The Yellowstone National Park Part 12

Upper Geyser Basin (near Castle Geyser) 7,300 "

Mouth of Spring Creek 7,600 "

Isa Lake, Continental Divide 8,300 "

Yellowstone Lake 7,741 "

Road at Mud Volcano 7,705 "

Canon Hotel 7,850 "

Junction Valley near Yancey's 6,150 "

Divide between the Black-tail and Gardiner 6,550 "

[AT] From profile of road system. For additional elevations, see list of names in Appendix A.

SCENERY.

The mountain scenery of the Park is not so imposing as that of Colorado and some other parts of the Rocky Mountain region; but it is more varied and beautiful. The eye is not wearied with the constant sight of vast and bare mountain cliffs, but finds relief in attractive lakes, streams, glades, parks, forests, and every combination of effects that helps to produce a beautiful landscape.

CHAPTER II.

Geology of the Park.

Nature seems, from the first, to have designed this region for a mountain park. In geological chronology it was near the close of the Cretaceous Period, that the lifting of the great mountain systems of the West into their present positions was practically finished. In the formation of these mountains, the general outline of the Yellowstone Park was already marked out, probably in much more striking features than at present. A vast rim of mountains, visible now in the Absaroka, Snowy, Gallatin, Teton, and Snake River Ranges, hemmed in the extensive area which has since become so famous. Subsequent events have greatly modified its original form, but the grand outlines at first determined are still distinctly visible.

In the Tertiary Period, which was next in order of time after the Cretaceous, changes of the greatest importance occurred, consisting princ.i.p.ally in the outpouring of enormous ma.s.ses of volcanic material.

The origin of these lava flows has been traced to a few craters, one of which was near Mt. Washburn, another in the Red Mountain Range, and a third near the sources of the Lamar River. Mt. Washburn has long been recognized as part of the rim of an ancient volcano. Both it and Mt. Sheridan, the two mountains which bore the princ.i.p.al part in working out the present features of that country, still remain the most prominent peaks from which the modern visitor can contemplate the work they have performed.

The outpourings at first consisted of andesitic lavas. They largely changed the appearance of the mountain ranges and to some extent filled up the interior basin. The flows were not continuous but were separated by long intervals of quiet, during which vegetation and the agencies of erosion were actively at work.

After the cessation of the andesitic eruptions, a quiescent period of great length ensued. Then came the period of rhyolitic flows, the centers of volcanic activity being as before Mts. Washburn and Sheridan. These flows built up the present Park plateau, and const.i.tute the great bulk of the rocks which the tourist now sees.

Following the period of rhyolitic eruptions, orographic agencies were active in producing extensive faults or displacements, which in certain localities radically changed the relative positions of the rocks.

The last exhibitions of volcanic energy were in the form of basaltic eruptions. These took place in part through ordinary volcanic craters, and in part through cracks or seams in the rocks, where they may still be seen forming extensive d.y.k.es. The basalt is of relatively limited extent, but its striking and picturesque forms wherever it appears make it more interesting to the tourist than any of the other rocks.

The great variety of superficial appearances which these volcanic rocks have a.s.sumed makes the Park one of the best laboratories in the world for their study.

The continuance of these various outpourings doubtless extended into Quaternary time. Then came the Glacial Epoch, the epoch of wide-spread ice-carving, which still further modified the surface of the country. The paths of the ancient glaciers have in several instances been made out and their transported material may readily be distinguished. One glacier flowed from the Gallatin Range eastward across Terrace Mountain, where it joined another moving westwardly from the Absaroka Range. The united streams continued down the Gardiner and Yellowstone Valleys, in which vast ma.s.ses of drift still mark their ancient route.

Glacial action and the common agents of denudation have given the Park country its present general aspect. These later modifications have indeed been extensive, and the great variety of form now seen in the valleys, canons and hills is the result of their combined action. The Yellowstone Canon is a marked example of erosion on a large scale. A direct result of its formation was the partial draining of Yellowstone Lake, which had previously existed at a much higher level than now, and spread over the entire area of the present Hayden Valley.

Since the cessation of the basaltic lava flows there seem to have been no further lava outpourings in this region. The old volcanoes have been long extinct and their craters have been modified almost beyond recognition. But evidences of the power which once worked beneath them are still abundant, although no longer on so imposing a scale. It is the hot springs and geysers still in existence which partly render this region so widely celebrated. That this thermal action originates mainly in the same source of energy which once poured out the vast fields of lava, there is no reason to doubt. Many plausible explanations are advanced to account for the existence of subterranean heat, but whatever may be its real origin it is doubtless the same for both cla.s.ses of phenomena.

The action which is now observable has continued in an ever-decreasing degree since the close of the lava period. Over vast tracts of the Park plateau, the rocks are entirely decomposed to unknown depths by the ascending superheated vapors. Some idea of the extent of this action may be obtained at the Grand Canon, which has cut its way a thousand feet downward into the decomposed volcanic rock without yet reaching its bottom. The infinite variety of chemic products resulting from this decomposition has given the Canon its wonderful coloration.

The same condition largely prevails over the Park plateau. Where now are dense forests and no superficial evidence of unusual conditions, there will frequently be found, by digging beneath the surface, the familiar proof that thermal activity once prevailed there. In constructing the tourist route from the Upper Geyser Basin to the Yellowstone Lake, where for nearly the whole distance there is a complete absence of hot springs, the evidences of former volcanic activity were found to be abundant.

Facts like these clearly demonstrate that, from a geologic standpoint, thermal activity in the Park is gradually becoming extinct; and many persons, taking alarm at this evidence, imagine that the unique phenomena of the Yellowstone are of an evanescent character, and that the time is not far remote when they will be known only as matters of history. There is, however, no occasion for such misgiving. The present condition is the result of processes that run back probably for millions of years; certainly for periods of time compared with which recorded history is insignificant. The same rate of progress would produce no perceptible change in the lifetime of an individual.

Some who have visited the geyser regions more than once a.s.sert that, after an interval of several years, they observe a marked diminution in thermal activity. But this is probably because a second visit ordinarily makes a less vivid impression than a first. The weight of reliable evidence is certainly the other way. Mr. David E. Folsom, leader of the Expedition of 1869, made a tour of the Park during the present season of 1895. He says: "I had a very vivid recollection of all I saw twenty-six years ago, and I note no important change."

Professor Arnold Hague, probably the best living authority upon the scientific features of the Park, has compared the hot springs and geysers by means of authentic records covering intervals of several years, and he declares that he finds "no diminution in the intensity of action or in the amount of discharge from the springs and geysers, since they have been subject to careful observation." While it is certain that springs are constantly becoming inactive, it is no less certain that others replace them, and it may be confidently a.s.sumed that the progress toward ultimate extinction will be inappreciable in our time or for many generations to come.

The distribution of thermal springs over the surface of the earth is probably more general than is commonly supposed. Only one extensive area is practically without them, and that is the Continent of Australia. Africa, also, has very few. But in other parts of the globe they are found almost without number, ranging from the Equator to the Arctic Circle, and from sea-level to the lofty table lands of Thibet.

The three localities, however, in which they abound in such numbers and magnitude as to attract marked attention are, in the order of their discovery, Iceland, New Zealand, and the Yellowstone National Park. In extent, variety, and magnitude of accompanying phenomena, and in geologic age, the above order is reversed. Iceland has probably the most famous geyser in the world, princ.i.p.ally because it was for a long time the only known geyser, and consequently received a great deal of scientific attention; but judging from published descriptions it is clearly inferior to several now known in the Firehole Geyser Basin.

Three notable features of similarity in these geyser regions are the presence of volcanic rocks of remote or recent origin; proximity to the earth's surface of active sources of subterranean heat; and the presence of a great number of lakes. In all three cases, lava, heat and water are the characteristic geologic and physical accompaniments of those particular phenomena which will now be described more in detail.

CHAPTER III.

GEYSERS.

The hot springs of the Yellowstone National Park may be roughly divided into two cla.s.ses, eruptive and non-eruptive. To the first the term _geyser_ is applied, while the term _hot springs_ is restricted to the second. These two cla.s.ses pa.s.s into each other by insensible gradations and the line of demarcation it is not possible to draw. The following description will pertain only to those examples about which there is no doubt, and which may be taken as types of their cla.s.s.

A geyser may be defined as a periodically eruptive hot spring. The name, as might be expected, is of Icelandic origin, and comes from the verb _geysa_, _to gush_. The general characteristics of a true geyser, as ill.u.s.trated by the most perfect example known, Old Faithful in the Yellowstone Park, are the following:

(1.) There is an irregular tube descending from the earth's surface to some interior source of heat.

(2.) The mouth of this tube may be either a self-built mound or cone (as in the example), or simply an open pool.

(3.) Into this tube meteoric water finds its way and is subjected to the action of heat.

(4.) The result is an eruption and expulsion of the water from the tube with more or less violence.

(5.) The eruption is generally preceded by slight preliminary upheavals leading gradually to the final outburst.

(6.) After cessation of the eruption there is usually a considerable escape of steam.

(7.) A quiescent period, generally of indeterminate duration, follows during which the conditions necessary for an eruption are reproduced.

Geyser phenomena have attracted a great deal of scientific attention, and many theories have been advanced to explain them. Pa.s.sing over for the present the various less important views, attention will first be given to Bunsen's theory, because it is, upon the whole, the most satisfactory explanation yet advanced. This theory was a direct deduction from observations upon the Great Geyser of Iceland, and has been experimentally ill.u.s.trated by artificial examples.

The fundamental principle upon which it is based is the well known fact that the temperature of the boiling point of water varies with the pressure to which the water is subjected. At the sea level, under the pressure of one atmosphere (fifteen pounds to the square inch), the boiling point is about 212 degrees Fahrenheit. Under a pressure of two atmospheres it is 250 degrees; of three, 275 degrees; of four, 293 degrees, and so on. At an alt.i.tude like that of the Park plateau, where the atmospheric pressure is much less than at sea level, the normal boiling point is about 198 degrees, but the law of variation due to pressure conditions applies exactly as in lower alt.i.tudes.

If water, subjected to great pressure, be heated to a temperature considerably above that of its normal boiling point, and if then the pressure be suddenly relieved, it will almost instantaneously be converted into steam; a fact which always operates to enhance the danger from the explosion of steam boilers. Applying this principle to the case of an ordinary geyser, it will readily be seen that in the long irregular tube descending to great depths there are present the necessary conditions for subjecting the water to great pressure. At the surface the pressure is that of the weight of the atmosphere corresponding to the alt.i.tude; at a certain depth below (33 feet at the sea level, but less at higher alt.i.tudes) it is twice as great; at double this depth three times as great, and so on.

Suppose, now, that there is an interior heat at some point along the geyser tube well below the surface. The boiling point of water in the vicinity of the heat supply will be higher than at the surface in definite relation to its distance down. If the tube be of large diameter and the circulation quite free, the water will never reach this point, for it will rise nearer the top, where the boiling point is lower and will pa.s.s off in steam. The spring will thus be simply a boiling or quiescent spring. But if the tube be comparatively small and if the circulation be in any way impeded, the temperature at the source of heat will rise until it reaches a boiling point corresponding to its depth. Steam will result, and will rise through the water, gradually increasing the temperature in the upper portions of the tube. After a time the water throughout the entire tube becomes heated nearly to the boiling point and can no longer condense the steam rising from below; which then rapidly acc.u.mulates until its expansive power is great enough to lift the column above and project some of the water from the basin or cone. This lessens the weight of the column and relieves the pressure at every point. In places where the water had been just below the boiling point, it is now above, and more steam is rapidly produced. This throws out more water, still further lightens the column, and causes the generation of more steam, until finally the whole contents of the tube are ejected with terrific violence.

From this explanation it is apparent that any thing which impedes the circulation of water in the geyser tube will expedite the eruption.

The well-known effect of "soaping geysers" may thus be accounted for.

As oil thrown upon waves gives a viscosity to the surface, which greatly moderates their violence, so does the addition of soap or lye make the water of the geyser tube less free to circulate, and thus hasten the conditions precedent to an eruption.

The apparently contrary process of violently agitating the water of the geyser, as by stirring it with a stick, sometimes produces the same effect; but this results from the sudden forcing upward of ma.s.ses of superheated water, instead of allowing them to rise and gradually cool.