Geology glossary

Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid.

Sediments are also transported by wind (aeolian processes) and glaciers. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice transported sediments. Simple gravitational collapse also creates sediments such as talus and mountainslide deposits as well as karst collapse features. Each sediment type has different settling velocities, ... -> See whole entry

An instrument that displays vibrations and movements in the Earth = the recording of a seismometer.

Traditional seismographs transfer the recorded shaking to a precise pencil that writes a continuous shake line onto a sheet of paper wrapped around a turning drum.

The drum slowly turns at steady speed and at the same time, the pencil is slowly moved horizontally, so that the line forms a continuous spiral line on the paper until it is filled. Each turn of the drum (or each line on the unwrapped... -> See whole entry

Shield volcanoes are volcanoes that mainly erupt fluid (usually basaltic) lava flows that are able to travel over long distances and thus construct over time broad, gentle slopes. They are called shield volcanoes, because they resemble the shape of a warriors' shield.

Shield volcanoes are volcanoes that mainly erupt fluid (usually basaltic) lava flows that are able to travel over long distances and thus construct over time broad, gentle slopes. They are called shield volcanoes, because they resemble the shape of a warriors' shield.

While stratovolcanoes, the other major morphological type of volcanoes, are representative for most subduction-type volcanoes, sh... -> See whole entry

Skylights are openings in the roof above a lava tube, from where the flowing lava flow can be seen. Usually, these holes are caused by the simple collapse of the roof of the tube.

A rare phenomenon, where a visible vortex ring of steam and gas is expelled from a volcanic vent.

Under special conditions, gas and steam expelled from a vent can form gas rings. It probably requires a particular geolometric configuration of a circular vent exit, as well as expulsion of gas in individual puffs with just the right velocity.

This phenomenon is quite rare, but has been witnessed at several volcanoes, including Stromboli and Etna. At Etna, a spectacular period lasting several mo... -> See whole entry

Strombolian eruptions are the smallest type of explosive eruptions. Strombolian eruptions consist of intermittent, generally relatively small explosions or weak pulsating fountains of fluid (usually basaltic) lava from a single vent or crater. They are called so after the type locality of Stromboli volcano (Eolian Islands, Italy), which has been in strombolian activity for probably more than 2000 years.

An individual strombolian explosion is the result of sudden release of volcanic gasses. The typical rhythmic occurrence is caused by gradual accumulation of gas bubbles beneath a weakly solidified plug at the top of the magma column at the vent surface until the gas pressure is high enough to erupt through it, ejecting with it both solid and liquid spatter from the magma. -> See whole entry

The adjective "tectonic" refers to processes, properties, or resulting features related to the deformation (breaking and slow, plastic deformation) of rocks over large sections of the upper mantle and crust (lithosphere). It is usually applied to large-scale features and processes, in the km scale and app. Smaller miniature tectonic processes are sometimes called micro-tectonic.

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Tephrite is an type of volcanic (extrusive) rock with low silica content, similar to basalt, but containing foid minerals (e.g. nephelinite, leucite) along with plagioclase. The composition of tephrite is called tephritic.

Tephritic refers to the mineral composition of tephrite, an type of volcanic (extrusive) rock with low silica content, similar to basalt, but containing foid minerals (e.g. nephelinite, leucite) along with plagioclase.