SOME EFFECTS OF THE ERUPTION OF KRAKATOA
Besides the sound waves in the air, there were waves in the waters of
the ocean. Suddenly, without any warning, the people of Batavia were
surprised by a huge wave that, crossing the Straits of Sunda, entered
the ship canal before referred to as connecting the city with the
ocean, and, rising above the brick wall, poured over the surrounding
country.
Although Batavia was 100 English miles from Krakatoa, yet after
travelling this distance the wave was sufficiently strong to enter
the city and flood its streets with water to a depth of several feet.
Fortunately, the loss of life was small in the city of Batavia, but
very great in the surrounding towns and villages.
The ocean waves varied in height at different times of the eruption.
The greatest were from fifty to eighty feet high. Just imagine the
effect of a wave twice the height of an ordinary house. The waves
caused great damage to the shipping in the neighborhood. In one
instance, a vessel was carried one and a half miles inland and left on
dry land thirty feet above the level of the sea.
The total loss of life by the waves has been estimated at 35,000
people; besides this, of course, there was a great amount of property
destroyed. The greatest loss was in the immediate neighborhood of
Krakatoa. Gigantic waves swept over the lowlands lying near the
shores of Sumatra and Java, where over areas several miles in width
nearly everything was destroyed, the houses, trees, and people being
swept away and the surface of the land greatly changed. The towns of
Karang and Anjer, as well as numerous smaller villages, were almost
completely destroyed.
The seaport town of Anjer, by far the most important of the above
towns, was almost completely swept away. The heavy stone lighthouse
was so completely obliterated that no traces of its heavy stone
foundations could afterwards be found. The Rev. Phillip Neale,
formerly a British chaplain at Batavia, from whose account of the
eruption of Krakatoa some of the above facts have been taken, tells
of the brave action of the keeper of the lighthouse at Anjer. Besides
his work as lighthouse keeper, to see that the light was constantly
burning during the night, he was charged with telegraphing to Batavia
the names of all passing vessels. On the fateful morning of the great
catastrophe, observing that the sun did not rise, he kept the light of
the lighthouse burning, and, notwithstanding the danger to which he
was exposed, continued at his post in order to send word to Batavia of
the passing of an English steamer. While doing this the lighthouse was
swept away and the brave man perished.
The following verbal account of the destruction of the port of Anjer
was given by a Dutch pilot stationed at Anjer. This description is
quoted by the Rev. Mr. Neale from an article prepared by him for
publication in "The Leisure Hour."
"I have lived in Anjer all my life, and little thought the
old town would have been destroyed in the way it has. I am
getting on in years, and quite expected to have laid my
bones in the little cemetery near the shore, but not even
that has escaped and some of the bodies have actually been
washed out of their graves and carried out to sea. The
whole town has been swept away, and I have lost everything
except my life. The wonder is that I escaped at all. I can
never be too thankful for such a miraculous escape as I had.
"The eruption began on the Sunday afternoon. We did
not take much notice at first, until the reports grew
very loud. Then we noticed that Krakatoa was completely
enveloped in smoke. Afterwards came on the thick darkness,
so black and intense that I could not see my hand before
my eyes. It was about this time that a message came
from Batavia inquiring as to explosive shocks, and the
last telegram sent off from us was telling you about
the darkness and smoke. Towards night everything became
worse. The reports became deafening, the natives cowered
down panic-stricken, and a red, fiery glare was visible
in the sky above the burning mountain. Although Krakatoa
was twenty-five miles away, the concussion and vibration
from the constantly repeated shocks were most terrifying.
Many of the houses shook so much that we feared every
minute would bring them down. There was little sleep for
any of us that dreadful night. Before daybreak on Monday,
on going out of doors, I found the shower of ashes had
commenced, and this gradually increased in force until at
length large pieces of pumice stone kept falling around.
About six A. M. I was walking along the beach.
There was no sign of the sun, as usual, and the sky had a
dull, depressing look. Some of the darkness of the previous
day had cleared off, but it was not very light even then.
Looking out to sea I noticed a dark, black object through
the gloom, travelling towards the shore.
"At first sight it seemed like a low range of hills rising
out of the water, but I knew there was nothing of the kind
in that part of the Sunda Strait. A second glance--and a
very hurried one it was--convinced me that it was a lofty
ridge of water many feet high, and worse still, that it
would soon break upon the coast near the town. There was
no time to give any warning, and so I turned and ran for
my life. My running days have long gone by, but you may
be sure that I did my best. In a few minutes I heard the
water with a loud roar break upon the shore. Everything
was engulfed. Another glance around showed the houses
being swept away and the trees thrown down on every side.
Breathless and exhausted I still pressed on. As I heard
the rushing waters behind me, I knew that it was a race
for life. Struggling on, a few yards more brought me to
some rising ground, and here the torrent of water overtook
me. I gave up all for lost, as I saw with dismay how high
the wave still was. I was soon taken off my feet and borne
inland by the force of the resistless mass. I remember
nothing more until a violent blow aroused me. Some hard,
firm substance seemed within my reach, and clutching it,
I found I had gained a place of safety. The waters swept
past, and I found myself clinging to a cocoanut palm-tree.
Most of the trees near the town were uprooted and thrown
down for miles, but this one fortunately had escaped and
myself with it.
"The huge wave rolled on, gradually decreasing in height
and strength until the mountain slopes at the back of
Anjer were reached, and then, its fury spent, the water
gradually receded and flowed back into the sea. The sight
of those receding waters haunts me still. As I clung to
the palm-tree, wet and exhausted, there floated past the
dead bodies of many a friend and neighbor. Only a mere
handful of the population escaped. Houses and streets were
completely destroyed, and scarcely a trace remains of where
the once busy, thriving town originally stood. Unless you
go yourself to see the ruin you will never believe how
completely the place has been swept away. Dead bodies,
fallen trees, wrecked houses, an immense muddy morass and
great pools of water, are all that is left of the town
where my life has been spent. My home and all my belongings
of course perished--even the clothes I am wearing are
borrowed--but I am thankful enough to have escaped with my
life and to be none the worse for all that I have passed
through."
As is common in cases of earthquake waves a great depression in the
level of the sea occurred at places great distances from Krakatoa. For
example, at the harbor of Ceylon, the water receded so far that for
about three minutes the boats were left high and dry, and then a huge
wave carried them with it as it rushed over the land.
Perhaps one of the best evidences of the immense power of ocean waves
is to be seen in the massive blocks of white coral rock that were
washed up by the waves, on parts of the coast of Java for distances of
from two to three miles from the ocean. Many of these blocks weighed
from twenty to thirty tons. Indeed, some of them reached the weight of
from forty to fifty tons.
It is probable that the island of Krakatoa and its neighboring smaller
islands formed portions of a huge cone about eight miles in diameter,
that has been broken up at some very remote but unknown time by,
perhaps, a greater catastrophe than that of August, 1883.
In the Straits of Sunda the water was raised fifty feet to eighty
feet above the ordinary level, and produced tremendous destruction
especially on the coasts of Java and Sumatra, sweeping away many
villages and drowning many thousands of people. The wave had a
velocity of progression of nearly 400 miles per hour, or eight times
faster than an ordinary express train.
When it is said that the _velocity of progression of the wave_ was
nearly 400 miles per hour, it is not meant that a body floating on
the ocean, such, for example, as a ship, would have been carried
forward at this high velocity, but would merely rise and fall in a
to-and-fro swing to about the height of the wave; that is, fifty to
eighty feet according to what may have been the height. As in the
case of the sound waves these motions of water covered or passed over
nearly all the waters of the earth. The waves progressing toward the
west, crossed the Indian Ocean reaching to the coast of Hindostan, and
Madagascar, and sweeping around the southern part of Africa, finally
reached the coasts of France and England, as well as the eastern part
of North and South America. Sweeping towards the east, they reached
the coasts of Australia, New Zealand, and crossing the vast Pacific
Ocean were felt at Alaska and the western coasts of North and South
America.
But besides the enormous waves caused by the eruption, there were
marked changes in the level of the land. Large portions of the coast
of Sumatra and Java were almost annihilated, much of the original
surface near the coast being submerged, and places that were formerly
dry land are now covered with water to a depth of from 600 to 900 feet.
The enormous amount of material thrown into the air by the forces
of the eruption is especially characteristic of this phenomenon.
Such quantities of pumice stone and ashes fell from the clouds that,
sinking in the water and collecting on the bed of the channel, they
changed the depth of the water, so as to render navigation dangerous.
Indeed, the Sebesi Channel, lying on the north of the island of
Krakatoa was completely blocked by a huge bank of volcanic material,
portions of which projected above the water, forming two smaller
islands. These, however, have since been washed away by the waves.
We will not attempt to give at present any explanations as to the
causes of this great volcanic eruption, since the different theories
as to the cause of volcanoes will be better understood when other
volcanic eruptions have been described. It is sufficient here to say
that if a large quantity of water should have suddenly reached a
great mass of molten rock, frightful explosive eruptions would have
occurred, and if the island was resting on a submerged crater its
sudden disappearance may be explained.
Another great wonder connected with the explosive eruption of Krakatoa
was the enormous heights to which the fine dust was thrown up into
the air. It has been asserted that during the most intense of these
eruptions the particles reached elevations of perhaps more than
twenty-five miles above the level of the sea. Carried by the winds,
the fine particles remained suspended in the air for many months,
and gave rise to magnificent sunlight effects, such as early dawn,
lengthened twilights, lurid skies, and gorgeous sunsets of a reddish
tint. There were also caused curious haloes, as well as green and blue
moons.
The fine dust particles consisted of minute crystals of feldspar and
other minerals, and when examined under the microscope presented the
appearance shown in Fig. 4.
These mineral substances permitted a portion of the light to pass
through them, thus producing wonderful optical effects in the
atmosphere either because they acted like minute prisms and so
produced rainbow colors, or because they turned the rays of light out
of their course as to produce what is called interference by color
effects of a nature similar to the colors seen in mother-of-pearl,
rainbow coal, or in the wing cases of many beetles. The explanations
of these phenomena are too difficult for a book of this character.
An explosive volcanic eruption is a very terrifying and wonderful
phenomenon. Frightful roaring sounds are suddenly heard, the earth
shakes for many miles around, when suddenly a vast quantity of molten
rock, and sometimes huge stones, are thrown out of the crater high up
into the air. So great is the force that throws these materials out
of the opening that heavy masses of rocks often are ejected very much
faster than the projectiles from the largest guns that are used in any
of the navies of the world.
[Illustration: FIG. 4. VOLCANIC DUST AS IT APPEARS UNDER THE
MICROSCOPE]
As the molten lava cools and falls in the form of prodigious clouds
of ashes, cinders and dust, for many miles around the volcano, even
the light of the sun is obscured, and one cannot see the hand before
the face. Some of the materials in these clouds are so light that they
remain suspended in the air for many hours, often indeed for many
days, and sometimes even for years. The heavier particles, however,
soon begin to fall, and before long the earth's surface both around
the volcano, and often at considerable distances from it, is covered
with a thick layer of ashes.
The sounds accompanying a volcanic eruption are often terrifying. Amid
shakings and tremblings of the earth's crust, known as earthquakes,
there are occasionally heard noises like the explosion of huge guns.
Sometimes these sounds follow one another so rapidly that they produce
an almost continuous roar. Through the roar of the explosion a
curious crackling noise can be heard, due to the fragments of stone
hurled out of the crater striking against one another, especially as
the stones which are thrown out of the crater and have commenced to
fall back again to the earth, are struck by others that are still
rising.
Immense quantities of ashes, stones, vapor and gases are thrown
upwards for great distances into the air, while, at the same time, a
lava stream pours over the lowest side of the crater. As the column
of ashes and cinders reaches its greatest height in the air, it
begins to spread outward on all sides, rapidly growing like a huge
dark mushroom. This soon shuts out the light of the sun, and from it
showers of red hot ashes and cinders fall to the earth.
It would be extremely dangerous to be on the side of the volcanic
mountain during an explosive eruption; for, even should you escape
falling into an opening in the side of the mountain, you might be
killed by the huge stones that are constantly falling on all sides
around the opening, or might be buried under the vast showers of red
hot ashes that are poured down from the dense clouds overhanging the
mountain, or suffocated by clouds of sulphur vapor that rush down its
sides.
When at a safe distance the sight is certainly magnificent. There is
no light from the sun. All would be in pitch darkness but for the
reddish glare thrown upwards by the red hot lava, by the glowing
showers of ashes that are being rained down on the sides of the
mountain, or by terrific lightning flashes, due to the discharge of
the immense quantities of electricity produced by the forces of the
eruption.
Naturally a great volcanic eruption can cause a considerable loss of
life and property. When a large lava stream begins to flow down the
sides of the mountain, it cannot be stopped, and should it flow toward
a village or town it is likely to destroy the town completely. Besides
this, the vegetation of the country for many miles around is destroyed
by the showers of red hot ashes that fall from the sky. The houses of
neighboring cities are similarly ruined by the great conflagrations
thus set up. Further destruction is also caused by large streams of
mud that rush down the slopes of the mountain, or by huge waves set
up in the ocean. If the volcano is situated, as most volcanoes are,
near the coast, the showers of ashes and falling stones may set fire
to vessels in the neighborhood, or the progress of such vessels may be
seriously retarded by layers of ashes or pumice stone that float on
the surface. Sometimes these layers are so thick as actually to bring
ships to a complete standstill.
It must not be supposed that volcanoes are in a constant state of
eruption. On the contrary, nearly all volcanoes, after an eruption,
become _quiet_ or _inactive_. The air soon clears by the ashes
settling, and the sunlight again appears. A crust forms over the
surface of the lava, which rapidly becomes hard enough to permit one
to walk over it safely. The vegetation, which has been destroyed by
the hot ashes, again springs up, and, if the volcano happens to be
situated within the tropics, where there is an abundance of moisture,
the land soon again becomes covered by a luxuriant vegetation. Most of
the people, who have escaped sudden death during the eruption, return
to the ruins of their houses; for it is a curious fact that no matter
how great has been a volcanic eruption, or how far-reaching the ruin,
the survivors, as a rule, do not appear to hesitate to return to their
old neighborhood. In a few years the fields are re-cultivated, the
villages are rebuilt, and the people apparently forget they are living
over a slumbering volcano, which may at any time again burst forth in
a dangerous eruption.
A volcano that throws out molten rock, vapor and gases is known as an
_active volcano_. An active volcano, however, is only correctly said
to be in a state of eruption when the quantity of the molten rock,
lava or vapor it throws out is greatly in excess of the ordinary
amount.
Sometimes the volcanic activity so greatly decreases that the molten
rock or lava no longer rises in the crater, but, on the contrary,
begins to sink, so that the top of the lava in the crater is often
at a considerable distance below its edges. The lava then begins to
harden on the surface, and, if the time is sufficient, the hardened
part extends for a considerable distance downward. In this way the
opening connecting the crater with the molten lava below becomes
gradually closed, the volcano being thus shut up, or corked, just as a
bottle is tightly closed by means of a cork driven into the opening at
its top so as to prevent the escape of the liquid it contains.
It may sound queer to say that a volcano has its crater so corked up
as to prevent the escape of the lava, but the idea is nevertheless
correct and helpful. To realize the size of these huge volcanic corks
one must remember that the craters of some volcanoes are several miles
across. A volcano thus choked or corked up is said to be _extinct_.
When we speak of an extinct volcano we do not mean that the volcano
will never again become active. A volcano does not cease to erupt
because there are no more molten materials in the earth to escape, but
simply because its cork or crust of hardened lava has been driven in
so tightly that the chances of its ever being loosened again seem to
be very small. But small as the chances may seem we must not forget
that the volcano may at any time become active, or go into its old
business of throwing out materials through its crater. A volcano in
an extinct condition is not unlike a steam boiler, the safety valve
of which has been firmly fixed in place. If the steam continues to be
generated in the boiler, it is only a matter of time when the boiler
will blow up, and the explosion will be all the greater because the
safety valve did not allow the steam to escape earlier.
Sometimes an intermediate class of volcanoes called _dormant_ is
introduced between active volcanoes on the one hand and extinct
volcanoes on the other. The name dormant volcano, or, as the word
means, _sleeping volcano_, is objectionable, since it might lead one
to think that an extinct volcano is not sleeping but dead, and this is
wrong.
Since the plug of hardened lava in the volcanic crater is generally at
a much lower level than the top of the crater, the crater will soon
become filled to a greater or less depth with water, produced either
by the rain, or by the melting of the snow that falls on the top of
the mountain. Crater lakes, often of very great depths, are common in
extinct volcanoes.
Of course, when an extinct volcano again becomes active, two things
must happen if the eruption is explosive. In the first place, the
force of the explosion must be sufficiently great to loosen the
stopper or plug of hardened lava which stops it. In doing this the
mass is broken into a number of fragments that are thrown forcibly
upwards into the air. After rising often for great heights they soon
fall again on the sides of the mountain.
But besides the breaking up of the stopper, the lake in the crater of
the volcano is thrown out along with the cinders or ashes, producing
very destructive flows of what are called aqueous lava or mud streams.
These streams flow down the sides of the mountain, carrying with them
immense quantities of both the ashes thrown out during the eruption,
or those that have collected around the sides of the crater during
previous eruptions. Very frequently, these streams of aqueous lava
produce greater destruction than the molten lava.
If you have ever watched common ants at work clearing out or enlarging
their underground homes, in a piece of smooth gravel walk in your
garden, you can form some idea why the mountain immediately around a
volcanic crater is conical in shape. If the colony of ants happens
to be fairly large, you can see an almost unbroken stream of these
industrious little animals, each bearing in its mandibles a small
grain of sand or gravel brought up from some place below the surface.
Carrying it a short distance from the opening, it throws it on the
ground, rapidly returning for another load. In this way there is
heaped up around all sides of the opening a pile of sand or gravel,
the outward slopes of which gives the pile a conical form. You have,
probably, noticed that the steepness of the slopes depends on the size
of the grains; for the larger these grains the sharper or steeper the
slopes, the very fine grains producing flat mounds or cones.
It is the same with a volcanic cone. The materials that are thrown
upwards into the air, falling again on the mountain, collect around
the crater on all sides, thus giving it the characteristic cone-like
shape of the volcanic mountain. Where nothing occurs to disturb
the formation of the cone its height above the level of the sea
will gradually increase. Very frequently, however, during explosive
eruptions, a large part of this cone will be blown away by the
force of the eruption only to be again built up during some later
eruption. Indeed, in the case of volcanic islands, the force of a
great volcanic eruption is sometimes so great that not only is a large
volcanic mountain blown entirely away, but a hole is left, where it
had been standing, that extends further downwards below the level
of the sea than the top of the mountain extended previously above
it. The above are some, but by no means all, the wonders attending
volcanic eruptions. We shall refer to others in subsequent chapters in
describing particular eruptions.