The Savannah morning news. (Savannah, Ga.) 1900-current, 1902-05-25

occurred in the midst of a plain. and
built UP lava cones" or low mounds,
with immensely expanded bases. illus
trations are furnished in Southern Ida
no, in which the cones formed are only
three hundred or four hundred feet
high, but have a breadth at the base
of eight or ten miles. In the class of
eruption illustrated by these examples,
there is an absence of fragmental ma
terial, such as explosive volcanoes hurl
into the air. and a person may stand
within few yards of rushing stream
of molten rock or examine closely the
opening from which il is being poured
out, without danger or serious incon-
venience.
When Eruptions Become Violent.
The quiet volcanic eruptions are at
tended by the escape of steam and
gases from the molten rock, but the
lava being in a highly liquid state, the
steam and gases dissolved in it escape
quietly and without explosions. If,
however, the molten rock is less COM
pletely fluid, or in a viscious condition.
the vapors and gases contained in 1t
find difficulty in escaping, and may be
retained until, becoming concentrated
in large volume, they break their way
to the surface, producing violent ex-
plosions. Volcanoes in which the lava
extruded is viscous. and the escape of
steam and gases is retarded until the
pent up energy bursts all bounds, are
of the explosive type. One character
istic example is Vesuvius
When steam escapes from the
summit of volcanic conduit
which. in plain terms, is a tall vessel
| filled with intensely hot and more or
Vicious liquid-masses of the liquid rock
blown into the af nd 20
build up rim or crater about the
place of discharge. Commonly the
lava in the summit portion of con-
ruit becomes chilled and perhaps hard
ened, and when a steam explosion oc-
ours this crust is shattered and the
fragments hurled into the cir and con-
tributed to the building of the walls
of the inclosing crater. The products of
explosive volcanoes are vapor and
gases, in certain instances, at least,
largely free hydrogen and free oxygen
The explosions although commonly as
cribed to the violent escape of steam
may in part be due to the union of
the oxygen and hydrogen present. The
liquid rock escapes as streams of lava
flows, and in part is blown into the
air. The liquid or plastic projectiles
produced in this manner may be be-
come sufficiently solid to retain their
form on striking, and are termed vol
canic bombs. They frequently have a
spindle shape, with twisted ends. show
ing that they rotated while in the air
about an axis; but in other instances
they fiatten on striking, and may even
be so nearly liquid that the material
composing them spreads out as a thin
cake when it comes to rest Bombs are
frequently found several miles from the
volcano that elected them, and fiat
tened and even thin lava cakes are
sometimes abundants at distance of
one or two miles from the place where
they began their aerial Journeys.
The solid rock blown out by vol
canoes consists uusally of highly vesic-
ular material which hardened on the
surface of the column of lava within
a conduit and was shattered by explo
sions beneath it. These fragments vary
in size from dust PARTICLES up to
masses several feet in diameter, and
during violent eruptions are hurled
miles high. The larger fragments COM
monty fall near their place of origin,
and uusally furnish the principal part
of the material of which craters are
built, but the gravel-like kernels, Ia
DILL, may be carried laterally several
miles il wind is blowing, while the
dust is frequently showered down on
thousands of square miles of land or
sea. The solid and usually angular
fragments manufactured in this man
ner vary in temperature, and may still
be red hot on falling.
Volcanoes of the explosive type not
uncommonly discharge streams of lava,
which may flow many miles. In GER
tain instances these outwellings of
LIQUID rock occur after severe earth
quakes and violent explosions, and may
have all the characteristics of quiet
eruptions. There is thus no funda-
mental difference between the two
types into which it is convenient to di-
vide volcanoes.
Mountains Below Their Heads on.
In extreme examples Of explosive vol
canoes, the summit portion of a crater,
perhaps several miles in circumfer-
ence and several thousand feet high.
Is blown away. Such an occurrence is
recorded in the case of the volcano
Caseguina, Nicaragua, in 1885. Or. an
entire mountain may disappear. being
reduced to lapilli and dust and blown
into the air as in the case of Kraka-
toa in the Strait of Sunda, in 1888.
The essential feature Of a volcano, as
stated above, is tube or conduit, lead
ing from the highly heated sub-crust
portion of the earth to the surface,
through which molten rock is forced
upward to the surface. The most
marked variations in the process de-
pend on the quantity of molten rock
extruded, and on the freedom of escape
of the steam and gases contained in
the lava.
The cause of the rise of the molten
rock in a volcano is still a matter of
discussion. Certain biologists contend
that steam is the sole motive power:
while others consider that the lava is
forced TO the surface owing 70 pressure
on the reservoir from which IL comes,
The view perhaps most favorablY en-
tertained az present In reference to
the general nature Of volcanic erup-
lions. IL that the rigid outer portion OF