Volcanic rock or lava that is made up of 45% to 54% silica and is generally rich in iron and magnesium. Characteristically dark in color, volcanoes with runny/flowing lava is predominantly basaltic in nature.

A descriptive term applied to volcanoes that are predominantly basaltic in composition (45%-54% silica).

Ballistic projectile
A large fragment of lava (generally > 64 mm in size) that follows a ballistic trajectory when ejected from the volcano. These rocks are called ‘blocks’ if they were solid at the time they were fragmented and ‘bombs’ if they were liquid. They usually land within 2 km of the vent but can travel as far as 5 km, or even further if the eruption is very explosive

Base Surges
A cold pyroclastic surge commonly generated by phreatic and phreatomagmatic explosions.

Solid pyroclastic fragments greater than 64mm in diameter while still fluid.

Relatively hard, solid rock that commonly underlies softer rock, sediment or soil.

A piece of molten or semi-molten rock which is blown out during an eruption. Bombs vary in size from 2 ½ inches to many feet in diameter and they often change shape during their flight or upon impact.

Body wave
A body wave is a seismic wave that moves through the interior of the earth, as opposed to surface waves that travel near the earth’s surface. P and S waves are body waves. Each type of wave shakes the ground in different ways.

Before present (used when quoting radiocarbon ages where the ‘present’ refers to 1952).

Modern seismometers that record over a wide band of frequencies (0.02 to 50 Hz)