ~ 

FIGURE 9.-Continued. 

95 

Pj e:ooe 

t!J 
30° 

0 

I 

0 

120° II 0° 100° 

....... 

~ . ·---- 1 r·--. 

I i 

i 

\ 

-----·--·-r "C. -------·-r 

. • ,, 

• 

200 

I I 

200 400 

., 

i 

(.) 

'? 

t., ..... 

400 MILES I I 

600 KILOMETRES 

i \ 

i \ ;-----

------( ( 

~ 

I 

I 

t--------------.......... i . I 

I 

- -- --'---., • j 

r----------- -- 1 

I 

I 

I 

--- I ·----------

;------

I 

I 

! 

I 

I 

I 

I ____ j 

FIGURE 10.-Reduced heat-flow ( q*) measurements in the United States- References are the same ad those in figure 8. 

96 
' i 

90° 

/ 

1 

. 

l 

' .\ 

----------~} 

~----

') 

_, 

) 

--------,r· 

I 

\, 

') 

,......, 

i 

·, 

+~ 0.5 HFU 

e 0.5-1.0 HFU 

80° 

\ \ \ 

1 

\ 

I 

I 

\ 

\ 

~ 

> • == 1.6HFU 

FIGURE 10.-Con.tinue<t. 

97 
30° 

0 

I 

0 

120° 

200 

I I 

200 400 

fiQO 

I 

-·---·--.. ______ ..._ 

JOQO 

-----~---11~?·-----~-

1 \ 

I \ 

r---------~-----< 

I 

---, _________ I _ ,------

I 

I 

I 

I 

I 

I 

I 

I 

~~~~§~~~~~~~~~~~~----' 

400 MILES I I 

600 KILOMETRES 

FIGURE 11.-Map showing probable extent of hot (stippled), normal (white), and cold (dotted) crustal regions of 

the United States based on data in figures 9 and 10. Physiographic provinces (largely generalizee from Fenneman (1946)) do not necessarily represent hP.at-flow provinces. 

98 
90° 

r' 

? 

l -, 

., __________ .... 1 

_, 

) 

--------,r· 

{ 

\, 

') 

....... 

; 

-........... 

80° 

\ \ 

\ FIGURE H.-Continued 

99 
DISCUSSION 

The maps of observed heat flow (fig. 9) and 

reduced heat flow (fig. 10) are the basis for construction of the map (fig. 11) showing the location of the hot, normal, and cold crustal regions 

of the United States. Clearly, the data are not 

sufficiently numerous to define accurately the 

limits of the regions. Moreover, n1any of the observations themselves are weak in that they are 

based on assumed conductivities or on temperatures obtained under less than ideal conditions. 

Undue reliance should not be placed on individual 

values without reference to the original sources. 

Temperature profiles (fig. 12) based on the 

exponential model with [{ = 6 illustrate the range 

of temperatures that might be expected within 

each type of province. If one wishes to adjust the 

temperatures for slightly different parameters, it 

is useful to recall that : ( 1) Temperatures are 

inversely proportional to conductivity (K=6) 

for a given heat flow and that a temperature corresponding to a different conductivity /{ can be 

obtained by multiplying by 6/K, and (2) an 

increase of 0.1 HFU in q* results in an increase 

in temperature of 1.67°0 per km of depth. 

The temperature profiles (fig. 12A and B) for 

the Sierra Nevada type (cold) and the eastern 

type (normal) indicate that temperatures of 

economic interest are deep even for regions of 

high radioactive heat generation (A=20), which, 

as pi"Pviously indicated~ are limited in oeeurrence 

and in areal <~xtent. To be sure, temperatures under a thiek blanket of ]ow-conductivity sediments 

1night be 50°C or so highe.r~ but the geographic.al 

extent of sueh regions is small. ""Tith eurrent drilling teehnology, provinees of the cold or nonnal 

type hold lit.tle promise for geothermal exploitation exc('pt coneeivably in very local areas. 

The temperatures at depths less than 5 km in 

the Basin and Range (hot) type are not particularly attraetive either. at least as expressed in 

figure 120 and 12D, _especially in view ~f the fact 

that the values of A> 10 are practically unknown 

in this region. However~ the temperatures and 

heat flows are sufficiently high that the existence 

of a thick low-conductivity blanket in a given locality eould raise the temperatures to levels of 

eeonomic interest. 

The temperatures in figure 120 and 12D (A = 5) 

may not represent the maxima to he expected on 

a regional scale in the high-heat-flow provinoos. 

Indeed, heat flows much higher (q* >1.8, q>2.5) 

than those used to construct the temperature profiles for A= 5 have been observed (Blackwell, 

1971 ; Sass and o-thers, 1971 ; Roy and others, 

1968a, 1972; Decker and Smithson, 1975; Reiter 

and others, 1975; Urban and Diment, 1975; 

USGS, unpub. data). If the thernal regime is 

entirely conductive, such values require partial 

1nelting near the base of the crust ( ,_.30 km) or 

within the lower crust, or intrusion of magma 

into the crust. On the other hand, the anomalously high values could result from shallow 

hydrologic disturbance (not evident in the interval of measurement ,_.300 m) or from deep hydrothermal convection. 

Reeent and more detailed investigations in 

northern N evacla and southern Idaho strengthen 

the notion that the Battle Mountain heat-flow 

high, as originally proposed by Sass and others 

( 1971), is indeed a region of anomalously high 

heat flow and not n1erely a consequence of aberrations involving local hydrothermal activity. Perhaps some anomalously high heat flows observed 

in other regions are also inclieative of high temperahu~s (with respect to fig. 120 and 12D on a 

regional scale. The data are not ade'luate to prove 

or disprove such speculation. 

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Am. Assoc. Petroleum Geologists-U.S. Geol. Survey, 

1975, Geothermal gf'adient map of North America: 

U.S. Geol. Suryey, scale 1:5,000,000. (in press) 

Birch, F., 1948, The effects of Pleistocen~ climatic v·ariations upon geothennal gradients: Am. Jour. Sci., v. 

246, p. 729-760. 

-- 1954, Heat from radioactivity, in Faul, H., ed. 

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Birch, F., and Clark, H., 1940, The ther"'lal conductivity 

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Birch, F., Roy, R. F., and Decker, E. R., 1968, Heat 

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Blackwell, D. D., 1969, Heat flow in the northwestern 

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Union Geophys. Mon. 14, p. 169-184. 

100 
X: 

IG. 

ILl 

.:::I 

100 200 

q* .. 0.11 HFU 

0 • 10 ICM 

EASTERN TYPE 

q* • 0.8 HFU 

0 • 7.5 ICM 

:BASIN AND P.AN6~ TYPE (low) 

I q* = l.Lf HFU 

I D = 10 1<11 

I 

D = JO 1<11 

300 

I Space I PosSIBLE PoWER PRODUCTION Heating _ 

A 

8 

c 

D 

FIGURE 12.-Temperature profiles for various types of provinces in .the United 

States based on an exponential decrease of radioactive heat generation (A) 

with depth and uniform conductivity (K=6 meal/em S°C). Units of q and q* 

are HFU (1 HFU=1X10-G cal/cm2 s), and rmits of A are HGU (1 HGU= 

1X1<113 cal/cm3 s). 

101 
--- 1974a, Terrestrial heat flow and its implications 

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Costain, J. K., and ·wright, P. M., 1973, Heat flow at 

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8698. 

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W H. K., ed., Terrestrial heat flow : Am. Geophys. 

Union Geophys. Mon. 8, p. 7-23. 

--- 1970, Heat flow and radioactivity in Australia: 

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I.~achenbruch, A. H., 1968, Preliminary g•"'othermal model 

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73, p. 6977-6989. 

--- 1970, Cmstal temperature and I "'at production: 

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Geophys. Research, v. 76, p. 3852-38~. 

Lachenbruch, A. H., and Sass, J. H., 1973, thermomechanical aspects of the Sun Andr£'!lS fault system, 

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. p. 3-1-3-184. 

Rao, R. U. M., and .Jessop, A. M., 1975, A comparison of 

the thermal characters of shields: Canadian Jour. 

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southwestern Virginia: Jour. G~ophys. Research, v. 

78, p. 1323-1333. 

Reiter, M., Edwards, C. L., Hartman, H., and 'Veidman, 

C., 1975, Terrestrial heat flow along the Rio Grande 

rift, New Mexico and southern Colo".'ado: Geol. Soc. 

America Bull., v. 86, p. 811-818. 

102 
Roy, R. F., Blackwell, D. D., and Decker, E. R., 1972, 

Continental heat flow, in Robertson, E .C., ed., The 

nature of the solid earth: New York, :McGraw-Hill, 

p. 506--544. 

Roy, R. F., Decker, E. R., Blackwell, D. D., and Birch, 

F., 1968a, Heat flow in the United States: Jour. 

Geo·phys. Research, v. 72, p. 5207-5221. 

Roy, R. F., Decker, E. R., and Blackwell, D. D., 1968b, 

Heut generation of plutonic rocks and continental 

heat flow provinces : Earth and Planetary Sci. 

Letters, v. 5, 1-12. 

Sass, J. H., Lachenbruch, A. H., and Jessop, A. M., 1971, 

Uniform heat flow in a deep hole in the Canadian 

shiE~ld and its paleoclimatic implications: Jour. 

Geophys. Research, v. 76, p. 8586-8596. 

Sass, J. H., Lachenbruch, A. H., Munroe, R. J. Greene, G. 

W., and Moses, T. H., 1971, Heat flow in the western 

United States: Jour. Geophys. Research, v. 76, p. 

6371fH>413. 

Sass, J. H., and Munroe, R. J.,1974, Basic heat-flow data 

from the United States: U.S. Geol. Survey open-file 

rept. 7 4-9, 450 p. 

Shelton, J. W., Horn, M K., and Lossley, R. H., 1974, 

Relation of geothermal patterns to major geologic 

features in U.S.: Am. Assoc. Petroleum Ge1l., Ann. 

Mtg. Abstracts, v. 1, p. 82. 

Slack, P. B., 1974, Variance of terrestrial heat flow between the North American c~aton and the Canadian 

shield: Geol. Soc. America Bull. v. 85, p. 519-522. 

Urban, T. C., and Diment, W. H., 1975, Heat flow on the 

south flank of the Snake River rift: G~l. Soc. 

America Abs. with Programs, v. 7, p. 648. 

Urban, T. C., Diment, W. H., and Baldwin, A. L., 1974, 

Basic heat-flow data from eastern United f',i:ates, in 

Sass, J. H., and Munroe, R. J., eds., Basic heat-flow 

data from the United States: U.S. Geol Survey 

.open-file rept., 74-9, p. 6-1 to 6-66. 

Warren, A. E., Scl:ater, J. C., Vacquier, V., and Roy, R. F., 

1969, A comparison of terrestrial heat flow and 

transient geomagnetic fluctuations in southwestern 

United States: Geophysics, v. 34, p. 463-478. 

103 
Assessment of Geothermal -Resources of the United States-1975 

Geothermal Resources in Hydrothermal Convection Systems 

and Conduction-Dominated Areas 

By Manuel Nathanson and L. J. P. Muffler 

Reported here are estimates of the parts of the 

resource base of heat in hydrothermal convection 

systems and conduction-dominated are.as that can 

be considered as resources or reserves. These estimates involve analysis of physical recoverability, 

con version or utilization efficiency, and economics. 

The definition of terms used in this report and 

elsewhere in this circular deserves en1phasis and 

reiteration here. The geothermal resource base is 

all of the stored heat above 15°C to a 10-km depth 

(Muffler, 1973). Geothermal resources are defined 

as stored heat, both identified and undiscovered, 

that is recoverable by using current or nearcurrent technology, regardless of cost. Geothermal resources are further divided into three 

categories based on cost of recovery : 

1. Subrnarginal geothermal resou.rces, recoverable 

only at a cost that is more than two times 

the current price of competitive energy 

systems, 

2. Paramarginal geothermal resources, recoverable at a cost between one and two times 

the current price of competitive energy, 

and 

3. Geothermal reserves, those identified resources 

recoverable at a cost that is competitive 

now with other commercial energy resources. 

Undiscovered resources that are economically recoverable are not differentiated in this report but 

would be the economic equivalent of reserves. 

This report considers only hydrothermal convection systen1s and conduction-dominated areas. 

Recoverability of geopressured resources is considered by Papadopulos and others (this circular) , and recoverability of magma resources IS 

treated by Peck (this circular) . 

HIGH-TEMPERATURE HYDROTHERMAL 

CONVECTION SYSTEMS 

Renner, White, and Williams (this circular) 

have calculated that the heat stored in identified 

high-temperature ( > 150°C) hot-water convection 

systems outside of national parks is 238 X 1018 cal 

and that perhaps five times as much heat occurs 

in undiscovered hot-water convection systems, 

again excluding national parks. The smn of these 

two numbers, 1,400 X 1018 cal, is th~ geothermal 

energy from hot-water convection systems potentially available for utilization. In the following 

discussion, we apply generalized r~.-eoverability 

factors and conversion efficiencies presented by 

Nathenson (1975b) to estimate the _potential for 

electrical generation from various types and 

grades of hydrothermal convection systems. An 

economic analysis defines the variables that most 

strongly affect power production ani emphasizes 

the sensitivity of economics to flo-vr rates from 

individual "'ells. 

Recoverable electrical energy 

The calculation of recoverable electrical energy 

from a high-temperature hydrothermal convection system involves three major steps : 

1. Estimation of what part of the l'ydrothermal 

convection system is porom~ and permeable rook, 

2. Estimation of the fraction of stored heat in 

the porous and permeable volume that 

can be recovered at the surface, 

104 
3. Calculation of the efficiency with which thermal energy at the wellhead can be converted 

to electrical energy in the power plant. 

The recover81bility factors used for hydrothermal convection systems are based on techniques 

for extracting energy from porous, permeable 

rock. The volumes tabulated by Renner, White, 

and 'Villiams (this circular), however, are the 

volumes of the heat reservoirs. The porous, permeable parts of the heat reservoir can range from 

only a small fraction to nearly all of the heat 

reservoir. In the resource calculations presented 

here, we assume that on the average only 50 percent of ·the he81t reservoir is porous and permeable. 

·Our calculation of hydrothermal convection resources is based entirely on extracting the stored 

heat from a volume of porous and permeable rock, 

neglecting recharge of heat by either conduction 

or movement of wa.ter. The potential for heat recharge hy conduction is neglected because it is 

very sn1:all compared to expected rates of production from any volume of rock greater than a few 

cubic kilometres. Likewise, for n1ost of the hotwater systems of the United States, the natural 

discharge of thermal waters is low compared to 

reasonable production rates, and, accordingly, 

the potential for heat recharge by upflow of hot 

water to most reservoirs is probably low and can 

be neglected. The validity of this assumption can 

be assessed only after extensive production histories have been obtained for a reservoir. In those 

systems in which heat recharge by upflow of hot 

water is shown to be important, our resource 

estimate will have to be raised accordingly. 

Although the recharge potential of heat is neglected in our resource calculations, the potential 

and, in faot, the need for cold water recharge are 

not. 

We have analyzed two possible methods for 

extracting energy from a liquid-filled volume of 

porous and permeable rocks. The first n1ethod 

assumes that the porous, permeable volume is 

virtually closed to inflow of water and is produced by boiling to stean1 by using the energy 

in the rock. The second method assumes that 

natural and artifical recharge of cold water is 

used to recover much of the heat from the reservoir by means of a sweep process. 

The fraction of stored energy recovered in the 

prooess of boiling the water in a porous volume 

of rock depends on the amount and pressure of 

the produced steam, which in turn are de~rmined 

by the porosity and the initial temperature of the 

system. The pressure of the produced steam must 

be high enough to drive the steam thro·,gh the 

porous medium and up the well at a significant 

rate; a reasonable assumption is that the pressure 

of the steam must be at least 8 bars (N athenson, 

1975b). At a given reservoir temperature, this 

restriction constrains the range of poro~ity for 

which boiling is a viable recovery scheme. At 

2000<C, the upper limit for the porosity is about 

0.05, and the fraction of stored energy obtained 

is about 0.2. At 250°C, the upper limit for the 

porosity is about 0.12, and the fraction of stored 

energy obtained is a,.bout 0.4. A:t porosities below 

this limit the fraction of stored energy obtained 

decreases with decreasing porosity in ·a nearly linear fashion. This production scheme is severely 

limited if there is significant recharge of TVater to 

the reservoir; recovery by boiling is then possible 

only if steam in the dried zone and water in the 

recharge zone are produced simultaneously in order to keep the zone of boiling moving into new 

I'egions of the reservoir. In summary, the restricted range of porosity, ten1perature, and the 

recharge over which the boiling 1nethod will work 

limits its applica-tion to rather special circumstances, in particula.r to vapor-dominated systems 

(see below) . 

The second production scheme involves the use 

of natural and/ or artificial recharge of co] d water 

to drive hot water in a reservoir to the pr'lducing 

wells. A-s the water sweeps through the h ':lt rock, 

its ten1perature is raised by removing ener:;nr from 

the rock. The influence of heat conduction on this 

process takes place on two length scales. On the 

microscale of pores filled with water in a rock 

matrix, conduction makes the temperature of 

the rock and the pores come to equilibrium in a 

matter of a few minutes. On the scale of a volume 

of rock several hundred metres on a side having 

one zone of cold water and rock and a second 

zone of hot water and rock, conduction with no 

fluid movement spreads out an initiall:·r sharp 

change in temperature to a smooth transition of 

only 60 m thickness in ·a period of a decade 

(N athenson, 1975b). As cold water sweep~ into a 

hot reservoir, conduction may be analyz'-"'d to a 

first approximation by superposition O:"l.to the 

n10venl'ent of the temperature front, resulting in 

the pre-mature breakthrough of cooler water into 

105 
the hot zone. Another factor in the sweep process 

is the rotation of an initially vertical interface 

between cold water and hot water in a porous 

medium, owing to the difference in hydrostatic 

pressure on the two sides of the interface. Although this rotation is ret·arded by the energy 

stored in the rock, it also tends to cause premature 

breakthrough of cold water into the hot zone. 

These processes cannot be evaluated rigorously 

but can be combined qualitatively to yield an estimate that one-half of the energy stored in a reservoir of porous, permeable rock in a hot-water 

system can he recovered. Taking into account that 

only one-half of the heat reservoir is likely to be 

porous and perm·eable, the fraction of the 

resource base estimates of Renner, White, and 

Williams (this circular) that can be recovered 

as thermal energy at the surface is 0.25. 

Vapor-dominated reservoirs are assumed to contain steam as the pressure-controlling phase, with 

liquid water immobilized in the pores by surface 

forces (Truesdell and White, 1973). Production 

results primarily from the boiling of this pore 

water to steam, although in later stages there may 

be some boiling fron1 an inferred deep water 

table. Because the liquid fraction in a vapordominated reservoir is small, the pressure and 

temperature of steam produced in the boiling 

process are generally close enough to the initial 

values for the system that ample pressure remains 

to drive the steam to and up the well. The fraction of stored energy that may be recovered, 

calculated by considering an energy 'balance for 

the boiling process, is critically dependent on the 

average liquid saturation, as indicated by the 

values in table 15. 

Efficiencies for converting the.rmal energies to 

electrical energies for a number of different surface technologies have been calculated by N a thenson ( 1975b). The choice of the optimum cycle 

is dependent on resource ten1perature, efficiency 

of conversion, cost, and special reservoir problems 

such as high dissolved solids, high gas contents, 

deposition of scale, and environmental factors. 

Current technology for hot-water systems consists 

of a single-stage flash to a steam-water mixture, 

separation of the steatn and water, and use of the 

steam in a condensing turbine. A two-stage flash 

plant is being installed at the Hatchobaru system 

in Japan (Aikawa and Soda, 1975), and other 

technologies are in development. The choice and 

availability of a particular technolo~ n1ay determine whether a given system is economically 

viable or not, but this choice requires detailed 

know ledge of the reservoir characteristics of the 

system and of the economics of alternative conversion technologies. Since detailed reservoir 

knowledge is generally unavailable and the development of conversion technologies is in a rapid 

state of flux, no attempt is made h~re to analyze 

individual systems. Instead, for hot-water systems 

we use the the representative conversion efficiencies given in table 15 for the fraction of heat 

above 15°C converted to electricity (Nathenson, 

1975b). Vapor-dominated systems trnd to produce 

steam in the range of 180° to 240°C temperature; 

the conversion efficiency corresponding to this 

temperature range is approximately 0.2 (N a thenson, 1975b). 

Defining Q as the heat stored atove 15°C and 

er as the · recovery lactor, the electrical energy 

produced is 

E=Qe,. (1) 

(for Q in multiples of 1018 cal, E in megawatts 

electrical times centuries (MW e ·cent) is 1,327 

Qer). The recovery factors given in table 15 are 

used to convert stored heat into potential electrical ene-rgy for all iden~ified con 1recti ve hydrothermal systems with temperaturer above 150°C 

outside of the national parks (table 16). Only 

those with sufficient data to give an estimated 

volume greater than the minin1urr. volume used 

by Renner and others (this circular) appear by 

name in taLle 16. This minimum Y0lume corresponds to a stored heat of about 0.2 X 1018 cal. The 

total electrical energy from the identified convective systems in table 16 is 8,000 MWe·cent, or 

27,000 MW e for 30 years.* The lo,.,ations of the 

systems identified by name in tabh 16 are plotted on maps of the United States (fig. 13) as 

large dots. 

The Geysers is the only vapor-dominated 

system in table 16, and it also contains the only 

measured geothermal reserves for electrical energy. Since the recoverable ener~r of a vapordominated system depends so critically on the 

average water content (which can only be roughly 

estimated from the limited public data) , a reserve 

estimate cannot be determined reli~tbly. Average 

• !The conversion to a 30 year period a "~umes that each 

MW·cent of electricity can be produced at a rate of 3.33 MW 

for 30 years. This assumption applies to all similar conver- sions throughout this circular. 

106 
Table 15.-Recovery factors (er) for electric power generation 

Vapor-dominated systems (above 200°C) 

Water content as fraction of 

total volume 0.01 0.02 0.03 

Fraction of stored energy recovered as heat* 0.020 0.039 0.059 

e = recovery factor = fraction r of stored energy recoverable 

as electrical energy at a 

conversion efficiency of 0.2* 0.004 0.008 0.012 

*Volume of porous, permeable part assumed to be one-half of heat 

Hot-water systems 

Temperature range oc 150-200 200-250 250-300 

Conversion efficiency 0.08 0.10 0.12 

er = recovery factor = fraction 

of stored energy recoverable 

as electrical energy** 0.02 0.025 0.03 

.. 

0.05 

0.097 

0.019 

rese:rvoir. 

**Volume of porous, permeable part assumed to be one-half of heat re~ervoir. 

One-half of the thermal energy in the porous, permeable part assume1 recoverable for a net recovery of 25% of the thermal energy. 

107 
Table 16.-Estim.ated potential electric energy from identified high-temperature hydrothermal cor'Vection system, 

each with estimated stored heat equal to or greater than 0.3 x 1018 cal (from Renner and others, this 

circular) 

Subsurface 

Temperature Volume 

°C km3 

Alaska 

Geyser Bight 210 8 

Hot Springs Cove 155 4 

California 

The Geysers 240 140 

Surprise Valley 175 250 

Morgan Springs 210 10 

Sulphur Bank mine 185 3.75 

Calistoga 160 9 

Skagg•s H.S. 155 3 

Long Valley 220 450 

Coso H.S. 220 336 

Salton Sea 340 108 

Brawley 200 27 

Heber 190 100 

East Mesa 180 56 

Idaho 

Big Creek H.S. 175 3 

Sharkey H. S. 175 3 

Weiser area 160 70 

Crane Creek 180 60 

108 

Stored 

Heat 

1018 cal 

0.9 

0.3 

18.9 

24 

1.2 

0.4 

0.8 

0.3 

55 

41 

21 

3 

11 

5.5 

0.3 

0.3 

6.1 

5.9 

Recovery 

Factor 

0.025 

0.02 

0.019 

0.02 

0.025 

0.02 

0.02 

0.02 

0.025 

0.025 

0.03 

0.025 

0.02 

0.02 

0.02 

0.02 

0.02 

0.02 

Electrical 

Pote"ltial 

MW e •cent 

30 

8 

477 

637 

4'0 

11 

21 

8 

1825 

1360 

836 

100 

292 

146 

8 

8 

162 

157 
Table 16.-Estimated potential electric energy from identified high-temperature hydrothermal convection 

systems, each with estimated stored heat equal to or greater than 0.3 x 101 8 cal (from Renner and 

others, this circular) --<:ontinued 

Subsurface Stored Recovery Electrical 

Temperature Volume Heat Factor Potential 

oc km3 1018 cal er MW e •cent 

Nevada 

Baltazar H.S. 170 3 0.3 0.02 8 

Pinto H.S. 165 7.5 0.7 0.02 19 

Great Boiling (Gerlach) S. 170 25 2.3 0.02 fl 

Sulphur H.S. 190 10 1.1 0.02 (. "~ .. 

Beowawe H.S. 240 42 5.7 0.025 1P9 

Leach H.S. 170 10 0.9 0.02 24 

Stillwater area 160 25 2.2 0.02 58 

Soda Lake 165 12.5 1.1 0.02 29 

Brady H.S. 214 30 3.6 0.025 119 

Steamboat Springs 210 16 1. 9 0.025 63 

New Mexico 

Valles caldera 240 130 18 0.025 597 

Oregon 

Mickey H.S. 210 12 1.4 0.025 46 

Alvord H.S. 200 4.5 0.5 0.025 17 

Hot Lake 180 12 1.2 0.02 32 

Vale H.S. 160 100 8.7 0.02 231 

Neal H.S. 180 4 0.4 0.02 11 

Lakeview 160 16 1.4 0.02 37 

Crumps Spring 180 8 0.8 0.02 21 

109 
Table 16.--Estimated potential electric energy from identified high-temperature hydrotherma1 conveoaon 

systems, each with estimated stored heat equal to or greater than 0.3 x 1018 cal (from Renner and 

others, this circular) ~ontinued 

Subsurface Stored Recovery Electr~cal 

Temperature Volume Heat Factor Potential 

oc km3 1018 cal er MW e ·cent 

Utah 

Roosevelt (McKean) H.S. 230 8 1.0 0.025 33 

Cove Fort-Sulphurdale 200 22.5 2.5 0.025 83 

Total: 

Other systems estimated 

to have minimum volume 

Identified Resources: 

water content at Larderello, Italy, appears to be 

about 1 percent of total volume for a reservoir 

2 km thick ( N athenson, 1975a). Assuming this 

value for The Geysers, equation 1 with the value 

for 1 percent (table 15) yields a reserve estimate 

of only 100 MWe·cent or 333 MWe for 30 years. 

On thermodynamic grounds, Truesdell and Whit~ 

(1973) maintain that the average water content 

at The Geysers is considerably greater than that 

at Larderello and may be as much as 9 percent. 

More complete calculations for the conductive 

heat losses from the steam in the well to the 

surrounding rocks using the method of N a thenson (1975a) show that the water content estimated from the theory of Truesdell and White 

( 1973) is closer to 5 percent than 9 percent. Using 

the value of 5 percent, the potential of The Geysers is 4 77 MW e ·cent or 1,590 M'V e for 30 years, 

and this value.iappears in table 16. 

Using an alternate method, wells at The Geysers initially produce an average of about 150,000 

lb/hr (19 kg/s); 2X106 lb/hr (252 kg/s) are 

needed to generate 110 MWe (Finney, 1973). 

Initial well spacings are on the order of 40 acres 

( 0.16 km2 ) with infill wells drilled as needed to 

maintain declining flows. Renner and others (this 

circular) estimate the reservoir area to be 70 

km2

• Assuming that a 40-acre spacing for new 

zones can be maintained, the potential of The 

Geysers is 3,570 MWe for a 30-year life or 1,070 

MW e ·cent, which is more than double the figure 

252 x 1018 cal 7833 MW·cent 

5 X 1018 ·cal 133 MW·cent 

257 X 1018 cal 796f MW·cent 

if a 5-percent water content is assumed. The assumptions in this second calculation are such that 

1,070 MW e ·cent seems likely to ~ in error on 

the high side. Accordingly, we have chosen to use 

the results of the first calculation ( 477 MWe· 

cent) in table 16. The resolution of this discrepancy may lie in such factors 3 s a reservoir 

extending below the arbitrary bottomr at a 3-km 

depth (Renner and others, this circrlar), a water 

content higher than 5 percent, a ratio of volume 

of porous and permeable parts to volume of heat 

reservoir that is higher than 0.5, well spacing 

th'at should be larger than the assu--ned 40 acres, 

or steam production that results partly from 

boiling from a deep brine zone. 

The high-temperature hydrothermal convection 

systems are technologically exploitaP~, and therefore their recoverable heat conter~s are a resource. If the heat of a given system cannot be 

recovered because there is not a por<Jns, permeable 

reservoir, then that system is· considered to be 

part of the resource base rather th~tn a resource 

until a recovery technology is available. 

&onomic constraints 

The cost of geothermal power c~.n be broken 

down into various components: exploration costs, 

land-acquisition costs, costs of production wells, 

cost of fluid-transmission facilities, plant costs, 

fluid-disposal costs, and cost of mora.y. Although 

the cost of production wells is a ~·mall fraction 

of the total cost, it is the cost facto:r that has the 

110 
\\ 

\ 

\ . '\ 

' \ 

\ 

----~---~---r---. I i 

/ i i i 

! \ I • 

I ! 

I '· : \ 

-------. __ j 

\ .. 

) 

" 

.... I . , ._,. ....... __ ~ '{ 

j 

; 

j 

I 

i 

I 

-·-l---1:- .::l-_ ! ' ""F---. I I ·--; 

j 

! 

----

\ 

\ . ' 

! 

I 

j 

i 

I 

i 

I 

I 

! 

----~--------··- --.,. ______ _ 

~-·-·-·--~---·-·-- -· 

; 

; 

i 

i 

; 

i 

i 

i 

; 

i-·-·-·--·-·--·-·--

1 

; 

I 

--, 

i 

i 

I 

j 

i 

j 

\ 

\ 

\ 

. -t·-----------------· 

i 

i 

j 

j 

i 

I -----·----~--1 _______ _ ; 

i 

j 

! • 

j 

t--·-·-·------· ; 

i 

; 

i 

-------·r··--· 

' i 

I 

\ 

\ 

i 

\ 

I 

\ 

; -----., ' ., 

j 

j 

; 

; 

i 

; 

; 

j 

; 

; 

; 

'v•"' 

0 200 

I ,•, ,',' I I 

0 200 400 

• T > 150°C 

+ T < 150°C 

; 

i 

i 

i r--·--..1-·-·-·- --~... __ j 

400 MILES 

600 KILOMETRES 

I 

i 

i ________ j 

\ ,··"··--.. '· ... J : ' '\,. ....... J ,, 

\ 

-··""·-.,~"'tf"-'\., 

FIGURE 13A.-Locations of hydrothermal convection systems with temperatures above 90°0 and stored heat greater 

than or equal to 0.3Xl<f8 cal. 

111 
.... 

1-L 

t.-0 

~ 

~~ C) 

Principal Islands of 

HAWAII 

0 190 2?0MI. 

I I I I 1EIO" 0 100 200 300 KM. 

1 --- ---/ - ~.,."*""'"" / 

~ 

<;?' 

,;:? 

\ 0 

-~ ~· ••. "'d'.d...!'i.~ 

'0 , ...... ~ 

1!15" 

100 

··p.W ~~~~- zoo 

17!1"W 

ALASKA 

zoo 300 

•oo 

•oo IIILES 

• T> 150°C 

+ T< 150° C 

FIGURE 13B.-Locations of hydrothermal convection systems with temperatures above 90°0 and stored heat greater than or equal to 0.3Xl()l8 cal. 
greatest range and the most uncertainty and 

that is therefore critical in determining whether 

development of a given field is likely to be. economically feasible. Although each production well 

can be assigned an average cost, the total cost of 

production wells is a direct ftmction of the nunlber of wells that need to be drilled to supply 

sufficient steam for the generating plant under 

consideration. This number in turn depends on 

the reservoir temperature and the average well 

productivity. Although the minimum reservoir 

temperature commonly can be estimated prior to 

drilling by using chemical geothermometers, average well productivity can be detern1ined only 

after extensive investment in drilling and testing. 

Accordingly, the uncertainty in average well productivity is a major financial uncertainty in any 

geothermal developn1ent. Inasmuch as the division of geothermal resources into reserves, paramarginal resources, and submarginal resources is 

based on economics, these uncertainties impact 

any attempt to evaluate geothermal resources. 

The following analysis indicates the degree to 

which the cost attributable to production wells 

is sensitive to well productivity. Consider a well 

of average mass flow M that is productive for a 

time T and costs 0 dollars to drill and case. This 

well can produce a certain amount of electricity 

per kilogram of produced fluids [ Wact]. Representative values for Wact for vapor-dominated 

and hot-water systems are given in table 17. The 

rate of energy flow (power) produced by the 

well is . 

E=MWact• (2) 

The part of the power cost in mils per kilowatthour (milsjkWh) that pays for the well is called 

c. Assuming that the well flow is constant and 

produces revenue evenly over the period T, then 

the original cost of the ,well 1nust be escalated by 

a factor 1 + e to allow for the cost of money. The 

value of the produced energy needed to pay for 

the well is then ETc, and the escalated cost of the 

well is 0 ( 1 + t:). Equating value and cost and 

rearranging, we obtain 

(3) 

Some estimates of drilling cost 0 as a function 

of depth are given in table 18 where the values 

for 2 and 3 km are based on recent geothermal 

experience (C. H. Bloomster, oral commun., 

1975), and the other values are based on estimates 

made for crystalline rocks (Shoemaker, 1975). 

Taking the well life T as 20 years and the interest rate as 10 percent, the cost-of-money factor 

1+t: is 20/8.514=2.349. The cost-of-money factor 

together ,-with the data in tables 17 and 18 has 

been used to prepare figure 14. 

Figure 14A shows the electric power production per well as a function of mass flow for several reservoir temperatures and for vapor-dominated and hot-water systems, using the data of 

t~ble 17 and equation 2 . Points are shown for 

Wairakei from the values of Axtlnann (1975) 

and for units 5 and 6 of The Geysers f.-om the 

data of Finney (1973). The 250°C line for hotwater systems was calculated by assuming a twostage flash system. The W airakei point r lots below this line because its efficiency is low owing to 

its single-flash system. Figure 14B shows the 

electric power per well as a function of tl'<:', value 

of the energy needed to pay for the ,~ell for 

several well costs from _the data in tabla, 4 and 

equation 3. The electric power per well for The 

Geysers and \V airakei are the same as in figure 

14A. The value. needed to pay for the well at 

W airakei was caluculated on the basis of 20-year 

life and $150,000 drilling cost for de~ths of 

about 1 km. The value needed to pay for a well 

at The Geysers was calculated on the basis of a 

15-year life and $500,000 drilling cost for wells 

drilled to near 3 km depth. This shorter lifetime 

was assumed because of the decline in rate of 

flow at The Geysers. 

Two points should be made about the calculations for The ~Geysers and W airakei. First, although they are very different systems, the return needed to pay ·for a well works out to be close 

to the san1e (0.7 and 0.85 mils/kWh, respectively). Second, the total cost of power involves 

many additional costs above the value needed 

to pay for a well. Calculations by Clarence 

Bloomster of Battelle Pacific Northwest Laboratories, discussed in Lucking (1975),. show total 

power cost for a systen1 like The Geysers to be 10 

mils/kvVh 4.7 being the cost of producing 

steam from the reservoir, of which only 0.7 is 

needed to pay for an individual well by equation 

3. Calculations for an analog of "r airakei single 

flash but with reinjection) yield a total power 

cost of 20 mils/kWh, with 13 clue to costs of 

producing ste-am from the reservoir, of which 

only 0.85 is needed to pay for an individual 

well by equation 3. 

113 
Table 17.-Typical values for electric energy produced per kilogram of reservoir fluid (wact) as a function of 

source temperatures 

Hot water 

Temperature oc 

kW·s 

wact in k9 

150 

33 

200 

70 

250 300 

120 177 

Vapor-dominated, saturated steam 

Temperature °C 

wact in kW·s 

kg 

150 

430 

Although the calculated values in figure 14 are 

only a part of the total, an important trend is 

shown by the diagrams. Since geothermal power 

must compete with 1nany other power sources, 

the total value of the power is fixed by market 

forces at a particular time and place. If we 

assume that only a certain number of 1nils per 

kilowatt-hour is available to pay for the well, 

then we can use figure 14 to estimate the minin1um 

flow needed to make a particular resource competitive. Taking the value needed to pay for a 

well of 1.5 mils/kWh in figure 1 14B and projecting it vertically to a $300,000 well cost, the 

power level needed from each well is about 2.7 

MW e as determined by horizontal projection. 

The same horizontal projection may then be 

extended into figure 14A to show how the required 

mass flow from each well varies with temperature 

200 250 

550 620 

and resource type. Required flows in the vapordominated systems are relatively hw. Becaust:: 

of this, more expensive wells can b€ drilled, but 

still at a profit. For the hot-water systems, the 

required minimum flows become very large at the 

lower temperatures. As the value n('~ded to pay 

for a well and the cost of the well vary with time 

and specific circumstances, figure 14 may be used 

to estimate required well flows. F<'r high well 

costs such as $1 to $5 million, the value needed to 

pay for a well must be increased if the minimum 

well flow for economic operation is not to be 

unreasonably large. ~ ote that the use of figure 

14 is only sen1iquantitative. Specific systems and 

technology should be evaluated by making a 

detailed cost study such as the progrt~.m of Bloomster and others (1975). 

Table lB.-Drilling cost model 

Depth km 1 2 3 5 10 

Average cost per metre $150 $150 $167 $200 $500 

Drilling time days 15 .. 25 30-50 75-150 150-250 750-1100 

Cost ( 1 o3) $150 $300 $500 $1000 $5000 

114 
The interpretation of figure 14A requires consideration of the factors influencing the flow of a 

well produced ·by flashing discharge (Nathenson, 

197 4). For flash eruptions, a limit is imposed by 

the frictional pressure drop in the well at very 

high rates of flow. At 200° to 250°C in a 25-cmdianleter well, flowing friction limits the rate to 

about 200 to 250 kg/s. From figure 14, a constant 

value of 1.5 mils/kWh needed to pay for a well 

at these ~sumed rates of flow yields possible 

total well costs of $1.5 to $2.5 million. In many 

cases, however, flows are limited not by flowing 

friction in the well but by the available permea;bility and ·permissible pressure drop in the reservoir, resulting in a n1uch lower value of well flow 

for a field. For example, before it was perforated 

at a higher level, Mesa 6-1 well had a flow of approximately 14 kg/s with a flashing level at about 

1,300 m below ground level. Thus, -a pressure drop 

of 110 bars could yield only 14 kg/s from the formation because of restricted permeability. On 

the other end of the spectrum, because of very 

high permeabilities, flows in some wells at W airakei are 130 kg/s in only a 20-cm casing. At temperatures close to 150°C, and in some hightemperature fields, downhole pumps are likely 

to be used to provide additional drive and to 

maintain pressures that prevent the boiling of 

water and deposition of scale.· The pumps are 

likely to provide on the order of 10 bars increased 

pressure (Mathews and McBee, 1974), which 

could be of great assistanCe in low-temperature 

systems where it may be desirable to keep the 

fluid all liquid. However, this would not greatly 

improve a high-temperature flashing well in rocks 

of low permeability where stimulation may be 

more advantageous. 

Reserves and resources 

To determine where each of the systems listed 

in table 16 fits into reserves, paramarginal resources, and submarginal resources, the next step 

is to apply figure 14 to each system. Although 

the temperature is known for each of these systems at least by geochemical methods, the average 

well flows are known for only a few of these systems. In lieu of an objective analysis, subjective 

decisions were made as to the most likely divisions 

between the various categories. The most important single factor is temperature; reservoirs 

above 200°C are most likely to contain ·reserves. 

Other data that are utilized to yield the division 

shown in table 19 of the resources of hydrothermal convection systems for the generation 

of electricity are significant size and lack of severe 

problems such as high salinity or fluid supply 

suspected to be inadequate. The reserves (known 

and inferred) are about equal to the para1narginal 

resources. The submarginal resources arE, smaller 

than either of the higher categories bec~.use the 

150°C lower limit assun1ed by Renner, W"ite, and 

Willian1s (this circular) ren1oves m·any systems 

that would he submarginal if included. Also, the 

exploration of the systems at temperatur~ a·bove 

but near to 150°C has not been as systemr.tic as at 

the higher temperatures. 

The undiscovered resources given in table 19 

have been estimated on the basis that O:'le times 

the identified resources of vapor-domin~.ted systems will be found in the United Statef' outside 

of the national parks and that five times the 

identified resources of hot-water systenlF will be 

found (Renner and others, this circular) . 

INTERMEDIA T&TEMPERATURE 

HYDROTHERMAL CONVECTION SY::'TEMS 

The identified hydrothermal convect~'.ln systems with predicted temperatures from 90° to 

150°C have been discussed and their e8timated 

heat contents tabulated by Renner, W1·ite, and 

"Tilliams (this circular) . The factors affecting 

physical recoverability are muc.h the same as 

those for the high-temperature systems except 

that boiling in the reservoir is unlikel:r to be 

important. Accordingly, the previous estimate 

of one-fourth of the stored energy recoverable as 

thermal energy at the surface from high-temperature systems should also apply to the sy~,tems of 

intermediate temperature. Table 20 sh'.lws the 

identified hydrothermal convection sys+ems of 

intermediate temperature, those above tb?- minimum volume of Renner, White, and 1~Tilliams 

(this circular) being listed by name. The data on 

size of most of these systems are very limited, 

and many may be significantly larger than the 

minimum estimates. The sum of the heBt stored 

in the identified systems in table 20 is 3~5 X 1018 

cal, of which 263 X 1018 is predicted for I'runeauGrandview, Idaho, and 30X1018 cal for·F':Iamath 

Falls, Oregon. If the estimates of volume and 

temperature by Renner, White, and 1~Tilliams 

115 
50 

240°C 

~200 300°C //150 250 

/// Q) 

-~~ 200 

3: 

~ 

_iiO ~ ~~~ oc 

c'' //, ,~' _j 

w 

3: Y/ X<.,-/' 150 

0: 

w 

a.. 

0: 

w /// 3: 

0 

a.. rr--- u 

-

I I 0: 

Iu 

w 

_j 

w 

5 10 50 

MASS FLOW, KG/S 

100 200 

FIGURE HA.-Electrie power per weH as a function of mass flow for various temperatures of hotwater -and vapor-dominated systems. 

(this circular) for Bruneau-Grandview are confirmed by drilling~ this system is indeed im1nense. 

Until a specific use is chosen for such systems, 

the fraction of the energy that can be applied 

to beneficial use cannot be specified. As discussed 

in N athenson(l975b), energy equivalent to a temperature drop of 10° to 20°C can readily be extracted for direct use; this energy is more than 

can be obtained from 150°C water in converting 

thermal energy into electricity. 

In order to obtain some perspective on the 

predicted 345 X 1018 cal of stored heat in the identified systems in table 20, the amount of beneficial heat may be calculated. The tern1 beneficial 

heat as used in this report is thermal energy 

that can be applied directly to its intended nonelectrical use; beneficial heat phu' waste heat 

equals initial available heat. Assuming that onefourth of the stored energy is I'ecoverable at the 

surface and that the efficiency of utilization is 

0.24 (20°C temperature drop at 101°C, 32°C at 

150°C), the recovery factor is (0.24) X (0.25) = 

0.06~ and the beneficial heat is ( O.OC) ( 345 X 1018 ) 

cal= 20.7 X l01 s cal. If this usable her•,t we.re to be 

supplied by electrical energy, it w~uld require 

(20.7) (1327) =27,000 MW ·cent. Thus, if the 

institutional problems can be resolved, this resource has significant potential. 

The economics of process heating present several complications. The first of thef~ is that the 

value per calorie depends on the te .. nperature of 

the resource. As the resource temperr.ture becomes 

116 
50~----------------------------------------------~ 

Q) 

~ 

~ 

_; 10 

.....J 

w 

~ 

0:: 

w 

a.. 5 

0:: 

w 

~ 

0 

a.. 

u 

0:: 

...... 

u 

w 

.....J 

w 

0.5~----~----~~~~~~~--~--~--~~~~~~~ 

0.1 0.5 1.0 5.0 IO.C 

VALUE NEEDED TO PAY FOR A WELL IN Ml LS/KWH 

FIGURE 14B.-Electric power per well as a function of value needed to pay for the well for various well costs. 

lower, various end uses are no longer possible 

because some minimum temperature is needed, 

and the market is thus diminished. Hot water 

can only be transmitted a few tens of kilometres, 

so a user must either be available at the site or 

be induced to move to the site. If no potential 

user is already in the area, one must be located 

and persuaded to come to the area (in electricity 

production, the local power company is always 

the potential customer). The exploitation of geothermal resources for direct heating is similar 

to electricity production 1

In that exploration and 

development of the field can only be done by an 

organization designed for high-risk operations, 

such as a resource exploration company or an 

oil company. 

Assuming that these organizational p~blems 

are solved as potential direct uses become attractive, the chances for improved economics are 

high. The costs of this kind of expl')itation 

involve exploration, field development, and construction of transmission system. If the transmission costs can be kept low by near-site use, the 

lack of an expensive power plant permitE a relatively low investment per energy unit. 

Because of the lin1ited knowledge in this country of the economics of using geothermal energy 

for direct heating, the division of the resource 

into reserves and paramarginal and subn1arginal 

resources is not feasible. The sum of the ic·~ntified 

systems in table 20 is reported as a total ic~ntified 

resource of 20.7 X 1018 cal. The undiscov'llred re117 
Table 19.-Resources of hydrothermal convection systems for the generation of electrical power in 

megawatt centuries (not including national parks) 

Identified Undiscovered 

Reserves (Measured and inferred) 

3500 MW•cent 

~ Paramarginal Resources ~ 

~ 

Resources 

3500 MW•cent 

Submarginal Resources 

>1000* MW•cent 

38000 MW•cent 

*The small amount of submarginal as compared to paramarginal resources results from the 150°C lower 

temperature limit assumed by Renner and others (this volume}; this lower limit removes many systems. which would be submarginal if included~ Also, exploration of systems at temperature above but near 

t9 150°C has not been as systematic asof systems at the higher temperatures. 
Table 20.-Intermediate-temperature hydrothermal convection systems with stored heat greater than or equal to 

0.3 x 1018 cal (from Renner and othets, this circular) 

Subsurface Volume Storer.t 

temperature km 3 heat 

oc 1018 cal 

ALASKA 

Okmok caldera 125 6 0.4 

CALIFORNIA 

Wendel-Amedee area 140 14 1 . 1 ~Jilbur H.S. area 145 32 2.5 

Randsburg Steam Well 125 3.75 0.3 

Glamis' (East) 135 6 0.4 

Dunes 135 9 0.6 

COLORADO 

Cottonwood Springs 110 6 0.3 

Mt. Princeton Springs 115 7.5 0.5 

HAWAII 

1955 Eruption area, East Rift 150? 4 0.3 

Puulena area, East Rift 150? 4 0.3 

IDAHO 

Stanley Hot Spring 110 6 0.3 

N.E. Boise Thermal Area 125 8 0.5 

Bruneau-Grandview 145 3375 263 

Near Banbury 140 12 0.9 

Near Cedar Hill 120 9 0.6 

Raft River Thermal Area 140 30 2.3 

Wayland Hot Spring 130 7.5 0.5 

NEVADA 

Near Soldier Meadow 115 12 0.7 

Double Hot Spring 145 20 1 .6 

Fly Ranch Hot Spring 130 16 1 . 1 

Hot Springs Point 125 7.5 0.5 

Buffalo Valley Hot Spring 130 10 0.7 

OREGON 

Mt. Hood 125 4 0.3 

Klamath Fa 11 s 120 480 30 

Summer Lake Hot Spring 140 6 0.4 

Fisher Hot Spring 130 4.5 0.3 

Near Harney Lake 135 4.5 0.3 

UTAH 

Monroe (Cooper) Hot Spring 120 7.5 0.5 

TOTAL: 311 x 1018 cal 

Other systems estimated to have minimum volume 34 x 1018 ca 1 

Total, all s~stems: 345 X 1018 cal 

119 
sources are estimated to be three times the known 

resources (Renner ~nd others, l this I circular) or 

62.1 X 1018 cal. If these predicted quantities are 

confirmed in future investigations, they are likely 

to become increasingly attractive for a variety 

of uses as alternative sources of energy become 

more expensive and unreliable. 

SOLIDIFIED IGNEOUS SYSTEMS 

The re,source base in igneous systems has been 

discussed and their estimated heat contents and 

solidification states tabulated by Smith and Shaw 

(this circular). The problems and possibilities 

of obtaining energy from the Inolten parts of 

igneous systems are discussed by Peck (this circular). With current technology, the heat stored 

in the molten parts is not recoverable, and this 

large quanity of heat represents an attractive 

target for research. Much heat is also stored on 

the margins of the molten systems and in the nowsolidified systems. Some of these systems without 

associated hydrothermal convection systems may 

still have temperatures significantly above the 

temperatures indicated by regional heat flow. 

These areas constitute the most favorable targets 

for recovery using hydraulic fractures to produce 

circulation loops in a body of low-permeability 

rock (the "hot dry rock" of Smith and others 

( 1973). Inasmuch as many problems need to be 

solved before this is a proven concept, the stored 

heat cannot be considered ·a resource until the 

technology has been proven. 

The basic scheme for recovering energy from 

hot dry rock involves drilling a hole several 

kilometres into hot rock, creating a large hydraulic fracture about 1 km in diameter, and casing 

the hole nearly to its bottom. A second hole is 

then drilled to intersect the top of the fracture. 

Cold fluid is injected into the deep hole as hot 

fluid is produced from the shallow hole. Assuming 

that such a circulation loop can be created, the 

power output is strongly dependent on the behavior of the circulation loop. Harlow and Pracht 

( 1972) suggest that permeability and porosity 

will grow from cracking due to stress caused by 

thermal contraction. If this happens, the volume 

of rock through which the water is flowing will 

grow with time, and nearly constant power levels 

can be maintained. The fraction of stored energy 

so obtained at the surface is likely to be similar 

to that for hydrothermal convection system. Well 

flows in this case are determined by crack thickness and length and available pres:1ure drive due 

to buoyancy and any pumping. It is also possible 

that porosity will not be created. In this case, 

heat transfer from the rock to the water flowing 

in the crack is by conduction. As sl''lWn by Nathenson (1975b), the fraction of stored energy obtained at the surfaee is then likely to be one-half 

of the value for hydrothermal convection systems. 

The temperature of produced fluids deelines with 

time, and most utilization schemes do not tolerate 

much variation in ten1pera.ture. The well flows 

in this case are determined by crack size and the 

chosen values for abandonment time and temperature. Answers to the various questions about this 

technique should he provided by research programs currently underway. 

CONDUCTION-DOMINATED AREAS 

The conductive thermal regime of the upper 

10 km of the E-ft,rth has been discussed and heat 

contents tabulated by physiographic province 

(Diment ~ncl others, this circular). Because of the 

limited knowledge of radioactive :r~at generation 

and thermal conductivities, temperatures at depth 

cannot be specified completely, but broad limits 

can be put on them. The only parts of the resource 

base that are currently recove.ra;ble in ·addition to 

geopressured areas are the sedin1entary basins 

of adequate permeability. Lc w-temperature 

waters for direct heating can h;:, recovered by 

the sweep process discussed by N athenson 

(1975b). Possible areas of higher-than-normal 

heat flow include parts of the Salton Trough not 

associated with hydrothermal convection systems, 

individual basins of the Basin and Range province, and the Rio Grande .rift. Other basins in the 

normal heat-flow provinces are alro possible, but 

temperatures do not increase rapidly unless conductivities are low, thus providing a "thermal 

blanket" (Diment and others, this circular). The 

recovery of such energy is likely to be generally 

submarginal, but more data are recuired. 

Most of the heat stored in the conductive areas 

of the United States is in rocks toC' low in permeability to be considered recoverable. Except in 

unusmtlly favorable combination~ of high reduced heat flow, high radioactive h~at production, 

and/or a low-conductivity blanket, temperatures 

are not high ( Diment and others, this circular). 

If a hydrofracturing scheme is proven in the 

120 
especially favorable areas associated with igneous 

systems, the same scheme may be applicable to 

other less favorable areas of the United States. 

REFERENCES CITED 

Aikawa, Kentaro, and Soda, Masahiro, 1975, Advanced 

design in Hatchobaru geothermal power station 

[abs.]: United Nations Symposium on the Development and Use of Geothermal Resources, 2d. San 

Francisco, abs. no. VII-1. 

Axtmann, R. C., 1975, Environmental impact of a geothermal power plant: Science, v. 187, no. 4179, p. 

795-803. 

Bloomster, C. H., Cohn, P. D., DeSteese, J. G., Huber, 

H. D., La Mori, P. N., Shannon, D. W., Sheff, J. R., 

'Valter, R. A., 1975, Geocost: A computer program 

for geothermal cost analysis: Battelle Pacific Northwest Laboratories BNWL-1888 UC-13, 46 p. 

Finney, J. P., 1973, Design and operation of the Geysers 

Power Plant, in Kruger, Paul and Otte, Carel, eds., 

Geothermal energy-resources, production, s timulation: Stanford, Calif., Stanford Univ. Press, p. 

145-161. 

Harlow, F. H., and Pracht, W. E., 1972, A theoretical 

study of geothermal energy extraction : Jour. 

Geophys. Research, v. 77, no. 35, p. 7038-7048. 

Lucking, J. C., 1975, Economics of producing electric 

power from hydrothermal convection systems: U.S. 

Geological Survey open-file rept. (in prep .. ). 

Matthews, H. B., and McBee, W. D., 1974, Geothermal 

down-well pumping system : Conference on Research 

for the Development of Geothermal Energy Resources, Pasadena, Calif., Proc., p. 281-291. 

Muffier, L. J. P., 1973, Geothermal, in Probst, D. A., and 

Pratt, W. P., eds., United States mineral resources: 

U.S. Geol. Survey Prof. Paper 820, p. 251-261. 

Nathenson, Manuel, 1974, Flashing flow in hot-water 

geothermal wells: U.S. Geol. Survey, Jour. Research, 

v. 2, no.6, p. 743-751. 

Nathenson, Manuel, 1975a, Some reservoir er~ineering 

calculations for the vapor-dominated svstem at 

Larderello, Italy: U.S. Geol. Survey open-file rept. 

75-142, 47 p. 

Nathenson, Manuel, 1975b, Physical factors determining 

the fraction of stored energy recoverable from 

hydrothermal convection systems and conductiondominated areas: U.S. Geol. Survey open-file report 

75-525, 38 p. 

Shoemaker, E. M., ed., 1975, Continental drilling: 

Carnegie Inst. Washington Pub., 65 p. 

Smith, Morton, Potter, R., Brown, D. and Am')dt, R. L. 

1973, Induction and growth of fractures in hot rocks, 

in Kruger, Paul and Otte, Carel, eds., Geothermal 

energy-resources, production, stimulation : Stanford Calif., Stanford Univ. Press, p. 251-268. 

Truesdell, A. H., and White, D. E .• 1973, Production 

of superheated steam from vapor-dominated geothermal reservoirs: Geothermics, v. 2, p. 145-164. 

121 
Assessment of Geother;mal 'Resources of the United States-1975 

Recoverability of Geothermal Energy Directly from Molten Igneous Systems 

By D. L. Peck 

A very large quantity of heat in molten "igneous 

magma systems at depths less than 10 km has 

been identified by Smith and Shaw (this circular). On the basis of existing geological and geophysical data, they have listed 17 inferred 1nolten 

bodies of silicic and intermediate composition in 

the conterminous United States, 24 bodies of 

mainly intermediate con1position in Alaska, and 

1 basaltic body in Hawaii. The total estimated 

heat energy in these systems is at least 25,000X 

1018 cal, 30 or more times the estimated he•at 

content of all hydrothermal systems in the United 

States at depths less than 3 km. Only a fraction 

of the estimated energy_ is in the molten bodies 

themselves-much of it is in the solidified margins of the bodies and the adjacent country 

rocks. The heat content of the molten or partly 

molten bodies is estimated to be 13,000 X 1018 cal, 

contained in magma at temperatures between 

650° and 1,200°C. The large inferred volumes 

and cross-sectional areas of a number of these 

bodies make them suitable targets for geophysical 

exploration. 

Unfortunately, this large quantity of heat is 

not presently recoverable and may never be so. 

The tops of the inferred magma bodies lie at estimated depths that are all greater than 3 km and 

mostly are still deeper. Formidable technological 

problems will have to be solved before the resource can be tapped. The technology for drilling 

at these temp~ratures and pressures, for example, 

is not available at present and may not be developed for many years. The feasibility of utilizing the energy contained in magma is presently 

being evaluated by Sandia Laboratories under a 

project that was started in 1974 (Colp, 1974) 

with the support of the Energy Research and 

Development Adn1inistration. This report is 

based on the results of that project to date, particularly a workshop on mag1na (March 1975) 

sponsored by Sandia Laboratories and the U.S. 

Geological Survey. 

The critical problems involved in recovering 

energy directly from molten igneou~ systems can 

be analyzed in terms of the three major stages 

in developing the energy of such a body : ( 1) 

Finding a magma body and determining its size, 

depth, composition, heat content, e+c., by remote 

techniques; (2) drilling into the body and emplacing a heat-transfer device sufficiently strong 

and corrosion resistant to last an appreciable 

period; and (3) extracting energy from the body 

at a sufficient rate· to amortize dev·~lopment and 

production costs. The critical technical problems 

involved in each stage are discussed in the following sections. Because the solution of several of 

these problems, particularly the critical problem 

of drilling, lies some years in tb~ future, no 

attempt is made to analyze the eco:"lomics of direct utilization of magma energy. 

EXPLORATION 

To extract energy directly frmr. magma, we 

must first find magma. Because of the very large 

costs of drilling such a body, the lo~ation, depth, 

and shape of the body and the heat content and 

heat-transfer properties of the ma .~a need to 

be determined by remote techniqu('B. Geological 

and geophysical techniques provide powerful tools 

for these tasks and have led to the listing of the 

41 inferred bodies in t~ble 8· (Smith and Shaw, 

this circular) . Although these methods are not 

122 
unequivocal, magma bodies have been identified 

with considerable probability beneath Yellowstone National Park, Long Valley in California, 

and Kilauea Volcano in Hawaii. 

A large body of data on the outer margins and 

internal structures of shallow intrusive bodies has 

been gathered in geologic study of older exhumed plutons; such as those associated with 

mining districts throughout the Western United 

States and in many other areas of the world. 

The depths and temperatures of intrusion can 

be estimated by geologic analysis, comparison of 

rock compositions with experimentally studied 

systems, and mineral geothermometers and geobarometers. The geology at the surface above a 

specific body, such as the structure and the composition, distribution, and age of young volcanic 

rocks, provides clues to the shape, depth, composition, and stage of evolution of the intrusion. 

Geophysical techniques-particularly seismic, 

electrical, gravimetric, and magnetic methodscan be used to identify the body if its characteristic dimensions are greater than half its depth. 

Improvement of several of the more promising 

techniques would lead to a greater ability to determine the critical physical and chemical parameters of a magma body by remote methods. Exhumed magma bodies need to be reexamined 

with a view toward reconstructing their structure 

and dynamics during emplacement and early 

cooling. Various geophysical techniques need to 

be tested on known magn1a bodies~ such as the 

Kilauean lava lakes and the inferred magma below Yellowstone Park. The physical properties 

of magma, such as compressional and shear wave 

velocities, electrical conductivities, and density, 

need to be determined as a function of temperature (650° to 1,200°C), pressure (1 to 2,000 bars), 

oxygen fugacity, and water content. 

DEVELOPMENT 

Development of the energy of a molten igneous 

system entails drilling into the magma, probably 

at depths of 3 to 6 km (pressures of 1 to 2 kb) 

and temperatures of 650° to 1,200°C, and extracting heat. During the drilling and throughout the 

exploitation stage, the borehole must remain undeformed, and the materials of the heat-extraction system must resist corrosion. 

Drilling technology appears at the present 

time to be the most critical limiting factor in the 

technological feasibility of direct development of 

magma energy. Magma, at least degassed molten 

basaltic lava, has been penetrated many t:mes by 

drilling through the shallow crust of s~agnant 

Hawaiian lava lakes. However, present drilling 

technology at the pressures of 1 to 2 kb ~~~levant 

to this discussion is limited to temperatures below 250°C. Major innovations in technolc ey will 

be neJded to reach the magma. 

A related problem is the development of equipment for in-hole sampling and 1neasurement of 

in situ physical parameters at these pressures and 

temperatures. The eventual development of a 

magma body will probably require a seri~ of successively deeper drill holes, with detailed sampling at each stage of the pore fluids for c'lemical 

analysis (particularly corrosive components) and 

in situ measurement of such parameters as temperature, pressure, stress, and bulk properties 

including pe.rn1eability c3!tion di:ffusivity, and 

density. Such measurements are essential to 

sharpen geophysical interpretations, to de+.ermine 

the strength and ductility of the rocks, and to 

develop drilling techniques and strategy. 

The stability of the borehole during drilling, 

emplacement of heat-extraction devices, and en..: 

ergy production may be serious proble"'l.s, depending on the strength and the stress field of 

the country rocks and solidified margin of the 

magma body in this hot, high-pressure Emvironment. An experimental rock -deformation program is in progress tmder the Sandia pr')ject to 

determine the answers. The nature of t]'<>, local 

stress field around n1olten bodies can be studied 

in general by petrofabric studies of exposed wallrock of ancient plutons, but the stress field around 

a specific -body under development can be determined only by in situ measurements. 

The performance of the heat-recovery system 

needs to be determined by in-hole tes~ing of 

equipment before exploitation to insure that the 

inserted materials retain their 1nechanical and 

chemical integrity. Current knowledge a"bout the 

behavior of alloys and ceran1ics and the c'lemical 

composition of magmas and hydrothermd fluids 

is sufficient for a general approach to th(\, problem. For a specific magma body, however, anumber of physical and chemical parameters of the 

magma and any related hydrothermal activity 

above the n1agma must be determined in ord~r 

to select the proper n1aterials and predict their 

reliable performance. 

123 
HEAT EXTRACTION 

Development of an efficient and durable heatextraction system is, of course, fundamental for 

the successful development of magma energy. Essentia-l to the economic exploitation of a specific 

body of magma is a favorable heat-transfer 

coefficient for the magma over a 10- to 30-year 

plant life. 

Sandia Laboratories is currently investigating 

several heat-extraction systems. The initial concept is to use a closed system with a long, heatexchanger tube in the magma, water for steam 

generation as a working fluid, and a conventional 

turbine generator. Other techniques under consideration include the use of gas as a working 

fluid and solid-electrolyte fuel cells to increase 

the efficiency of energy extraction. Plans are to 

extend laboratory tests of a single heat-exchanger 

tube and boiler to field tests in a Hawaiian lava 

lake or other suitable locality. 

The heat-transfer coefficient of magmas of different compositions is a significant factor in 

evaluating the feasibility of magma-energy utilization. Will magma in a body under development 

convect" at a sufficient rate near the heat exchanger 

to increase the rate of extraction of heat significantly over the conductive rate~ If not, could 

this increased rate be induced by the injection of 

aqueous solutions~ If the natural or induced convection is not appreciable, then extraction of heat 

directly from a molten body probably would not 

be economically feasible. Preliminary calculations 

by Hardee ( 197 4) of long-term heat-extraction 

rates from basaltic magma using a long tube 

heat exchanger with H20 as the working fluid 

yielded rates of only 1 kW /m2 for nonoonvecting 

magma but rates several orders of magnitude 

higher for vigorously convecting magma. Most 

magma bodies are very probably below liquidus 

temperatures and consist of mixtures of melt and 

crystals with the possible addition of a gas 

phase. Relevant critical properties that need to 

be determined are ( 1) the distribution of liquid, 

crystals, gas, and ·temperature in typical bodies; 

(2) the viscosity and density of crys+a.l-liquid-gas 

mixtures; and (3) the heat-transf1~r coefficients 

over a range of temperatures for magmas of different compositions. 

CONCLUSIONS 

Molten igneous systems represent a large part 

of our geothermal resource base, but that energy 

cannot be recovered directly at the present time 

or in the foreseeable future. Whether direct utilization is feasible is not certain. The most critical 

problems appear to be as follows: 

1. Improvement of techniques and development 

of technology for locating, evaluating, 

drilling, sampling, in situ measuring of 

physical parameters, and extracting heat 

at the temperatures (650° to 1,200°0) and 

pressures (1 to 2 kb) in the l'lstile chemical environment aJI.ticipated in the vicinity of magma bodies; 

2. Keeping drill holes at these depths and temperatures open and stable during drilling 

and long periods of heat ext.raction; 

3. Will natural convection in the magma appreciably increase heat extracthn rates over 

thel'IJlal conduction~ If not. can convection be induced~ 

4. Can these problems be solved with sufficient 

assurance to justify the exp~nses of drilling and exploiting an inferred body~ 

REFERENCES CITED 

Colp, J. L., 1974, Magma 'I'ap-the ultimate geothermal 

energy program: Circum-Pacific Energy and Mineral Resources Conference •at Honolulu, Hawaii, Aug. 

28, 197 4, 19 p. 

Hardee, H. C., 1974, Natural convection in a spherical 

cavity wilth uniform internal heat ger~tion, Sandia 

Laboratories SLA-74-0089, March, 1.974. 20 p. 

124 
Assessment of Geothermal Resources of the United States-1975 

Assessment of Onshore Geopressured-Geothermal 

Resources in the Northern Gulf of Mexico Basin 

By S. S. Papadopulos, R. H. Wallace, Jr., J. B. Wesselman, and R. E. Taylor 

Geopressured zones in the northern Gulf of 

Mexico basin are known to occur in Tertiary 

sediments beneath an area of over 278,500 km2 , 

extending from the Rio Grande in Texas northeastward to the vicinity of the mouth of the Pearl 

River in Louisiana and from the landward 

boundary of Eocene growth faulting southeastward to the edge of the Continental Shelf (see 

fig. 15). During the course of this study, it was 

found that geopressured zones occur also in unmapped Cretaceous sediments underlying the 

~ertiary sediments and extending further inland 

under an additional area of at least 52,000 km2 • 

This study assesses in a general way the resource potential of geopressured-geothermal 

reservoirs within the onshore part of Tertiary 

sediments under an area of more than 145,000 

km2 along the Texas and Louisiana gulf coast. 

This assessment covers only the pore fluids of 

sediments that lie in the interval between the top 

of the geopressurecl zones and the maximum 

depth of well control, that is, a depth of 6 km 

in. Texas and 7 km in Louisiana. 

The resource potential of geopressured reservoirs within ( 1) onshore Tertiary sediments in 

the interval between the depth of maximum well 

control and 10 km, (2} offshore Tertiary sediments, and ( 3) Cretaceous sediments were not 

included in this assessment. It is estimated, however, that the potential of these additional geopressured reservoirs is about 1 % to 2 lh times 

that of those assessed in this study. 

The resource potential of waters in geopressured-geothermal reservoirs was first brought to 

public attention by Hottman (1966, 1967). Since 

that time, Jones (1969, 1970) and Wallaoo (1970) 

have discussed and attempted to exph,.in subsurface physical conditions that combine to produce geopressured-geothermal reservoirs. Several 

analyses of the potential use of geopr':'Ssuredgeothermal energy for electrical power generation 

and estimates of the magnitude of the resource 

have been presented (Parmigiano, 1973; Herrin, 

1973; Wilson and others, 1974; Durham, 1974; 

Myers and others, 1974; Dorfman and Kehle, 

1974; House and others, 1975). 

Unlike other geothermal areas that are being 

considered for the development of energy, the 

energy potential of the waters in the geopressured-geothermal areas of the northern Gulf of 

Mexico is not limited to thermal ener;zy. The 

abnormally high fluid pressures that b~.ve resulted from the compartmentalization of the 

sand and shale beds that contain these ho+ waters 

are a potential source for the develop~ent of 

mechanical (hydraulic) energy. In ~.ddition, 

dissolved natural gas, primarily methane, contributes significantly to the energy potr.ntial of 

these waters. 

In contrast to geothermal areas of the Western 

United States, available subsurface inf<'~ation 

is abundant for the geopressured-geothermal 

area of the northern Gulf of Mexico basin. The 

area has been actively explored for oil and gas 

since the 1920's, and probably more than 300,000 

wells have been drilled in search of petroleun1 

deposits in the Texas and Louisiana gulf coast. 

A large amount of the information obtair~d from 

these wells has been made available to the U.S. 

Geological Survey for use in ongoing projects 

125 
......,. 

~ 

100° gao 96° 94° 

0 50 100 MILES I I I I I I 

0 50 100 150 KILOMETRES 

30° 

Gulf of Me)licO 

28° 

26° 

41c.t,co 

100° 98° 96° 94° 

92o 90° 

( 

, ... 

r MISSISSIPPI 

L 0 U I ~---------------~ S I.A N A I 

92o 

' ' ' .. , 

90° 

28° 

26° 

FIGURE 15.-Location map showing the extent of the assessed geopressured zones and their division into subareas (AT1, BT1, and so on). 
examining the hydrogeology of the northern 

Gulf of Mexico basin. Of the vast quantities of 

data on subsurface conditions that are in the files 

of these projects, only a sinall fraction was used 

in this study. As noted, many promising areas 

were not included. The data presented here represent general conditions in the various regions outlined. Information on geologic struoture, sand 

thickness, ten1perature, and pressure were adequate for the purpose of this study. On the other 

hand, sufficient dat:a on porosity, permeability, 

and salinity were not available. Note that conditions presented here nre idealized and represent 

best estimates based on the rather small san1ple of 

the total available data that were examined within the limited period of time availahle for this 

preliminary assessment. The basis on which 

various data presented in this chapter were 

detern1ined, calculated, or assumed is discussed 

1n the "Appendix" to this report. 

DIVISION OF THE STUDY AREA INTO 

SUBAREAS 

For this investigation, the study area, which 

encmnpasses 89,038 km2 in Texas and 56,227 km2 

in Louisiana, w·as divided into 21 subareas (fig. 

15). The boundaries of these subareas were selected on the basis of the geologic history and 

structure of the study area. 

Since Mesozoic time, great river systems have 

been dumping large volumes of sand and clay 

along the northern Gulf of Mexico shoreline and 

shifting its loc~s gulfward. The process is continuing today. Interconnected fault trends or 

flexure faults· developed along the gulfward margin of each sedimentary sequence as it was overridden by its successor. Con1partmented sand and 

shale beds between these fault trends lie roughly 

parallel to the shoreline of the Gulf of Mexico. 

Age of the deposits, as well as fault trends, decreases coastward. The "A" trend (fig. 15) generally coincides with the subsurface distribution 

of Eocene Wilcox sediments; the "B" trend with 

Jackson-Y egua beds; the "C" trend with FrioVicksburg; the "D" trend with Frio; the "E" 

trend with Frio-Anahuac; and the "F" trend 

with Miocene and younger deposits. 

These features provided the basic concept for 

subdivision of the study area. Structural geologic 

maps of excellent quality prepared for. the U.S. 

Geological Survey by Peppard, Souders, and Associates were used to delineate faults that bound 

these trends and form the boundaries of the subareas along the trends. Massive shale secuences, 

although expected to contribute significant 

amounts of water to adjacent sand beds, are assumed to form the subarea boundaries perpendicular to the various trends. 

The geopressured zone to be assessed within 

each subarea was assumed to extend fr'lm the 

average depth at which pressure exceeds hydrostatic down to the maximum depth of wa.ll control. On the basis of an examination of 5 to 

about 95 wells in each subarea, depending on its 

size, the depths of 6 km in Texas and 7· km in 

Louisiana were chosen as reasonable lower limits 

to which available well control could be extrapolated. 

The areal extent of each subarea, as determined 

by planimetric methods, the average depth to 

the top of geopressure, and the average pressure, 

temperature, and salinity at or near the rridpoint 

betwe~n the assumed upper and lower limits of 

the geopressured zone in each suoorea ~.re presented in table 21. These average values, which 

were determined as explained in the "AprQ,ndix," 

are assumed to be representative of conditions in 

each subarea. 

IDEALIZED "CONCEPTUAL RESERVOIRS" 

The sediments within the geopressured zones of 

the study area form a very complex hydrogeologic system. They consist of interbedded sand 

and shale layers that range in thickness from less 

than 1 to more than 1,000 m. A thorough analysis 

of such a system requires data and an interpretation of a complexity that is beyond the scope of 

this study. To simplify the analysis, the geopressured zone within each subarea was idealized 

as a "conceptual reservoir." The effect of using 

these idealized conceptual reservoirs on the energy assessments that are presented in thi~ report 

is discussed after each assessment. 

The conceptual reservoirs were assumed to 

have a total thickness equal to the assume-! thickness of the geopressured zone in each subarea 

and to consist of a single sand aquifer underlain 

and overlain by two single confining shde beds. 

Both the sand aquifer and the confinirg· shale 

beds were assumed to be continuous and to exist 

throughout each subarea. The assumed thi~lrne.sses 

and properties of the sand aquifers anc1 of the 

127 
Table 21.-Areal extent and average pressure, temperature, and salinity conditions in each sub~rea 

Average Average AveraCle 

depth depth salinity 

Areal to top of to Averaqe Average --------- Subarea Extent geopressure midpoint pressure temperature 

km2 MN/m2 No. of TDS 

km km oc samples q/ I 

AT1 8,948 2.36 4.18 82.4 186 16* 

ATL 2 20,965 2.47 4.23 78.5 156 20* 

qTl 13,588 1.82 3.91 74.6 170 362 30 

BT2 5,595 2.32 4.16 81.4 150 50 38 

cr1 8 ,'230 2.47 4.23 81.4 172 20 24t 

or1 4,861 2.92 4.4f 88.3 172 95 23 

DT2 5,155 2.68 4.34 86.3 169 2 33 

DT3 7,425 2.41 4.20 80.4 153 67 28 

DTL4 5,102 2.62 4.31 83.4 141 18 46 

DL 5 7,015 3.01 5.01 102.0 164 222 65** 

OL6 3,729 3.05 5.02 104.0 160 14 5stt 

ETl 5,400 2.96 4.48 83.4 168 34 34t 

ET2 1,938 2.63 4.32 83.4 166 24 17 

ET3 7,496 2.37 4.19 80.4 146 65 27 

ETL4 3,461 2.63 4.31 87.3 140 14 52 

EL 5 8,144 3.66 5.33 106.9 165 39 90** 

EL6 8,849 3.32 5.16 105.0 159 87 83 

EL7 6,249 2.99 5.00 100.1 146 9 26 

n, 2,269 3.11 4.55 86.3 171 5 15t 

FL 2 4,707 3.76 5.38 105.0 148 46 84tt 

Fl3 6,139 3.88 5.44 110.8 151 11 45tt 

Total 145,265 ··------ * Estimated; samples not available. 

t Salinity as NaCl calculated from spontaneous potential of well logs; number of samples refers to 

number of well logs. ** Only few samples from deep zones are included. 

tt No samples from deep zones are included. 

128 
Table 22.-Assumed thickness and properties of sand and shale beds in idealized "conceptual reservoirs" 

Sand aquifer Upper shale bed Lower shale bed 

Total 

Reservoir reservoir No. of Extrapolated Average Average Assumed Assumed Assumed Assumed 

thickness wells thickness permeability porosity thickness porosity thickness porosity 

km km md % km % km % 

AT1 3.64 13 0.63 20 18 1.80 .,6 1.21 12 

ATL1 3.53 33 0.91 35 21 1.40 17 1.22 11 

BT1 4.18 9 0.56 15 18 1.89 18 1. 73 12 

BT2 3.68 6 0.55 20 20 1.82 17 1. 31 11 

cr1 3.53 5 1.14 20 19 1.37 17 1.01 11 

or1 3.08 9 1.22 25 19 1.19 16 0.67 11 

DT2 3.32 4 0.54 20 20 1.74 16 1.04 11 

~ OT3 3.59 7 0.55 25 20 1. 71 16 1.33 12 ~ 

~ 

DTL4 

3.38 8 0.41 30 21 1. 75 16 1.22 ll 

DL5 3.99 15 0.56 ~5 20 2.22 14 1.21 10 

OL6 3.95 4 0.76 25 20 2.14 14 1.05 10 

ET1 3.04 4 1.50 20 19 0.88 16 0.66 11 

ET2 3.37 4 0.61 30 20 1.63 16 1.13 11 

ET3 3.63 12 0.74 35 21 1.63 17 1.26 11 

ETL4 3.37 9 0.42 30 21 1.90 16 1.05 11 

EL5 3.34 13 0.67 40 21 1.78 13 0.89 10 

EL6 3.68 12 0.75 40 21 1.95 14 0.98 10 

EL7 4.01 7 1.02 40 21 1.87 15 1.12 9 

FT1 2.89 4 0.93 25 20 1.18 15 0.78 11 

FL2 3.24 6 0.90 50 22 1.49 13 0.85 10 

FL3 3.12 9 0.66 40 22 1.73 13 0.73 9 
confining shale beds for each of the idealized conceptual reservoirs are presented in table 22. Also 

shown on this table are the number of wells used 

in each subarea to extrapolate the cun1ulative 

thickness of sand beds observed in wells to the 

assu1ned 6- or 7-km bottmn of the geopressured 

zones. The permeability of both the upper and 

lower shale beds in all the conceptual reservoirs 

was assumed to have a uniform value of 0.0001 

n1illidarcy (mel) and therefore is not given in 

this table. This per1neability for the confining 

shale beds is low enough to provide an effective 

barrier for the n1aintenance of high pressures in 

the sand aquifers but also high enough to account 

for the significant amounts of water that these 

undercon1pacted shale beds are expected to contribute from storage in response to pressure declines in the sand aquifers. Other calculated aquifer parameters and water properties used in the 

evaluation of these idealized conceptual reservoirs 

are given in table 23. The storage coefficients presented in this table are based on an assumed uniform specific storage of 3.3 X 10- 6 per metre for 

the sand aquifers. Similarly, a unifonn "shortterm" specific storage of 3.3 X 10- 4 per metre was 

assumed for the confining shale beds. For further 

details on the assumptions and the methods used 

in calculating the para1neters in table 23, and on 

other parameters used in the analysis, the reader 

is referred to the "Appendix." 

ASSESSMENT OF THE ''FLUID RESOURCE 

BASE" 

The term "fluid resource base" as used in this 

report refers to the energy contained in the waters 

stored in the sand and shale beds of geopressured 

reservoirs. These waters are hot, confined under 

high pressures, and assun1ed to contain dissolved 

methane. Thus, the fluid resource base consists of 

the thermal energy, the mechanical energy, Q,nd 

the methane contained in these waters. The fluid 

resource base as defined above was assessed for 

each of the 21 conceptual reservoirs in the study 

area. The results of this assessment are presented 

in table 24. 

The volume of water stored in the sand and 

shale beds of each reservoir was calculated by 

using the assumed sand and shale bed thicknesses 

and porosities shown in table 22. The thennal energy in this volume of stored water was taken as 

the heat content above 15°C. "In situ" densities 

(see table 23)-that is, densities. cc~rected to the 

average pressure, temperature, and salinity conditions given in table 21-and an average specific 

heat of 4,100 joules per kilogram per degree Celsius ( J /kg/°C), corresponding to thf, average pressures and temperatures, were used to assess the 

thern1al energy of each reservoir. ':':'he volume of 

dissolved methane was obtained by using the calculated methane content (see table 23), converted 

to thermal energy by assuming a heat equivalent 

of 3.77 X 107 J /standard 1113 of methane. 

The 1nechanical energy in each reservoir was 

calculated as the energy that could be produced 

by the volume of water that would be released 

from storage in the sand and shale beds if the 

hydraulic head throughout the conceptual reservoir declines to the land surface. No tin1e limitations were placed on the decline, but it was assumed that the decline is linear '""'ith time and 

that, therefore, the average operating head would 

be equal to one-half- the initial hfad. 

To provide a basis for comparison with the 

thermal energy in other geothermal systems assessed in the various reports of this circular, the 

totals of the estimates of table 24 are summarized 

here in terms of their equivalent: 

OaZorles 

Thermal energy -------------------------- 10,920Xl()18 

Methane: 

Volume: 6.7Xl014 standard m3 

Thermal equivalent 

Mechanical energy : 

6,030Xl()18 

Thermal equivalent ------------------ 50Xl()18 

Total thermal equivalent ---------- 17,000Xl()18 

This preliminary assessment of the fluid resource base of geopressured-geothermal reservoirs 

within the onshore Tertiary sediments of the 

northern Gulf of Mexico basin indicates that 

the energy stored in the waters of these reservoirs is very large. However, this assessment is 

based on idealized conceptual resf~voirs and on 

several assumptions about the physical properties 

of the reservoirs and of the waters stored in them. 

The possible effects of this idealization of the 

reservoirs and of the assumptionf' made in the 

assessment are discussed ·briefly below. 

Discussion of the reliability of fluid resource. base assessment 

The mechanical energy con1pone~t of the fluid 

resource base is so small com pared to the other 

two components that any discussi0n of possible 

errors in its assessment is not war·anted. There130 
Table 23.-calculated aquifer parameters and water properties used in this study 

-~--------- -------

Aquifer Parameters Water Properties 

Reservoir Hydraulic Transmissi- Storage Average Density Methane:~t 

head* vity coefficient ·r- content 

(LSD) In situ At surface** 

m 10-4 m2/s 10-3 kg/m 3 kg/m 3 3 3 std. m /m 

----------- ---

AT1 4,750 6. 1 2.1 941 893 11.0 

ATL 2 4,060 15.0 3.0 966 925 8.4 

BT1 4,010 4. 1 1.8 961 920 9.5 

BT2 4,310 5.3 1.8 980 944 7.5 

cr1 4,450 11.0 3.8 957 913 8.9 

or1 4,920 15.0 4.0 96_0 913 9.1 

DT2 4,740 5 .. 2 1.8 %9 ~23" 9.2 

DT3 4,210 6.7 1.8 975 934 8.0 

DTL4 4,220 6.0 1.4 997 957 7.3 

DL 5 5,360 6.8 1.8 1,003 949 8.0 

DL6 5,590 9.2 2.5 1,000 946 8.3 

ET1 4,300 15.0 5.0 969 925 8.8 

ET2 4,560 8.9 2.0 958 914 9.4 

ET3 4,170 13.0 2.4 981 940 7.8 

ETL4 4,550 6.1 1.4 1,005 962 6.7 

EL 5 .5,340 13.0 2.2 1,022 964 8.0 

EL6 5,340 15.0 2.5 1,020 965 7.7 

EL7 5,330 20.0 3.4 988 939 8.5 

FT1 4,590 11.0 3. l 963 908 10.2 

FL2 5,040 22.0 3.0 1,028 975 7.3 

FL 3 5,830 13.0 2.2 1,003 948 8.2 

* Based on average pressure and in situ density. 

t At average pressure, temperature, and salinity. 

** At saturation pressure and average temperature and salinity. 

tt· Based on solubility of methane at average pressure, temperature, and salinity. 

131 
Table 24.-Assessment of the "fluid resource base" 

Volume ~1ethane Energ~ r~echani ca 1 of \tater Thermal energy Reservoir in storage energy Volume Thermal 

eouivalent 

lo12 m3 1020 J 10 12std. m 

3 1020 J 1020 J 

AT1 4.91 32.4 54.0 20.4 0.1 

f\TL 2 11.80 66.1 99.4 37.5 0.2 

sr1 8.81 53.8 83.7 31.6 0.2 

BT2 3.14 17.0 23.6 8.9 0.1 

cr1 4.62 28.5 41.1 15.5 0.1 

or1 2.39 14.8 21.7 8.2 0.1 

DT2 2.56 15.6 23.5 8.9 0.1 

DT3 4.04 22.3 32.3 12.2 0.1 

DTL4 2.55 13.1 18.6 7.0 0.1 

DL 5 3.82 23.4 30.6 11.5 0.2 

DL6 2.06 12.2 17. 1 6.5 0.1 

ET1 2.69 16.3 23.7 8.9 0.1 

ET 2 0.99 5.9 9.3 3.5 0.0 

ET3 4.28 22.6 33.4 12.6 0.1 

ETL4 1. 73 8.9 11.6 4.4 0.1 

EL5 3.75 23.6 30.0 11 . 3 0.1 

EL6 4.61 27.7 35.5 13.4 0.2 

EL7 3.70 19.6 31.5 11.9 0.1 

FT1 1.02 6.3 10.4 3.9 0.0 

FL2 2.25 12.6 16.4 6.2 0.1 

FL3 2.67 14.9 21.9 8.3 0.1 

----

Totals: 78.39 457.6 669.3 252.6 2.3 

132 
fore, the discussion is' limited to the thermal and 

methane energy components. The variables directly involved in the assessment of the thermal 

and methane energy components of the fluid resource base are the volume of water stored in the 

geopressured zone and its density, specific heat, 

temperature, and methane content. 

The volume of the stored water depends on the 

thickness and porosity of the sand and shale beds. 

The estimates of cumulative sand and shale bed 

thicknesses are relioable (see the "Appendix"). 

The fact that the sand and shale consist of several interbedded units rather than the massive 

si;ngle beds that are assumed for the conceptual 

reservoirs does not affect the volume of water 

stored in them. The porosities of the sand beds 

were estimated from data above or just below the 

top of the geopressured zone, and that of the 

shale beds from porosity /depth-of-burial relations for the gulf coast shale be.ds (Dickinson, 

1953). The porosities given in table 22 could be 

in error by two or three percentage points. This 

would result in an error of about 20 peroent in 

the estimated volume of stored water. The estimates of average temperature and the calculations of the in situ density and specific heat are 

fairly reliable, and their combined error could 

not be more than 5 percent. In contrast, the estimates of methane content are not very reliable. 

No actual measurements of the methane content 

of wa:ters from the geopressured zone were a vailable. The assumed methane content is based on 

the solubility of methane at the average temperature, pressure, and salinity of the reservoir 

waters, as deduced from the knowledge that 

waters in nongeopressured zones of the gulf coast 

contain dissolved gas, primarily methane, at or 

near saturation (see the "Appendix"). 

A lower bound for the fluid resource -base assessment can be obtained by completely neglecting the mechanical energy component, conservatively assuming that the methane content is onefourth of that used in the assessment and assuming that the possible errors discussed above are 

all in the direction of reducing rather than increasing the energy. This lower bound is 398.3 X 

1020 J ( 9,500 X 1018 cal), or about 56 percent of 

the estimate otherwise obtained-still a very large 

amount. 

ASSESSMENT OF RECOVERABLE ENERGY 

The recoverability of energy from geoprcssured 

reservoirs ultimately depends on the amount of 

water than can be produced by wells tapping 

these reservoirs. Therefore, to assess the recoverable energy, a development plan that specifies 

the production period, the desired flow rate of 

wells, and the allowable drawdown (or wellhead 

pressure) needs to be selected. The num her of 

wells that can be placed under this plan and the 

total produotion of water are then determined. 

The flow rate and the number of wells are interdependent (fig. 16). Note that for a given set 

of reservoir and well conditions and for a specified drawdown and production period, tr~ flow 

rate varies with the well spacing and consequently with the number of wells that are placed 

in a reservoir. As the well spacing increafes, the 

flow rate per well also increases until a maximum 

flow rate is reached. This maximum flow rate 

corresponds to a spacing at which interference 

between wells becomes negligible, and it is controlled mainly by the transmissivity of th€, reservoir (Papadopulos, 1975). At a smaller well 

spacing, well interference causes the flow rF~te per 

well to decrease. However, as the well S:'"lacing 

decreases, th~ number of wells that can be placed 

in a reservoir increases faster than th~ rate at 

which the flow rate per well decreases. Therefore, 

the total production from the reservoir, that is, 

the product of the number of wells anc1 their 

flow rate, also increases with decreasing well 

spacing. 

A development plan for recovering energ:r from 

geopressured reservoirs cannot be selected only 

on the basis of hydrogeologic factors. Economi_c 

and environmental factors also have to 1::~ considered and will probably govern the selootion of 

the development plan. An optimum plan would 

be one that maximizes economic benefits and 

minimizes the environmental effeots of the development. Distinction should be made here between a plan that is economically feasible and an 

optimum plan. Any plan that has a benefit-cost 

ratid larger than one (including tangible or intangible environmental costs) is economically 

feasible. Among several economically f,~asible 

plans, the one providing for the maximum net 

133 
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10-51 IIIII J . I I I I ! I I t I I I I I 1 I 3 4 [, I P e 1Q { .; 4 r;:, 

WELL SPACING, IN KILOMETRES WELL SPACING, IN KILOMETRES 

FIGURE 16.-Variation of well spacing with the ratio of flow rate to the 20-year formation drawdown for each of the 

conceptual res·ervoirs. 
benefits is the optimum· plan. Intuitively, because 

of the high cost of drilling deep wells in geopressured reservoirs, a plan that develops the 

reservoirs with wells having the maxinn1m possible flow raJte m·ay appear to be the most desirable. 

However, such a plan is the least likely to be the 

optimum for the developrnent of the reservoir. 

For example, in the conceptual reservoir AT ~ 

wells placed at a spacing of about 40 km would 

be producing at the rnaximum possible flow rate 

for wells in this reservoir, which is 3.3 X 10- 4 

m3/s per metre of drawdown (see fig. 16). One 

such well can be placed in every 1,600 km2 of 

area. On the other hand, if wells are placed at 

one-half this spacing, that is, 20 km apart~ the 

flow rate decreases only slightly to 3.1 X 10- 4 

m3/s per metre of drawdown. At this spacing, 

four wells can be placed in the same 1,600-km2 

area. Assuming that both of these development 

plans are economically feasible ·and that costs per 

well are nearly the same, the one-well plan would 

have a slightly higher benefit-cost ratio than the 

four-well plan. However~ the net benefits from 

the four-well plan would be almost four times 

those of the one-well plan. Thus~ if only these two 

plans were to be considered, the four-well plan 

would be the optimum. 

Selection of an optimurn plan of development 

obviously requires complex studies of economic 

and environmental factors. In the absence of such 

economic and environmental studies, which are 

beyond the scope of .this report, three assumed 

development plans were selected to provide 

"order-of-m-agnitude"-type assessments of the energy recoverable from the conceptual reservoirs. 

The assumed development plans consist of a 

basic plan, to be referred to -as Plan 1, and of 

two modifications of this basic plan, referred to 

as Plan 2 and Plan 3. 

Plan 1 is the following: The conceptual reservoirs are to be developed with 0.23-m-diameter 

wells, each capable of sustaining a flow rate of 

0.15 m3/s for a period of 20 years at :a wellhead 

pressure that gradually declines to ·a minimum 

value of 14 meganewtons per square metre (MN/ 

m2 ), or 2,000 lb/in2, at the end of the 20-year 

production period. This basic plan has been used 

in previous studies (Parmigiano, 1973; Papadopulos, 197 5) . However, the selection of this 

plan, and of its modifications discussed below, has 

been completely arbitrary. The data provided in 

this report and figure 16 can be us:-.d to evaluate 

possible development plans other tl'('l,n those considered here. Examples illustrating the use of 

figure 16 for evaluating various plans are given 

in the "Appendix." 

The results of the assessment of recoverable energy from each of the conceptual refervoirs, under 

the assumed Plan 1~ are presented in table 25. 

These results are summarized her~, in terms of 

their equivalent: 

OaZorieB 

Thermal energy -------------------------- 229.4X1()18 

Methane; 

Volume : 13.8 X 1012 standard m3 

Thermal equivalent ------------------- 124.2X1ot8 

Mechanica'l en~rgy : 

Thermal equivalent ------------------- 9.4X1ot8 

Total thermal equivalent ------------ 363.0X1ot8 

Recovery of this energy, which is about 2.1 percent of the total fluid resource base, requires 

17,160 wells at -a spacing ranging f'~On1 2.3 km in 

subarea EL7 to 3.9 km in subarea BT 1• 

The mechanical energy component of this assessment is only 2.6 percent of the total recoverable energy. To recover this small percentage of 

energy, the wellhead pressure is restricted to a 

minimum of 14 MN/m2 • The head equivalent of 

this pressure is about 1,500 n1, or about one-third 

of the initial head in most of the conceptual 

reservous. 

In Plan 2, recov·ery of the mecr~nical energy 

is neglected by removing this restriction on wellhood pressure and allowing the w~lls to use almost the entire initial head over th~ 20-year production period. The energy recoverable under 

Plan 2 consists of only thermal and methane 

energy. The results of this assessment are : 

OaZorieB 

Thermal energy -------------------------- 358.8X1018 

Methane: 

Volume: 21.6X1012 standard m3 

Thermal equiV'alent ------------------- 193.6X1()18 

Total thermal equivalent ----------- 552.4X1ot8 

The number of wells required k recover this 

energy, which is about 3.3 percent of the fluid resource base, is 25,840 with well spacings that 

range from 1.9 to 2.9 km. 

Plans 1 and 2 do not consider any restrictions 

that might be imposed by environrnental factors. 

Subsidence, for example, could p1se major re136 
Table 25.-Assessment of "recoverable energy" under the assumed basic development plan, Plan 1 

Available Flow rate- Number Volume Methane Enerqy 

formation drawdown Well of of water Thermal 

Reservoir drawdown ratio spacing wells produced enerqy Volume Thermal Mechanical 

equiva1e"'t energy 

m 10-5 m2/s km 1010 m 3 1018 J lo10std. 3 

m 1018 J 1018 J 

AT1 3,060 4.9 3.1 930 8.80 58.5 96.7 36.5 2.1 

ATL 2 2,410 6.2 3.1 2,180 20.64 117.1 173.3 65.4 4.5 

sr1 2,370 6.3 3.9 890 8.43 52.2 80.1 30.2 1.8 

BT 2 2,690 5.6 3.5 450 4.20 23.6 32.0 12. 1 l.O 

cr1 2,780 5.4 2.6 I ,210 11 .46 71.5 102.0 38.5 2.6 

or1 3,250 4.6 2.4 840 7.95 49.6 72.4 27.3 1.9 

DT2 3,090 4.9 3.2 500 4.73 29.3 43.6 16.5 1.1 

DT 3 2,580 5.8 3.5 600 5.68 31.9 45.5 17.2 1.3 

DTL4 2,620 5.7 3.7 370 3.50 18.4 25.6 9.7 0.8 

oL5 3,730 4.0 2.9 830 7.86 48.4 62.9 23.7 2.1 

DL6 3,950 3.8 2.5 590 5.59 33.3 46.4 17.5 1.5 

ETl 2,640 5.7 2.4 930 8.80 54.2 77.5 29.2 2.0 

ET2 2,900 5.2 3.2 190 1.80 10.8 16.9 6.4 0.4 

ET 3 2,550 5.9 3.2 730 6.91 37.0 53.9 20.4 1.5 

ETL4 2.950 5.1 3.5 280 2.65 13.9 17.8 6.7 0.6 

EL5 3,730 4.0 2.7 1 '110 10.51 66.2 84.1 31.7 2.8 

EL6 3,730 4.0 2.6 1 '31 0 12.40 75.1 95.5 36.0 3.3 

EL 7 3.680 4.1 2.3 1 '180 11.17 59.8 95.0 35.8 2.9 

FTl 2,920 5.1 2.7 310 2.93 18.1 29.9 11.3 0.7 

FL2 3,430 4.4 2.5 750 7.10 40.1 51.8 19.6 1.8 

FL 3 4,180 3.6 2.5 980 9.28 52.0 76.1 28.7 2.6 ----

Totals 17 '160 162.33 961 .0 1,379.2 520.4 39.3 

137 
strictions to the maximum drawdowns that can 

be used in developing geopressured reservoirs, especially near coastal areas of low elevation. 

Crude estimates, obtained by calculating the 

volume of water contributed from storage in the 

shale beds of the conceptual reservoirs (see the 

"Appendix") and assuming that this will result 

in equal emnpaetion of the shale beds and that 

this compaction, in turn, will be transmitted to 

the land surface without reduetion, indieate that 

average subsidence under Plan 1 could range 

from about 5 to over 7 m. 

In Plan :3, the nutximum drawdown is restricted, or the, wellhead pr,essure inereased, sueh 

that the ,average subsidence, calculated as described above, does not exeeed 1 m. The energy 

recoverable under Plan 3 is: 

Thennal energy ------------------------- Methane: 

Volume: 3.2xl012 standard m3 

Thermal equivalent ------------------ Mechanical energy, thennal equivalent ____ _ 

Total thermal equivalent -----------

Calories 

53.1X1018 

28.8X1018 

3.3Xl0u> 

85.2Xl018 

Recovery of this energy, whieh is about 0.5 percent of the total fluill resource base, requires 

about 3,970 wells placed at spacings I'anging from 

4.8 to 7.2 km. 

These assessments consisted uutinly of cletermining the well spacing and consequently the 

number of wells that can be developed in each 

conceptual reservoir under the assumed plans. 

Techniques developed in the evaluation of the 

energy potential of a ''typical" gulf coast geopressured reservoir (Papadopulos, Hl75) were 

used to prepare for each conceptual reservoir a 

plot of the variation of the flow rate per unit 

20-year forn1ation drawdown, that is, the drawdown in the aquifer just outside the well, which 

is equal to the drawdown in the well less the pipe 

friction and other losses, against well spacing for 

wells placed on a square grid. These plots are 

shown in figure 16. To prepare these plots, the 

transmissivity and storage copffieients for each 

sand aquifer (see table, 23) and the assumed hydraulic properties of tlw confining shale beds ( se<' 

the "Appendix") were used in well-flow equations that take into account the effects of leakage 

from storage in the shale beds (Hantush, Hl60). 

For reservoirs where tlH' hydranlie properties of 

the sand aquifers WC're the same or very similar, 

as for example BT2 and DT2, only one plot was 

prepared. 

The 20-year available formation drawdown for 

each reservoir was calculated by subtracting from 

the initial hydraulic head of the reservoir the 

assumed maximum drawdown, or the head corresponding to the assun1ed 1ninimum wellhead pressure, and the pipe friction losses (se~ the "Appendix") for the assumed well diameter and flow 

rate. The ratio of the flow rate to the available 

dra wdown was then used to determine well spacing from figure 16. The area of infuence of each 

well was assumed to be equal to the square of the 

well spacing. The areal extent of each reservoir 

(se.e table 21) was then divided b? this area of 

influence to determine the number of wells that 

can be placed in a conceptual re~.ervoir under the 

assumed deve.lopment plan. 

The thermal and methane energy in the volume 

of water produced over the 20-year production 

period were calculated in a manr~r similar to 

tha.t used in the assessment of the fluid resource 

base, e.xe('lpt that de.nsity at satur~.tion pressure 

(see. table 23) and an average saturation pressure 

fo;pecific heat of 4,850 '-T/kg/°C (see the "Appendix") were used in the thermal energy calculations. 

On the basis of previous studief of the timedrawdown behavior of wells in idealized geopressured reservoirs having similar properties 

(Papadopulos, 1975), the "aver2''Se operating 

head" for the production of mechanical energy 

over the 20-year period was assuned to be the 

initial head less the pipe friction losses and less 

two-thirds of the 20-year formatio:'\ drawdown. 

The recoverable energy assessments presented 

above are only energy at the wellhead. Although 

the n1ethane is a resouree that cr.n be direetly 

marketed, thermal and mechanical energy probably will have to be converted to a more readily 

usable :form of energy such as electrical energy. 

Additional large energy losses will result from 

this conversion. The e-fficiency of co:'lverting thermal energy at the wellhead to ele~trical energy 

has been estimated to be 8 percent by N athenson 

and Muffler (this circular). The e.fihiency of converting mechanioal e.nergy to electrical energy is 

assumed to be 80 percent, although efficiencies as 

high as 90 percent have been used by House and 

otlH'rs (1975). App1ying these conversion efficiencies to the thermal and mechanical energy 

138 
components of the recoverable energy assessments 

results in the following estimates of electrical 

energy in megawatt· centuries and of electrical 

power in mega watts for the 20-year period : 

Development plan Electrical Electrical 

and energy power 

energy resource (MW•cent) (MW (20 yr)) 

Plan 1: 

Thermal energy ____ 24,380 121,900 

Mechanical energy __ 9,970 49,850 

Total ------------ 34,350 171,750 

Plan 2: 

Thermal energy ____ 38,140 190,700 

Plan 3: 

Thermal energy ____ 5,690 28,450 

Mechanical energy __ 3,560 17,800 

Total ------------ 9,250 46,250 

Note that, because of the one-order-of-magnitude 

difference in the conversion efficiencies for the two 

kinds of energy resource, the mechanical energy, 

which constituted only a very small pereentage 

of recoverable energy at the wellhead, under both 

Plan 1 and Plan 3, provides 29 percent and 38.5 

percent, respeetively, of the recoverable electrical 

energy. 

The variation in the recoverable energy with 

the eonditions imposed in different development 

plans further indicates the importance of detailed economic and environmental studies in 

seleeting an optimum development plan. It should 

be emphasized again that the assessments presented here ( 1) are not based on such economic 

and environmental studies, (2) are of the orderof-nragnitude type, and (3) -could ·be completely 

different than assessments based on an optimun1 

plan. 

In addition to subsidence~ briefly diseussed 

above, studies are also needed to determine the 

feasibility of disposing of t.he waste water hy 

injecting it into shallower saline aquifers, as suggested by Wilson, Shepherd, and I\:anfman 

(1974) and House, Johnson, and Towse (1975) 

or by diseharging it into the Gulf of Mexieo. Th~ 

geochemistry of the waters and the shale beds is 

another factor that needs to be studied. The Inenlbrane properties of the shale beds could play an 

important role in determining the amounts and 

quality of the waters that are contributed from 

the shale beds. The chemistry of the water could 

also create corrosion problems in the wells that 

would affect their flow rates. Another factor that 

could influence the economics of development and 

that needs to be investigated is the feaf;bility of 

converting unsuccessful or depleted oil and gas 

wells into production wells from the geo~ressured 

reservoirs. This list is by no means com'J)lete, but 

it points out the complexity of arriving at an 

optimum development plan for recovering energy 

from the goopressured reservoirs. 

Discussion of the reliability of the recoverable energy 

assessments 

The rnost important factor in the recoverable 

energy assessments is the total volume of water 

produeed by wells. The effect of selecting difierent development plans on the volume of produeed 

water has already been emphasized. Therefore 

the discussion here is limited to the reliability of 

the presented assessn1ents. Under the selected development plans that speeified the flow rate, the 

reliability of the produeed volume esti1nates depends on the effeets of the idealization of the reservoirs and on the reliability of the well-spacing 

determinations. 

The conceptual reservoirs were assum£'d to consist of a single sand bed underlain and overlain 

by two single shale beds that are eontinuous and 

exist throughout each subarea. The assmnption of 

two single confining shale beds would normally 

result in a smaller contribution of ws ter from 

storage than that expected in a system of interbedded sand and shale. However, this effect has 

been accounted for by assuming a lar~er than 

usual permeability for the shale beds (see the 

"Appendix"). Theoretically, assuming a single 

thick sand bed instead of multiple s:'lnd beds 

having the same total thickness would not have 

any effect sinee the transmissivity (hydraulic conductivity times thickness) is the same for both 

cases. However, underlying this theor~r is the 

assumption that in both cases the wells are open 

throughout the sand beds. Multiple completion of 

the wells in every sand bed would not be practically possible. Therefore, in the actual multiplesand-bed systems, wells would probably be completed only in the thick sand beds. Assur'ling that 

thick sand beds constitute at least 50 p~rcent of 

the cumulative sand thickness, the transmissivities 

of the conceptual reservoirs could be in error by 

about 50 percent. 

Existenee of t,he reservoirs through'lut each 

subarea should not be confused with continuity. 

Sinee the assumed development plans require a 

139 
large number of wells in each subarea, artificial 

boundaries would be created between wells. 

Thus, the effect of having compartmentalized 

reservoirs instead of one continuous reservoir 

would not be so critical, provided these compartments exist throughout the area and are larger 

than the area of influence of each well, that is, 

the square of the well spacing. The wells from 

the logs of which sand-·bed thicknesses were determined were rather uniformly distributed over 

the study area. These logs as well as others examined during the course of this study and of 

previous studies of the hydrogeology of the gulf 

coast indicate that sand -bed sequences exist 

throughout most of the study area, except in the 

areas where massive shale sequences were chosen 

as the boundaries of the subareas. Therefore the 

assumption that the reservoirs exist throughout 

the study area could result, at most, in an error 

of about 20 percent in the number of wells. 

The well spacing at a specified flow rate depends on the available drawdown and on the hydraulic parameters of the reservoir. The available drawdowns that were used in the assessments were calculated from the initial hydraulic 

head and the imposed wellhead conditions. The 

initial hydraulic heads were based on the average 

reservoir pressures, which are fairly reliable (see 

the "Appendix"). Therefore large errors in the 

assumed drawdowns are not likely. Furthermore, 

the available drawdowns are so large that, even 

if they are in error by 50 or 100m, the flow rate/ 

drawdown ratio does not change by much. Consequently, the well spacing that is determined 

from figure 16 by using this ratio will also not 

change appreciably. 

Permeabilities, which were used to calculate 

transmissivities, are believed to be the least reliable of the reservoir data used in this study. If 

permeabilities are assumed to be overestimated by 

50 percent, and this error is combined with the 

50-percent error assumed to be due to the idealization of the reservoirs, the transmissivities will be 

reduced to one-fourth of those assumed in table 

23. Therefore the effect of having one-fourth of 

the assumed transmissivities was examined. Under Plans 1 and 2, the drawdowns are large, ranging from 3,000 to 5,000 m, and cause the flow rate/ 

drawdown ratios to be small, from about 3 X 10- 5 

to 6X10- 5 m3 /s/m. At this range of flow rate/ 

drawdown ratios, the curves in figure 16, each of 

which is for a different set of transn1issivities and 

storage coefficients, are close to eac r other; therefore the well spacing does not vary much with the 

hydraulic parameters of the reserroirs. On the 

average, a 75-percent reduotion in transmissivities 

was found to increase well spacing under these 

two plans by about 0.5 km and to cause a reduction of about 25 percent in the nunber of wells. 

Under Plan 3, the dra wdowns are small, ranging 

from 750 to 1,200 m, ·and resu1t in flow rate/drawdown ratios from 1.25 X 10- 4 to 2.0 X 10-4 m3 /s/m. 

'\Vi thin this range, well spacing varies considerably with the hydraulic parameterE of the reservoir. Under this ·plan, a reduction of 75 percent in 

transmissi vi ties reduces the number of wells by 

about 60 percent. 

Lower bounds for the recoveral:le energy assessments are obtained by combining the effeots 

of the two factors discussed above on the volume 

of produced water, by assuming that methane 

content may be only one-fourth of saturation, and 

by assuming a combined error of al"lUt 5 percent 

in temperature, density, and specific heat. These 

lower bounds are: 

Lower bounds 

I (lO~I eal )_ 

Percent of 

ori ?inaJ assessments 

Plan 1 ------------ 155.0 

Plan 2 ------------ 233.5 

Plan 3 ------------ 19.5 

43 

43 

23 

The corresponding lower bounds for conversion 

of thermal and mechanical energy to electrical 

energy and to power are: 

Plan 1 -------- Plan 2 -------- Plan 3 --------

Lower bounds 

Electrical EJectrieaJ 

energy powe:"" (MW•cent) (MW (20 yr)) 

19,850 99,25() 

21,730 108,654'\ 

2,880 14,40" 

Percent of 

originaJ assessment• 

58 

58 

31 

Note that, because the greatest redu~tion is in the 

e~imates of methane, the reduction in the recoverable electrical energy is not a~ large as the 

reduction in energy at the wellhead. Also, if all 

the possible errors assumed in ol'~aining these 

lower bounds are valid, the resulting reservoir 

conditions may require completely different development plans for assessing the recoverable 

energy. 

ACKNOWLEDGMENTS 

Data and assistance from Exxon, Shell, Amoco, 

Atlantic-Richfield, Mobil, Sun, Phillips, and 

140 
Chevron in particular and the petroleum industry in general are gratefully acknowledged. More 

than 6,600 reservoir data records provided by the 

Computer Projects Unit of the Bureau of Natural 

Gas were a significant contribution to this study. 

REFERENCES CITED 

Culberson, 0. L., and McKetta, J. J., Jr., 1951, Phase 

equilibria in hydro carbon-water systems, III-The 

solubility of methane in water at pressures to 

10,000 PSIA : Am. lust. Mining Engineers Petroleum 

Trans., v. 192, p. 223-226. 

Dickinson, George, 1953, Geological aspects of abnormal 

reservoir pressures in Gulf Coast Louisiana : Am. 

Assoc. Petroleum Geologists Bull., v. 37, no. 2, p. 

41~32. 

Dorfman, Myron, and Kehle, R. 0., 1974, Potential geothermal resources of Texas: Texas Univ. Bur. Econ. 

Geology Circ. 7 4--4, 33 p. 

Durham, C. 0., Jr., 1974, Proposed geopressured energy 

investigation: Louisiana State Univ., School Geoscience Rept., 38 p. 

Haas, J. L., Jr., 1970, On equation for the density of 

.vapor-saturated NaCl-H20 solutions from 75° to 

325°C: Am. Jour. Sci., v. 269, p. 489-493. 

Hantush, M. S., 1960, Modification of the theory of 

leaky aquifers: Jour. Geophys. Research, v. 65, no. 

11, p. 3713-3725. 

Herrin, E., 1973, Development of geothermal reservoirs 

from over-pressured areas beneath the Gulf Coast 

Plain of Texas, final report: Air Force Office of 

Scientific Research TR-73-1344; March 1973, NTIS 

No. AD 766855, 148 p. 

Hottman, C. E., 1966, U.S. Pat. No. 3,258,069, June 28, 

1966. 

-- 1967, U.S. Pat. No. 3,330,356, July 11, 1967. 

House, P. A., Johnson, P. M., and Towse, D. F., 1975, 

Potential power generation ·and gas production from 

Gulf Coast geopressure reservoirs: California Univ., 

Lawrence Livermore Lab. Rept. 51813, 40 p. 

Jones, P. H., 1969, Hydrology of Neogene deposJts in the 

northern Gulf of Mexico basin: Louisiana Water 

Resources Research lust. Bull., GT-2, 105 p. 

----- 1970, Geothermal resources of the northern 

Gulf of Mexico basin : GeothermiC's, Spec. Issue 2, 

Part 1, p. 14-26. 

Meyer, C. A., McClintock, R. B., Silvestri, G. J., and 

Spencer, R. C., 1968, 1967 ASME steam tables (2d 

ed.) : Am. Soc. Mechanical Engineers, 328 p. 

Myers, B., Nelson, R., Howard, J., and Austin, R., 1973, 

Some elements of the northern Gulf of Me:dco basin 

geopressure energy source: California r"'iversity 

Lawrence Livermore Report UCRL-74807, 27 p. 

O'Sullivan, T. D., and Smith, N. 0., 1970, The solubility 

and partial molar volume of nitrogen and methane 

in water and in aqueous sodium chloride from 50° 

to 125° and 100 to 600 Atm: Jour. Phys. Chemistry, 

v. 74, no. 7, p. 1460-1466. 

Papadopulos, S. S., 1975, The energy potentitJl of geopressures reservoirs : Hydrogeologic factorf : Energy 

Conf. Proc. Austin, Texas, June 2-4, 1975. (in press) 

Parmigiano, J. M., 1973, Geohydraulic energy from geopressures aquifers: Louisiana State Univ., Baton 

Rouge, La., M.S. thesis, 104 p. 

Schmidt, G. W., 1973, Interstitial water comporUion and 

geochemistry of deep Gulf Coast shales t-Q.d sandstone: Am. Assoc. Petroleum Geologists Bull., v. 

57, no. 2, p. 321-337. 

Streeter, V. L., 1962, Fluid mechanics (3d ed.): New 

York, McGraw-Hill, 555 p. 

Wallace, R. H., 1970, Abnormal pressures and potential 

geothermal resources in the Rio Grande er..,bayment 

of Texas : Symposium on Abnormal Subsurface Pressure, 2d, Proc. Louisiana State Univ., Baton Rouge, 

La., p. 87-104. 

Wilson, J. S., Shepherd, B. P .. and Kaufmar, Sidney, 

1974, An analysis of the potential use of gf~Othermal 

energy for power generation along the Texas Gulf 

Coast: Dow Chemical U.S.A., Texas Div., 63 p. 

APPENDIX 

Discussion of Data Used in Assessment of Onshore Geopressured-Geothermal Resources in the Northern Gulf of Mexico Basin 

This appendix discusses the basis on which 

data presented in the various tables of this report 

were determined, calculated, or assumed. Other 

untabulated data and equations used in the assessments presented in this report are also discussed. Examples illustrate the use of the data for 

evaluating energy recovery plans other than those 

presented in the main text of the report. 

DATA ON AVERAGE CONDITIONS IN 

SUBAREAS 

Average depth to top of geopressure 

Geopressure, as used in this report, refers to a 

fluid pressure that is higher than hydrostatic. For 

the average salinities of 60 to 80 g/1 that are 

found in the hydrostatic, or normally pressured, 

141 
zones of the gulf coast, this corresponds to a 

vertical pressure gradient greater than 10.5 kilonewtons per square metre per metre (kN/m2 /m), 

or 0.465 lb/in2 /ft. In the southern half of the 

Texas coastal plains, a "top geopressure" map furnished by a major oil company was used to determine the average depth to the top of geopressure 

within each subarea. Pressure measurements 

available within the mapped area numbered 

from 22 to 432 detern1inafions per subarea. Outside the n1apped area, in the northeastern Texas 

coastal plain and in coastal Louisiana~ average 

depth to the top of geopressure was determined 

by using computer-derived shale density plots, 

well records, and geophysical log examination. 

Less control, therefore, was used in these areas 

because of the time required to process information. 

Average pressures 

Pressures at the midpoint depth of each subarea were obtained by averaging pressure data on 

shale density determinations from geophysical 

logs and on mud weights recorded within various 

depth intervals. Selected wells that approached or 

penetrated the midpoint depth were used. The 

resulting pressure determinations were compared 

with bottom-hole shut-in pressure measurements 

made during wireline or drill-stem testing and 

initial reservoir pressure measurements recorded 

with the Texas Railroad Commission or the U.S. 

Bureau of Nat ural Gas. Agreement between the 

data sets was very good. 

Average temperatures 

Temperature data were derived from measurements made during electrical well logging operations. These measurements were adjusted to 

equilibrium conditions using a correction equation developed by the American Association of 

Petroleum Geologists Geothermal Survey of 

North America. Mean depths of occurrence for 

six isogeothermal surfaces (70°C, 100°C, 12o,oc, 

150°0, 180°C, and 250°C) and average midpoint 

temperatures were calculated for each county 

(or parish) in the study area. County determinations were averaged to obtain midpoint temperatures within each subarea. Temperature control 

was most abundant within 20 southern Texas 

counties (Rio Grande en1bayment area). In this 

area, approximately 1,150 wells from a project 

data file of 11,000 reached or exceeded midpoint 

depths. Control was limited to about five wells per 

county in the northeastern half of the Texas 

coastal plain and in southern Louisiana. 

Salinity 

Salinity estimates were based upc"'l an evaluation of ·all chemical analyses from the geopressure interval available to the U.8 Geological 

Survey. In some instances, data frmn outside the 

interval n1ay have been included. In the southern 

Texas coastal plain (areas CT1, DT1, and E'"£1), 

salinities computed from electric logs (total dissolved solids and NaCl) were al~o available. 

Con1puted salinities in table 21 reprr,~ent an average of the salinity of each significant sand bed 

occurring in the interval from the tcry of the goopressure zone to the total depth of the well. In 

areas DT 1 and ET 1, calculated values were used 

as best ,available data. In area CT1, sufficient 

data were available for use of both sampled and 

calculated salinities. Results were very similar 

( 23,000 mg/1 versus 22,000 mg/1 tc~al dissolved 

solids). Most sampled data and many computed 

values used in these estimates were from the 

upper part of geopressured reservoirs. Within 

the geopressured zone, an irregular decrease in 

salinity with depth is usually obF~rved. Thus, 

average salinity values, shown on table 21 are 

probably high for the average mic.point depth. 

DATA ON PROPERTIES OF A CONCEPTUAL 

RFSERVOIR 

Thickness 

Sand aquifer.-The thickness of the sand acquifer was determined by averaging cumlative 

sand-bed thicknesses and percentage of sand for 

a number of wells within each subarea, as shown 

in table 22, in the interval between t.he top of the 

geopressure zone at the well location and the total 

depth of the well. This percenta~e was then 

applied to the interval between the, average top 

of goopressure and the 6- or 7-km depth (that 

is, the total thickness of the conceptual reservoir) 

to obtain an extrapolated thickness for the idealized aquifer. 

Confining shale beds.-The total thickness of 

the shale beds was calculated as the difference 

between the total thickness of the conceptual reservoir and the extrapolated sand-t~d thickness. 

This total shale-bed thickness wa~ distributed 

142 
between an upper shale bed and a lower shale bed 

by assuming the following: ( 1) the vertical 

flow in an undeveloped reservoir is steady ; therefore, if the permeability of both the underlying 

and overlying shale beds is assumed to be the 

same, the hydraulic gradient across them should 

be also the same, and ( 2) the fluid pressure at 

the bottom of the lower shale bed should not 

exceed 95 percent of the lithostatic pressure. 

Porosity and permeability 

Sand aquifer.-Porosity measurements from 

sidewall and conventional cores, representing 

thousands of wells drilled in the gulf coast, show 

a general decreasing trend with depth. Permeability values also tend to decrease with depth, 

the 1owest values being measured in the vicinity 

of the top of the geopressure zone. A highly 

variable but general increase in permeability 

occurs at intermediate depths within the zone of 

geopressure. Data available for the sand aquifer 

porosity-permeability estimates in table 22 were 

heavily weighed by samples from the uppermost 

sand beds of the geopressured zone and lowermost sand beds of the hydrostatic zone (that is, 

the "tightest" interval). Data from project files, 

published reports, regulatory agencies, and petroleum industry and industry service companies 

were organized and analyzed on an area-by-area 

basis. Observed permeabilities ranged from 0.1 

to \000 md and porosities from 12 to 30 percent. 

Real data from horizons selected for the idealized 

aquifers were scarce or absent from available 

records. The averages presented are generally 

not representative of the idealized aquifer zone. 

From the range of values observed and from conversations with petroleum industry scientists, it 

is probable that permeabilities of 100 to 400 mel 

are found in the more massive sand beds at 

depths greater than 4 km. The porosity of these 

sand beds could also be larger by as much as 5 

percent. 

Confining shale beds.-As in the case of the 

sand beds, the porosity and permeability of shale 

beds tend to decrease with depth, but a general 

increase of these parameters occur within the . 

geopressured zone. Schmidt (1973) reports that, 

in a well at the Manchester Field in Louisiana, 

shale-bed porosity decreased to 12 percent 

at a depth of 3.0 km, just above the top of geopressure, and then suddenly increased to 17 percent at a depth of 3.4 km, within the geopressured 

zone, gradually decreasing again to 12 percent 

rut a depth of 4.5 km. In the absence of S'lfficient 

specific d·ata on shale-bed porosities within the 

study area, . porosities for the shale beds were 

estimated by using (1) a plot of burial depth 

against porosity of the gulf coast shale beds, 

presented by Dickinson (1953), and (2) the 

assumed midpoint depths for the upr~r and 

lower shale beds. As stated in the rep'>rt, the 

permeability for all shale beds of the cor~sptual 

reservoirs was assumed to be 0.0001 m<l. This 

value of permeability is about two to three 

orders of magnitude higher than the permeability 

of normally compacted shale beds. Shde beds 

within the geopressured zone are undercompacted 

however, resulting in permeabilities larg~r than 

those of compacted shale beds. Furthermore, 

under actual reservoir conditions of interbedded 

shale and sand beds, several shale beds would be 

draining from both sides to adjacent sand beds 

that are developed, contributing a much larger 

amount of water to the sand beds than the shale 

beds of the idealized conceptual reservoir, which 

consist of only two beds, each draining on only 

one side. Thus, it is believed that for the analyses 

of this study .• which are based on the oor~eptual 

reservoirs, the assumecl shale-bed permeability is 

reasonable. 

Hydraulic head 

The hydraulic head above the midpoint of each 

conceptual reservoir was calculated by dividing 

the average pressure by the in situ denf1ty and 

the gravitational acceleration. This head v:as converted to head above land surface by sub~racting 

the average depth to the midpoint. Within the 

sand aquifer, this hydraulic head was assumed 

to be uniform. Within the upper confinirg shale 

beds, the head was assumed to vary uniformly 

from zero at the top, that is, hydrostatic, to the 

head of the sand aquifer at the bottom. T~,~ same 

hydraulic gradient was assumed to occur in the 

lower shale bed. As explained earlier, this assumption was also used in determining the shalebed thicknesses. 

Hydraulic conductivity 

The estimated or assumed sand- and sl' ".le-bed 

pern1·eabilities in millidarcys were converted to 

permeabilities in square metres. These permeabili143 
ties were then multiplied by the gravitational 

acceleration and divided by the average viscosity 

of the reservoir waters to obtain the hydraulic 

conductivities of the sand aquifer and of the 

confining shale beds. 

Specific storage 

The specific storage-that is, the vohune of 

water that a unit volume of the reservoir would 

release from storage under a unit decline of head 

-had to be assmned for both the sand aquifer 

and the eonfining shale beds. A specific storage 

coefficient of 3.3 X 10- 6 per 1netre was assun1ed 

for the sand heels in all of the conceptual reservoirs. 

The confining shale beds, which are undercompacted and expected to have a high compressibility, were assumed to have a speeific storage of 3.3 X 10- 4 per Inetre. This high specific 

storage, however. was used only for the "shortterm'' effects of the recoverability calculations. In 

determining the total volume of storage that could 

be released from storage, needed for the assessment of the mechanical energy component of the 

resource base, the average decline of head in the 

shale beds was first converted to an equivalent 

increase in burial depth by assuming a lithostatic 

pressure gradient of 22.6 kN /nl2 /m ( 1.0 lb/in2 I 

ft). The porosity corresponding to this equivalent 

burial depth was determined from the previously Inentioned plot of burial depth and porosity 

(Dickinson, 1953). The difference between the 

original porosity and the new porosity was then 

used to calculate the volume1 released from storage. 

Transmissivity and storage coefficients 

The transmissivity and storage coefficients for 

the sand aquifers were obtained by n1ultiplying 

the calculated hydraulic conductivities and the 

assumed specific storage for the sand aquifers by 

their extrapolated thickness. 

DATA ON WATER PROPERTffiS 

Density 

The "at surface" density of the geothermal 

waters-that is, the density at saturation pressure and at the average temperature and salinity 

-was calculated from data given by Haas 

(1970). The "in situ" density-that is, the density at the average pressure, ten1perature, and 

salinity-was calculated as follo~s. Densities 

for freshwater at the average ten1perature were 

calculated both at saturation pressure and at the 

average pressure using the 1967 P.SME Steam 

Tables (Meyer and others, 1968). The percent 

change of the freshwater density from saturation 

to average pressure was then applied to the atsurface density to calculate the in situ density. 

Methane content 

Gases dissolved in normally pressured gulf 

eoast fonnation waters consist primarily of 

methane. Minor amounts of other hydrocarbons 

plus carbon dioxide and nitrogen arc also present. 

Methane usually represents more than 95 pereent of the total vohnne. Assuming all of the 

dissolved gas to be 1nethane and correcting for 

salinity, data frmn dissolved gas aralyses of 134 

water samples taken frmn Tertiary sands in 79 

Texas wells were found to approximate saturated 

conditions as described by Culber2on and McJ{e.tta ( 1951, fig. 5, p. 226). Th~se sa1nples were 

frmn norn1ally pressured horizons. The highest 

pressure recorded was about 22 MN /m2 (3,200 

lb/in2 ), the highest temperature was about 102°0, 

and the highest dissolved gas content was 3.064 

standard m3 /nl3 reeorded from ·a water sam.ple 

with :J5.000 mg/1 total clissol vecl solids. 

Although the dissolved gas content of waters 

from geopressured zones has not been measured, 

on the basis of the above observation<;' these waters 

were assun1ed to be methane saturated. The 

methane content was determined by using curves 

of methane solubility in freshwater presented by 

Culberson and McKetta (1951, fig. 5, p. 226), 

which were extended and modified to correct for 

salinity by using an extension of a solubility 

table from O'Sullivan and Smith (1970, p. 1461). 

These extensions and modifications vrere in accord 

with trends shown and are nonline~.r. 

Kinematic viscosity 

For the range of the average pressures and 

temperatures of the reservoirs, the l·inen1atic viscosity of freshwater varies fron1 1.75 X 10- 7 to 

2.25X10- 7 m2 /s (1967 ASME E'team Tables, 

Meyer and others, 1968 ) . On this basis, an average kinematic viscosity of 2 X 10- 7 m2 /s was assumed for the calculations of transmissivities and 

hydraulic conductivities, and of the Reynold's 

number needed in the determination of pipe friction losses. 

144 
Specific heat 

The specific he.at of freshwater at the average 

temperatures found in the geopressure.cl reservoirs ranges from 4,060 t() 4,160 J /kg/°C at the 

average pressures and frmn 4,290 to 4,430 J/ 

kg/°C a:t saturation pressure (1967 ASl\fE Steam 

Tables, Meyer and others, 1968 ) . In this 

study, average values of 4,100 and 4,350 J /kg/°C 

were used for the specific heat at the average 

reservoir pressures and at saturation pressures, 

respectively. 

PIPE FRICTION AND WELL-FLOW 

EQUATIONS 

The head loss, hz, due to pipe friction in wells 

was calculated by using the Darcy-\Veisbach 

equation (Streeter, 1962), which, in terms of flow 

rate Q, well radius 'l'w, and well depth L, is expressed as 

h Q2L 

l=f·---

471"2l'-tv5g 

where f is a friction factor and g is a gravitational acceleration. The Reynold's number for 

the ·assumed flow rate, well radius, and kinematic viscosity was calculated to be 4.2 X 106 , a 

roughness coefficient of 1.65 X 10- 5 per metre 

was assumed for the well casing, and the friction factor corresponding to this Reynold's nunlber and roughness coefficient was found to be 

0.0118 by interpolating in a Moody diagram 

(Streeter, 1962). 

The well-flow equation used in the preparation 

of figure 16 is the "modified leaky aquifer" e.quation presented by Hantush (1960). The equation, 

which describes the. drawdown distribution s 

around a well producing at a constant rate Q 

from an infinite confined aquifer, allows for the 

effects of leakage from storage in both the upper 

and lower confining beds. The equation has the 

form 

where 

and 

Q s=-FJ('u., f3) 

471"T 

u=r2S/4Tt, 

{3=·r>../4. 

>..= (l{'S's/TS)lh+ (l{"S"s/TS)lh. 

and in which II (u, f3) is a tabulated function. 

r is distance from the well, T and 8 are the transmissivity and storage coefficients of the aquifer, 

respectively, t is time since the p1·oduction 

started, and /i', S's and /1", S"s are the hydraulic conduetivity and speeifie storage of the upper 

and lower confining heels, respectively. The equation iR valid for ""relatively small times" of t less 

than both (b') 28's/10J{' and (b")2S" 8 /10l{". 

For the smallest shale-bed thickness uswl in this 

study this relatively ~mmll time eovers a period 

up t() about 100,000 ( ! ) years. 

In the assmned recovery plans in which wells 

are plaee.d on a square grid. eaeh well can be 

assumed to be loeated at the eenter of a square 

re.se.rvoir having the dimensions of the wo.ll spacing. To apply the above equation, whieh is for 

an infinite aquifer, to a bouncle.d square aquifer, 

the method of images was used. The formation 

drawdown at the. well face was caleulatecl for a 

unit flow rate and different well spaeings, and 

the results were expressed in terms of the flow 

rate/drawdown ratio as shown in figure 16. 

The volume of leakage-that is, the volume of 

water eontrilmted from storage in the CQnfining 

beds-whieh was used to obtain erude esti1nates 

of possible subside.nee., as stated in the main text 

of this section, was ealenlated from the following equation (Hantush, 1960) : 

VL=Y 1--,;,/-+-[1-e*erfc(y;}i:)] 

{ 

'J 1 l 

y;;r;r 'YJt 

where 'YJ= T>..2/S, 

F=Qt=volume of produced water, 

and in whieh e:r: is the. exponential function and 

erfc (;r), the complementary error function, 

which are both tabulated funetions. Other symbols are as previously defined. Although Hantush (1~60) presents this equation for aquifers 

of infinite e.xtent, it ean be. shown that the equation iR equally applieable to hounded aquifers 

without modification. 

ILLUSTRATIVE EXAMPLES 

The following three examples illustrate the use 

of figure 16 for evaluating dPvelopment plans 

other than those considered in this report. It is 

assumed that a.Jl alternate plans will have a 20-

year production period. 'V ell diameters are also 

assumed to he of 0.23-m diameter. However, the 

curvPs in figure 16 are very insensitive to well 

diameter, and as sneh they ean be used for wells 

145 
of different dian1eter. Pipe friction losses, on the 

other hand, would increase very rapidly with decreasing well diameter. 

In the examples, the following symbols are 

used: 

Q = Flow rate of wells, 

ST = Drawdown in wells, 

'l'w = "\V ell radius. 

.Nw = Number of wells, 

D w = Depth of wells, 

Ts = Sand aquifer thickness, 

Tshu = Upper shale-bed thiek11ess, 

D gp = De.pth to top of geopre.ssnre, 

hL = Pipe frietionlosses, 

S1 = 20-y·par formation drawdown, 

l = "\V ell spacing, 

Aw = Area of influence of wells, 

A.T = Areal extent of reservoirs, 

02o = Average subsidence at the end of the 20-

year production period, and 

V L = Volume of leakage from storage In the 

confining shale beds. 

Emam.plei 

Given: 

find: 

Solution: 

Q=0.20 m3/s and 

ST=2,000 Ill, 

N "' in reservoir A 'I;_ for the specified Q 

and ST. 

Dw=Dgp+T.+Tshu 

From table-s 21 and 22: 

Dw=2,360+630+1.800=4,790 m. 

From pipe friction los.-; equation given in 

thi·s "Appendix": 

hL=300 m, 

Sr=ST-liL 

=2,000-300=1,700 m, m1d 

Q/S'r=1.18X10-4 m2/s. 

From figure 16 : 

l=5.3 km, and 

Aw=l2=28.1 km2

• 

From tahle :n : 

.h·=R.94.S km2

, and 

N w=A.T/A.w=318. 

Example II 

Given: 

find: 

Solution: 

Ema.mple III 

Given: 

find: 

Solution: 

1=10 km, and 

ST=2,000 m, 

() in reservoir AT1 for the specified l and 

S1·· 

~~rom figure 16: 

Q/Sr=2.35X10-4 m2/S, and 

S 1=Q/2.35X10-4 

=4.250 Q. 

From the pipe frietion loss equation with 

f=O.Ol18, Du,=4,790 111, and rw=0.115 m. 

11 [,=7 ,260 Q2 

BT=Sr+IIJ,=2,000 m, 

or 

7,260 Q2+4.250 Q-2,000=0. 

Soh'ing this quadratic equation and taking the poi':dtiYe root: 

(1=0.31 lll3/S 

Q=0.20 m' /~. and 

G;o=1.5 Ill 

N ""' l, and BT in reservoir AT1 for the 

specified Q and C20. 

From leakage equation given in this 

"Appendix": 

rr, =5.52X107 m3

, 

A .. u· =rdf,;o, 

Nuo 

=36.~ km2

, 

=}lT/liw, 

=243, and 

=v A.w, 

=6.06 km. 

From figure 16 : 

Q/Br =1.42X10-4 m3/s/m, and 

Br =0.20/1.42X10-4 

=LUO m 

}~rom pipe friction equation given in this 

"Appendix": 

11 L =300 m, and 

BT =Sr+ltL, 

=1.410+300, 

=1,710 m. 

Once the numbers of wells or the flow rate 

has been cle.termined, the volume of water that 

ean be produeed from the reservoir, and hence 

the energy reeoverable under the d~velopment 

plans of the above examples,ean be er1culated. 

146 
Assessment of Geother-mal Resources of the United States-1975 

Summary and Conclusions 

By D. E. White and D. L. Williams 

The appraisal of the geothermal resources of 

the United States presented here is as factual as 

we can provide fron1 available data. Much effort 

has been made in each individual chapter to specify the uncertainties and assumptions involved 

in each estimate; we urge that these uncertainties be kept in mind. The estimates should be 

regarded as first attempts that will need to be 

updated as new information becomes available. 

This assessment consists of two major parts: 

( 1) estimates of total heat in the ground to a 

depth of 10 km and ( 2) estimates of the part of 

this total heat that is recoverable with present 

technology, regardless of price. No atten1pt has 

been made to consider most aspects of the legal, 

environmental, and institutional limitations in exploiting these resources. 

DEFINITIONS 

Resource-related terms used in this circular 

are defined as follows : Geothermal resource ba.r;;e 

includes all of the stored heat above 15°C to 10 

km depth (under all 50 States). Geothermal resources are defined as the stored heat, both identified and undiscovered, that is recoverable using 

current or near-current technology, regardless of 

cost. Geothermal resources are further divided 

into three categories based on cost of recovery : 

(1) submarginal geothermal resources, recoverable only at a cost . that is more than two times 

the current price of competitive energy systems; 

(2) paramar.ginal geothermal resources, recoverable at a cost between 1 and 2 times the current 

price of competitive energy; and ( 3) geothermal 

reserves are those identified resources recoverable 

at a cost that is competitive now with other 

energy resources. The distinction betw~en resource base and resources is technologic, in contrast to the distinctions between submarginal resources, paran1arginal resources, and reserves, 

which are economic. 

RESOURCE BASE 

The three major categories of the resource base 

are shown in table 26. 

The hydrothermal convection systems of category 1 (Renner and others, this circula~) occur 

where circulating water and steam are tl'.'ansferring heat from depth to the near surfa(>,e; they 

tend to occur in areas of unusually gr"lat heat 

supply and favorable hydrology. These systems 

are relatively favorable for geothermal development because high temperatures occur near the 

ground surface and drilling costs are low. We 

have a sound basis for optimism that many concealed hydrothermal systems exist,and that they 

can be discovered (see Renner and otho.rs, this 

circular). 

The ho~, young igneous (volcanic) sy;;:tems of 

category 2 (Smith and Shaw; this circular) occur in regions where molten magma las been 

generated deep in the Earth's crust or mantle and 

has intruded upward into the shallow crust. 

Silicic magma (equivalent to granite where 

crystallized) commonly comes to rest as large 

masses at depths of a few kilometres, thus conserving its heat; basaltic magma, beir.g much 

n1ore fluid, is commonly erupted at the surface, 

where its heat is rapidly dispersed. Many young 

igneous systems and a few older still-hot. systems 

147 
Table 26.-Estimated heat content of geothermal resource base of the United States (heat in the ground r without 

regard to recoverability) 

Identified systems 

Number Heat Content, 1018 calli 

1. Hydrothermal convection systems 

(to 3 km depth, ~10,000 ft, near 

the maximum depth drilled in geotherma 1 areas). 

Vapor-dominated (steam) systems 3 

High-temperature hot-water 

systems {over 150°C) 63 

Intermediate-temperature hotwater systems (90° to 150°C) 224 

Total 290 

2. Hot igneous systems (0 to 10 km) 

Molten parts of 48 best known, 

including Alaska and Hawaii 

C rys ta 11 i zed parts and hot 

margins of same 48 

Total 

3. Re ional conductive environments 

0 to 10 km; all 50 states subdivided 

into 19 heat-flow provinces of 3 

basic types, Eastern, Basin-andRange, and Sierra Nevada). 

Total, all states 

26 

370 

345 

rv741 

"-·13 ,000 

rvl2,000 

~25,000 

"-·8 '000 '000 

Identified + estimate 

for undiscovered 

Heat Conten; 

1018 ca 1.1.. 

rv50 

rvl,600 

rvl,4CO 

'\·3,050 

'\,1 00 ,oco 

rv8,000,0CO 

Overall total (as reported, without 8,025,741 8,103,050 

regard to ~ig~ificant figures and uncerta1nt1es) 

ll 1018 calories equivalent to heat of combustion of rv690 million barrels of 

petroleum or ~154 million short tons of coal. 

148 
are identified but are not yet evaluated in detail. 

Estimates of the heat content of hot igneous systems, both evaluated and unevaluated, are included in· table 26. All these are favorable target areas 

in exploring for concealed hydrothermal convection systems. 

The stored heat of the conduction-dominated 

environments, category 3, is huge in quantity, 

even _though temperatures are low, because so 

much area and volume are involved (Diment 

and others, this circular) . Most of the heat is 

transferred from the deep, hot interior by thermal 

conduction through solid rocks, but some is generated by normal radioactivity of roc)rs, mainly 

in the upper crust. The entire United States is 

subdivided into 19 heat-flow provinces that, with 

present limited data, are classified into three 

basic types, each with characteristic trends in 

temperature with depth. The Basin and Range 

type has the highest temperature gradients; the 

eastern and Sierra Nevada types have much 

lower gradients except in special areas, such as 

.the gulf coast, which constitutes a special part 

of the resource base. Three kinds of potential 

energy are available from the geopressured pore 

fluids, including geothermal energy, n1echanical 

energy fron1 the overpressured fluids, and nlethane dissolved in the pore waters. Heat flows 

of the gulf coast are presumed to be similar 

to the eastern type, but adequate data are lacking. Ten1perature gradients however, ar£ higher 

than in most of the eastern· region because the 

high-porosity sediments of the gulf coast have 

low thermal conductivities. 

In general, the average heat content of rocks 

is considerably higher in the Western United 

States than in the East. This also helps to explain why the most favorable hydrothermal convection systems and the hot young igneous systems also occur in the West. 

The anamolous heat of the hydrothermal convection and the hot igneous systems can be considered as "hotspots" superimposed on regional 

conduction-dominated environments. About 0.01 

percent of the total heat stored beneath the 

United States to a depth of 10 km is in identified 

hydrothermal convection systems, and about 0.3 

percent is in the best known of the hot igneous 

systems. If our estimates of the undiscovered and 

unevaluated "hotspots" are valid (table 26), the 

corresponding percentages are 0.04 and 1.2. 

RECOVERABILITY 

The useful heat recoverable from identified 

systems with present or near-current teclmology 

and prices ( =reserves) and at as much ar double 

present prices ( = paramarginal resources) exists 

almost entirely in the hydrothermal corvection 

systems of the Western States (table 27) and the 

geopressured sedimentary environment of the 

gulf coast (table 28). 

Resources of the most attractive identif.~d convection systems (excluding national parks) with 

predicted reservoir temperatures above 150°0 

( --300°F) hav~ an estimated electrical production potential of about 8,000 MW ·cent, cr about 

26,000 MW for 30 ye.ars (Nathenson and MufHer, 

this circular) 4 Assumptions in this conversion 

are: ( 1) one-half of the volume of the her.t reservoirs is porous _and permeable, (2) one-half of 

the heat of the porous, permeable parts i:;- recoverable in fluids at the wellheads, and (3) the 

conversion efficiency of heat in wellhead fluids to 

electricity ranges from .about 8 to 20 percent, 

depending on temperature ·and kind of flrid (hot 

water or steam). The estimated overall e~ciency 

of conversion of heat in the ground to electrical 

energy generally ranges from less than 2 to 5 

percent, depending on type of system an<l reservoir temperature. 

In order to divide the resources of tl~ hightemperature convection systems into reser~res and 

paramarginal and submarginal resources, each 

system should have been analyzed individually 

for economic and physical recoverability. In general, the necessary physical data are net available; few systems have been drilled o:-:- tested 

extensively, and the necessary economic data are 

not well known. No hot-water system in the 

United States has yet been produced e:xtonsively. 

Thus, in lieu of an objective analysis, subjective 

evaluations were made for the three resource 

categories. The most important single factor is 

temperature; reservoirs above 200°0 are most 

likely to contain reserves. Other utili.zed data include indicated magnitude of the resen~()ir and 

indicated. lack of severe problems, such as high 

salinity and inadequate fluid supply. 

4 A megawatt. century of electricity is a unit of ene•gy equiva- lent to 1 MW (1,000 kW) of power being producP.d for 100 

years (or 3.33 MW for 30 years). Approximately 1,000 MW 

(the capacity of many modern nuclear power plants) is required to satlsfx the electrical needs of an average city o~ 1 milllon 

people. 

149 
Table 27 .-Geothermal resources of hydrothermal convection systems assumed recoverable with pr~sent and 

near-current technology and without regard to cost (Nathenson and Muffler, this circular) 

High-temperature systems 

(>1500C; for generation 

of electricity) 

Identified resources 

Reserves 

Paramarginal resources 

Submarginal resources 

Undiscovered resources 

Intermediate-temperature 

systems (90° to 1500C; 

mainly non-electrical 

uses) 

Identified resources 

Undiscovered resources 

TOTAL 

Heat in 

ground 

10l8calll 

257 

1,200 

345 

1,035 

2,837 

Heat at 

well-head 

l018cal.Y 

64 

300 

86 

260 

710 

Conversion 

efficiency 

0.08 to 0.2 

0.08 to 0.2 

0.24 

0.24 

Beneficial 

heatY 

1 ol8cal 

20.7 

62.1 

82.8 

Electrical 

energy 

MW·cen~ 

3,500 

3,500 

>1 ,ooo§./ 

.,P,,OOO?.f 

46,000 

MW for 

30 y"!ars 

§! 

11 ,700 

11 ,700 

> 3,3oo§./ 

126,7001! 

153,400 

lJ 1o18cal {a billion-billion calories) is equivalent to heat of combustion of 690 million barrels of 0il or 154 million short ton~ of coal; these estimates exclude the national parks. 

~ Assumed recovery factor 0.25 for all convective resources. 

~ Thermal energy applied directly to its intended thermal (non-electrical) use; lol8cal of beneficial heat, if supplied by electrical energy, would require at least 1,330 MW·cent (or 4,400 MW for 30 years); however, a user of this geotherma 

energy must be located or must relocate close to the potential supply; insufficient data available to predict demand or to subdivide into reserves, paramarginal, and submarginal resources. 

~ Unit of electrical energy; 1 MW-cent is equivalent to 1000 KW produced continuously for 100 years. 

~ Assumes that each MW-cent of electricity can be produced at rate of 3.33 MW for 30 years. 

§! Small because of exclusion of systems with temperatures below lSOOC. 

Z! Perhaps as much as 60 percent will be reserves and paramarginal resources; costs of discovery and dP.velopment are more speculative than for identified resources. 

150 
....... 

c:71 

....... 

Table 28.-Geothermal resources of geopressured sedimentary environments assumed recoverable with present and near-current technology and without 

regard to cost (Papadopulos and others, this circular) 

Heat 1n Percent Heat equivapore flui?s, recovery lent at ~?ll10l8cal- (heat only) head - 1ol8cal 

.Gulf Coast geopressured 

fluids in sediments of 

Tertiary age; assessed 

on-shore parts only, to 

depth ranging up to 7 km. 10,920 

Plan l, maximizes total 

recovery over 20-year period; no pressure decline below 2,000 psi; 

17,160 wells; subsidence 

estimated 5 to ~7 m. 

Thermal energy 

Methane (thermal 

equivalent) 

Mechanical energy 

(thermal equivalent) 

TOTAL 

0.021 229.4 

124.2 

9.4 

30J.U 

Conversion 

efficiency 

0.08 

0.80 

Electrical 

energy, 

MW·cent '1! 

24,380 

§_/ 

9,970 

34,35oY 

MW for 

30 years 

~ 

81,260 

§.! 

33,230 

, 4 ,49o§/ 

!! Thermal energy only; 1018cal is equivalent to heat of combustion of 690 million barrels of oil. 

2/ All plans assume 0.15 m3;sec flow rate per well and saturation of water with methane, but reliable data lacking. 

3! Unit of electrical energy; 1 MW·:ent is equivalent to 1000 kw produced continuously for 100 yrs. 4; Estimates made for 20 yr. production period; converted to 30 yrs. to be consistent with other estimates - of this circular. 

5/ Methane assumed recovered but not used locallv for electricitv. 

§! Perhaps in part reserves but mostly paramarginal, depending on environmental and other costs. ~ Thermal equivalent of methane included in heat at well-head but excluded from electrical energy; recoverable 

part hi~hly speculative because of unknown porosities and permeabilities, but probably largely submarginal; 

note that the recoverable fraction for these environments is assumed to be lower than that for the assessed 

resources. 

lU No detailed assessment but considered likely to exist in California and other states. 
Table 28.-Geothermal resources of geopressured sedimentary environments assumed recoverable with present and near-current technology and without 

regard to cost (Papadopulos and others, this circular )-Continued 

Heat in Percent Heat equiva- Conversion Electrical MW for 

pore fl ujjs, recovery lent at ~11- efficiency energy,Y 30 years 

10l8ca1 (heat only) head MW·cent ~ 

' HJ18cal 

Plan 2, assumes drawdown 

to land surface, unrestricted subsidence, and 

mechanical energy not 

utilized; 25,850 wells; 

estimated average subsidence >7 m. 

Thermal energy 0.033 358.8 0.08 38,140 127 '1 00 

Methane (thermal 

equivalent) 193.6 §! §! 

Mechanical energy ..... {thermal equivalent) C11 

~ 

TOTAL 552.4 38, 14o§/ 121,1 oofu' 

Plan 3, limits estimated 

average subsidence to -vl m; 

4,000 wells. 

Thermal energy 0.005 53.1 0.08 5,690 19,000 

Methane (thermal 

equivalent) 28.8 §! §! 

Mechanical energy (thermal equivalent) 3.3 0.80 3,560 11,900 

TOTAL 85.2 9,2soW 3o,9oofu' 

Oth~~ ·u~3~~~~~~~ ?l~t~ ~f 

Gulf Coast geopressured environment, on-shore 

and off-shore to 10 km.Z/ 22,000 >500 >50,000 >166,700 

Other geopressured environments to 10 km.Zif 11,000 >250 >25,000 > 83,300 
Nearly one-half of the production potential 

from the identified systems ( 3,500 MW ·cent or 

nearly 12,000 MW for 30 years) is considered to 

be reserves, recoverable with present prices and 

technology. Paramarginal resources recoverable 

at as much as twice present prices and with existting and near-current technology ·are also estimated to be 3,500 MW ·cent or about 12,000 MW for 

30 years. In addition, high-temperature resources 

in undiscovered convection systems, using the 

estimntes of Renner, White, and Williams (this 

circular) and the conversion efficiencies expected 

of these systems (N·athenson and Muftler, this 

circular), are estimated to be 38,000 MW ·cent 

or wbout 5 times that of the identified hot-water 

systems, excluding the national parks. Of the 

undiscovered resources, a considerable fraction 

is likely to be recoverable at present prices and 

technology, but a larger part will probably be 

paramarginal. 

All of the intermediate-temperature convective 

resources (90° to 150°C) are submarginal for the 

generation of electricity, but, under favorable 

conditions, some are utilizable now for space 

heating and industrial uses. The potential for 

nonelectrical uses may attract new industry in 

many places because the supply is relatively dependable and because the overall efficiency of the 

direct use of the geothermal energy for heating 

is greater than for generating electricity for the 

same purposes (Nathenson and Muftler, this circular) . The beneficial heat that can be recovered 

in favorable circumstances, assuming that a need 

occurs near the same locality as the potential 

supply, totals 20.7X1018cal in identified systems 

(table 27); this is equivalent to about 14.3 billion 

barrels of oil. 

The heat content of pore fluids of the assessed 

onshore geopressured parts of the gulf coast to 

depths up to 7 km (Papadopulos and others, this 

circular) is shown in table 28. This heat component excludes all heat contained in rooks and 

minerals and also excludes the potential ener 6Y 

of dissolved methane and ·~the mechanical e:r1ergy 

from excess pressure. The recoverable part of the 

total fluid resource base depends critically on the 

specific plan (or plans) selected for reservoir 

development. Factors that can be emphasized 

include: ( 1) maximizing total recovery from the 

reservoirs, (2) maximizing production from mdividual wells, ( 3) establishing some minimum 

pressure decline that limits subsidence of the 

land surface resulting from production, and ( 4) 

varying the utilization of methane and m~hanical energy relative to thermal energy. A major 

uncertainty concerns the actual content of methane in geopressured fluids. Saturation of methane 

at reservoir temperatures, pressures, and salinities is assumed, but reliable data are not yet 

available. Three different production plr.ns (of 

the many possible plans) are summarized in table 

28. 

Assuming that mechanical energy is c-..nvertible into electricity with 80 percent efficier~y and 

therm·al energy at reservoir temperatures is convertible into electricity with 8 percent e:rciency 

(Papadopulos ·and others, this circular), Plan 1 

can recover .34,400 MW ·cent of electricity; Plan 

2, 38,100 MW ·cent; and Plan 3, 9,250 M1~ ·cent. 

Each projection is only for the assessed onshore 

part of the gulf coast. The energy available from 

methane, which is not limited to utilization at 

the wellhead and is best considered in this' geotherm·al assess1nent as a valuable byproduc~., is not 

included. The potential value of the metb:'l,ne, if 

present in the ~assumed contents, is somewhat 

greater than that of the geothermal and rnechanical energies. For any one kind of e.ner~~ alone, 

the geopressured fluids are probably parf.\.marginal or subm·arginal resources; when all kinds of 

potential energy ~are recovered, a small 1''lt significant part of the total resource may be considered as reserves, with much of the renainder 

as paramarginal resources. 

This 'assessment of reooverability of ~~eopressured- geothermal resources of the gulf coast is 

necessarily focused on physical recoverability 

regardless of cost. Economic assessments are 

greatly oom·plicated by the three kinds of potentially available energy, as well ·as by possible 

environmental problems of subsidence and wastewater disposal. Populated areas near th£, shoreline are relatively sensitive to subsidence, so their 

potential geothermal resources may not be utilized, aJt least not until the subsidence effects can 

be quantified in other less sensitive a:N.as. Although three ·alternative development plans were 

used in evaluating ·all of the 21 subareas of Texas 

and Louisiana ( Papadopulous and others, this 

circular), different production plans can be chosen 

153 
for each subarea, tailored to its tolerance of subsidence and other :factors. 

The very large heat contents of magma, hot 

dry rocks near volcanic centers, and most conduction -dominated parts of the resource base are not 

now geothern1al resources because the necessary 

recovery technology has not yet been developed. 

Recovery technology for the hot dry rocks is now 

receiving much attention and may be developed 

in the :future. 

CONCLUSIONS 

1. The geopressured fluids o:f the gul:f coast have 

a huge geothermal potential. The energy 

deliverable at the wellhead in the assessed 

onshore part of the gulf coast varies according to production plan but is likely to 

range :from 9,000 to 35,000 MW ·cent 

(31,000 to 115,000 MW for 30 years). This 

range excludes the energy equivalent of 

recoverable methane, which is probably at 

least equal in value, but relia;ble data are 

lacking. Other geopressured parts o:f the 

gulf coast and the United States probably 

have at least 3 times In ore potential energy 

in pore fluids than the evaluateu part, but 

the recovera;ble fraction may be considerably less because of lower average porosity 

and permeability to be expected in older 

and more deeply buried sedimentary rocks. 

Cost analyses of these huge geopressured 

resources are not attempted here. Such 

analyses must consider alternate plans for 

reservoir development but require better 

data than ·are now available on reservoir 

permeabilities, the quantity and value of 

recoverable methane, the environmental 

costs related to compaction of reservoirs 

·and disposal of effluent, the value of 

any incidental petroleum recovered from 

geothermal production, and possible utilization of wells already drilled for oil 

and gas. Much of this resource is probably 

paramarginal under present conditions, 

but some part is probably recoverable 

now from ·areas where the environmental 

impact is low. 

2. The high-temperature convection systems 

( > 150°0) of interest for the generation 

of electricity are dominantly in the western conterminous United States, but some 

are in Alaska and Hawaii. The identified 

systems are estimated to h2 ve reserves of 

3,500 MW ·cent o:f electric~ty, producible 

at present prices and technology, and 

about equal potential in pal'amarginal resources. Undiscovered reso1rces of hotwater systems are predictei to be about 

5 times greater than identified resources 

(excluding Yellowstone Park), and undiscovered vapor-dominated systems may 

be as much as the identified resources. 

Sixty-three specific localities are identified that probably have reservoir temperatures above 150°0; these and other 

favorable volcanic areas ar1~ available for 

detailed exploration and assessment. The 

total energy recoverable with present 

technology from undiscov(~red resources 

is estimated to be about 38,000 MW ·cent, 

with perhaps 60 percent recoverable at 

prices as much as double present prices. 

3. The intermediate-temperature convection systems (90° to 150°0) have n1uch potential 

for supplying thermal energy for home 

and industrial heating, thereby releasing 

oil and gas for more critical uses. If 25 

percent of the stored energy is recoverable 

at the surface and the efficirllcy of utilization of wellhead energy is 0.24 (20°C 

temperature drop ·at 100°C, and 32°C at 

150°0), the overall recovery factor is 

0.06, and the potential ber~ficial heat is 

20.7 X 1018 cal (table 27). If this heat were 

to be supplied by electric;lll energy, the 

equivalent of 27,500 MW ·cent would be 

required (efficiency of electrical to thermal assumed 100 percent). This resource 

clearly has significant potential wherever 

the demand for thermal energy can be 

located or relocated close to the potential 

supply. Two hundred an-i twenty-four 

identified systems are tentatively included 

in this category, but most of the predicted 

resources are in only a few large systems. 

4. The hot igneous magma systems and some 

areas of high regional temperature 

gradients provide relatively favorable 

areas for utilizing the he~.t of hot dry 

rock, provided that satisfa ~tory methods 

154 
of recovery can be developed. The potential resources are huge; temperatures near 

or above 315°C at 10 km and 200°C at 6 

km are likely to characterize parts of the 

favorable conduction-dominated environments such as much of the Basin and 

Range province; most of the hot igneous 

systems are likely to have even higher 

temperatures. 

5. Disregarding cost, the total magnitude of 

geothern1al resources that can be recovered by present and near-current technology is very large. The identified higntemperature convection systems and the 

evaluated onshore parts of the gulf coast 

geopressured system are estimated to have 

a production potential of about 42,000 

MW ·cent (using Plan 1 ; 140,000 MW for 

30 years) ·of' recoverable electricity, equivalent to 140 Hoover Dams or 140 average modern nuclear power plants. The 

undiscovered convection systems and the 

unassessed geopressured parts of the gulf 

coast and other sedimentary basins have 

a production potential that is not yet 

known but may be at least 100,0C 0 MW · 

cent (or 330,000 MW for 30 year:;"). Perhaps half of this total can be rr~"A>vered 

with existing technology at prices that 

range up to double present costs. 

6. These assessments represent our best e.~timates 

of .the Nation's geothermal resourc>-es as of 

June 1975. More precise estimates will 

require detailed investigations of the 

areas tabulated in this report as well as 

other areas that will be discovered. These 

investig3!tions tnust include extensive 

drilling, reservoir evaluations, and research to ·at-tain a better understanding of 

the characterist~cs of these system~. 

155 * U.S. Government Printing Office: 197')_281-359/47