EAS205 Lecture : Topic 3 - Volcanoes.pdf
8 May 2014
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Source from upper mantle (~50 to 250 km in depth) Composition determines: activity type, shape, possible types of hazards. Composition: mixture of sio2, fe, mg and other elements. Areas with silica-enriched magmas (continental and water rich materials) Usually more felsic lavas, but also found with gaseous mafic lavas. Mor: 65 km long; volume = 5 to 20 km3/yr. Columbia and snake rivers area, usa: 1. 5 km thick over a 150,000 km2 area. Volcanic domes: more felsic lavas; usually intermediate. Cascades and rocky mountains (mount st. helens) Explosion caused by water boiling in pores and fractures. Generally occurs in volcanoes adjacent to or surrounded by water. Rapid emptying of the magma chamber during eruption. A new cinder cone wizard island. Lots of property damage, usually little loss of life. 1973, heimay, iceland harbour at westman islands. Range from ash (1/16 mm) to bombs and blocks (house-sized) Volcanic ash eruption: mainly ash and dust (<1/16 mm) of rock fragments and glass.
