Glossary of Terms

Bathymetry: The study of underwater depth

Caldera: The resulting formation from a volcano ejecting material causing the top of the volcano to fracture and collapse creating a bowl-shape.

Lahar: A hot mudflow containing ash and pyroclastic material from an eruption.  Commonly caused when hot ash hits snow.

Parasitic Cone: A vent (tiny volcano) that grows out of a larger volcano.

Pyroclastic flow: A very fast-moving flow of ash, rock and gas (tephra) that rolls down an erupting volcano. Also know as nuée ardente.

Rhyodacite: A type of igneous (volcanic) rock that is halfway between dacite and rhyolite.

Scoria: red, black or gray igneous (volcanic) rock that is filled with holes from gases escaping as the rock cools.

Tephra: A general term for fragments of igneous (volcanic) rock that is blasted into the air during an eruption.  Tephra can be as small as ash or as large as boulders.

Tuff: Ash that has become compacted into a solid layer on the ground.

Quaternary: a period of geologic time that runs from two million years ago to now.

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Crater Lake National Park Trust
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