andesite	Volcanic rock (or lava) characteristically medium dark in color and containing 54 to 62 percent silica and moderate amounts of iron and magnesium.
ash (volcanic)	Fine fragments (less than 4 mm in diameter) of volcanic rock formed by a volcanic explosion or ejection from a volcanic vent.
basalt	Volcanic rock (or lava) that characteristically is dark in color, contains 45 to 54 percent silica, and is rich in iron and magnesium.
Bishop Tuff	Deposit of rhyolite ash and pumice erupted during formation of Long Valley caldera.
caldera	A large basin-shaped volcanic depression with a diameter many times larger than included volcanic vents; may range from 2 to 50 km across.
cumulo-volcano	A dome-shaped volcano constructed of multiple lava domes and flows.
dacite	Volcanic rock (or lava) that characteristically is light in color and contains 62 to 69 percent silica and moderate amounts of sodium and potassium.
lava	General term for magma (molten rock) that has been erupted onto the surface of the Earth.
magma	Molten rock beneath the surface of the Earth.
moat	The annular lowland between the resurgent dome and the walls of a large caldera.
pumice	Frothy volcanic rock formed by the expansion of gas in erupting lava.
resurgent dome	The central highland in many large calderas formed by gradual upwarping of the caldera floor after caldera collapse as a result of renewed magma intrusion.
rhyodacite	Volcanic rock (or lava) that is intermediate in composition between rhyolite and dacite.
rhyolite	Volcanic rock (or lava) that characteristically is light in color, contains 69 or more percent of silica, and is rich in potassium and sodium. Low-silica rhyolite contains 69 to 74 percent silica. High-silica rhyolite contains 75 to 80 percent silica.
silica	Silicon dioxide, the most abundant rock-forming compound on Earth.

More information about volcano terms and features

• Photoglossary of many more volcano terms

• Photo gallery of the Long Valley area