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Geology glossary

Updated: Feb 1, 2023 21:33 GMT -

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lava fountain

Volcanology
Lava fountain on Etna volcano (June 24, 2001)
Lava fountain on Etna volcano (June 24, 2001)
Jets of fluid lava propelled into the air from an erupting vent, driven by expanding gasses.
Lava fountains are sustained jets of (usually very) fluid lava into the atmosphere. Lava fountains occur commonly on basaltic volcanoes such as Kilauea, or Etna.
The fountain gains its momentum by the expansion of gas bubbles that dissolve from the magma as pressure falls while it is rising in the conduit.
Heights, appearance, duration and erupted volumes of lava fountains can vary greatly. St... Read all

lava lake

Volcanology
The lava lake of Nyiragongo volcano, DRCongo (Jan. 2006)
The lava lake of Nyiragongo volcano, DRCongo (Jan. 2006)
Lava lakes are accumulations of larger volumes of liquid lava above one or several vents, usually contained within a crater on the summit of the volcano.
Volcanoes with eruptions that produce long-lasting lava lakes are relatively rare; some volcanoes are famous for their lava lakes: Kilauea (Hawaii), Erta Ale (Ethiopia), Nyiragongo (at present probably the most violent lava lake in the world, about 120 meters wide), Ambrym volcano (Vanuatu), Mt Erebus (Antarctica) and a few others with sometimes smaller lakes. Read all

lava trees

Volcanology
Lava trees on the eastern Rift zone Kilauea volcano, Hawaii
Lava trees on the eastern Rift zone Kilauea volcano, Hawaii
The lava coating around a tree trunk left by an invading liquid lava flow.
When a liquid lava flow invades a forest, often, the lava does not overthrow the larger trees, but flows around their trunks. At the very contact of the hot lava to the bark, a thin layer of the lava is quenched sufficiently to form an isolating coating around the trunk. The tree itself most often burns down slowly, eventually falling down onto the lava.
The typical lava trees are formed when af... Read all

liquefaction

Earthquakes
An aftermath of the 2019 Luzon Earthquake in the Philippines. Liquefaction affected the base filling material under the approach to the bridge. This caused that part of the road to slightly subside due to a weakened base. (source: Photograph by Renz Lazatin, 2019)
An aftermath of the 2019 Luzon Earthquake in the Philippines. Liquefaction affected the base filling material under the approach to the bridge. This caused that part of the road to slightly subside due to a weakened base. (source: Photograph by Renz Lazatin, 2019)
Very intense earthquakes may sometimes cause the solid ground to act as though it was muddy liquid. This earthquake-induced phenomenon is called Liquefaction. This occurs in areas where the ground is composed of particles with plenty of spaces where water could sneak into (be water-saturated) as in sandy soils and uncompacted soils.
Liquefaction occurs when the very intense shaking of the earthquake causes the pore water pressure in the soil to increase, leading to loss of strength and stability of the soil. This results to the ground acting as though it was liquified.
After the shaking ends, the soil immediately turns solid and holds anything caught sinking in it, in place. Another hazard related to this is the colla... Read all

magma

Volcanology
Molten rock within a volcano or underneath the earth's surface. Once magma reaches the surface it is called lava.

Related keywords (2):

explosive - lave

magnitude

Earthquakes
A number that characterizes the relative size of an earthquake. Different scales are used, but the most common is the logarithmic Richter scale. where most quakes are between 0 (tiny) and 9 (extremely large quake). Each step on this scale indicates a 10 fold energy increase of an earthquake.
Felt quakes are normally above magnitude 2.5 on this scale.
Magnitude is based on measurement of the maximum motion recorded by a seismograph(sometimes for earthquake waves of a particular frequency), corrected for attenuation to a standardized distance.
Several scales have been defined, but the most commonly used are (1) local magnitude (ML), commonly referred to as œRichter magnitude, (2) surface-wave magnitude (Ms), (3) body-wave magnitude (Mb), and (... Read all

mainshock

Earthquakes
A mainshock is the largest earthquake in a sequence, sometimes preceded by one or more foreshocks, and almost always followed by many aftershocks.

Related keywords (2):

aftershock - foreshock

minette

Minerals
Minettes are a variety of igneous rock with phenocrysts of biotite, and with or without phenocrysts of hornblende, augite with a high diopside content, and olivine.
Examples where minettes are found include the Navajo Volcanic Field of the Colorado Plateau and the Mexican Volcanic Belt, where he youngest minettes on the earth are found in the Mascota volcanic field.

mud volcano

Volcanology
Sidoarjo mud volcano (East Java)
Sidoarjo mud volcano (East Java)
Mud volcanoes are no true volcanoes, but vents that erupt mud, as fine sediemtn is squeezed upwards by prezzurized water, steam and gas escaping from deeper deposits.
A mud volcano is a vent on the surface erupting mud and gas or steam, but no lava. Mud volcanoes are usually not the result of volcanic processes, but more generally related to environments where pressurized deposits at depth occur that release gas and steam, which mixes with fine-grained sediments to form mud. Temperatures are much cooler than at volcanic processes. The largest structures are 10 ... Read all

obsidian

Volcanology
Obsidian from the Rocce Rosse lava flow on Lipari island (Italy)
Obsidian from the Rocce Rosse lava flow on Lipari island (Italy)
Black volcanic glass
Obsidian is a naturally occurring glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly through the glass transition temperature and freezes without sufficient time for crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where cooling of the lava is rapid. Because of the lack of cr... Read all

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