NATURAL HISTORY OF GEYSERS AND OTHER THERMAL SPRINGS.
In Icelandic speech the word _geyser_ means simply _rager_, and is
applied indiscriminately to all turbulent fountains of water or mud.
The most violent and noisy "rager" on the island being the great
intermittent spouting spring near Haukadal, it naturally gained for
itself the title, The Geyser; and being the earliest known and most
remarkable fountain of the kind, its native common name was adopted in
other languages as the generic name for all springs of its class.
The history of this great, but no longer the greatest geyser, begins
in the early part of the fifteenth century, when its eruptions are
mentioned in Icelandic records. In the middle of the seventeenth
century the Bishop of Skalholt noticed its daily discharges. A hundred
years later Olafsen and Povelsen described it as having three or four
eruptions a day, some of them attaining the height of 300 feet,
including, doubtless, the uprush of vapor. The depth of its tube was
then 72 feet; now it is commonly given as 74, though Commander Forbes,
R. N., claims that it is not so deep by ten feet. In 1774 Von Troil
estimated the height of the ejected column at 92 feet. Seventeen years
later, Stanley gave 96 feet as its greatest height. Forty yards west
of the Geyser this traveller found a rival, called the Strokr, (in
English, the Churn,) playing to the height of 130 feet. The same year,
1789, an earthquake destroyed the mechanism of the Strokr, converting
it into a quiet reservoir of boiling water, whereupon its name was
transferred to the present Strokr, which then became especially active
and noisy. In 1804 the Geyser had regained somewhat of its ancient
power, erupting every six hours to the height of 200 feet; and the
original Strokr had repaired its tube so that it could lift a column
to nearly the same height and sustain it for a much longer period.
During the next five years the power of the Geyser fell off a half,
and its paroxysms became much less frequent--Hooker estimating its
column, in 1809, at 100 feet, and Mackenzie, a year later, at 90 feet,
its eruptions taking place every thirty hours. At the same time the
Strokr played every ten or twelve hours, sixty feet high, for the
space of thirty minutes. In 1815 the periods had changed again, the
Geyser erupting every six hours, to an average height of 80 feet,--the
jets occasionally reaching 150 feet, while the Strokr had prolonged
its quiet intervals to twenty-four hours. Of late years the Geyser's
violent eruptions seldom occur oftener than once in thirty hours,
and do not exceed 100 feet in altitude, and generally averaging 70
or 80 feet. Between these eruptions are usually two minor spirts,
attaining from 30 to 50 feet. The Strokr is exceedingly irregular in
its operation, and generally requires a dose of turf to bring on an
exhibition.
A grand eruption of the Geyser has been admirably described by
Commander Forbes.
"Twice during the night," he says, "I was aroused by the unearthly
complaints of _The_ Geyser; but beyond the vast clouds of vapor which
invariably follow each detonation, and a gentle overflowing of the
basin, they were false alarms. As morning was breaking it sounded an
unmistakable 'reveille,' which would have roused the dead: and I had
barely time to take up my position at the brink of the old 'Strokr'
before full power was turned on. Jet succeeded jet with fearful
rapidity, earth trembled and the very cone itself seemed to stagger
under the ordeal. Portions of its sides, rent with the uncontrollable
fury it had suddenly generated, were ripped off and flew up in volleys,
soaring high above water and steam, whilst the latter rolled away
in fleecy clouds before the light north wind, and catching the rays
of the morning sun just glistening over the Jökul tops in the East,
was lustrous white as the purest snow. Discharge succeeded discharge
in rapid succession for upwards of four minutes, when, apparently
exhausted and its basin empty, I scrambled up to the margin, intending
to have a good look down the tube, which I imagined must also be
empty; but the water was still within a few feet of the brink, and
boiling furiously. Hastening back to my former position, the basin
filled rapidly, and I was just in time to witness the most magnificent
explosion of all. Everything seemed to depend on this superhuman
effort, and a solid, unbroken column of water twenty-five feet in
circumference, was hurled upwards, attaining an altitude very near 100
feet. Here the column paused for a moment before reversing its motion,
then fell listless and exhausted through the volumes which followed
it into its throbbing cup, again to undergo its fiery ordeal at the
threshold of the infernal regions."
Grand as this display must have been, it was but a momentary spasm,
a feeble effort compared with the terrific force which sustains the
Giant's river-volume, with a steady uprush two hundred feet high, for
the space of three hours and a half. There are many, perhaps scores,
of geysers in the Firehole Basin, which--even in midsummer, when their
action is weakest--far surpass the glory of Iceland.
But what is the origin of the power that sustains these wonderful
eruptions? And what is the cause of its intermittent action?
Fortunately these questions are not only answerable, but the answers
are susceptible of demonstration, as Professor Tyndall has shown in his
admirable lectures on heat considered as a mode of motion, wherein he
gives the following lucid description of the mechanism and development
of the Great Geyser of Iceland: in principle the description applies
equally to the geysers of Firehole Basin, and all other springs of the
kind.
"It consists of a tube seventy-four feet deep and ten feet in diameter.
The tube is surmounted by a basin which measures from north to south
fifty-two feet across, and from east to west sixty feet. The interior
of the tube and basin is coated with a beautiful smooth silicious
plaster, so hard as to resist the blows of a hammer; and the first
question is, how was this wonderful tube constructed--how was this
perfect plaster laid on? Chemical analysis shows that the water holds
silica in solution, and the conjecture might therefore arise that the
water had deposited the silica against the sides of the tube and
basin. But this is not the case: the water deposits no sediment; no
matter how long it may be kept, no solid substance is separated from
it. It may be bottled up and preserved for years as clear as crystal,
without showing the slightest tendency to form a precipitate. To answer
the question in this way would moreover assume that the shaft was
formed by some foreign agency, and that the water merely lined it. The
geyser basin, however, rests upon the summit of a mound about forty
feet high, and it is evident from mere inspection that the mound has
been deposited by the geyser. But in building up this mound the spring
must have formed the tube which perforates the mound, and hence the
conclusion that the geyser is the architect of its own tube.
If we place a quantity of geyser water in an evaporating basin
the following takes place: in the centre of the basin the liquid
deposits nothing, but at the sides where it is drawn up by capillary
attraction, and thus subjected to speedy evaporation, we find silica
deposited. Round the edge a ring of silica is laid on, and not until
the evaporation has continued a considerable time do we find the
slightest turbidity in the middle of the water. This experiment is the
microscopic representative of what occurs in Iceland. Imagine the
case of a simple thermal silicious spring, whose waters trickle down
a gentle inclosure; the water thus exposed evaporates speedily, and
silica is deposited. This deposit gradually elevates the side over
which the water passes until finally the latter has to take another
course. The same takes place here, the ground is elevated as before,
and the spring has to move forward. Thus it is compelled to travel
round and round, discharging its silica and deepening the shaft in
which it dwells, until finally, in the course of ages, the simple
spring has produced this wonderful apparatus which has so long puzzled
and astonished both the traveller and the philosopher."
The time required for the construction of the Great Geyser tube has
been estimated by Commander Forbes as ten or eleven centuries, on the
following grounds: a bunch of grass, placed under a little fall made by
the ejected water, receives, in twenty-four hours, a coating of silica
the thickness of a thin sheet of paper, or about one five-hundredth
part of an inch. At this rate it would take 1036 years to build up
the 762 inches, which, according to his measurement, is the depth
of the tube. In evidence of the probable truth of this estimate he
makes note of the following facts: first, there is no notice of this
fountain in the early history of the colonization of the island 986
years ago, at which time the tube would have been only three feet deep,
and its eruptions too slight to attract attention; second, 436 years
afterwards, when the tube would have been twenty-six feet deep, and the
eruptions proportionately important, the Geyser is mentioned; third,
accurate records of all occurrences were kept by the early inhabitants,
and if so remarkable a phenomenon had existed at the time, it could not
have been left unnoticed.
The phenomena attending a geyser-eruption--the filling of the basin
with water, the agitation of the water, with deafening detonations,
the escape of steam, and so on--have been sufficiently described in
the preceding chapters. Their causes have been ingeniously explained
by Professor Bunsen, who succeeded in determining the temperature of
the geyser-tube, throughout its entire length, a few minutes before
an eruption. The annexed diagram shows on the left the observed
temperatures of the water at different depths, and on the right
the temperatures at which water would boil, taking into account
the pressure of the atmosphere increased by the presence of the
superincumbent column of water. The degrees have been changed from
Centigrade to our familiar Fahrenheit standard, disregarding fractions.
[Illustration]
It will be observed that in no part of the tube does the water reach
the boiling point. The nearest approach to it is at A, thirty feet from
the bottom; out even here the water is some four degrees below the
temperature at which it could boil. How then is an eruption possible?
Professor Tyndall's explanation is in substance this: Suppose that by
the entrance of steam from the ducts near the bottom of the tube the
geyser column is elevated six feet, a height quite within the limits
of actual observation; the water at A is thereby transferred to B.
Its boiling point at A is 255°, and its actual temperature is 251°;
but at B its boiling point is only 249°, hence when transferred from
A to B, the heat which it possesses is in excess of that necessary
to make it boil. This excess of heat is instantly applied to the
generation of steam; the column is thus lifted higher, and the water
below is relieved of pressure, and its boiling point lowered. More
steam is generated; this lifts the column still higher, and compels the
generation of more and more steam, until the whole upper portion of the
column bursts into ebullition, and the water, mixed with steam-clouds,
is projected into the atmosphere, and we have the geyser eruption in
all its grandeur.
One confirmation of this theory of Bunsen's is that small stones
suspended in the lower part of the geyser-tube are not thrown out
during an eruption; and a stronger confirmation lies in the fact that
all the peculiarities of geyser action can be imitated. Professor
Tyndall uses for this purpose an apparatus consisting of a tube of iron
six feet long, surmounted by a basin, and heated by fires underneath.
To imitate, as far as possible, the conditions of the geyser, he
encircles the tube with a second fire, two feet from the bottom. As the
water in the tube becomes heated, the phenomena of geyser eruption
are repeated in miniature with beautiful regularity. By stopping the
mouth of the tube with a cork, the enforced explosions of the Strokr
are reproduced; and by similar simple devices the action of all other
eruptive springs may be accurately imitated.
All through the Firehole Basin and around Yellowstone Lake are many
extinct geysers; sometimes, as in the case of Old Faithful, an active
geyser is surrounded by a number of deserted cones, the remains of
ancient "roarers." What occasions their decline? Earthquakes may, and
no doubt frequently do, derange their mechanism, as observed in the old
Strokr. But most of them probably die a natural death, from old age and
decrepitude.
"A moment's reflection," says Professor Tyndall, "will suggest that
there must be a limit to the operations of the geyser. When the tube
has reached such an altitude that the water in the depths below,
owing to the increased pressure, cannot attain its boiling point, the
eruptions of necessity cease. The spring, however, continues to deposit
its silica, and often forms a _Laug_, or cistern. Some of these, in
Iceland, are forty feet deep. Their beauty, according to Bunsen, is
indescribable. Over the surface curls a light vapor; the water is
of the purest azure, and tints with its lovely hue the fantastic
incrustations on the cistern walls; while at the bottom is often seen
the mouth of the once mighty geyser. There are in Iceland vast, but
now extinct geyser operations. Mounds are observed whose shafts are
filled with rubbish, the water having forced a passage underneath and
retired to other scenes of action. We have, in fact, the geyser in its
youth, manhood, old age, and death here presented to us. In its youth
as a simple thermal spring; in its manhood, as an eruptive column; in
its old age, as the tranquil _Laug_; while its death is recorded by
the ruined shaft and mound, which testify the fact of its once active
existence."
All that Professor Tyndall describes so eloquently of Iceland,
exists in our Grand National Park in infinitely greater variety, and
magnitude, and splendor. And much more: Iceland has no Gardiner's
River. To find the nearest approach to the marvels of White Mountain
Hot Spring, we must go to the opposite side of the globe--to New
Zealand. In the celebrated Lake District of the North Island is a
region of hot springs, far exceeding in extent and variety all the
others in the world, save those of the Yellowstone. First of all, says
Hochstetter, the most marvellous of the Rotomahana marvels is the Te
Tarata--the Tattooed Rock--with its terraced marble steps projecting
into the lake. The spring lies about eighty feet above the lake, on a
fern-clad hill-slope, in a crater-like excavation, with steep reddish
sides, from thirty to forty feet high, and open only toward the lake.
The basin of the spring is about eighty feet long and sixty wide,
filled to the brim with perfectly transparent water, which in its
snow-white basin appears of a beautiful blue, like the blue turquoise.
Immense clouds of steam curl up from the surface, obstructing the view,
but the noise of boiling and seething is always audible. The water is
slightly salt, but not unpleasant to the taste, chemically neutral,
and possesses petrifying, or rather incrusting qualities, in a high
degree. The deposit is silicious, like that of the Iceland springs and
the springs around Yellowstone Lake, not calcareous, like those of
Gardiner's River; yet the system of terraces built up by the deposit
on the hill-slope has the same appearance of a cataract plunging over
a series of natural shelves and suddenly turned to stone. The deposits
cover an area of about three acres, a mere trifle compared with the
square miles of similar formations on Gardiner's River and in the
Yellowstone Basin.
In the same neighborhood is a system of bubbling mud-pools, miniature
copies of those on the Yellowstone above the falls. The principal
group, lying in a ravine nearly a quarter of a mile long, is described
by Dr. Hochstetter as follows:
"The entrance to the ravine is overgrown with a thicket and rather
difficult of access; it also requires considerable caution, as
suspicious places have to be passed, where the visitor is in danger of
being swallowed up in heated mud. Inside, the ravine has the appearance
of a volcanic crater. The bare walls, utterly destitute of vegetation,
are terribly fissured and torn, and odd-looking rocky serratures,
threatening every moment to break loose, loom up like dismal spectres
from red, white and blue fumarole-clay--evidently the last remains of
decomposed rocks. The bottom of the ravine is of fine mud, scattered
with blocks of silicious deposit, like cakes of floating ice after a
thaw. Here, a big caldron of mud is simmering; there, lies a deep basin
of boiling water; next to this is a terrible hole, emitting hissing
jets of steam, and further on are mud-cones from two to five feet
high, vomiting hot mud from their craters with dull rumblings, and
imitating on a small scale the play of large fire volcanoes." The gay
colors of the Yellowstone mud-springs are frequently exhibited in the
volcanic lake district of New Zealand, and so indeed are most of the
other phenomena we have been studying, though on a far less magnificent
scale. For example, the grandest "Firehole basin" on the island
occupies the Shallow valley of a little stream the Waikato, for the
distance of a mile. It is but a cabinet exhibition comparatively, yet
the learned geologist of the _Novara_ expedition grows eloquent in his
description of it. "In the morning a dense fog lay upon the Waikato,
but it soon vanished, the sun shone brightly into the valley, and
now--what a sight! In its swift course, forming rapids after rapids,
the Waikato was plunging through the deep valley between steep-rising
mountains; its floods whirling and foaming round two small rocky
islands in the middle of the river, were dashing with a loud uproar
through the defile of the valley. Along its banks white clouds of steam
were ascending from hot cascades falling into the river, and from
basins full of boiling water shut in by a white mass of stone. Yonder
a steaming fountain was rising and falling; now there sprung from
another place a second fountain; this also ceased in its turn; then two
commenced playing simultaneously, one quite low at the river bank, the
other opposite on a terrace; and thus the play continued with endless
changes, as though experiments were being made with grand waterworks,
to see whether the fountains were all in perfect order, and whether
the waterfalls had a sufficient supply. I began to count the places
where a boiling waterbasin was visible, or where a cloud of steam
indicated the existence of one. I counted seventy-six points, without,
however, being able to survey the whole region, and among them were
numerous intermittent geyser-like fountains with periodical eruptions
of water."
[Illustration: THE GREAT CAÑON AND LOWER FALLS OF THE YELLOWSTONE.]
The picture is admirably drawn, but could the artist have done so
well with the stupendous chasm of the Grand Cañon? or the thousand
volcanic vents of Firehole Basin with their deafening detonations,
their immeasurable evolutions of water and steam? It is possible,
but scarcely probable. The incomprehensible grandeur of the scene
would have awed, astounded, bewildered him, and like our Yellowstone
explorers, he would have despaired of grouping the myriad marvels into
one grand effect, and contented himself with setting down a few details
of form and color.
In following the exploration of the Yellowstone country and Firehole
Basin, the reader has doubtless observed, in the passage from the quiet
springs of Gardiner's River to the erupting fountains further on, that
there is a complete change in the nature of the deposits. The mounds
and terraces built up by the former have for their basis _lime_, those
of the latter _silica_. Dr. Hayden attributes the calcareous deposits
to the deep bed of limestone underlying the springs, but not all
waters have the power of disolving lime so freely, nor could ordinary
water take from the trachytic lavas below the silicious springs around
Yellowstone Lake and in the Firehole Basin, the silica that appears
so abundantly in their deposits. There must be other forces at work.
What are they? "Both kinds of springs," says Dr. Hochstetter, in
his chapter on New Zealand springs, "owe their origin to the water
permeating the surface and sinking through fissures into the bowels
of the earth, where it becomes heated by the still existing volcanic
fires. High-pressure steam is thus generated, which, accompanied by
volcanic gases--such as muriatic acid, sulphurous acid, sulphuretted
hydrogen and carbonic acid--rises again toward the colder surface and
is there condensed into hot water. The overheated steam and the gases
decompose the rock beneath, dissolving certain ingredients which are
deposited on the surface. According to Bunsen's ingenious observations,
a chronological succession takes place in the coöperation of the gases.
The sulphurous acid acts first. It is generated where rising sulphur
vapor comes in contact with glowing masses of rock. Wherever vapors of
sulphurous acid are constantly formed, there acid-springs or solfataras
arise. Incrustations of alum are very common in such places, arising
from the action of sulphuric acid on the alumina and alkali of the
lavas; another product of the decomposition of the lavas is gypsum,
or sulphate of lime, the residuum being a more or less ferruginous
fumarole clay, the material of the mud-pools. After the sulphurous
acid comes sulphuretted hydrogen, produced by the action of steam on
sulphids; and by the mutual decomposition of sulphuretted hydrogen
and sulphurous acid sulphur is formed, the characteristic precipitate
in all solfataras, while the deposition of silica is either entirely
wanting or quite inconsiderable, and the smell of sulphuretted hydrogen
is but rarely noticed. These acid springs have no periodical outbursts
of water.
In course of time the source of sulphurous acid becomes exhausted, and
sulphuretted hydrogen alone remains active. The acid reaction of the
soil disappears, yielding to an alkaline reaction by the formation of
sulphids. At the same time carbonic acid begins to act upon the rocks,
and the alkaline bi-carbonates thus produced dissolve the silica, which
on the evaporation of the water is deposited in the form of opal or
quartz or silicious earth, and thus the shell of the springs is formed,
on the structure of which the periodicity of the outburst depends....
The deposition of silica in quantities sufficient for the formation
of this spring-apparatus in the course of years, takes place only in
the alkaline springs. Their water is either neutral or has a slightly
alkaline reaction. Silica, common salt, carbonates and sulphates are
the chief ingredients dissolved in it. In the place of sulphurous
acid the odor of sulphuretted hydrogen is sometimes observed in these
springs.... By the gradual cooling of the volcanic rocks under the
surface of the earth the hot springs themselves gradually die out,
for they too are but a transient phenomenon in the eternal change of
created things."