A Field-Trip Guide to

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Volcanic, Hydrothermal, and 

Glacial Activity in the Region

- OCT 0 6 1994

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A Field-Trip Guide to 

Yellowstone National Park, 

Wyoming, Montana, and Idaho 

Volcanic, Hydrothermal, and 

Glacial Activity in the Region

By Robert O. Fournier, Robert L. Christiansen, 

Roderick A. Hutchinson, and Ken L. Pierce

U.S. GEOLOGICAL SURVEY BULLETIN 2099

Originally Prepared for the 7th International Symposium on 

Water-Rock Interaction (WRI-7), Park City, Utah, July 1992

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For sale by

U.S. Geological Survey, Map Distribution

Box 25286, MS 306, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Text and illustrations edited by James W. Hendley II

Library of Congress Cataloging-in-Publication Data

N A field-trip guide to Yellowstone National Park, Wyoming, Montana, and Idaho volcanic, hydrothermal, and glacial activity in the 

region / by Robert O. Fournier ... [et al.].

p. cm. (U.S. Geological survey bulletin ; 2099)

"Originally prepared for the 7th Interational Symposium on Water-Rock Interaction (WRI-7) Park City, Utah, July 1992." 

Includes bibliographical references. 

Supt. of Docs, no.: I 19.3:2099

1. Hot springs Yellowstone National Park Guidebooks. 2. Volcanism Yellowstone National Park 

Guidebooks. 3. Glacial landforms Yellowstone National Park Guidebooks. 4. Yellowstone National Park 

Guidebooks. I. Fournier, R. O. II. Series. 

QE75.B9 no. 2099 

[QE528] 

557.3 s dc20

[551.2'1'097 8752] 94-13139

CIP

Cover Basins at Mammoth Hot Springs of Gardiner's River (Hayden, 1883, fig. 1). 

Title Page Giant Geyser in action (Hayden, 1883, fig. 6, modified).
CONTENTS

Glossary....................................................................................................................... V

General information and brief summary of trip......................................................... 1

Introduction to Yellowstone........................................................................................ 3

Detailed itinerary......................................................................................................... 5

Day 1 Jackson Hole, Wyoming, to Old Faithful.............................................. 5

Stop 1 Windy Point turnout.................................................................. 5

Stop 2 Lunch at String Lake................................................................. 6

Stop 3 Willow Rats overlook............................................................... 7

Stop 4 West Thumb Geyser Basin........................................................ 7

Stop 5 Old Faithful Lodge cabins, Upper Geyser Basin...................... 10

Day 2 Upper, Midway, and Lower Geyser Basins........................................... 12

Stop 6 Biscuit Basin.............................................................................. 14

Stop 7 Midway Basin............................................................................ 18

Stop 8 Firehole Lake and Steady Geyser............................................. 18

Stop 9 Fountain Paint Pot Walk............................................................ 19

Stop 10 Porcupine Hills and Y-13 drill hole....................................... 19

Stop 11 Lunch in Lower Geyser Basin................................................. 20

Stop 12 The Y-3 drill site and Pocket Basin explosion crater............ 20

Stop 13 Firehole Canyon ...................................................................... 22

Day 3 Travel Old Faithful to Mammoth Hot Springs ...................................... 23

Stop 14 Morris Geyser Basin................................................................ 23

The Porcelain Terrace and Porcelain Basin loop trail................... 25

The Back Basin loop trail.............................................................. 28

Steamboat Geyser ................................................................ 28

Cistern Spring....................................................................... 29

Porkchop Geyser Crater........................................................ 29

Echinus Geyser..................................................................... 30

Characteristics and origin of acid-sulfate waters................. 30

The Y-9 drill hole................................................................. 31

Stop 15 Picnic lunch in the Norris region............................................ 31

Stop 16 Roaring Mountain.................................................................... 31

Stop 17 Obsidian Cliff.......................................................................... 31

Stop 18 Hoodoos................................................................................... 33

Stop 19 Overlook above Mammoth Hot Springs................................. 33

Stop 20 Mammoth Hot Springs............................................................ 35

Day 4 Mammoth Hot Springs to Jackson Hole................................................ 35

Stop 21 Overlook of lower Grand Canyon at The Narrows................ 35

Stop 22 Washburn overlook.................................................................. 36

Stop 23 Artist Point............................................................................... 37

Stop 24 Lunch at Buffalo Ford picnic area.......................................... 37

Stop 25 Mud Volcano area.................................................................... 37

Stop 26 Le Hardys Rapids.................................................................... 38

Stop 27 Yellowstone Lake.................................................................... 39

Stop 28 Snake River overlook.............................................................. 40

Selected references...................................................................................................... 41

Appendixes:

A. Supplemental information supplied to field-trip participants in

addition to this field guide....................................................................... 45

B. Activity of selected geysers in Yellowstone National Park,

spring 1992............................................................................................... 46

in
IV CONTENTS

FIGURES

1. Location and major features of Yellowstone National Park............................................................................... 2

2. Map of Yellowstone National Park, Wyoming, showing 0.6-Ma Yellowstone caldera, two resurgent 

domes, active and recently active hydrothermal features, major faults, and locations of selected 

named thermal areas............................................................................................................................................ 4

3. Locations of roads and field trip stops in Yellowstone National Park............................................................... 5

4-7. Photographs showing:

4. View of Teton Range as seen from Stop 1............................................................................................ 6

5. String Lake and Teton Range as seen from Stop 2 .............................................................................. 6

6. Old sinter at shore of Yellowstone Lake, West Thumb Geyser Basin.................................................. 8

7. Fishing Cone, West Thumb Geyser Basin............................................................................................. 8

8. Measured pressure versus depth in U.S. Geological Survey research wells drilled in Yellowstone

National Park....................................................................................................................................................... 8

9. Photograph of air view of Upper Geyser Basin ................................................................................................. 10

10. Geologic map showing route and stops between Upper Geyser Basin and Norris Geyser Basin.................... 11

11. Photograph of Beehive Geyser in eruption, Geyser Hill, Upper Geyser Basin................................................. 13

12. Schematic diagram showing approximate reservoir temperatures beneath Upper and Lower Geyser 

Basins and effects of subsurface boiling with steam loss on bicarbonate relative to chloride in the 

shallowest reservoirs........................................................................................................................................... 14

13. Distribution of fresh obsidian and hydrothermal minerals in groundmass of core from

U.S. Geological Survey Y-7 drill hole............................................................................................................... 15

14. Distribution of fresh obsidian and hydrothermal minerals in groundmass of core from

U.S. Geological Survey Y-8 drill hole............................................................................................................... 16

15. Section through U.S. Geological Survey Y-7 and Y-8 drill holes, showing pressures, temperature 

contours, and inferred self-sealing by deposition of hydrothermal minerals in originally permeable 

ground.................................................................................................................................................................. 17

16^23. Photographs showing:

16. Blocks of zeolite-cemented sediments blown from Black Opal Pool, Biscuit Basin........................... 17

17. Mud pots se"en at high point on Fountain Paint Pofnature walk, Lower Geyser Basin....................... 19

18. Clepsydra Geyser, Fountain Paint Pot nature walk, Lower Geyser Basin............................................ 20

19. Air view of Pocket Basin hydrothermal explosion crater ..................................................................... 21

20. Floor and rim of Pocket Basin hydrothermal explosion crater............................................................. 21

21. Mud pots located on the southern flank of Pocket Basin...................................................................... 22

. 22. Flow-front breccia exposed in Firehole Canyon.................................................................................... 23

23. Firehole Falls in Firehole Canyon held up by nearly vertical, erosionally resistant flow layers

in the Nez Perce Creek flow................................................................................................................... 23

24. Generalized geologic map showing route and stops between Norris Geyser Basin and Mammoth *v 

Hot Springs.......................................;.................................................^ 24

25. Sketch map of Norris Geyser Basin showing topographic features, U.S. Geological Survey drill holes

Y-9 and Y-12 and locations of selected hot springs and geysers .......................................................... :........... 25

26-27. Photographs showing:

26. Porcelain Basin, viewed from near the Norris museum, Norris Geyser Basin..................................... 26

27. Hot spring activity at Porcelain Terrace, Norris Geyser Basin ............................................................. 27

28. Sulfate (804) versus deuterium (8D) relations for Norris Geyser Basin thermal waters.................................. .27

29-31. Photographs showing: - -

29. A typical small eruption of Steamboat Geyser, Norris Geyser Basin................................................... 28

30. Eroded ground resulting from infrequent big eruptions of Steamboat Geyser,

Norris Geyser Basin ......................................;........................................................................................ 28

31. Silica terrace formed by waters discharged from Cistern Spring.......................................................... 29

32. Chloride (Cl) versus sulfate (SO4) relations for waters collected at different times from

Cistern Spring, Echinus Geyser, and U.S. Geological Survey Y-12 drill hole................................................. 29
CONTENTS V

33-43. Photographs showing:

33. Porkchop Geyser, Norris Geyser Basin.................................................................................................. 30

34. Roaring Mountain................................................................................................................................... 32

35. Obsidian Cliff ................................................... 32

36. Large landslide with blocks of white travertine in foreground and The Koodoos,

composed of blocks of travertine in a landslide deposit....................................................................... 33

37. Main travertine terrace seen from overlook above Mammoth Hot Springs and travertine

terrace at Mammoth Hot Springs........................................................................................................... 34

38. Stratified andesitic breccias of the Absaroka Volcanic Supergroup capped by columnar-jointed

basalt flows............................................................................................................................................. 35

39. View from the Calcite Springs overlook showing the lower Grand Canyon at The Narrows............. 35

40. View looking east from Washburn overlook on the north side of Dunraven Pass............................... 36

41. Lower Falls seen from Artist Point........................................................................................................ 37

42. Hydrothermally altered rhyolite exposed in the walls of Grand Canyon of the

Yellowstone............................................................................................................................................. 38

43. Black Dragon's Cauldron, Mud Volcano area ....................................................................................... 39

44. Vertical displacement and topographic profiles along eastern leveling line from Lake Butte to

Canyon Junction.................................................................................................................................................. 40

45. Photograph showing view of Cathedral Group of peaks from Snake River overlook...................................... 41

TABLES

1. Preferred values for the average rates of discharge of deep high-temperature component of thermal 

water, chloride in that water, and heat (before boiling during upflow) from selected thermal areas in 

Yellowstone National Park.................................................................................................................................. 5

2. Chemical analyses of selected thermal waters from Yellowstone National Park.............................................. 9

3. Chemical compositions of selected thermal waters in Lower Geyser Basin..................................................... 18

4. Chemical compositions of selected thermal waters, Norris Geyser Basin......................................................... 26

GLOSSARY

Adiabatic. In thermodynamics, pertaining to the relationship 

of pressure and volume when a gas or fluid is compressed or expanded without either giving or receiving 

heat. Compression may result in gas condensing to liquid, and expansion may result in liquid evaporation (or 

boiling) to gas. Although there is no change in the heat 

content of the system, there is a change in temperature.

Adiabatic expansion. An increase in volume with no 

change in heat content of the system but with a decrease 

in temperature. For example, water at high temperature 

(>100°C) and high pressure (>1 atmosphere) that flows 

upward toward the Earth's surface experiences a decrease in pressure that eventually results in boiling 

(evaporation) and a decrease in temperature of the system. However, the total heat content, distributed between the remaining liquid water and new-formed steam 

remains constant.

Andesite volcanism. Volcanic activity characterized by eruption or extrusion of lava intermediate in composition

between rhyolite (relatively rich in silica, sodium, and 

potassium) and basalt (relatively rich in calcium and 

magnesium). Many of the high volcanoes in the Cascade 

Range of Washington and Oregon and in the Andes Range 

of South America are composed mostly of andesitic lavas.

Clinoptilolite. A zeolite mineral that is relatively rich in 

potassium.

Curie-point isotherm. The temperature above which minerals in a rock loose their magnetic properties.

Dacite. A fine-grained igneous rock that is similar in composition to andesite but containing less calcium and 

more silica.

End moraine. A mound of unsorted and unstratified rock 

deposited at the lower end or front of a glacier where 

the advancing ice sheet melts.

Fluidal layers. As applied to a flowing lava, layers of liquid magma with relatively low viscosity within solid 

and (or) relatively viscous material composed of crystals and glass.
VI CONTENTS

Geothermometer. Dissolved components in a mineral, 

liquid, or gas that can be used to determine the temperature at which chemical equilibrium was last attained. For many hot spring waters, the concentrations 

of certain dissolved constituents, such as silica, commonly can be used to estimate the temperature of the 

underground reservoir supplying water to the spring.

Glacial erratics. A rock fragment carried by glacial ice 

and deposited some distance from the outcrop from 

which it was derived. Size ranges from a pebble to 

greater than a house-sized block.

Gneiss. A metamorphic rock formed by regional metamorphism in which bands or lenticles of granular 

minerals alternate with bands or lenticles in which 

minerals having flaky or elongate prismatic shapes 

predominate.

Graben. An elongate body of rock, bounded by faults on 

its long sides, that has been drooped downward in respect to the surrounding rock.

Granitic rock. A term loosely applied to any light-colored 

coarse-grained igneous rock containing the mineral 

quartz as an essential component along with feldspar 

and some dark-colored minerals that are rich in iron 

and magnesium.

Hydration rim. A layer or rind of water-rich glass produced by slow diffusion of water vapor into obsidian 

at close to atmospheric conditions of temperature and 

pressure.

Hydrostatic head. The height of a vertical column of 

water whose weight, if of unit cross section, is equal 

to the hydrostatic pressure.

Hydrostatic load. The weight of a vertical, column of 

water of unit cross section; the hydrostatic pressure.

Hydrothermal activity. Chemical and physical activity 

relating to the flow of hot water through rock.

Hydrothermal alteration. Alteration of minerals and rock 

as a result of reactions with hot, water-rich solutions.

Igneous rock. A rock that solidified from molten or partly 

molten material; for example a magma.

Kame gravels. Gravels deposited by a subglacial stream 

at the margin of a melting glacier.

Lenticle. A large or small lens-shaped stratum, body of 

rock, or rock fragment.

Liquidus temperature. The temperature above which a 

particular chemical system is completely liquid. For 

natural systems, a given magma will be entirely liquid 

at higher temperatures and a mixture of crystals and 

liquid (silicate melt) at a slightly lower temperature.

Loess. Fine-grained usually homogeneous material that is 

now generally believed to have been deposited from 

wind-blown dust.

Magma. Naturally occurring mobile molten rock material, 

generated within the Earth and capable of intrusion and 

extrusion, from which igneous rocks are thought to be 

derived through solidification and related processes.

Magnetotelluric soundings. An electromagnetic method 

of surveying in which natural electric and magnetic 

fields in the Earth's crust are measured. The measurements provide a means of determining differences in 

the electrical conductivity of rocks at different depths 

in the crust.

Metamorphic rock. Any rock derived from preexisting 

rocks by mineralogical, chemical, and (or) structural 

changes, essentially in the solid state, in response to 

marked changes in temperature, pressure, shearing 

stress, and chemical environment, generally at depth 

in the Earth's crust.

Metamorphism. The processes and conditions that create 

metamorphic rock.

Moraine. A mound, ridge, or other distinct accumulation 

of unsorted and unstratified rock debris deposited by 

direct action of glacial ice.

Mordenite. A zeolite mineral that is relatively rich in calcium and sodium.

Obsidian-hydration measurements. Measurements of the 

thickness of the hydration rim that has been produced 

by water vapor slowly diffusing into freshly chipped 

surfaces of obsidian. The thicknesses of such rims or 

rinds can be used to determine the length of time that 

the obsidian has been exposed to water vapor.

Perched bodies. Pools of water that are separated from an 

underlying main body of water by a zone in which 

pore spaces in the rock are unsaturated (pore spaces 

completely or partly filled with water vapor instead of 

liquid water).

Perlitic glassy rhyolite. Rhyolite lava rich in glass that 

has cracked, owing to contraction during rapid cooling. The cracks form small rounded grains of glass or 

spheruloids.

Permeability. The property or capacity of a porous or 

fractured rock and sediment or soil to transmit a fluid.

Phenocrysts. Relatively large crystals in an igneous rock 

composed mostly of significantly smaller-sized crystals.

Potentiometric surface. An imaginary surface representing the total head of ground water and defined by the 

level to which water will rise in a well. The water 

table is a particular potentiometric surface.

Radiogenic. Said of a product of a radioactive process; for 

example, lead produced from the decay of radioactive 

uranium.

Regional metamorphism. Metamorphism affecting an 

extensive region.
CONTENTS vn

Rhyolite-basalt volcanism. Volcanism characterized by 

the simultaneous or closely spaced in time eruptions 

of rhyolite and basalt magmas.

Seismic attenuation. A reduction in amplitude or energy 

of seismic waves as they pass through rock.

Seismic focal depth. The depth below the Earth's surface 

at which an earthquake initiates.

Silicic crystalline rocks. Igneous and metamorphic rocks 

in the Earth's crust that are relatively rich in silica, as 

opposed to relatively unconsolidated sediments and igneous rocks poor in silica, such as basalt.

Siliceous sinter. The lightweight porous opaline variety of 

silica deposited as an encrustation by precipitation 

from the waters of geysers and hot springs.

Stock. A stock is a body of igneous rock emplaced in the 

Earth's crust that is less than 100 km2 in surface expression. Some stocks were once magma chambers 

beneath volcanoes.

Spherulite. A rounded or spherical mass of needle-shaped 

crystals, commonly of feldspar, radiating from a central point.

Travertine. Fine-grained calcium carbonate deposited 

from hot-spring water. Precipitation of calcium carbonate is the result of separation of carbon dioxide 

from the water as it emerges at the Earth's surface.

Zeolite. A general term for a large group of hydrous aluminosilicates with sodium, potassium and calcium as 

their chief metals.

A Field-Trip Guide to Yellowstone National Park,

Wyoming, Montana, and Idaho 

Volcanic, Hydrothermal, and Glacial Activity in the Region

By Robert O. Fournier, Robert L. Christiansen, Roderick A. Hutchinson1 , and Ken L. Pierce

GENERAL INFORMATION AND BRIEF 

SUMMARY OF TRIP

This field-trip guide was originally prepared for the 

7th International Symposium on Water/Rock Interaction 

(WRI-7) held in July 1992 in Park City, Utah. A large and 

diversified group of earth scientists and accompanying 

family members participated in this 3 1/2-day field trip 

that focused on water/rock interactions over widely ranging temperatures and pressures in the Yellowstone/Grand 

Teton region. Emphasis was placed on the geochemical 

and hydrologic characteristics of the thermal waters in the 

major "geyser basins" of Yellowstone National Park. Information specific to the WRI-7 trip about logistics, lodging, and meals has been deleted from the present guide. 

The scientific content remains mostly unchanged, except 

for the addition of a glossary, two illustrations, all photographs, and some text previously presented to the field-trip 

participants in supplementary materials (see appendix A).

Most of the geyser basins in Yellowstone National 

Park are on a high volcanic plateau at elevations of 2,000 

to 2,200 m and are surrounded by much higher mountain 

ranges. In the middle of summer there generally are cool 

evenings and early mornings and warm afternoons. Visits 

to the localities described require short walks, mostly on 

boardwalks, but some are on what may be wet ground. No 

long, strenuous climbs are required. Expect brief afternoon 

thunder showers, particularly at Old Faithful. Please remember that the collecting of any kind of sample in a 

national park is prohibited except by those who have 

specific sampling permits issued by the National Park 

Service. Field-trip participants are asked to leave geologic picks and hammers at home or in their luggage 

while in Yellowstone National Park.

Caution

Thermal areas are both delicate and dangerous. 

Special caution should be exercised when visiting 

them to avoid damage to yourself and to the fragile 

environment. Please stay on boardwalks where they 

are present. Boiling pools of water commonly are covered by thin crusts of sinter that build inward from 

the sides of hot-spring pools. Assume that all water 

flowing in streams in and near thermal areas is hot 

enough to cause pain and blistering if you step into 

this water.

U.S. National Park Service, Yellowstone National Park, Wyoming 

82190.

Manuscript approved for publication May 16, 1994.

Day 1 Travel north through the Grand Teton National Park into Yellowstone National Park (fig. 1). Stops 

are made along the way to view the spectacular scenery 

and to discuss the glacial and structural history of the 

Teton Mountains and Jackson Hole, Wyoming. Lunch is at 

String Lake, a small lake with spectacular mountain scenery. After lunch, proceed to Yellowstone National Park, the 

scene of some of the largest known Quaternary eruptions 

of rhyolitic lava flows and caldera-forming ash-flow tuffs. 

Stop at the West Thumb thermal area on the shore of Yellowstone Lake to look at hydrothermal manifestations and 

their relation to volcanic, glacial, and postglacial processes. Thick and extensive deposits of sinter have been deposited from hot-spring waters in the West Thumb region 

since the last glaciation (Pinedale glaciation that ended 

10,000-15,000 years ago). (Note that here and in the remainder of this field guide "sinter" refers exclusively to 

siliceous material deposited at the Earth's surface by flowing hot water.) From West Thumb proceed to Old Faithful, 

arriving in time to explore the Upper Geyser Basin before 

dinner. Two nights are spent at Old Faithful.

Day 2 Most of the day is spent walking in the Upper, Midway, and Lower Geyser Basins within the Yellowstone caldera, where many hot springs, geysers, mud pots, 

and good exposures of silica- and zeolite-cemented sediments will be seen. Specialized bacteria, algae, and diatoms grow in the thermal waters, and various chemical

1
A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

precipitates are actively being deposited in different pools, 

including amorphous silica, calcite plus manganese oxides, 

smectites, native sulfur, and iron sulfides. Effects of a thick 

cover of glacial ice on hydrothermal activity are viewed 

and discussed. Particular attention is focused on Pocket 

Basin, a large oblong crater about 0.75 km in maximum 

length that formed as the result of hydrothermal eruptions. 

Day 3 Travel from Old Faithful to Mammoth Hot 

Springs. On the way, stop at Norris Geyser Basin, where

both neutral- and acid-chloride thermal waters emerge from 

ash-flow tuffs and hydrothermally altered glacial deposits. 

At Norris there are seasonal variations in the degree of 

boiling during upflow, and there is seasonal underground 

mixing of chloride-rich and sulfate-rich waters. Native sulfur and amorphous sulfides of arsenic and antimony are 

common in this basin. Between Norris and Mammoth, make 

brief stops at Roaring Mountain and Obsidian Cliff. Plan to 

arrive at Mammoth in time to walk along the extensive

112° nr 110°

MONTANA

v

CENTENNIAL RANGE

\ i __ / -,. __ /.-- _NA

45°

44°

10 20i

30i40 50 KILOMETERS

Figure 1. Location and major features of Yellowstone National Park. Dotted lines outline calderas; dashed lines, 

resurgent domes; I, first-cycle caldera; II, second-cycle caldera; III, third-cycle (Yellowstone) caldera; double lines

show major roads in region. Jackson Hole, Wyoming, is just 

off map, a few kilometers south of Moose. (From Christiansen and Hutchinson, 1987).
INTRODUCTION TO YELLOWSTONE

system of trails leading to bicarbonate-rich hot springs that 

emerge from Mesozoic sedimentary rocks and that form 

ever-changing mounds and thick terraces of travertine.

Day 4 Travel from Mammoth Hot Springs back to 

the Tetons and Jackson Hole via the eastern route through 

Yellowstone Park. This provides an opportunity to view 

from a distance thermal areas where petroleum is being 

carried to the surface in the hot-spring waters. Stop at the 

Grand Canyon of the Yellowstone River, where a steepsided gorge about 30 km long and ranging from about 300 

to 500 m in depth has been cut into a thick section of 

hydrothermally altered volcanic rocks, and at the Mud Volcano area, where violent fumarolic activity and acid-sulfate 

alteration is the surface expression of a small vapor-dominated hydrothermal system. The route passes through the 

Yellowstone caldera along a traverse where repeated leveling measurements made over many years showed a rapid 

rate of caldera uplift (about 2.5 cm/yr) before 1984, followed by a rapid rate of caldera subsidence (also about 2.5 

cm/yr) since 1985.

INTRODUCTION TO YELLOWSTONE

Yellowstone Park is situated on a high volcanic plateau that sits astride a region of active crustal extension. 

The plateau and the adjacent region to the west have been 

the most seismically active area of the Rocky Mountains in 

historic time (Smith and Braile, 1984). In 1872 the Yellowstone region became the first national park in the world, 

largely through the recognition that it displays some of the 

largest and most spectacular hot-spring and geyser activity 

on Earth. Early scientists recognized that this hydrothermal 

activity was related to the same causes as the recent volcanism in the region. Only in the last few decades has it been 

realized that the compositionally bimodal rhyolite-basalt 

volcanism of the Yellowstone Plateau volcanic field (Boyd, 

1961; Christiansen and Blank, 1972; Christiansen, 1984) is 

younger than about 2.2 Ma and completely distinct from 

the predominantly andesitic volcanism of the Eocene Absaroka volcanic field (Smedes and Prostka, 1972). The major 

hydrothermal activity recognized in Yellowstone National 

Park (White and others, 1975; Fournier, 1989) is related in 

time and origin to postcaldera magmatism in the youngest 

of three calderas. These three calderas resulted from voluminous rhyolitic ash-flow eruptions at 2.0, 1.3, and 0.6 Ma. 

Each of these caldera-forming ash-flow eruptions was preceded and succeeded by large eruptions of rhyolitic lava. 

The last eruption of rhyolitic lava was about 70,000 years 

B.P. (Christiansen, 1984). More than 6,500 km3 of erupted 

magma make the Yellowstone Plateau volcanic field one of 

the major Quaternary volcanic fields on Earth.

Current activity includes not only the high-temperature hydrothermal systems but distinctive seismicity and a 

spatial and temporal pattern of historic rapid uplift or inflation followed by deflation (Pelton and Smith, 1979, 1982; 

Jackson and others, 1984; Hamilton, 1985; Dzurisin and 

others, 1986; Meyer and Lock, 1986; Dzurisin and Yamashita, 1987) that is difficult to explain by processes that do not 

involve magmatic activity. In addition, a variety of geophysical anomalies coincide with the 0.6-Ma Yellowstone 

caldera that, taken together, indicate that magma or partially 

molten rock may be present at depths ranging from about 5 

to 10 km, and possibly as shallow as 3 km beneath parts of 

the eastern half of this caldera (Eaton and others, 1975; lyer 

and others, 1981; Lehman and others, 1982; Smith and 

Braile, 1984; Benz and Smith, 1984; Brokaw, 1985). These 

anomalies include low densities (Blank and Gettings, 1974), 

large convective and conductive heat flows (Fournier and 

others, 1976; Morgan and others, 1977; White, 1978), a 

magnetic low and shallow calculated Curie-point isotherms 

(Smith and others, 1974; Bhattacharyya and Leu, 1975; 

Eaton and others, 1975), low seismic velocities (lyer and 

others, 1981; Daniel and Boore, 1982), high seismic attenuation (Benz and Smith, 1984; Brokaw, 1985), a sharp increase in electrical conductivity at a depth of about 5 km, 

shown by magnetotelluric soundings (Stanley and others, 

1977), and a lack of seismic focal depths deeper than about 

3 to 4 km beneath much of the caldera (Fournier and Pitt, 

1985). Heat-flow considerations indicate that magmatic 

temperatures could be attained at a depth about 0.5 km 

deeper than the depth of the transition from seismic to aseismic conditions (Fournier and Pitt, 1985).

Chemical compositions of Yellowstone's thermal 

waters have been determined by many investigators starting over 100 years ago. Of particular importance are large 

compilations by Gooch and Whitfield (1888), Alien and 

Day (1935), Rowe and others (1973), Thompson and others (1975), and Thompson and Yadav (1979).

The exceptional hydrothermal activity at Yellowstone results from a combination of (1) an abundant supply of recharge water that comes primarily from snow that 

accumulates on the surrounding high mountains, particularly to the north and northwest (based on isotopic data for 

hot-spring waters from Truesdell and others (1977) and 

unpublished U.S. Geological Survey (USGS) analyses of 

meteoric waters in the region by Robert O. Rye and by 

Tyler B. Coplen), where faulted and folded permeable sedimentary rocks provide permeability for the infiltrating 

water, (2) a huge magmatic heat source at a relatively 

shallow depth of 4 to 5 km beneath the 0.6-Ma Yellowstone caldera, and (3) frequent and widespread seismic activity that reopens channels of fluid flow that become 

clogged by hydrothermal alteration products and mineral 

precipitates. Upflow of thermal waters is controlled mainly 

by fracture systems. Important zones of fracturing in the 

Yellowstone caldera are near the outer edge of the main 

ring fracture and at the flanks of the two resurgent domes 

(fig. 2). Outside the caldera, hydrothermal activity is pronounced along a network of faults in a zone extending
A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

northward from Norris Geyser Basin through Mammoth 

Hot Springs. Most of the surface expression of hydrothermal activity is on the northwest side of the caldera, the 

side facing the likely direction of maximum water recharge, as determined by isotopic data.

Within the very seismically active Yellowstone region, water likely circulates to the depth at which brittle 

fracturing is present. Earthquake hypocenters indicate that 

this depth is about 4 to 5 km beneath the Yellowstone caldera and as deep as 1-5 to 20 km a few kilometers to the 

side of the caldera. Furthermore, the transition from brittle 

to plastic behavior of silicic crystalline rocks in the Earth's 

crust is likely to occur at about 370 to 400°C for reasonable 

strain rates in tectonically active regions (Fournier, 1991). 

Thus, the limit of downward circulation of meteoric water 

in the Yellowstone hydrothermal system is likely to be the 

depth where temperatures are about 350 to 400°C. An independent line of evidence, based on brine-gas phase equilib0 10 20 30 40 50 KILOMETERS

Figure 2. Map of Yellowstone National Park, Wyoming, showing 

0.6-Ma Yellowstone 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. Letter codes show approximate locations of 

major thermal areas mentioned in text: BC, Boundary Creek; CH, 

Crater Hills; GC, Grand Canyon; HLB, Heart Lake Basin; HSB, 

Hot Springs Basin; JC, Josephs Coat Hot Springs; LB, Lower 

Geyser Basin; MB, Midway Basin; MH, Mammoth Hot Springs; 

MV, Mud Volcano; NB, Norris Geyser Basin; SB, Shoshone Basin; 

UB, Upper Geyser Basin; WS, Washburn Hot Springs; WT, West 

Thumb; YL, Yellowstone Lake (stippled area). Outline of Yellowstone National Park shown for reference. (Figure revised and redrawn after Christiansen, 1984.)

rium considerations, indicates that the maximum likely 

temperature that can be attained by a fluid of the composition exhibited by the Yellowstone waters is about 425°C 

(Fournier and Pitt, 1985; Fournier, 1987). At temperatures 

higher than about 425°C the water would separate into a 

very saline brine and relatively dilute gas (steam) as it 

flowed upward toward the surface.

A general model of the Yellowstone hydrothermal 

system has hypersaline brine filling fractures in the deepest 

parts of the hydrothermal system. The brine is overlain by 

relatively dilute water that either floats on top of this brine 

or is separated from the brine by a region of "self-sealed" 

rock. Although there is ho direct evidence for the presence 

of the hypersaline brine, it is inferred to be present because 

aqueous magmatic fluid that is evolved from a crystallizing 

magma at a depth of about 4 to 5 km must dissociate to a 

hypersaline brine and a coexisting aqueous gas that is rich 

in CC>2 and sulfur compounds. Above the brine there is a 

series of successively shallower "local reservoirs" where 

more permeable rocks are sandwiched within less permeable rocks. Upward convecting waters flow relatively quickly through fractures in otherwise less permeable rocks (such 

as ash-flow tuff) and reside for relatively long times at a 

nearly constant temperature in volumes of rock (reservoirs) 

that have greater inherent porosity and permeability (such 

as reservoirs in rubble at the bottom and top of rhyolite 

flows). Chemical and isotopic reequilibrium is attained between water and rock at successively lower temperatures as 

waters ascend from deeper to shallower reservoirs. On the 

basis of tritium analyses, Pearson and Truesdell (1978) concluded that Yellowstone hydrothermal systems appear to 

contain mixtures of two waters one from an open wellmixed reservoir of relatively short residence time (presumably a cold reservoir at a shallow depth) and the other from 

a reservoir containing little or no tritium (presumably a hot 

and deeper reservoir). The estimated rates of discharge of 

water, chloride, and heat for selected thermal regions and 

for all of Yellowstone Park are given in table 1.

The Yellowstone Plateau and adjacent upland areas 

were largely covered by ice during the last two major glaciations the Bull Lake and Pinedale glaciations and 

these had major impacts on the hydrothermal activity. The 

Bull Lake glaciation (about 160-130 ka) correlates with 

late Illinoian glaciation in the Midcontinental United States 

(Pierce and others, 1976). Pinedale glacial deposits (about 

10 to more than 30 ka) correlate with the Wisconsin glaciation in the Midcontinental United States. The estimated 

thickness of glacial ice during the Pinedale glaciation in 

the Upper and Lower Geyser Basins region is as much as 

570 m, at Norris about 740 m, and at Mud Volcano about 

1,070 m. When glaciers covered the Yellowstone Plateau, 

the potentiometric surfaces for ground water in the underlying rocks were raised hundreds of meters above the 

ground surface, allowing boiling-point curves in regions of 

upflow to attain higher temperatures at given depths and at
DETAILED ITINERARY

Table 1. Preferred values for average rates of discharge of deep 

high-temperature component of thermal water (containing 412 mg/ 

kg chloride), chloride in that water, and heat (before boiling during 

upflow) from selected thermal areas in Yellowstone National Park.

[From Fournier and others, 1976; Foumier, 1989. Mammoth Hot Springs (1), measurements made in 1960's. Mammoth Hot Springs (2), measurements made in 1980's, 

assumes that deep component of hydrothermal fluid contains 170 mg/kg chloride and 

flows from a reservoir with maximum temperature of 90°C (calculated using data in 

Sorey, 1991). Difference in estimated chloride discharges in the 1960's and 1980's at 

Mammoth Hot Springs is within uncertainty of the measurements, and difference in 

the calculated discharge of heat is due to different assumptions about chloride concentration and temperature of deep water. , not calculated]

Region

Upper Geyser Basin ------

Lower Geyser Basin - --

Morris and Gibbon Geyser

Basins.

Mammoth Hot Springs (1)

Mammoth Hot Springs (2)

Tntal nnrlf __ 

Deep water 

(m 3 /s)

0.417

0.985

0.310

0.228

0.590

i inn

Chloride 

(g/s)

172

406

128

94

100

Mfi

Heat 

(cal/s)

155xl06

369x1 O6

116xl06

85x1 O6

53xl06

mnvin6

Area 

(km2 )

11

36

the points of discharge at the Earth's surface beneath the 

ice (Muffler and others, 1971; Bargar and Fournier, 1988). 

This situation is analogous to oceanic hot-spring systems 

that, because of the weight of the overlying ocean water, 

can have temperatures in the >300°C range at the points 

where they discharge on the ocean floor. The net result of 

the raising of potentiometric surfaces and boiling-point 

curves was that excess thermal energy became stored in 

rock at shallow depths during glacial periods. When the 

glaciers receded, this excess energy was available to enhance geothermal circulation and to produce large hydrothermal explosive eruptions of water and rock (Muffler and 

others, 1971).

Articles by Smith and Christiansen (1980), Christiansen (1984), Smith and Braile (1984), Fournier and Pitt 

(1985), and Fournier (1989) summarize current thought 

about the evolution of the Yellowstone Plateau volcanic 

field and the associated hydrothermal activity.

Figure 1 shows the road system in the Yellowstone 

National Park/Teton National Park region and major features in Yellowstone. Figure 3 shows the locations of stops 

within Yellowstone National Park, with numbers corresponding to stop numbers in the "Detailed Itinerary."

Acknowledgments. Material presented in other field 

guides and road logs prepared by Christiansen and Hutchinson (1987), Christiansen (1989), and Pierce and Good 

(1982, 1990) has been of great help in the preparation of 

this guide. We are also greatly indebted to our colleagues, 

L.J. Patrick Muffler, Alfred H. Truesdell, and Donald E.

f Washburn ) * a Rainbow 

LLL Spnngs /&& o O Snrinn; Springs

Mud Volcamr'jK 24 A

2 5 ^(i 2 6 stonelop M°untain

10 MILES

Figure 3. Locations of roads and field-trip stops in Yellowstone 

National Park. Numbers correspond to stop numbers in detailed 

itinerary.

White, who have spent many years working with us in 

Yellowstone Park and who have contributed greatly to our 

knowledge of the Yellowstone region magmatic-hydrothermal system.

DETAILED ITINERARY

DAY 1 JACKSON HOLE, WYOMING, 

TO OLD FAITHFUL

The original field-trip group started early in the 

morning at Park City, Utah, and traveled by chartered bus 

to Wyoming, arriving at Jackson Hole about 11:30 a.m.

STOP 1 WINDY POINT TURNOUT

Windy Point Turnout is on the inner road of Grand 

Teton National Park about 2.5 km past the national park 

entrance at Moose, Wyoming.
A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

View Teton Range and Jackson Hole. Figure 4 

shows the view of the Teton Range from Windy Point. To 

the northwest is the central, highest part of the Teton Range 

including the Grand Teton (altitude 4,198 m). The glaciated 

core of the Teton Range exposes Late Archean metamorphic rocks (mostly gneisses) intruded by Proterozoic granitic rocks. The northern and southern thirds of the range are 

capped by layered rocks, mostly of Paleozoic age. Just 

south of the stop, the forested hills are loess-mantled deposits of the next-to-last glaciation (Bull Lake?). The sagebrush bench extending more than 10 km north from the 

stop is outwash gravel of the last glaciation (Pinedale). Further north are the west-tilted blocks of Signal Mountain, 

Huckleberry Ridge, Wildcat Ridge, and others, some of 

which are capped with the Huckleberry Ridge Tuff (2 Ma) 

erupted from the oldest caldera of the Yellowstone Plateau 

volcanic field. To the west, at the foot of the Teton Range, 

the recently burned area is underlain by Pinedale moraines 

from the Tetons.

STOP 2 LUNCH AT STRING LAKE

Quaternary geology along the Teton Range front. 

String Lake is at the base of the Teton Range (fig. 5). West 

across the lake and 100 m above it is the postglacial scarp 

of the Teton fault. Late Pleistocene debris from local Teton 

glaciers is offset about 20 m across the fault on a scarp that 

is 35 m high and as steep as 40°. String Lake is situated 

between two Pinedale moraines that had different source 

areas. Just upstream from String Lake are end moraines of 

a large glacial lobe fed by glaciers from the Yellowstone 

Plateau and from the Teton Range. Just downstream from 

String Lake are Pinedale moraines of a local glacier from 

the Tetons (Cascade Canyon). Moraines deposited by this 

glacier also are responsible for the formation of Jenny 

Lake. The lunch stop in the intervening area between the 

two moraines is on glacial outwash. The outer Pinedale 

moraines of the Cascade Canyon glacier are buried by this 

outwash, whereas younger moraines are not. Obsidian-hy-

-^ Figure 4. View of Teton 

Range as seen from Stop 1.

Figure 5. String Lake and Teton Range as seen from Stop 2.
DETAILED ITINERARY

dration measurements of obsidian from a well east of the 

Jenny Lake Lodge suggest that outwash nearly 100 m thick 

accumulated during the last glaciation (unpub. data, K.L. 

Pierce, USGS).

STOP 3 WILLOW FLATS OVERLOOK

Late Cenozoic volcanic rocks, structural evolution, 

and glaciation of northern Jackson Hole. The west-tilted 

Teton Range, with its high-standing Precambrian core to 

the south, becomes lower to the north and exposes northdipping Paleozoic and Mesozoic sedimentary rocks. This 

relation and the high structural relief of the Tetons are 

composite features of the northwest-trending Gros VentreTeton uplift of Laramide age and the late Cenozoic northtrending west-tilted normal-fault block of the modern 

Tetons. Signal Mountain can be seen just south of the 

overlook. On and around Signal Mountain, ash-flow tuffs 

and tuffaceous sediments are tilted into the Teton fault 

with ages and dips as follows: 2 Ma, 11°; 4 to 6 Ma, 22°; 

about 10 Ma, 20 to 27°. The post-2-Ma rate of tilt is similar to a rate of tilt calculated from offset of glacial deposits viewed at the lunch stop. This progression suggests that 

the main fault offset started after the 4- to 6-Ma tuff was 

deposited and has continued at a high rate throughout the 

Quaternary (1-2 mm/yr).

You are standing inside the moraines of the youngest 

of three phases of the last or Pinedale glaciation (Pierce 

and Good, 1990). During the earliest phase, the combined 

Buffalo Fork and Pacific Creek glacial lobes from the east 

and northeast flowed westward through this area and 

scoured a 200-m-deep trough on the north side of Signal 

Mountain. In the later, Jackson Lake phase, the Snake 

River and Pacific Creek lobes from the north and northeast 

joined and flowed south to the type-Jackson Lake moraines that occur around the southern margin of Jackson 

Lake. As these lobes receded, they separated, and meltwater streams deposited kame gravels between them, such as 

those between Emma Matilda Lake and Christian Pond off 

to the east. Willow Flats in the foreground is a postglacial 

subirrigated alluvial fan that has built southward to Signal 

Mountain, forming the present outlet of Jackson Lake. The 

Jackson Lake Dam was built on fine-grained sediment that 

fills a 200-m-deep glacial trough. The dam was recently 

redesigned and rebuilt at a cost of $82 million to strengthen sediment beneath the dam that could liquefy during an 

earthquake on the Teton fault.

STOP 4 WEST THUMB GEYSER BASIN

Hydrothermal activity and its volcanic setting. 

Like most geyser basins of the Yellowstone Plateau, West 

Thumb Geyser Basin (West Thumb) is controlled by the 

ring-fracture zone of the Yellowstone caldera. It is localized where the zone is intersected by a line of young intracaldera rhyolitic vents that extend north-northwest across 

the caldera between aligned tectonic fault zones to the 

north and south to form the Central Plateau. The lake 

basin of West Thumb is a deep subcircular extension of 

Yellowstone Lake, the main basin of which is 10 km to 

the east. West Thumb had its origin as a relatively small 

caldera within the much larger Yellowstone caldera during 

a pyroclastic event that was part of the mainly lava-producing postcollapse volcanism of the past 150,000 years. 

The north, east, and south margins of the West Thumb caldera have been largely buried by younger rhyolite flows. 

To the east, beyond Yellowstone Lake, are the Absaroka 

Mountains, which are outside the Yellowstone caldera. To 

the southeast is Flat Mountain, the truncated north face of 

which is part of the southern margin of the Yellowstone 

caldera.

Walk along the boardwalk loop through the basin 

from the parking lot to the lake shore and back. Hot 

springs and geysers in the West Thumb Geyser Basin are 

perhaps more variable in temperature and discharge than 

in any major thermal area of Yellowstone. Thick sinter deposits (fig. 6) exposed along the shore of the lake to the 

north of the present hydrothermal activity show that the 

areal extent and probably also the rate of discharge of 

thermal water were once much greater than at present. 

Even at present, there are large variations in the distribution and volume of discharge of thermal waters. Activity 

in the basin is sometimes quite vigorous, with new springs 

and increased geyser activity, while at other times the rate 

and temperature of spring discharge is diminished, allowing abundant bacteria growth to occur closer to vents. The 

small cones of silica that emerge from lake water close to 

the shore (fig. 7) probably formed and grew in height at a 

time when the level of the lake was lower than today.

Many people have speculated that episodic ingress of 

cold Yellowstone Lake water into the hot-spring system is 

responsible for the variation in thermal activity. The isotope-chloride relations for West Thumb are poorly understood but may offer support for this idea. In a plot of 818O 

(a measure of the oxygen isotopic composition of a particular substance, such as water or a mineral, compared to the 

isotopic composition of a standard, expressed in parts per 

thousand) versus chloride, several West Thumb hot-spring 

waters plot as much as about 2 parts per thousand (ppt) 

above the trend line for most Yellowstone thermal waters 

(Truesdell and Fournier, 1976). This might be the result of 

mixing with a small amount of partly evaporated lake 

water. Generally in the Yellowstone hydrothermal system, 

"self-sealing" (probably mainly by amorphous silica deposition) and relatively high pressures within the hot-spring 

plumbing system effectively keep local ground waters 

from entering the discharging hydrothermal system. Research drilling into Yellowstone's hydrothermal systems 

has shown that the fluid pressures of the thermal waters are
A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

Figure 6. Old sinter at shore of Yellowstone Lake, West Thumb Geyser Basin.

Figure 7. Fishing Cone, West Thumb Geyser Basin.

equal to or greater than the hydrostatic pressure that would 

be exerted by a column of cold water extending downward 

from the Earth's surface (fig. 8). Pressures in excess of 

those calculated for hot-water hydrostatic conditions with 

free discharge at the surface result from throttling of fluid 

flow at and near the points of spring discharge.

Compositionally the discharging alkaline-chloride 

waters at West Thumb are virtually identical to the Black 

Sand-type waters (Fournier, 1989) found in the Upper and 

Lower Geyser Basins. In table 2, compare the analysis of 

Lakeshore Geyser water (No. 2) at West Thumb with the 

analysis of Punch Bowl water (No. 6), a Black Sand-type 

water, in the Upper Geyser Basin. These waters have nearly 

identical molar ratios of bicarbonate/chloride and relatively 

low chloride concentrations. Silica and cation geothermometers indicate a reservoir temperature of about 200 to 210°C.

PRESSURE, IN BARS 

10 20 30

CO

a: LU

ui

100

200

a.

HI

a

300

I

Figure 8. Measured pressure versus depth in U.S. Geological 

Survey research wells drilled in Yellowstone National Park. Also 

shown for reference is calculated ideal hydrostatic pressure resulting from weight of a column of cold water extending up to 

land surface compared to ideal hydrostatic pressure resulting 

from weight of a column of boiling water. (From Fournier, 

1983).

Waters emerging in different springs and geysers commonly 

undergo different degrees of boiling and steam loss on the 

way from the reservoir to the surface. These different 

amounts of steam loss account for the variations in the
DETAILED ITINERARY 

Table 2. Chemical analyses of selected thermal waters from Yellowstone National Park.

[ , no data]

Analysis No.

Locality

Name

Sample No.

Date

Temp. (°C)

pH

SiO2(mgkg~')

Al

Fe

Ca

Mg

Na

K

Li

NH 4

HCO 3

SO4

a

F

B

Reference

1

Mammoth

Hot Springs

Y-10

drill hole

Y-10

09/13/69

70

7.48

88

0.01

2.4

450

80

161

69

1.8

1.0

997

800

171

4.2

3.8

1

2

West

Thumb

Lakeshore

Geyser

J7484

10/09/74

90

7.76

2.0

0.51

408

20

3.24

_

531

55

261

14.5

3.3

2

3

Shoshone

Basin

Washtub

Spring

T7214

09/72

81

9.00

328

0.14

0.05

0.4

0.05

365

16

1.0

0.1

406

48

328

25.5

2.8

3

4

Heart Lake

Basin

Unnamed

T7348

09/73

93.5

9.48

366

0.9

0.01

382

21

6.6

306

100

365

36

2.4

3

5

Lower Geyser

Basin

Ojo

Caliente

J7560

95

7.74

230

0.75

0.01

330

10

3.6

246

26

326

30

3.8

2

6 7

Upper Geyser Upper Geyser

Basin

Punch

Bowl

J7836

94

8.33

312

0.67

0.02

420

17

3.8

590

19

289

28

3.8

2

Basin

8

Grand

Canyon

Ear Unnamed spring at

Spring Sevenmile Hole

J7956

94

8.49

371

0.82

0.01

319

27

4.9

_

146

19

415

24

3.6

4

J7615

09/29/76

91

8.61

534

0.5

0.02

366

58

3.45

_

223

85

427

12.8

16

2

9

Norris Geyser

Basin

Porcelain

Terrace

J7528

93.5

654

0.06

2.12

0.03

404

81

5.8

_

47

31

669

5.8

9.9

2

10

Norris Geyser

Basin

Cinder

Pool

J7908

92

3.57

329

6.3

0.12

346

81

3.9

_

0

147

569

6

8

4

Analysis No.

Locality

Name

Sample No.

Date

Temp. (°C)

PH

SiO2(mgkg ')

Al

Fe

Ca

Mg

Na

K

Li

NH 4

HCO 3

SO4

a

F

B

Reference

References:

11

Norris Geyser

Basin

Echinus

Geyser

J7846

93

3.2

278

0.60

4.9

0.52

166

50

0.7

_

0

337

108

5.6

3.0

4

12

Crater

Hills

Crater Hills

Geyser

J7804

09/28/78

88

3.18

676

5.64

1.04

640

133

6.9

_

0

566

890

27.5

20

4

13

Upper Geyser

Basin

Iron

Spring

_

1920s

91

3.7

365

2

Trace

77

28

4

0

231

1

1.2

2.2

5

14

Hot Springs

Basin

Unnamed

YF448

06/22/69

89

2.66

317

37.1

3.75

187

16

0.04

171

0

1530

0.1

0.8

5.05

3

(1) Unpublished data, U.S. Geological Survey (R.

15

Josephs Coat

Hot Springs

Unnamed

YF451

06/26/69

86

1.82

333

4.1

0.39

7

17.1

0.01

57.3

0

1830

0.1

0.07

3

Barnes, analyst).

(2) Thompson and Yadav ( 1 979).

(3) Thompson and others ( 1 975).

16

Josephs Coat

Hot Springs

Unnamed

YF452

06/26/69

94

9.38

238

3.4

0.01

109

19

0.18

22.4

335

24

5.4

3.7

0.36

3

(4)

(5)

(6)

17

Upper Geyser

Basin

Hillside

group

T9-10

83

8.62

170

0.13

7.9

0.27

150

7.7

0.83

0.1

251

14.2

72

12

1.17

3

Unpublished data, U.S.

Alien and Day (1935).

18

Boundary

Creek

Unnamed

J7930

92

7.94

210

4.1

0.10

181

11.2

1.2

0.51

259

10

107

19.1

1.0

6

19

Washburn

Hot Springs

Unnamed

J7304

09/22/73

91

8.00

247

2

4.10

9.7

6.5

0.1

270

107

900

7

0.1

6.6

3

20

Washbum

Hot Springs

Unnamed

YF429

06/22/69

86

0.2

17.2

9.3

27.1

13.7

0.1

658

8.2

1950

2

0.5

7.84

5

Geological Survey (J. M. Thompson, analyst).

Thompson and Hutchinson (1980).

absolute concentrations of the elements found dissolved in 

the alkaline-chloride thermal waters.

Mud pots and (or) cloudy to muddy nonoverflowing 

pools of water (acid-sulfate in composition) tend to be 

present at higher elevations in West Thumb and other geyser 

basins, and discharging silica-depositing alkaline-chloride

waters are present at lower elevations. The acid-sulfate waters occur where H2S in steam condensate has been converted to sulfuric acid by bacterial activity. Acid attack on the 

surrounding rock produces clays and muds that diminish 

vertical permeability and allow perched bodies of ground 

water to form and persist. Even though these acid-sulfate
10 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

bodies appear to be nondischarging, tracer studies show that 

there is considerable horizontal flow of water into and out of 

these springs (Brock, 1978). The acidity comes from bacterial oxidation of native sulfur and H^S to H2SC>4 in 'he cool 

muds surrounding the boiling pools.

The yellow, orange, and green colors seen in some of 

the pools and bordering the runoff channels are commonly 

referred to as "algae" mats but are actually bacteria colonies. The higher the temperature of the water, the lighter 

the color of the bacteria mat. Notice that silica deposits on 

and in these organic mats yield spongy sinter deposits that 

are characteristic of this environment of deposition.

STOP 5 OLD FAITHFUL LODGE CABINS, 

UPPER GEYSER BASIN

Explore Geyser Hill and see an eruption of Old 

Faithful Geyser before dinner.

Background information on the geology and hydrothermal activity in the Upper to Lower Geyser Basin region. The western part of the Yellowstone caldera is 

drained by the Firehole River, which flows northward 

through a series of large open valleys, including the Upper 

(fig. 9) and Lower Geyser Basins and narrow constrictions 

that have been formed by incomplete merging of postcaldera lava flows that have advanced from different directions. The hills surrounding the valleys are part of a general 

constructional volcanic topography of the Madison and 

Central plateaus. Generally, the uppermost parts of the hydrothermal plumbing systems of the geyser basins occur in 

surficial deposits that are composed mostly of sand and 

gravel deposited during the last (Pinedale) glaciation. However, in some places hot springs and geysers issue directly 

from rhyolitic bedrock. The road along the river between

Old Faithful and Madison Junction provides access to the 

most outstanding display of hydrothermal features in the 

world, including more than two-thirds of all known naturally erupting geysers. Measurements of Firehole River flow 

rates and compositions above and below individual geyser 

basins, combined with information about hot-spring underground reservoir temperatures and water compositions, has 

allowed estimates to be made of the total mass and heat 

flux from individual basins (table 1).

In the Old Faithful area of Upper Geyser Basin, 

views from Old Faithful Inn and from the walkway between it and the National Park Service Visitor Center show 

the geologic setting of the basin between rhyolitic lava 

flows of the Madison Plateau to the west and the Mallard 

Lake structural dome to the east. A graben that branches 

from the axis of the Mallard Lake dome is apparent on the 

skyline east of Old Faithful. This dome, rejuvenating the 

postcollapse western resurgent dome, rose early in the renewed voluminous rhyolitic volcanism of the past 150,000 

years. Plagioclase-rich older postcollapse rhyolites crop 

out around the west and south base of the structural dome 

and form the poorly exposed bedrock of Upper Geyser 

Basin, but the uplifted 150,000-year-old sanidine-rich Mallard Lake flow tops the dome (fig. 10). The Elephant Back 

flow, also about 150,000 years old, partly buries the east 

flank of the dome, demonstrating the dome's rapid rise 

early in the period of renewed rhyolitic activity.

Old Faithful, Yellowstone's best known geyser, is but 

one of dozens in the Upper Geyser Basin. A list of selected 

active geysers as of spring 1992 is given at the back of this 

field guide (see appendix B). Geysers are springs that erupt 

intermittently. Much of our understanding of geyser activity comes from the classic work of White (1967). It is conceivable that a cold spring could erupt intermittently as a

Figure 9. Air view of Upper Geyser Basin.
DETAILED ITINERARY 11

geyser as a result of the slow and steady accumulation of amounts of silica are dissolved from the surrounding rocks,

gas in an underground cavity. At Yellowstone National Some understanding of subsurface hydrothermal processes,

Park the geysers are fed by boiling waters discharged from including the mechanism of geyser eruptions, is gained

high-temperature deeper reservoirs in which substantial through the resolutions of two seeming anomalies. First,

4 6 8 10 KILOMETERS i

Paintpot Hill Dome

^Plateau Flow'

Nez Perce Creek Flow

Spruce i

Creetfe:;! 

Flow y:

Older Younger Flows

Figure 10. Geologic map showing field-trip route and stops between Upper Geyser Basin and Norris Geyser 

Basin. Shaded areas show named Quaternary rhyolitic lava flows and domes, with darker shades corresponding to older units. Large numbers show stop locations. (From Christiansen and Hutchinson, 1987).
12 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

neighboring springs may have nearly identical temperatures and water compositions but greatly different water 

levels; for example, Solitary Geyser discharges about 40 m 

above most springs in Upper Geyser Basin. Second, some 

hot springs erupt as geysers, but most do not. Research 

drilling in Yellowstone (White and others, 1975) showed 

that below about 30 m most reservoirs are "overpressured" 

relative to calculated ideal hot-water hydrostatic pressure 

(fig. 8) as a result of partial "self-sealing" of the waterbearing fractures by precipitated silica and zeolites. Water 

levels are controlled by permeabilities and flow rates in the 

upflow channels, which are regulated through the competing effects of seismic fracturing and self-sealing and by 

subsurface outflow (leakage) near ground level. In general, 

the rate of discharge of water from deep in the system 

would be faster than the actual rate of discharge if upflow 

in the shallow part of the system were not restricted by a 

series of throttles. Pressure discontinuities that occur across 

these throttles result in the observed overpressures in the 

shallow parts of the hydrothermal system. The net result is 

boiling-point temperatures above those expected for local 

hydrostatic load and very unstable conditions in which 

massive boiling and rapid discharge of water can be triggered as a result of a slight pressure decline. Such a pressure decline may result from the opening of a new fracture 

or widening of an old fracture during an earthquake or by 

the upward surge of a slug of steam that displaces water 

from a geyser tube.

In the Upper Geyser Basin a typical boiling spring, 

discharging at 92°C, rises from a subsurface reservoir 

where the temperature is near 205 to 215°C. The rising 

water cools by more or less steady-state processes including loss of heat by conduction through the channel walls, 

adiabatic expansion (boiling) as pressure declines during 

upflow, and evaporation from the hot-spring pool. In contrast, non-steady-state processes prevail in order for geyser 

activity to occur (White, 1967). There is likely to be cycling from mainly conductive cooling (a geyser eruption 

not imminent) to mainly adiabatic expansion (little conductive cooling and initiation of a geyser eruption imminent). 

The following scenario is typical of many geyser eruptions 

and draws heavily upon the model of White (1967). At the 

start of a cycle, shortly after a geyser eruption has occurred, 

water from deep in the system flows upward and refills a 

shallow water-holding reservoir immediately below the 

geyser. Continued convective flow heats the surrounding 

rock until the entire water-rock system is at the boilingpoint curve for the prevailing fluid pressure. There is a 

progressive change from mainly conductive cooling to 

mainly adiabatic boiling of the upflowing fluid. With the 

increase in boiling there is an increase in the amount of 

steam that is formed. Early in the cycle, bubbles composed 

of steam and noncondensable gas, such as CO2 , that form 

in the upward convecting fluid rise through the overlying 

water column. However, with less conductive cooling the

mass fraction of steam steadily increases, and eventually 

steam starts to move upward through the geyser tube as a 

slug, lifting and ejecting the overlying water. As a slug of 

gas bubbles reaches the surface there is a momentary decline in pressure within the geyser tube, and this reduction 

in hydrostatic head may be sufficient to cause flashing 

(rapid conversion of liquid water to steam) in the shallow 

reservoir, resulting in the expulsion of large quantities of 

water. This expulsion results in further reductions in pressure deeper in the system, and a chain reaction of rapid 

boiling at ever greater depths is initiated. During an eruption, water and heat are discharged much faster from the 

shallow holding reservoir than they are recharged, requiring 

a time of repose between eruptions to "reload" the system.

A variety of behavior in major geysers can be observed in Upper Geyser Basin, including (1) eruptions that 

average 27 m in height from the large sinter cone at Castle 

Geyser, (2) eruptions to average heights of 60 m from 

Grand Geyser, which fountains through a broad pool, and 

(3) eruptions from Riverside Geyser, which jets a water 

column about 22 m high at an angle over the Firehole 

River. Figure 11 shows an eruption of Beehive Geyser, 

one of the larger geysers on Geyser Hill. Old Faithful has 

particularly interesting eruptive intervals that are a function of the duration of the preceding eruption. Eruption 

durations are bimodally distributed between 1.5 and 5.5 

minutes; long eruptions are followed by long intervals 

(70-120 minutes) whereas short eruptions are followed by 

short intervals (30-65 minutes). The 40-m-tall average 

height of Old Faithful eruptions is independent of eruptive 

interval or duration.

DAY 2 UPPER, MIDWAY, AND 

LOWER GEYSER BASINS

The entire day will be spent in the Upper, Midway, 

and Lower Geyser Basins. Figure 10 shows the locations of 

planned stops. The walks will not be strenuous. Wet and 

muddy ground may be encountered at Pocket Basin.

Typical compositions of thermal waters in the Upper 

and Lower Geyser Basins are shown in tables 2 and 3. 

Figure 12 shows schematically the likely hydrologic conditions within the hydrothermal system(s) beneath Upper, 

Midway, and Lower Geyser Basins. Knowledge of the 

changing behavior of CO2 dissolved in thermal water with 

decreasing temperature is vital to understanding variations 

in composition of hot-spring waters in the Yellowstone region. At temperatures of 270°C and higher, most CO2 dissolved in water is nonreactive. As temperature decreases, 

CO2 reacts with water to form H2CO3 , and with further 

cooling, the H2CO3 dissociates to H+ and HCO^. At about 

200 to 220°C, hydrolysis reactions involving the hydrothermal fluid and minerals in the wall rock consume much of 

the H+ and liberate an equal number of moles of Na+, yield-
DETAILED ITINERARY 13

ing dissolved sodium bicarbonate. Now consider the flow 

paths and reservoir temperatures shown in figure 12. There 

is good evidence from enthalpy-chloride relations that an 

intermediate reservoir (or multiple reservoirs) at about 

270°C is present beneath the Upper and Lower Geyser Basins and that in some places water boils as it moves from 

that reservoir to shallower and lower-temperature reservoirs. All or most of the steam and noncondensable gas, 

such as CO2, that separate from boiling water flowing upward toward the 215°C reservoir beneath Geyser Hill takes 

a separate path to the surface so that the portion of the 

boiling water that reaches the Geyser Hill reservoir is depleted in CO2 and gas, in general. Thus, there is little CO2 

available to form carbonic acid that would otherwise react

Figure 11. Beehive Geyser in eruption, Geyser Hill, Upper Geyser Basin.

to form sodium bicarbonate. Some waters that flow to the 

surface from the Geyser Hill reservoir undergo maximum 

boiling (adiabatic expansion), other waters cool entirely by 

conductive loss of thermal energy to the surrounding rock, 

and still others cool partly by boiling and partly by condensation. The range in concentrations of dissolved constituents 

that results from no boiling at one extreme to maximum 

boiling at the other provides a powerful method of estimating temperatures of subsurface reservoirs that feed the 

springs. This method relates temperature to the specific 

heat, or enthalpy, of the reservoir fluid and to the amount of 

steam that can separate from a superheated fluid as it decompresses during upflow. See Fournier (1989, p. 25-28) 

for a discussion of the use of enthalpy-chloride and enthalpy-silica diagrams to estimate reservoir temperatures 

beneath the Upper Geyser Basin. In contrast to the hydrothermal fluids that emerge at Geyser Hill, waters flowing 

from the 270°C reservoir toward Black Sand-type reservoirs 

(about 205°C and Cl = HCO^ in equivalents) either do not 

boil as they flow upward, or most of the steam that forms 

stays with the liquid until reaching the shallower Black 

Sand-type reservoir. This fluid does have significant quantities of CO2 available for subsequent reaction with rock to 

form sodium bicarbonate. Thus, the Geyser Hill-type waters 

and the Black Sand-type waters flow to the surface from 

reservoirs that are not greatly different in temperature 

(about 215°C versus about 205°C), but they are greatly 

different in C1/HCO3 . Partial loss of steam or partial conductive cooling in migration from a deeper reservoir to a 

shallower Black Sand-type reservoir will result in waters 

with intermediate C1/HCO3 ratios. Indeed, regions of intermediate C1/HCO3 are found between Geyser Hill-type and 

Black Sand-type waters. 3He/4He isotopic data are compatible with the above model in that 3He is relatively depleted 

in waters that have high C1/HCO3 ratios, a condition which 

is indicative of underground loss of CO2 and other gases 

(Kennedy and others, 1987). Most of the steam that takes a 

separate path toward the surface condenses in ground water 

at high elevations, yielding NaHCO3-rich waters, such as 

those discharging at Hillside Springs. Some of this steam 

discharges directly to the atmosphere through acid-sulfate 

pools that become acid as a result of oxidation of H2S 

carried in the steam.

Variations in rock type conceivably also may affect 

C1/HCO3 ratios in the Upper and Lower Geyser Basins. In 

the Upper Geyser Basin, the thermal waters at Geyser Hill 

emerge directly from lithic rhyolite, whereas those at the 

Black Sand Basin emerge from obsidian-rich sands, and it 

is possible that glassy volcanic sediments may play a role 

in "fixing" CO2 as HCO^. However, in the Upper Geyser 

Basin it is likely that the reservoirs supplying water to the 

Black Sand-type waters (C1/HCO3=1) and to the Geyser 

Hill-type waters (C1/HCO3>3) are well within the underlying rhyolite flow or flows. In these reservoirs, water/rock 

reactions occur that fix C1/HCO3 ratios, dissolved silica,
14 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

and cation ratios at temperatures of 200 to 215°C. The geologic map of the Old Faithful quadrangle (Christiansen 

and Blank, 1974) shows that the Biscuit Basin flow underlies much of the Upper Geyser Basin, including Geyser 

Hill. This flow is a perlitic vitrophyre of flow-brecciated 

rhyolite. It appears to underlie all or most of the other 

flows that surround Upper Geyser Basin. Thus, it is likely 

that all or most of the waters in the Upper Geyser Basin 

come in contact with this rhyolite that initially contained 

abundant glass. Although it is true that many of the Geyser Hill-type waters emerge directly from this rhyolite 

(and from the Mallard Lake flow) with no overlying obsidian sediments, other Geyser Hill-type waters do not, 

such as a group of springs to the west of the Old Faithful 

Inn. Also, in some places Black Sand-type waters emerge 

from rhyolite with no apparent overlying obsidian-rich 

sediments. For the above reasons, variations in rock type 

probably play a minor, if any, role in fixing C1/HCO3 ratios. The most plausible explanation for the differences in 

C1/HCO3 ratios exhibited by the Upper and Lower Geyser 

Basins' waters appears to be different degrees of subsurface boiling and escape of CO2-rich steam prior to the 

thermal water entering the shallowest reservoir directly 

supplying fluid to the springs and geysers.

STOP 6 BISCUIT BASIN

Sites of the Y-7 and Y-8 drill holes and small modern hydrothermal explosions. The Biscuit Basin parking 

lot is situated at the northern downstream margin of the 

Upper Geyser Basin hydrothermal system. Here about 50 

to 55 m of hydrothermally altered obsidian-rich bedded 

sands and gravels overlie altered rhyolite flow breccia and 

associated pumiceous tuff of the Biscuit Basin flow (Keith 

and others, 1978). The sediments probably are outwash 

stream deposits from receding glaciers of Pinedale age; 

Black Sand-type water (fig. 12) discharges here. Figures 13 

and 14 show subsurface temperatures and hydrothermal alteration products (mostly zeolites and clays) encountered 

in the USGS research drill holes Y-7 (a relatively cool 

well at the north end of parking lot) and Y-8 (a relatively

Fumaroles

Acid-sulfate 

pools Hillside 

Springs

Local Recharge

_____i____ 

Steam condensatex

215°C Reservoir 

Cl-» HCO3-

/270°CReservoir\

I Cl- and CO2 J

A A A

^~ "*>

Deepest Reservoir 

350-425°C

Hypersaline Brine \ 

/'(>15-25 weight percent salt)

/

\ \ 

\ I

Magmatic Heat

Figure 12. Schematic diagram showing approximate reservoir temperatures beneath Upper and Lower Geyser Basins and effects of 

subsurface boiling with steam loss on bicarbonate relative to chloride in the shallowest reservoirs.
DETAILED ITINERARY 15

hot well only 125 m away at the southeast margin of parking lot, near a cluster of hot springs and small geysers). 

The zeolites are dominantly clinoptilolite and mordenite, 

and the clays are dominantly montmorillonite and celadonite. Positive wellhead pressures were encountered in the 

Y-8 drill hole (the well erupts like a geyser when the wellhead valve is opened), whereas water does not flow from 

the Y-7 drill hole when the wellhead valve is opened. The

TEMPERATURE, IN DEGREES CELSIUS

50 100 150

50-

LLJ 

HI

CL 

LLJ 

Q

100-

150-

200-

I

I

' I '

\ 

I

\

\

\

\

\

9 9 999

I

J

-10

-20

EXPLANATION

 40

-50

-60

-70

CO

LU

Q. 

UJ 

Q

Sandstone 

and siltstone

Biscuit Basin flow 

(flow breccia)

m > UJ 111 LU |,'|W UJ UJ

u. Z H~ I * - 

95i§3l|3§§! 

S g S^ g ^Sd g 9

W < O

s 5 ?

Q

o o

SILICA ZEOLITES CLAYS

Figure 13. Distribution of fresh obsidian and hydrothermal minerals in groundmass of core from U.S. Geological 

Survey Y-7 drill hole. Column on left shows generalized 

stratigraphic section. Horizontal lines at right indicate 

samples studied in detail, and starred samples were chemically analyzed for major elements. Width of mineral columns shows relative abundance based mainly on X-ray 

diffraction data and petrographic study. Interpolation between data points assumes linear variation. Dashed line 

connects data points of bottom-hole temperatures, and 

solid line is reference boiling curve for pure water. (From 

Keith and others, 1978, p. A7).
16 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

water level in the Y-7 drill hole rises and falls as the water 

level in the Firehole River seasonally rises and falls. Subsurface temperature relations between the two drill holes 

are shown in figure 15. Whole-rock samples of rhyolite 

from the Y-7 and Y-8 drill holes have been studied for 

Th-U isotope disequilibrium by Sturchio and others (1987) 

and for Ra-Th isotope disequilibrium by Sturchio and others (1989). These authors conclude that U was added to the

rock about 19,000 years ago, but thereafter the system became "closed" to U transport when pore-water chemistry 

changed from oxidizing (surface water) to reducing (thermal water). The 226Ra/230Th ratios correlated with Th-normalized Ba concentrations (Sturchio and others, 1989). 

These data indicated that zeolite-water ion exchange has 

been operating for at least 8,000 years in the Y-7 and Y-8 

region and that a water flux ranging from about 2.5 to 23

TEMPERATURE, IN DEGREES CELSIUS

50 100 150

EXPLANATION

50-

tnLLJ 

LL

LJJ 

Q

100-

ISOBiscuit Basin flow 

(pumiceous tuff)

200 -

250-

-80

SILICA ZEOLITES CLAYS

Figure 14. Distribution of fresh obsidian and hydrothermal minerals in groundmass of core from U.S. Geological Survey 

Y-8 drill hole; data shown in same manner as in figure 13. Depths below 82.3 m not shown because of general uniform 

alteration mineralogy from 63.0 to 153.4 m depth. (From Keith and others, 1978, p. A8).
DETAILED ITINERARY 17

ALTITUDE, 

METERS 

2225-1

2200-

2175-

2150-

2125-

2100-

2075-

2050-

Y-8 Nearby springs

/Sinter Roadbed x Q,

^oT/5

 Water table

Firehole River

,Pond \

N

ALTITUDE, 

FEET

-7300

_ Sand and gravel 

n-1-7 (originally highly permeable)

-7200

-7100

Flow breccia 

(originally permeable)

'0^4 (SS) , .Pumiceoustuff 

1 ' (originally permeable)

25 50 METERS

^2.45

EXPLANATION

2.31 jj, 

Water overpressure in kg/cm2 Directjon gnd a| itative 

as measured at surface ra,e of therma, f|ow

-0.11 

Water levels below ground ex- .-. . . ' 

pressed as negative pressure Decreased permeability due 

relative to surface, ,n kg/cm2 Jo deposP.on Qf hyJQ_

 120° thermal minerals 

Temperature contour °C

 - -7000

-6900

L 6800

Figure 15. Section through U.S. Geological Survey Y-7 and Y-8 drill holes, showing pressures, temperature contours, and inferred 

self-sealing by deposition of hydrothermal minerals in originally permeable ground (from White and others, 1975, p. 21).

(cm3watei/cm3rock)yr~1 is required over that period of time 

to account for the isotopic compositions (Sturchio and others, 1989). It appears that during the climactic stage of the 

Pinedale glaciation (20,000-40,000 years ago; Pierce, 

1979) cold-water recharge into the hydrothermal system 

took place in the Biscuit Basin region (the margin of the 

hydrothermal system). Later, as the ice melted, the direction of fluid flow reversed and the region became one of 

discharge.

Proceed across the bridge over the Firehole River 

and go only as far as Sapphire Geyser. On the west side 

of the Firehole River, to the north side of the boardwalk, a 

few large blocks of zeolite-cemented sands and gravels can 

be seen lying on the ground near Black Opal Pool, a large 

pool of warm water (fig. 16). This pool and adjacent Wall 

Pool are hydrothermal explosion craters that emerged in 

the spring of 1925 and that may have been deepened by 

additional eruptions during the winter of 1931 to 1932. 

Sapphire Pool/Geyser Crater is located farther uphill on the 

north side of the boardwalk. Prior to the 1959 magnitude7.5 Hebgen Lake earthquake that was centered a few kilometers outside the western boundary of Yellowstone Park 

(fig. 1), Sapphire was a relatively small boiling spring. A

Figure 16. Blocks of zeolite-cemented sediments (arrows) blown 

from Black Opal Pool, Biscuit Basin.
18 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

Table 3. Chemical compositions (mg/kg) of selected thermal waters in Lower Geyser Basin.

[Compositions of waters from the drill holes probably have been affected by reactions at uncertain temperatures between water and "fresh" rock in uncased parts 

of wells. , no data]

Name SiO, Na Ca Mg S0 4 HCO,

Steady Geyser

Surprise Pool

Clepsydra Geyser

Spring by Y- 13

Y-l 3 drill hole

Ojo Caliente

Y-3 drill hole

213

280

414

222

230

85

333

380

341

299

317

270

16

15

13

19

28

9

11

15.10

0.47

0.50

0.77

1.50

1.10

1.26

0.05

0.14

0.01

0.01

0.22

0.02

0.02

0.4

3.2

2.8

4.6

3.7

4.5

3.5

; 44

313

325

312

256

331

278

27

25

22

23

31

27

19

165

365

380

274

291

249

177

10

24

22

31

28

33

30

0.5

3.1

3.5

4.3

3.2

4.0

3.6

short time after the earthquake it erupted explosively, enlarging its pool size to that which you see today and sending a sheet of boiling water about 0.3 m deep surging 

downhill to the south. Many large blocks of sinter were left 

scattered about the terrace after the explosion, but as these 

blocks have dried out, they have disintegrated and are 

quickly disappearing.

STOP 7 MIDWAY BASIN

Excelsior Geyser Crater and Grand Prismatic 

Spring. Rhyolitic flow-front scarps of the 117±8-ka West 

Yellowstone flow emplaced between the last two glaciations (Bull Lake and Pinedale glaciations) form the valley 

walls to the west. Just across the river is the Midway Geyser Basin, where Excelsior Geyser Crater discharges boiling waters to the Firehole River. The crater was enlarged 

to its present size by eruptions of water and debris, some 

of which was ejected as far as 150 m from the crater, during 1878 and the 1880's. Cross the river and follow the 

boardwalk past Excelsior Geyser Crater and Grand 

Prismatic Spring. The first eruptions of Excelsior since 

the 1880's were in the summer of 1985. Grand Prismatic 

Spring, just beyond, is nearly 90 m across and reveals 

graded colors from the clear blue boiling waters of its center to lower-temperature bands around its margins that are 

brightly colored by cyanobacteria. In the distant southwest 

is Twin Buttes, formed of hydrothermally cemented Pleistocene glacial sediments deposited by localized hydrothermal melting of the ice. The buttes enclose a complex 

hydrothermal explosion crater. The crater eruptions were 

not hydromagmatic but were strictly hydrothermal, probably occurring as the hydrostatic head in a glacial thermal 

lake was catastrophically lowered during one or more glacial-outburst floods (Muffler and others, 1971). The large 

obsidian-sand plain filling the West Yellowstone basin 

probably was built by the same, or similar, glacial-outburst 

floods (Pierce, 1979). Beyond Lower Geyser Basin, the 

skyline ridge along Mount Jackson and Purple Mountain 

is the northwest rim of the Yellowstone caldera (fig. 10).

Across the road from the parking area, a conspicuous 

bluff exposes perlitic glassy rhyolite with well-developed 

flow layering. This plagioclase-rich early postcollapse rhyolite probably was emplaced into a caldera lake. Most of the 

glassy intracaldera rhyolites of Yellowstone are virtually 

nonhydrated and obsidianlike, though commonly fractured. 

The hydrated perlitic glass of this outcrop is suggestive of 

high-temperature hydration, which probably occurred during emplacement of this rhyolite flow. This observation supports the interpretation that the flow was emplaced into a 

caldera lake. (Similar perlites can be seen farther east in 

Yellowstone Park, where the younger Hayden Valley flow 

plowed into and was diked by the plastic sediments of a 

glacial lake.)

STOP 8 FIREHOLE LAKE AND STEADY GEYSER

Steam-heated waters depositing travertine and manganese-oxides. You have come slightly uphill from 

where sinter-depositing hot springs and geysers prevail. 

Large parts of the Midway and Lower Geyser Basins are 

floored by sinter or silica-rich silts composed mainly of 

diatom tests. At the head of the small valley where Firehole Lake is located there is a large discharge of relatively 

dilute thermal water that now precipitates travertine and 

manganese oxides. At an earlier time, however, silica-depositing hot-spring activity occurred here. No stream of 

cold meteoric water flows from the narrow valley that extends to the east. Apparently, meteoric water in this local 

drainage basin mostly infiltrates into the ground, where it 

becomes heated to about 170°C by interaction with and 

condensation of CO2-rich superheated steam that flows upward from the deeper boiling chloride-rich water (fig. 12). 

The CO2-rich mixture of heated ground water and steam 

condensate reacts with the surrounding rock, extracting Ca 

as it flows laterally to discharge points at elevations above 

the discharge points of the alkaline-chloride springs. Compare the composition of water from Steady Geyser with 

Surprise Pool (table 3). The tritium content of Steady Geyser was studied by Pearson and Truesdell (1978). In 1970
DETAILED ITINERARY 19

its water contained about 7 tritium units (Tu), and in 1974 

about 9 Tu. They concluded that this change in tritium 

with time cannot be explained by a simple model of mixing of waters from a well-mixed tritium-bearing reservoir 

and zero-tritium water. Walk along the boardwalk to get 

a close view of Steady Geyser.

STOP 9 FOUNTAIN PAINT POT WALK

Hot springs, geysers, fumaroles, and mud pots. The 

Fountain Paint Pot area is the most convenient place in 

Yellowstone Park where one short walk displays good examples of the four principal types of hydrothermal discharge 

features hot springs, geysers, fumaroles, and mud pots. 

Distributions of these discharge features allow relations between the ground surface and local static water levels in the 

boiling system to be readily inferred. The large, clear hot 

springs are chloride-rich and nearly neutral, representing 

unrestricted discharge of hot waters from a reservoir. Geysers result from the effects of variations in plumbing geometry, discharge rate, and heat loss in the hot-spring system. 

Fumaroles (steam vents) discharge through fractures where 

only vapor finds access to the surface. New fumaroles were 

opened here during the magnitude-7.5 Hebgen Lake earthquake of 1959. During dry seasons, the fumaroles vent only 

vapors. In wet seasons, shallow condensation of steam 

mixed with locally derived meteoric water can drown the 

fumaroles, and the oxidation of F^S forms small acid-sulfate 

hot springs. The acid waters attack their enclosing rocks and, 

with enough decomposition of the rocks, form mud pots or 

(with ferric-oxide coloration) paint pots (fig. 17).

Take the loop trail to view the hydrothermal activity. The boardwalk trail around the Fountain Paint Pot 

area leads to a group of geysers that share episodic exchanges of discharge function. These include Fountain, 

Morning, Clepsydra (fig. 18), Jet, Spasm, and Jelly geysers. For most of the time since the 1959 Hebgen Lake 

earthquake, Clepsydra has been a perpetual spouter rather 

than a true (episodically erupting) geyser. Also visible 

from this walk are other features of Lower Geyser Basin 

and its surroundings (fig. 10). Note the broad expanse of 

siliceous sinter. Much of the basin floor that is not sinter is 

diatomaceous alluvial sediment (see the geologic map of 

Lower Geyser Basin by Muffler, White, Truesdell, and 

Fournier, 1982). The wide meadows of the basin are 

bounded by flow-front scarps of young rhyolitic lava flows 

of the Madison Plateau on the west and the Central Plateau on the east. In the western part of the basin is Twin 

Buttes. The Pocket Basin hydrothermal-explosion crater 

(Muffler and others, 1971) is visible to the north as a low 

tree-covered rim near the center of the basin, rising as 

much as 21 m above the basin floor. To the northeast are 

the ragged Porcupine Hills, another group of hydrothermally cemented glacial hot-spring deposits. Visible 13 km 

to the north are the northwestern wall and rim of the Yellowstone caldera.

STOP 10 PORCUPINE HILLS AND Y-13 DRILL HOLE

Interactions of hot springs with glacial ice. Walk 

to the Y-13 drill site collared in siliceous sinter near 

the largest hot spring between the two Porcupine Hills.

Figure 17. Mud pots seen at high point on Fountain Paint Pot nature walk, Lower Geyser Basin.
20 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

The Porcupine Hills are composed of sands, gravels, and 

cobbles that are believed to have been deposited as a result of local melting of glacial ice where hot water discharged at the base of a glacier that slowly moved across 

this area during the Pinedale glaciation. These sediments 

have been altered by hydrothermal activity and are now 

cemented with zeolites and clay minerals. At the time of 

the Pinedale glaciation, the potentiometric surface for 

ground water was elevated to far above the present ground 

surface, allowing temperatures in upflowing parts of the 

hot-spring system to become much hotter than at present 

(in otherwords, the temperature of the boiling-point curve 

increased at given depths). The raised potentiometric surface also allowed hot water to flow upward through the 

pile of glacial sediments (Porcupine Hills) that now stand 

well above the floor of Lower Geyser Basin. Contouring 

of the glacial surface indicates that ice was about 500 m 

thick above the Y 13 drill site during the Pinedale glaciation. Fluid-inclusion studies (Bargar and Fournier, 1988) 

suggest that the temperature of the fluid at the point of 

discharge from the earth beneath the glacier could have 

been as high as 240 to 250°C. Micrometer-sized particles 

resembling microorganisms have been found in liquid-rich 

fluid inclusions in hydrothermal quartz crystals in core 

samples from the Y-13 drill hole (Bargar and others, 

1985). The fluid inclusions containing these strange particles were obtained from depths of 59.5 m, 102.1 m, and 

102.5 m. The present temperature at 102.1 m is 190°C, 

whereas the filling temperatures of the inclusions from 

that depth range from 190 to 280°C. It is believed that the 

microorganism-like particles became trapped in pseudosecondary fluid inclusions during the last glaciation when

there was vigorous upflow at this locality and when temperatures may have been below boiling because of the effect of the ice on pore-fluid pressures. Compositions of 

waters from the Y-13 drill hole and the boiling spring 

near Y-13 are given in table 3.

STOP 11 LUNCH IN LOWER GEYSER BASIN

A convenient place to eat lunch is at the Fountain 

Flat Drive picnic area. Restroom facilities are available.

STOP 12 THE Y-3 DRILL SITE AND 

POCKET BASIN EXPLOSION CRATER

Walk toward the river to Ojo Caliente spring. 

Caution: A thin silica crust extends over part of Ojo 

Caliente. The site of the Y-3 drill hole is 76 m north and 

2 m higher than Ojo Caliente Hot Spring. The temperature-depth profile, stratigraphy, and hydrothermal alteration encountered in Y-3 are given in Bargar and Beeson 

(1985). Compositions of waters from Ojo Caliente and the 

Y-3 drill hole (88 m depth) are given in table 3. The reservoir supplying water to Ojo Caliente has a temperature 

of about 175°C. Fluid inclusions in quartz obtained from 

Y-3 core samples show that subsurface temperatures at 

this location were higher during the time of the last glaciation (Pinedale glaciation that ended 10,000 to 15,000 years 

ago) (Bargar and Fournier, 1988; Bargar and Beeson, 

1985), and contouring of the glacial surface indicates that 

there was about 475 m of ice above the Y-3 drill site. The 

hydrothermal alteration assemblage differs from that enFigure 18. Clepsydra Geyser, Fountain Paint Pot nature walk, Lower Geyser Basin.
DETAILED ITINERARY 21

countered in the Y-7 and Y-8 drill holes in that the Y-3 

assemblage includes a greater variety of alteration products, including mixed-layer clays and illite, which generally forms at >200°C. The illite probably formed during the 

last glaciation, when subsurface temperatures were higher 

than at present. Recall that the Y-8 area probably was a 

zone of cold-water recharge rather than hot-water discharge during the main stage of the Pinedale glaciation, as 

indicated by the oxidizing nature of fluids in the area prior 

to about 19,000 years ago.

Ojo Caliente spring is located on the west flank of 

the Pocket Basin (fig. 19) hydrothermal explosion crater 

described by Muffler and others (1971). Refer to their 

publication for a geologic map (their fig. 4) and a discussion of the mode of formation. In brief, Pocket Basin is 

one of several large hydrothermal explosion features in

Yellowstone Park that are thought to have formed during 

the waning stage of the last glaciation. These explosions 

generally occurred where there was vigorous upflow of 

thermal water during glaciations and discharge of hot 

springs beneath the ice; these conditions are indicated by 

thick accumulations of water-worked sediments that were 

derived from the melting ice. Horizontally bedded siltstones (probably lake deposits) were encountered in the 

Y-3 drill hole and are present in the explosion debris on 

the flanks of Pocket Basin. It is likely that a rapid draining 

of a local lake in the region lowered the hydrostatic head 

to such an extent that pore water flashed to steam, producing the explosion. Cross the road near Ojo Caliente 

spring and follow the fishermen's trail along the river 

into Pocket Basin (fig. 20). Climb to the top of the crater rim to get a good view of the basin. Examine the

Figure 19. Air view of Pocket Basin hydrothermal explosion crater (elongated 

meadow in center of photograph, ringed by trees and high ground). Large vapor 

plume (arrow) in right foreground rises from Ojo Caliente pool located outside of 

Pocket Basin near the Firehole River. U.S. Geological Survey Y-3 drill site is near 

the tree line to left of Ojo Caliente pool. Mud pots are located on high ground at 

distant side of Pocket Basin.

Figure 20. Floor and rim of Pocket Basin hydrothermal explosion crater, looking east from where 

main trail enters the crater.
22 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

blocks of silicified and hydrothermally altered sediments 

that form the rim of the crater, looking for evidence of 

repeated explosive hydrothermal activity at this locality.

Exercise extreme caution in approaching hot 

springs, as many in this region have thin silica crusts 

around their edges that are underlain by boiling water. 

Follow the fishermen's trail to the far side of Pocket 

Basin and then turn left to climb onto the eastern flank 

of the crater. There, a series of interesting mud pots and 

mud cones can be observed (fig. 21). Note that the "mud" 

is dominantly white, which is in contrast to the mud in 

other mud-pot areas in Yellowstone Park where brown, 

red, and cream colors generally prevail. The reason for the 

white color is that the mud pots at Pocket Basin are in a 

region that was once a silica terrace. The "mud" is dominantly finely divided silica, with little clay present. The 

black material that can be seen "floating" on some of the 

muddy water is very fine grained iron sulfide. Return the 

way you came along the river trail. Do not take the 

more direct route across the crater floor, as it is likely 

to take you over dangerous and (or) very muddy 

ground.

STOP 13 FIREHOLE CANYON

Flow structures in rhyolite lavas. North of Lower 

Geyser Basin the Firehole River flows into the Firehole 

Canyon. A one-way 3.2-km-long scenic-loop road provides 

good views of flow structures in the rhyolitic lavas. The 

course of the river through the canyon is topographically 

controlled along the contact between two rhyolitic lava 

flows the 150,000-year-old Nez Perce Creek flow that 

vented on the Central Plateau and flowed westward across 

the area and the 117,000+8,000-year-old West Yellowstone 

flow (J.D. Obradovich, in Pierce, 1979) that forms the marginal scarp of the Madison Plateau, across the river to the 

west. The glacial sequence relates to these flows as follows: (1) emplacement of the older flow (~150 ka), (2) 

glacial streamlining of the older flow during the Bull Lake 

glaciation, (3) emplacement of the young (117ka) flow, 

and (4) glacial deposition during Pinedale time on the 

younger flow.

Outcrops along the road demonstrate especially clearly some internal features typical of viscous rhyolitic lavas. 

Shortly after turning onto the one-way loop, the road approaches the little-modified flow-front scarp of the West 

Yellowstone flow, which is across the Firehole River. The 

gray glassy carapace and steeply dipping contorted flow 

layering are conspicuous, even from across the river. A short 

distance beyond, in the roadcut on the left of the road where 

the road turns southward and climbs above the river, is a 

noteworthy outcrop of the upper flow breccia of the Nez 

Perce Creek flow. Viscous lavas generally flow by marginal 

shear and pluglike movement of a more or less fluid core.

Their chilled surfaces break up into rafts of blocky rubble, 

some of which is dumped at the front and partly overridden 

by the still-moving flow in tractor-tread fashion. The result

Figure 21. Mud pots located on the southern flank of Pocket 

Basin. A, Flows of viscous mud; B, small mud volcanoes; and 

C, pools of violently boiling muddy water, which are more 

common in the spring and early summer at Pocket Basin.
DETAILED ITINERARY 23

is an enveloping flow breccia (fig. 22). This outcrop along 

the south side of the roadcut demonstrates fluidal layers 

locally arrested in the process of brecciation. The fluidal

layers themselves are seen to intrude the glassy upper flow 

breccia formed in earlier stages of brecciation. The blocks 

have various textures, some hydrated, others more obsidianlike, and some partly devitrified. These porphyritic rhyolite 

glasses are generally fractured on a centimeter scale, resulting in their rapid reduction to obsidian-rich sand and gravel, 

the material that makes up the glacial deposits in the area. 

Following the loop road southward, further examples of 

fluidal layering and varied degrees of brecciation in the 

upper part of the Nez Perce Creek flow can be followed 

through a series of roadcuts. Firehole Falls, below a large 

parking area, is held up by nearly vertical, erosionally resistant flow layers in the Nez Perce Creek flow (fig. 23). The 

marginal scarp of the younger West Yellowstone flow continues to form the western rim of the canyon across the river.

DAY 3 TRAVEL OLD FAITHFUL TO 

MAMMOTH HOT SPRINGS

Take a bag lunch, as there are no restaurant facilities along the way. Most of the morning will be spent 

walking through Norris Geyser Basin. Try to arrive at 

Mammoth Hot Springs early in the afternoon to allow 

plenty of time to explore the huge travertine terrace. Locations of today's stops are shown in figure 24.

STOP 14 NORRIS GEYSER BASIN

Long-term and seasonal changes in hydrothermal 

activity. The geology and thermal activity of Norris Geyser Basin is described in detail and beautifully illustrated 

in U.S. Geological Survey Professional Paper 1456 by

Figure 22. Flow-front breccia exposed in Firehole Canyon. A, Rounded blocks of chilled lava in matrix of smaller rock and glass fragments and B, detail of flow-banded 

magma within breccia showing fluidal layers locally arrested in process of brecciation.

Figure 23. Firehole Falls in Firehole Canyon, held up by nearly 

vertical, erosionally resistant flow layers in the Nez Perce Creek 

flow.
24 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

Mammoth 

/Hot Springs ^

Older Younger Flows

10 KILOMETERS

Figure 24. Generalized geologic map showing field-trip route and stops between Norris Geyser Basin and 

Mammoth Hot Springs. Stippled areas show Quaternary rhyolitic flows and domes; hashed areas show preTertiary and Tertiary rocks (older than Yellowstone Plateau volcanic field); white areas are mostly surficial 

deposits with some exposures of Huckleberry Ridge Tuff, Lava Creek Tuff, and Swan Lake Flat Basalt. 

Heavy lines indicate faults ball and bar on downthrown side. Large circled numbers show stop locations. 

(Modified from Christiansen and Hutchinson, 1987).
DETAILED ITINERARY 25

White and others (1988). Unfortunately this publication is 

presently out of print but can be found in USGS and many 

university libraries. Morris Geyser Basin is a large area of 

varied hydrothermal activity that is easily examined on 

two loop trails from the visitor center. One loop goes to 

Porcelain Terrace and Porcelain Basin and the other to the 

Back Basin. Before starting your walk through Norris, 

note that the National Park Service trail guide is inexplicably oriented with west toward the top of the map. 

Figure 25 shows locations of selected springs and geysers mentioned in the text.

The Norris Geyser Basin (Norris) is noted for (1) the 

highest-erupting geyser (Steamboat) presently active anywhere in the world, (2) "acid-chloride" geyser activity in 

Porcelain Basin, and (3) the highest reservoir temperatures 

in Yellowstone Park. In contrast to other parts of the park, 

at Norris there is a yearly basinwide hydrothermal disturbance or event (generally in the fall) that is characterized 

by (1) increased turbidity of many hot springs, (2) increased discharge of thermal water and steam, (3) extreme 

fluctuations in temperatures of pools, and (4) in some 

years, small hydrothermal explosions (White and others,

No 2 */> PORCELAIN 

Opal TERRACE

Little Whirligig 

PORCELAIN BASIN

Green Dragon

CONTOUR INTERVAL 

25 FEET

7550

Figure 25. Sketch map of Norris Geyser Basin showing topographic features, U.S. Geological Survey drill holes Y-9 and Y-12, and 

locations of selected hot springs and geysers. Contours show equal 

altitude. No. 1 and No. 2 show locations of springs represented by 

analyses 1 and 2, table 4. Stippling has been added to accentuate 

the topographic relief in Norris Geyser Basin region. Darker shading indicates higher elevations.

1988). This "disturbance" has some characteristics of a basinwide subterranean geyser eruption.

At Norris, over 360 samples of thermal waters have 

been collected and analyzed for major dissolved constituents from about 70 hot springs and geysers over a period 

of 108 years (for example, Gooch and Whitfield, 1888; 

Alien and Day, 1935; Rowe and others, 1973; Thompson 

and others, 1975; Thompson and Yadav, 1979; Kharaka 

and others, 1990). The results provide a remarkable and 

unique picture of areal and temporal variations in water 

compositions, mostly resulting from underground mixing 

of neutral-chloride and acid-sulfate waters that have reacted with rock at high temperatures after mixing. Representative chemical analyses of thermal waters at Norris are 

shown in table 4.

Bedrock of the Norris area is the Lava Creek Tuff, 

much of which has little primary permeability, whereas in 

the Upper and Lower Geyser Basins bedrock generally is 

rhyolitic lava that appears to have good primary permeability in brecciated material at tops and bottoms of flow 

units and at flow fronts.

THE PORCELAIN TERRACE AND 

PORCELAIN BASIN LOOP TRAIL

Walk through the visitor center to Porcelain 

Basin and Porcelain Terrace. From the visitor center, 

looking out to the north over Porcelain Basin (fig. 26), 

much of what at first appears to be white hot-spring deposits is actually the acid-leached Lava Creek Tuff. Although the waters that discharge in Porcelain Basin and in 

the 100 Spring Plain (beyond the low hills on the far side 

of the basin) are supersaturated in respect to amorphous 

silica, very little sinter is deposited there because the water 

has a low pH (3-4). In contrast, at Porcelain Terrace at the 

east side of Porcelain Basin (fig. 27), silica is depositing 

from pH-neutral waters at the fastest rate of any place in 

Yellowstone Park. At this locality, Cl-rich and SO4-poor 

water flows directly to the surface from the deepest and 

hottest reservoir at Norris (275-325°C, based on silica and 

Na-K-Ca geothermometry, A 18O(SO4-H2O), A 13C(CO2- 

CH4), and on mixing models).

The Y-12 drill hole is situated at the south end of 

Porcelain Terrace near the tree line. It attains a temperature of 238°C at a depth of 332 m. Very little permeability 

or hydrothermal alteration was encountered in the Lava 

Creek Tuff, the only rock unit encountered in the Y-12 

drill hole (White and others, 1988). The 8D (a measure of 

the hydrogen isotopic composition of a particular sample 

compared to the hydrogen isotopic composition of a standard, expressed in parts per thousand) value of 149.5 for 

water obtained from this well was critical for the determination of the likely isotopic composition of the deep water 

in the hydrothermal system (Truesdell and others, 1977). It 

also sparked the search for isotopically light recharge
26 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO 

Table 4. Chemical compositions (mg/kg) of selected thermal waters, Norris Geyser Basin.

Analysis 

No. Name

1

2 

3

4

5

6

7

8 

9

10

11

12

13

South base Porcelain Terrace 

South base Porcelain Terrace 

South base Porcelain Terrace

Little Whirligig

Sulfur Dust

Porkchop 

Porkchop

Echinus Geyser 

Echinus Geyser

Opal Spring

Harding

Y- 12 drill hole

Y-9 drill hole

Date

07/03/75 

09/02/90 

09/06/90

09/27 77 1

09/12/61

09/18/60 

06/??/89

11/15/81 

09/15/86

09/19/60

06/07/71

09/13/69

09/16/69

Ref.

1 

2 

2

3

4

4 

5

2

2

4

3

2

2

°C

92 

88 

89

91

50

72 

92

90

90

93

238

195

P H

7.00 

2.82 

5.36

3.20

2.75

7.45 

8.50

3.14 

3.06

1.90

3.53

7.86

8.58

SiO2

589 

520 

665

420

280

435 

741

257 

296

168

325

352

412

Na

400 

334 

400

349

250

526 

388

151 

148

5

26

377

268

K

93 

100 

112

83

57

66 

91

45 

52

2

18

21

16

Ca

2.60 

1.82 

2.82

2.50

4.50

6.40 

3.60

3.70 

4.30

0.70

0.90

1.90

0.80

Mg

0.01 

0.21 

0.08

0.50

0.15

0.50 

0.06

0.52 

0.52

0.25

0.20

0.04

Li

7.18 

4.07 

5.36

5.30

3.50

7.40 

6.60

1.00 

0.75

0.05

0.09

1.43

0.98

Cl

675 

527 

634

607

427

860 

687

125 

117

5

2

528

80

SO4 HCO3

24 

133 

99

113

197

33 

23

170 

360

760

123

34

43

60 

0 

32

0

0

18 

62

0 

0

0

0

79

488

References: (1) Thompson and Yadav (1979).

(2) Unpublished U.S. Geological Survey data.

(3) Thompson and others (1975).

(4) Rowe and others (1973).

(5) Kharaka and others (1990).

Figure 26. Porcelain Basin, viewed from near the Norris museum, Norris Geyser Basin.

water for the Yellowstone hydrothermal system. An analysis of a water sample collected from the Y-12 drill hole is 

shown in table 4 (No. 12). The most significant chemical 

information provided by this sample is the chloride concentration of 528 mg/kg. This value is probably close to 

the concentration of chloride in the deep reservoir beneath 

Norris prior to any separation of steam during upflow. The 

relative concentrations of cations in the sample reflect the 

reaction of hot water with glass-rich ash-flow tuff at an

unknown temperature in the range 190 to 238°C. There 

are uncertainties about the depth(s) and temperature(s) 

where fluid(s) enters the drill hole.

Along the top of Porcelain Terrace, and elsewhere in 

topographically high regions surrounding the geyser basins 

at Norris, nondischarging, boiling pools of low-chloride, 

acid-sulfate waters are found (for example, Opal Spring, 

No. 10, table 4). At Porcelain Terrace these acid-sulfate 

pools all formed after the 1959 Hebgen Lake earthquake,
DETAILED ITINERARY 27

when newly formed fractures allowed the hot-spring waters to leak sideways and flow onto the ground at slightly 

lower elevations at the side of the terrace. Prior to this 

earthquake only silica-depositing neutral-chloride waters 

discharged from the top of the terrace. Cavities in the sinter that were once filled with water are now partly drained, 

and the rock beneath the sinter is now being attacked and 

leached by boiling sulfuric acid-rich water. The sinter is 

decaying and crumbles relatively easily. Because of these 

factors, Porcelain Terrace is one of the more dangerous 

places in Yellowstone Park.

At the side of Porcelain Terrace relatively high-chloride (550-800 mg/kg) low-sulfate (10-50 mg/kg) pH-neutral waters generally issue from a deep reservoir with an 

estimated temperature of 270 to 325°C. Analysis No. 1, 

table 4 (south base Porcelain Terrace), is typical of thermal 

waters issuing along a north-trending zone at the west side 

of Porcelain Terrace. However, for short periods of time 

after basinwide hydrothermal disturbances, pH-neutral 

springs at Porcelain Terrace may become acid by mixing 

with a sulfate-rich water that appears to have equilibrated 

with rock at a high temperature (>200°C) before mixing. 

One usually neutral-chloride spring was sampled on the 

first day of a seasonal hydrothermal disturbance (No. 2, 

table 4); its pH was 2.82 and its sulfate concentration was 

133 mg/kg. Four days later its pH had increased to 5.36 

and its sulfate concentration had dropped to 99 mg/kg (see 

No. 3, table 4). Chemically, waters from this and other 

nearby springs generally have been found to be very similar in composition to analysis 1 in table 4. Perhaps the 

most significant information provided by this spring is that 

the more-acid water contained helium with a higher 3He/ 

He ratio than the less-acid water (B.M. Kennedy, written 

commun., 1991), and it also had a 8D isotopic composition 

almost as heavy as the water in boiling acid-sulfate pools 

in the region (fig. 28) that have undergone considerable 

evaporation. One might be tempted to conclude that the 

acid-sulfate-rich composition of analysis 2 in table 4 is the 

result of simple mixing of the neutral chloride-rich water

Base Porcelain Terrace 

during "event"

Acid-sulfate pools

Green Dragon

Base Porcelain Terrace

normal Echinus

\

 I I I I 

100 200 300 400 

SULFATE, MILLIGRAMS PER LITER

500

Figure 28. Sulfate (SO4) versus 6D (deuterium) for Norris Geyser Basin thermal waters. See text for discussion.

, Mft^^^j^l^^^

Figure 27. Hot spring activity at Porcelain Terrace, Norris Geyser Basin.
28 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

from deep in the system with acid-sulfate water that percolates downward from boiling pools at the top of Porcelain 

Terrace. However, note that in figure 28 the mixing trend 

from the "normal" sulfate-poor water issuing at the base of 

Porcelain Terrace to the acidic sulfate-rich water collected 

during the yearly Morris "event" does not project to compositions normally found in acid-sulfate pools. Also, the 

3He/4He data of B.M. Kennedy (written commun., 1991) 

strongly suggested that the acidity of the "event" water issuing at the base of Porcelain Terrace is not the result of 

simple downward infiltration of acid-sulfate water from 

pools at the top of Porcelain Terrace.

Moving west from Porcelain Terrace through Porcelain Basin and moving to the northwest through 100 

Spring Plain (fig. 25) there is a decrease in chloride, an 

increase in sulfate, a decrease in pH (for example, Little 

Whirligig and Sulfur Dust, Nos. 4 and 5, respectively, 

table 4), and the estimated reservoir temperature decreases 

to about 200 to 230°C. All of the acid-chloride waters in 

the Porcelain Basin and 100 Spring Plain regions plot 

along the trend shown by the "normal" and "event" waters 

at the base of Porcelain Terrace in figure 28. These waters 

also are relatively rich in 3He/4He compared to other Norris waters.

As you walk through Porcelain Basin note the bright 

green color of a few of the hot-water discharge channels. 

This color is produced by cyanobacteria (Cyanidium sp.) 

that require low-pH environments, in contrast to the yellow, red, and brown organisms and precipitates of the 

near-neutral discharge channels.

THE BACK BASIN LOOP TRAIL

As you approach the Norris visitor center from 

the parking lot, the trail that branches to the left leads 

past Steamboat Geyser into the Back Basin. In the Back 

Basin a series of reservoirs with different temperatures are 

present so that waters with similar chloride concentrations 

attain chemical equilibrium with rock at a variety of temperatures ranging from about 210 to 300°C before rising 

to the Earth's surface. Reservoirs of sulfate-rich waters 

with moderate chloride also exist in the Back Basin region, and as at Porcelain Terrace, annual mixing of sulfate-rich and sulfate-poor waters occurs in the Back Basin 

(well documented for Cistern Spring, Fournier and others, 

1986). Some waters in the Back Basin, such as those from 

Green Dragon Spring, are always acidic and appear to be 

the result of mixing of chloride-rich water from deep in 

the hydrothermal system with acid-sulfate water that infiltrates downward from surface pools (fig. 28).

As you walk through the Back Basin note the large 

amount of old silica that is now decaying and collapsing 

into what were once water-filled cavities within the sinter. 

To the northwest the Back Basin is bordered by the Ragged

Hills, low hills of hydrothermally cemented kame deposits 

that likely formed beneath a glacier by melting of the ice 

due to hot-spring activity. Features of particular interest in 

the Back Basin are Steamboat Geyser, Cistern Spring, Echinus Geyser (erupts about once an hour), and Porkchop Geyser Crater and its hydrothermal explosion debris (fig. 25 and 

"Trail Guide to Norris Geyser Basin," see appendix A).

STEAMBOAT GEYSER

Steamboat Geyser exhibits two modes of eruption. 

Generally, it erupts every few minutes to a height of a few 

meters (fig. 29). On rare occasions, it erupts massive 

amounts of water 70 to 120 m high. All of the conspicuous erosion around this geyser has occurred since 1960 

and is the result of water discharged during the big eruptions (fig. 30).

Figure 29. A typical small eruption of Steamboat Geyser, Norris 

Geyser Basin.

Figure 30. Eroded ground resulting from infrequent big eruptions of Steamboat Geyser, Norris Geyser Basin.
DETAILED ITINERARY 29

CISTERN SPRING

Cistern Spring has been active since about 1966, and 

the silica terrace that now surrounds the pool has formed 

since then (fig. 31). Note how fallen trees have played a 

major role in the formation of the sinter terrace. Cistern 

Spring was sampled more than 100 times during a 25-year 

period. Monthly collections of water from 1976 to 1985 

showed that increased boiling preceded yearly hydrothermal disturbances and that chloride content decreased and 

sulfate content increased immediately following the onset 

of these disturbances (Fournier and others, 1986). The 

mixed waters of Cistern Spring lie along the trend shown 

in figure 28 for the base of Porcelain Terrace waters. 

Figure 32 shows C1-SO4 relations for Cistern Spring waters. The variations shown in figure 32 result partly from 

different amounts of mixing of different waters and partly 

from different degrees of steam loss (adiabatic expansion) 

during upflow (Fournier and others, 1986).

PORKCHOP GEYSER CRATER

Between 1960 and 1989 Porkchop Geyser Crater 

evolved from an intermittently flowing spring, to a geyser, 

to a perpetually spouting geyser, and finally to its present 

condition after a hydrothermal explosion in September 

1989 (fig. 33). Porkchop now discharges water mainly 

from a hotter (presumably deeper) neutral-chloride reservoir where dissolved silica concentrations and K/Na ratios 

are relatively high (No. 7, table 4) and the reservoir temperature is likely to be in the range 275 to 300°C. In 1960 

it discharged from an apparently different (presumably

shallower) reservoir where pH-neutral water had reacted 

with rock at lower temperatures (215-230°C), yielding 

lower concentrations of dissolved silica and lower K/Na 

values (No. 6, table 4). A gradual change in the composition of water discharged by Porkchop Geyser over the period 1960 to 1990 was documented by Fournier and others 

(1991), who showed that the calculated temperature at 

which the discharged water last equilibrated with rock (the 

presumed reservoir temperature) increased by about 60 to 

70°C during that same period of time, accompanied by the

«40( 

J 350 H 

S 300'

00

I 250-

OS

2 200

w 100 q -o 0

H - o

fc 50'

0 1 ' i ' ' ' ' i ' ' ' i '' ' ' i ' ' i *^ri | i 

100 200 300 400 500 600 700 

CHLORIDE, MILLIGRAMS PER LITER

Figure 32. Chloride (Cl) versus sulfate (SO4) for waters collected at different times from Cistern Spring (circles), Echinus Geyser (dots), and U.S. Geological Survey Y-12 drill hole (star).

Figure 31. Silica terrace formed 

by waters discharged from Cistern Spring. Morphology is controlled mostly by distribution of 

fallen trunks of trees killed by 

hot water, Morris Geyser Basin.
30 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

increase in eruptive activity that culminated in a hydrothermal explosion that destroyed the geyser.

ECHINUS GEYSER

Echinus Geyser is named for spiny dark-red iron- and 

arsenic-rich coatings of silica that once coated the sides of 

its pool and the cobbles in its runoff channel. For about the 

last 20 years these silica spines have been slowly overgrown by white to gray relatively smooth silica encrustaFigure 33. Porkchop Geyser, Norris Geyser Basin. A, Quiescent pool in 1984; B, in eruption in 1986; and C, after 

hydrothermal explosion in 1989.

tions. Echinus discharges large amounts of acid-sulfate 

water (Nos. 8 and 9, table 4) during its fairly predictable 

eruptions, which occur about every 50 to 60 minutes. However, it also has long periods of inactivity. If it is in its usual 

predictive mode of behavior, it is worth waiting to witness 

an eruption of this geyser. The waters discharged by Echinus are chemically and isotopically different from other 

thermal waters found in Yellowstone Park; sulfate is relatively high, whereas the isotopic composition of its water is 

relatively light (fig. 28). The concentration of sulfate in 

Echinus water ranges widely, whereas there is relatively 

little change in chloride concentration. Figure 32 shows Cl864 relations for 53 samples from Echinus collected from 

1884 to 1986, mostly during 1980 to 1983. The pH of the 

Echinus waters (3.0-3.5) appears to be buffered by the assemblage kaolinite-muscovite at about 195 to 215°C (the 

silica geothermometer temperature range). The Na/K values 

found in the Echinus waters are inconsistent with equilibration involving dissolved constituents and alkali feldspars at 

about 190 to 215°C, whereas K/H values are consistent 

with the assemblage kaolinite-muscovite. Fragments of 

banded marcasite and pyrite are sometimes ejected from 

Echinus during its larger geyser eruptions. Two samples of 

iron sulfide from Echinus were recently analyzed for trace 

elements and were found to be anomalously rich in As, Tl, 

and Sb (T.E. Keith, written commun., 1992).

CHARACTERISTICS AND ORIGIN OF ACID-SULFATE WATERS

The acid-sulfate waters at Norris that originate by 

oxidation of H2S where steam and other gases bubble 

through surficial pools of perched ground water and condensed steam have relatively heavy 5D and 5 O values 

(Truesdell and others, 1911) and are strongly depleted in 

Na relative to K as a result of nonequilibrium acid dissolution of silicic volcanic rocks (for example, Opal Spring, 

No. 10, table 4). Many steam-heated acid-sulfate pools 

also are strongly depleted in Li relative to K (for example, 

Harding, No. 11, table 4). Conversely, discharging acidsulfate waters that equilibrated underground with rock at 

>190 to 200°C have significantly higher Na/K ratios than 

waters from steam-heated acid-sulfate pools and K/Li 

weight ratios less than 80 (generally in the range 40-60).

The 834S (a measure of the sulfur isotopic composition of a sample compared to the sulfur isotopic composition of a standard, expressed in parts per thousand) values 

for sulfate dissolved in several Yellowstone Park thermal 

waters, including some from Norris, were determined by 

Truesdell and others (1978). The waters from deep in the 

Norris hydrothermal system, issuing at the base of Porcelain Terrace, have 534S values of about +18, whereas all of 

the sulfate-rich waters have 834S values of about 0 to +6. 

According to Truesdell and others (1978) the +18 value 

reflects high-temperature (270-300°C) equilibrium fractionation of sulfur isotopes between H2S (initial S34S=0)
DETAILED ITINERARY 31

and sulfate derived by oxidation of H2S; this high-temperature oxidation must occur deep in the hydrothermal system. In contrast, the sulfate derived by nonequilibrium 

oxidation of H2S at and near the ground surface has 6 S 

close to 0. Native sulfur at Norris has 634S values ranging 

from about +1 to +3 (Schoen and Rye, 1970).

Oxidation of H2S at depth using oxygen initially dissolved in meteoric recharge water can account for only 

about 13 mg/kg of the dissolved sulfate in waters deep in 

the hydrothermal system. Oxidation at and near the water 

table of H2S initially carried in steam, followed by downward percolation, may account for some of the sulfate and 

acidity found in the underground acid-sulfate-chloride waters at Norris (particularly waters such as Green Dragon, 

fig. 28), but mass and thermal balance considerations, and 

light 8D and 818O values, make it difficult to account for 

all of the sulfate in Echinus waters by the present-day oxidation of H2S in and around nearby surface pools. The 

mass and thermal balance problems may be explained if 

old deposits of native sulfur occur locally at relatively 

shallow depths in the Norris area. Sulfur-consuming bacteria (Sulfolobus sp.) are very effective at generating sulfuric 

acid using native-sulfur deposits and oxygen in the cool 

margins of hydrothermal systems (Brock, 1978). Such native-sulfur deposits could be related to early volcanic activity that produced silicic domes south of Norris and 

underwent subsequent burial either by later volcanic flows 

or by glacial material deposited on hot ground. Cold 

ground water, after picking up sulfate where it comes in 

contact with old native sulfur, could then flow toward the 

(Norris) hydrothermal system where it mixes with and becomes heated by a small amount of chloride-rich water 

and steam from deep in the system. The 634S of the dissolved sulfate and 8D of the water from Norris observed 

by Truesdell and others (1977, 1978) are compatible with 

this interpretation.

The origin of the sulfate-rich water that is characteristic of Porcelain Basin and 100 Spring Plain is uncertain. 

This water appears to be relatively uniform in composition 

and is widespread. The highest 3He/4He ratios (>8-9 relative to atmospheric concentrations) in Norris waters are 

found in Porcelain Basin and 100 Spring Plain waters 

(B.M. Kennedy, written commun., 1991), and the 5D in 

these waters is also relatively heavy. The possibility cannot be ruled out that there is a component of magmatic 

gas containing SO2 that is entering parts of the Norris hydrothermal system.

THE Y-9 DRILL HOLE

The Y-9 drill hole is located at the northeast edge of 

the main Norris parking lot. This hole attained a depth of 

248 m and a maximum temperature of 195°C. Water collected from it is shown by sample 13, table 4. In contrast 

to other Norris waters, the Y-9 water is relatively rich in

bicarbonate and relatively poor in chloride. Superheated 

steam enters this drill hole through a nearly vertical kaolinite-coated fracture at a depth of 64 m (White and others, 1975). It is likely that some of this CO2-rich steam 

condenses in the drill hole and that this condensate becomes ponded in the relatively impermeable bottom of the 

drill hole, where it reacts with wall rock at 170 to 190°C. 

Apparently a small component of "normal" thermal water 

in the region is mixed with the condensate.

STOP 15 PICNIC LUNCH IN THE NORRIS REGION

The closest official picnic spot with toilet facilities is 

located about a mile east of Norris Geyser Basin. From 

Norris Junction take the road to Canyon Village, the road 

leading into the picnic area will be on the left-hand (north) 

side of the main road.

STOP 16 ROARING MOUNTAIN

Acid-sulfate alteration of tuff. Much acid-sulfate 

alteration and fumarolic activity occurs along the northtrending corridor from Norris to Mammoth Hot Springs. 

Bedrock is mostly the Lava Creek Tuff, but vents for local 

rhyolitic and basaltic eruptions are found in this corridor 

of volcanic and hydrothermal activity. Roaring Mountain 

was named in 1885 by Arnold Hague and Walter Weed, 

both of the USGS, for the loud noise produced by its 

steam vents. It is a bluff composed of the hydrothermally 

altered Lava Creek Tuff with numerous fumaroles and 

small acid-sulfate seeps (fig. 34). The fumaroles are now 

generally inconspicuous on warm sunny days but can be 

impressive in cool cloudy weather. Schoen (1969) measured the rate of sulfate discharge from Roaring Mountain 

into the small stream that drains the area. He recorded an 

average discharge of about 1,180,000 grams of sulfate per 

day. Averaged over the area of acid-altered ground, about 

9.2 g/m2/day of sulfate is produced by bacterial oxidation 

of H2S.

Although not visible from the road, the top of Roaring Mountain is a flat mesa-like bench. In the central part 

of this bench are several large craters in the Lava Creek 

Tuff. Around these craters is an apron of angular rock 

fragments in a muddy matrix. The craters were formed by 

hydrothermal explosions, which threw bedrock fragments 

and mud out for distances of as much as 0.8 km. These 

hydrothermal explosions probably occurred when a lake 

surrounded by stagnant glacial ice drained rapidly, as discussed previously for the origin of Pocket Basin (Stop 12).

STOP 17 OBSIDIAN CLIFF

From the parking area, Obsidian Cliff can be seen to 

lie along the margin of a rhyolitic lava flow that abuts the
32 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

Figure 34. Roaring Mountain.

wall of a paleovalley near here. Large columnar joints 

mark the base of the flow near the road, and steep contorted flow layering is visible near the top of the flow (fig. 

35). Obsidian Cliff is an excellent locality to examine rhyolitic obsidian and its crystallization textures. (Specimen 

collecting is not allowed.) Some visitors to this locality 

are somewhat disappointed to find that clear undevitrified 

blocks of obsidian are uncommon; sites once used by Native Americans to quarry crystal-free obsidian for implements are located away from the road along other margins 

of the same flow.

Characteristic textural features are readily seen in 

talus boulders at the base of the cliff near the road. The 

rhyolite here is entirely free of phenocrysts, indicating that 

the magma erupted above its liquidus temperature. The obsidian occurs in basal and marginal chilled zones of the flow, 

which has a pumiceous top and a crystallized interior that is 

seen in a single gully exposure. Fluidal laminations are 

distinct in the talus boulders and are generally marked by 

bands of small gray spherulites that formed by partial hightemperature devitrification of the rhyolitic glass. Further 

devitrification is represented by larger pinkish spherulites 

and lithophysae, generally 1 to 5 cm. Lithophysae are hollow spherulites lined by concentric shells of small crystals 

generally tridymite, alkali feldspar, and minor accessory 

minerals such as fayalite separated by open interspaces. 

The lithophysae represent high-temperature vapor exsolution and crystallization of minerals from the vapor phase.

The Obsidian Cliff flow was dated by John Obradovich (1992) as 183,000±3,000 years old. Three thicknesses of hydration rims occur on different cracks in the

Figure 35. Obsidian Cliff.

Obsidian Cliff flow and averaged 16.2, 14.5, and 7.9 |J.m 

thick (Friedman and others, 1973). The 16.2-|0.m-thick rim 

corresponds to the original cooling of the flow. The 14.5- 

and 7.9-|J,m thick rims are very similar in thickness to the
DETAILED ITINERARY 33

hydration rims on glacial abrasion cracks in obsidian from 

the Bull Lake and Pinedale end moraines near West Yellowstone (Pierce and others, 1976). The hydrated cracks 

are thought to result from glacial loading, which first occurred in Bull Lake and then in Pinedale time. During the 

Pinedale glacial recession, about 15,000 years ago, the icecap on the Yellowstone Plateau had melted, and glaciers 

from the Gallatin Range (west of here) deposited glacial 

erratics on top of Obsidian Cliff (Pierce, 1979).

STOP 18 KOODOOS

Travertine landslide deposit. The Koodoos are a 

blocky landslide deposit of bedded Pleistocene travertine 

from Terrace Mountain, which rises above the road to the 

west (fig. 36). The morphology of the Terrace Mountain 

travertine deposit is unusual compared to other travertine

Figure 36. A, Large landslide with blocks of white travertine in 

foreground. In distance is Mt. Everts, consisting of Cretaceous 

sandstones and shales capped by Huckleberry Ridge Tuff. Photograph taken from top of Terrace Mountain. B, The Hoodoos, 

composed of blocks of travertine in a landslide deposit.

deposits in the Mammoth Hot Springs region of Yellowstone Park in that no fissure ridges or cascading terraced 

mounds are evident. Layering is monotonously horizontal, 

and no trees or other woody materials have been found 

imbedded in this travertine. This travertine may have 

formed as a result of the emergence of CC^-rich springs at 

the bottom of a lake throughout a long period of time, 

suggesting that much erosion has occurred in the Mammoth Hot Springs region since deposition of the travertine. 

U-Th age determinations on the travertine by N.C. Sturchio (Pierce and others, 1991) yield an age of 406±30 ka. 

This relatively old age is consistent with the observation 

that Pinedale glacial deposits occur on top of the Terrace 

Mountain travertine.

STOP 19 OVERLOOK ABOVE MAMMOTH HOT SPRINGS

Geologic and topographic setting of Mammoth. Geologic, geochemical, and hydrologic relations in the Mammoth Hot Springs (Mammoth) region are described in a 

series of chapters in Sorey (1991). Mammoth is situated on 

the steep western side of the Gardner River valley. The 

bedrock consists of Mesozoic sandstones and shales, which 

are prone to landsliding. A thick limestone (not exposed) 

that is a regional aquifer underlies the Mesozoic rocks. To 

the south is the Bunsen Peak dacitic stock of Eocene age. 

Pleistocene travertine caps Terrace Mountain to the west. 

To the east, Mount Everts consists of Cretaceous shales and 

sandstones, capped by the Huckleberry Ridge Tuff. Northward the valley opens toward the glaciated Yellowstone 

River Valley. In the Yellowstone River Valley are other 

Pleistocene travertine terraces above the town of Gardiner, 

Montana, which have ages of about 15,000, 20,000, and 

50,000 years old by U-Th dating (Pierce and others, 1991). 

Farther north are Precambrian to Eocene rocks of the glaciated Snowy Range.

The hydrothermal activity at Mammoth is described 

in detail by Bargar (1978). Mammoth is different from any 

of the other thermal areas of this guide. In contrast to the 

silica-depositing hot waters described previously, Mammoth is presently the world's largest carbonate-depositing 

spring system (fig. 37). The characteristic form of the deposits is a large travertine terrace. Older travertine underlies Mammoth Hot Springs village and much of the slope 

all the way down to the Gardner River. The oldest travertine deposits at Mammoth have been dated at about 10,000 

years B.P. (Pierce and others, 1991). The waters of Mammoth Hot Springs, with a subsurface reservoir temperature 

of 73°C, are cooler than those of the geyser basins. These 

waters (1) rise through Paleozoic and Mesozoic sedimentary rocks, including limestones, (2) are high in dissolved 

carbonate and sulfate, and (3) release excess CO2 as they 

discharge because of lower pressure at the surface. The 

deposited travertine initially forms ridgelike mounds above
r

34 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

the water-bearing fractures. The water pools and evaporates behind these mounds, losing CO2 to the atmosphere 

and depositing carbonate as it flows across the rims of the 

pools to enlarge the terraces.

The reservoir rock for the thermal waters discharging 

at Mammoth is probably limestone. Various explanations 

have been proposed to account for the heat that is discharged. One possible explanation is that heat extracted

Figure 37. A, Main travertine terrace seen from overlook above Mammoth Hot Springs; B, travertine 

terrace at Mammoth Hot Springs.
DETAILED ITINERARY 35

from the Yellowstone caldera magmatic system is carried 

northward by deeply circulating chloride-rich hydrothermal 

fluids that move through extensional faults in the NorrisMammoth corridor. In this explanation these chloride-rich 

fluids mix with cooler ground water in the Mammoth region and then pick up bicarbonate and sulfate by reaction 

with calcite and gypsum in the local sedimentary rocks. 

Another possible explanation is that a local magmatic heat 

source exists beneath Roaring Mountain or Obsidian Cliff 

and that hydrothermal fluids flow from this heat source to 

the south, toward Norris, and to the north, toward Mammoth. A third possible explanation is that a local heat 

source exists beneath the Mammoth region, perhaps a crystallized but still relatively hot body of basalt. A high value 

of He/ He relative to air of 8.4 in water from the Y-10 

drill hole indicates that a relatively undiluted mantle component of helium is being discharged with waters from 

Mammoth Hot Springs (Kharaka and others, 1991).

STOP 20 MAMMOTH HOT SPRINGS

Explore the travertine terrace using the U.S. National Park Service map of the trails at Mammoth and, 

if available, the USGS Bulletin on Mammoth by Bargar (1978) as your guides (see appendix A). The upper 

terrace loop drive will take you past the Y-10 drill site. 

A good view of a tension fissure that has opened along 

the top of a fissure ridge mound can be seen at White 

Elephant Back Springs (Bargar, 1978, southwest corner 

of plate 1).

DAY 4 MAMMOTH HOT SPRINGS TO 

JACKSON HOLE

This is a long drive leaving time for a minimum 

number of stops. If time is available, an overnight stay 

at Canyon Village or Lake is advised, leaving additional time to visit the Grand Canyon of the Yellowstone 

area.

STOP 21 OVERLOOK OF LOWER GRAND CANYON 

AT THE NARROWS

Early Pleistocene and volcanic stratigraphy and petroleum-bearing Calcite Springs. Proceed up the stairs 

and along the walkway. Here the Yellowstone River has 

cut a deep gorge in well-stratified andesitic breccias of the 

Absaroka Volcanic Supergroup and latest Cenozoic basalt 

flows (fig. 38). The full depth of this gorge and Calcite 

Springs can be seen from the overlook (fig. 39).

Several late Cenozoic canyons have been filled and 

recut in this area. The geologic sequence is (1) Eocene 

Absaroka Volcanic Supergroup; (2) quartzite-rich stream

gravel capped by the 2-Ma Junction Butte Basalt; (3) a 

younger canyon cut into the Junction Butte Basalt then 

filled with 1.30+0.01-Ma ash (Obradovich and Izett, 1991), 

gravels, lake sediments, and till containing striated boulders

Figure 38. Stratified andesitic breccias of Absaroka Volcanic Supergroup capped by columnar-jointed basalt flows.

Figure 39. View from Calcite Springs overlook showing lower 

Grand Canyon of the Yellowstone at The Narrows. Steaming 

ground near river (arrow) shows location of Calcite Springs, 

which emerge from hydrothermally altered rock.
36 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

and Precambrian granitic rocks this sequence is overlain 

by ~1.0-1.5-Ma basalt and the Lava Creek Tuff (0.6 Ma); 

and (4) beyond the far canyon wall, Alden Paleovalley, 

filled with Pinedale glacial deposits. The canyon beneath 

the overlook is called "The Narrows" and was cut by the 

Yellowstone River following the last glaciation. Less than 

1.6 km upstream is Tower Falls, where Tower Creek plunges into this postglacial canyon alongside the postglacial 

Koodoos, which are almost as tall as the canyon is deep.

Calcite Springs is a geothermal area that takes its 

name from masses of milky white calcite crystals nearby. 

Barite crystals are also common. Oil seeps and tarry residues issue from fissures and conduits lined with euhedral 

sulfur crystals. Seeps extend as much as 60 m up from river 

level and occur in altered Absaroka andesitic breccias.

Hydrocarbons in Yellowstone thermal waters have 

been described by Love and Good (1970) and Clifton and 

others (1990). The hydrocarbon-bearing springs occur in 

an arcuate southeastward- to eastward-trending area 115 

km long in northwestern Wyoming. The main points at 

which these springs discharge in Yellowstone are at Tower 

Bridge, Calcite Springs, and Rainbow Springs (about 18 

km southeast of Calcite Springs). The following quotes 

Clifton and others (1990, p. 169).

Petroleum from Calcite Springs occurs as vapor condensates in steam vents. Detailed geochemical analyses show a 

complex origin for the petroleum fluid. Deeply buried, hydrothermally altered sedimentary rocks are believed to have 

contributed a high temperature pyrolysate consisting largely 

of polynuclear aromatic hydrocarbons and heterocyclic 

compounds. Shallow sedimentary rocks, which are also hydrothermally altered, have contributed large amounts of aromatic and polar compounds, as well as minor amounts of 

hydrocarbons. The Permian Phosphoria Formation is suggested as a likely source rock for the bulk of the oils. Autochthonous pyrolysates and lipids from thermally altered 

surface and near-surface bacterial and land plant debris 

have also been introduced to the vents. The latter may have 

been introduced by downward percolating meteoric water.

The oil from Rainbow Springs is a highly paraffinic, low-S 

crude oil, depleted in light hydrocarbons. Unlike the Calcite 

Springs samples, the oil from Rainbow Springs is believed 

to have originated from a single sedimentary source rock 

with little or no hydrocarbon contributions from subsurface 

biota. The oil contains a unique molecular marker assemblage that suggests both gymnosperm and angiosperm input 

and places the age of the source unit in the Tertiary. Consideration of the local stratigraphy and water temperatures 

limits the probable source zone to the Eocene Aycross Formation, a syn-volcanic lacustrine mudstone. Calculation of 

deep water temperatures indicates that this unit is exposed 

to thermal waters in an extensive near-surface aquifer. Such 

conditions are consistent with the widespread surface manifestations and biomarker kinetic models.

Consideration of the petroleum chemistry and regional hydrodynamics indicates that the Yellowstone Park oils did not

migrate into the park from distant sources. The chemical data 

are also inconsistent with the oils being generated and 

trapped prior to Tertiary volcanism. At both Calcite Springs 

and Rainbow Springs, oil generation appears to be contemporaneous and is attributed to thermal alteration of relatively 

shallow sedimentary rocks by hydrothermal fluids.

Chemical geothermometers indicate that at Calcite 

Springs the temperature of the reservoir from which the 

fluids discharge is about 150 to 170°C.

STOP 22 WASHBURN OVERLOOK

Overview of Yellowstone caldera from its north wall, 

the Washbum Range. On the far (north) side of Dunraven Pass, which we have just crossed, the road traverses 

the north half of Washburn volcano, a major center of the 

Absaroka volcanic field of Eocene age. The south half of 

the Washburn volcano is downdropped within the Yellowstone caldera. We are now essentially on the northern wall 

of the caldera. In the foreground is the tree-covered surface of the Canyon flow, which abuts the caldera wall 

from within (fig. 40). The Grand Canyon of the Yellowstone cuts the flow in middle distance. Beyond is the low 

rise of Sour Creek dome, broken by a northwest-trending 

graben. To the east are the Mirror Plateau and Absaroka 

Mountains. Far to the southeast are the Red Mountains 

and, visible on a clear day, the Teton Range. The caldera 

rim can be followed from the Washburn Range, across the 

Grand Canyon, to the ridge with a prominent crescentic 

grassy area and beyond to the ridge on the far side of 

Broad Creek. The Canyon flow and Sour Creek dome 

block the view of the wall beyond, but it continues along 

the far shore of Yellowstone Lake and in front of the Red 

Mountains, which are 55 km away. The southwest skyline 

is the Central Plateau, and farther to the west is Madison

Figure 40. View looking east from Washburn overlook on 

north side of Dunraven Pass. Hydrothermally altered 

patches of white ground in middle distance mark location 

of Washburn Springs. Grand Canyon of the Yellowstone is 

between Washburn Springs and Sour Creek Dome, seen in 

background.
DETAILED ITINERARY 37

Plateau, which is 55 km away but still within the western 

margin of the Yellowstone caldera.

Andesitic debris-flow breccia or conglomerate in the 

adjacent roadcut is cut by a 4-m-thick silicic andesite dike 

of the Eocene Washburn volcanic center. Till-mantled outcrops of andesitic breccia and a few lava flows continue 

up the road toward Dunraven Pass. The top of Mt. Washburn (alt 3,123 m) was striated by north-flowing ice from 

an icecap occupying the Yellowstone Lake basin (Pierce, 

1979).

The hydrothermally altered patches of ground that 

can be seen below us in the distance mark the location of 

Washburn Springs. The waters at that locality are noted 

for their relatively high NH4, high 804, and low Cl concentrations; amounts of dissolved NH4 and sulfate are 

highly variable, as is the pH, which ranges from slightly 

acid to alkaline. Alien and Day (1935) noted that the gases 

there contain appreciable methane (13.2 percent) and 

ethane (1.15 percent). Representative chemical analyses 

are listed in table 2, Nos. 19 and 20. It is likely that organic material in sediments is being distilled at high temperatures and high pressures at the base of a vapor-dominated 

system, producing steam that is rich in organic gases and 

NH3>H2S in the vapor. The steam rises and then condenses near the Earth's surface, where the accompanying H2S 

is oxidized to sulfuric acid, which is immediately converted to ammonium sulfate by excess NH3-

STOP 23 ARTIST POINT

Grand Canyon of Yellowstone. Walk down short 

trail (about 100 m) to the constructed overlook. The

deeper part of the Grand Canyon is carved into the intensely altered Canyon flow. Upstream, the flow is relatively unaltered, and Lower Falls drops 94 m across a 

resistant ridge of steeply dipping flow layers (fig. 41). 

Downstream about 2 km the flow is again relatively unaltered. In the highly altered and colorful part of the canyon 

(fig. 42), hydrothermal activity remains vigorous near river 

level, although it is hard to see from the canyon rim unless 

the day is cold and humid. Alteration along the deep, narrow part of the Grand Canyon is controlled by the buried 

ring-fracture zone of Yellowstone caldera and by crossing 

fractures. Precanyon sedimentary rocks at the rim of the 

canyon on both sides are bleached white by surficial acidsulfate alteration; rhyolite deeper in the canyon was pervasively pyritized and then oxidized to the yellowish colors 

that give the Yellowstone region its name. Across the canyon is an abandoned channel segment at about half the 

present depth of the canyon. That channel was filled by 

sediments behind an ice dam of Bull Lake(?) age downstream and was probably kept free of ice, at least during 

stagnation of the ice sheet, by local thermal activity. On 

the skyline to the west, above Lower Falls, is the Solfatara 

Plateau flow at the north end of the Central Plateau.

The compositions of the thermal waters discharged 

from springs deep in the canyon are similar to alkalinechloride waters found in the Upper and Lower Geyser Basins.

STOP 24 LUNCH AT BUFFALO FORD PICNIC AREA

The suggested picnic spot is about a mile south of 

the Mud Volcano area. It offers nice facilities near the Yellowstone River.

STOP 25 MUD VOLCANO AREA

A small vapor-dominated system. The Mud Volcano area is an excellent example of a small vapor-dominated hydrothermal system. The thermal discharge is gas-rich, 

and the enclosing rocks and surficial deposits are intensely 

altered. The acidic thermal waters probably reflect shallow

Figure 41. Lower Falls seen from Artist Point.
38 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

condensation above a reservoir in which liquid water is 

subordinate to steam in fractures and pore spaces; steam is 

the pressure-controlling phase (White and others, 1971). 

Gases including F^S rise with the steam and dissolve in 

the condensate to produce the acid waters.

A USGS research drill hole (Y-l 1), north of the main 

parking area and between the road and the river, provided 

some of the data on which the concept of vapor-dominated 

hydrothermal systems is based (White and others, 1971). 

The thermal waters at Mud Volcano are typical of acidsulfate waters in which there is little chloride and compositions are controlled by nonequilibrium water/rock reactions 

in a near-surface oxidizing environment. Brock (1978) 

studied the rate and mode of generation of sulfuric acid in 

the pools at Mud Volcano and concluded that most of the 

acidity comes from bacterial oxidation of elemental sulfur 

at the cool margins of the pools by Sulfolobus sp. Even 

though these boiling pools show little to no surface discharge, there is seepage in and out through their permeable 

sides. Brock (1978) measured rates of seepage by adding 

known amounts of chloride and measuring the rate of dilution. For Moose Pool and Sulfur Caldron his measurements 

give 818 and 452 L/hr, respectively. The amount of sulfate

Figure 42. Hydrothermally altered rhyolite exposed in walls of 

Grand Canyon of the Yellowstone. View from Artist Point looking downstream.

discharged by these pools was estimated to be 44,352 and 

24,504 g/day, respectively.

Very high He/ He ratios, up to 16 times the atmospheric ratio, are found at Mud Volcano. These are the most 

3He-enriched gases in Yellowstone Park (Craig and others, 

1978; Kennedy and others, 1985). Fournier and others 

(1989) attributed the variations of 3He/4He ratios throughout the park mainly to variations in permeability and hydrologic conditions. Recall that most 3He is derived from a 

mantle source, whereas 4He is a product of radioactive decay reactions that occur in the crust. Deep waters tend to 

have high HerHe ratios, and shallow waters tend to have 

low 3He/4He ratios. The 3He/4He ratios tend to be relatively low in the thermal waters that discharge in the Upper 

and Lower Geyser Basins because considerable deep subsurface boiling occurs there, and helium preferentially partitions into the steam, which takes a separate path to the 

Earth's surface from the water. The residual helium-depleted water then picks up radiogenic 4He from the wall rock 

in intermediate-depth reservoirs, and there also is a decrease in the 3He/4He ratio where there is subsurface mixing with meteoric water. The net result is waters that have 

relatively low absolute concentrations of dissolved helium 

and relatively low He/^He ratios. In contrast, at Mud Volcano the 3He-rich steam that separates from boiling water 

at great depth moves upward through relatively impermeable rock, and there is little opportunity for contamination 

by 4He-rich local ground waters. Because the total helium 

concentration in the steam is relatively high and because 

that helium is relatively rich in 3He, the He/ He ratio is 

not changed significantly by the leaching of radiogenic He 

from the wall rock as the steam moves upward.

Temporal changes in activity in the Mud Volcano 

area appear to correlate with local seismicity. Only 

Pinedale glacial deposits are exposed in the Mud Volcano 

area, except for a single outcrop of the Lava Creek Tuff at 

Dragon's Mouth Spring and outcrops near Sulfur Caldron. 

Walk the well-maintained loop trail starting from either the north or south end of the parking lot. Black 

Dragon's Cauldron (fig. 43) is at the topographic high 

point on the trail. From above Mud Geyser at the south 

end of the loop trail, a good view to the east shows the 

west flank of the Sour Creek Dome broken by a graben of 

the Elephant Back Fault Zone.

STOP 26 LE HARDYS RAPIDS

Inflation and deflation of Yellowstone caldera. Following the 1959 magnitude-7.5 Hebgen Lake earthquake, 

a level line was run across the Yellowstone caldera that 

indicated a significant uplift had occurred since the previous level line was run in 1923. Subsequently, several additional level lines have been run to monitor this uplift 

(Pelton and Smith, 1979, 1982; Dzurisin and others, 1986; 

Dzurisin and Yamashita, 1987; Dzurisin and others, 1990).
DETAILED ITINERARY 39

It is not known when the uplift started, but it continued 

until 1984 with an average rate of uplift of about 19.5+1 

mm/yr between 1976 and 1984. The caldera stopped rising 

during the 1984 to 1985 period and since then has been 

subsiding at rates as high as 35±7 mm/yr. However, the 

rate of subsidence has recently decreased. Le Hardys Rapids is near the center of this inflation and deflation (fig. 

44). Although most of the level lines were run in the eastern part of Yellowstone Park, on the southwest flank of the 

Sour Creek resurgent dome (fig. 1), level lines along the 

southwest flank of the Mallard Lake resurgent dome also 

have shown a similar pattern of uplift followed by subsidence. It appears that the entire Yellowstone caldera has 

been subjected to these movements. 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, 1985; Meyer and 

Lock, 1986). Late Holocene uplift at Le Hardys Rapids 

has backflooded the Yellowstone River so that it has become an extension of Yellowstone Lake. The timing of cycles of uplift/subsidence using cores that contain materials 

suitable for carbon-14 dating is currently being studied by 

K.L. Pierce, USGS. Preliminary results indicate that uplift/ 

subsidence events in the past generally have been of longer duration and higher in amplitude than those that have 

occurred this century. The cause of the uplift/subsidence is 

still under investigation. This deformation may be related 

to various mechanisms, including (1) episodic accumulation of magmatic fluids at the top of a crystallizing magma 

with pressure buildup, followed by leakage of fluids and

pressure decline, (2) episodic intrusions of new pulses of 

magma, (3) regional stresses, or (4) a combination of these 

processes.

Walk down the boardwalk to the river. The roadcut across the road exposes only Pinedale alluvial deposits, but the Yellowstone River cuts down into an upthrown 

fault block of the Lava Creek Tuff. The erosionally resistant near-basal spherulitic zone forms the rapids. The Lava 

Creek Tuff here is uplifted within the Yellowstone caldera 

on the flank of the Sour Creek resurgent dome. Outcrops 

across the river are the Lava Creek Tuff overlain by 

Pinedale glacial deposits. The fault that brings the spherulitic zone up to the level of exposure here can be seen 

across the canyon; it and other northeast-trending faults 

that cut the Sour Creek Dome are parts of the Elephant 

Back Fault Zone, a complex graben coaxial with the axis 

of historical uplift and subsidence within the Yellowstone 

caldera.

Below Le Hardys Rapids, in the direction from 

which we have come, the road follows a straight segment 

of the Yellowstone River controlled by a northwest-trending fault that locally breaks the Sour Creek Dome.

STOP 27 YELLOWSTONE LAKE

View across the main Yellowstone Lake Basin. To the 

northeast is Stonetop Mountain (in the southern part of the 

Sour Creek resurgent dome in the eastern part of the Yellowstone caldera), which has a prominent area of hydrothermal

Figure 43. Black Dragon's Cauldron, Mud Volcano area.
40 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

alteration (Sulphur Hills) on its south side. Beyond the south 

(right) flank of Stonetop Mountain is Pelican Cone, which is 

a peak of Eocene andesites of the Absaroka Volcanic Supergroup outside the eastern margin of the caldera. The margin 

continues south along the west front of the Absaroka Mountains to Lake Butte, seen over Stevenson Island, then follows 

the east shore of Yellowstone Lake as far to the right as the 

area of view. The high plateau rising toward the Absaroka 

Mountains is underlain mainly by the Lava Creek Tuff. 

Beyond the southern part of the lake, the Two Ocean Plateau 

is a gently west-tilted fault block the easternmost basinrange fault block south of the Yellowstone Plateau.

STOP 28 SNAKE RIVER OVERLOOK

Overview of geologic and glacial relations. The 

Snake River overlook is an excellent place to view the distant Teton Mountains (fig. 45). It is also a good place to 

observe Pinedale moraines and outwash deposits. The 

southern part of the Yellowstone-Absaroka ice mass 

formed three glacial lobes that flowed into Jackson Hole. 

These lobes are named for the drainages they occupied 

(from east to west): Buffalo Fork, Pacific Creek, and Snake 

River (Pierce and Good, 1990). The succession of glacial 

lobes and associated moraines reflects westward migration 

of the center of gravity of the Yellowstone-Absaroka glacial source area, probably in response to orographic buildup on the western downwind side of the icecap. Great 

volumes of quartzite-rich outwash accumulated and buried 

much of these moraines. Here at the overlook we can see 

moraines of the Burned Ridge phases of the Buffalo ForkPacific Creek lobes. Stones in the moraine across the road 

to the east and in moraines to the south are dominated by 

roundstones that are typical of quartzite of the Pinyon ConCO

CC

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EXPLANATION

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 + 1984,85 survey

_ + 1984,86 survey

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44 A A AAA**

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EXPLANATION

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DISTANCE, IN KILOMETERS

Figure 44. A, Vertical displacement and B, topographic profiles along eastern leveling line from 

Lake Butte to Canyon Junction. Displacement profiles are based on successive surveys from 1976 

to 1987. Also shown, locations of selected benchmarks and place names. Elephant Back Fault Zone 

intersects leveling line at Le Hardys Rapids (benchmark DA 3 1934). (From Dzurisin and others, 

1990).
SELECTED REFERENCES 41

Figure 45. View of Cathedral Group of peaks from Snake River overlook, Stop 28.

glomerate with lesser amounts of Precambrian crystalline 

rocks, Paleozoic limestone, Pennsylvanian sandstone, and 

Eocene andesite rocks, all of which are indicative of a Yellowstone-Absaroka glacial source area. The dropoff to the 

north is a depositional ice-contact slope formed at an ice 

front. The outwash was largely carried by Spread Creek, 

which flowed westward along the south of the glacier toward this stop. Looking across the river to the right of the 

Burned Ridge moraine, the lower terrace level can be seen 

to extend northward to its source at the Jackson Lake moraines. This terrace is pitted with numerous potholes. 

Looking down the Snake River, the prominent lowermost 

terrace marks the lowest level eroded by multiple floods 

during the Jackson Lake phase.

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SELECTED REFERENCES 43

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1982, Geologic map of Upper Geyser Basin, Yellowstone 

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Pierce, K.L., Adams, K.D., and Sturchio, N.C., 1991, Geologic 

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44 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

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Map 1-711, scale 1:125,000, 1 sheet.

White, D.E., 1967, Some principles of geyser activity, mainly 

from Steamboat Springs, Nevada: American Journal of Science, v. 265, p. 641-684.

 1978, Conductive heat flows in research drill holes in 

thermal areas of Yellowstone National Park, Wyoming: U.S. 

Geological Survey Journal of Research, v. 6, p. 765-774.

White, D.E., Fournier, R.O., Muffler, L.J.P., and Truesdell, A.H., 

1975, Physical results of research drilling in thermal areas of 

Yellowstone National Park, Wyoming: U.S. Geological Survey Professional Paper 892, 70 p.

White, D.E., Hutchinson, R.A., and Keith, T.E.C., 1988, The geology and remarkable thermal activity of Norris Geyser Basin, 

Yellowstone National Park, Wyoming: U.S. Geological Survey Professional Paper 1456, 84 p.

White, D.E., Muffler, L.J.P., and Truesdell, A.H., 1971, Vapordominated hydrothermal systems compared with hot-water 

systems: Economic Geology, v. 66, p. 75-97.
APPENDIX A. SUPPLEMENTAL INFORMATION 45

APPENDIX A. SUPPLEMENTAL INFORMATION SUPPLIED TO FIELD-TRIP 

PARTICIPANTS IN ADDITION TO THIS FIELD GUIDE.

The maps and articles listed below were distributed to the WRI-7 field trip participants. They provide additional information 

about many of the subjects discussed in this guide. The trail guides are available at a nominal charge from the U.S. National Park 

Service, and many of the geologic maps are for sale in Yellowstone National Park at Visitor Centers.

Maps:

Grand Teton National Park Official Map and Guide (U.S.

National Park Service). 

Yellowstone National Park Official Map and Guide (U.S.

National Park Service). 

Trail Guide to the Upper Geyser Basin. 

Trail Guide to Fountain Paint Pot and Firehole Lake

Drive.

Trail Guide to Norris Geyser Basin. 

Trail Guide to Mammoth Hot Springs Area. 

Trail Guide to Mud Volcano. 

Surficial Geologic Map of Yellowstone National Park

(U.S. Geological Survey Map 1-710). 

Geologic Map of Yellowstone National Park (U.S. Geological Survey Map 1-711). 

Geologic Map of Upper Geyser Basin (U.S. Geological

Survey Map 1-1371 by Muffler and others, 1982). 

Geologic Map of Lower Geyser Basin (U.S. Geological

Survey Map 1-1373 by Muffler and others, 1982).

Articles:

Effects of Potential Geothermal Development in the Corwin Springs Known Geothermal Resources Area, Montana, on 

the Thermal Features of Yellowstone National Park (Sorey, ed., 

1991, U.S. Geological Survey Water-Resources Investigations 

Report 91-4052).

Effects of Glacial Ice on Subsurface Temperatures of Hydrothermal Systems in Yellowstone National Park, Wyoming 

Fluid-Inclusion Evidence (Bargar and Fournier, 1988).

Geochemistry and Dynamics of the Yellowstone National 

Park Hydrothermal System (R.O. Fournier, 1989).

Geology and Thermal History of Mammoth Hot Springs, 

Yellowstone National Park, Wyoming (Bargar, 1978, U.S. Geological Survey Bulletin 1444; contains a 1:4,800 map of Mammoth Hot Springs). .

History and Dynamics of Glaciation in the Northern Yellowstone National Park Area (Pierce, 1982; abstract with two figures).

Hydrothermal Alteration in Research Drill Hole Y-3, Lower 

Geyser Basin, Yellowstone National Park, Wyoming (Bargar and 

Beeson, 1985, U.S. Geological Professional Paper 1054-C).

Hydrothermal Explosion Craters in Yellowstone National 

Park (Muffler and others, 1971).

Obsidian Hydration Dating and Correlation of Bull Lake 

and Pinedale Glaciations Near West Yellowstone, Montana 

(Pierce and others, 1976).

Quaternary Geology of Jackson Hole, Wyoming (Pierce 

and Good, 1990).

The Track of the Yellowstone Hot Spot Volcanism, 

Faulting and Uplift (Pierce and Morgan, 1992).

Yellowstone Magmatic Evolution Its Bearing on Understanding Large-Volume Explosive Volcanism (R.L. Christiansen, 

1984).
46 A FIELD-TRIP GUIDE TO YELLOWSTONE NATIONAL PARK, WYOMING, MONTANA, AND IDAHO

APPENDIX B. ACTIVITY OF SELECTED GEYSERS IN 

YELLOWSTONE NATIONAL PARK, SPRING 1992.

[Data of R.A. Hutchinson, U.S. National Park Service, Yellowstone National Park. Special thanks are extended to the Yellowstone National Park naturalist staff, especially 

Tom Houghan and Ann Deutch, and all the Thermal Volunteers who have contributed extensive amounts of personal time in monitoring and determining current geyser 

activity of the park. Supers, super long eruptions that are interspersed with more numerous regular eruptions]

Geyser Interval Duration Height (m)

Upper Geyser Basin

Old Faithful

Anemone

Artemisia

Aurum

Beehive

Castle

Daisy

Depression

Fan and Mortar

Fantail

Giant

Giantess

Grand

Grotto

Lion

Little Cub

Oblong

Penta

Plate

Plume

Rift

Riverside

Splendid

Sunset Lake

Vault

74.46 minutes

7-13 minutes (avg. 7 min.)

1 1 hours, 36 minutes (1990)

4 hours, 2 minutes

1 8 hours, 49 minutes

10 hours, 54 minutes

100 minutes

6 hours, 18 minutes

Rare; 2-4 days

Dormant

Irregular, rare; most recent: 10/20/91

Irregular, rare; most recent: 3/25/92

7 hours, 23 minutes (longer if rift active)

~6 hours, longer for marathons

65 minutes within a series

1 1 hours, 13 minutes for a series of one or more eruptions.

76 minutes

Undetermined (7 hours, 17 min. in 1989)

<1 day to >5 days, irregular

103 minutes

42 minutes; varies diurnally

Hours to days

7 hours, 8 minutes

Dormant

Dormant

Rare; 57 minutes in an eruptive series

1.5-5.5 minutes

20-45 seconds

5.5-25 minutes

0.9- 1.2 minutes

4.5-5.25 minutes

15-20 minutes

3.5-4.5 minutes

2.5-3.5 minutes

60-90 minutes

1-5 minutes

90-1 15 minutes

12-43 hours

9-16 minutes

Hours

2-6 minutes

1-15 minutes

6-8 minutes

2-3 minutes

2.5-4 minutes

1-1.5 minutes

Hours

20 minutes

4-10 minutes

Seconds

3-20 minutes

32-56

1-2

2-9

4-6

40-55

20-25

20-30

1-2

15-35

2-9

45-60

20-55

40-60

4-6

15-20

1-2.5

3-8

1-2

1-2

6-8

1-2

20-25

25-45

0.5-5

1-4

Midway Geyser Basin

Excelsior

Flood

Opal Pool

Till

West Flood

Dormant since 9/16/85

10-42 minutes; bimodal pattern

Dormant, rare

Active, undetermined, est. 8-9 hours

42 minutes

1.5-2 minutes

8-8.5 minutes

20 minutes

30 minutes

0.5-2 minutes

8-25

2-4

6-20

4-7

0.5-1.5

Lower Geyser Basin

Great Fountain

White Dome

Pink Cone

Morning

Fountain

Clepsydra

Deep Blue

Deep Blue's Satellite vent

Kaleidoscope

Unnamed 1964 blowout

Imperial

11-15 hours

Irregular; 19-271 minutes

15 hours, 14 minutes (1989 avg.)

Dormant since 8/29/91

-6-9 hours

Almost continuous

20-30 minutes

Dormant

Irregular

Irregular, now rare

Dormant (continuous minor boil)

45-60 minutes

2 minutes

1 hour

10-25 minutes

Irregular

Hours-Days

2.5-3.5 minutes

Continuous

0.5-2 minutes

Not applicable

Months

25^5

7-9

4-6

15-45

9-25

6-10

1-13

10-15

1-10

10-14

0.5-1

Norris Geyser Basin

Steamboat

Echinus

Ledge

Porkchop

Vixen

4 days-50 years; latest 10/2/91

50-60 minutes

Supers: 2-3 hours

Dormant

Destroyed 9/5/89 by hydrothermal explosion

Very rare

3-40 minutes

7- 13+ minutes

Supers: 30-60+ minutes

5-90+ minutes

47+ months

Seconds

70-120

10-30

10-30

20-35

3-11

1-3
180 OrtonHan, 155$. Oval Mad

The Onto State University 

Cofumous. OH 43210
SELECTED SERIES OF U.S. <3EQL0G!QAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly).

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Professional Papers are mainly comprehensive scientific reports of wide and lasting interest and importance to professional 

scientists and engineers. Included are reports on the results of 

resource studies and of topographic, hydrologic, and geologic 

investigations. They also include collections of related papers 

addressing different aspects of a single scientific topic.

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results of resource studies and of geologic and topographic investigations, as well as collections of short papers related to a specific 

topic.

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significant interpretive results of hydrologic investigations of wide 

interest to professional geologists, hydrologists, and engineers. The 

series covers investigations in all phases of hydrology, including 

hydrogeology, availability of water, quality of water, and use of 

water.

Circulars present administrative information or important scientific information of wide popular interest in a format designed for 

distribution at no cost to the public. Information is usually of shortterm interest.

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areas.

Oil and Gas Investigations Charts show stratigraphic information for certain oil and gas fields and other areas having petroleum 

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Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or 

irregular areas at various scales. Pre-1971 maps show bedrock 

geology in relation to specific mining or mineral-deposit problems; 

post-1971 maps are primarily black-and-white maps on various 

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Hydrologic Investigations Atlases are multicolor or black-andwhite maps on topographic or planimetric bases presenting a wide 

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principal scale is 1:24,000, and regional studies are at 1:250,000 

scale or smaller.

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