The Strange Adventures of a PebbleHawksworth, Hallam
Science
The Strange Adventures of a Pebble
Hawksworth, Hallam
Geology -- Juvenile literature; Physical geography -- Juvenile literature
It does look it, doesn't it? But, what is still more striking, it
_isn't_ a mountain with a hole in it at all, if you mean, as the
little girl in the geography class meant, that it was once an ordinary
mountain and then had a hole put through it. For a long time it was
thought that volcanoes were simply mountains through which fire and
lava from the interior had forced its way. Finally, however, some
scientist thought perhaps of his Proverbs 6:6. In any event wise as he
must have been--how else could he have been a scientist?--he went to
the ant, learned her ways and became wiser. It was by noticing how the
ants build their little craters with the sand and clay they carry from
their underground homes that men got the idea that volcanoes may be
built up in much the same way. So they set to observing Mr. Volcano's
habits more closely, and sure enough, the ant had told the answer! The
stones, lava, cinders, and the stone dust called "volcanic ash" are
shot out by the explosion, and coming down in showers pile around the
opening, as the ant piles the pellets around the entrance to her nest.
As the explosions keep on the crater is piled higher and higher, and
the stones, cinders, and things, rolling down the sides, spread the
pile out at the bottom, much as the ant drops pellets over the edge
of her growing pile, and so both the cone-like ant-hill and the big
volcanic cone are built up.
WHY THE VOLCANO DOES NOT SMOKE
But here is something about volcanoes that will surprise most people.
They throw mud, they throw stones, but they don't smoke. What we call
smoke is the steam that makes--or at least helps make--the explosion.
It often has the color of brown smoke because of the rock which has
been blown into dust. Neither do volcanoes make "ashes." What is called
"ash" is this rock powder, made when the rocks are blown into pieces by
the sudden expansion of the water in them into steam.
WHY VOLCANOES SEEM TO FLAME
Neither do volcanoes flame, although they are supposed to. Only rarely
does flame issue from a volcano, and then only to a moderate extent,
due to the burning of the hydrogen gas. What seem to be huge flames
are the lights from the molten lava in the crater shining back on the
steam clouds above; and these apparent flames rise and fall and vary in
brightness because of the rise and fall of the lava.
But the greatest of volcanic eruptions--that is, the welling up
of melted rock from within the earth--have not built cones. The
lava spread out into vast plains in India and Abyssinia and in our
northwestern coast States. Great cracks in the earth cross one
another. It is at the crossroads that the volcanoes are apt to form,
while out of the cracks leading up to these crossroads the lava spreads
in sheets. Mount Shasta began at one of these traffic centres. It is a
big brother of the landscape which it overlooks.
[Illustration: "BUT VOLCANOES DO NOT SMOKE!"
Public-domain text, read in full here on John Shaqi.
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