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| VOLCANOES. Mountains of Smoke and Fire. |
A volcano is a rupture within the crust of a
planetary-mass object, like Earth, that permits hot lava, volcanic ash, and
gases to flee from a magma chamber below the surface. On Earth, volcanoes are
most frequently found wherever tectonic plates are branching or converging, and
most are found underwater.
A volcano is created when hot liquid rock, ash and
gases escape from an opening in the Earth's surface. The molten rock and ash
solidify as they cool, forming the distinctive volcano form shown here. As a
volcano erupts, it spills lava that flows slope.
Earth's crust is 3 to 37 miles (5 to 60 kilometers)
thick, in keeping with the U.S. Geological Survey. It's jerky into seven major
and 152 smaller items known as tectonic plates, according to a 2016 paper by
Christopher Harrison at the University of Miami. These plates float on a layer
of magma — semi-liquid rock and dissolved gases. At the boundaries of those
plates — wherever they move past, are pushed underneath, or move removed from
each other — magma, that is lighter than the surrounding solid rock, is
commonly ready to force its way up through cracks and fissures. Magma will
explode from the vent, or it can flow out of the volcano like an overflowing
cup. Magma that has erupted is termed lava.
Deep under the Earth's surface, it's so hot that even
rock melts. Sometimes this molten rock, called 'magma', is pushed up to the
surface. At this point it is referred to as 'lava'. And the opening or vent
that lets the lava out is a volcano.
A volcano may explode violently, throwing out rocks
for miles around. Or it may push lava out so that it flows away, cools, and
hardens. Some volcanoes release clouds of poisonous gas or huge clouds of ash.
Volcanoes can even do all these things underwater.
Most volcanoes have been around for a very long time.
Many haven't erupted for years and have cooled off. Volcanoes that are not
going to erupt again are called 'dead volcanoes'.
VOLCANOES. Mountains of Smoke and Fire.
Some volcanoes still give off smoke. These 'sleeping
volcanoes' may 'wake up' one day and erupt again. Mount Vesuvius in Italy slept
for a thousand years. But one day in AD 79 it suddenly woke up. Its eruption
hurled out hot ash and rocky fragments that buried the city of Pompeii. A hot
mudflow buried nearby Herculaneum. Because the remains are so well preserved,
the area has been named a World Heritage site.
But not all volcanoes are destructive. When a volcano
throws out vast amounts of lava and debris, it piles up into a mountain. The
Hawaiian Islands and the island of Iceland were created in this way.
Other volcanoes help provide heat and energy. Many
Icelandic homes get their hot water from springs heated by volcanic steam. This
steam can also be used to produce electricity. Plants grow very well in the
rich soil left by volcanoes. And valuable gems, such as diamonds, can sometimes
be found in the rocks that are thrown out by volcanoes.
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