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Geology glossary

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basalt

Volcanology
Basaltic columnar-jointed lava (Iceland)
Basaltic columnar-jointed lava (Iceland)
The most common type of volcanic rock, with a relatively low silica content and typically erupted at shield volcanoes.
Basalt is the usually hard and black volcanic rock formed from (liquid) balsalitc lava. Balsaltic lava contains less than about 52 percent silica (SiO2) by weight. Because of its low silica content, it has a low viscosity (resistance to flow). Therefore, basaltic lava can quickly and easily flow more than 20 km from a vent. The low viscosity typically allows volcanic gases to escape without genera... -> See whole entry

base surge

Volcanology
Base surge deposits from the great Minoan eruption on Santorini (ca. 1613 BC)
Base surge deposits from the great Minoan eruption on Santorini (ca. 1613 BC)
Base surges are ground hugging, fast outward moving and turbulent, dilute clouds of gas and ash. They result from water magma interactions (violent steam explosions). During the 1965 eruption of Taal volcano (Philippines), such base surges were first observed. Some of them traveled 4 km and killed 189 people. Base surges were first identified during ocean nuclear weapons explosions in the Pacific.... -> See whole entry

bentonite

Minerals
Bentonite from the Greek island of Milos
Bentonite from the Greek island of Milos
Bentonite is an absorbent aluminium phyllosilicate generally impure clay consisting mostly of montmorillonite.
Bentonite is an absorbent aluminium phyllosilicate generally impure clay consisting mostly of montmorillonite. There are a few types of bentonites and their names depend on the dominant elements, such as K, Na, Ca, and Al. As noted in several places in the geologic literature, there are some nomenclatorial problems with the classification of bentonite clays. Bentonite usually forms from weathering... -> See whole entry

block

Volcanology: (volcanic) block
Large ballistically ejected block on Santorini (Greece)
Large ballistically ejected block on Santorini (Greece)
Volcanic blocks are solidified rock fragments greater than 64 mm in diameter. Blocks commonly are ejected during explosive eruptions and consist of older pieces of the volcano's edifice, e.g. parts of the conduit, lava domes or older lava flows.
During violent eruptions, blocks of up to several meter size can be thrown to several km distance. For example, during the Minoan eruption (ca. 1613 BC) of the Santorini volcano in Greece, meter-sized blocks were thrown to up to 7 km horizontal distance and impacted violently into the ground, some of them destroying houses of ancient settlements. The time some of these blocks spent on their trajec... -> See whole entry

bomb

Volcanology: volcanic bomb
Large bomb ejected from Etna volcano's SE crater.
Large bomb ejected from Etna volcano's SE crater.
Ejected fragments of fresh magma larger than 64 mm in diameter, often shaped aerodynamically during their flight.
Volcanic bombs are lava fragments larger than 64 mm in diameter that were ejected while still viscous and partially molten. Many bombs acquire rounded aerodynamic shapes during their travel through the air. Volcanic bombs include breadcrust bombs, ribbon bombs, spindle bombs (with twisted ends), spheroidal bombs, and "cow-dung" bombs. -> See whole entry

breadcrust bomb

Volcanology
Breadcrust bomb, ca. 50 cm long, from Lokon volcano (N-Sulawesi, Indonesia)
Breadcrust bomb, ca. 50 cm long, from Lokon volcano (N-Sulawesi, Indonesia)
Perfectly shaped breadcrust bomb from Nea Kameni, Santorini (Greece)
Perfectly shaped breadcrust bomb from Nea Kameni, Santorini (Greece)
Volcanic bomb with a cracked surface, similar to bread, caused by the slow expansion of the interior gas bubbles while cooling.
A breadcrust bomb is a volcanic bomb with a cracked and checkered surface, sometimes resembling the surface of a loaf of bread. The cracks develop when the outer surface of a partially molten lava fragment cools to form a brittle surface and then subsequently cracks as the hot interior expands due to the continued growth of gas bubbles. -> See whole entry

 

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