Dr. Peal has reached conclusions which present an imaginary picture of the interior structure of the great geysers of the Park, that bears a striking resemblance to what the two caves of the Black Hills prove to be the true conditions; although it is evident he had in mind caverns of no such vast extent, nor of so complicated a system of cavities and tubes. He overlooked an important feature, however, in not accepting Professor Comstock's idea of the tube having a double curve. The double curve is, or was, conspicuous in both the caves. Unfortunately, its perfection in Wind Cave was necessarily partially sacrificed to make the passage traversable for visitors; but in describing the enormous labor of opening up the cave, Mr. McDonald showed how an arching "crawl" had been worked down by blasting, and the depression beyond filled to raise it to the desired level for securing the present easy passage at the bottom of the main tube, which is the entrance passage. This double curve in the tube is simply the rough original of the S trap of sanitary plumbing. In both caves it is somewhat irregular and deformed, but the familiar "trap" is easily recognized. The destruction of one of the Yellowstone geysers was, no doubt, due to the breaking of the S. One of the many reasons for establishing military control over the Park is said to have been the disastrous results following the introduction of a large quantity of soap into the geyser to cause a premature eruption. The impatience of the party was rewarded by an eruption accompanied by explosions that shook the earth for a great distance, and the geyser has not been seen in action since.
Dr. Peal finds the theories advanced for the generation of steam unsatisfactory and insufficient, especially in the class of geysers having a long steam period. He says: (page 423)
"The Castle Geyser differs from Old Faithful and the Bee Hive mainly in the fact that it has a long steam period, during which the steam pours out or is pushed from the geyser throat with great violence and a terrific noise. There appear to be only two possible explanations of this difference, viz., either an accumulation of immense volumes of steam in the Castle, or an instantaneous formation of steam throughout the length of the geyser tube. The former, to our mind, is untenable, because it seems impossible that the water, which is exhausted in fifteen minutes, should exert enough power to keep down the immense amount of steam that escapes for more than an hour. According to Bunsen's theory, it can be readily explained. The relief afforded by the first part of the eruptions allows the superheated water to rise rapidly, and before it can reach the top or orifice of the tube it is all converted into steam from the top downward with inconceivable rapidity, and must be forced out with the terrific violence which is noted in the case of the Castle. On page 208 we have expressed the opinion that it is the oldest geyser in the region, and it seems to us that a greater length in the tube, with a consequent greater supply of water, will account for the difference between the Castle and Old Faithful, the latter of which we consider one of the youngest geysers in the Upper Geyser Basin."
A study of the Caves in connection with the active Geysers indicates that the theory he suggests and then rejects, is probably the true explanation of the difference between the two kinds of geysers. It seems that the length of the tube must necessarily have more effect on the height of the jet than on the generation of steam; as after an eruption the tube is hotter than at any other time and therefore the generation of steam in it should be less than usual, unless the fresh inflow of water was cold. Then if the storage cavities are broad but low, the steam cannot accumulate above the water; but when the pressure becomes sufficient to force a passage through the tube, the water and steam are expelled together until the pressure is exhausted. But if the storage chambers are vertical fissures, as Wind Cave illustrates, vast quantities of steam must accumulate above the water level in the main reservoirs before the pressure can become sufficient to expel the water in the tube, after which steam alone continues to rush out until the pressure is so relieved that it can no longer force a passage through the water remaining in the trap, when quiet is restored. By the constant addition of fresh water from the surface, by percolation or other usual ways of sinking, the necessary conditions for the generation of steam are maintained with surprising regularity.
The differences in the shape and general arrangement of the cavities and tubes of the two caves, indicate that their action as geysers was very unlike. Wind Cave evidently sent a rather slender column to a great height, nearly perpendicular, and the water eruption was followed by a long steam period. Crystal Cave ejected a much larger jet more frequently, at a low angle of inclination, the eruption was sooner over, and was not followed by a steam period of any consequence.
Thus it can be seen that the caves of the Black Hills prove the theories in regard to geyser action in Yellowstone Park, and those theories, in turn, prove the past history of the caves. The study of geyser action also shows that the conical or dome shape of some of the cave chambers is not due to the whirl of incoming floods, as in other regions, but to jets of water forced up from lower levels.
Perhaps the finest geyser basin, and possible cave, ever in existence was destroyed when the Grand Cañon of the Yellowstone became a cañon. Evidences of the former conditions in control of this gorgeously brilliant scene are neither wanting nor doubtful. Steam constantly issues from numerous small vents in the cañon walls, and a field glass reveals miniature geysers in action down in the depth of the cañon, nearly half a mile below the top of the wall; while the entire cañon shows, in both the color and character of its rocks, that chemical agencies have wrought changes here that have not been effected in other exposures of similar nature. It seems not improbable that the relation of Yellowstone River to the Grand Cañon was the same as, at the present time, is that of the Firehole to the Upper, Middle, and Lower Geyser Basins: and that an explosion of great force was followed by a general collapse instead of the usual eruption of one of the grandest geysers; one result being the sudden precipitation of the river into a new, beautiful, and totally unexpected channel. After its great leap of two hundred and ninety-seven[6] feet at the Lower Fall, the river flows in a brilliant, narrow line of emerald green, broken by the white foam of frequent cascades, between magnificent walls of yellow, white, pink, and red of most vivid hues.
[6] Measurement by the Hayden Party.