Geological Survey Bulletin 1444 Geology and Thermal History of Mammoth Hot Springs

Perhaps the most outstanding characteristic of the hot springs at Mammoth is the rapidity of change. A hot spring may dry up at one location and a new spring begin flowing a short distance away within a few days. Also, a spring may have a large discharge one day, be completely dry the next day, and flow again the following week. Numerous detailed observations of rapid changes in thermal activity at Mammoth have been recorded by park naturalists and other observers through the years, but such detailed records are beyond the scope of this report. Instead, tables 5 and 6 and this section summarize the major changes in hot-spring activity that have been recorded since the Hayden Survey.

Recorded history and temperatures of named thermal springs at Mammoth Hot Springs, 1870-1974 (table 5).

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Recorded history and temperatures of unnamed thermal springs at Mammoth Hot Springs, 1954-1974 (table 6).

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Terrace Mountain Travertine

The top of Terrace Mountain is capped by 15 to as much as 75 m (Hayden, 1872; Allen and Day, 1935) of horizontally bedded, dense travertine (fig. 21) which, according to Hayden, may have precipitated from hot springs in the bottom of a lake. A small patch of travertine on the west side of Bunsen Peak (fig. 2) is probably contemporaneous with the Terrace Mountain travertine (Allen and Day, 1935). The Hoodoos and Silver Gate (figs. 2, 21) are part of a landslide deposit that is composed largely of travertine from Terrace Mountain.

Terrace Mountain (on the skyline) and chaotic landslide blocks of Silver Gate (foreground) (fig. 21).

Schlundt and Moore (1909) calculated that the travertine from Terrace Mountain was deposited about 20,000 years ago. Their age calculation, based on the rate of decomposition of the radioactive element radium, is not now regarded as accurate, because of numerous possible errors of which they were unaware at the time. A more recent age determination, based upon thorium-uranium isotope ratios, yielded a date of 63,000±9,000 years for travertine from Terrace Mountain (Rosholt, 1976). The latter date is in good agreement with the geologic evidence, in that Terrace Mountain is clearly older than the Pinedale glacial deposits (10,000-50,000 years ago) that mantle it (fig. 22). In any case, both lines of evidence point to the fact that the hot springs that deposited the travertine have been inactive for many thousands of years.

Boulders on top of Terrace Mountain (fig. 22). Boulders were deposited by a glacier of Pinedale age. (Photograph courtesy of L. J. P. Muffler, U.S. Geological Survey.)

Pinyon Terrace

The remainder of the travertine deposits, which extend continuously from Pinyon Terrace to the Gardner River, as well as a few scattered outcrops found in Snow Pass and near the Sheepeater Canyon Bridge (fig. 2), are all younger than Pinedale age (Allen and Day, 1935). Young, horizontally bedded travertine deposited on top of Pinedale glacial deposits can be seen along part of the north-south tensional fracture near the east edge of Pinyon Terrace (a small section of the fracture is shown in the lower left corner of pl. 1).

The only record of hot-spring activity on the densely forested Pinyon Terrace is a spring (with a temperature of 41.8°C in 1925) labeled simply Pinyon Terrace in Allen and Day's (1935) table of hot-spring temperatures for Mammoth Hot Springs. They also mention "a few oozing springs" (presumably cold) but do not indicate the location of any of the springs.

There are no active hot springs on this terrace now. However, hot gases escape through underground channels near the east edge of the terrace, and acid alteration is in progress there (near the vapor vent in southwest corner of area shown on pl. 1). Native sulfur (S) and gypsum (CaSO₄•2H₂O) are precipitated there as a result of fumarole activity. Vapor vents are quite common on the travertine terraces; however, acid-altered areas occur at only a few locations (Bargar and Muffler, 1975) where the hot vapors contain enough hydrogen sulfide to form gypsum and sulfur deposits.

Old terraces between Hotel Terrace and the Gardner River

The region of major hot-spring activity is between Pinyon Terrace and Hotel Terrace; the area between Hotel Terrace and the Gardner River has few thermal springs (pl. 1). One spring with a very large rate of discharge is the source of Hot River, which emerges from beneath an old, partly collapsed travertine ledge near the level of the Gardner River (fig. 23). The discharge channel is about 2.7 m wide and 0.6 m deep, and the stream flows for about 130 m before emptying into the river. Its underground route can be followed upstream for an additional 140 m through a series of collapse features (pl. 1), one of which (MHS—1) contains visible flowing water.

Hot River (fig. 23). Hot carbonated spring water undercut the old horizontally bedded travertine deposits until individual blocks collapsed under their own weight. Direction of flow is toward viewer.

The spring which feeds Hot River has the greatest discharge of any hot spring in Yellowstone National Park. Several discharge measurements reported by Allen and Day (1935) show that the flow of Hot River ranges from about 33 to 40 m³/min, with the average flow being slightly greater than 38 m³/min. A more recent measurement by R. O. Fournier and D. E. White (U.S. Geol. Survey, 1967) is about 41 m³/min. Much of the flow of this thermal spring probably consists of water that previously issued from other hot springs and trickled down into underground channels feeding Hot River. Allen and Day also suggest that the variation in temperature of Hot River at different times of the year may be caused by dilution with cold meteoric water.

Derivation of the name Hot River is uncertain; however, H. M. Majors III (unpub. data, 1962) indicates that the name probably originated with a group of U.S. Geological Survey scientists, headed by Arnold Hague, who studied the geology of Yellowstone Park in the 1880's. Hot River has also been called "Boiling River" (H. M. Majors III, unpub. data, 1962), "Warm-Stream Creek," and "Chestnutville" (Haines, 1974).⁵

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⁵According to Majors (unpub. data, 1962), many of the thermal features at Mammoth were named by members of the Hague expedition or by early visitors and residents of the area, and several of the hot springs and terraces have borne more than one name, as did Hot River.

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Early maps of Mammoth Hot Springs (Hayden, 1872; 1883) show three or four hot springs (temperatures less than 49°C) near the level of the Gardner River 100 m or so upstream from Hot River and two thermal spring areas (temperatures about 60°C) between the base of Hotel Terrace and the road to Gardiner. The only subsequent reference to hot-spring activity at either location was Majors' (unpub. data, 1962) description of a spring on the river bank about 100 m above Hot River. In May 1974, one small spring (MHS—2) was found near the location Majors described, but there were only a few vapor vents between Hotel Terrace and the road to Gardiner (pl. 1).

Hotel Terrace

The only recognizable hot-spring orifice on Hotel Terrace is the defunct fissure ridge on the east edge of the terrace (pl. 1). No hot-spring activity has ever been recorded on this terrace, but two vapor vents can often be seen on cold mornings.

An age determination by Prof. Herman Schlundt (reported in Bauer, 1933) indicates that the travertine of Hotel Terrace was deposited about 3,200 years ago. This age and the one for Liberty Cap are not regarded as numerically accurate but are probably of the right order of magnitude.

Hymen Terrace

Hymen Terrace is a small inactive terrace at the southwest edge of Hotel Terrace. An extinct hot-spring cone, about 14 m high and 6 m in diameter at the base (Allen and Day, 1935; H. M. Majors III, unpub. data, 1962), dominates the setting of Hymen Terrace (fig. 8). Indeed, this long-dead hot-spring orifice, named Liberty Cap by the 1871 Hayden expedition (Hayden, 1872), reigns supreme over the entire Mammoth Hot Springs.⁶

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⁶According to Schlundt's age dating, Liberty Cap was formed about 2,500 years ago (reported in Bauer, 1933).

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Hymen Springs, inactive since about 1936 (C. M. Bauer, unpub. data, 1946) was evidently a major attraction on Hymen Terrace from the time of the earliest recorded observation in 1870 (Peale, 1883) until the 1930's. In recent years, the only active thermal spring on this terrace (Roadside Spring) was located near the north end of the Liberty Cap parking lot (C. C. Alleman, unpub. data, 1962); however, its vent is not discernible at the present time.

Opal Terrace

Opal Spring and Terrace lie at the base of Capitol Hill just across the Grand Loop Road east of Liberty Cap (pl. 1). Evidently Opal Spring was inactive at the time of the Hayden Survey; however, Crowe (1933) indicated that it may have been active during the early 1890's. After being dormant for a number of years, Opal Spring began flowing again in about 1926 (D. P. Merrill, unpub. data, 1963) and has remained intermittently active to the present time.

During the 1940's, travertine deposited by Opal Spring began encroaching upon a tennis court in the northern part of the terrace. The spring eventually won the battle for space. In 1947 the tennis court was removed in compliance with the park's policy of not interferring with natural processes (J. S. Desanto, unpub. data, 1962).

Two small hot springs on Opal Terrace were active in 1974 (pl. 1). Spring MHS—3 began flowing about 1970 (G. T. Morrison, unpub. data, 1970), and spring MHS—4 has apparently been intermittently active since 1963 (W. R. Phillips, unpub. data, 1963). A third spring (MHS—5), situated on the grassy bank south of Opal Terrace, is merely a warm seep with very little flow; however, travertine is being deposited along its runoff channels.

Palette Terrace

The two principal hot springs on Palette Terrace are Palette Spring (also known as Old Palette Spring) and New Palette Spring (sometimes referred to as Palette Extension). Palette Spring has been intermittently active at least since 1878 (Hayden, 1883), while the recorded activity of New Palette Spring dates back to about 1944 (D. P. Merrill, unpub. data, 1963).

Hot-spring activity occurs at three other locations on or near Palette Terrace. Spring MHS—6, situated at the base of the terrace below New Palette Spring, discharged a minor amount of hot water in 1972 and 1973 but was. dormant in May 1974. The other two springs (MHS—7 and —8) apparently have had recurrent activity since 1964 (W. R. Phillips, unpub. data, 1964).

Cavern and Reservoir Springs

Cavern and Reservoir Springs lie southeast of and at or slightly below the level of Palette Terrace (pl. 1). Cavern Spring's recorded activity dates back to 1955; however, this spring probably discharged for some time prior to 1955. Condon (1955) indicated that the large cavern (evidently the source of the name Cavern Spring) previously located here was nearly sealed by travertine deposition.

Reservoir Springs have been intermittently active since the days of the Hayden Survey. Originally these springs were named Bath Springs because the tepid water was channeled into nearby bath houses (Peale, 1883).

Peale (1883) provided the only record of a hot spring known as Little Joker, which apparently was located east of the Grand Loop Road across from spring MHS—6. On the west side of the road, a spring called Fan or Little Spouter evidently was active between 1961 and 1973; however, this spring was not found in May 1974. C. C. Alleman (unpub. data, 1961) indicated that the spring was about halfway between Cavern and Reservoir Springs, and J. J. Whitman (unpub. data, 1973) placed it directly east of Cavern Spring.

Minerva Terrace

Minerva Terrace contains two currently active hot springs. Minerva Spring (fig. 9), originally named Cleopatra (Hayden, 1883), issues from a fissure ridge (see pl. 1) and is depositing a well-developed series of terracettes. Although dormant for short periods of time (N. W. Scherer, unpub. data, 1932; G. C. Crowe, unpub. data, 1 932), Minerva has discharged almost continuously since the days of the first Hayden expedition and has been one of the most colorful and popular attractions at Mammoth Hot Springs.

The spring now named Cleopatra has been active at least since 1906 (Schlundt and Moore, 1909) and was originally called Diana Spring (a name that apparently persisted until sometime in the 1920's). According to D. P. Merrill (unpub. data, 1969), Cleopatra was one of the most active and popular springs at Mammoth during the 1930's; however, since the 1940's, this spring has been characterized by only minor intermittent discharge.

Main Terrace

Main Terrace (fig. 3) contains some of the largest and most consistently active hot springs at Mammoth, including Blue, Canary, Jupiter, Main, Naiad, New Blue, and Trail Springs. Large amounts of water discharging from these springs and the colorful algae living in the hot springs and their runoff channels have made this terrace an outstanding attraction since the days of the Hayden Survey.

Hayden's (1872) first map of Mammoth Hot Springs shows a thermal spring named Blue Spring⁷ near the northwest corner of Main Terrace. Apparently when the spring ceased flowing, the name "Blue Springs" was given to the hot springs that subsequently appeared near the center of the terrace (Weed, 1889). Later renewal of discharge near the former site of Blue Spring led to the name New Blue Springs, which has been retained to the present time. Schlundt and Moore (1909) indicated that both springs were active in 1906; however, very little information on the activity of New Blue Springs was found except for recent years. On the other hand, several observations through the years suggest that Blue Springs have been characterized by persistently recurrent discharge.

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⁷Blue Spring was named for the apparent blue color of the water; however, it should be pointed out that the water is clear rather than blue. This spring and a few other deep thermal pools at Mammoth only appear blue because of scattering and absorption of light rays (Alien and Day, 1935).

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The southwest corner of Main Terrace is the site of relatively recent (since 1962) thermal activity originating from a group of hot springs collectively known as Trail Springs (evidently from their position near the old trail in that part of the terrace). The volume of water discharging from these springs has varied considerably. In 1971, the flow from Trail Springs covered nearly an acre (G. T. Morrison, unpub. data, 1971), whereas in May 1974, there was only minor discharge from a single vent.

Mound, Pulpit, and Jupiter (Marble) Terraces top the steep scarp along the eastern face of Main Terrace. Algae living in the fluctuating runoff channels of Canary, Main, Jupiter, and Naiad Springs usually decorate parts of these slopes with an array of splendid colors. As the runoff channels change course along the face of the terraces, the algae die and the dry travertine deposits soon become white and then dingy gray.

Canary Spring, near the southeast corner of Main Terrace (fig. 3) has had intermittent discharge since the 1870's (table 5). Originally called "Sulphur Spring" (Hayden, 1883), this hot spring probably owes both names to filamentous sulfur-depositing bacteria commonly found growing in the waters of some thermal springs.

The two large depressions near the east edge of Main Terrace (pl. 1) were named Main Springs by the first Hayden expedition because that was the site of the principal hot-spring actiyity at that time (Hayden, 1872). Through the years, the two pits have been alternately full and empty (table 5). In 1972, the larger of the two was filled with hot water (fig. 3) but was dry again in May 1974.

Mound Terrace, in the northeast corner of Main Terrace, is a fissure-ridge deposit. The line of hot springs along the southern part of the fissure, called Jupiter Springs, evidently has been intermittently active since the 1870's. Naiad Spring, perched on the eastern face of Mound Terrace and apparently having a subterranean channel independent of the fissure ridge, has had recurrent discharge since at least 1878.

Prospect Terrace

Prospect Terrace (fig. 3), an old travertine terrace with only minor recorded hot-spring activity, probably was named for the scenic view of the lower terraces from a section of its eastern rim called The Esplanade (H. M. Majors III, unpub. data, 1962) (pl. 1). The part of the rim that protrudes peninsulalike out over Main Terrace is an old defunct hot-spring deposit, named Fissure Ridge by the Hayden Survey (Hayden, 1883). The only record of thermal activity on this ridge is Peale's (1872) observation that the fissure, extending along the entire length of the rounded linear mound, was lined with sulfur crystals deposited by vapor escaping from the gurgling waters far below.

Cupid Spring, in the notch between Fissure Ridge and the mass of Prospect Terrace (fig. 10), has a recorded history of fluctuating but nearly continuous discharge since about 1931, when the spring deposits began sealing a cave called Cupid's Cave (W. B. McDougall, unpub. data, 1931). The only other prior records of hot-spring activity at this location describe geyserlike discharge, in which two small springs intermittently spurted hot water to a height of about 1 m (Peale, 1872). There are no true geysers at Mammoth Hot Springs; however, if gas comes out of solution in sufficient volume and rate, the water can be ejected to a height of several centimeters or more.

A vapor vent located just across the Terrace Loop Road west of Cupid Spring marks the former site of Baby Spring (pl. 1). This hot spring, possibly named for its small size, was intermittently active during the years 1932-65 (table 5). Three other currently active hot springs on Prospect Terrace are Prospect Springs (intermittently active since about 1954 (C. C. Alleman, unpub. data, 1954)), spring MHS—9 (having recurrent discharge since about 1963 (unpublished data from the naturalists' files)), and spring MHS—10 (minor flow in 1973 and 1974).

Narrow Gauge Springs and Cheops Mound

One of the best examples of an active fissure ridge is Narrow Gauge Springs (fig. 24), which apparently was named for the ridge's resemblance to an old-time narrow-gauge railroad track bed (H. M. Majors III, unpub. data, 1962). Narrow Gauge Springs, intermittently active since about 1890 (Guptill, 1890), may have had its greatest recorded activity in the late 1920's, when Joyner 1928c) counted 180 hot springs and 70 vapor vents along the top of the ridge.

Narrow Gauge Terrace (fig. 24). This feature is a fissure ridge that is intermittently active (table 5).

Cheops Mound, another fissure ridge located just south of Narrow Gauge Terrace, has no recorded activity; however, it is shown as a hot spring on one of the old maps of Mammoth Hot Springs (Hague, 1904). The north side of the mound has an excellent series of well-preserved old terracette deposits.

Angel Terrace and Glen Springs

Angel Terrace, intermittently active from the 1870's until about 1 953 (table 5), was periodically a very popular attraction when large volumes of water inundated the ter races, allowing the colorful algae to grow profusely. In fact, H. M. Majors III (unpub. data, 1962) indicated that this terrace was apparently named for the delicate, celestial imagery of the pink microorganisms that lived in the hot springs and runoff areas.

One of the smaller active fissure-ridge formations, named Glen Springs, lies in a hollow between two older nearly parallel fissure ridges just north of Angel Terrace (fig. 17). This spring is somewhat hidden from view, which may account for the scanty record of its activity; however, the available data (table 5) suggest that Glen Springs has been intermittently active since the 1870's.

Highland Terrace area

The Highland Terrace area, as defined by Peale (1883) and later by G. D. Marler (unpub. data, 1961), includes all the travertine deposits in the southwestern part of the area shown on plate l. The northeastern part of this area is known as Highland Terrace. No hot-spring activity has been recorded on the old fissure ridge called The Buttress. New Highland Springs have been intermittently active since at least 1928 (Arnold, 1928b), and from the late 1950's to the present this group of springs has been one of the most spectacular areas at Mammoth.

Highland Spring was intermittently active from 1871 until about 1970 (table 5). The remaining springs on Highland Terrace proper (Cedar Tree Spring and springs MHS—11, —12, and —13) all have very short records of activity (tables 5, 6). Spring MHS—11 currently discharges only a trickle of water from a few vents along a rather small, slightly rounded fissure ridge, whereas the rate of flow of the other three springs has ranged from less than 4 L/min to about 40-80 L/min during the years of observati0n (1972-74).

Several of the remaining hot springs in the Highland Terrace area are small pools ranging from a meter to about 50 m in diameter. Bath Lake, the largest of the pools, has completely dried up at least twice during its recorded history, once during the 1920's (Arnold, 1928b) and again in the 1950's (G. D. Marler, unpub. data, 1961). The supply of hot water that feeds Bath Lake began flowing again after the 1959 Hebgen Lake earthquake; the earthquake is not known to have been directly responsible (G. D. Marler, unpub. data, 1962).⁸

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⁸In the past, numerous earthquakes have been felt at Mammoth Hot Springs, some of which caused landslides at Golden Gate and structural damage to roads and buildings in the area (Fischer, 1971). While such disturbances in the Earth's crust probably caused changes in hot-spring activity at Mammoth, few such changes have been recorded, perhaps because the thermal-spring activity is so variable.

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Evidently the name Bath Lake originates from this warm pool's early popularity as a bathing spot (H. M. Majors III, unpub. data, 1962). Early tourists who swam in Bath Lake probably viewed the experience with mixed emotions: Wingate (1886) indicated that, although he enjoyed the warm soothing water, his skin became encrusted with calcium carbonate to the extent that his body appeared to be whitewashed.

Another hot-spring pool, about 25-28 m in diameter and known as Painted Pool, is located just south of Bath Lake (pl. 1). Apparently the name Painted Pool was originally given to a smaller pool (Hague, 1904; novv MHS—18), but probably when the small pool became dormant, the name was switched.

Several additional small pools, most of which are unnamed (pl. 1), occur in the Highland Terrace area; the only named pools are Sulfur Spring, Soda Spring, and Poison Spring. The exact location of Sulfur Spring, which first appears on the 1871 map of Hayden (1872), is uncertain, but the spring with this name on plate 1 is in a strongly acid-altered area that contains gypsum and sulfur (Bargar and Muffler, 1975).

The name Soda Spring has at various times been applied to at least three springs, most often to a warm spring in a grassy area about 180 m west of Painted Pool (pl. 1). However, a cold spring in Snow Pass (fig. 2) and the spring in a marshy area 30 m north of Squirrel Springs also have had this name (Gooch and Whitfield, 1888; Allen and Day, 1935).

Poison Spring, located about 150 m southwest of Painted Pool (pl. 1), has a cavelike cavity at its southern terminus. W. R. Phillips (unpub. data, 1962) indicated that numerous birds have been asphyxiated by carbon dioxide gas in the cave.

One of the few active isolated cone-type hot springs (spring MHS—24, fig. 25) occurs about 30 m southwest of Poison Spring. This spring is particularly notable as representing an early stage in the development of a cone such as Liberty Cap (fig. 8).

Spring MHS—24 (fig. 25). Pencil above small stick (circled) protruding from lower part of deposit is about 15 cm long. When first observed in September 1972, the height of the spring was exactly equal to the level of the stick. In September 1973, the cone was about 74 cm high, and by the following May, the date of this photograph, it had grown to a height of nearly 94 cm. Reddish-brown color is due to algae. Yellowish fibrous material surrounding the orifice of the spring is bacteria.

The Highland Terrace area also contains several active and numerous inactive fissure ridges. Devil's Kitchen Springs, Orange Spring Mound (including Tangerine Spring) (fig. 16), Squirrel Springs, and White Elephant Back Springs and Terrace (figs. 13, 18) have all been intermittently active since the 1870's.