Cascade Volcanoes

Types of Volcanoes

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Mount St Helens

Smoking Mountains

Cascade Mountains Volcano Map The map at right shows some of the active and potentially active volcanoes along the west coast of the US. In Washington State, Mount Baker, Glacier Peak, Mount Rainier, and Mount St. Helens have been active within the last 2,000 years. As the population around each volcanic area grows the possibility of a disastrous eruption increases. The United States Geological Survey (USGS) has a Cascades Volcano Observatory (CVO) that studies these and other volcanoes. Geologists at the CVO monitor for signs of activity, assess hazards and gather scientific information to warn the public of impending eruptions.

Cascade volcanoes are the composite type and build very steep sides. These volcanoes also have very thick magmas that tend to hold in expanding volcanic gases and steam. Tremendous pressure builds up inside the volcano and often leads to explosive and dangerous eruptions.

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USGS Cascades Volcano Observatory
USGS Live Volcano Camera

Geology Terms

Here are some basic terms used on this page. Find more geology terms in the Glossary.

Ash: Fragments of less than 2 millimeters in diameter of lava or rock blasted into the air by volcanic explosions.
Basalt: Volcanic rock caused by partial melting of the Earth's crust.
Caldera: A large volcanic depression, commonly circular or elliptical when seen from above, caused by a volcano collapsing into itself.
Cinder Cone: A circular or oval cone made up of small fragments of lava from a single vent that have been blown into the air, cooled and fallen around the vent.
Composite Volcano: A steep-sided volcano composed of many layers of volcanic rocks, usually made from high-viscosity (thick like honey) lava, ash and rock debris (broken pieces).
Dome: A steep-sided mound that forms when viscous (thick like honey) lava piles up near a volcanic vent (opening at the surface).
Fumarole: A vent that releases volcanic gases and steam.
Lahar: A mixture of water and rock debris that forms on the slopes of a volcano. Also known as a mudflow or debris flow. The term comes from Indonesia.
Pumice: A light-colored volcanic rock containing lots of bubbles from trapped gases. This rock can sometimes float on water.
Pyroclastic Flow: A hot, fast moving and high-density (thick like a dust storm) mixture of ash, pumice, rock fragments and gas formed during explosive eruptions.
Shield Volcano: A volcano shaped like a bowl in the middle with long gentle slopes made by basaltic lava flows.
Vent: An opening at the surface where magma, gas and steam erupt.
Volcano: A vent at the surface where magma, gas and steam erupt. Also, the landform constructed by volcanic material.

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