Chapter 5: Volcanoes

Eruption

The release of lava and/or pyroclastic debris from a volcanic vent.

Volcano

An erupting vent through which molten rock reaches the Earth's surface or the hill or mountain built from the products of eruptions.

Lava flow

Sheets or mounds of lava that flow onto the ground surface or seafloor in molten form and then solidify.

Viscosity

The resistance to flow of lava, which depends on chemical composition.

Lava tube

The empty spot left when a lava tunnel drains; happens when a surface of a lava flow solidifies while the inner part of the flow continues to stream downslope.

Pyroclastic flow

A fast-moving avalanche that occurs when hot volcanic ash and debris mix with air and flow down the side of a volcano.

Magma chamber

A large, underground, irregularly shaped zone with magma.

Shield volcanoes

Broad, gentle domes formed by low viscosity lava that spreads out in thin sheets over large areas.

Stratovolcanoes

Composite volcanoes with interleaved layers of lava, tephra, and pyroclastic debris, emphasizing internal layering.

Calderas

Large circular depressions with steep walls and a fairly flat floor, formed after an eruption as the center of the volcano collapses into the drained magma chamber below.