VOLCANOES OF THE UNITED STATES
For some readers this may be a surprising chapter heading, for it is a
general impression that there are no volcanoes in the United States.
It is true that practically all of the volcanoes of this country are
dormant or extinct. They have, however, at one time been exceedingly
active, and, if reports are correct, some of them were active during
comparatively recent times.
Nearly all of the volcanoes of the United States lie west of the
meridian of Denver. These volcanoes belong to two distinct types,
either the Vesuvian type with built up cones, or the plateau or
fissure type already referred to.
The following brief description of the volcanoes of the United States
has been collated, for the greater part, from Wallace's excellent book
on the volcanoes of North America.
Crossing the United States on the Southern Pacific Railroad one's
attention is caught, in Arizona, by a magnificent group of mountains
known as the San Francisco Mountains. The highest peak of these
mountains reaches 12,562 feet above the level of the sea, and 5,700
feet above the surface of the plateau on which the mountains stand.
[Illustration: FIG. 18. THE UNITED STATES]
According to G. K. Gilbert, the San Francisco Mountain group is formed
of a variety of lava known as trachyte, that is of comparatively
recent ejection, possibly of a geological age called the Tertiary. The
lava forming the mountains escaped through a number of crater cones,
some of which can still be seen in the neighborhood. Some of these
craters are now in almost as perfect a condition as the day they were
formed. Indeed, to one looking at them from a neighboring elevation,
they appear so fresh, and so little affected by the climate, that one
might almost believe that the lava had just flowed out of the craters,
and has not yet hardened. Nevertheless, geologists are sure they have
been formed long before man appeared on the earth. In one of these
craters a lake of fresh water has collected.
Another extinct volcano of the United States is Mt. Taylor in New
Mexico, nearly east of the San Francisco Mountains. This mountain
rises from the surface of a high table-land, or, as it is called
in this part of the world, a _mesa_. The surface of the plateau is
covered with a thick lava stream from which Mt. Taylor rises to
a height of 11,390 feet above the level of the ocean. This mesa,
or table-land, is forty-seven miles in length from northwest to
southeast, and about twenty-three miles in breadth. Its general
elevation is about 8,200 feet. The plateau rises about 2,000 feet
above the surface of the level land that surrounds it. All these
2,000 feet have been removed by erosion. The table-land from which
Mt. Taylor rises has not been eroded by the action of the rain,
rivers, and other weathering agencies like the surface of the country
surrounding it, because of a covering of lava that has been spread
over its surface to a depth of about 300 feet.
Mt. Taylor is formed almost entirely of lava that has escaped through
a single opening and has built up a high cone around it. The volcano
is now quite extinct, so that the original form of the mountain has
been greatly changed by erosion.
You will remember, when we were discussing the general subject of
volcanoes, in the beginning of this book, that we spoke of volcanic
mountains being bottled up after an eruption, by the hardening of
the lava which remained in the crater and the tube that connects the
crater with the place from which the lava had been derived. We then
spoke of this hardened mass being known as a _volcanic plug_, or
stopper, explaining how the volcano could never again erupt through
its old crater unless it could develop sufficient force to blow out or
remove this stopper.
Now besides the crater at the top of Mt. Taylor there were several
others in the eroded region surrounding the mesa, or high table-land,
from which Mt. Taylor rises. When, therefore, the erosion which
removed the 2,000 feet of rocks on all portions of the old mesa that
were not protected by the coating of lava, these old mountain plugs
were too hard to be worn away or eroded, and were, therefore, left
projecting into the air like vast pyramids.
If you should ever visit Mt. Taylor and should go to the eastern
border of this mesa, and look over the eroded plain, you would see in
the lowlands a part of the places from which the 2,000 feet of matter
have been slowly eroded. Dutton describes the beautiful panorama that
is to be seen as follows:
"The edge of the mesa suddenly descends by a succession of
ledges and slopes, nearly 2,000 feet into the rugged and
highly diversified valley-plain below. The country beneath
is a medley of low cliffs and bluffs, showing the browns
and pale yellows of the Cretaceous sandstones and shales.
Out of this confused patchwork of bright colors rise
several objects of remarkable aspect. They are apparently
inaccessible eyries of black rock, and at a rough guess, by
comparison with the known altitudes of surrounding objects,
their heights above the mean level of the adjoining plain
may range from 800 to 1,500 feet. The blackness of their
shade may be exaggerated by contrast with the brilliant
colors of the rocks and soil out of which they rise, but
their forms are even more striking."
These black piles are the _necks_ or lava plugs of extinct volcanoes.
They rise above the level of the plain because, being harder than
the surrounding rocks, they have resisted erosion. In some cases
these necks or plugs have been converted by shrinkage, on cooling,
into beautiful columns, somewhat of the type of the basaltic columns
of the Giant's Causeway. It would be difficult to count the number
of volcanic necks that can be seen near the edge of the mesa. One's
attention is at once attracted to some dozen of these piles, which are
especially striking on account of their great size, and ominous black
color, but the number is by no means limited to this dozen. There are
hundreds of them.
Fig. 19 gives some idea of a part of the view from the edge of the
mesa, and Fig. 20 the appearance of two of these volcanic necks.
But besides high volcanic mountains such as the San Francisco
Mountains and Mt. Taylor, there are, in different parts of the United
States, to be found fragments of huge craters from which, in the
geological past, immense quantities of lava have escaped. In some
instances these craters are but fragments of huge craters, that, like
the crater of Mt. Somma, in Vesuvius, have been nearly completely
blown away by some unrecorded explosion during the far past.
[Illustration: FIG. 19. PANORAMA FROM THE MESA AT THE EDGE OF MT.
TAYLOR _From U. S. Geological Survey_]
A crater of this type, known as Ice Springs Crater, is situated in the
desert valley west of the Wahsatch Mountains, some 125 miles south
of Salt Lake City, Utah. This crater is especially interesting from
the fact that it occupies a position on a plain that was formed by
the deposition of sediment in an immense lake that covered this part
of the United States very long before man lived on the earth. We
are alluding to Lake Bonneville, a lake that existed in a geological
time known as the Glacial Epoch. This lake occupied the territory now
filled by the Great Salt Lake of Utah, but towards the close of the
Glacial Epoch it was immensely larger than it is now. This can be
shown not only by the presence of shore lines, that are clearly marked
on the sides of the surrounding mountains, but also by the ancient
lake beaches, and deltas, that are common in the district, so that
instead of there being the comparatively limited area of Great Salt
Lake as marked on the maps of to-day there was a lake that had an area
of 19,750 square miles, that covered an area on which at least 200,000
people dwell.
[Illustration: FIG. 20. VOLCANIC NECKS, EDGE OF MESA AT MT.
TAYLOR _From U. S. Geological Survey_]
A similar lake, known as Lake Lehontan, existed at the same time,
covering large areas in the western parts of Nevada.
Coming now to Ice Springs Craters in Utah, we find here three small
craters formed of scoriæ and lapilli (volcanic ashes consisting of
small angular stony fragments). Near them lies a fragment of a much
larger crater known as the Crescent. In some respects this crater was
not unlike the crater of Somma that surrounded Mt. Vesuvius. It was
not, however, as large, having a diameter of only 2,200 feet. From
these craters streams of basalt flowed until they covered considerable
areas.
A still more recent crater known as Tabernacle Crater is situated
four miles south of the Ice Springs Crater. Tabernacle Crater takes
its name from the building known in Salt Lake City as the Tabernacle.
According to Gilbert, this crater was formed at a time when Lake
Bonneville stood at a comparatively low level, or when the water was
only from fifty to seventy-five feet above the bottom of the valley
on which the crater now stands. At that time an explosive volcanic
eruption occurred on the bottom of the lake, and the rim of the
crater, built up by this explosion, was gradually pushed above the
surface of the lake, so as to shut out its waters.
Extinct volcanic craters, not unlike those of Utah, occur also near
Ragtown, in Nevada, in a district known as the Carson Valley Desert,
in one of the broadest areas of what was once Lake Lahontan. Ragtown
is twenty-two miles southwest of Wadsworth on the Central Pacific
Railroad. At the present time there are two circular depressions or
volcanic craters filled with pools of strongly alkaline water known
as the Ragtown Pond, or Soda Lake. The large lake covers an area of
268-1/2 acres. Its greatest diameter is over 4,000 feet. Without going
into a detailed description it will suffice to say that the larger
crater probably was destroyed by an explosive volcanic eruption.
Another intensely alkaline lake that fills an extinct volcanic crater
is the Mono Lake, situated in Mono Valley in California at the eastern
base of the Sierra Nevadas. It has an area of about 200 square miles.
The centre of the lake has two small islands named Pacha and Negit.
Immediately south of Mono Lake are a number of craters that occupy
portions of what was once apparently a fissure extending in a general
north and south direction. The highest of these craters are in the
neighborhood of 2,500 feet.
But leaving these inconspicuous craters, let us briefly examine some
of the higher mountain peaks of the United States that are of volcanic
origin. One of the most conspicuous of these is Mt. Shasta. This
mountain is situated in California, at the northern end of the Sierra
Nevadas. It has a height of 14,350 feet. It is a snow-clad mountain of
a conical form, and is a conspicuous object in the landscape, because
it stands alone.
Mt. Shasta is a double-coned mountain. Besides the cone on its summit
there is a well-developed cone known as Shastina on the western side
of the mountain, 2,000 feet lower than the main summit.
There are well-defined lava streams on the slopes of Mt. Shasta. One
of these, which issued from the southern side of the mountain at
an elevation of 5,500 feet, divided into two streams. One of these
streams is twelve miles in length. The other entered the canyon of the
Sacramento River, thus displacing the water.
Coming now to the Cascade Mountains, in Oregon and Washington, we
will find in them a number of giant peaks of volcanic origin. The
most important of these are in regular order from south to north, as
follows: Mt. Pitt, 9,760 feet; Mt. Mazana, 8,223; Mt. Union, 7,881;
Mt. Scott, 7,123; Three Sisters, Mt. Jefferson, 10,200, and Mt. Hood,
11,225, in Oregon; Mt. Adams, 9,570; Mt. St. Helen's, 9,750; Mt.
Rainier, 14,525, and Mt. Baker in Washington, 10,877.
Nearly all these mountains have craters either on their summits or on
their sides. They are extinct volcanic mountains, that were, for the
most part, thrown up during the Tertiary Geological Period, so that
they have all been greatly affected by erosion.
One of the most remarkable of the above volcanic mountains is Mt.
Mazana, in Oregon. This mountain has on its summit an approximately
circular cavity from five to six miles in diameter, that is occupied
by a lake of water known as Crater Lake. This lake is 6,239 feet above
the level of the sea, and has a depth of 1,975 feet. It is surrounded
by nearly vertical walls ranging from 900 to 2,200 feet deep, so that
the vast caldera of which this great depression consists has a depth
of at least 4,000 feet.
Mt. Pitt, situated about sixty miles north of Mt. Shasta, in southern
Oregon, has a regularly shaped volcanic cone, and the remnant of a
crater at its summit. The Three Sisters and Mt. Jefferson lie to
the north of Mt. Pitt. Like the others they are ancient volcanic
mountains. But little is accurately known concerning them.
Mt. Hood, 11,225 feet high, rises from the crest of the Cascade
range in Northwest Oregon, about twenty-five miles south of the
Columbia River. Mt. Hood is an exceedingly majestic mountain. At its
summit there are only portions of the walls of the original crater.
When ascended in 1888, streams of sulphur vapor were escaping from
fumaroles on its northeastern slopes, at an elevation of 8,500 feet
above the sea.
Mt. Adams and Mt. St. Helen's lie to the north of Mt. Hood. Mt. Adams
about sixty miles to the north, and beyond this, Mt. St. Helen's.
Accurate information concerning the summit of Mt. Adams is still
lacking. Mt. St. Helen's in Washington has more of a conical summit.
Russell states that according to frontiersmen, St. Helen's has been
in a state of activity within the past fifty years. A French-Canadian
asserts that the mountain was in actual eruption during the winter of
1841-43, that at this date the light from the volcano was sufficiently
bright to enable one to see and pick up a pin in the grass at midnight
near his cabin some twenty miles distant. Mt. St. Helen's was ascended
in 1889, when fumaroles were found on the northeast side.
Mt. Rainier in Washington is plainly visible from Puget Sound. It is
a most magnificent mountain. The summit has a bowl-shaped crater, of
an almost perfectly circular form. The inside of the crater, when
last ascended, was filled to within thirty or thirty-five feet of its
rim with ice and snow. There was, however, evidences of heat, since
numerous jets of steam were seen issuing from its interior rim.
Mt. Baker, Washington, is the northernmost of the volcanoes of the
Cascade Mountains, south of the boundary line between the United
States and Canada. But little is known of this mountain. The summit
appears as a conical peak from Puget Sound, so that its form would
seem to show that it is of volcanic origin. According to Gibbs,
officers of the Hudson Bay Company, as well as the Indians, declared
that Mt. Baker was in eruption in 1843, when it broke out at the same
time as Mt. St. Helen's, covering the country with ashes.
There are but few volcanoes in the Rocky Mountains which extend from
north to south through the United States at a considerable distance to
the east of the Sierra Nevadas and Cascade Ranges. The Spanish Peaks,
situated in the southeastern part of Colorado about sixty miles south
of Pueblo, are the remains of ancient volcanoes. Two of the most
prominent of these peaks rise from 12,720 to 13,620 feet above the sea.
We shall make no effort to attempt to describe the volcanic mountains
that may exist in those portions of the Rocky Mountain Ranges or the
Cascade Range lying in Canada. Comparatively little is known of them,
but inasmuch as volcanic activity has been manifested in Alaska, it
would seem highly improbable, as Russell remarks, that volcanoes
should suddenly cease at the northern boundaries of the United States
and then begin again at the most southern part of Alaska. It will be
sufficient to say that Mt. Edgecome, situated on an island in the
neighborhood of Sitka, is of volcanic origin, and that the Aleutian
Islands, beginning at Alaska on the east at the head of Cook's Inlet,
extend westward through the Peninsula of Alaska to the Peninsula of
Kamtschatka for a distance of nearly 1,600 miles. This belt, which
is called by Russell "the Aleutian Volcanic Belt," contains numerous
volcanoes that are known to have been active in historical times.
Mt. Wrangell, on the Copper River, 200 miles northeast of the head
of Cook's Inlet, is a lofty volcanic mountain that is said to have
been in eruption in 1819, and at the time of last report was still
throwing out columns of steam. While much remains to be ascertained
about the volcanoes of the Aleutian Islands, it would appear that
there are active volcanoes on twenty-five of these islands, on which
some forty-eight craters have been found. Eruptions are common in the
district.