CONCLUSION.
After a visit to the marvelous caverns of the Black Hills, much may be
added to the pleasure already enjoyed, through the explanatory activity
of the Yellowstone National Park, where even the wonderful combinations
of beauty and grandeur are by no means the full measure of attraction
and charm. Here is found evidence to verify theories concerning the
caves, and those theories in turn contribute in no small degree to a
satisfactory understanding of the mysteries of geyser action. For
scientific study the two regions should be taken together, since the
natural conditions are practically the same, and the chief difference
lies in the stages of development; the present of the Park explaining
the recent past of the Hills, while the present of the Hills foretells
the future of the Park. It seems that Nature, with a full appreciation
of the limits and restrictions binding our powers to penetrate certain
secrets of an intermittent force, has in this great western country
carefully prepared what might quite properly be termed a progressive
course of study, wherein each locality makes plain a special point that
somewhere else appears obscure.
As has been said in the preceding chapters, the two great caves in the
Black Hills of South Dakota cannot be accounted for by the same methods
as are recognized as being responsible for the slow excavation of the
best known caves of the United States. Although there is every
indication that both these caves have been subject to the action of
enormous volumes of water, there is equally positive evidence that
neither was ever the scene of a flowing cave-river. The lowest levels in
both show the narrowest fissures and the heaviest deposits of crystal,
by which we infer that the water was held in confinement here, while all
the higher passages or channels bear witness to the water's flow. But
many of these channels in Crystal Cave, or indeed we might say, most of
them, present an unmistakable record of the gauge of the water stage at
different periods. During the earlier time, when the volume of water and
consequent pressure were greatest, frictional motion must have been
limited to the main channel connecting with the vent, and the high gauge
of water maintained a fairly uniform degree of heat near its surface. In
consequence of these conditions geyser action, probably, was constant,
and chemical activity was such that great chambers were formed and then
decorated, as already described, with wonderful masses of crystal. As
the water gauge receded to lower levels the higher chambers became
storage basins for water and steam forced up by the pressure from below,
and the time required for these to fill and accumulate sufficient
pressure to continue the ejectment, formed the periods between eruptions
after the geyser became intermittent. It was during this stage that the
sharp crystals in many of the channels, now called passages, were worn
down to smooth surfaces; and later, when water occupied only the lowest
level, and the great geyser had become reduced to merely a steam vent,
the channels immediately connecting with that level were in their turn
subjected to the same smoothing process, and then all action ceased.
As no two of the glorious geysers of the Yellowstone Park are alike,
neither do the two great caves of the Hills indicate that they should be
so. The vent-tubing of each is quite unlike that of the other in all the
essential governing points of length, size, shape, angle of inclination
and power-conserving bends. And the differences extend in an almost
equally marked degree throughout the vast and complicated succession of
storage chambers and their connecting channels. The small vent of Wind
Cave shows that the ejected jet was far from being equal to that of the
Crystal Cave in volume; but the nearly perpendicular long arm of its
tube shows also that its jet attained a much greater height, even
supposing that it should be necessary to make some allowance for a short
elbow at the top.
Dr. Hayden's geological party gave much attention to the Yellowstone
Park while its wonders were new to the world, and observations were made
at various times during the period included between the years 1869 and
1870. The special study, and full report of the geysers became the duty
of Dr. A.C. Peal, whose descriptions and conclusions were published in
U.S. Geological Survey Report, 1878, Part II. In the final pages of his
report he quotes the leading authorities on geyser action, and applies
the principles of their theories, according to his own judgment, to the
geysers of the park. Since copies of this report are not now easily
obtained, nor even always accessible to the increasing number of
personages who visit the park, it may be well to quote from him some of
the theories he discussed and the opinions he expressed. On page 416,
beginning the chapter with the derivation of the word geyser from the
Icelandic word _geysa_--to gush, he continues:
"We now come to the definition of a geyser. It may be defined to be a
periodically eruptive or intermittent _hot_ spring, from which the water
is projected into the air in a fountain-like column. The analogy between
geysers and volcanoes has frequently been noticed and the former have
often been described as volcanoes which erupt heated water instead of
melted lava. We have italicized the word hot in the definition just
given, because springs containing a large amount of gas may simulate
geysers.
"The difference between geysers and ordinary hot springs is not readily
explained, nor even always recognized. The difference between a quiet
thermal spring and a geyser in active eruption is very marked, but
between the two there is every grade of action. Some geysers appear as
quiet springs, as for instance the Grand Geyser during its period of
quiescence. Others might easily be mistaken for constantly boiling
springs, as in the case of the Giant Geyser, in which the water is
constantly in active ebullition. This is true also of the Strockr of
Iceland. Many of the springs, therefore, that in the Yellowstone Park
have been classed as constantly boiling springs may be unsuspected
geysers. The Excelsior Geyser was not discovered to be a geyser until
eight years after the setting aside of the park. Almost all constantly
boiling springs have periods of increased activity, and those which
spurt a few feet into the air have been classed as pseudo-geysers.
"It has been noticed that geysers occur where the intensity of volcanic
action is decreasing. In the neighborhood of active volcanoes, such as
Vesuvius, the temperature appears to be too high, and the vapor escapes
as steam from what are called stufas. When the rocks at the surface are
more cooled the water comes forth in liquid form.
"We will now pass to the various geyser theories that have been proposed
by different writers."
Dr. Peal then proceeds to give the theories of Sir J. Herschell and Sir
George McKenzie, but as they are accepted and extended by others, we may
pass on to Bischof's, of which Dr. Peal says: "Very similar to
McKenzie's theory is the one adopted by Bischof in his Researches on the
Internal Heat of the Globe (pages 227, 228). It is really the theory of
Krug Von Nidda, who examined the geyser in 1833. Bischof says:
"'He (Krug Von Nidda) takes it for granted that these hot springs derive
their temperature from the aqueous vapors rising from below. When these
vapors are able to rise freely in a continued column the water at the
different depths must have a constant temperature equal to that at which
water would boil under the pressure existing at the respective depths;
hence the constant ebullition of the permanent springs and their boiling
heat. If, on the other hand, the vapors be prevented by the complicated
windings of its channels from rising to the surface; if, for example,
they be arrested in caverns, the temperature in the upper layers of
water must necessarily become reduced, because a large quantity of it is
lost by evaporation at the surface, which cannot be replaced from below.
And any circulation of the layers of water at different temperatures, by
reason of their unequal specific gravities, seems to be very much
interrupted by the narrowness and sinuousity of the passage. The
intermitting springs of Iceland are probably caused by the existence of
caverns, in which the vapor is retained by the pressure of the column of
water in the channel which leads to the surface. Here this vapor
collects, and presses the water in the cavern downward until its elastic
force becomes sufficiently great to effect a passage through the column
of water which confines it. The violent escape of the vapor causes the
thunder-like subterranean sound and the trembling of the earth which
precedes each eruption. The vapors do not appear at the surface until
they have heated the water to their own temperature.
"'When so much vapor has escaped that the expansive force of that which
remains has become less than the pressure of the confining column of
water, tranquility is restored, and this lasts until such a quantity of
vapor is again collected as to produce a fresh eruption. The spouting of
the spring is therefore repeated at intervals, depending on the
capacity of the cavern, the height of the column of water, and the heat
generated below.'" Dr. Peal continues:
"Bishof says that the eruptions of the Geyser and Strockr agree exactly
with this explanation and he accounts for the two distinct classes of
eruption observed in the Geyser as follows:
"'The two distinct classes of eruption in the geyser which we have
already mentioned seem to be attributable to two different cavities. A
small cavity fills quicker, and, therefore, empties itself more
frequently; a larger one fills slower, empties itself seldomer, but with
greater violence.'"
Bunsen's theory is the next considered and is somewhat similar to
Bischof's but with notable differences. After taking temperatures at
different points in the Geyser tube his first conclusions are that:
(1) The temperature in the geyser tube increases as we descend.
(2) At no point does the water in the tube attain the temperature of
ebullition which it should have under the pressure to which it is
subjected, but the temperature depends on the time that has elapsed
since the last eruption. As a great eruption comes near it approaches
the boiling point.
(3) At the depth of about forty-five feet the difference between the
temperature of the water and the calculated boiling point for that
pressure is the least.
The main point of his theory appears to be that an eruption takes place
when the water in the tube reaches the boiling point, and to account for
it, "He supposes that the column in the central tube communicates by a
long and sinuous channel with some space, be it what it may, which is
subjected to the action of the direct source of subterranean heat. The
temperature gets raised above the boiling point, due to the pressure,
and a sudden generation of steam is the result. This steam rises in the
column of water, which, being cooler, causes it to condense. Gradually
the heat of the water is raised until the water of the channel must
boil, and the steam therefore cannot condense, but must accumulate and
acquire a gradually increasing tension. The condensation of the bubbles
possesses a periodic character, and to this is due the uplifting of the
water in what Bunsen calls conical water hills, which are accompanied by
the subterranean explosions."
Prof. Comstock is quoted as thinking "Bunsen's theory has not yet been
proved adequate to explain the more prominent features of geyser
eruptions. Nor does it, in his opinion, account for all the differences
between geysers and hot springs, and he proposes a structural
hypothesis which combines Bischof's and Bunsen's theories."
This hypothesis is illustrated by a figure in which a reservoir partly
filled with water is connected with the surface by a tube having a
double curve, and he explains that the water collecting in the depressed
curve should confine the steam, rising from the reservoir in the other
curve until the pressure is sufficient to cause an eruption. His theory
of action being that the water in the reservoir remains in equilibrium
at a certain level, and the constant heat fills the space above with
vapor, which heats the water held in the downward bend of the tube, and
that also evolves vapor which fills the balance of the tube to the vent.
When the combined pressure of this vapor and water are overcome by the
expansion of vapor accumulated above the reservoir, they are forced out,
and followed by a portion of the water of the reservoir. This theory is
in the report of Captain Jones on Northwestern Wyoming.
The last theory cited by Dr. Peal is that of S. Baring-Gould, "Who
visited the Iceland geysers in 1863, and thinks that a bent tube is
sufficient to explain the action of the Great Geyser. He took an iron
tube and bent it in an angle of 110°, keeping one arm half the length of
the other. He filled the tube with water and placed the short arm in the
fire. For a moment the surface of the liquid remained quiet, and then
the pipe began to quiver; a slight overflow took place, without any sign
of ebullition, and then suddenly, with a throb, the whole column was
forced high into the air. With a tube, the long arm of which measured
two feet and the bore of which was three-eighths of an inch, he sent a
jet to the height of eighteen feet. Steam is generated in the short arm
and presses down the water, causing an overflow until the steam bubble
turns the angle, when it forces out the column in the long arm with
incredible violence."
Dr. Peal now goes on to say:
"Of the theories that we have just enumerated, perhaps no one is
adequate to explain all the phenomena of geyser action. Bunsen's theory
comes nearest to it, and in the simplest kinds of geysers is a
sufficient explanation. The variations and modifications in the geyser
tubes and subterranean water passages must undoubtedly be important
factors entering into any complete explanation of geyser action. Now, of
course, we can see what the conditions are at the surface, but in our
experiments we can penetrate to a very inconsiderable distance. We have,
therefore, no data to present on these points, and investigations of
this branch of the subject will have to be carried on in an artificial
manner; that is artificial geysers will have to be constructed, and
various modifications made in the tubes until results are reached
analogous to those seen in natural geysers. If water in a glass tube be
heated with rapidity from the bottom, it will be expelled from the tube
violently, and if boiled in a kettle which has a lid and a spout, either
the lid will be blown off or the water will be forced out through the
spout. The first case is an illustration, in part at least, of Bunsen's
theory, and the second exemplifies the theories which presuppose the
existence of subterranean cavities with tubes at or near the surface.
According to the former we must suppose that the layer of rock,
extending seventy-five to seventy-seven feet below the surface, contains
sufficient heat to account for geyseric phenomena; or else that the
geyser tube has some opening, either at the bottom or on the sides, by
which steam and superheated water have access to it from a considerably
greater depth where the temperature is very high. At these depths
caverns probably exist." * * * *
"That such cavities exist is more than probable. On page 405 I have
indicated my belief, that all geysers are originally due to a violent
outburst of steam and water, and under such conditions, irregular
cavities and passages are more likely to be formed than regular
tubes." * *
"In view of what we have just written, Bunsen's conclusion (No. 2)
would have to be modified somewhat. His conclusion was that at no point
in the tube did the water attain the temperature of ebullition which it
should have under the pressure to which it is subjected. As far as this
relates to the straight tube in which his temperatures were taken, it
may be so; but if he could have taken temperatures in the side conduit,
I have little doubt he would soon have reached a point where the
temperature would not only be at the boiling point for that depth but
even exceed it. In the Yellowstone Park we obtained a number of surface
temperatures which were above the boiling point. In the Great Geyser of
Iceland, the mass of water in the tube prevents this condition at the
surface, and when it takes place opposite the aperture an eruption is
caused. In the main, however, I am inclined to accept Bunsen's theory,
especially as it seems to me to require subterranean cavities in which
the water must be heated. Whether these are caverns, enlargements of
tubes, or sinus channels, appears to me to be of no consequence, except
as the interval or period of the geyser might be affected by the form of
the reservoir holding the water."
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.
FOOTNOTES:
[6] Measurement by the Hayden Party.