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Volcano
Exhibit
The Earth's crust is made up of hard, solid rocks. Beneath the
surface pressures may heat rock into a dense liquid called magma.
The expanding material is forced into cracks and long narrow openings
called fissures within the Earth's rock layers. If the magma forces
through the surface it may erupt explosively, as with Mt. St.
Helens, or spread out on the surface as a lava
flow.
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