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 characterized by lots of lava during eruptions and gentle slopes. Cinder Cone: A volcano made of cinders that are blown into the air.
Composite:A volcano built of alternating layers of cinders and lava. Composite volcanoes are characterized by steep slopes and violent eruptions.
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.
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.