Ann. Rev. Earth Planet. Sci. 1989. 17:13-53
ANNUAL
REVIEWS
Further
Quick links to online content
GEOCHEMISTRY AND
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
DYNAMICS OF THE
YELLOWSTONE NATIONAL
PARK HYDROTHERMAL SYSTEM!
Robert O. Fournier
US Geological Survey, Menlo Park, California 94025
INTRODUCTION
The magmatic-hydrothermal system at Yellowstone National Park is
unique among presently active systems in regard to its unparalleled geysers,
tectonic environment, and magnitude of caldera-forming volcanic activity.
However, over geologic time, systems like Yellowstone have been common
and appear to have been responsible for the formation of many important
basc-metal and precious-mctal ore deposits. For these reasons, Yellow­
stone has received a great amount of scientific attention. Geologic inves­
tigations in Yellowstone began with the Hague expedition in the late 1 800s,
and the results of the first chcmical analyses of thermal waters from the
Park's many hot springs and geysers were published in 1 88 8 by Gooch &
Whitfield ( 1 888). Since then, numerous investigators have studied the
hydrothermal system and its geologic environmcnt, and data collectcd
over a span of a hundred years are available for comparison and
interpretation.
THE GEOLOGIC AND GEOPHYSICAL SETTING
The geologic setting and geophysical characteristics of the Yellowstone
National Park region have been described by many investigators. Par­
ticular attention is called to summaries by Smith & Christiansen ( 1 980),
1 The US Government has the right to retain a nonexclusive royalty-free license in and to
any copyright covering this paper.
13
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
14
FOURNIER
Christiansen (1 984), Smith & Braile ( 1 984), Fournier & Pitt ( 1 985), and
the Yellowstone National Park Task Group ( 1 987). Yellowstone Park is
situated on a high volcanic plateau that sits astride a region of active maj or
crustal extension. This plateau and the adjacent region to the west have
been the most seismically active area of the Rocky Mountains in historic
time (Smith & Braile 1 984). According to Christiansen ( 1 984), volcanism
in the Yellowstone region has been active for the last 2.2 Myr, and the
erupted lavas and tuffs have been predominantly rhyolitic and sub­
ordinately basaltic. M ajor caldera-forming eruptions of silicic pyro­
clastics occurred about 2.0, 1 . 3, and 0.6 Ma (Figure 1 ), and each of
these was preceded and succeeded by large eruptions of rhyolitic lava.
The last eruption of rhyolitic lava was about 70,000 yr B .P. (Christiansen
1 984).
A variety of geophysical anomalies coincide with the 0.6-Ma Yellow­
stone caldera that, taken together, indicate that the magmatic system at
Yellowstone is still vigorous and that temperatures in excess of 3 50°C exist
at very shallow depths. These anomalies include low densities (Blank &
Gettings 1 974), large convective and conductive heat flows (Fournier et al
1 976, Morgan et al 1 977, White 1 978), a magnetic low and shallow cal­
culated Curie-point isotherms (Smith et al 1 974, Bhattacharyya & Leu
1 975, Eaton et al 1 975), low seismic velocities (Iyer et al 1 98 1 , Daniel &
Boore 1 982);high seismic attenuation (Benz & Smith 1 984, Brokaw 1 98 5),
a sharp increase in electrical conductivity at a depth of about 5 km, shown
by magnetotelluric soundings (Stanley et al 1 977), and a lack of seismic
focal depths deeper than about 3-4 km beneath much of the Yellowstone
caldera (Fournier & Pitt 1 985). In addition, there has been a spatial
and temporal pattern of historical deformation-inflation followed by
deflation (Pelton & Smith 1 979, 1 982, Jackson et a11 984, Hamilton 1 985,
Dzurisin et al 1 986, Meyer & Lock 1 986, Dzurisin & Yamashita 1 987)­
that is difficult to explain by processes that do not involve magmatic
activity.
The combined geologic and geophysical data support a model in which
magma or partially molten material underlies much of the O.6-Ma Yel­
lowstone caldera at depths ranging from about 5 to 1 0 km, and possibly
as shallow as 3 km beneath portions of the eastern half of the caldera
(Eaton et a1 1 975, Iyer et a1 1 98 1 , Lehman et a1 1 982, Smith & Braile 1 984,
Benz & Smith 1 984, Brokaw 1 985) . A sharply bounded sei,smic low-velocity
zone in the western part of the Park was reported by Lehman et al ( 1 982)
that would have been compatible with the presence of partially molten
rock at a depth of 3-4 km in a N-S belt just to the west of Upper Geyser
Basin and extending to Shoshone Geyser Basin. However, Lehman et al
( 1 982) cautioned that this low-velocity zone might be fictive, the result of
15
YNP HYDROTHERMAL SYSTEM
\
'-\.,"'-
(
'.,
'/
,
,-�.
'--
.
-"
MH����--------''-.
1.
•
I
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
r�
I
I
f.q,.
\'-" "a:
1.....1"\. MJ._.
-,
)CS
> '
�
�
, I
/
\
'TB
.�...
\
-.
',\
)
.
;
<'9
\.
\
\.
(}
�B
\.
,--.
...
'\.
\
./ ...:)
,f'
, .r' __ J
,.-'
\
10
Figure 1
20
30
40
50km
Locations of major rivers draining Yellowstone National Park (dot-dashed lines)
and calderas of the Yellowstone Plateau volcanic field: northeast-slanting lines within the
2.0-Ma first-cycle caldera, northwest-slanting lines within the 1 .3-Ma second-cycle caldera,
and horizontal lines within the O.6-Ma third-cycle caldera. Crosshatched areas show re gions
of caldera overlap. Letter codes show river names and approximate locations of places
mentioned in text: BC, Boundary Creek; CH, Crater Hills; CS, Calcite Springs; FAR,
Falls River; FHR, Firehole River; GAR, Gardner River; GBR, Gibbon River; GC, Grand
Canyon; HL, Heart Lake; HLB, Heart Lake Basin; HSB, Hot Springs Basin; JC, Josephs
Coat Hot Springs; LB, Lower Basin; LL, Lewis Lake; LR, Lamar River; MB, Midway Basin;
MH, M ammoth Hot Springs; MJ, Madison Junction; MR, Madison River; MV, Mud
Volcano; NB, Norris Basin; RS, Rainbow Springs; SB, Shoshone Basin; SJ, Smoke Jumper;
SL, Shoshone Lake; SR, Snake River; TB, Tower Bridge; UB, Upper Basin; WS, Washburn
Hot Springs; WT, West Thumb; YL, Yellowstone Lake; YR, Yellowstone River. Outline
of Yellowstone National Park shown for reference. Figure revised and redrawn after
Christiansen (1984).
an attenuation problem in which very weak first arrivals were not detected.
Subsequent seismic experiments with better recording-station coverage
have shown that, indeed, there was an attenuation problem with the earlier
data, and that a 4.0 km s -I low-velocity zone does not exist at a shallow
level beneath the western part of the Park (Brokaw 1 985).
16
FOURNIER
DISTRIBUTION AND TYPES OF
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
HYDROTHERMAL ACTIVITY
The distribution of active and recently active hydrothermal features in
Yellowstone is shown in Figure 2. They are mostly within the O.6-Ma
Yellowstone caldera, close to the outer edge of the main ring fracture
zone or at the margins of two resurgent domes. Tn addition, pronounced
hydrothermal activity occurs in a linear band along a system of faults
extending northward from N orris Geyser Basin through M ammoth Hot
Springs.
o
10
20
3.0
40
50 km
�'----�'----'�--�.�---'�--�'
Figure 2
Map of Yellowstone National Park, Wyoming, USA, showing O.6-Ma Yel­
lowstone caldera, two resurgent domes, active and recently active hydrothermal features
(solid black), major faults (solid lines outside caldera region), and locations of selected named
thermal areas (key to place names given in Figure 1 legend). Figure redrawn after Christiansen
(1984).
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP HYDROTHERMAL SYSTEM
17
Representative analyses of thermal waters from major hydrothermal
localities in Yellowstone are shown in Table 1 . Waters from many of the
Yellowstone hot springs and geysers were collected and analyzed in the
late 1 800s (Gooch & Whitfield 1 888), and a later exhaustive study was
carried out in 1 925-30 by Allen & Day ( 1 935). Investigators who have
collected and analyzed the thermal waters and gases since 1 959 include
Noguchi & Nix ( 1 963), Scott ( 1 964), Mazor & Wasserburg ( 1 965), Gunter
& Musgrave ( 1 966), Schoen & Rye ( 1 970), Muffler et al ( 1 97 1), Gunter
( 1973), Mazor & Fournier ( 1 973), Rowe et al ( 1973), Thompson et al
( 1 975), Truesdell et al ( 1 977), Craig et al ( 1 978), Kim & Craig ( 1 979),
Thompson & Yadav ( 1 979), Kennedy et al ( 1 982, 1 985, 1 987), M azor &
Thompson ( 1 982), and Truesdell & Thompson ( 1 982). Although changes
in the behavior of individual hot springs and geysers are common within
the Park, there has been no significant change in the range of water
compositions exhibited by the hot springs and geysers for at least a century,
and probably much longer.
Most of the hydrothermal activity in the western half of the Park is
typical of hot-water systems in which fluid pressures steadily increase
downward and the maximum temperature attainable at a given depth is
given by a boiling-point curve based on hydrostatic conditions. All of the
major geyser basins in Yellowstone Park, except Norris and Heart Lake,
lie within the portion of the 0.6-Ma Yellowstone caldera that overlaps the
2.0-Ma caldera (Figure 1, horizontal line pattern overlaying northeast line
pattern). Rhyolite flows precede the ash-flow eruptions that formed the
2.0-Ma caldera, and it is likely that other rhyolite flows partly filled this
caldera prior to the ash-flow eruptions that formed the 0.6-Ma caldera.
Therefore, within the portion of the 0.6-Ma caldera that overlaps the 2.0Ma caldera, the general sequence of volcanic rocks is likely to be precal­
dera rhyolite flows, relatively impermeable 2.0-Ma ash-flow tuff, per­
meable rhyolite flows, relatively impermeable 0.6-Ma ash-flow tuff, and
permeable rhyolite flows. Thus, relatively permeable rhyolite flows are
present at various depths that can serve as fluid reservoirs within rela­
tively impermeable ash-flow tuff.
In the eastern part of the O.6-Ma caldera, where it does not overlap the
2.0-Ma caldera, most of the caldera fill is likely to be relatively impermeable
2.0-Ma and 0.6-Ma ash-flow tuffs with little interlayered permeable rhyolite
flow material, although one major rhyolite flow caps some of the ash-flow
tuff. In this part of the caldera, vapor-dominated hydrothermal activity
is prevalent in which fluid pressures remain nearly constant through a
significant depth interval (White et al 1971). This is also the part of the
Park in which magma or partly molten material may be closest to the
surface (Lehman et al 1 982).
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
00
Table 1
Chemical analyses of selected thermal waters from Yellowstone National Park
Locality
Name
5
3
Number
"r1
10
Mammoth
West
Shoshone
Heart
Lower
Upper
Upper
Grand
Norris
Norris
Hot Springs
Thumb
Basin
Lake Basin
Basin
Basin
Basin
Canyon
Basin
Basin
Y-IO
Lakeshore
Washtub
Unnamed
Ojo
Punch
Ear
Unnamed
Porcelain
Cinder
drill hole
Geyser
Spring
Caliente
Bowl
Spring
Sevenmile
Terrace
Pool
17528
17908
Hole
Sample No.
Date
Temp. eC)
pH
SiO, (mg kg-I)
Al
Fe
Ca
Y-IO
17484
T7214
T7348
09/13/69
10/09/74
09/72
09/73
70
7.48
90
7.76
0.01
0.14
2.4
0.05
450
9.48
366
17956
17615
09/29/76
95
1-74
230
94
8.33
312
94
8.49
371
91
93.5
8.61
534
0.9
0_75
0.67
0.82
0.5
2.12
0.05
0.01
0_01
0.02
0.01
0.Q2
0.03
408
69
20
3.24
365
16
1.0
329
0.06
0.4
161
92
3.57
654
0.51
Na
1.8
93.5
17836
2.0
80
NH,
9.00
328
88
Mg
K
Li
81
17560
6.3
0.12
382
330
420
319
366
404
346
21
10
17
27
58
81
81
6.6
3.6
3.8
4.9
3.45
5.8
3.9
0.1
1.0
HeO,
997
531
406
306
246
590
146
223
SO,
800
55
48
100
26
19
19
85
31
147
CI
171
261
328
365
326
289
415
427
669
569
36
30
28
24
F
4.2
14.5
25.5
B
3.8
3.3
2.8
2
3
Reference'
2.4
3-8
2
3.8
3.6
4
47
12.8
5.8
16
9.9
2
2
6
0
e
::<:I
§::<:I
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
Table 1
(Continued)
Number
Locality
Name
Sample No.
Date
Temp. Cc)
pH
SiO, (mg kg-I)
AI
11
[2
13
14
Norris
Crater
Upper
Hot Springs
Basin
Hills
Echinus
Crater Hills
Iron
Geyser
Geyser
Spring
17846
93
3.2
278
Basin
17804
09/28/78
88
3.18
676
1920s
9[
3.7
365
Basin
Unnamed
16
15
17
18
19
20
Hot Springs
Upper
Boundary
Washburn
Washburn
Hot Springs
Basin
Creek
Hot Springs
Hot Springs
Unnamed
Unnamed
Hillside
Unnamed
Unnamed
Unnamed
Josephs Coat Josephs Coat
group
YF448
YF451
YF452
06/22/69
06/26/69
06/26/69
89
2.66
3[7
86
94
333
83
9.38
1.82
T9-10
238
8.62
170
0.60
17930
92
7.94
21()
17304
09/22/73
91
YF429
06/22/69
86
8.00
247
0.2
0.13
Fe
Ca
Mg
Na
K
4.9
5.64
0.52
1.04
166
50
Li
640
133
0.7
NH,
Trace
77
28
6.9
37.1
3.75
187
16
0.04
4
171
4.1
3.4
7.9
0.39
0.01
0.27
17.1
0.01
57.3
109
19
0.[8
()
()
0
0
0
335
337
566
23[
1530
1830
24
CI
108
890
F
5.6
B
3.0
Referencea
4-
27.5
20
0.1
1.2
2.2
USGS (R.
(2) Thompson & Yadav (1979)
(3) Thompson et al (1975)
0.8
5.05
0.07
0.83
0.1
251
[4.2
5.4
72
3.7
12
0.36
1.17
Barnes, analyst)
18[
1 1. 2
1.2
0.51
259
10
(4) Unpublished data, USGS
(5) Allen & Day (1935)
(J.
M.
(6) Thompson & Hutchinson (1980)
Thompson, analyst)
2
17.2
9.7
27.1
6.5
13.7
4.10
0.1
270
107
900
9.3
0.1
658
8.2
1950
107
19.1
1.0
6
4
• References:
(I) UnpUbliShed data,
0.1
7.7
22.4
SO,
HC03
1 50
4.1
0.10
0.1
6.6
0.5
7.84
i
'1i
:t:
><
0
:;:J
0
>-l
51
:;c
�
:>
t"'
VJ
><
VJ
>-l
rI1
�
......
'-0
20
FOURNIER
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
Hot- Water Systems
The typical surface expression of a high-temperature hot-water system is
boiling hot springs, possibly with geyser activity, that discharge significant
quantities of neutral to slightly alkaline water. The famous geyser basins
of Yellowstone National Park are probably the best examples in the world
of this type of hydrothermal activity. These include Upper, Midway,
Lower, West Thumb, and Shoshone Geyser Basins within the caldera and
Heart Lake and Norris Geyser Basins just outside the caldera (Figure 2).
Thermal waters tend to emerge where faults cut across the topographically
low basins, and hydrothermal activity is most pronounced at the inter­
sections of faults. The waters are mostly chloride rich (Table I, numbers
2-9) and deposit siliceous sinter that over the years has accumulated in
thick mounds and terraces. However, acid-sulfate boiling pools with little
or no discharge of liquid water (Table 1 , number 1 3) and mud pots occur
in some of the geyser basins where upflowing boiling water is only a few
meters below the land surface. In these instances, the residual liquid-water
fraction generally flows laterally a relatively short distance to emerge as a
boiling spring in a topographically low area. The steam that separates
from boiling, alkaline-chloride waters generally contains H 2 S that oxidizes
to H2S04 when it comes into contact with air in perched pools of ground­
water. Examples of steam-heated acid-sulfate features above shallow, boil­
ing, alkaline-chloride water are Iron Spring in the Upper Geyser Basin
(Table 1, number 1 3), the Fountain Paint Pot in the Lower Geyser Basin,
and the Thumb Paintpots at West Thumb.
Hydrothermal fluids that issue from all the geyser basins cited above
flow to the surface from reservoirs that have temperatures ranging from
about 1 800 to 270°C (Fournier et al 1976) at minimum depths of 1 00 to
550 m (estimated using theoretical boiling-point versus depth curves for
hydrostatic conditions). These reservoirs are situated within thick
sequences of rhyolitic lava flows and ash-flow tuff of relatively uniform
chemical composition.
Thermal waters at Mammoth are very different from those in the geyser
basins. The Mammoth thermal waters flow to the surface through a thick
sequence of sedimentary rocks that includes limestone, dolomite, and
gypsum-hearing shales. Consequently, they are rich in bicarbonate and
sulfate (Table 1 , number 1 ). Relatively high concentrations of calcium and
magnesium and low silica concentrations reflect a low temperature of
water-rock equilibration at Mammoth: An isothermal temperature of 73°C
was measured in a 1 1 2.8-m well, and 88°C was estimated by chemical
geothermometry (White et al 1 975). At higher temperatures magnesium
and calcium are removed from solution, mostly as silicates and carbonate,
YNP HYDROTHERMAL SYSTEM
21
and the fluid becomes richer in sodium and potassium. I n general, thick
travertine deposits, such as those found at Mammoth, are found only
where limestone is in the section traversed by the thermal fluid and res­
ervoir temperatures are less than about 1 00--1 20°C.
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
Vapor-Dominated Systems
In vapor-dominated systems, steam and other gases (mainly CO2 and some
H2S) fill open fractures throughout a significant vertical extent beneath a
cap that acts as a throttle, and liquid water is present mainly in pore
spaces. The vapor-dominated zone essentially acts as a heat pipe, with
rising steam carrying thermal energy upward and volumetrically small
amounts of liquid water, formed by condensation of steam, flowing back
downward. The cap at the top of the vapor-dominated zone is generally
considered to be relatively impermeable rock that may support a zone of
perched water that is a mixture of local meteoric water and condensed
steam. Temperatures and pressures commonly change very little within
the vapor-dominated zone, which (in consequence) is underpressured with
respect to a normal hydrostatic system. The existence of a hydrostatically
underpressured system requires either that the vapor-dominated region be
perched above the surrounding lowlands in topographically high terrain or
that a region of relatively low permeability surrounds the vapor-dominated
zone, effectively preventing the free movement of cold groundwater into
the system.
Typical surface expressions of underlying vapor-dominated systems are
fumaroles, acid-sulfate boiling pools with little or no discharge of liquid
water (Table 1 , numbers 14 and 1 5), mud pots, and absence of nearby
alkaline-chloride thermal waters issuing at the surface. Throughout much
of the relatively high plateau region in the east-central part of the Park,
violently boiling, steam-heated pools of acid-sulfate water containing little
chloride and with little or no visible discharge of liquid water dot barren
landscapes composed predominantly of residual quartz, clays, sulfates,
and native sulfur. Vapor-dominated conditions are thought to underlie
much of this region (White et aI1 97 1), and a vapor-dominated system has
been confirmed by research drilling at Mud Volcano (White ct al 1 975,
Zohdy et al 1 973). Mud Volcano is the most accessible of these localities,
but other major acid-sulfate thermal manifestations are at Hot Springs
Basin, Josephs Coat Hot Springs, and Washburn Hot Springs (Figure 1 ).
Within the heat-pipe zone of large vapor-dominated systems, such as
The Geysers in California and Larderello in Italy, the temperature is
generally about 240°C with a corresponding vapor pressure of water about
33 bars (White et al 1 97 1 ). In my experience, temperatures at the tops of
small vapor-dominated zones that have been explored by drilling in various
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
22
FOURNIER
parts of the world generally range from about 1 50° to 200°C, and thus the
steam that heats the overlying fumaroles, mud pots, and acid-sulfate pools
generally separates from the liquid-water fraction at a pressure of at least
5 to 1 5 bars. Therefore, upflowing steam that is rich in CO2 with minor
H2S may condense underground at a temperature above 150°C and react
with the surrounding rock. This reaction produces a solution rich in
sodium bicarbonate, poor in chloride (only a small amount of chloride is
leached from the local rock), and poor in sulfate (oxygen is not available
to oxidize H2 S much below the water table) (Table 1 , number 16). The
spring from which sample number 1 6 in Table 1 was collected is a very
small, continuously discharging, superheated spring in a region of boiling,
steam-heated pools that exhibit little or no discharge of liquid water.
Chemical geothermometry (Fournier 1 9 8 1 ) applied to this water indicates
a temperature of water-rock reaction of about 1 80-190°C. The com­
position of a nearby nondischarging, steam-heated pool is shown by sam­
ple number 1 5 in Table 1 . The latter water contains abundant sulfate
derived from the oxidation of H2S that is streaming through the pool, a
relatively large amount of the volatile constituent ammonia, very little
chloride, and ratios of cations indicative of decomposition of rock with
little water-mineral equilibration in the process.
All the chloride-poor thermal waters in the eastern part of the Park
contain relatively high concentrations of ammonia (e.g. numbers 14-16,
Table 1). The highest reported ammonia concentrations have been found
in feebly discharging hot springs in the Washburn Hot Springs region,
about 1 km north of the northern rim of the Grand Canyon of ·the
Yellowstone, where Allen & Day ( 1 93 5) found 893 mg kg- 1 NH4 and 2444
mg kg-1 S04 in one thermal water. Subsequent collections and analyses
of thermal waters from this area by the US Geological Survey (USGS)
confirm that the predominant dissolved constituent in the fluids is
ammonium sulfate, and silica is the next most abundant dissolved con­
stituent (Thompson et al 1 975). The amounts of dissolved ammonium
sulfate in different springs are highly variable, however. Examples of
thermal waters from the Washburn Hot Springs area are given in Table 1
(numbers 19 and 20). Allen & Day (1935) noted that the gas collected from
this locality contains appreciable methane ( 1 3 .20%) and ethane ( 1 . 1 5 %)
and concluded that the organic gas and ammonia are probably derived
from distillation of buried sediments. In general, this conclusion appears
to be justified, especially in view of the occurrence of hydrocarbons at
three localities in the eastern part of the Park: Tower Bridge, Calcite
Springs, and Rainbow Springs (Figure 1 ). Love & Good (1 970) studied
the hydrocarbons in thermal waters from these localities and from other
localities in an arcuate southeastward- to eastward-trending area about
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP HYDROTHERMAL SYSTEM
23
1 15 km long in northwestern Wyoming, and they concluded that the
source of the hydrocarbons could be Paleozoic or Mesozoic sediments that
underlie the surficial volcanics.
Evidently, hot water flushes petroleum from sedimentary rocks deep
underground, and mixtures of water and petroleum rise together along
fractures to the base of a vapor-dominated system situated beneath Wash­
burn Hot Springs. There, distillation at high temperature and high pressure
results in steam that is rich in organic gases and for which NH3> H2S.
Where this steam condenses at shallow levels, the accompanying H 2S is
oxidized to sulfuric acid, which is immediately converted to ammonium
sulfate by excess NH3 (A. H. Truesdell, oral communication, 1 988). This
results in a water that is slightly alkaline, containing mostly dissolved
ammonium sulfate (Table 1 , numbers 1 9 and 20).
The Mirror Plateau (that includes the eastern resurgent dome and Hot
Springs Basin, Figure 2) and Mud Volcano regions may not be the only
places within Yellowstone Park where vapor-dominated hydrothermal
systems occur. Boiling, acid-sulfate pools and mud pots occur throughout
an extensive area of acid-altered rock in the Smoke Jumper Hot Springs
region (Figures 1 , 2), which lies astride the Continental Divide. The outer
edge of the main fracture of the 0.6-Ma Yellowstone caldera is thought to
pass just to the west of this area of hydrothermal activity. It is possible
that relatively dilute thermal waters with high proportions of bicarbonate
to chloride found in the Boundary Creek region near the southwest corner
of the Park (Figure 2 and Table 1 , number 1 8), and similar waters flowing
from the Hillside group of hot springs in the Upper Geyser Basin (Table
1 , number 1 7), are in part steam condensate that flowed laterally away from
the topographically high Smoke Jumper Hot Springs system (Thompson &
Hutchinson 1 980).
Transition from Hot- Water- to Vapor-Dominated
at End of Glaciation
The surface expression of the hydrothermal system beneath the Mirror
Plateau has not always been characterized by acid-sulfate activity. Old,
decaying geyser mounds and soil-covered siliceous sinter deposits are
common throughout this region. Such sinter deposits form only where
alkaline-chloride thermal waters flow over the ground. Therefore, the
hydrothermal system has changed from hot-water- to vapor-dominated
since the end of the last glaciation, about 1 4,000 yr B.P.
During glaciation, fluid pressures within the hydrothermal system
increased and decreased in proportion to thc thickncss of the ice cover
(discussed in detail later). The increased hydrostatic head was probably
sufficient to inhibit the development of a vapor-dominated system or even
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
24
FOURNIER
to temporarily condense a preexisting vapor-dominated condition. After
the ice disappeared, it is likely that many years were required to generate, or
regenerate, vapor-dominated conditions at depth. Also during the waning
stage of glacial activity, ice probably remained within the gorge of the
Grand Canyon of the Yellowstone after the ice sheet had melted from the
adjacent plateau. Ice filling the Grand Canyon would have kept the regional
water table high, allowing alkaline-chloride hot springs to flow at relatively
high elevations. As the ice in the gorge diminished in volume, the water
table slowly lowered through rock that had previously been heated to very
high temperatures by upflowing thermal waters. This could cause the
hydrothermal activity in topographically high places to change from out­
flow of alkaline-chloride water to discharge of high-pressure steam, throt­
tled by poor permeability within highly altered and silicified rocks and by
perched NaHCOrrich groundwater that serves to keep a pressure lid on
the system. Alkaline-chloride waters still emerge at topographically low
places in the eastern part of the Yellowstone caldera, such as deep within
the Grand Canyon of the Yellowstone, where rapid erosion has cut a steep
gorge more than 350 m deep, and at Rainbow Springs, which is about 1.8
km NW of Hot Springs Basin and only about 50 m lower in elevation.
This suggests that some of the vapor-dominated hydrothermal activity in
the eastern part of the Park may be relatively shallow rooted. However,
in a region of generally impermeable rock underlain by a large heat source,
it is possible that there may be rapid lateral transitions from shallow,
alkaline-chloride hot-water to deep vapor-dominated conditions. Gravity
and P-wave velocity data are compatible with the presence either of partial
melt or a very deep and extensive vapor-dominated system extending from
Hot Springs Basin to beneath the eastern resurgent dome (Lehman et al
1 982, Smith & Braile 1 984).
FACTORS AFFECTING THERMAL FLUID
COMPOSITIONS
Fluid-Rock Interactions
The total dissolved solids in hydrothermal fluids are controlled in great
part by the availability and solubilities of salts that can be leached from the
wall rocks through which the fluids flow, augmented by anions contributed
from the influx of acid gases (mainly CO2 at Yellowstone). There is the
possibility, however, that some salinity may be contributed by a very small
amount of deep brine of magmatic origin that mixes with a large amount
of dilute water of meteoric origin (Fournier & Pitt 1 985). The maximum
amount of magmatic water mixed with water of meteoric origin cannot be
more than about 0.2-0.4% (discussed later).
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP HYDROTHERMAL SYSTEM
25
The effect of rock type on fluid compositions at Yellowstone was men­
tioned previously with regard to the relatively low-temperature bicar­
bonate- and sulfate-rich waters at Mammoth that issue from sedimentary
rock, compared with the chloride-rich waters that issue from rhyolitic
volcanic rocks. However, at high temperatures the effect of rock type is
generally greatly diminished because magnesium becomes incorporated in
clays and micas and the solubilities of CaC0 and CaS04 decrease as
3
temperature is increased, allowing waters to become relatively rich in alkali
chlorides. The compositions of the alkaline-chloride waters that issue in
hot springs reflect water-rock equilibration in rhyolitic rocks at estimated
temperatures ranging from about 1 60° to 350°C (Fournier et al 1976,
Truesdell & Fournier 1 976, McKenzie & Truesdell 1 977). However, lead
isotope data for hot-spring deposits (travertine and siliceous sinter) indi­
cate that all the thermal waters in the Park have a component that has
been in contact with sedimentary rock (Leeman et aI1977).
Cation ratios are controlled by temperature-dependent hydrolysis and
base-exchange reactions involving dissolved constituents and minerals in
the wall rock. Hydrothermal alteration of rhyolitic material encountered
in several relatively shallow drill holes has been described in a series of
reports (Honda & Muffler 1 970, Keith & Muffler 1 978, Keith et al 1978,
Bargar & Beeson 1981, Bargar & Muffler 1982). In general, glass-rich
rhyolitic material has altered to a variety of zeolites, clays, micas, and
hydrothermal K-feldspar. Minerals commonly found in veins i nclude
amorphous silica, chalcedony, quartz, calcite, fluorite, pyrite, iron oxides,
and various clays and micas.
Decompressionai Boiling and Underground
Mixing of Waters
In addition to rock-water interactions, decompressional boiling and under­
ground mixing of different waters are important processes that affect
hydrothermal fluid compositions in the hot-water systems at Yellowstone.
For example, variations in chloride and bicarbonate in Upper Basin ther­
mal waters, shown in Figure 3, result from varying degrees of conductive
cooling and decompressional boiling and from mixing of different thermal
waters that come from reservoirs that have only slightly different tem­
peratures. Waters that have cooled conductively without boiling as they
flowed slowly upward to the surface fall along line AC. At the other
extreme, waters that have undergone maximum decompressional boiling
without significant conductive cooling fall along line BD. One end-member
water has an initial composition prior to boiling shown by point A (the
Geyser Hill-type water of Fournier et aI 1 976), and the other has an initial
composition shown by point C (the Black Sand-type water of Fournier et
26
FOURNIER
700
600
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
ill
-0300
·C
o
::c 200
o
100
100
200
300
400
Bicarbonate,
Figure 3
500
600
mg/kg
700
Chloride vs. bicarbonate for waters from Upper Geyser Basin. Bicarbonate
concentrations are adjusted for the decrease in bicarbonate and the formation of carbonate
that occurs at shallow levels by the reaction 2HCOj == COj2+H20+C02• The cluster of
dots labeled M represents waters that are mixtures of thermal and dilute, cold groundwaters.
al 1 976). Waters that plot below line AC have been diluted by shallow
groundwaters. The Hillside group of springs (triangles) may have a com­
ponent of steam condensate that would account for relatively high con­
centrations of bicarbonate relative to chloride, as discussed previously in
the section on vapor-dominated systems.
The range in chloride concentrations shown by boiling and nonboiling
hot-spring waters that are geographically close together and that have
similar ratios of dissolved constituents (e.g. CI/HC03) can be used to
estimate the temperature of the reservoir supplying water to the springs
(Fournier 1 979). This is conveniently accomplished by making use of
enthalpy-chloride relations, as shown in Figure 4. All the available data for
thermal waters from Geyser Hill in Upper Basin that have Cl/HC0 3> 3 (in
equivalents) have been plotted in this figure. Enthalpies were obtained
from steam tables (Keenan et al 1 969) and are those of thc residual liquid
at the measured collection temperature. In Figure 4 the initial enthalpy
and chloride concentration of the reservoir fluid (point R) are given by the
intersection of line SB, drawn from steam to the highest measured chloride
concentraton (point B, assumed to have undergone maximum possible
boiling), with the line drawn parallel to the enthalpy axis through the
lowest chloride concentration (point A, assumed to have cooled entirely
by conduction because of a very low rate of discharge and a temperature
YNP HYDROTHERMAL SYSTEM
27
600
500
B
(1l
.::£.
"-.400
�II:R
0 ___
(1l
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
E
�300
Q)
-0
·c
0200
-.C
U
100
0
0
Figure 4
500
1000
1500
Enthalpy,
2000
J/ 9
2500
s
3000
Enthalpy vs. chloride for waters from Upper Geyser Basin.
less than the boiling temperature). Thus, prior to decompressional boiling
and/or conductive cooling, the initial reservoir fluid contained about 360
mg kg -l chloride at an enthalpy of about 920 J g - l (2 I S°C). To the extent
that the naturally discharging spring waters do not cover the entire range
of "maximum possible boiling" to "entirely conductively cooled"
conditions, the estimated initial enthalpy and chloride in the reservoir
water will be in error. Also, in the above process care must be taken to
exclude waters that have low chloride concentration because of mixing
with dilute, usually cool groundwaters, such as the waters represented by
the cluster of dots labeled M in Figure 3. Commonly, dilution with shallow
groundwaters can be detected by increased concentrations of Mg in the
resulting mixed water and by flow rates that seem too large to be com­
patible with conductive cooling.
Silica can be used even more effectively than chloride to estimate the
temperature of the reservoir that is feeding a group of hot springs and
geysers because of the constraint that the solubility of quartz controls the
concentration of silica in the reservoir fluid. Figure S is an enthalpy-silica
diagram that shows the solubility of quartz (Fournier & Potter 1 982) and
measured silica in the Geyser Hill waters that were plotted in Figure 4. As
with the enthalpy-chloride relations shown in Figure 4, the range in silica
concentration plotted in Figure S can be used to determine the enthalpy
FOURNIER
28
600
500
B
�400
""
01
0
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
E 300
A
0
u
:= 200
(f)
E
.,
100
Ql
0
en
0
500
Figure 5
Enthalpy vs. silica for waters from Upper Geyser Basin.
1000
1500
Enthalpy.
2000
Jig
2500
3000
(converted to temperature with steam tables) and silica concentration in
the reservoir fluid prior to boiling (point R). Point R coincides with the
solubility of quartz curve and also has the same enthalpy as point R
in Figure 4. The enthalpy-silica and enthalpy-chloride data present a
remarkably consistent picture.
Variations in the amount of boiling and different amounts of mixing of
two or more waters can be exhibited by samples collected at different times
from a single spring, as shown by frcqucnt sampling and analyses of waters
from Cistern Spring in Norris Basin (Fournier et al 1 986). Waters from
this spring were collected and analyzed five times from May 1966 through
June 1 975. During that period the chloride concentration ranged from 455
to 475 mg kg-I, except for the last sample (290 mg kg- I ) that was collected
one month before a local magnitude 6. 1 earthquake. Because the 38%
decrease in chloride might have been a prccursor of the earthquake, a
monthly collection and analysis was made of Cistern Spring from 1 976 to
1 985 to check for possible changes in composition preceding subsequent
earthquakes. The results, in terms of CI and S04 , are shown in Figure 6,
along with data for Echinus Geyser, Steamboat Geyser, and springs with
low sulfate collected at Porcelain Terrace (all in Norris Basin). Since 1 975,
no correlation with seismic activity has been found, but large changes in
the chloride/sulfate ratio and the degree of boiling have been observed
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
•
400
•
• Echinus Geyser, pre-1979
� .
•
\ I.
Ol
.::c
CD
E
ai
to. ,
to.
' 1979-1980
Acid-sulfate seeps
Springs with lowest sulfate
1<Oown-hole sample, Y-12
+ Calculated
composition before boiling
A
\
200
c:.
\
\
�
�
•
"
�t
I
\I-�
¥.�
300
Cistern Spring
• Steamboat Geyser
M
\- 100
---
---
---
,;---
�
't:I
-
:\:;.:;:. •
��'
n··
�
.
0
0
200
�
.5
. .
*-.!I"
400
-
600
"
.....
,,�
Chloride vs, sulfate
for Cistern Spring and other selected thermal waters from Norris
>
t""
'"
Chloride, mg/kg
Figure 6
i
Geyser Basin
(from Fournier et aI1986),
�
tv
�
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
30
FOURNIER
that correlate with widespread seasonal boiling phenomena that occur in
Norris Basin every August or September. In Figure 6 thc lcast boiled
waters lie closest to the chloride-sulfate mixing line passing through point
M' and the star indicating the composition of water collected from the Y1 2 research well drilled at Porcelain Terrace by the USGS (White et al
1 975). More extensively boiled waters lie farther above this line. The data
are interpreted as indicating mixing of three types of water: a chloride-rich
and sulfate-poor component with a temperature> 260°C , a chloride-poor
and sulfate-rich component with a temperature < 200°C, and a dilute,
relatively cool component with little chloride or sulfate (Fournier et al
1 986). Thc most pronounccd mixing (dccrease in chloride and increase in
sulfate) occurs immediately after episodes of intense boiling. Variations in
intensity of boiling apparently are related to changes in pressure within
the hydrothermal system that are affected by several factors, including
seasonal changes in water table, self-sealing by mineral deposition, clogging
of channels by clay suspended in flowing waters, geyser eruptions, defor­
mation and fracturing induced by tectonic forces, and hydrofracturing.
DISSOLVED GASES RELATIVE TO AN
ENTHALPY-CHLORIDE M ODEL
Enthalpy-Chloride Relations
Using chemical geothermometers, ranges in composition resulting from
different proportions of boiling and conductive cooling (as in Figures 36), and limited information from relatively shallow drill holes, Fournier et
al ( 1 976) estimated chloride concentrations, temperatures, and enthalpies
of the shallowest reservoirs supplying thermal waters to the various geyser
basins east of the Continental Divide and plotted the data on an enthalpy­
chloride diagram, similar to Figure 7. They concluded that all the inves­
tigated waters could be related to a deep water containing about 400 mg
kg-' chloride at an enthalpy of 1 570 J g-' (about 335-340°C) by boiling
(lines radial to the enthalpy of steam) and by mixing with a cold dilute­
water component (lines approximately radial to the origin). Truesdell
& Fournier (1 976) performed a similar analysis, including water from
Shoshone Geyser Basin west of the Continental Divide, and concluded
that a deep "parent" water might have a temperature as high as 350-370°C.
A major underlying assumption in the construction and interpretation of
Figurc 7 is that both boiling (with separation and removal of steam
from contact with the residual liquid) and mixing of fluids occur deep
underground as well as near the surface, and that there may be complete
or partial water-rock equilibration along the flow path or within a reservoir
at an intermediate depth after boiling or mixing of fluids has occurred.
YNP HYDROTHERMAL SYSTEM
31
1000
900
800
0'1
� 700
.......
0'1
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
E
Q)
"'0
'
;::
CH
600
NBO
500
GB
Sy
400
0
..c
U
300
MH
0
200
100
0
Figure 7
O
c.�
0
500
HS
ST
1000
1500
Enthalpy,
2000
Jig
2500
3000
Enthalpy of liquid water vs. chloride for various aquifers. Letter codes as follows:
7M, Sevenmile Hole; BS, Black Sand-type water; CH, Crater Hills; CW, cold water; DUB,
deep Upper Basin 270°C water; GB, Gibbon; GH, Geyser Hill-type water; HL, Heart Lake
Basin; HS, Hillside Springs; LB, Lower Basin high chloride/bicarbonate water; MB, Midway
Basin; MH, Mammoth Hot Springs; MJ, Madison Junction; NB, Norris Basin; P, the deep
parent water of Fournier et al (1 976); R, deepest and hottest reservoir fluid; SS, Shoshone
Basin high-chloride water; ST, steam; SY, Sylvan Springs.
The model that is presented in Figure 7, though very speculative, provides
a reasonable framework for interpreting gas and isotope data.
Fournier et al (1976) suggested that 270De water might be widespread
beneath Upper and Lower Geyser Basins in a permeable zone at an
intermediate depth between deeper, higher temperature water and shal­
lower 20Q-2 l 5De local reservoirs that feed the hot springs and geysers. In
the construction of Figure 7 this 2700e water (point DUB) was assumed
to be a mixture of the deeper � 3400e water (point P) and cold, dilute
water (point eW), and it was further assumed that no conductive cooling
occurred before or after mixing. Therefore, the 270De water would be
expected to contain all or most of the gases originally present in the deeper
water (Fournier 1 9 8 1 ), plus an atmospheric component of gas dissolved
in the diluting water and a small amount of additional gas that might be
leached from the local rock, such as radiogenic argon (Kennedy et al 1 987).
In contrast, waters that have undergone considerable boiling and loss of
steam moving from the deeper reservoir to a shallower reservoir, such as
32
FOURNIER
Norris, are expected to be somewhat depleted in deep-component gases.
The distribution and variations in the compositions of the major gases
(primarily CO2) and the noble gases (including their isotopes) in the various
Yellowstone waters are consistent with this model.
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
Carbon Dioxide and Bicarbonate
Waters in shallow reservoirs feeding springs in Lower Basin, Midway
Basin, the western and northern parts of Upper Basin, the Sevenmile Hole
region of the Grand Canyon of the Yellowstone, and Shoshone Geyser
Basin all cluster close to the mixing line drawn from the 270°C water (point
DUB, Figure 7) to dilute water. Departures from that line can be the result
of a small amount of conductive cooling and/or a small amount of boiling
of waters moving from the deeper to the more shallow reservoirs. Again,
the thermal waters in these shallower reservoirs would be expected to
contain all or most of the gaseous components originally present in the
deeper reservoirs, but modified by the gases in the diluting water and by
reactions with the wall rock. In these waters, little CO2 has been lost by
partitioning into a separating steam phase. Therefore, CO2 is available to
form carbonic acid and react with the wall rock as temperatures decrease,
resulting in higher bicarbonate concentrations (e.g. Black Sand-type
water) than are present in waters that have lost CO2 by boiling at high
temperature before they equilibrated chemically with rock in a lower
temperature reservoir (e.g. Norris and Geyser Hill-type waters) (Fournier
1 98 1 ). The chloride-rich, low-sulfate, pH-neutral thermal waters at Norris
have Cl/HC0 3 ratios > 1 3, the Geyser Hill-type waters (Figure 3, type
A) have ratios ranging from about 3 to 8, and the Black Sand-type
waters have ratios ranging from about 0.8 to 1 .0.
Noble Gases and Their Isotopes
The early studies of the relative abundances of dissolved gases, including
Ne, Ar, Kr, and Xe, in the thermal waters of Yellowstone (Mazor &
Wasserburg 1 965, Gunter & Musgrave 1 966, Mazor & Fournier 1 973,
Gunter 1 973) were interpreted as indicating that these gases originate
largely from infiltrating meteoric water saturated with atmospheric gases.
However, dissolved gas abundances are affected by processes deep within
the hydrothermal system. Fluid samples collected from research wells,
subject to the least contamination by atmospheric gases, were found to be
markedly depleted in noble gases compared with the expected values for
20°C air-saturated water. Some samples carried a radiogenic component,
as indicated by 4°Arp6Ar ratios higher than the atmospheric value and by
strong enrichments in 4 He relative to the other noble gases (Mazor &
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP HYDROTHERMAL SYSTEM
33
Fournier 1 973). Craig et al ( 1 978) and Welhan ( 1 9 8 1 ) presented 3 HerHe
isotope data that indicate a subcrustal component of gas eHe) in the
Yellowstone thermal waters. The largest leakage of 3 He was detected at
Mud Volcano, where a 3Hej4 He ratio about 1 6 times the air ratio was
detected. More extensive sampling by Kennedy et al (1985) confirmed the
results of Craig et al (1978) and Welhan (1981) and provided broader
coverage throughout the Park.
Kennedy et al ( 1 985) analyzed the abundances of five stable noble gases
and the isotopic compositions of He, Ne, and Ar for 66 gas and water
samples representing 1 9 different regions of hydrothermal activity. The
isotopes of Kr and Xe were also determined in a few samples and found
to be of normal atmospheric relative abundance. Kennedy et al explained
their results by mixing of three source components: magmatic, crustal, and
atmospheric, each having a characteristic noble gas isotopic range, with
high 3He indicative of a magmatic source. In addition to the 3He anomaly
at Mud Volcano, Kennedy et al ( 1 985) found 3Hej4 He 1 3.4 times the air
ratio at Gibbon, 1 0.4 times the air ratio at Crater Hills, 9.5 times the air
ratio at Shoshone, and generally about 7 times the air ratio elsewhere
within the caldera. Except in the southwest region of the Park at Boundary
Creek, the maximum 3Hej4 He decreased rapidly to values < 3 times the
air value immediately outside the caldera. High 3Hej4 He anomalies were
not found associated with either of the two zones of low seismic velocity
(4.0 km S - I) reported by Lehman et al ( 1 982) that have been widely cited
as possibly indicating a body of partially molten material at a depth of 34 km beneath the caldera. The lack of 3 HerHe anomalies associated with
the western anomaly is not surprising in view of more recent data that have
shown that the western anomaly is fictive (Brokaw 1 985). The anomaly at
Mud Volcano and Crater Hills was attributed to a relatively shallow depth
to the Curie-point isotherm and coincidence with a zone of maximum
present-day uplift within the caldera (Kennedy et al 1 985). The 3 Hej4 He
anomaly at Gibbon was considered to be somewhat of an enigma, possibly
reflecting the fact that the youngest rhyolite lavas in the Park (Doe et al
1 982) occur there.
Kennedy et al ( 1 987) studied 1 2 different springs in Lower Geyser Basin
and found that the 3HerHe ratio ranged from 2.7 to 7.7 times the air
ratio and increased with total bicarbonate concentration. Because the total
bicarbonate concentration is a function of the availability of CO2, which
in turn is a function of deep boiling with phase separation prior to COT
bicarbonate conversion (as previously discussed), Kennedy et al ( 1 987)
concluded that boiling and dilution of a single thermal fluid could explain
their gas data for Lower Basin. They also noted that a fluid that boils to
a greater extent loses a larger proportion of 3 He, as well as CO2, leaving
�
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
34
FOURNIER
a helium-poor residual fluid in which the isotopic composition of helium
will be strongly affected by the addition of radiogenic helium.
An alternative interpretation of the district-wide helium data of Ken­
nedy et al ( 1 985), based on the Lower Basin model of Kennedy et al ( 1 987),
is that 3HetHe ratios throughout the caldera and in immediately adjacent
regions are controlled mainly by boiling and mixing. Within most of the
western part of the 0.6-Ma Yellowstone caldera, where locally derived
meteoric waters circulate relatively freely through rhyolite lava flows, a
considerable amount of mixing of the deep component with shallow water
occurs, followed by adsorption of radiogenic 4He from the surrounding
permeable rocks. Thus, an initially high 3HerHe ratio that is about 1 6
times the air ratio everywhere deep within the caldera may be generally
reduced to less than 7 times the air ratio at shallow levels. Exceptions are
in those few places where little shallow mixing of the ascending liquid
occurs, and where steam that separates at very high temperatures makes
its way to the surface with little or no dilution by other steam formed at
shallow levels where local meteoric water boils. It may be more than
coincidence that the highest 3 HerHe ratios all have been found at the
margin of or outside the boundary of the 2.0-Ma caldera shown by Chris­
tiansen ( 1 984) and, therefore, outside the region where relatively permeable
rhyolite flows are likely to be found deep within the caldera between
different ash-flow tuff units, as discussed previously.
At Crater Hills the one flowing hot spring (Table 1 , number 1 2) is
located within the 0.6-Ma caldera and at the projected eastern edge of the
2.0-Ma caldera. This is a likely site for prolonged and intense hydrothermal
activity since the formation of the first caldera. The hot spring at Crater
Hills has the highest chloride concentration of any thermal water in the
Park ( 1 044 mg kg- 1 measured by Allen & Day 1 935) and the highest
chemical geothermometer temperatures (270-300°C). This water appears
to represent the most direct upward leakage of fluid from deep in the
system.
Enthalpy-chloride relations (Figure 7) suggest that the parent water
deep in the system (point R) has a minimum enthalpy of about 1 700 J
g - l (about 350°C) and contains about 450 mg kg- 1 Cl. Water cools
adiabatically by decompressional boiling in moving [rom point R to the
reservoir feeding the hot spring at Crater Hills, but evidently the evolved
steam and other gases remain essentially in contact with the residual liquid.
This requires relatively impermeable surrounding rock. The proximity to
the Mud Volcano vapor-dominated system suggests that this is likely to
be the general situation in that part of the Park because low permeability
is required to maintain a hydrologically underpressured zone next to a
zone of hot-water upflow from deep in the system. Low permeability within
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP
HYDROTHERMAL SYSTEM
35
the upper part of the stratigraphic section also provides a mechanism by
which steam that forms deep under the Mud Volcano region rises to the
surface with little contamination by gases in steam derived by boiling,
shallow, local meteoric water. At Gibbon the hot-spring waters and gases
issue from relatively impermeable ash-flow tuffs. There the enthalpy-chlor­
ide relations (Figure 7) show that the water in the local shallow reservoir
has about the same chloride concentration as that in the deep parent water.
Therefore, the Gibbon water may have cooled conductively without mixing
while flowing from deep in the system to a more shallow level. In this
event, the initial concentrations of noble gases in the deep water would
tend to be preserved, modified mainly by leaching of radiogenic com­
ponents from the shallow reservoir rocks.
METEORIC RECHARGE OF THE HYDROTHERMAL
SYSTEM
Craig et al ( 1 956) compared stable isotopes in Yellowstone thermal waters
with those in local meteoric water and concluded that any possible mag­
matic water contribution is less than a few percent. Although the interpre­
tation of the stable isotope compositions of hot-spring waters is made
difficult by considerable dilution of ascending deep water by relatively
locally derived meteoric water and by subsurface boiling that results in
fractionation of isotopes between steam and the residual liquid, the general
conclusions of Craig et al ( 1 956) still appear to remain valid after the
collection and analyses of many more samples.
Taking account of variations in chloride concentrations and of oxygen
and deuterium isotopic abundances in thermal waters in the Park that
result from boiling and mixing, Truesdell et al ( 1 977) proposed two end­
member models for the behavior of steam that forms by decompressional
boiling of an ascending solution. The first is a '''single-stage'' model in
which all the steam remains mixed with the water and separates near a
single temperature, and the second is a "continuous" model in which steam
is physically separated from the water as it is formed. A multiple-stage
model that produces results intermediate between single-stage and con­
tinuous steam separation appears to be applicable to many natural hot­
spring waters in Yellowstone. Truesdell et al ( 1 977) assumed a temperature
(360°C) and chloride cvncentration (3 1 0 mg kg- I ) of a deep thermal water
(taken from the enthalpy-chloride model of Truesdell & Fournier 1 976)
and used the measured temperature, chloride concentration, and isotopic
composition of water collected from the Y- 1 2 drill hole to calculate the
relative deuterium concentration «(jd) of the deep-water component, using
the (j (del) notation in which the isotopic concentration is reported as parts
36
FOURNIER
per thousand difference from a standard, where
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
(jd = [(rsample/rsMow) - l]
x
1 03 ,
(1)
rsample i s the ratio of deuterium t o hydrogen i n the sample, and rSMOW is the
ratio of deuterium to hydrogen in standard mean ocean water. They
concluded that the chloride-(jd relations for Norris, Lower, Upper, and
Shoshone Geyser Basins are compatible with boiling of mixtures of the
deep water with cold, dilute (SOC, 2 mg kg- I Cl) meteoric water, varying
in (jd according to locality in the Park. In addition, the data strongly
suggest that recharge to the deep thermal water must be either precipitation
from areas remote from the geyser basins or ancient precipitation from a
cooler period. The major conclusions of Truesdell et al ( 1 977) would not
be changed significantly by assuming a higher temperature for the Y- 1 2
water (it probably cooled conductively from at least 270°C rather than
238°C) and a higher chloride concentration in the deep, 360°C thermal
water. Unpublished stable isotope analyses of an extensive suite of samples
collected and analyzed by Robert O. Rye and additional stable isotope
analyses by Tyler B. Coplen indicate that the most likely recharge area for
the deep component of the geothermal water is in mountainous regions
north and northwest of the caldera, where deep snow accumulates each
winter.
GEOTHERMAL HEAT FLUX
The total convective heat flux in chloride-rich water and associated steam
from all the Yellowstone thermal areas east of the Continental Divide was
estimated in 1 966-67 to be about 4.0 x 1 0 1 6 cal yr- I , or 5 . 3 x 1 09 W by
the river chloride inventory method (Fournier et al 1 976). Nearly all the
chloride discharged by the hot-spring waters eventually enters the four
major rivers that drain the Park: the Yellowstone and Madison Rivers
east of the Continental Divide, and the Snake and Falls Rivers west of the
Divide (Figure 1 ). The Firehole River (draining the Upper, Midway, and
Lower Geyser Basins) and the Gibbon River (draining Norris Geyser
Basin) join to produce the Madison River. Fournier et al ( 1 976) used
enthalpy-chloride information (Figure 7) to estimate the chloride con­
centrations of the waters in the shallow reservoirs feeding individual geyser
basins and the chloride concentration of the water deep in the hydro­
thermal system before decompressional boiling and before near-surface
mixing (point P with 400 mg kg- I Cl). Measured rates of discharge of the
rivers and of the chloride carried by those river waters were then used to
calculate the rate of total discharge of the deep component of the hot­
spring water. The method automatically compensates for boiling and
mixing of thermal waters as they rise. Corrections are required, however,
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP HYDROTHERMAL SYSTEM
37
for background chloride contributed to the rivers by precipitated rain and
snow and by low-temperature weathering of rock. The background Cl
generally amounts to about 1-2 mg kg- l in the nonthermal component of
the river water, depending on the proportion of water from different
nonthermal sources. (For example, snow melt that has not penetrated into
the ground is lower in Cl than nonthermal groundwater that has been
underground a long time in contact with various types of rock). A sum­
mation of the results for the Yellowstone and Madison Rivers, plus an
additional 5% assumed for the thermal discharge into the Snake and Falls
Rivers, gave a figure of 1 0 1 1 kg yr- l for the deep component of the
hydrothermal water and 4 x 1 07 kg yr-l for the chloride carried by that
water in 1 966- 67 (Fournier et al 1 976, Fournier & Pitt 1985). For a
minimum initial water temperature of 340°C, the total amount of heat
discharged by that water is 5.3 x 1 09 W, which translates to an average
heat flux of about 2000 mW m - 2 over the entire 2500 km2 of the Yel­
lowstone caldera. The above estimates are not changed significantly when
the higher chloride and higher enthalpy values of point R in Figure 7 are
used for the deep water instead of those of point P.
Norton & Friedman (198 5) reported results of monitoring the chloride
flux from the Yellowstone, Madison, Snake, and Falls Rivers for the 1 983
water year, extending from September 1, 1 982, through August 3 1 , 1 983.
They calculated a total chloride flux of about 5.8 x 1 07 kg yr- 1 in these
river waters, of which about 5.5 x 1 07 kg yr- l were estimated to be con­
tributed by thermal water. They also found that the chloride flux from
thermal waters into the drainage west of the Continental Divide is about
26% of the total for the Park, much higher than the 5% estimated by
Fournier et al (1 976). When 26% thermal water, rather than 5%, for the
region west of the Continental Divide is applied to the 1 966-67 data, a
revised flux of thermal water chloride of 4.8 x 1 07 kg yr- 1 is obtained.
This is 1 7% less than the thermal water Cl flux for the Park reported by
Norton & Friedman ( 1 985).
The chloride flux measured in 1 983 appears to be exceptionally high
compared not only with the 1 966-67 measurements, but also with measure­
ments made in subsequent years (USGS, unpublished data). Figure 8
shows calculated instantaneous thermal water chloride fluxes for the Madi­
son River during the 1 983 and 1 985 water years and during 1 966-67. A
correction of 1 mg kg- 1 Cl for the non thermal contribution has been
applied to the data shown in Figure 8. The wide scatter in the data after
day 250 corresponds with periods of high river discharge during the spring
and early summer melting of snow. During high stages of river discharge,
the calculated fluxes of chloride have a greater uncertainty because small
percentage errors in chloride analyses and flow measurements are mag­
nified and because discharge measurements, obtained from rating curves,
38
FOURNIER
Madison River
1 500
U
Ql
� 1 000
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
0'
e
0...
I
X
:::J
'+-
Ql
-0
'C
0
..c
U
500
O �rr....-rrr""rrTT..-rrr..-rrrTT,,-r....-r
350
50
1 00
1 50
200
250
300
o
Day number (water year)
Figure 8
Calculated chloride flux vs. day of water year for the Madison River. Water year
starts September 1 and ends August 3 1 of succeeding calendar year. Triangles indicate data
for 1966, dots for 1 967, circles for 1 983, and asterisks for 1985.
are less precise as a result of changing channel profiles that require recali­
bration of rating curves. Also, during high stages of river flow, slight
differences in the assumed background chloride correction make a big
difference in the calculated flux of thermal water, However, uncertainties
in the background chloride correction can be minimized with the aid of a
log-log plot of river discharge rate versus river chloride. This is done by
extrapolating to the assumed CI concentration in the deep parent water
using theoretical mixing curves that have fixed shapes, as shown in Figure
9. By this method it is easy to see at what discharge rate the correction for
background chloride becomes negligible.
Using data in Fournier et al ( 1 976) and unpublished data of the USGS,
I have calculated approximate ranges of the instantaneous flux of total
thermal water discharged by all the chloride-rich hot-spring systems in the
Park for the years 1 966- 67 and the water years 1 983-86 (Figure 1 0). In
assembling the data with which Figure 10 was constructed, no attempt
was made to check the validity of the most extreme data points or to use
conductivity data to estimate chloride concentrations between times when
water samples were collected for analyses. The circles show where most of
the data plot for low stages of river flow. The data presented in Figure 1 0
YNP HYDROTHERMAL SYSTEM
39
.. 400
Cl
..,
.....
Cl
1 00
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
E
10
+ 1966 -67
• 1984-85
1 ��������������������
10
1
1 00
1 000
Flow,
Figure 9
cfs
Logarithmic plot of flow rate vs. dissolved chloride for the Gibbon and Firehole
Rivers. Calculated mixing curves are for an assumed end-member deep thermal water
containing 400 mg kg- 1 chloride and non thermal waters containing I and 2 mg kg- 1 chloride,
respectively.
6
5
"
QJ
�
E
co
�
0
u::
4
3
t t
2
O �--�--��----L---�--�1 966-67
1 9 83 1 984 1 985 1 986
Water year
Figure 10
Range in calculated instantaneous fluxes of thermal water vs. year. Circles show
most common flux during low stages of river flow.
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
40
FOURNIER
clearly show about a 1 5-20% increase in flux of thermal water and heat
during the 1 983 water year compared with the other years. Interestingly,
this anomalously high flux of thermal water occurred during the year
preceding the 7.3 magnitude M t. Borah earthquake on October 28, 1 983.
A little over three months before that earthquake the flux of thermal water
decreased to what appeared to be more normal values, and then a month
before that earthquake the flux of thermal water again increased to anom­
alously large values. Apparently, Norton & Friedman ( 1 985) did not
directly compare their data with the results of measurements made in
1 966-67 at comparable stages of river flow and did not conclude that there
were significant differences between the two data sets, except in regard to
the assumed flux of chloride from thermal water into the Snake and Falls
Rivers. However, they did note an increase in chloride flux commencing
early in October 1 983 and culminating shortly after the Mt. Borah earth­
quake. F uture detailed analyses of river flow, temperature, and con­
ductivity data collected hourly from 1 982 through 1 987 are likely to reveal
significant variations in the total flux of thermal waters since 1983.
EFFECTS OF GLACIAL ICE COVER ON THE
HYDROTHERMAL SYSTEM
A series of research wells drilled at several thermal localities in Yellowstone
Park (White et al 1 975) have provided information about present tem­
perature-pressure-depth relations. Near major zones of active convective
upflow of thermal water, present temperatures follow boiling-point curves
appropriate for water tables at the present land surface, with hydrostatic
pressures equivalent to a cold rather than hot column of overlying water
(Fournier 1983). Muffler et al ( 1 9 7 1 ) postulated that boiling-point curves
and rock temperatures were raised within the upper parts of some hot­
spring systems at Yellowstone during times of glacial cover, and that
sudden decreases in the water table (as by draining of an ice-dammed lake)
resulted in major hydrothermal explosive activity. Primary and secondary
fluid inclusions in material from several cored holes in Yellowstone
National Park (White et a1 1 975) have been studied by Bargar & Fournier
( 1 988) to quantify thermal effects that may have accompanied a raising of
the water table and the corresponding boiling-point curve during times of
thick glacial ice cover. The results from two holes (Y-6 and Y- 1 3) have
been reported as parts of other investigations (Bargar & Beeson 1 984,
B argar et al 1 985).
Mineral samples containing fluid inclusions suitable for study were
found in drill cores from 8 of 1 3 wells drilled by the USGS. Primary,
pscudosecondary, and secondary liquid-rich fluid inclusions in quartz and
fluorite were utilized to determine a range of homogenization temperatures
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP HYDROTHERMAL SYSTEM
41
(Th) a t given depths. Within zones o f major hydrothermal upflow, fluid
inclusion Th values all were found to be equal to or higher (commonly 2050°C and up to 1 55°C higher) than present temperatures at the depth of
collection. The greatest range in Th values was found in material collected
from the Y- I 3 drill hole in Lower Geyser Basin (Bargar et al I985). In the
absence of glacial ice, topographic constraints place a limit of about 1 201 50 m on the maximum depth of any lake occupying Lower Geyser Basin.
The elevation of the water table over Lower Geyser Basin required to raise
boiling-point curves sufficiently to account for the observed fluid inclusion
Th values ranges from 425 m (a conservative estimate that does not include
the highest Th values because of possible necking-down phenomena after
entrapment) to 750 m (a liberal estimate that includes all the data). Thus,
it appears that glacial ice is required to account for the boiling-point curve
elevation. The estimated thickness of the glacial ice over Lower Basin
during the last glaciation required to explain the fluid inclusion data is
within the range estimated by other criteria (K. L. Pierce, written com­
munication, 1 988).
Away from zones of major upflow, Th values were all found to be equal
to or lower than present temperatures (commonly 1 0- 20°C and as much as
60°C lower). The lower paleotemperatures at the margins of hydrothermal
upflow may be attributed to lower rates of discharge of warm water and/or
higher rates of recharge of cold water in the past, probably during periods
of glacial cover.
INTERACTION OF CIRCULATING WATER
WITH THE HEAT SOURCE
In most current models of magmatic-hydrothermal systems (Lister 1 974,
1 980, 1 983, Hardee 1 982, Sleep 1 983, Fournier & Pitt 1 985), relatively
dilute meteoric water circulates along fractures above and to the sides of
a magmatic heat source. The water is separated from very hot crystalline
rock or magma by an impermeable zone where quasi-plastic deformation
prevents brittle fracture and maintains low permeability. Heat extracted
by the circulating water slowly cools the system, allowing thermal cracking
and faulting to progress inward so that water steadily migrates deeper
into the heat source while attaining about the same maximum temperature.
Although there is no direct evidence about the maximum temperature
attained by the convecting hydrothermal fluid, enthalpy-chloride relations
(Figure 7) provide a means of estimating a likely minimum temperature
deep in the system, about 340-350°C. An approximate upper limit for the
temperature likely to be attained by the water in the hydrothermal system
that convects to the surface can be estimated from positions of boiling­
point and condensation-point curves (Fournier 1 987) in temperature-pres-
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
42
FOURNIER
sure space for a dilute chloride-rich water about equivalent in salinity to
a 0.7 wt% NaCI solution (Fournier & Pitt 1 985). For the restricted range
of compositions of the relatively dilute solutions that issue at the surface
at Yellowstone, these fluids could not have attained temperatures higher
than about 420°C at a depth of 4 km and 430°C at 5 km. Exceeding these
temperatures would have resulted in an ascending solution intersecting the
stability field of gas plus brine, resulting in the formation of a small amount
of highly saline brine and a large amount of very dilute steam (Fournier
& Pitt 1 985, Fournier 1 987).
The likely depth of circulation of hydrothermal fluids also is a matter
of conjecture. Deep drilling in other presently active hydrothermal systems
has shown that permeability at temperatures above about 300°C is con­
trolled mainly by fractures. Precipitation of minerals and quasi-plastic flow
are particularly efficient at decreasing permeability by closing fractures at
temperatures above about 3 50-400°C (Fournier & Pitt 1 985). Therefore,
sustained circulation of hydrothermal fluids at these high temperatures
is likely to take place only where the rocks are subjected to repeated
brittle fracture that counteracts the processes that decrease permeability.
Focal depths of well-located earthquakes are deeper than 1 5 km out­
side the Yellowstone caldera, but within the caldera they seldom exceed
4-5 km. Evidently the rocks below 3-4 km are too weak as a result of
high temperatures (> 350°C) to sustain sufficient differential stress for
seismic activity to occur (Smith & Bruhn 1 984, Fournier & Pitt 1 985).
Therefore, the maximum depth of sustained fluid flow at hydrostatic
pressure is probably about 4-5 km within the caldera and deeper at the
sides.
If the assumption is made that thermal energy is transferred uniformly
by conduction from the heat source across a 2500 km2 surface, through
hot dry rock to the base of circulation of the hydrothermal system, a
thermal gradient of about 700° to l OOO°C km - I is required to sustain the
average convective thermal output (Morgan et al 1 977, Fournier & Pitt
1 985). To account for both the large convective heat flux and the lack of
earthquakes below about 4-5 km, it is likely that magmatic temperatures
are attained beneath some portions of the caldera at depths as shallow as
about 4.5-5.5 km, about the same depth range indicated by the various
other geophysical methods.
CRYSTALLIZATION OF MAGMA AS A SOURCE
OF HEAT AND AQUEOUS FLUIDS
If the heat carried in the advective flow of water from the system were
supplied entirely by the latent heat of crystallization of rhyolite magma,
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP
HYDROTHERMAL SYSTEM
43
about 5 x 1 0 " kg yr- 1 of magma (about 0.2 km3 yr- 1 ) would be required
to furnish that heat (Fournier & Pitt 1 985). In contrast, cooling already
crystalline rock by 300°C (to reduce the temperature from about 730° to
430°C) will furnish about the same amount of heat that can be obtained
from the latent heat of crystallization of the same volume of rhyolitic
magma (using a latent heat of crystallization of75 cal g - l and heat capacity
of 0.25 cal g - l °C- 1). Thus, crystallizing about 0 . 1 km3 of rhyolitic magma
and then cooling it about 300°C could furnish the heat carried to the
surface by the hot-spring system . A lack of water-bearing minerals in the
rhyolite erupted at Yellowstone coupled with the presence of the mineral
fayalite suggests that the initial magma contained not more than 1 to 2 wt
% dissolved water (Hildreth et al 1 984). The chloride contained in fresh
obsidian glass shows that the minimum initial chloride concentration in
the magma was 1 500 mg kg-1 (Wes Hildreth, oral communication, 1 984).
Strong partitioning of this chloride into an aqueous magmatic fluid that
separates upon slow crystallization of the magma will produce a fluid
containing a minimum of 1 2 to 25 wt% salt. The maximum quantity of
water that could be liberated by crystallizing 0.2 km3 yr- I of magma
initially containing 2 wt% water is 8.8 x 1 09 kg yr- 1 , and a minimum of
about 7 x 1 08 kg yr- 1 of chloride would be liberated with that water. For
comparison, recall that about 1 0 " kg yr- 1 water (not including water
incorporated by near-surface dilution) and 4 x 1 07 kg yr- 1 chloride are
discharged by the hot-spring system. Thus, a maximum of about 9 wt%
of the deep component of hot-spring water could be magmatic, but
only about 6 wt% of the available chloride can be discharged with that
water. The deficiency of chloride in the discharged thermal water may
be interpreted in two ways: (a) Thermal energy is supplied mainly
by cooling already crystalline rock with little thermal input from the
latent heat of crystallization of magma; or (b) brine evolved from presently
crystallizing magma is ponding beneath the dilute hydrothermal system,
and little of this magmatic water is incorporated into the convecting me­
teoric system. (A mixture of about 0.2-0.4% magmatic fluid with 99.699. 8 % meteoric water could account for all the chloride discharged by
the Yellowstone hot springs.) It was noted previously that stable isotope
data also suggest that very little, if any, magmatic water is discharged
by the hot springs (Craig et al 1 956, Truesdell et al 1 977). The pre­
ferred model of Fournier & Pitt ( 1 985) is one in which the thermal energy
carried to the surface by the convecting hot-spring water comes in part
from crystallizing magma and in part from cooling crystalline rock,
and that relatively dense brine liberated from the crystallizing magma
is accumulating at depth beneath dilute, much less dense hydrothermal
waters.
44
FOURNIER
LONGEVITY OF PRESENT HYDROTHERMAL
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
ACTIVITY
Uranium series disequilibrium studies (Sturchio et al 1 987) of cores from
the Y-7 drill hole in Biscuit Basin, Yellowstone National Park, indicate
that there was significant uranium mobility 1 5,000-20,000 yr ago, cor­
responding to a period of time when glaciation would have allowed tem­
peratures to be significantly higher at the depths penetrated by the drill
hole. Unpublished uranium series disequilibrium studies of cores from
other drill holes show that vein ages are generally much younger than the
ages of the volcanic host rocks (N. C. Sturchio, written communication,
1 988).
Bargar & Fournier ( 1 988) observed that Th values of primary and
secondary liquid-rich fluid inclusions trapped in hydrothermal minerals
sampled from within major zones of upflow are all equal to or greater than
presently measured rock temperatures at the point of collection. This is
strong evidence that the thermal waters have not been cooler than present
temperatures since formation of the host minerals. Also, because the
presence of glacial ice seems to be required to explain elevated boiling­
point curves, it can be concluded that hydrothermal activity beneath the
major geyser basins has been continuous since sometime within or before
the last glaciation, a minimum of 1 4,000-45,000 yr. The fluorite and much
of the hydrothermal quartz used in the Bargar & Fournier ( 1 988) study
were deposited relatively late in the sequence of hydrothermal events, after
most of the surrounding rock had already been thoroughly altered by
hydrothermal activity, but before the last glacial ice decreased in thickness
to less than 450-750 m. The data are consistent with a model in which
hydrothermal activity within the 0.6-Ma Yellowstone caldera started soon
after the formation of that structure and continued unabated thereafter,
with significant variations in intensity and places of discharge in response
to pulses of volcanism and the waxing and waning of glacial episodes.
Ovcr thc minimum time span during which hydrothermal activity
appears to have operated at about its present intensity ( 1 5,000 yr since the
end of the last glaciation), a largc amount of thermal energy has been
extracted from the system, both by convection and conduction, as indi­
cated above. Ifwe use the assumed thermodynamic properties of materials
given in Fournier & Pitt ( 1 985), the calculated amount of heat extracted
just by advection of chloride-rich water from the hydrothermal system in
1 5,000 yr could be supplied by subsolidus cooling over a 350°C range (for
example, from 750° to 400°C) of a crystalline body of rock 1 .2 km thick
beneath the entire caldera (2500 km2), or by the latent heat associated with
crystallizing a body of magma 1 .2 km thick beneath the entire caldera with
YNP
HYDROTHERMAL SYSTEM
45
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
no change in temperature of the system. Crystallizing a body of silicic
magma 0.6 km thick and then cooling it by 350°C would also provide the
required thermal energy. Again, these are minimum requirements, as the
total flux of heat from the system is undoubtedly larger than the number
estimated from the chloride flux. The chloride flux method does not pro­
vide information about hear' carried to the surface by steam separated
from convecting liquid that cools and flows back downward into the
system, or about a purely conductive component of heat flow.
VOLUMETRIC CHANGES ASSOCIATED WITH
CRYSTALLIZATION OF MAGMA
Cooling of hot but already crystalline rock should lead to thermal con­
traction and a subsidence of the caldera floor. However, a significant uplift
of the caldera has been measured over the period 1 923-84 (Pelton & Smith
1 979, 1 982, Dzurisin et a1 1 986, Dzurisin & Yamashita 1 987). This inflation
stopped in 1 985, and deflation occurred in 1 986 (Dzurisin & Yamashita
1 987). Studies of raised and submerged shoreline terraces show that there
has been episodic uplift interspersed with local deflation of the caldera
throughout the Holocene (Hamilton 1 985, Meyer & Lock 1 986). Meertens
& Levine ( 1 985) have suggested that the uplift is the result of horizontal
compressive strain, but this does not appear to agree with focal mecha­
nisms of earthquakes within the caldera and the generally extensional
tectonic environment of the region. Also, the average horizontal strain
rates measured in the northeast part of the caldera and in the Hebgen
Lakc region to the northwcst of thc caldcra from September 1 984 to
August 1 987 appear to preclude regional tectonic movements as a primary
cause of the inflation and deflation (unpublished data of J. C. Savage and
D. Dzurisin).
Two mechanisms that might account for both the episodic inflation and
deflation of the caldera each require crystallization of rhyolitic magma in
amounts that are compatible with the thermal budget for the magmatic­
hydrothermal system. Both mechanisms may operate to varying degrees
at the same time. The first involves episodic intrusion of basalt from the
mantle into the upper crust at the base of a silicic magma chamber at a
depth of about 1 0- 1 5 km, and continuous crystallization of rhyolitic
magma at a depth of about 4-5 km. The thermal energy discharged by the
advecting thermal waters at Yellowstone could be supplied by the latent
heat of crystallization of about 0.2 km3/yr of rhyolitic magma, with no
change in temperature within the igneous part of the system (Fournier &
Pitt 1 985). If purely conductive heat loss and heat carried upward by
convecting hydrothermal fluids that do not discharge at the surface also
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
46
FOURNIER
were taken into account, the amount of magma required to supply the
thermal flux from the magmatic-hydrothermal system would be cor­
respondingly higher. Crystallization of 0.2 km3 of rhyolitic magma would
lead to a volumetric contraction of about 0.0 1 4 km\ provided that the
evolved, aqueous-rich magmatic fluid all escaped into the overlying hydro­
statically pressured hydrothermal system. Thus, if the latent heat of crys­
tallization of magma is an important source of thermal energy for the
hydrothermal system and if the evolved magmatic fluids continuously and
efficiently escape from the system, then the normal state of deformation
of the caldera is likely to be deflation at a rate that is close to the observed
rate of subsidence since 1 985. Inflation will occur only during periods of
episodic intrusion of basalt from the mantle into the crust at a rate fast
enough to more than compensate for the decrease in volume resulting
from crystallizing rhyolite magma. Stability at the caldera floor will occur
only when the volume increase resulting from basalt intrusion at the
base of the relatively high-level magma chamber just balances the volume
decrease resulting from crystallizing rhyolite at the top of the chamber
The second mechanism that can account for rapid fluctuations from
inflation to deflation involves entrapment of aqueous magmatic fluids at
lithostatic pressure beneath self-sealed rock and the episodic release of
these fluids into the hydrostatically pressured system (Fournier & Pitt 1 985,
Fournier 1 988). Self-sealing at the base of the hydrostatically pressured
hydrothermal system may occur as a result of chemical transport and
precipitation of vein minerals and ductile flow of rock that becomes rela­
tively weak at temperatures exceeding 400°C (Fournier & Pitt 1 985). lf the
magmatic fluid that is liberated during crystallization of 0.2 km3 yr- I of
rhyolitic magma containing about 2 wt% water is trapped at litho static
pressure at a depth of 4-5 km, there will be a net volume increase of about
0.026 km3 yr- I ; more than enough t o account for the observed rate o f
inflation of the caldera from 1 923 t o 1 984. The density of the magmatic
gas phase is not particularly sensitive to the initial ratio of water to
chloride in the magma, because at the likely depth and temperature of
crystallization, the magmatic fluid will dissociate to a small amount of
very saline brine plus relatively dilute gas, as previously discussed. Episodic
hydrofracturing and injection of pore fluids that have accumulated at
lithostatic pressure into the hydrostatically pressured hydrothermal system
would result in episodic deflation of the caldera. The pressure surge associ­
ated with this injection of magmatic fluid may be accommodated entirely
or in part by an increased rate of flow of thermal water from the system,
by a decrease in the rate of recharge of cold meteoric water into the system,
or by condensation of a relatively small amount of steam accompanied by
a slight rise in the level of the interface between liquid and steam within a
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP HYDROTHERMAL SYSTEM
47
deep vapor-dominated region that appears to be widespread in the eastern
part of the Park. Also, episodic rupturing of self-sealed rock that separates
regions of litho static and hydrostatic pore-fluid pressures could account
for some of the seismic swarms that occur within the caldera.
Although the above calculations and speculations do not demonstrate
conclusively a causal relationship between the uplift and liberation of fluid
from crystallizing magma, they do show that the volumetric effects of
liberating a magmatic fluid could be important if the latent heat of crys­
tallization of magma is an important source of energy for the hydro­
thermal system. Future attempts will be made to determine whether a
statistically significant increase in the rate of hot-water discharge has
coincided with a change from inflation to deflation of the caldera. A major
problem in the interpretation of the data is the large effect that the Mt.
Borah earthquake appears to have had upon the hot-spring discharge rate.
However, even if there is no detectable increase in the rate of discharge of
thermal water coinciding with the onset of deflation, we cannot rule out
the possibility that depressuring of magmatic water is a major contributing
factor, because the volumetric effects may be most pronounced within the
cold recharge part of the system and within the vapor-dominated zones.
MANTLE BASALT AS THE ULTIMATE SOURCE
OF THERMAL ENERGY AT YELLOWSTONE
It is generally agreed that continuing injection of basaltic magma ( 1 200I 300°C) from the mantle into the crust over a long period of time supplies
the thermal energy to melt crustal material, forming large volumes of silicic
magma at 800-900°C (Christiansen 1 984). Crystallizing and cooling ( 1 200°
to 860°C) about 0.08 km3 yr- I of basalt could furnish the heat for the
present-day Yellowstone hydrothermal system. This yearly volume of
basalt is about seven times more than the historic measured average rate
of volumetric inflation of the Yellowstone caldera. If mass (either cooled
basaltic magma or dense crystalline material) is not convecting or settling
downward into the lower crust and mantle beneath the Yellowstone cal­
dera to counterbalance the buoyant upflow of hotter basaltic magma, then
the Yellowstone volcanic system as a whole is cooling at present and the
amount of silicic melt (if any) in the shallow part of the system is steadily
decreasing.
CONCLUSIONS
Meteoric water, derived in great part from precipitation on mountains
to the north and northwest of the Yellowstone caldera, convects at hydro-
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
48
FOURNIER
static pressure to a depth of about 4--5 km within the caldera and attains
a maximum temperature of about 350-430°C. This water picks up about
300-500 mg kg- I Cl from the rock through which it passes and also picks
up gaseous components liberated from magma and crystalline magmatic
rocks. Cation ratios are fixed by temperature-dependent water-rock reac­
tions. There is a possibility that some or even most of the chloride in the
relatively dilute hydrothermal system is derived by interaction with an
underlying brine of magmatic origin that is postulated to be present at
depth. Even though some variation in chloride is likely to occur in the
deepest parts of the convecting system, these variations appear to be
small, probably because rocks with similar compositions occur at depth
throughout the caldera, and because there has been a lot of flushing of
dissolved constituents by hydrothermal advective flow throughout a 2Myr interval of volcanic activity. Thus, the assumption in the application
of boiling and mixing models that a deep "parent" water has a uniform
chloride concentration is probably a good first approximation for use in
estimating conditions deep in the system.
Heated fluid convects upward and to various degrees in different places
boils and/or mixes with shallow fluids of more local meteoric origin. Water­
rock chemical reequilibration occurs in relatively shallow local reservoirs
that directly feed individual geyser basins. Variations in dissolved gases in
general, and in 3HerHe ratios in particular, can be explained entirely in
terms of variation in underground boiling and mixing of deep and shallow
waters. During periods of glaciation, temperatures in zones of major
hydrothermal upflow increased at given depths as a result of elevation
of boiling-point curves by increased hydrostatic head. Vapor-dominated
systems in the eastern part of the Park formed at the close of the last
glaciation partly as a result of a lowering of the water table by flow toward
the Grand Canyon of the Yellowstone and partly in response to a large
input of thermal energy beneath a thick sequence of relatively impermeable
rock. The convective heat discharged by the hydrothermal system is gen­
erally about 4 x 1 0 1 6 cal yr- 1 , but an approximate 20% increase was
observed in 1 983, the year preceding the Mt. Borah earthquake. Hydro­
thermal activity has been continuous at about its present level for at
least 1 5,000 yr and probably much longer. It is not known whether the
magmatic-hydrothermal system, as a whole, is presently cooling down or
heating up. The thermal energy that drives the hydrothermal convection
can come entirely from the cooling of already crystalline rocks, entirely
from the latent heat of crystallization of silicic magma at a depth of about
4--5 km, or from a combination of the two. The recent uplift of the
Yellowstone caldera suggests that the injection of magma into the system
and/or the liberation of fluid from a crystallizing magma are processes
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP HYDROTHERMAL
SYSTEM
49
that are presently active. If magmatic fluids are presently being liberated
from a crystallizing siliceous magma at a depth of 4-5 km, they should
dissociate to highly saline brine plus relatively dilute gas. Very little (if any)
of that brine is becoming incorporated into the portion of the hydrothennal
system that convects to the surface. The magmatic fluid is ponding beneath
the dilute fluid and/or is being trapped in a region where pore-fluid pres­
sures are lithostatic. Accumulation of magmatic fluids at litho static pres­
sure and episodic injection of portions of this fluid into the hydrostatically
pressured system may account for the observed inflation and deflation of
the caldera. However, the observed uplift and subsidence also may be
accounted for by episodic intrusion of basalt from the mantle into the
upper crust at a depth of about 1 0- 1 5 km and continuous crystallization
of silicic magma at about 4-6 km without accumulation of magmatic gases
at lithostatic pressure. Uplift would occur only when the rate of basalt
intrusion more than compensated for the normal subsidence resulting from
crystallization of rhyolitic magma. At this time the most plausible model
for the magmatic-hydrothermal system is one in which the thermal energy
carried to the surface by the advecting hot-spring water comes in part from
crystallizing silicic magma and in part from cooling crystalline rock, and
in which brines are accumulating deep in the system. It is likely that
crystallization and cooling are occurring at some levels while new magma
accumulates at others.
ACKNOWLEDGMENTS
Since I first started working on the Yellowstone hydrothermal system in
1 969, I have benefited greatly from collaboration with many colleagues in
the USGS, with special thanks to A. H. Truesdell, L. J. P . Muffier, J. M.
Thompson, G. W. Morey, J. J. Rowe, and particularly Donald E. White,
who first introduced me to the joys of studying the hydrogeochemistry of
Ycllowstone's thermal waters and who has tried to keep me on the right
track ever since. Over the years the National Park Service (N PS) has been
and continues to be very supportive of our research in the Park. R. A.
Hutchinson of the NPS has been especially helpful in collecting hot-spring
water samples for analyses from remote regions and in monitoring the
chemical behavior of various thermal waters over many years. D. R.
Norton and Irving Friedman of the USGS have been deeply involved with
a cooperative USGS-NPS program to monitor the chloride flux in the
major rivers in Yellowstone since 1 982, and they have provided me with
much of the data for calculating the recent convective heat flux from the
system .
50
FOURNIER
Literature Cited
Allen, E. T., Day, A. L. 1935. Hot springs of
the Yellowstone National Park. Carnegie
Inst. Wash. Publ. 466. 525 pp.
Bargar, K. E., Beeson, M. H. 1 98 1 . Hydro­
. thermal alteration in research drill hole
Y-2, Lower Geyser Basin, Yellowstone
National Park, Wyoming. Am. Mineral.
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
66: 473-90
Bargar, K. E., Beeson, M. H. 1984. Hydro­
thermal alteration in research drill hole
Y-6, Upper Firehole River, Yellowstone
National Park, Wyoming. US Geol. Surv.
Prof Pap. 1054-B. 24 pp.
Bargar, K. E., Fournier, R. O. 1 988. Effects
of glacial ice on subsurface temperatures
of hydrothermal systems in Yellowstone
National Park, Wyoming: fiuid-inclusion
evidence. Geology 1 6 : 1 077-80
Bargar, K. E., Muffler, L. J. P. 1 982. Hydro­
thermal alteration in research drill hole Y­
I I from a vapor-dominated geothermal
system at Mud Volcano, Yellowstone
National Park, Wyoming. Guideb. Wyo.
Geol. Assoc. Ann. Field Conf , 33rd, pp.
1 39-52
Bargar, K. E., Fournier, R. 0., Theodore,
T. G. 1985. Particles in fluid inclusions
from Yellowstone National Park-bac­
teria? Geology 1 3 : 483-86
Benz, H. M . , Smith, R. B. 1 984. Sim­
ultaneous inversion for lateral velocity
variations and hypocenters in the Yel10wstone region using earthquake and
controlled source data. J. Geophys. Res.
89: 1 208-20
Bhattacharyya, B. K., Leu, L. K. 1 975.
Analysis of magnetic anomalies over
Yellowstone National Park: mapping of
Curie point isothermal surface for geo­
thermal reconnaissance. J. Geophys. Res.
80: 4461-65
Blank, H. R. Jr., Gettings, M. E. 1974. Com­
plete Bouguer gravity map: Yellowstonc­
Island Park region. US Geol. Surv. Open­
File Map 74-22, scale 1 / 1 25,000
Brokaw, M. A. 1 985. Upper crustal interpre­
tation of Yellowstone delerminedfrom ray
trace modeling of seismic refraction data.
MS thesis. Univ. Utah, Salt Lake City.
1 80 pp.
Christiansen, R. L. 1984. Yellowstone mag­
matic evolution: its bearing on under­
standing large-volume explosive volcan­
ism. In Studies in Geophysics: Explosive
Volcanism: Inception, Evolution, and Haz­
ards, pp. 84-95. Washington, DC: Natl.
Acad. Press
Craig, H . , Boat, G., White, D. E. 1956. Iso­
tope geochemistry of thermal waters. Natl.
Acad. Sci. Nat. Res. Counc. Publ. 400: 2939
Craig, H., Lupton, J. E., Wei han, J. A.,
Poreda, R. 1 978. Helium isotope ratios
in Yellowstone and Lassen Park volcanic
gases. Geophys. Res. Lett. 5: 897-900
Daniel, R. G., Boore, D. M. 1 982. Anom­
alous shear wave delays and surface wave
velocities at Yellowstone caldera, Wyom­
ing. 1. Geophys. Res. 87: 273 1 --44
Doe, B. D., Leeman, W. P., Christiansen,
R. L., Hedge, C. E. 1982. Lead and stron­
tium isotopes and related trace elements
as genetic tracers in the upper Cenozoic
rhyolite-basalt association of the Yellow­
stonc Plateau voleanic field, U.S.A. J.
Geophys. Res. 87: 4785-4806
Dzurisin, D., Yamashita, K. M. 1 987.
Vertical surface displacements at Yellow­
stone caldera, Wyoming, 1 976-1985. J.
Geophys. Res. 92: 1 3 ,753-66
Dzurisin, D., Yamashita, K. M . , Johnson,
D. J. 1 986. Preliminary results of precise
leveling and trilateration surveys in Yel­
lows tone National Park, Wyoming, 1 985.
US Geot. Surv. Open-File Rep. 86-265-B.
28 pp.
Eaton, G. P., Christiansen, R. L., Iyer,
H. M . , Pitt, A. M . , M abey , D. R., et a!.
1975. Magma beneath Yellowstone Nat­
ional Park. Science 188: 787-96
Fournier, R. O. 1 979. Geochemical and
hydrological considerations and the use of
enthalpy-chloride diagrams in the pre­
diction of underground conditions in hot­
spring systems. 1. Volcanol. Geotherm.
Res. 5: 1 - 1 6
Fournier, R. O. 1 98 1 . Application o f water
geochemistry to geothermal exploration
and reservoir engineering. In Geothermal
Systems: Principles and Case Histories, ed.
L. Rybach, L. J. P. Muffler, pp. 109 43.
New York: Wiley
Fournier, R. O. 1983. Active hydrothermal
systems as analogucs of fossil systems. In
The Role of Heat in the Development
of Energy and Mineral Resources in the
Northern Basin and Range Province. Geo­
thermo Res. Counc. Spec. Rep. No. 13, pp.
263-284
Fournier, R. O. 1 987. Conceptual models of
brine evolution in magmatic-hydro­
thermal systems. In Hawaiian Volcanism.
US Geol. Surv. Prof Pap. 1350, ed. R. W.
Decker, T. L. Wright, P. H. Stauffer, pp.
1487-1 506
Fournier, R. 0. 1 988. Hydrothermal activity
in relation to late Holocene dynamics in
Yellowstone caldera, Wyoming. Proc.
Conf Sci. in Nat!. Parks-Toward the
Year 2000, Fort Collins, Colo., 1986, Vol.
3 , pp. 92-107
Fournier, R. 0., Pitt, A. M. 1985. The Yel­
lowstone magmatic-hydrothermal system.
Trans. Geotherm. Counc. Int. Symp. Geo-
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
YNP HYDROTHERMAL SYSTEM
thermo Energy, ed. C. Stone, lnt. Vol., pp.
3 1 9-27
Fournier, R . 0., Potter, R. W. II. 1 982. An
equation correlating the solubility of
quartz in water from 25° to 900°C at pres­
sures up to 1 0,000 bars. Geochim. Cosmo­
chim. A cta 46: 1 969-73
Fournier, R. 0., White, D. E., Truesdell,
A. H. 1 976. Convective heat flow in Yel­
lowstone National Park. Proc. UN Symp.
Dev. and Use of Geotherm. Resour., San
Francisco, 1975, I : 73 1 -39. Washington,
DC: US Govt. Print. Off.
Fournier, R. 0., Thompson, J. M ., Hutch­
inson, R. A. 1 986. Fluctuations in com­
position of Cistern Spring, Norris Geyser
Basin, Yellowstone National Park, WY variable boiling and mixing 1962-1985.
Extended Ahstr., Int. Symp. Water-Rock
Interaction, 5th, Reykjavik, Iceland, pp.
206-9
Gooch, F. A . , Whitfield, J. E. 1 888. Analyses
of waters of the Yellowstone National
Park, with an account of the methods of
analysis employed. US Geol. Surv. Bull.
47. 84 pp.
Gunter, B . D. 1973. Aqueous phase-gaseous
phase material balance studies of argon
and nitrogen in hydrothermal features at
Yellowstone National Park. Geochim.
Cosmochim. Acta 37(3): 495-5 1 3
Gunter, B . D . , Musgrave, B . C . 1 966. Gas
chromatographic measurements of hydro­
thermal emanations at Yellowstone Na­
tional Park. Geochim. Cosmochim. A cta
30: 1 1 75-89
Hamilton, W. L. 1 98 5 . Deformation models
for interpreting warped H olocene terraces
of Yellowstone Lake and the Yellowstone
River at the Yellowstone caldera, Wyom­
ing. E05, Trans. Am. Geophys. Union 66
(46): 853 (Abstr.)
Hardee, H . C. 1982. Permeable convection
above magma bodies. Tectonophysics 84:
1 79-95
Hildreth, W., Christiansen, R. L., O'Neil,
J. R. 1984. Catastrophic isotopic modi­
fication of rhyolitic magma at times of
caldera subsidence, Yellowstone Plateau
volcanic field. J. Geophys. Res. 89: 833969
Honda, S . , Muffler, L. J. P. 1 970. Hydro­
thermal alteration in core from research
drill hole Y- I , Uppcr Geyscr Basin, Yel­
lowstone National Park, Wyoming. Am.
Mineral. 55: 17 14-37
Iyer, H. M . , Evans, J. R., Zandt, G., Stewart,
R. M . , Cookley, J. M . , Roloff, J. N. 198 1 .
A deep low-velocity body under the Yel10wstone caldera, Wyoming: delineation
using teleseismic P-wave residuals and tec­
tonic interpretations. Geol. Soc. Am. Bull.
92: 792-98
Jackson, S. M . , Smith, R. B., Olson, T. L.
51
1984. Recent uplift of the Yellowstone cal­
dera from precision gravity measure­
ments. Eos, Trans. Am. Geophys. Union
65(45): 1 1 1 8 (Abstr.)
Keenan, J. H., Keys, F. G., Hill, P. G.,
Moore, J. G. 1 969. Steam Tables. New
York: Wiley. 162 pp. (Int. Ed . - M etric
Units)
Keith, T. E. c., M uffler, L. J. P. 1978. Min­
erals produced during cooling and hydro­
thermal alteration of ash flow tuff from
Yellowstone drill hole Y-5. J. Volcanol.
Geotherm. Res. 3: 373-402
Keith, T. E. c., White, D. E. , Beeson, M . H .
1 97 8 . Hydrothermal alteration and self­
sealing in Y-7 and Y-8 drill holes in north­
ern part of Upper Geyser Basin, Yel­
lowstone National Park, Wyoming. US
Geol. Surv. Prof Pap. I054-A. 26 pp.
Kennedy, B . M., Smith, S. P., Reynolds,
J. H. 1 982. Noble gases in Yellowstone
Park. Eos, Trans. Am. Geophys. Union 63:
1 145 (Abstr.)
Kennedy, B. M . , Lynch, M. A . , Reynolds,
J . H . , Smith, S. P. 1 985. Intensive sam­
pling of noblc gases in fluids at YcJlow­
stone: I. Early overview of the data; re­
gional patterns. Geochim. Cosmochim.
Acta 49: 1 25 1-61
Kennedy, B . M., Reynolds, J. H., Smith,
S. P., Truesdell, A . H. 1 987 . Helium iso­
topes: Lower Geyser Basin, YeJlow­
stone National Park. J. Geophys. Res. 92:
12,477-89
Kim, K., Craig, H . 1979. Radioactivities of
hot springs in Yellowstone Park. Eos,
Trans. Am. Geophys. Union 60(46): 94445 (Abstr.)
Leeman, W. P., Doe, B. R . , Welhan. J. 1977.
Radiogenic and stable isotope studies of
hot-spring deposits in Yellowstone Na­
tional Park and their genetic implica­
tions. Geochem. J. 1 1 : 65-74
Lehman, J. A. , Smith, R. B. , Schilly, M . M o o
Braile, L. W . 1 9 8 2 . Uppcr crustal structure
of the Yellowstone caldera from delay
time analyses and gravity correlations. J.
Geophys. Res. 87: 271 3-30
Lister, C. R. B. 1974. On the penetration of
water into hot rock. Geophys. J. R. As/ron.
Soc. 39: 465-509
Lister, C. R. B. 1 980. Heat flow and hydro­
thermal circulation. Ann. Rev. Earth
Planet. Sci. 8: 95- 1 1 7
Lister, C . R . B . 1 983. The basic physics of
water penetration into hot rock. In Hydro­
thermal Processes at Seafloor Spreading
Centers, ed. P. A. Rona, K. Bostrom, L.
Laubier, K. L. Smith, Jr., pp. 1 4 1-68. New
York: Plenum
Love, J . D., Good, J. M. 1970. Hydro­
carbons in thermal areas, northwestern
Wyoming. US Geol. Surv. Prof Pap. 644B. 23 pp.
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
52
FOURNIER
Mazor, E., Fournier, R. O. 1 973. More on
noble gases in Yellowstone National Park
hot waters. Geochim. Cosmochim. Acta
37(3): 5 1 5-25
Mazor, E., Thompson, J. M. 1982-. Evo­
lution of geothermal fluids deduced from
chemistry plots: Yellowstone National
Park (U.S.A.). J. Volcanol. Geotherm. Res.
1 2: 3 5 1 --60
Mazor, E., Wasserburg, G. J. 1 965. Helium,
neon, argon, krypton, and xenon in gas
emanations from Yellowstone and Lassen
Volcanic
National
Parks.
Geochim.
Cosmochim. Acta 29: 443-54
McKenzie, W. F., Truesdell, A. H. 1 977.
Geothermal reservoir temperatures esti­
mated from the oxygen isotope com­
positions of dissolved sulfate and water
from hot springs and shallow drill holes.
Ceothermics 5: 5 1 -62
Meertens, c., Levine, J. 1 98 5 . Compressive
tectonic strain as a possible mechanism
for long-term vertical deformation of the
Yellowstone caldera. Eos, Trans. Am.
Ceophys. Union 66(46): 853 (Abstr.)
Meyer, G. A . , Lock, W. K. 1986. Origin
and deformation of Holocene shoreline
terraces, Yellowstone Lake, Wyoming.
Geology 14: 699-702
Morgan, P., Blackwell, D. D., Spafford,
R. E. 1 977. Heat flow measurements in
Yellowstone Lake and the thermal struc­
ture of the Yellowstone caldera. J. Geo­
phys. Res. 82: 3 7 1 9-32
Muffler, L. J. P., White, D. E., Truesdell,
A. H. 1 97 1 . Hydrothermal explosion cra­
ters in Yellowstone National Park. Geol.
Soc. Am. Bull. 82: 723--40
Noguchi, K., Nix, J. 1 963. Geochemical
studies of some geysers in Yellowstone
National Park. Proc. Jpn. Acad. 39: 37075
Norton, D. R . , Friedman, I. 1 985. Chloride
flux out of Yellowstone National Park. J.
Volcanol. Geotherm. Res. 26: 23 1 -50
Pelton, J. R., Smith, R. B. 1979. Recent crust­
al uplift in Yellowstone National Park.
Science 206: 1 1 79-82
Peiton, J. R., Smith, R. B. 1982. Con­
temporary vertical surface displacements
in Yellowstone National Park. J. Geophys.
Res. 87: 2745-5 1
Rowe, J. J., Fournier, R. 0., Morey, G. W.
1 973. Chemical analysis of thermal waters
in Yellowstone National Park, Wyoming,
1 960-- 1 965. US Ceol. Surv. Bull. 1303. 3 1
pp.
Schoen, R., Rye, R. O. 1 970. Sulfur isotope
distribution in solfataras, Yellowstone
National Park. Science 1 70: 1 082-84
Scott, R. C. 1 964. Records of post­
earthquake chemical quality of ground
water. In The Hebgen Lake Montana
Earthquake of A ugust 1 7, 1959. US Ceol.
Sum. Prof Pap. 435, pp. 1 79-84
Sleep, N. H. 1983. Hydrothermal convection
at ridge axes. In Hydrothermal Processes
at Seafloor Spreading Centers, ed. P. A.
Rona, K. Bostrom, L. Laubier, K. L.
Smith, Jr., pp. 7 1-82. New York: Plenum
Smith, R. B . , Braile, L. W. 1984. Crustal
structure and evolution of an explosive
silicic volcanic system at Yellowstone
National Park. In Studies in Geophysics:
Explosive Volcanism: Inception, Evolution,
and Hazards, pp. 96-- 1 09. Washington,
DC: Nat!. Acad. Press
Smith, R. B., Bruhn, R. L. 1 984. Intraplate
expansional tectonics of the Eastern
Basin-Range: inferences on structural
style from seismic reflection data, regional
tectonics, and thermal-mechanical models
of brittlc-ductile deformation. J. Geophys.
Res. 89: 5733 62
Smith, R. B., Christiansen, R. L. 1980. Yel­
lowstone Park as a window on the earth's
interior. Sci. Am. 242: 1 04- 1 7
Smith, R. B . , Shuey, R. T., Freid1ine, R.,
Otis, R., Alley, L. 1 974. Yellowstone hot
spot: new magnetic and seismic evidence.
Geology 2: 45 1-55
Stanley, W. D., Boehl, J. E., Bostick, F. X.,
Smith. H. W. 1 977. Geothermal signif­
icance of magnetotelluric sounding in
the eastern Snake River Plain-Yellow­
stone region. J. Geophys. Res. 82: 250 1 14
Sturchio, N. c., Binz, C. M . , Lewis, C. H .
III. 1 98 7 . Thorium-uranium disequilib­
rium in a geothermal discharge zone
at Yellowstone. Geochim. Cosmochim.
Acta 5 1 : 2025-34
Thompson, J. M . , Hutchinson, R. A. 1 980.
Boundary Creek thermal area of Yel10wstone National Park: II. Thermal
water analyses. Trans. Geotherm. Resour.
Counc. 4: 1 89-92
Thompson, J. M . , Yadav, S. 1979. Chemical
analyses of waters from geysers, hot
springs and pools in Yellowstone National
Park, Wyoming, from 1974-1978. US
Geol. Surv. Open-File Rep. 79-704. 49 pp.
Thompson, J. M., Presser, T. S., Barnes,
R. B., Bird, D. B. 1 975. Chemical analy­
sis of the waters of Yellowstone National
Park, Wyoming, from 1965-1973. US
Ceol. Surv. Open-File Rep. 75-25. 59 pp.
Truesdell, A. H., Fournier, R. O. 1 976. Con­
ditions in the deeper parts of hot spring
systems of Y cllowstonc National Park,
Wyoming. US Geol. Surv. Open-File Rep.
76-428. 29 pp.
Truesdell, A. H., Thompson, J. M. 1 982. The
geochemistry of Shoshone Geyser Basin,
Yellowstone National Park. Guideb. Wyo.
Geol. Assoc. Ann. Field Conf , 33rd, pp.
1 53-59
Truesdell, A. H . , Nathenson, M . , Rye, R. O.
YNP HYDROTHERMAL SYSTEM
Annu. Rev. Earth Planet. Sci. 1989.17:13-53. Downloaded from arjournals.annualreviews.org
by RICE UNIVERSITY - FONDREN LIBRARY on 02/27/10. For personal use only.
1977. The effects of subsurface boiling and
dilution on the isotopic compositions of
Yellowstone thermal waters. J. Geophys.
Res. 82: 3694-3704
Welhan, J. A. 198 1 . Carbon and hydrogen
gases in hydrothermal systems; the search
for a mantle source. PhD thesis. Univ.
Calif., San Diego, La Jolla. 2 1 6 pp.
White, D. E. 1978. Conductive heat flows
in research drill holes in thermal areas of
Yellowstone National Park, Wyoming.
US Geol. Surv. J. Res. 6: 765-74
White, D. E., Muffler, L. J. P., Truesdell,
A. H. 1 97 1 . Vapor-dominated hydrother­
mal systems compared with hot-water sys­
tems. Econ. Geol. 66: 75-97
53
White, D. E . , Fournier, R . 0 . , Muffler,
L. J. P., Truesdell, A. H. 1975. Physical
results of research drilling in thermal areas
of Yellowstone National Park, Wyo­
ming. US Geol. Surv. Prof Pap. 892.
70 pp.
Yellowstone National Park Task Group.
1 987. The Objectives for Deep Scientific
Drilling in Yellowstone National Park.
Washington, DC: Natl. Acad. Sci. 69 pp.
Zohdy, A. A. R., Anderson, L. A., Muffler,
L. J. P. 1973. Resistivity, self-potential,
induced-polarization and surveys of a
vapor-dominated
geothermal
system.
Geophysics 38(6): 1 1 30-44