Volcanic diversity

Lassen Volcanic National Park is home to more than one volcano

Geologists classify volcanoes into four major types, all of which can be found at Lassen Volcanic National Park.

Lassen Peak is one of the largest plug dome volcanoes in the world. Plug domes are formed by lava too viscous to flow far, so it piles up around a vent and the resulting peak grows from within. As the inside grows, the outside surface shatters and fragments flow to the volcano’s sides.

Composite volcanoes are also sometimes known as stratovolcanoes, and are generally steep-sided, roughly symmetrical, and huge. Though there are no standing composite volcanoes in the Lassen area today (the nearest is Mount Shasta), 11,000-foot Mount Tehama dominated the region millions of years ago. The park’s Brokeoff Mountain was once part of Mount Tehama.

Shield volcanoes are built by thousands of flat lava flows that build up like layers of paint, creating a broad, gently sloping peak. Lassen park’s Prospect Peak is a shield volcano.

Cinder cones are built by light lava particles ejected high into the air from a single vent, then falling back down to pile on top of each other. Cinder Cone at Lassen Volcanic National Park was formed by an eruption about 350 years ago.

—Ken Smith