Terms
A process that causes rocks to gradually break or crumble into smaller pieces
The point underground where an earthquake begins
Focus
A volcano that has erupted recently or is considered likely to erupt in the near future
Active
This is formed when eruptions composed mostly of tephra build up cone-shaped mountains
Cinder-cone
Physical forces such as flowing water, ice, or windblown sand break down the rock
Physical weathering
The strength of an earthquake
Magnitude
A volcano that erupted many years ago and although now inactive, may erupt again
Dormant
Formed when alternating layers of fluid lava and tephra build up a steep symmetrical mountain, often with a small crater at the top
Composite
Natural acids slowly eat into a rock and break it apart
Chemical weathering
The place at ground level that is directly above the focus of an earthquake
Epicenter
A volcano that has not erupted in recorded history or is unlikely ever to erupt again
Extinct
Fluid lava surges from the vent like water from a fountain
Formed when large amounts of fluid, runny lava gradually build up a dome-shaped volcano
Shield volcano
The regions of the earth where most of the world's earthquakes occur
Seismic belts
A depression at the top of a volcano
Crater
Globs of hot lava are flung into the air where they harden into volcanic bombs in a series of noisy but mild eruptions
Strombolian
An underwater mountain range in the ocean where plates of the earth's crust are moving away from each other
Mid-oceanic range
The scale used to measure the strength of an earthquake
Richter scale
A huge, bowl-shaped depression formed when an empty magma chamber collapses after a volcanic eruption
Caldera
Hot clouds of gas and dust are expelled high into the air, usually quite violently
Plinian