SOME FEATURES of YELLOWSTONE NATIONAL PARK' IRWIN B. DOUGLASS2 Northern Montana College, Ha-,
Yellmstone National Park affords a n un@rallekd opportunity to study some of the chemical reactions that take place in Nature's laboratory. The reacting substances in Yellmstone are the gases rising from the uncooled magmatic masses far b e l m the surface, the characteristic rocks of the region, the ground w t e r which penetrates the rocks to varying depths, and the atmospheric oxygen which interacts with certain of the magmatic gases. The hot springs are of great variety, for each represents the result of a peculiar set of conditions found b e l m the surface at that point. I n this @per the characteristics
Montana
of the different types of springs and the chemical phenomena associated with the phase of volcanism found i n Yellmstone are discussed.
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Y
ELLOWSTONE National Park as a region containing many natural wonders has become well known to people from all over the world. The geology Of the region and the causes of the thermal phenomena are explained annually to hundreds of ' Published with the permission of the Director, National Park thousands of visitors the representatives of the Se~ce. ' Temporary Ranger Naturalist, Yellowstone National Park. National Park Service. The chemical story, on the 422
other hand, is less well known and was imperfectly eruptions which scattered volcanic bombs and ash understood until 1935 when Allen and Day of the Car- over wide areas. In some places the dbbris accumunenie Geophysical Laboratory published the results of lated to a depth of over two miles. The depositheir masterly work. The author's experience as a ranger naturalist in Yellowstone has convinced him that this fascinating chemical story should be made more readily available for students of chemistry and others interested in the chemistry of natural phenomena. For a more exhaustive treatment of the subject and for the evidence supporting certain statements made in this paper the reader is referred to the monumental treatise of Allen and Day, from which most of the material has been taken. The presentation, however, is that which might be employed were the author to enjoy the privilege of having a group of chemists a t an evening campfire program in Yellowstone Park. THE GEOLOGICAL HISTORY OF YELLOWSTONE NATIONAL PARK
The area which is now included in Yellowstone National Park was once a part of the great trough which lay between prehistoric Appalachia and Cascadia, extending north and south from the present Gulf of Mexico to the Arctic Ocean. During the alternate advance and recession of the seas in this trough, the beds of shale, sandstone, and limestone were laid down to a depth of many thousands of feet. Toward the close of the Cretaceous Period (sixty to one hundred million years ago) part of the bottom of the trough was forced up as the first Rocky Mountains. Subsequent erosion carried away much of the height of these mountains and then followed the second Rocky Mountaii YELLOWSTONE CANYON HAS BEEN ERODED TAROUGH RHYOLITE EXTENSIVELY DECOMPOSED BY THERMAL GASES. THELOWER FALLS IS LOCATED AT A POINT WHERETHE ROCK period of uplift. UNALTERED At some time during the IS PRACTICALLY second uplift the earth's crust became weakened in the region of Yellowstone National tion of this material took place during periods sepaPark, and violent volcanoes broke forth. These early rated by thousands of years. On some precipitous periods of activity were characterized by explosive cliffs in the park where streams have eroded through the
agglomerate there are a dozen or more layers of petrified trees-trees which a t one time grew on soil formed from volcanic d6bris of an earlier period and were then buried in a later eruption. Some of these fossil trees are ten feet in diameter. TABLE 1
vo~cnmcGbsss mom Y-OWSTON=P
a ' COI 01 H, CH, Nz A H27. Swn ~ l ~ G r o ~ I e r ~ i n N96.55 o r - 0.00 0.40 0.10 0.45 2.50 100.00 tir ~~i~ Spting in Porcelain 89.20 1.40 2.30 0.55 0.55 0.00 100.00 Locolily
Basin
G~~~in
+
0.90 3.40 0.00 10.60 85.10 0.00 1m.00
Upper Ensin Pirehole Pool in Ian. 63.05 5.46 0.00 1.55 29.95 0.00 100.00 Earin One of Washburn 81.15 0.00 0.2513.20 3.70 0.55 100.00'
S?riW
Cslcrte Springs in 93.20 0.00 0.00 Tower Falls area Mammoth Hot Spling 99.55 0.10 .1voiter . Terra%
0.00 1.30
5.50 100.00
0.35 0.00 100.00
-
-
selsted from -my analyses to illustrate the madmum amount of each constituent. 6 A complete analysis of the superheated gases (temperature 138%) from this vent gave: H.0, 99.600; COX. 0.386; HzS, 0.010; Hz, 0.002: CH,, negligible; N, A, 0.00. =This gas contained 1.15 vr cent. &He.
+
The forces of erosion cut deeply into the volcanic deposit until a t a time variously estimated a t from eight to twenty-five million years ago the.main part of what is now Yellowstone National Park was a great basin surrounded by lofty mountains. There followed another periodof volcanicactivity and into thishsin tremendous quantities of rhyolitic lava poured. Whether the flow was continuous or intermittent is a ques,tion for others to decide, but the result was the same as though a huge lake of lava had been formed which was twenty-five to forty miles wide and three thousand feet deep. The rhyolite solidified and formed a level
level that from an airplane one seems to be looking down upon a wooded portion of the prairie. THE CAUSES OF THERMAL ACTIVITY
The surface evidences of volcanism mav be classified in three phases. The first is the erupti;e stage when molten rock or rock fragments are being expelled from vents in the earth's crust by the expulsive forces, in large part a t least, of confined volcanic gases. In the second or fumarole stace volcanic cases are escaninn" " from cracks or breaks in the surface of the ~reviouslv expelled material or of the native rocks. During this phase the escape of subterranean heat is so rapid that any rain or other surface water is immediately evaporated and thus is prevented from penetrating below the surface. The third phase develops when the surface rocks cool sufficientlyto permit the penetration of ground water. In this stage the depth to which the ground water penetrates will be very largely determined by the surface topography and i t is conceivable that an area of shallow or negligible penetration may be very near one where the penetration takes place to a much greater depth. In any event the rising gases encounter the descending water and some of the constituents of the gases dissolve and condense in the water, heating and acidifying it so that i t has the power to attack the rocks through which i t circulates. When the water reappears a t the surface i t is hot and contains many dissolved or colloidally dispersed constituents derived from the gases and from the rocks. In Yellowstone National Part the first phase of volcanism has long since disappeared. The third stage is the predominant feature of the region, although
-
.
TABLE 2 W ~ r s ANALTSBS a OI SPP~NOS ZN VBLLOWSTONB PAX (In pa*
Sawu
Ii
Rauing Mountain Fountain Paint Pot Paint Pot near Mud Volcano
13.3 0.87
NIII No
K
Mg
Ca
Fe
per Million) A1 SiO,
CI
SO,
SnDi
Con
BCOa &Os
B
As06
Told
Acid Arcor
Big Sulfur Pool near Mud Volcano Devil's Ink Pot, Washburn Sotine A l k d i m A& Excelsior Geyser Old Paithful Sapphire Pool
-
N0rri.i Basin. Pool Spring No. 17 Sotins No. 7
4
8
9
4 17
1 1
2.58 140
9
21 21
43.2
26
16
17 11
0.2
709
24
8 12
0 0 0
410 372 453
14 0 31 17 Trace
15 247 Trace 0.8 176 1
704
33 59
45
201
834
14 17
146
540
3149
90
5.8 2320
6 5
4 3.8
40
3.7
3 4 4 Trace
1
3
0
237 271 357 435 321 307
121
2 2 21 Trace 15 2
562 100 66
21 0 400
0
0
8 18 12
20 22 22
1650 1360 1684
Congress
3.0 0.07 0
21 458 108 28 485 91 0 483 120
3 2 2
10 8 6
8 2 4
3 3 0
509 034 414 764 576 802
56 71
338
0
Tr-
46 169
503 188 35
0 1
0
29
0
871
38. 30
5.0 4.5
2260 2010 2080
T&~L&Z Area
Mammoth Hot Spring, Jupiter Turaee
143
plateau of 8000 feet average elevation amid the surrounding mountains. In the millions of years since the last rhyolite solidified the plateau has been intersected by streams and has been eroded somewhat by glacial action, but in general contour it remains so
528 Trace
there are a dozen or more vents from which gases are escaping a t much higher temperatures than the boiling point of water, indicating that the fumarole stage has not entirely disappeared. The hottest vent observed registered 138'C.
Some idea of the extent of the thermal activity in the park may be gained from the fact that there are some three thousand hot springs scattered in groups unevenly over an area roughly sixty by thirty miles. Basing their calculations on the total flow of the springs and on the average temperature of the water Allen and Day estimate that there are some 220,000 kilogramcalories of heat, or enough to melt three tons of ice, given out every second. This entirely disregards all heat lost by evaporation. The intensity of the thermal activity was well illustrated in a test hole drilled in the Norris Basin. A temperature of 205'C. and a steam pressure of three hundred pounds per square inch were encountered within two hundred sixty-five feet of the surface. THE CHARACTER OF THE MAGMATIC GASES
to form a crystalline rhyolite or a granite. The superheated steam vents in Yellowstone are good evidence that there, too, steam is coming to the surface from the magmatic masses which are still uncooled and uncrystallized far down below the surface. Allen and Day are of the belief that this steam may constitute ninetynine per cent. of the original gas. The gas analyses of Table 1 indicate that in Yellowstone as well as in other volcanic regions carbon dioxide, hydrogen sulfide, hydrogen, methane, nitrogen, and argon are constituents of the magmatic gases. Some of the nitrogen and argon and all of the oxygen found in some samples are believed to result from atmospheric contamination in the upper strata. The ethane and larger quantities of methane in other samples are believed to be distillates from sedimentary rocks, as is also the excessive amount of ammonia found in some waters. Hydrogen chloride and hydrogen fluoride are com-
The collection of the gases issuing from an active volcano may be hazardous, but once accomplished the identity and relative abundance of the constituents of the gas mixture can be determined with certainty. In Yellowstone, on the other hand, the mag.matic masses from which the gases are believed to be issuing lie a t such a great depth that direct analysis of the gases is impossible. Careful analyses have been made of the gases esca~incr from certain vents and springs, but it is recognized that these may contain atmospheric contami. .. nants or other gaseous A-ario,zoi park smite ~ h ~ a ~ ~ products which have ON ROARING MOUNTAIN THE DEPICIENT SUPPLY O F GROUND W A T E R HASAIDEDIN PRODUCING AN distilled out of sedi- ACIDAREA.THESULFURIC ACIDFORMED BY THE OXIDATION OF THE HYDROGEN SULFIDE HASKILLED YEARSAGO THE GASES AND IS ACTIVELY LEACHING THE RHYOLITE.A NUMBERDP mentary rocks below ALL VEGETATION the surface, ~h~~ ESCAPED WITH A ROARING SOUND GIVINGTHE MOUNTAIN ITSNAME must, likewise, have lost certain original constituents which have been dis- mou constituents of volcanic gases, but one would solved or condensed before the gases reached the sur- hardly expect to find them issuing from the ground in face. Table 1 illustrates the results of several gas Yellowstone where the second phase of volcanism has analyses. Evidence for gases lost before the surface is almost entirely disappeared. Allen and Day made reached is derived from analysis of the spring waters of careful search for them in the gaseous emanations but the Park. Table 2 shows several typical water analyses found no trace. The fluoride and chloride content of and the significance of the various results will be the waters, however, may arise in part, a t least, from these gases which dissolve in the ground water and are pointed out later. neutralized through interaction with rock constituents. Steam has long been recognized as a constituent of In cavities of rocks blown out of Vesuvius and around volcanic gases. The torrential rains which frequently follow volcanic eruptions are believed to result from fumaroles in other volcauic regions there have been the condensation of the volcanic steam. The lava or observed sublimates of the chlorides and fluorides of magma carries water in solution, and if it solidifies as a sodium and potassium. To volatilize these compounds glass it retains more of this water than if it crystallizes and carry them to the surface would involve tempera-
.d,
. ~.
W
~ a p h
JOURNAL OF
tures much higher than any found a t the surface in Yellowstone. If they are present in the magmatic emanations originating below Yellowstone they must
CHEMICAL EDUCATION
fluoride content. Allen and Day believe that this explains the exceptional amounts-of chloride and fluoride ions found in the water from some springs. It has been calculated that from the Noms Geyser Basin alone the waters carry away six 'tons of chlorine each day. The water analyses have also given evidence that the magmatic emanations must also contain arsenic and boron in volatile forms and a t times may contain ammonia. The absence of sulfur dioxide from the list of magmatic gases may seem unusual in view of the statements commonly made in textbooks of general chemistry. In this connection Allen and Day state, "To say sulfur and sulfur dioxide never occur in magmatic emanations is to go beyond the range of available evidence, but in the hot-spring stage of volcanism all observations point to hydrogen sulfide as the firimary sulfur gas." THE SPRING WATERS OF YELLOWSTONE
condense in fissures and cracks of the rock when the gases enter the cooler surface zone. If such is the case deeply penetrating ground water might reach this zone and acquire an unusually high chloride and
Once during the summer of 1937 the author, in company with another ranger, hiked from Inspiration Point along the rim of the canyon of the Yellowstone River and down to the water at the point known as the Seven Mile Hole. The day was warm, and we had walked rapidly so that we could do some fishing before time to report again for duty. We overlooked carrying a canteen of water with us and, fearing to drink from the river because of sewage contamination above, we hunted until we found a beautiful little stream flowing through the woods of a side canyon. Eagerly we knelt to drink, but the water was so sour and astringent that it was almost impossible to hold it in our mouths. (We found later that it issued from a series of hot springs half a mile above.) Our thirst was such, however, that we had to drink. We quieted any fear of ill ef-
fects by thinking that if we swallowed quickly any sulfuric acid would not attack our teeth and since no more tooth buds were forming any fluorides in the water could not cause mottled enamel. An examination of the water analyses in Table 2 will illustrate the variable mineral content of the spring waters of Yellowstone. Allen and Day in their study found that the springs fall into four main classes: (1) those high in sulfate, low in chloride and acidic or nearly neutral, (2) those high in bicarbonate, chloride, and fluoride known as alkaline springs, (3) those apparently a mixture of waters of types (1) and (2), and (4) those characterized by much calcium bicarbonate and little silica. The last type of water is found principally in the Mammoth Hot Springs area. Of the first two types, most of the springs in a given locality will belong to a single type, the type being determined, apparently, by the topographical features which control the abundance of ground water, although occasionally springs of the two types are found not far from each other. In some springs the water seems to be a mixture of the two types. The sulfate or acid springs are almost invariably located in areas where one would not expect to find a very abundant supply of ground water. The odor of hydrogen sulfide in and around such pools and springs is pronounced and the water found in them is usually acid in reaction. The overAow from such springs, if any, is usually slight, and the springs are frequently surrounded by barren areas of leached rhyolite which look like patches of snow from a distance. Examination of the water in some of the pools and mud pots of the Norris Basin in 1932 revealed that in a t least one the pH was 1.93 and was below 2.6 in several others. The acid present in the water is sulfuric and has its origin, no doubt, in the oxidation of the hydrogen sulfide and free sulfur found so abundantly in such areas. The work of one investigator leads to the opinion that bacteria may play a part in the oxidation, but i t also seems reasonable to suppose that there may be some surface catalytic effect on the particles of disintegrated rhyolite and the finely divided silica which is precipitated from the spring waters. As might be expected, the presence of free sulfuric acid in the waters causes them to have a profound, disintegrating action on the rhyolite. Rhyolite is an acidic rock and consists for the most part of feldspars and silica, with comparatively small amounts of the basic dark-colored minerals. The silica itself does not seem to be attacked, but remains as a white, sandy material after the leaching of the other rock constituents. The feldspars are thoroughly decomposed with the aluminum going into solution where the acid is highest and in other cases precipitating as clay-like minerals. As might be expected, Alum Creek has its source in such an acid area. The silica from the silicate radicals partially precipitates as opal and partially remains dissolved or colloidally dispersed where there is sufficient water. Incrustations of the sulfates
of the rock metals often occur where the ground is dry enough to permit their accumulations. The alkaline areas differ from the acid or sulfate areas in several noteworthy respects. The water is alkaline, that from Old Faithful Geyser having a pH of 8.97, and instead of having a high content of sulfate, is high in bicarbonates, chlorides, and fluorides. The ions of the alkali metals almost entirely replace the more numerous metallic ions of the acid waters. The alkaline springs are almost exclusively found in areas where the topography would suggest an abundant and deep-seated supply of ground water. I n order to a~countfor the composition of the alkaline waters it is postulated that meteoric waters penetrate to great depth, carrying with them atmospheric oxygen which oxidizes the hydrogen sulfide before it ever reaches the surface. The odor of hydrogen sulfide
Nolionoi Pork S s r i w r Phrlogrwh JUPITER WHERETHE THE
TeRRAcE
AT
THE
MAMMOTHHOT SPRINGS.
THE FORMATION TRAVERTINE BECOMESCOVEREDWITH VARICOLORED ALGAE.IT SEEMS PROBABLE THAT THE PXOTOSYNTHETIC Acnvrru oa THESEPLANT'S PLAYS AN IMPORTANT PARTI N THE
HOTWATERIS FLOWING OVER
DEPOS~TION OF THE CALCIUM CARBONATE
and the deposition of free sulfur is not characteristic of the alkaline areas. At the bottom limits of the zone of ground water there must be active alteration of the rhyolite by the hot carbonic acid, which accounts for the bicarbonates in the water. If the waters penetrate deeply enough to reach the zone where the chlorides and fluorides of potassium and sodium have been deposited as the magmatic emanations cooled on approaching the surface rocks, the waters should acquire a chloride and fluoride content much greater than waters penetrating to a more shallow depth. This, in the opinion of Allen and Day, accounts for one of the principal differences between the acid and alkaline waters. In the alkaline areas there is much less evidence of rock alteration by the thermal waters than in the typically acid areas. In looking for evidences of rock alteration a well was drilled in the Upper Geyser Basin to a depth of four hundred feet. Fenner was unable
to detect any clay decomposition products in the core samples. He did, however, observe that the rhyolite of the core contained a higher percentage of potassium
ions for sodium ions in the rhyolite. The water issuing from the springs is notably higher in sodium than potassium. The belief that an exchan~eof chemical equivalents h i t a k e n place is strengthened by the fact that K%0 NaO CaO the ratio
+
+
A1203
is practically the same for the altered core samples as for the unaltered rhyolite. THE MAMMOTH HOT SPRINGS DEPOSITS
than an unaltered core sample from the bottom of the hole and other unaltered specimens from the surface. The most plausible explanation seemed to be that the thermal water as i t came toward the surface bearing potassium chloride in solution exchanged the potassium
The acid and alkaline areas discussed thus far are located in those parts of the park where rhyolite is the characteristic rock. In the Mammoth area, however, are springs of an entirely diierent type. Below the surface in this region the thermal waters, charged with carbon dioxide, come in contact with extensive beds of Paleozoic limestone. When the water breaks forth on the surface it has a high content of calcium bicarbonate. With the decrease in partial pressure of carbon dioxide the gas escapes from the hot solution and calcium carbonate precipitates in the form of travertine, building up huge terraces which often engulf large trees. The deposition of the travertine is undoubtedly aided by the hot water algae that grow luxuriantly on the terraces. In fact, the first deposition seems to be in filamentous strands and it seems possible that the algae by removing carbon dioxide for photosynthesis may be an important factor in bringing about the deposition. The travertine is built up vety rapidly as compared to the silica deposits of the geyser basins. Where the water flows continuously a growth of twelve inches a year is not uncommon. This rapid growth which brings about a damming of the water flow, together &th the fact that the hot carbonic acid has the ability to eat new channels through the old formations and break out a t unexpected points, results in the Mammoth Springs being in a continual state of change. The hot water
algae, which vary in color from the purest yellow to brown, pink, and dark red, grow only where the hot water is actively flowing. Because in recent years some of the hot water has flowed through channels beneath the terraces rather than over the surface, thus reducing the total area covered by the algae, the belief has arisen among some people, especially among those who demand the spectacular a t all times, that the springs are drying up and are no longer interesting. On the contrary, the active springs are as beautiful as ever. The radioactivity of the rocks has been employed in determining the age of various travertine deposits in the Mammoth area. The late Herman Schlundt determined the radium content of the present active terraces, those of an old terrace on which the park headquarters buildings now stand, and that on Terrace Mountain, a deposit which is definitely pre-glacial. Assuming that the amount of radium deposited with the travertine is the same today as when the older terraces were formed, Dr. Schlundt estimated that springs were active on Terrace Mountain more than fourteen thousand years ago and a t the present Headquarters site thirty-two hundred years ago.3
sediments of pyrite, sulfur, barite, and alunite. Oxides of iron produce brilliant effects in the Artists' Paint Pots. In Norris Basin and other acid areas red and yellow sul-
DEPOSITS I N ACID AREAS
In theacid areas the deposits around the springs are for the most part non-coherent and fine grained. They are either primary decomposition products of the rhyolite or secondary precipitates resulting from chemical reactions. Silica, if deposited, is usually as a fine-grained opal. Aluminum may be in the form of alumina or clay, and may be entirely absent if the leaching has been carriedout by strong acid. Free sulfur is common in cracks and cavities and in the porous ground. The acid springs are frequently turbid with fine-grained
-
Wanuscript report by Dr. Schlundt in the Yellowstone Library.
fides of arsenic are common. There is active deposition of a hard silicious sinter in only a few sulfate springs. DEPOSITS I N ALKALINE M E A S
Around the alkaline springs the deposit is of an entirely different character. The springs are usually clear
like shelf. The sinter is deposited very slowly around most springs, and dates in the 1880's which were carved in some geyser craters can still he seen. On the other hand, Allen and Day found one spring in the Porcelain Basin that deposited thirty-seven millimeters of silicious sinter on a test block of wood in one year. The factors affecting deposition of silica are little understood. Evaporation of the water leaves an insoluble residue whether the water dries on the geyserite formation or on a tourist's glasses. The spring water can be kept in glass containers for years without the silica precipitating, but if the water is frozen a white gelatinous mass separates which will not return to solution. On flats and in pools where there is an abundant growth of algae the deposition of the silica seems to be aided, hut in what way no one has satisfactorily explained. It is interesting to note that one of the blocks employed by Allen and Day in testing the rate of deposition of silica in the crater of Castle Geyser had only a thin incrustation a t the end of a year. On carefully oxidizing the wood in nitric and sulfuric acids, however, it was found that the silica had penetrated into the wood to a depth of four millimeters and every duct and cell were faithfully preserved as a cast of silica. We must conclude that in the one year's time the wood had started to petrify. Pieces of wood are often found in hot springs and frequently found buried under several inches of geyserite. Such pieces of wood are often so dense that it is evident they are well filled with silica. In addition to the deposits around the springs already described there are other minor areas where deposits of other kinds are forming. The Chocolate Pots along the Gibbon River, as their name implies, are cones of a dark brown color with MUD POT LOCATED NGART H E streaks of black. Chemical
and are surrounded by broad stretches of loose, white, sandy, disintegrated silicious sinter. Near the margins of the pools the sinter is a dense opal and takes an infinite variety of forms. There are biscuits around one pool, cauliflower heads around another, spherical particles called "geyser eggs" around another, spiny protuberances like coral around others, while out from the edges of many quiet pools the silica extends as a thin ice-
Trrr BURSTINGO F
A
PARTICULARLY LARGE GASBUBBLEIN MUDVOLCANO
A
analysis of the sinter shows 54.5 per cent. Fe, 17.2 per cent. Si02, 1.0 per cent. Mn02, 5.9 per cent. AhOs, and 19.3 per cent. H20 which is unlike any other sinter found in the park. A water analysis showed only six parts per million of iron, but this is in the ferrous state and when exposed to the air oxidizes to the ferric condition and precipitates as a hydrated oxide. The sinter of some typically alkaline springs is tinted by small quantities of various metallic oxides. Manga-
nese dioxide colors some a gray or black, while some of the geysers in the Shoshone Basin are characterized by a bronze sinter resulting from small quantities of iron oxide. THE COLOR OF CERTAIN ALKALINE SPRINGS The water of many of the deeper alkaline pools of the park has a pronounced blue color which has suggested such names as Indigo, Sapphire, and Gentian Pools. The water in Sapphire and Gentian Pools was subjected to careful examination during the work of Allen and Day. I t was found to give a pronounced Tyndall effect, showing that it contained colloidal particles. Spectroscopic examination of the light transmitted by the water showed that it had a greater ahsorption of the shorter wave-lengths than ordinary distilled water, so that if a person were to look out from the bottom of either pool the water would seem to have a yellowish color. When viewed from above, however, each pool is a brilliant blue. The most probable explanation of the color seems to be that there is preferential scattering of blue light by the colloidal particles.
Whether the colloidal particles responsible for such scattering are silica has not been definitely determined, but it seems reasonable to suppose that they are. THE MUD POTS
Among the most fascinating features of Yellowstone are the mud pots, craters sometimes fifty feet in diameter filled with thin clay and other finely divided minerals kept in a continual state of agitation by the
escape of gases, chiefly carbon dioxide. The mud pots are almost invariably found in areas deficient in ground water. They are springs without an outlet, and as the sulfuric acid leaches the rhyolite the clay and other decomposition products accumulate because there is no overflow to carry them away. Very often there is considerable variation in color depending on the purity of the clay and the degree to which i t is contaminated with free sulfur, arsenic sulfide, iron oxide, or black pyrite. SUPERHEATED WATER
Probably no other place in the world affords as good an opportunity to observe the properties of large quantities of water a t or near the boiling point as Yellowstone. In most elementary chemistry classes students are told that water boils when the temperature is reached a t which the vapor pressure of the water equals the atmospheric pressure. Little mention is made of the tendency for water to superheat, but there are hundreds of pools in Yellowstone in which the temperature of the surface water is higher than the normal boiling
point for that altitude. In some pools the superheat may amount to three centigrade degrees. Some points in the sutface of a pool may be much hotter than others
and a pool which is below boiling one minute may be superheated five minutes later. No pool offers a better example of superheated water than Sapphire Pool in the Upper Basin. This pool which is thirty feet or more in diameter and about
thirty-five feet deep is in reality a geyser and erupts to a height of two to four feet every twelve minutes. As the water starts to rise just before an eruption its surface is as smooth as though covered with oil, yet if dry sand is thrown into the water or it is stirred with a stick it boils violently. The explanation seems to be that the water is heated by magmatic steam in chambers and tubes below the visible bottom of the pool. When this hot water enters the bottom of the pool hydrostatic pressure prevents it from boiling, but in the wide pool there is opportunity for convection currents and the hot water from the bottom rises because of its lower density and reaches the surface a t a temperature above the normal boiling point. There it should boil, but because there are no nuclei about which the bubbles can form i t remains superheated until it cools by evaporation or spontaneously starts to boil. Just what part, if any, the dissolved and colloidallydispersed minerals play in preventing the water from boiling normally is uncertain. There has been much discussion of the part superheated water plays in geyser activity. Allen and Day took depth temperature measurements in many deep pools and geyser tubes, but in none did they find superheated water below the surface, i. e., they found no point a t which the temperature of the water exceeded the boiling point when atmospheric pressure and hydrostatic pressure were both considered. The observation of such geysers as Old Faithful and the Great Fountain just prior to eruptions, on the other hand, leads one to the belief that the temperature of the water in the tubes and chambers which constitute the plumbing system of the geyser must all he very near the boiling point. In Old Faithful the boiling of water in some small chamber or in the tube seems to fill the tube with a mixture of steam bubbles and water which, because of its lower density, reduces the hydrostatic pres-
sure and causes the water in the lower parts of the plumbing system to be superheated. The sudden boiling of the large masses of superheated water causes the eruption. I n the eruption of Great Fountain the water overflows from the wide pool in the open crater for an hour or more before the eruption occurs. Toward the end of the over-
of the extinct Excelsior Geyser 6ll one with dread, the geysers cause one to marvel a t the power stored up in the earth, but for pure beauty there is nothing in Yellowstone and few things in the United States to equal the canyon of the Yellowstone River below the Lower Falls. The green river flows a t the bottom of a gash seven hundred fifty to one thousand feet deep, the
flow the water in the crater seems to become more and more superheated, and larger quantities burst into spontaneous boiling until i t seems that the whole crater becomes one seething mass of bubbles. Then the eruption takes place. It seems evident that geysers must be in a very delicate state of balance just prior to an eruption. Beehive Geyser, which normally erupts only once or twice a season, will erupt in less than a minute if a cupful of soap chips is placed in the crater. Superheated springs which are never known to show geyser activity will erupt if treated in a similar manner. The practice of soaping geysers is illegal, but the full explanation of the action is a challenge to the physical chemist. Allen and Day devote several pages to possible explanations and conclude that the action is due in large measure to a lowering of the surface tension together with other factors less well understood.
sides of which have every shade of color from the white of the purest kaolin to the yellow of ocher and the rich reds of hematite. The colors are not stratified but are found in patches which blend into each other as though shaded by an artist's brush. Naturalists on duty a t Artist Point and Grand View have instructions not to intrude upon the silent appreciation of the visitors, but for those who ask questions there is an interesting story. The Yellowstone Canyon is a direct result of the same volcanic activity which has produced the geysers and hot springs. The canyon was eroded into the rhyolite of the plateau after the rock had been decomposed by the chemical action of the rising volcanic gases. There are several active geysers in the bottom of the canyon and many hot springs. On cool, damp days one can see wisps of steam rising from many points on the canyon walls, and as one hikes along the rim there is frequently detected the unmistakable odor of hydrogen sulfide. The rhyolite plateau in the region of the canyon was not uniformly attacked by the rising gases. Between
THE YELLOWSTONE CANYON
The mud pots of Yellowstone Park have a peculiar fascination, the huge boilimg pools such as the crater
Artist Point and Grand View the activity must have been particularly intense because the canyon is widest there and the decomposed rhyolite is disintegrated into
stituents of the rhyolite. Where the decomposition has been extensive and where there has been a leaching of the soluble iron com~oundsformed. the kaolin and sand are a glaring white. here the ferrous minerals of the rhyolite have been oxidized to form hydrated ferric oxides the color is yellow or brown, and where the heat has been more intense so as to bring about a dehydration of the oxides the color is red. In localized areas where thegases are still actively escaping there may be the deposition of free sulfur and yellow sulfide of arsenic to add to the color, but any contribution from these minerals is of minor importance. Only one who has stood on Inspiration Point and has seen the sun break out over the wet slopes of the canyon after a summer shower can appreciate what a symphony of color Nature produces with a few simple forms of iron oxide. EFFECTS OF GASES ON LIFE
As is frequently the case in volcanic regions the gases escaping from the ground in some localized areas in Yellowstone have an adverse effect on the wild life. In the Mammoth area many small caves on the inactive travertine terraces are so filled with carbon dioxide that birds or small animals seeking shelter in them are overcome. The number of birds that lose their lives in this way each year is not known, but without doubt it is much larger than one might suppose. In the eastern part of the park is a ravine known as Death Gulch where there is a particularly heavy escape of deadly gases. Mr. Frank Oberhansley, former Assistant Park Naturalist, made this observation in his diary for August 26, 1038: "Today District Ranger Lee Coleman and I visited Death Gulch. As we walked along the left bank of Cache Creek the emanation of sulfurous gas was decidedly noticeable. The weather was still and humid, and the gas was particularly heavy a t the lower end of the Gulch where we crossed it. We both became convinced that it would be unwise to attempt to walk up the Gulch. THE GEYSER TUBESHELPSWITHSTAND THE TERRIFIC PRESSURES DESymptoms were shaky knees, headache, and VELOPED DmlNO THE ERUPTIONS irritation of the respiratory system. I am certain that no animal could lonp endure the clay and gravel which slope down to the river at the fumes as they were today. However, the only dead angle of repose. At the Lower Falls, however, the animal seen was a pocket gopher lying dead a t the rhyolite is practically unaltered. On the steep wall of mouth of the Gulch. It appears that the larger animals the canyon just below the falls one can see a lace-like avoid the locality a t the present time (in 1880 W. H. design of cracks and fissures up which the magmatic Weed who named this feature reported finding cargases have come, changing the rock on each side of the casses of six bears in the Gulch and in 1897 Dr. T. A. crack to a lighter color. At the bottom of the canyon Jagger found eight bears in this 'natural bear trap')." one can find these cracks and can easily pick out the It remains for some future investigator to determine soft, decomposed rhyolite. whether the lethal effects are due to carbon dioxide or The colors on the canyon walls are a direct result of whether poisonous hydrogen sulfide is present in suffithe chemical action of the rising gases on the con- cient concentration to play a part.
Space does not permit the enumeration of all the chemical facts known about Yellowstone. Nor is it to be imagined that the knowledge we already have can fully explain all the chemical phenomena found there.
Much remains to be discovered, and chemists who aid in the solution of the many unsolved problems will contribute to a better understanding and greater appreciation of this remarkable region.
BIBLIOGRAPHY
(1) ALLEN,E. T. AND A. L. DAY."Hot springs of the Yellowstone National Park." Carneaie Institute of Washington, D. C.. Washington, D. C., 19c5, 525 pp. (2) BAWER, C. M.. "A preliminary paper on the geology of the Yellowstone National Park." U. S. Deot. of the Interior. ~ a t i o n a lPark Service, ~eliowstone~ & k wyoming. . (A preliminary paper for the use of ranger naturalists.) 15 pp. (3) HOWARD, A. D.. "Yellowstone through the ages." Columbia
University Press, New Yark City, 1938, 64 pq; (4) K E ~ N S W.. E.. "Death Gulch in 1888. 1897. and in 1936. Yelbwstone Nature Notes, 13, Nos. 9 .and 10, 52 (1936). ' (5) KNOWLTON. F. H., "The fossil forests of the Yellowstone National Park." IT. Government Printine Office. -~ S. .~ - . .., Washinr. t&, 0; c..i929.29 pp. (6) OBERHANSLEY. F. R., yell must on^. Nature Notes, 15, Nos.9 and l 0 , 4 9 (1938). ~
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