of Temperature Survey s at a Depth of 1 Meter 

Geothermal Exploration in Nevada

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1044-B

Use of Temperature Surveys at a Depth of 1 Meter 

In Geothermal Exploration in Nevada

By F. H. OLMSTED

GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1044-B

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1977
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Olmsted, Franklin Howard, 1921-

Use of temperature surveys at a depth of 1 meter in geothermal exploration in Nevada.

(Geohydrology of geothermal systems) (Geological Survey Professional Paper 1044-B)

Bibliography: p. B-25

Supt. of Docs. No.: 19.16.1044-B

1. Geothermal engineering-Nevada. 2. Geothermal resources-Nevada. 3. Earth

temperature-Nevada. I. Title. II. Series. III. Series: Unites States.

Geological Survey. Professional Paper 1044-B. 

TJ280.7.045 551.1*4 77-608303

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 

Stock Number 024-001-030284
CONTENTS

Page

Abstract ....................................................................................._^ Bl

Introduction ................................................................................ 1

Theoretical considerations ....................................................................................................................... 1

Equipment and methodology ................................................................................................................. 5

Field application in Soda Lakes area ................................................................................................. 5

Physical setting ................................................................................................................................... 5

Temperature survey in vicinity of steam well ......................................................................... 8

Temperature survey in November 1973 ..................................................................................... 8

Relations of 1-m temperatures to snowmelt patterns ............................................................. 9

Relations of 1-m temperatures to growth of Russian thistle ............................................... 12

Temperature surveys in June and September 1974 ............................................................... 12

Annual fluctuation in temperature at three sites ................................................................... 12

Correlation of temperatures at depths of 1 m and 20 m ....................................................... 12

Field application in Upsal Hogback area ......................................................................................... 16

Geology and topography ................................................................................................................. 16

Depth to water and ground-water movement ........................................................................... 16

Temperature survey on June 15, 1975 ......................................................................................... 16

Temperature survey on October 29, 1975 ................................................................................... 16

Temperature survey on December 2, 1975 ................................................................................. 16

Temperature at a depth of 30 m, September 1975 ................................................................... 21

Correlation of temperatures at depths of 1 m and 30 m ....................................................... 21

Conclusions ................................................................................................................................................... 21

References cited ........................................................................................................................................... 25

ILLUSTRATIONS

Page

FIGURE 1. Difference in average annual temperature between land surface and a depth of 1 m in relation to thermal conductivity

and geothermal heat flow .................................................................................................................................................................... B2

2. Idealized annual temperature fluctuations at land surface and a depth of 1 m for approximate conditions in western

Carson Desert area, Nevada .............................................................................................................................................................. 4

3. Topographic map of Soda Lakes-Upsal Hogback area showing temperatures at a depth of 30 m in shallow test wells,

configuration of water table, and direction of shallow ground-water movement in July 1975 .................................. 6

4. Map of Soda Lakes area showing character of materials to a depth of 1 m and the depth to the water table in shallow

test wells in December 1975 ..................................................................................................... . .... ....- ................................ 7

5. Map showing temperature at a depth of 1 m near steam well, November 23, 1973 .............................................................. 9

6. Map of Soda Lakes area showing temperature at a depth of 30 m, fall 1973 .......................................................................... 10

7. Map of Soda Lakes area showing temperature at a depth of 1 m on November 23,1973 and area of snowmelt in

January 1974 ..........................................................................._ 11

8. Map of Soda Lakes area showing density of Russian thistle on February 5, 1974 ................................................................ 13

9. Map of Soda Lakes area showing temperature at a depth of 1 m on June 15 and September 20,1974 .......................... 14

10. Fluctuations in temperature at a depth of 1 m at three sites in Soda Lakes area compared with fluctuations in air

temperature at Fallen Experiment Station during 1975 .......................................................................................................... 15

11. Correlation of temperatures at a depth of 20 m with temperatures at a depth of 1 m in Soda Lakes area,

September 1974 ............................................................... 17

12. Topographic map of Upsal Hogback area showing depth to the water table in test wells, configuration of the water

table, and direction of shallow ground-water movement in July 1975 ................................................................................ 18

13. Map of Upsal Hogback area showing temperature at a depth of 1 m, June 1975 .................................................................. 19

14. Map of Upsal Hogback area showing temperature at a depth of 1 m, October 29, 1975 ...................................................... 20

15. Map of Upsal Hogback area showing temperature at a depth of 1 m, December 2, 1975 .................................................... 22

16. Map of Upsal Hogback area showing temperature in test wells at a depth of 30 m, September 1975 ............................ 23

17. Correlation of temperature at a depth of 30 m with temperature at a depth of 1 m in Upsal Hogback area,

December 1975 ............................................................. 24

III
IV CONTENTS

TABLE

Page 

TABLE 1. Characteristics of idealized temperature waves at a depth of 1 m in western Carson Desert ............................................ B3
GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

USE OF TEMPERATURE SURVEYS AT A DEPTH OF 1 METER 

IN GEOTHERMAL EXPLORATION IN NEVADA

By F. H. OLMSTED

ABSTRACT

Temperature surveys at a depth of 1 m in the Soda Lakes and 

Upsal Hogback areas of the western Carson Desert, Nevada, had 

varying degrees of success in delineating temperature and heatflow anomalies at greater depths. Optimum results were obtained 

in a detailed survey of a small area near a f umarole and an abandoned steam well in the Soda Lakes area. At this location steam 

occurs above the water table and the unconfined water is at the 

boiling temperature at depths of only a few meters; also temperatures and heat flows are far above background values. Somewhat 

more equivocal results were obtained in surveys of a larger surrounding area in which the temperature range at 1 m was smaller 

than immediately adjacent to the fumarole and steam well, and 

in which perturbing effects of geologic, topographic, hydrologic, 

and other factors not related directly to geothermal heat flow are 

locally significant. Poorest results were obtained in surveys of 

the Upsal Hogback area, where temperature of the thermal water 

leaking into shallow aquifers is much less than that in the Soda 

Lakes area, the range in temperature at a depth of 1 m is correspondingly smaller, and the variability of the geology, topography, 

depth to the water table, and other perturbing factors is greater 

than that in the Soda Lakes area.

INTRODUCTION

In principle, temperature surveys at depths as 

shallow as 1 or 2 m could be used to delineate deeper 

thermal anomalies or areas of high geothermal heat 

flow, provided that temperature differences caused 

by extraneous factors were not so large as to mask 

the temperature differences caused by variations in 

heat flow. Some extraneous factors that affect 

shallow temperatures are local variations in the 

character and moisture content of the near-surface 

materials, topography, depth to the water table, 

vegetation, land use, and microclimate. The principal advantage of temperature measurements at such 

shallow depths in comparison with deeper measurements is their relatively low cost in both time 

and money.

Earlier investigators have reported both failure 

and success using shallow temperature surveys in 

geothermal exploration. In reviewing evidence from

a study of shallow temperature gradients in relation 

to anomalously high heat flow caused by oxidizing 

ore bodies, Levering and Goode (1963, p. 39) 

concluded that temperature measurements at depths 

of only 1 or 2 m were useless in detecting abnormal 

geothermal gradients at greater depths. Kappelmeyer (1957, p. 248-254) reached similar conclusions 

about the use of such measurements to find buried 

horsts, salt domes, or local concentrations of radioactive material, although he believed it possible in 

principle to outline areas underlain by fissures 

carrying thermal water upward into the shallow 

ground-water system. Kintzinger (1956), in fact, 

reported the successful use of 1-m temperature 

measurements in outlining an area near Lordsburg, 

N.M., underlain by hot ground water encountered 

in wells at depths of only 20-25 m.

The present paper (1) briefly reviews the theoretical 

difficulties and limitations of temperature measurements at 1 m depth in determining geothermal heat 

flow; (2) presents the results of field tests of the 

method at two geothermal anomalies in west-central 

Nevada, where fairly abundant comparative temperature data are available at depths below the zone 

affected by fluctuations in solar energy; and (3) 

evaluates the general applicability of the method in 

similar geologic, hydrologic, and climatic settings.

THEORETICAL CONSIDERATIONS

If it were possible to make sufficient measurements to define average annual temperature at the 

land surface and at a depth of 1 m, the temperature at 

1 m would be found to exceed that at the land surface, 

assuming the climate was not changing and heat 

transfer toward the surface was by conduction. The 

temperature difference in a horizontal uniform layer 

would be expressed as

10K

Bl
B2 GEOHYDROLOGY OF GEOTHERMAL SYSTEMS 

10 20 30 40 50 60

12

S 10 

u

V)

UJ 

UJ

cc 

o

UJ

Q

~ 8

O

o

O 

CC

u.

UJ

cc

D

< 

oc

UJ

0. 2

UJ

H

12

10

10 20 30 40 

HEAT FLOW, IN HEAT-FLOW UNITS

50 60

K=Thermal conductivity,

in millicalories per centimeter • degree • second

FIGURE 1. Difference in average annual temperature between land surface and a depth of 1 m in relation 

to thermal conductivity and geothermal heat flow.

where AT^-i is the temperature difference from land 

surface to a depth of 1 m, in degrees Celsius; Q is the 

geothermal heat flow (heat-flux density), in microcalories per square centimeter per second (y cal»cnv2 

 s-1 ); and K is the thermal conductivity of the layer, in 

millicalories per centimeter per degree per second 

(mcal»cm1.°C'1»s-1 ). In an area of so-called "normal" 

geothermal heat flow about 1 ycal-cm.-2^1 or 1 

HFU (heat-flow unit) the temperature difference in 

material having a thermal conductivity of 2 meal* 

cm- 1»°C- 1»s-1 would be only 0.05°C, which is barely 

within the range detectable by ordinary temperaturemeasuring equipment.

Temperature differences from land surface to a 

depth of 1 m for values of heat flow and thermal

conductivity representative of conditions in geothermal areas in west-central Nevada are shown in 

figure 1. A K (thermal conductivity) of 0.5 mcakcnv1 

 °C'1»s-1 would be typical of dry silt or fine sand; a K of 

4 mcal»cm -1»°C' 1»s-1 would be typical of wet coarse 

sand. Where the thermal conductivity is large, the 

temperature difference from 0 to 1 m is small, even 

for a heat flow of 100 times "normal." Low thermal 

conductivity, on the other hand, is associated with a 

large temperature difference (fig. 1).

For the simple case just described, if sufficient 

measurements could be made to define the average 

annual temperature at 1 m, the only problems in 

relating temperature at 1 m to geothermal heat flow 

would be variations in thermal conductivity with
TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA 

TABLE 1. Characteristics of idealized temperature waves at a depth of 1 m in western Carson Desert

B3

Kind of wave

"Weather" ..............................

Seasonal ..................................

Period

(days)

1

10

365

Amplitude at 

surface (°C)

15.0 

4.0 

15.0

Amplitude at 1 m depth (°C)

<x = 1.5 x lO^cm2 ^ 1

2.6 x 10-6 

0.029 

6.65

a. = 6.0 x 10-3cm2s'1

6.2 x 10-3 

0.34 

9.98

Timelag (days)

Oi = 1.5 x 10~3cm2 s~

2.46

7.8 

47.4

1 a. = 6.0 x lO-ocmV1

1.23 

3.9 

23.7

both place and time and variations with place in 

average annual temperature at the land surface. 

Variations in thermal conductivity are troublesome 

where the near-surface materials in the area of 

investigation are not uniform. Variations in average 

annual temperature are difficult to deal with where 

topography is irregular and vegetative cover is 

variable. As shown in figure 1, heat-flow differences 

of several tens of heat flow units could be masked 

completely by moderate variations in thermal 

conductivity or by differences in average annual 

temperature at the surface of only a few degrees 

Celsius. In spite of these potential problems, 

measurement of average annual temperatures at 1 m 

could be a powerful tool in geothermal prospecting if 

the area selected for study were fairly level and had 

uniform soils, vegetation, and land-use patterns.

The accurate determination of average annual 

temperatures at 1 m would require several sets of 

synoptic measurements during the year, such as at 

monthly intervals. However, because of this requirement, much of the advantage of 1-m temperature 

surveying over surveys at greater depth but at fewer 

sites is lost. Therefore, it is desirable to consider the 

advantages and disadvantages in using a single set 

of synoptic measurements at 1-m depth.

The principal advantages of a single set of 

measurements are the savings in time and expense 

and the prompt availability of the results for use in 

interpretation and decisionmaking in further exploration. The chief disadvantage is that, in dealing 

with a single set of synoptic measurements, another 

group of variables enters the problem: the areal 

variations in temperature related to differences in 

soil-temperature response to periodic and nonperiodic fluctuations in solar-energy input.

Although diurnal temperature waves are damped 

to amplitudes too small to be measured at 1 m in most 

climatic and geologic environments, fluctuations 

having longer periods, including the annual temperature wave, have significant amplitude at 1 m 

depth. In the simple case of a single homogeneous 

soil or rock layer of semi-infinite extent, the response 

at the base of the layer to harmonic fluctuations in 

temperature (sinusoidal waves) at the top surface or

land surface can be expressed by two equations:

(1)

(2)

where Ax is the amplitude of the temperature wave

at the base of layer x (°C), 

A0 is the amplitude of the temperature wave

at the land surface (°C), 

x is the thickness of layer x (cm), 

a is the thermal diffusivity of layer x (cm2

s-1 ), 

P is the period of the temperature wave (s),

and

tx - t0 is the time lag between the temperature 

waves at the land surface and at the 

base of layer x (s).

As shown by equations (1) and (2), the amplitude of 

a temperature wave decreases exponentially with a 

linear increase in depth, but the timelag increases 

linearly with a linear increase in depth. The longer 

the period of the wave at the surface, the greater will 

be the amplitude of that wave at any given depth.

In general, temperature waves at the land surface, 

which are caused by fluctuations in solar-energy 

input, may be grouped in three categories on the 

basis of their periods: (1) diurnal, (2) "weather," and 

(3) annual (or seasonal) waves. The periods of the 

first and third categories are indicated by their 

names and are regular. Waves of the second category 

are irregular in period and are caused by the passage 

of air masses of different meteorological characteristics.

Features typical of each of the three types of waves 

in the area of study, in west-central Nevada, are 

presented in table 1. The simple case of idealized 

harmonic temperature waves being damped conductively in a semi-infinite uniform medium is 

assumed. The two values of thermal diffusivity 

shown represent the approximate upper and lower 

limits found in the area of study. The periods and
B4 GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

- -10

-15 -15

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

©A ) Temperature at land surface. Wave amplitude=15°C

Temperature at 1 m, thermal diffusivity 

6.0 x 10~3 cm 2 s" 1 . Wave amplitude=10.0°C, 

timelag=23.7 days

(CJ Temperature at 1 m, thermal diffusivity 

^"^ 1.5 x IQr'cm^s" 1 . Wave amplitude2 

6.6° C; time lag =47.4 days

FIGURE 2. Idealized annual temperature fluctuations at land surface and a depth of 1 m for approximate conditions

western Carson Desert area, Nevada.

amplitudes of the waves at the land surface likewise 

are typical of conditions in west-central Nevada.

Stratification of near-surface materials produces 

effects on the temperature waves which may differ 

substantially from the effects in the uniform medium 

described above. Lachenbruch (1959) and Van Wijk 

and Derksen (1966, p. 177-180) have shown that the 

amplitude of a temperature wave at a given depth in 

a multilayered medium can range from several times 

smaller to somewhat larger than that in a single 

layer, depending.on the relative thermal properties, 

especially thermal inertia (contact coefficient), of the 

layers.

As stated earlier, the amplitude of the diurnal 

waves is too small to be measured in the range of 

conditions likely to be found in the study area. 

Although detectable with ordinary temperaturemeasuring equipment, the amplitude of the "weather" 

waves is not large enough to be a troublesome factor. 

The chief problems are associated with the longperiod annual waves, where differences in thermal 

diffusivity can result in differences in phase-lag time 

of several weeks and differences in amplitude of

more than 2°C from place to place. (See table 1 and 

fig. 2.) Owing to the combined effects of the 

differences in amplitude and timelag, the variations 

in temperature at 1 m from place to place exceed 4°C 

in midwinter and midsummer (fig. 2). Stratification, 

described above, can cause even larger differences. 

As shown in figure 2, these differences could be 

minimized by making the temperature surveys in 

early April or early October.

Although the difficulties described above appear 

formidable, they are only part of the entire problem. 

Other significant factors causing variations in 

temperature at 1 m not related to geothermal heat 

flow include variations in convective heat transport 

by water, vapor, and air, and variations resulting 

from areal variations in the solar-air-earth heat 

budget, such as the effects of topography, albedo, 

surface emissivity, wind, and vegetation. These 

factors could cause perturbations as large as those 

caused by the areal variations in thermal diffusivity 

and stratification. Added to these difficulties are the 

variations in thermal diffusivity with time as the 

moisture content of the near-surface materials
TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA B5

changes in response to precipitation and other 

weather factors. Clearly, there are serious obstacles 

to the successful use of synoptic temperature surveys 

at 1 m depth to determine geothermal heat-flow or 

temperature anomalies at depths below the range of 

solar-energy fluctuations. In spite of these obstacles, 

however, a practical test of the technique was 

believed warranted.

EQUIPMENT AND METHODOLOGY

Temperature measurements were made with a twobead thermistor mounted at the tip of an aluminum 

probe 1 m in length, connected by a 3-conductor cable 

to a solid-state Wheatstone bridge having a digital 

readout. Temperature was recorded to the nearest 

0.01 °C. Frequent calibration checks with a mercuryglass thermometer indicated an accuracy of about 

±0.3°C for individual measurements.

In soft coherent deposits, such as damp silt or clay, 

access holes were driven by hand with a light-weight 

steel driver. Most of the holes, in sandy deposits, 

were made with a soil auger 57 mm in diameter, 

lithologic character and moisture content of materials were recorded at each site.

After insertion of the temperature probe into the 

material at the bottom of the access hole, readings 

were made at regular time intervals and equilibrium 

temperature was computed by a method of extrapolation to infinite time described by Parasnis (1971).

FIELD APPLICATION IN SODA LAKES AREA

The first known thermal anomaly selected in 

which to field test the effectiveness of 1-m temperature surveying was northeast of Soda Lakes, in the 

west-central Carson Desert, about 12 km northwest 

of Fallen, Nev. (fig. 3).

Previous information pertinent to the study 

consisted of water-level data, chemical analyses of 

shallow ground water, and temperature-gradient 

measurements, all from test wells 20-50 m in depth, 

drilled by the U.S. Geological Survey and the U.S. 

Bureau of Reclamation in 1972 and 1973 (Olmsted 

and others, 1975, p. 99-118). Additional information 

included geologic studies by Morrison (1964), generalized gravity data (Wahl, 1965), and generalized 

aeromagnetic data (U.S. Geological Survey, 1972).

PHYSICAL SETTING

The Soda Lakes area is within the Carson Desert, a 

large basin in the rain shadow of the Sierra Nevada 

to the west. Precipitation averages less than 100 mm 

annually (Hardman, 1965), a small part of which is 

winter snow. Long-term average monthly air temperature at Fallen ranges from -0.3° C in January to 

22.8°C in July (National Oceanic and Atmospheric 

Administration, 1975). The severe aridity and 

summer heat and the generally sandy soils of low 

water-holding capacity limit the vegetation to 

scattered perennial shrubs and various annuals that 

grow during periods of excess soil moisture after 

heavy rains in the spring or early summer.

The Carson Desert is a topographic and structural 

basin occupied intermittently during the late Pleistocene and early Holocene by Lake Lahontan. The 

Soda Lakes thermal anomaly lies between two loci of 

late Quaternary basaltic eruptions: Soda Lakes to 

the southwest and Upsal Hogback to the northeast 

(fig. 3). The thermal area is underlain by unconsolidated clay, silt, and sand of Lake Lahontan, 

intertonguing fluvial, swamp, and marsh deposits, 

and windblown sand. Present topography, which 

consists of scattered undrained depressions and 

intervening sandy flats and dunes, is largely the 

result of wind scour during the early Holocene 

(Morrison, 1964). Local relief amounts to as much as 

10 m from the bottoms of wind-scoured depressions 

to the tops of adjacent sand ridges. The land surface 

slopes generally toward the north-northeast; altitudes in the area of the temperature survey range 

from 1,206 to 1,226 m above mean sea level. Sand and 

silt, chiefly of eolian origin, predominate within the 

0-1 m depth range; less extensive deposits include 

pebbly sand, probably of stream-channel origin, and 

clayey silt to silty clay, which represent bottom 

deposits of Lake Lahontan (fig. 4). The finer grained 

deposits are exposed in the sides and bottoms of the 

wind-scoured depressions.

Since the early 1900's, when irrigation began in 

the area to the south, the water table has risen 

beneath the surveyed area. The rise may have been 

as much as 10-15 m on the basis of a reported rise in 

stage of 18 m at Soda Lakes from 1906 to 1930 (Rush, 

1972). Depths to the water table range from about 4 to 

about 7 m beneath the sandy areas, but are less than 

2 m beneath the depressions (fig. 4). As shown by the 

contours on the water table for July 1975 (fig. 3), 

shallow ground water beneath the area moves 

generally toward the northeast.

Thermal water from considerable depths, perhaps 

several kilometers, moves upward along faultcontrolled conduits (Olmsted and others, 1975, 

p. 118). One of these channels steam to the land 

surface and boiling water to depths of only a few 

meters in the vicinity of a shallow well about 18 m 

deep near the southwest corner of sec. 28, T. 20 N., R. 

28 E. (fig. 3). The thermal water enters sand aquifers, 

some of which are 10 m or less below land surface,
B6 GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

118° 50'

T.20N.

39°50'

r- T.19 N.

Base from USGS 15 topo series. 

Soda Lake, Nevada

EXPLANATION 

1200 —- Water-level contour

Altitude of water-table, in meters above mean sea level. 

Arrows show inferred direction of ground-water flow

•——— 20 —— — Line of 20° C temperature at a depth of 30 m

18.0 Test well and temperature, in degrees Celsius, at a depth of 30 m

FIGURE 3.—Soda Lakes-Upsal Hogback area showing temperatures at a depth of 30 m in shallow test wells, 

configuration of water table, and direction of shallow ground-water movement in July 1975.
TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA BY

118° 50'

39°34'

^^^^^isSM^^^UK^^^^Mi^^^iM^i^K

39° 33'

^-— Contact, dashed where 

approximate

EXPLANATION

-meter temperature-measurement site 

Abandoned irrigation ditch 

_._—.—- Road or trail - 

Pond or lakebed 

Test well and depth to water table, in meters

Coarse sand, pebbly sand 

Medium sand

Fine sand

>r-£i-r- Silt

fZfZ4-i Clay

300 600 METERS

FIGURE 4.—Soda Lakes area showing character of materials to a depth of 1 m and the depth to the water table in shallow test wells

in December 1975.
B8 GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

through which it moves laterally toward the northeast. The temperature anomaly thus produced is 

strongly asymmetrical toward the northeast (fig 3).

TEMPERATURE SURVEY IN VICINITY OF STEAM WELL

The first temperature measurements at 1-m depth 

were made during November 1973 in the vicinity of 

an abandoned well, reported to have been originally 

about 18 m deep, near the southwest corner of sec. 28, 

T. 20 N., R. 28 E. (fig. 3). The site was selected because 

of suspected high near-surface temperatures. Evidence for a shallow thermal anomaly consisted of 

hydrothermal alteration of the sandy eolian deposits 

to kaolinite and iron hydroxides and oxides, steam 

issuing from the old well and from a nearby 

fumarole, and observed rapid snowmelt in an area 

coextensive with the exposures of hydrothermally 

altered deposits. Lateral spacing of the temperaturemeasurement sites ranges from about 5 m in the zone 

of highest temperature near the fumarole and steam 

well to more than 100 m on the margins of the 

strongest thermal anomaly, where temperatures at 1 

m were less than 30°C (fig. 5).

Temperature at 1 m ranged from less than 30°C to 

more than 90°C in a small linear band trending 

northeast and centered on the fumarole (fig. 5). 

Highest temperatures were associated with the area 

of most intense hydrothermal alteration and probably indicate the presence of steam near the surface. 

The temperature pattern suggests rising thermal 

water along a northeast-trending elongate or linear 

conduit, probably fault-controlled. Possible presence 

of a linear zone approximately perpendicular to the 

main zone is indicated by the temperature pattern 30- 

50 m northeast of the steam well.

The high temperatures probably result in large 

part from heat transport by steam rising from a 

boiling water table rather than chiefly by heat 

conduction through the altered clayey sediments 

above the water table. Depth to the water table 

within the area shown in figure 5 has not been 

measured, but measurements in nearby test wells 

indicate probable depths of 5-7 m outside the hottest 

part of the thermal anomaly.

TEMPERATURE SURVEY IN NOVEMBER 1973

Concurrently with the temperature survey of the 

small area adjacent to the old steam well, measurements were made in a much larger surrounding area. 

Earlier data from test wells ranging in depth from 9 

to 44 m indicated an asymmetrical northeasttrending thermal anomaly centered approximately 

at the steam well (fig. 6). Temperature at a depth of 30

m below land surface ranged from an inferred 

temperature of more than 120°C near the steam 

well—boiling temperature at hydrostatic pressure— 

to less than 20°C on the margins of the anomaly. 

Lateral temperature gradient toward the southwest 

was greater than that toward the northeast, and 

gradients along the northwest margin were greater 

than those along the southeast margin.

With a range in temperature of more than 100° C at 

30 m, it was anticipated that the temperature pattern 

at 1 m would reflect deeper temperatures and that, 

with much greater density of measurement sites, the 

temperature pattern at 1 m might reveal features not 

apparent from the data at 30 m shown in figure 6.

Because of concurrent other work, it was not 

possible to complete the measurements at about 100 

sites within a few days, as would have been desirable. Instead, the survey required nearly a month, 

from November 11 to December 7, 1973. Because 

temperature at 1 m changed considerably during this 

period, the temperature at each site was adjusted to a 

midperiod date of November 23 on the basis of 

repeated measurements at several sites. A linear rate 

of change of temperature during the period of 

measurements was assumed, and the same rate of 

change was used for all sites. Analysis of airtemperature data for the nearby weather station at

Fallen suggests that the actual change in temperature in the ground probably was irregular, in 

response to antecedent "weather" cycles, as discussed previously. Moreover, variations probably 

existed in the rate of temperature change from place 

to place, owing to both areal and temporal variations 

in thermal diffusivity. However, the differences 

between the interpolated temperatures used and the 

actual values are believed to be small—on the order 

of a few tenths of a degree Celsius at most sites.

Results of the temperature survey are shown in 

figure 7. Temperature on the margins of the 

anomaly, presumably where the geothermal heat 

flow is normal or nearly normal, was about 12°C; 

temperature in the warmest parts of the anomaly 

exceeded 90° C near the steam well and 30° C at 

another thermal high about 500 m south of the steam 

well. The general northeasterly alinement of the long 

axis and the asymmetry of the anomaly are similar 

to the temperature pattern at 30 m (compare figs. 6 

and 7). However, a significant difference is revealed 

by the greater density of the 1 m data: instead of one 

thermal maximum centered at the steam well, there 

were two en echelon elongate maxima, separated by 

a lower temperature trough, all oriented northeast. 

The zone of highest temperature northeast of the 

steam well, where the temperature exceeded 20°C,
TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA B9

• 22.3

N • 26.9

• 24.6

,25.9

EXPLANATION

>16.3

0 Measurement site and temperature at a depth 

26.9 of 1 m, in degrees Celsius

50 Line of equal temperature at a depth of 1 meter 

Interval, 10 degrees Celsius

S: Abandoned steam well 

F: Fumarole

24.8

50 METERS

• 17.7

FIGURE 5.—Temperature at a depth of 1 m near steam well, November 23, 1973.

extended almost 700 m northeast of the well; this fact 

suggests that a linear hydrothermal conduit or 

conduit system may extend at least that far northeast of the steam well.

RELATONS OF 1-M TEMPERATURE TO SNOWMELT 

PATTERNS

In early January 1974, after a brief snowfall of

about 50 mm, oblique aerial photographs of the area 

near the steam well were taken at low altitude from a 

U.S. Navy helicopter. Within 24 hours after precipitation ceased, ground temperatures and associated 

heat transfer from the land surface were sufficiently 

high to melt the snow completely from three small 

areas, as shown in figure 7. 

Two of the snowmelt areas clearly are coextensive
BIO GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

118°5T 118° 50'

39° 34'

39° 33'

EXPLANATION

• 1-meter temperature-measurement site 

___.—.—- Abandoned irrigation ditch 

__._ —. —- Road or trail

Pond or lakebed

25.7 (

70

Test well and temperature, in degrees Celsius, 

at a depth of 30 meters. Open circles denote 

test wells drilled after fall of 1973. 

S, abandoned steam well

Line of equal temperature at a depth of 30 meters. 

Interval, 10 degrees Celsius

300 600 METERS

FIGURE 6.—Soda Lakes area showing temperature at a depth of 30 m, fall 1973.
TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA Bll

118° 50'

39°34'

39° 33'

7Y(l|f%fel^'

S EXPLANATION

• 1-meter temperature-measurement site 

___.—.—- Abandoned irrigation ditch 

_.._ —. —- Road or trail

Pond or lakebed

— 22 '— Line of equal temperature at a depth of I meter

Interval, 2 degrees Celsius

Area of snowmelt

300 600 METERS

FIGURE 7.—Soda Lakes area showing temperature at a depth of 1 m on November 23,1973 and area of snowmelt in January 1974. 

Sites in northern and eastern parts of area not measured in November 1973.
B12 GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

with thermal maxima at 1 m as shown by the 

November 23, 1973 data, but a third area, on the 

southeast flank of the principal thermal anomaly, 

seems not to be related directly to the temperature 

pattern. However, comparison with the near-surface 

lithology and the depth to water (fig. 4) suggests that 

the third snowmelt area indicates a heat sink 

coincident with a wind-scoured depression. The nearsurface deposits in the depression are chiefly clay 

and silt of low thermal diffusivity in comparison 

with that of the damp sand of the surrounding area. 

Moreover, the depth to a warm water table is less 

than 2 m in the depression, as compared to a depth of 

more than 5 m in the surrounding higher, sandy 

area.

RELATIONS OF 1-M TEMPERATURES TO GROWTH OF 

RUSSIAN THISTLE

Color vertical aerial photographs taken in 

February 1974 revealed brown color patterns which 

were approximately coextensive with the areas of 

maximum temperature at 1 m depth in November 

1973 (fig. 8). Later inspection on the ground indicated 

that the brown patterns were caused by dense stands 

of dried-up Russian thistle (Salsola Kali L. var. 

tenufolia Fausch). The thistle appears to thrive in 

sandy soil, and the density and vigor of the stands 

correlate directly with the ground temperature 

(fig- 8).

TEMPERATURE SURVEYS IN JUNE AND SEPTEMBER 1974

In order to determine whether the configuration 

and extent of the 1-m anomaly changes with time, a 

survey was made northeast of the steam well in June 

1974, and areal coverage was extended beyond that 

of the November 1973 survey, mostly toward the east 

and northeast, in September 1974.

The June measurements indicated a pattern 

similar to that of the previous November, but with 

minor differences, probably related to areal variations in thermal diffusivity of the shallow materials. 

(Compare figs. 7 and 9.) The September 1974 

measurements showed that the thermal anomaly at 

1-m depth extended more than 2 km east and 

northeast of the center of the November 1973 

anomaly. A similar pattern at 30 m was established 

on the basis of extrapolated temperature gradients 

from measurements in 20-m-deep test wells drilled in 

October 1974.

ANNUAL FLUCTUATION IN TEMPERATURE AT THREE SITES

Monthly temperature measurements during 1975 

were made at three sites in order to determine 

differences in the nature of the annual temperature

wave in three different lithologic and thermal 

environments. The sites (fig. 9) were selected to 

represent the approximate range of temperature 

fluctuations throughout the surveyed area. Site 98, 

south of the thermal anomaly, is in sand of chiefly 

eolian origin. Depth to the water table averaged 

about 4.7 m in 1975. Site 67, also in predominantly 

sandy deposits but containing slightly more clay 

and silt than at site 98, is on the northwest flank of 

the anomaly. Depth to water averaged about 6.7 m in 

1975. Site 11, about 380 m southeast of the steam 

well, is near the north edge of the depression where 

snowmelt was observed in January 1974, as described earlier. The deposits at site 11 are lacustrine 

clay and silt having a moisture content greater than 

that at the other two sites.

As shown in figure 10, temperature at all three 

sites was always higher than the smoothed-average 

air temperature at Fallon Experiment Station; the 

amplitude of the annual temperature fluctuations 

was less at the three sites than at Fallon; and the 

temperature waves at the three soil sites lagged the 

annual air temperature wave at Fallon, as would be 

expected from theoretical considerations.

Differences among the three sites are apparent in 

figure 10. The temperature at site 11, the hottest 

location, differs from that at site 98, the coldest 

location, by amounts ranging from 3°C in late spring 

to about 11°C in early winter. The temperature 

difference between sites 67 and 98 ranges from less 

than 0.5°C in the spring to about 3°C in the fall. 

These temperature differences are largely the result 

of differences in thermal diffusivity at the three sites 

but are also related to differences in surface 

conditions and to the effect of a shallow water table 

at site 11. During most of the year, the thermal 

diffusivity of the damp clay and silt at site 11 was 

less than that of the sandier materials at the other 

two sites; this relation accounts in part for the 

smaller amplitude of the annual temperature wave 

at site 11. The smaller amplitude at site 11 probably 

is also caused by stratification and heat-sink effects 

of a warm, shallow water table. The range in 

temperature differences among the three sites during 

the year illustrates the danger of using synoptic 

temperature measurements at only one time during 

the annual cycle in trying to discern patterns related 

to variations in geothermal heat flow.

CORRELATION OF TEMPERATURES AT DEPTHS OF 1 METER 

AND 20 METERS

The evidence discussed above suggests that, in the 

Soda Lakes area, a temperature survey at a depth of 

1 m might provide a fairly reliable indication of the
TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA B13

118° 50'

39°34'

39° 33'

EXPLANATION

1-meter temperature-measurement site 

Abandoned irrigation ditch

_._—.—- Road or trail

Pond or lakebed

Dense stand

Very dense stand

300 600 METERS

FIGURE 8.—Soda Lakes area showing density of Russian thistle on February 5, 1974.
B14 GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

118° 50'

39°34'

- --

39° 33'

EXPLANATION 

• 1-meter temperature-measurement site 

__-.——— Abandoned irrigation ditch 

_. _ — —- Road or trail

Pond or lakebed

— 32 — Lines of equal temperature at a depth of I meter. 

Interval, 2 degrees Celsius. Solid lines represent

•••28 ••• temperature on September 20, 1974; dotted lines 

on June 15, 1974

O 98 Site of periodic temperature measurements at a 

depth of 1 meter during 1975

300 600 METERS

FIGURE 9.—Soda Lakes area showing temperature at a depth of 1 m on June 15 and September 20, 1974.
32

28

24

20

CO

33 16

ui 

u

CO

ui 12

QJ It

cc 

u

UI

0

-4

-8

-12

-16

- O

5-DAY MOVING-AVERAGE AIR TEMPERATURE 

AT FALLON, NEV.

SMOOTHED AVERAGE AIR TEMPERATURE AT FALLON, NEV.

I

JAN FEB MAR APR MAY JUN JUL AUG 

1975

SEP OCT 

FIGURE 10.—Fluctuations in temperature at a depth of 1 m at three sites in Soda Lakes area compared with fluctuations in air te

Experiment Station during 1975.
B16 GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

extent and configuration of a thermal anomaly at 

greater depths, below the range of influence of the 

annual weather cycle. A simple test of the reliability 

of a temperature survey at 1 m is a correlation of 

temperature at 1 m with temperature at 20 m at testwell sites where the deeper temperature data are 

available (fig. 11). The least-mean-squares linearregression equation is

720 = 8.43 TI - 180.7

where T2Q is temperature at 20 m and TI is 

temperature at 1 m in September 1974. The 

coefficient of determination, r 2 (a measure of 

variance), is 0.95, which indicates a fairly good fit to 

the least-mean-squares regression over a temperature range of nearly 100°C at 20 m and 11°C at 1 m. 

However, at temperatures less than 40°C at 20 m, the 

scatter of the data indicates a much poorer correlation in that temperature range.

FIELD APPLICATION IN UPSAL HOGBACK AREA

The second area studied was near Upsal Hogback, 

a group of low basalt cinder cones or tuff rings about 

12-16 km north-northeast of Soda Lake.

Previous information for the Upsal Hogback area 

was similar to that for the Soda Lakes area, except 

that shallow test drilling near the Hogback began 

about the same time as the 1-m temperature survey 

instead of preceding it.

GEOLOGY AND TOPOGRAPHY

The basalt cones or tuff rings of the Upsal 

Hogback were formed by intermittent eruptions, 

chiefly during an interpluvial time in the late 

Pleistocene when Lake Lahontan either was dry or 

stood at a level below the site of the eruptions 

(Morrison, 1964, p. 100). The cones are probably 

along a concealed fault or fault system which also 

intersects the Soda Lakes to the south-southwest. 

Near the Hogback, the post-Lake Lahontan blanket 

of sandy deposits that characterizes much of the 

Soda Lakes area consists only of scattered dunes in 

the north-central and eastern parts of the area. In 

contrast, sands and clays of Lake Lahontan, now 

eroded by both wind and water, crop out on the 

flanks of the Hogback. The land surface is characterized by a large contrast in albedo, from dark surfaces 

with a lag of basalt gravel to light exposures of 

lacustrine clay and silt. The largely bare, flat surface 

of Carson Sink, the sump for all the drainage in the 

region, extends into the northeast part of the area. 

Land-surface altitudes range from 1,270 m at the top 

of a cone near the south end of the Hogback to 

1,178 m in the Carson Sink (fig. 12).

DEPTH TO WATER AND GROUND-WATER MOVEMENT

Depth to the water table in July 1975 ranged from 

less than 1 m in the Carson Sink and adjacent low, 

flat areas to about 20 m on the margins of Upsal 

Hogback. The range in depth was considerably 

greater than that in the Soda Lakes area and, 

together with the greater topographic relief and the 

greater contrast in albedo, presented potential 

problems for the application of the 1-m temperaturesurvey method.

The general direction of ground-water movement, 

perpendicular to the water-table contours, is northward to eastward, toward the Carson Sink (fig. 12). 

The vertical component of ground-water movement 

is generally upward; the upward gradient increases 

toward the Carson Sink. However, on the flanks of 

Upsal Hogback, the upward gradient is small to zero, 

and at one site on the southwest side of the Hogback, 

the gradient is downward.

TEMPERATURE SURVEY ON JUNE 15, 1975

Temperature was measured at 1 m on June 15, 

1975, at the time the drilling of several test wells 

30-50 m deep was started north and east of the 

Hogback. One of the wells, about 2 km east of the 

northeast flank of the Hogback, had abnormally 

high temperatures and a temperature gradient of 

200°-300°C per km. Data from the first eight 1-m 

temperature holes were too sparse to be conclusive, 

but they suggested even higher subsurface temperature and gradients west of the test well toward Upsal 

Hogback (fig. 13).

TEMPERATURE SURVEY ON OCTOBER 29, 1975

By late October 1975, 20 test wells and 18 1-m 

temperature holes had been completed. Sites of some 

of the test wells were selected on the basis of the 1-m 

survey in June. However, the pattern of the anomaly 

indicated by the 1-m survey on October 29,1975 was 

appreciably different from that indicated by the 

survey on June 15. Instead of an increase in 

temperature toward Upsal Hogback, two thermal 

maxima appeared in the October survey. The first 

maximum was centered at the test well mentioned 

above, and a second, somewhat broader, maximum 

was centered about 2 km north of the Hogback (fig. 

14).

TEMPERATURE SURVEY ON DECEMBER 2, 1975

The final temperature measurements at 1-m depth 

near Upsal Hogback were made at 28 sites on 

December 2, 1975. The thermal anomaly defined by 

this survey was generally similar to that defined by
22

110

100

90

80

70

60

a

u. 

O

I

a. 

LU 

Q

<

<

ui 50

CC

D 

H 

< 

CC

UJ

a.

01

H 40

30

20

22

TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA 

24 26 28 30 32 34

B17

1

36

I

T20=8.43T1 -180.7 

r2=0.95

O

I

110

100

90

80

70

60

50

40

30

20

24 26 28 30 32 34 36

TEMPERATURE AT A DEPTH OF 1 m (T.,), IN DEGREES CELSIUS

FIGURE 11.—Correlation of temperatures at a depth of 20 m with temperatures at a depth of 1 m in Soda Lakes area, September 1974.
B18 GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

118° 45'

39 40

Base from USGS 15' topo series 

Desert Peak, 1951; Carson Sink, 1951; 

Soda Lake, 1951; Stillwater, 1950. 

.1.0

4 KILOMETERS

EXPLANATION 

Test well and depth of water table, in meters

1185 —— Water-level contour

Altitude of water table, in meters above mean sea level. 

Arrows show inferred direction of ground-water flow

FIGURE 12.—Upsal Hogback area showing depth to the water table in test wells, configuration of the water table, 

and direction of shallow ground-water movement in July 1975.
TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA

118° 50' 118°45'

B19

39°45'

39° 40'

Base from USGS 1S' topo series

Desert Peak, 1951; Carson Sink, 1951; L~ 

Soda Lake, 1951; Stillwater, 1950. EXPLANATION 

• Measurement site

—— 20 ^— Line of equal temperature at a depth of 1 meter 

Interval, 1 degree Celsius

FIGURE 13.—Upsal Hogback area showing temperature at a depth of 1 m, June 1975.
B20

118° 50'

GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

118° 45'

39° 45'

39° 40'

Base from USGS 15' topo series 

Desert Peak, 1951; Carson Sink, 1951; 

Soda Lake, 1951; Stillwater, 1950. EXPLANATION

• Measurement site

—18-—• Line of equal temperature at a depth of 1 meter.

Dashed where uncertain. Interval, 1 degree Celsius

FIGURE 14.—Upsal Hogback area showing temperature at a depth of 1 m, October 29,1975.
TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA B21

the October 29 survey, but there were some differences in detail, owing in part to the greater number of 

measurement sites for the December survey (fig. 15). 

The center of the thermal maximum east of the 

Hogback was about 400 m west of where it had been 

in late October, and the thermal minimum between 

the two maxima had a greater amplitude than it did 

in October.

TEMPERATURE AT A DEPTH OF 30 M, SEPTEMBER 1975

By September 1975, temperatures in the 20 shallow 

test wells near Upsal Hogback had stabilized 

sufficiently so that temperatures and temperature 

gradients below the zone of measurable annual 

fluctuation could be determined with fair accuracy. 

As shown in figure 16, the temperature at a depth of 

30 m defined a pattern that differed considerably in 

detail from the patterns indicated by three 1-m 

surveys from June to December 1975. The thermal 

maximum east of the Hogback, which was noted in 

the 1-m surveys for October and December, also was 

the maximum for the 30-m measurements in 

September. The amplitude of the anomaly at 30 m 

was about 12°C: temperature ranged from less than 

15°C on the northeast edge to more than 26°C at the 

center, at the test well described earlier. The amplitude of the equivalent anomaly at 1 m was about 3.3° 

-3.7°C in both the October and December surveys. In 

contrast to the fairly good agreement between 1-m 

and 30-m temperature anomalies east of the Hogback, the correlation between the patterns at the two 

depths appears to be rather poor in the rest of the 

Upsal Hogback area. The thermal maximum north 

of the Hogback delineated in both the October and 

December 1-m surveys did not appear as a separate 

maximum at 30 m: the minimum between the two 

maxima at 1 m was not present at 30 m.

CORRELATION OF TEMPERATURES AT DEPTHS OF 1 M 

AND 30 M

From the differences between the thermal anomalies at 30 m and 1 m described above, it might be 

inferred that the correlation of temperatures at the 

two depths also is poor. As shown in figure 17, this is 

indeed the case. The least-mean-squares linear 

regression of temperature at 30-m versus temperature at 1-m for December 1975 is

T30 = 1.02 TI +7.55

but r2 , the coefficient of determination, is only 0.23; 

this figure indicates a very poor correlation. Unlike 

the situation in the Soda Lakes area, where the 

amplitude of the thermal anomaly at 30 m exceeds 

100°C, the amplitude of the anomaly northeast of

Upsal Hogback is only 12°C. This difference in large 

part accounts for the good correlation in the first 

area and the poor correlation in the second.

CONCLUSIONS

The results of this study confirm the general 

principle that the utility of temperature measurements at a depth of 1 m in geothermal exploration is 

directly related to the magnitude of the temperature 

and heat-flow anomalies at greater depths and 

inversely related to the magnitude of perturbing 

influences such as local variations in the character 

and moisture content of the near-surface materials, 

topography, depth to the water table, vegetation, 

land use, and microclimate.

Temperature measurements at 1 m are most 

successful in delineating geothermal areas where 

lateral variations in temperature at greater depths 

are very large and where near-surface geothermal 

heat flows are thousands or tens of thousands times 

larger than background values. In the present study, 

the detailed survey of the small area surrounding the 

fumarole and abandoned steam well northeast of the 

Soda Lakes exemplifies the optimum case. There, the 

exceedingly high temperatures at 1 m, which exceed 

90°C near the fumarole, almost certainly reflect heat 

transfer by ascending steam rather than by conduction. In such a situation, closely spaced temperature 

measurements at 1 m may be used to determine the 

nature and configuration of the near-surface 

hydrothermal-discharge system. The technique is 

especially applicable to the study of hot-spring areas 

where subsurface leakage of thermal water from the 

conduit system is suspected, or to areas like the one 

surrounding the steam well, where steam rather 

than thermal water is present near the surface.

Somewhat more equivocal results are obtained 

with 1-m temperature surveys where convective heat 

transport by rising steam or hot water does not 

extend to the land surface or where geologic, 

topographic, hydrologic, and other factors not 

related directly to geothermal heat flow are highly 

variable. The temperature surveys of the Soda Lakes 

area in November 1973 and in June and September 

1974 are examples of this case. The general 

configuration of the thermal anomaly resulting from 

hydrothermal discharge into a shallow aquifer 

system had been established in that area on the basis 

of temperature surveys in test wells 20-50 m deep. 

Good correlation between temperature at 20 m and 

temperatures at 1 m at the test-well sites (fig. 11) 

suggested that the data for the 1-m surveys could be 

used with some assurance to infer the nature and 

configuration of the thermal anomaly at greater
B22

118° 50'

GEOHYDROLOGY OF GEOTHERMAL SYSTEMS

118°45'

39°45'

39°40

Base from USGS 1 s' topo series 

Desert Peak, 1951; Carson Sink, 19 51; ' 

Soda Lake, 1951; Stillwater, 1950 EXPLANATION 

• Measurement site

0 4 KILOMETERS

—— 13 —— Line of equal temperature at a depth of 1 meter. 

Interval, 1 degree Celsius

FIGURE 15.—Upsal Hogback area showing temperature at a depth of 1 m, December 2, 1975.
TEMPERATURE SURVEYS IN GEOTHERMAL EXPLORATION IN NEVADA

118°50' .118*45'

39°45'

B23

39°40'

Base from USGS is' topo series 0

Desert Peak, 1951; Carson Sink, 1951; ""—

Soda Lake, 1951, Stillwater, 1950. EXPLANATION

• Test well 

—— 18 ——

4 KILOMETERS

Line of equal temperature at a depth of 30 meters. 

Interval, 1 degree Celsius

FIGURE 16.—Upsal Hogback area showing temperature in test wells at a depth of 30 m, September 1975.
B24 GEOHYDROLOGY OF GEOTHERMAL SYSTEMS 

10 11 12 13 14 15

28

26

24

8

t 22

E

20

18

16

14

T30=1.02T1 +7.55 

r2=0.23 v

°0

28

26

24

22

20

18

16

14

10 11 12 13 14 15

TEMPERATURE AT A DEPTH OF 1 m (T.,), IN DEGREES CELSIUS

FIGURE 17.- -Correlation of temperature at a depth of 30 m with temperature at a depth of 1 m in Upsal 

Hogback area, December 1975.

depths in considerably greater detail than would be 

possible from the test-well data alone. Locally, 

however, particularly at wind-scoured depressions, 

the effects of topography, geology, and hydrology 

(especially depth to the water table) on temperature 

at 1 m are sufficiently large to overwhelm the 

temperature differences caused by lateral variations 

in geothermal heat flow. The large differences in the 

amplitude and phase of the annual temperature 

waves at a site in clay and silt of a wind-scoured 

depression in comparison with two other sites on 

sandy flats illustrate the need to allow for extraneous

factors in interpreting the shallow temperature data. 

The least favorable results are obtained with 1-m 

temperature surveys where the amplitude of the 

temperature anomaly at greater depths is relatively 

small, near-surface heat flows are from a few times to 

a few tens of times regional background values, and 

the perturbing effects of the nongeothermal influences are large. The temperature surveys of the 

Upsal Hogback area represent this case. There, the 

temperature of the thermal water leaking into 

shallow aquifers is much less than that in the Soda 

Lakes area, probably because of greater mixing with
REFERENCES CITED B25

shallow, cool ground water, and the range in depth to 

the water table, topographic relief, and variability of 

geologic materials are greater than in the Soda 

Lakes area. As a result, temperatures at a depth of 

1 m have little or no correlation with temperatures 

at greater depths.

The serious risk that arises in attempts to use 1-m 

temperature surveys in places like the Upsal 

Hogback area is the identification of thermal 

anomalies that are actually unrelated to true 

geothermal anomalies at greater depth. This problem is highlighted by the reportedly successful use of 

shallow temperature surveys for a variety of 

purposes unrelated to geothermal investigations. 

Such uses include mapping of buried shallow glacial 

aquifers (Cartwright, 1966, 1968; Carr and Blakely, 

1966; Parsons, 1970); correlation of shallow temperatures and temperature fluctuations with depth to 

water or depth to bedrock (Birman, 1969; Cartwright, 

1974); analysis of the effects of vegetative cover on 

the thermal regime of soils and subsoils (Singer and 

Brown, 1956; Pluhowski and Kantrowitz, 1963; Kane 

and others, 1975); mapping of buried water-bearing 

joints, fissures, or caverns in bedrock (Ebaugh and 

others, 1974); determination of stream reaches 

receiving ground-water discharge (Hollyday and 

others, 1972); and determination of the effect of 

various soil-management procedures in altering the 

thermal regime of agricultural soils (Van Duin, 

1963). All these uses have one principle in common: 

lateral variations in geothermal heat flow or in 

temperature below the depth of measurable annual 

temperature fluctuation are considered a perturbing 

influence and are treated in the analysis as "noise" 

in the data. Thus, to the extent that the types of 

studies listed above are successful, the use of shallow 

temperature measurements in geothermal studies 

would be unsuccessful, and vice versa. 

REFERENCES CITED

Birman, J. H., 1969, Geothermal exploration for ground water: 

Geol. Soc. America Bull., v. 80, p. 617-630.

Carr, D. R., and Blakely, R. F., 1966, Temperature variation at a 

depth of 30 cm in clay till and outwash sand and gravel, in 

Symposium on remote sensing of environment (ONR and 

AFCRL) 4th, 1966, Proceedings, University of Michigan, 

Willow Run Laboratories, Ann Arbor, Michigan, p. 203-214.

Cartwright, Keros, 1966, Thermal prospecting for shallow glacial 

and alluvial aquifers in Illinois [abs.]: Geol. Soc. America Abs. 

with Program, 1966 Annual Meeting, p. 36.

———1968, Temperature prospecting for shallow glacial and 

alluvial aquifers in Illinois: Illinois State Geological Survey 

Circ. 433, 41 p. 

-1974, Tracing shallow groundwater systems by soil temperatures: Water Resources Research, v. 10, no. 4, p. 847-855. 

Ebaugh, W. R., Greenfield, R. J., and Parizek, R. R., 1974, Temperature patterns in soil above caves and fractures in bedrock 

[abs.]: Geol. Soc. America Abs. with Programs, Cordilleran

Section 70th Annual Meeting, v. 6, no. 3, p. 171.

Hardman, George, 1965, Nevada precipitation map, adapted from 

map prepared by George Hardman and others, 1936: University of Nevada, Agricultural Experimental Station Bull. 183, 

57 p.

Hollyday, E. F., Scherer, L. R., and Hall, Thomas, 1972, Stream 

groundwater interface: Temperature gradients and groundwater discharge [abs.]: Geol. Soc. America Abs. with Programs, Annual Meetings, v. 4, no. 12, p. 541-542.

Kane, D. L., Luthin, J. N., and Taylor, G. S., 1975, Heat and mass 

transfer in cold region soils: Alaska University, College, 

Institute of Water Resources, Publication No. IWR-65, 50 p.

Kappelmeyer, O., 1957, The use of near-surface temperature 

measurements for discovering anomalies due to causes at 

depths: Geophysical Prospecting, v. 5, no. 3, p. 239-258.

Kintzinger, P. R., 1956, Geothermal survey of hot ground near 

Lordsburg, New Mexico: Science, v. 124, p. 629.

Lachenbruch, A. H., 1959, Periodic heat flow in a stratified 

medium with application to permafrost problems: U.S. Geological Survey Bull. 1083-A, 36 p.

Levering, T. S., and Goode, H. D., 1963, Measuring geothermal 

gradients in drill holes less than 60 feet deep, East Tintic 

district, Utah: U.S. Geological Survey Bull. 1172, 48 p.

Morrison, R. B., 1964, Lake Lahontan: geology of the southern 

Carson Desert, Nevada: U.S. Geological Survey Prof. Paper 

401, 156 p.

National Oceanic and Atmospheric Administration, 1975, Climatological Data, Nevada, Annual Summary 1975: U.S. Department of Commerce, NOAA (formerly U.S. Weather Bureau), 

v. 90, no. 13.

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. Geological Survey open-file report 75-56,267 p.

Parasnis, D. S., 1971, Temperature extrapolation in infinite time 

in geothermal measurements: Geophysical Prospecting, v. 19, 

p. 612-614.

Parsons, M. L., 1970, Ground-water thermal regime in a glacial 

complex: Water Resources Research, v. 6, no. 6, p. 1701-1720.

Pluhowski, E. J., and Kantrowitz, I. H., 1963, Influence of landsurface conditions on ground-water temperatures in southwestern Suffolk County, Long Island, New York, in Geological Survey research 1963: U.S. Geological Survey Prof. 

Paper 475-B, p. B186-B188.

Rush, F. E., 1972, Hydrologic reconnaissance of Big and Little 

Soda Lakes, Churchill County, Nevada: Nevada Department 

of Conservation and Water Resources, Water Resources Information Service Report 11.

Singer, I. A., and Brown, R. M., 1956, The annual variation of 

sub-soil temperatures about a 600-foot diameter circle: Am. 

Geophys. Union Transactions, v. 37, p. 743.

U.S. Geological Survey, 1972, Aeromagnetic map of parts of the 

Lovelock, Reno, and Millet 1° by 2° quadrangles, Nevada: 

U.S. Geological Survey open-file report, scale 1:250,000.

Van Duin, R. H. A., 1963, The influence of soil management on 

the temperature wave near the surface: Instituut voor Cultuur 

Technick en Waterhuishouding, Wageningen, Tech. Bull. 29, 

21 p.

Van Wijk, W. R., and Derksen, W. J., 1966, Sinusoidal temperature 

variation in a layered soil, ch. 6 in Van Wijk, W. R., ed., 

Physics of plant environment: Amsterdam, Holland, North 

Holland Publishing Company, p. 171-209.

Wahl, R. R., 1965, An intrepretation of gravity data from the 

Carson area, Nevada: Stanford University, Department of 

Geophysics, Student Report, Stanford University, California.

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