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.