THE VOLCANIC ISLAND OF HAWAII
The volcanic island of Hawaii, the largest of the Sandwich Island
chain, is situated in the mid Pacific, south of the Tropic of
Cancer. As shown in Fig. 5, this island chain consists of Hawaii,
Maui, Molokai, Oahu, Kauai, Nihau, and about eight large islands,
together with numerous small islands, extending in a general northwest
direction from Hawaii to Nihau, a distance of about 400 miles. Like
most volcanic islands they lie in more or less straight lines,
probably along fissures, in this case in two nearly parallel lines.
The island of Nihau, however, is an exception, the direction of the
greatest length being almost straight across the two parallel lines.
The Sandwich Islands lie 2,000 miles from San Francisco in deep water,
between 2,000 and 3,000 fathoms, or between 12,000 and 18,000 feet in
depth. This island chain consists of great volcanic mountains, that
had, at one time, fifteen active volcanoes of the first class. These
are now all extinct but three, and all of these are on the island of
Hawaii.
In his report to the United States Geological Survey for 1882-83,
Dutton states that the summit of Mt. Haleakala on East Maui is 10,350
feet above the sea level. Oahu has peaks on its eastern side 2,900
feet high, and peaks on the western side 3,850 feet high. The summit
of Kauai is probably 6,200 feet above the sea.
[Illustration: FIG. 5. THE HAWAIIAN ISLANDS _From U. S.
Geological Survey_]
It can be shown by deep-sea soundings that all these volcanic piles
are the summits of a gigantic mountain mass that rises abruptly from
the bed of the Pacific. There are reasons for believing that this
submarine chain continues for many hundreds of miles in the same
direction beyond Kauai.
The extinct volcano, Haleakala, on East Maui appears to have been in
eruption at a much later day than Mt. Kea, which is also an extinct
volcano. But the natives have no traditions of any eruptions.
The volcanoes on the other islands have been extinct for a very long
time judging from the extent of their erosion. Dutton is of the
opinion that the western islands of the chain have been extinct for
much longer times than the remaining islands.
The Sandwich Islands, also known as the Hawaiian Islands, are one of
the colonial possessions of the United States. The island of Hawaii is
about 2,000 miles from San Francisco. Honolulu, on the island of Oahu,
the principal seaport of the chain, has a pleasant climate, and is an
important coaling station for warships, commercial vessels, whalers,
and trading ships generally.
The principal product of the island is sugar cane.
The island of Hawaii, as shown in map, Fig. 6, consists of five
volcanic mountains and some small coral reefs. These mountains are:
Mt. Kea, on the north, 13,805 feet in height; Mt. Haulalai, in the
west central part of the island, 8,273 feet in height; Mt. Loa, in the
south central part of the island, 13,675 feet in height; Mt. Kilauea,
twenty miles east of the crater of Loa, 4,040 feet high at the Volcano
House, and 4,158 feet on the highest point on the west, and Kohala,
5,505 feet in height, running through the northwestern part of the
island, and the Kohala mountains in the northwestern part.
[Illustration: FIG. 6. HAWAII _From Dana's Manual of
Geology_]
Of these mountains, Mt. Loa and Kilauea are the only active volcanoes,
and are in frequent eruption. Mt. Haulalai was in eruption during
1804. Mt. Kea has not been active during historical times, while Mt.
Kohala has been inactive for so long a time that its slopes are deeply
gullied wherever the rivers flow down them.
As you can see from the map, Hawaii is very large. It has a length of
ninety-three miles from north to south, and a breadth of eighty miles
from east to west, its area is about 6,500 square miles. With the
exception of small patches of coral reefs, Hawaii is formed entirely
of lava, and is the largest pile of lava in the world with the single
exception of Iceland.
Where the islands of the Hawaiian chain have coral reefs extending
off their coasts, excellent harbors are found in the deep waters
between the islands and the reefs. Hawaii, however, has no extended
reefs of this character, and, consequently, no first-class harbors.
Hilo, on the eastern coast, is the best harbor, and is, therefore, the
principal settlement.
A very brief examination of the map of Hawaii will show you that there
are no rivers on the island, except on the sides exposed to the wind,
that is, on the northern and northeastern slopes. Since the yearly
rainfall on Hawaii is large, being in the neighborhood of a hundred
inches, you will understand that considerable rain water falls on the
island. In those parts of the island where it does not run off the
surface it must drain downward through the loose piles of broken rocks
or cinders. A rainfall of one hundred inches a year means that if all
the rain which falls on each square foot of surface was collected
in a flat vessel one foot square with vertical sides it would fill
the vessel to the depth of one hundred inches, or over eight feet.
The drainage of the rainwater downwards through these parts of the
island, must, therefore, be large.
Another curious fact you can notice on the map, is that the lava
streams of the past fifty years from Mt. Loa indicated by heavy
dotted lines, in no cases begin at the crater, but start at fairly
considerable distances from it. Later on in this chapter we shall
explain the reason for this curious fact.
Since practically the whole of Hawaii has been formed from the streams
of lava that have flowed at one time or another, you can understand
how great these flows must have been. But to do this fully you must
not only take into consideration the portions of the island that
lie above the ocean and reach into the air at its greatest height
to 13,805 feet above its surface, you must also remember that this
mountain rises from a deep ocean, so that if all the water were
removed, you would see Hawaii towering up above the former level
of the sea to the height of about 31,000 feet, or higher than Mt.
Everest, the highest point on the earth above the present sea level.
This would be, approximately, five and eight-tenths miles. You can
understand, therefore, how great the flow of lava must have been.
We shall begin the description of Hawaii with the active volcano of
Mt. Loa, or, as it is sometimes called in Hawaii, "The White Mountain."
You will remember that the eruption of Krakatoa was of the explosive
type. Practically no melted rock or lava escaped from the crater.
Indeed, if it had escaped it would not have been seen; for, not only
the cone near the crater, but also much of the mountain itself was
blown completely out of sight and covered by the waters of the ocean.
The eruptions of Mt. Loa are of an entirely different type. In Loa
there are no explosions, the eruptions being what are called the
non-explosive or quiet volcanic eruption type. It will be necessary to
explain some of the peculiarities of this kind of eruptions.
There is a great difference in the liquidity or the ease with which
different kinds of lava flow. Some lava is very thick or viscid,
or is sticky like thick molasses or tar, and therefore flows very
sluggishly. Other lava is thin or mobile, more closely resembling
water in the ease with which it flows. Now, in the case of a volcanic
mountain of fairly considerable height, where the lava possesses
marked liquidity, the lava as it rises from great depths in the tube
of the volcano seldom flows over the top or rim of the crater. This is
not because the force that brings the lava up is unable to carry it
a few thousand feet higher, so that it can run over the brim of the
crater, but because the walls of the volcanic mountains are unable to
stand the great pressure which the mass of liquid lava exerts against
their sides.
It can be shown that a column of liquid lava 500 feet high, will exert
a pressure on the walls of the crater of about 625 pounds to the
square inch. Therefore, in very high volcanic mountains, long before
the lava can reach the edge of the crater and overflow, the pressure
becomes so great, that cracks or fissures are made in the sides of
the mountain, through which the lava is quietly discharged; when, of
course, the level of the lava in the crater falls considerably. In
volcanoes of the explosive type, no matter what may be the condition
of lava, should a large quantity of water suddenly find an entrance to
a large body of molten lava at some distance below the surface, the
lava would be suddenly thrown explosively into the air, where being
chilled, it would afterwards descend in showers of ashes, cinders, or
volcanic dust.
In some volcanic mountains such as Mt. Loa, the crater, instead
of being situated at the top of a conical pass of ashes or other
material, consists of a pit-like depression, generally occupying a
level tract or plain at the top of the mountain. This pit is known
as a _caldera_, or _caldron_, or what you might, perhaps, call a
huge kettle or boiler. The pit has more or less vertical sides that
extend downwards for unknown depths to the place from which the lava
comes. The vertical walls of the caldera are not, however, smooth, but
exhibit numerous horizontal ledges, that mark places where portions of
the floor of the caldera were situated at different times.
At the bottom of the large pit or caldera on the summit of Mt. Loa
can be seen the level floor formed of hardened lava. This floor is
surrounded by vertical walls on which can be seen the broken edges of
the old lake bed.
Captain Dutton, in a paper on Hawaiian volcanoes, prepared for the
United States Geological Survey, and published in its Fourth Annual
Report for 1882-83, thus describes the appearance at the great crater
as it was in 1882.
"The summit of Mauna Loa (Mt. Loa), is a broad and large
platform about five miles in length and four miles in
width, within which is sunken the great caldera called
Mokuaweoweo. The distance from the point where we first
reach the summit to the brink of the pit is about a mile
and a half. The surface of the platform is much more rugged
than the slopes just ascended. It is riven with cracks, and
small faults,[2] and piles of shattered rock are seen on
every hand. Nowhere is there to be seen the semblance of
a cinder cone. Doubtless many eruptions have broken forth
from the various fissures on this summit, but only here
and there can insignificant traces of such catastrophes
be definitely distinguished. The absence of fragmental
ejecta (broken rock that are thrown out) is extraordinary.
The shattered blocks, slabs, and spalls (chips) which
everywhere cumber the surface appear to have resulted from
the spontaneous shivering and shattering of the lava sheets
by their own internal tensions as they cooled.
Fig. 7, taken from Dutton's report, gives the general shape of this
great caldera. Dutton's description of the same is as follows:
"The length of the main caldera is a little less than
three miles and its width about a mile and three-quarters.
Its floor, viewed from above, appears to be composed of a
series of flat surfaces occupying two distinct levels, the
higher upon the surface of the black ledge, the lower lying
within the ledge. Upon the western side is a small cinder
cone standing close upon the border of the black ledge.
It is the only one visible, either within the caldera or
upon the surrounding summit. Its height is about 125 or 130
feet. It was seen in operation, throwing up steam, clots of
lava, and lapilli (some of the larger pieces of fragmentary
lava) in the year 1878. The only other diversifications of
the floor are many cracks which traverse it, the larger of
which are distinctly visible from above. Some of them are
considerably faulted. There is no difficulty in recognizing
the fact that the whole floor has been produced by the
sinkage of the lava beds which once continued over the
entire extent of the depression, their undersides having
been melted off most probably by the fires beneath. The
lava beds in the immediate vicinity of the brink upon the
summit platform wear the aspect of some antiquity. They
have become brown and carious by weathering, and, although
no soil is generated, little drifts of gravel are seen
here and there mixed with pumice. Since the caldera was
formed there is no indication that the lavas have anywhere
overflowed its rim. And yet it is a very strange fact that
within a half mile, and again within a mile to a mile and
a half, lavas have been repeatedly erupted within the last
forty years from the summit platform, and have outflowed
at points situated from 700 to 900 feet above the level of
the lava lake within. Traces may also be seen, at varying
distances back of the rim, of very many eruptions in which
the rocks betoken great recency, although no dates can be
assigned to their occurrence."
[Illustration: FIG. 7. PANORAMA OF MOKUAWEOWEO _From U. S.
Geological Survey_]
[Illustration: FIG. 8. VIEW OF THE CRATER OF KILAUEA FROM THE
VOLCANO HOUSE _From U. S. Geological Survey_]
During his visit to this great pit, Captain Dutton succeeded in
climbing down the almost vertical walls on the side of the crater,
and, reaching the surface of the hardened lake, walked over it. It
must have required no little courage to thus venture on the thin
floor of a lake which he knew was filled to great depths with red hot
boiling lava, for he was walking over the surface of a slumbering
volcano, that might at almost any moment awaken, and opening, swallow
him and his companions. Through enormous cracks in the floor, he could
feel the heat from the molten mass, while, through the same openings
came suggestive whiffs of sulphur vapor.
During the eruption of this mountain, on January 23d, 1859, the light
from the glowing lava streams was bright enough to read fine print at
Hilo, a distance of thirty-five miles.
During the eruption of 1852, a stream of white-hot lava was thrown up
into the air from one of the fissures to a height of from 300 to 400
feet.
[Illustration: STONES AND LAVA THROWN UPWARDS--ERUPTION OF
MOKUAWEOWEO, HAWAII, JULY 4-21, 1899 _From a Stereograph,
Copyright, by Underwood & Underwood_]
When an eruption takes place in Mt. Loa the column of lava slowly
rises in the crater, threatening to overflow its lowest edges, but
before this can take place the pressure becomes so great that some
portion of the mountain below the crater is fractured and the lava
quietly escapes.
During some conditions of the mountain every fifteen or twenty minutes
a column of highly glowing lava is shot upwards like a fountain to
a height of 500 feet and over, falling back into the lake in fiery
spray. Unusual heights of these streams are generally followed by an
eruption.
These curious jets of molten rock certainly cannot be due to the
pressure of higher columns of lava, since the crater itself is near
the top of a high plain. They are believed to be due to steam formed
by the penetration of the rain water that falls on this part of the
mountain.
You can now understand why the lava streams escaping from Mt. Loa as
shown on the map, in Fig. 6, do not begin at the level of the crater;
for the discharge of the lava does not take place over the rim of
the crater, but through the cracks or fissures formed further down
the sides of the mountains. It must not be supposed, however, that
the fissures are limited to the sides of the mountain where they can
be seen. They probably occur in many places below the surface of the
water on some part of the bed of the ocean.
The crevices that are formed in this manner in the sides of the
mountain vary greatly in size, some being so narrow that the lava
scarcely flows through them at all but simply fills up the crevice,
hardens on cooling, and mends the cracks in the mountains, in the way
that a crack is mended in a piece of china by the use of glue or in
a wall of masonry by mortar. Through the largest crevices or cracks,
however, large lava streams may continue to flow often for several
weeks, or even longer.
Sometimes, especially towards the close of the eruptive flow, the
lava may escape disruptively, so that small cones are formed along
the lines of the fissures. Cones of this character are called lateral
cones, and in the case of a volcanic island, where the lava flows out
below the level of the water, the lateral cones sometimes project
above the water and form volcanic islands or dangerous shoals that
impede navigation.
When the lava pours out of a crevice in the side of the mountain, a
river of molten rock rushes down the slopes, at first like a torrent,
but on reaching the more nearly level ground, it spreads out in great
lava lakes or fields, the surface of which takes on the characteristic
black appearance of basalt, a certain kind of glass, for the lavas of
Mt. Loa are generally basaltic. After an eruption the hardened floor
of lava in the caldera, being no longer supported by the liquid mass
formerly below it, falls in, leaving a large cavity with only the
edges of the old floor clinging to the sides of the pit.
It will be interesting to give a short account of some of the great
lava streams that have been poured out at different times from Mt. Loa.
In the great eruption of August 11th, 1855, the lava escaped through
fissures from two to thirty inches in width. Then, flowing in a
continuous stream, it did not stop until it was within five miles of
Hilo.
In the eruption of January 23d, 1859, the lava stream flowed towards
the northwest on the east side of Haulalai, reaching the sea in eight
days.
The eruption of March 27th, 1868, was characterized by severe
earthquake shocks, one of which, occurring on the second of April,
destroyed many houses and produced huge fissures in the earth. These
shocks produced great earthquake waves that reached distant coasts.
Mt. Kilauea, lies at a lower level towards the east. This crater is
situated at 4,040 feet above the level of the sea, and is nearly 6,000
feet below the caldera on the top of Mt. Loa.
Fig. 8, taken from the United States Geological Survey, Fourth
Annual Report, for 1882-83, shows a view of Kilauea from the Volcano
House. Dutton gives the following description of the appearance of
Halemaumau, the pit crater or caldera of Kilauea.
"In front of us and right beneath our feet, over the crest
of a nearly vertical wall, more than 700 feet below, is
outspread the broad floor of the far-famed Kilauea. It
is a pit about three and a half miles in length, and two
and a half miles in width, nearly elliptical in plan and
surrounded with cliffs, for the most part inaccessible to
human foot, and varying in altitude from a little more than
300 feet to a little more than 700 feet. The altitude of
the point on which we stand is about 4,200 feet above the
sea....
"The object upon which the attention is instantly fixed
is a large chaotic pile of rocks, situated in the centre
of the amphitheatre, rising to a height which by an
eye estimate appears to be about 350 to 400 feet. From
innumerable places in its mass volumes of steam are poured
forth and borne away to the leeward by the trade wind. The
color of the pile is intensely black....
"Around it spreads out the slightly undulated floor of the
amphitheatre, as black as midnight. To the left of the
steaming pile is an opening in the floor of the crater,
within which we behold the ruddy gleams of boiling lava.
From numerous points in the surrounding floor clouds of
steam issue forth and melt away in the steady flow of the
wind. The vapors issue most copiously from an area situated
to the right of the central pile, and in the southern
portion of the amphitheatre. Desolation and horror reign
supreme. The engirdling walls everywhere hedge it in. But
upon their summits, and upon the receiving platform beyond,
are all the wealth and luxuriance of tropical vegetation
heightening the contrast of the desolation below...."
[Illustration: FIG. 9. CRATER OF KILAUEA _From Dana's Manual
of Geology_]
Fig. 9 represents the pit-like crater of Kilauea as it appeared after
the eruption of 1886. Here, as will be seen, there are several lakes
of lava, the largest of which is known as Halemaumau. The eruption of
1886, like all the eruptions of Kilauea, consisted of the escape of
the lava from an opening on the side of the mountain below the crater,
and a sinking in of the hardened floor of the crater. The figure also
shows the position of the New Lake that lies east of Halemaumau. The
extent and appearance of each of these lakes are constantly changing,
both as to height and area.
Dutton gives the following description of the appearance of the lake
of lava, and some curious phenomena that occur on its surface. He is
describing the general appearance of the pool of molten lava covered
as it is with a hardened black crust:
"The surface of the lake is covered over with a black
solidified crust showing a rim of fire all around its edge.
At numerous points at the edge of the crust jets of fire
are seen spouting upwards, throwing up a spray of glowing
lava drops, and emitting a dull, simmering sound. The heat
for the time being is not intense. Now and then a fountain
breaks out in the middle of the lake and boils freely for a
few minutes. It then becomes quiet, but only to renew the
operation at some other point. Gradually the spurting and
fretting at the edges augment. A belch of lava is thrown
up here and there to the height of five or six feet, and
falls back upon the crust. Presently, near the edge, a
cake of the crust cracks off, and one edge of it bending
downwards descends beneath the lava, and the whole cake
disappears, disclosing a naked surface of liquid fire.
Again it coats over and turns black. This operation is
repeated edgewise at some other part of the lake. Suddenly
a network of cracks shoots through the entire crust. Piece
after piece of it turns its edge downwards and sinks with
a grand commotion, leaving the whole pool a single expanse
of liquid lava. The lake surges feebly for awhile, but soon
comes to rest. The heat is now insupportable, and for a
time it is necessary to withdraw from the immediate brink."
It is very curious to think of cakes of hardened lava floating on the
surface of molten lava, but, of course, this is just as natural as
cakes of ice floating on the surface of water; for a cake of hardened
lava is, as you will understand, only a cake of frozen lava, and,
being lighter than the molten lava, must, of course, float on its
surface.
The disappearance of these cakes of frozen lava and their remelting is
still more curious, and can be explained as follows: The frozen or
solidified mass of black basalt is a trifle lighter than the lava on
which it is floating only while its temperature is high, and therefore
expanded by heat. As soon as it cools, its density increases, and when
it becomes a little greater than that of the liquid lava, it begins to
sink and soon disappears.
[Illustration: FIG. 10. SECTIONS OF KILAUEA AT DIFFERENT
PERIODS _From Dana's Manual of Geology_]
Professor Dana, who has made a careful study of the phenomena of
Kilauea, shows in Fig. 10, a cross section of Kilauea at different
times. Before the eruption of 1823, the depth of the crater was from
800 to 1,000 feet. At the eruption the bottom 600 to 800 feet, making
the depth of Kilauea over this deeper central part about 1,500 feet.
The varying depths at different dates are clearly marked on the
drawing.
The eruptions of Kilauea generally occur as follows:
First there is a slow rising of the lava in the crater. This rising
continues until the pressure is so great that the mountain is ruptured
at some lower place. Next a discharge of the lava and a sinking to a
level in the conduit that will depend on the position of the crevice.
Then a gradual falling in of the hardened floor of the lake, a portion
of the horizontal walls remaining on the sides of the caldera.
The eruption of Kilauea, however, has not always been of the quiet
type. There was an eruption in the year 1789 that would appear to
have been of the explosive variety. The following account is given by
Dana as taken from a history of the Sandwich Islands by the Rev. I.
Dibble, published in 1843:
"The army of Keoua, a Hawaiian chief, being pursued by Kamehamoha,
were at the time near Kilauea. For two preceding nights there had
been eruptions, with ejections of stones and cinders. The army of
Keoua set out on their way in three different companies. The company
in advance had not proceeded far before the ground began to shake and
rock beneath their feet, and it became quite impossible to stand.
Soon a dense cloud of darkness was seen to rise out of the crater,
and, almost at the same instant, the thunder began to roar in the
heavens and the lightning to flash. It continued to ascend and spread
around until the whole region was enveloped, and the light of day
was entirely excluded. The darkness was the more terrific, being
made visible by an awful glare from streams of red and blue light,
variously combined through the action of the fires of the pit and the
flashes of lightning above. Soon followed an immense volume of sand
and cinders, which were thrown to a great height, and came down in a
destructive shower for many miles around. A few of the forward company
were burned to death by the sand, and all of them experienced a
suffocating sensation. The rear company, which was nearest the volcano
at the time, suffered little injury, and after the earthquake and
shower of sand had passed over, hastened on to greet their comrades
ahead on their escape from so imminent a peril. But what was their
surprise and consternation to find the centre company a collection
of corpses! Some were lying down, and others were sitting upright,
clasping with dying grasp their wives and children, and joining noses
(the mode of expressing affection) as in the act of taking leave. So
much like life they looked that at first they supposed them merely
at rest, and it was not until they had come up to them and handled
them that they could detect their mistake." Mr. Dibble adds: "A blast
of sulphurous gas, a shower of heated embers, or a volume of heated
steam would sufficiently account for this sudden death. Some of the
narrators who saw the corpses, affirm that though in no place deeply
burnt, yet they were thoroughly scorched." As you will see in Chapter
XI, this sudden and awful death due to highly heated air and dust
particles, caused even a greater loss of life in the catastrophic
eruption of Pelée, in Martinique on May 8, 1902.
By reason of its situation at a lower level on the slopes of Mt. Loa,
Kilauea was at one time thought to be one of the craters lower down
on the slopes of Loa. This was the opinion of Professor Dana when he
examined the district in 1840. Since this time the region has been
more carefully studied, and Mt. Loa and Kilauea, are now generally
regarded as separate and independent volcanoes, neither of which acts
as a safety valve for the other.
We shall not attempt in this chapter to say anything concerning the
sources or places from where these great supplies of lava have been
drawn. This will be left to some subsequent chapter, after we have
described still other volcanoes.
The outlines of mountains like Mt. Loa or Kilauea differ greatly from
mountains like Vesuvius; their slopes, like the slopes of all other
Hawaii volcanoes, have an inclination which does not exceed 10°.
The lava streams, therefore, as they flow down the mountains, move
more slowly than they would were the slopes more precipitous, as in
mountains like Vesuvius.
There have been many eruptions of Kilauea. That which occurred in the
year 1840, was of great magnitude (see map, Fig. 6), and began in a
fissure southwest of the crater. The principal eruption, however,
broke out about twelve miles from the sea coast, and about twenty-five
miles east of Kilauea. Here an enormous mass of lava forming a stream
nearly three miles wide reached the ocean at Nanawale.
When an eruption takes place on Mt. Loa through a fissure at the
height of 10,000 to 13,000 feet the length of the lava streams is
frequently as great as twenty-five to thirty miles. Often the lava
though hardening at the surface will continue to flow underneath
through huge tunnels, of which the top and sides are composed of
solidified parts of the same lava stream. After the flow has ceased
long hollow tunnels often remain. If the lower end of such a tunnel
containing molten lava is momentarily closed, the pressure of the
lava above may not only burst through the obstruction, but may even
throw the lava upwards in jets 300 to 700 feet high. Probably most of
you have seen illumined fountains where jets of water are beautifully
lighted up by different colored electric lights placed below them.
Such fountains, however, can but poorly compare either in beauty or
grandeur with these wonderful lava fountains, common on the slopes of
Mt. Loa during an eruption.