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Geology glossary

Updated: Feb 1, 2023 22:24 GMT -

sediment

Geology
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, ... Read all

seismic waves

Earthquakes
Diagram showing the elements of an earthquake. (source: Tarbuck, Lutgens, and Tasa. 2012. Essentialsof Geology. 11th Ed. Page 337)
Diagram showing the elements of an earthquake. (source: Tarbuck, Lutgens, and Tasa. 2012. Essentialsof Geology. 11th Ed. Page 337)
During an earthquake, large amounts of energy are released from the hypocenter or focus (i.e. point where the quake occurs) in the form of seismic waves. These cause the vibrations felt during a proper quake.
As a thought experiment, try imagining throwing a pebble in the middle of pond. Ripples will form from the point of contact between the pebble and the water surface, and propagate outwards ... Read all

seismograph

Earthquakes
A seismograph at a volcano observatory in Indonesia
A seismograph at a volcano observatory in Indonesia
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... Read all

shield volcano

Volcanology
Mauna Loa shield volcano (Big Island, Hawaii)
Mauna Loa shield volcano (Big Island, Hawaii)
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... Read all

skylight

Volcanology
Skylight on Etna volcano (Italy)
Skylight on Etna volcano (Italy)
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.

Related keywords (1):

Coulée de lave

smoke ring

Volcanology: volcanic smoke ring, gas ring, steam ring
Etna's Bocca Nuova crater in 2000, emitting smoke rings
Etna's Bocca Nuova crater in 2000, emitting smoke rings
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... Read all

strain

Earthquakes
The amount of deformation (change in size, shape, or volume) experienced by a rock as a result of stress.

There are three stages of deformation that rocks pass through when stress is applied:
- Elastic: strain is reversible
- Ductile: strain is irreversible
- Fracture: strain is irreversible and the rock has broken

Related keywords (1):

stress

stress

Earthquakes
The force per unit area applied to a rock.

There are different types of stress:
- Uniform: when forces are acting equally in all directions
- Tensional or Extensional: stretches the rock
- Compressional: squeezes the rock
- Shear: causes slippage of the rock along a plane

Related keywords (1):

strain

strombolian eruption

Volcanology
Strombolian eruptions from vents of Stromboli volcano, Eolian Islands, Italy
Strombolian eruptions from vents of Stromboli volcano, Eolian Islands, Italy
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. Read all
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