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Geology glossary

Updated: Feb 1, 2023 23:28 GMT -

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tephrite

Volcanology
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

Volcanology
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.

tremorSynonym of: volcanic tremor

Volcanology
Seismogram signal examples from volcanic earthquakes: Volcano Tectonic (VT) Low Frequency (LF), hybrid (mix of VT and LF), Very Low Frequency (VLF), and Tremor. Volcano name/date in lower left. (image: USGS)
Seismogram signal examples from volcanic earthquakes: Volcano Tectonic (VT) Low Frequency (LF), hybrid (mix of VT and LF), Very Low Frequency (VLF), and Tremor. Volcano name/date in lower left. (image: USGS)

tumulus

Volcanology
Tumulus with strange shapes, on the lava flow field of the 1614-24 eruption of Mt. Etna, Italy.
Tumulus with strange shapes, on the lava flow field of the 1614-24 eruption of Mt. Etna, Italy.
From Latin "tumulus" = "little hill", tumuli (pl.) are uplifted sections of pahoehoe lava crust caused by pressure from still fluid lava accumulating beneath the hardened crust.
Tumuli are a characteristic feature of all pahoehoe lava flow fields, such as prominent on Kilauea volcano, Hawaii, but also many other basaltic volcanoes including Etna. Read all

VAAC

Volcanology: Volcanic Ash Advisory Centre
Coverage of the globe by the 9 VAAC.
Coverage of the globe by the 9 VAAC.
Volcanic Ash Advisory Centers (VAAC) are research centres who monitor volcanic ash clouds in real time. Each time, a volcano erupts a significant ash cloud, short reports are issued and transmitted directly to air control centres. The 9 VAAC are located in London, Toulouse, Tokyo, Darwin, Anchorage, Washington, Montreal and Buenos Aireas and collectively cover most of the globe.
The Volcanic Ash Advisory Centers (VAAC) are groups of experts and government-funded bodies to montor volcanic ash clouds all over the planet in real time. As Europe experienced in April 2010, volcanic ash clouds are hazardous for aircraft and must be avoided to fly through, even if that means cancellation of flights.

As of 2010, there are 9 VAAC located in different areas and each focussing m... Read all

viscosity

Volcanology
The ability of a liquid to flow. Basalt magma has a relatively low viscosity making it runny, whereas rhyolite magma has a high viscosity making the magma thick and sticky.

Related keywords (2):

explosive - lava dome

volcanic dike

Volcanology: volcanic dike
Exposed volcanic dike on Santorini (Greece)
Exposed volcanic dike on Santorini (Greece)
Pathways of rising magma inside vertical fissures.
Dikes are imaginable as the veins of a volcano, the pathways of rising magma. A dike is called a -usually more or less vertical- flat, sheet-like magma body that cuts unconformingly through older rocks or sediments.

Most dikes can be described as fractures into which magma intrudes or from which they might erupt. The fracture can be caused by the intrusion of pressurized magma, or vice versa, ... Read all

volcanic tremor

Volcanology
Seismogram signal examples from volcanic earthquakes: Volcano Tectonic (VT) Low Frequency (LF), hybrid (mix of VT and LF), Very Low Frequency (VLF), and Tremor. Volcano name/date in lower left. (image: USGS)
Seismogram signal examples from volcanic earthquakes: Volcano Tectonic (VT) Low Frequency (LF), hybrid (mix of VT and LF), Very Low Frequency (VLF), and Tremor. Volcano name/date in lower left. (image: USGS)
Volcanic tremor is a continuous seismic signal with regular or irregular sine wave appearance and low frequencies (0.5-5 Hz).
Volcanic tremor is usually in the form of harmonic tremor which has a very uniform appearance, whereas spasmodic tremor is pulsating and consists of higher frequencies with a more irregular appearance.
Tremor can be caused by different processes inside the volcano, including resonance triggered by magma flowing through cracks and vents, or continuous low-frequency earthquakes so closely spaced th... Read all

volcaniclastic

Volcanology
A volcaniclastic rock or loose deposit made of (older) volcanic fragments.

Volcanology

Volcanology
The science of studying volcanoes.
Volcanology comprises the study of volcanoes and volcanic phenomena and is mostly regarded as a sub-part of geology, but is interwoven with other science disciplines as well: chemistry, physics, but also sociology, history, archaeology. Read all

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