GEOLOGY 1 Lecture Notes - Lecture 14: Pumice, Mount Pinatubo, Viscosity
Document Summary
Magma, when it comes out of the ground, will be in one of two forms: lava (liquid) or pyroclastic material (hot particles) Magma reaches the surface by coming through either. Pipe-like conduit and vent brings magma to surface. Eruptions range from calm to violent (depends on magma composition) Stratovolcano (composite cone)- lava and pyroclastic, felsic to intermediate material, 6km high. Shield volcano- lava, mafic material (calm eruption), Stratovolcano because their magma composition is felsic or intermediate. Therefore, the magma has high viscosity and high water content. This leads to high, steep-sided volcanoes because of the pyroclastic ash that piles up with steep-sides. And because the sticky magma flows slowly down the sides maintaining step slopes of the volcano. As magma rises to the surface, there is a decrease in pressure. The gas (steam) bubbles try to expand and get out. Also, stratovolcanoes occur along continental margins where people like to live (i. e. subduction zones, destructive plate margins)
