GEOG306 Lecture Notes - Lecture 12: Lahar, Stratovolcano, Therma
6 Jul 2016
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Rift (a. k. a spreading centres ): mostly undersea, lots of magma, little explosivity e. g. laki, iceland 1783. 50 days of lava equal to 1/2 volume of amazon river. Subduction zones: mostly on land, lots of explosivity, little magma (e. g. pinatubo, st. helens, Masses of slowly rising mantle rock can emerge away from edges of tectonic plates. Volcanoes divided into three main types: basalt volcanoes, pyroclastic cones, stratovolcanoes. The development of these volcanoes is influenced by larger-scale plate tectonics and by the chemistry of the magma. Magma is molten rock which flows beneath the surface of the earth. When magma is ejected from a volcano onto the surface of the earth, it is called lava. Forms a relatively thin flow; covers dozens of km. Pahoehoe: lava flows with smooth tops + ropy surfaces. Repetitive eruptions of basalt lava build up over time to form shield volcanoes. Characterized by low viscosity basalt flows, gentle slopes, and large size.
