A type of lava flow having a rough surface with sharp, spiny projections. Aa means "hard on the feet" in Hawaiian.
A volcano that is erupting or has erupted in recorded history.
A fine grained, dark-colored rock rich in iron and magnesium and relatively poor in silica; the common lava of Hawaii and Craters of the Moon.
Blue Dragon Lava
A type of pahoehoe flow with a bright blue sheen on its surface. The blue color is produced by a thin veneer of crude "glass" that forms on the flow's surface.
Small, very porous fragments of frothy rock ejected from a volcano.
A steep sided hill formed by the accumulation of cinders expelled from a volcanic vent.
A bowl- or funnel-shaped depression, generally in the top of a volcanic cone. The vent for volcanic material.
A crack in the earth's surface from which volcanic material may erupt.
Magma which has reached the earth's surface.
A hollow tunnel formed when the outer part of a flow has hardened and the inner, still molten material subsequently drains out.
Molten rock beneath the earth's surface.
Mantle Plume Theory
A theory which states that localized hot spots deep in the earth's mantle periodically release "plumes" of molten material which slowly rise to the surface. Hot spots are fixed and do not move. However, the crust of the earth slowly moves across them, generating volcanic activity.
A type of lava flow with a smooth, billowy surface. The Hawaiian term means ropy.
Rafted Block (Monolith)
A large block of old cinder-cone walls which has been transported by a lava flow to a new location.
A volcano with a broad, low profile, the shape of a flattened dome, built up by repeated flows of very fluid lava. Common on the Snake River Plain, but not at Craters of the Moon.
A thick, pasty clot of lava.
A low, steep-sided cone built of blobs of sticky lava that have piled up around a vent.
An impression left in the lava of the charred surface of a tree.
A channel in the earth's surface from which volcanic material erupts.
A vent in the surface of the earth through which magma, gases and ash erupt.
Volcanic Rift Zone
An array of volcanic fissures along which repeated eruptions occur.