Volcano - VOLCANISM: How to build an Hawaiian How to build...

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Unformatted text preview: VOLCANISM: How to build an Hawaiian How to build an Hawaiian volcano volcano *Magma = lava + volatiles* (L4) & CD:IP/D Volcanoes • When magma reaches the surface it is called an lava and an eruption occurs which – can be explosive , and produce pyroclastics • pyroclastics are rock fragments made from magma with high gas content that has exploded – can be effusive , and produce lava • lava is molten rock on the Earth’s surface • A structure created by eruptions of magma – can be accumulations of pyroclastic material, lava, or both – also includes magma transport system (plumbing) Where does the magma come from? From the Hot Spot in the Astenosphere* * Supply is steady! Where does the magma reside? In magma chambers 2-5 km below the volcanoes Volcano Shapes • The shape of a volcano is the result of the type of magma it is built from – low-silica magmas have low viscosity* • produce fast- moving, thin lava flows that can travel long distances • gentle-sloped volcanoes • less likely to be explosive – high-silica magmas have high viscosity • produce slow-moving, thick lava flows • steep-sided volcanoes • tend to be explosive [* F of SiO2, temp, gas] mafic felsic “thin” “thick” most Hawaiian igneous rocks Shield Volcanoes • Repeated eruptions of low-viscosity (basaltic) lava forms shield volcanoes • So called because they are broad, flat cones resembling a shield laying on the ground – results from the piling up of numerous long, thin lava flows – kind of volcanoes found in Hawaii – “ drive-in volcanoes ” – Remember! 3 things come out of a volcano! • Solid (tephra), liquid (lava) & gases (volatiles) Shield Volcano Mauna Loa, a shield volcano Structural Features of Shield Volcanoes • Calderas – large (several km diameter) collapse features found at the summits of volcanoes – roughly outline the location of the magma chamber – can be location of eruptions • Rift Zones – long, narrow zones of weakness of the volcano’s flanks where eruptions also take place – can continue under the ocean – are also areas of concentrated dike intrusion Structural Features of Shield Volcanoes • Pit craters – small collapse features on rift zones and caldera floors – do not necessarily produce lava...
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This note was uploaded on 04/20/2011 for the course GG 103 taught by Professor Herrero-bervera during the Summer '10 term at University of Hawaii, Manoa.

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Volcano - VOLCANISM: How to build an Hawaiian How to build...

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