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Geology glossary

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earthquake

Earthquakes
An earthquake (also called quake, tremor or temblor, rumbling etc) is the shaking of the surface of the earth resulting from a sudden release of energy in the Earth's interior, usually by sudden movements along fault lines. This movement releases energy that propagates as seismic waves.
The size of earthquakes is determined by the amount of energy released in this process. It can range in size between many orders of magnitude and is commonly given as a number on the logarithmic Richter scale. It ranges from so tiny that they are not felt and can be only detected by the most sensitive modern instruments (seismometers) to so strong that entire regions are shaking violently.

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effusive

Volcanology: effusive (volcanic) eruption
An effusive vent at Mt Etna volcano
An effusive vent at Mt Etna volcano
A lava flow is the result of an effusive eruptions (here Mt. Etna in Nov 2006)
A lava flow is the result of an effusive eruptions (here Mt. Etna in Nov 2006)
Effusive means flowing out of lava as opposed to explosive eruptions.
If magma is sufficiently fluid and if it is not framented by expanding gasses when reaching the surface vent, it can erupt to form lava flows. This is called effusive eruption. The opposite of effusive is explosive, i.e. fragmentation of magma. -> See whole entry

epicenter

Earthquakes
The point on the Earth’s surface vertically above the point (focus or hypocenter) in the crust where an earthquake occurs, i.e. where the seismic rupture nucleates.

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hypocenter

explosive

Volcanology: explosive (volcanic) eruption
A small explosive eruption at Mt Etna volcano
A small explosive eruption at Mt Etna volcano
Explosion of magma at Krakatau at the beginning of a vulcanian eruption
Explosion of magma at Krakatau at the beginning of a vulcanian eruption
Explosive eruptions occur, when the erupting magma is ejected as fragments into the air, as opposed to effusive eruptions producing lava flows.
Explosive eruptions are called so, when the erupting magma is fragmented when exiting the conduit. The reason are expanding gasses from the magma itself or external water e.g. from an aquifer. The resulting fragments of the magma itself are called tephra, and consist in small and large pieces: Ash, lapilli and bombs are the typical products of explosive eruptions.

The reason for explosive eruptio... -> See whole entry

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