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ESC Chapter 12

Terms

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A lava of intermediate composition that has a higher silica content than basalt, erupts at lower temperatures and is more viscous. Extrusive equivalent of diorite. 
Andesitic Lava
An extensive sheet of hard volcanic tuff
Ash-flow deposit
A lava of mafic composition that has a low silica content, erupts at high temperatures, and flows readily. Extrusive equivalent of gabbro.
Basaltic lava
A large, steep-walled, basin shaped depression formed after a violent eruption in which large volumes of magma are discharged, when the overlying volcanic structure collapses catastrophically through the roof of the emptied magma chamber.
Caldera
A bowl-shaped pit found at the summit of most volcanoes, centered on the vent.
Crater
A volcanic vent formed by the explosive escape of gases and often filled with breccia.
Diatreme
A volcanic eruption emanating from an elongated fissure rather than a central vent.
Fissure eruption
An immense basaltic lava plateau extending many km in flat, layered flows originating from fissure eruptions. 
Flood basalt
A volcanic center found at the beginning of progressively older aseismic ridges or within a continent far from a plate boundary. Hypothesized to be the surface expression of a mantle plume.
Hot Spot
The circulation of water through hot volcanic rocks and magmas, producing hot springs and geysers on the surface.
Hydrothermal activity
A torrential mudflow of wet volcanic debris produced when pyroclastic or lava deposits mix with rain or the water of a lake, river, or melting glacier. 
Lahar
A voluminous emplacement of predominantly mafic extrusive and intrusive igneous rock whose origins lie in processes other than "normal" seafloor spreading. Include continental flood basalts, ocean basin flood basalts, and aseismic ridges.
Large igneous province
A narrow, cylindrical jet of hot, solid material rising from deep within the mantle and thought to be responsible for intraplate volcanism.
Mantle plume
A volcanic rock fragment ejected into the air during an eruption.
Pyroclast
The lava that is richest in silica, making it the stickiest and the least fluid kin of lava. It erupts at  temperatures of only 600 to 800 degrees C. 
Rhyolitic lava
A broad, shield-shaped volcano many tens of kms in circumference and more than 2 km high built by successive flows of fluid basaltic lava from a central vent.
Shield volcano 
A concave-shaped volcano containing alternating layers of lava flows and beds of pyroclasts.
Stratovolcano
The total system of rocks, magmas, and interactions needed to describe the entire sequence of events from melting to eruption.
Volcanic geosystem
A hill or mountain constructed from the accumulation of lava and other erupted materials.
Volcano

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