GEO 120 Lecture Notes - Lecture 9: Stratovolcano, Viscosity, Volcanism
13 Oct 2016
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Geo 120 - lecture 9 - divergent plate boundaries - elizabeth laliberte. Uplift of a broad area, crust is heated and expanded. Tensional stress causes rifting; rocks falling down. Crust is thin but at high elevation. Earthquakes in the basin and range province. Normal faulting from tensional stress (hanging wall is moving downward with respect to the foot wall) Occur in relatively cold, brittle upper crust. Only up to magnitude 7. 5 because the region is so hot. Many types of volcanoes and volcanic products in continental rift zones. Magma that melts its way through the thick silica-rich crust becomes enriched in silica. Steep sided lava domes and composite volcanoes. Magma is more like low silica basalt from mantle. Low silica magma with a lot of gas. Fluid, mafic magma erupts and spreads out as low profile shield volcanoes. Once plate rifts apart, only basaltic lava. As it cools it is under tension from all sides.
