Volcanoes are special cone shaped
mountains with bowl-like craters at
the
top. They contain vents which lead to
pools of melted rock below. The thin
top layer of the earth is solid and called
the crust. Beneath is the
mantle, which
extends almost 2,000 miles down to the
core. The core is molten due to intense
heat at the center. Liquid rock under
the surface is called magma. If it flows
onto the surface, it is called lava. |
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There are two main types of magma.
Granite magma is sticky and flows very
slowly. It traps a lot of gas and steam
which can cause pressure to build up.
When the pressure is great enough, it
blows out in an explosive eruption. The
other type is called basalt magma. It
flows more easily and gases escape
rather than building up. Basalt magma
usually flows quietly and causes rivers
of rapidly moving, brightly glowing lava. |