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What IS A VOLCANO?. A volcano is a place where lava reaches the surface. There are three types of volcanoes:. Shield Volcano: A gently-sloped volcano. Cinder Cone: A volcano made of cinders that are blown into the air. Composite: A volcano built of alternating layers of cinders and lava.
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Mount Shasta is a composite volcano. Over the last 10,000 years, Mt. Shasta has erupted on average once every 800 years. During the 3,500 years the volcano has erupted about once every 300 years. The most recent eruption may have occurred in 1786 A.D.
Diamond Head is an eroded Cinder (Tuff) Cone. Early sailors mistakenly thought glistening calcite crystals inside the tuff rocks were diamonds, leading to the incorrect name. Diamond Head formed when hot magma rising up a conduit hit ocean water, causing large explosions that threw exploded magma particles (tuff) into a broad ring.
Kohala is a shield volcano. • Kohala is the oldest of the subaerial volcanoes that make up the Island Of Hawaii. Kohala is considered to be extinctbecause it has not erupted for 60,000 years.