111-pp7 - UNIVERSITY OF SOUTH ALABAMA Last Time 1 GY 111...

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1 GY 111: Physical Geology GY 111: Physical Geology UNIVERSITY OF SOUTH ALABAMA Lecture 7: Volcanic Landforms, Features and Case Studies Lecture 7: Volcanic Landforms, Features Lecture 7: Volcanic Landforms, Features and Case Studies Last Time 1. Review of where volcanoes occur 2. Properties of magma/lava (viscosity) 3. Basic types of volcanoes Where Volcanoes Occur Divergent Plate Boundaries Rapid rise of magma to surface because of multiple fractures and faults (low resistance) Magma (molten rock inside the Earth) rises upwards along fractures and fault as plutons (inverted tear drop-shaped blebs 100’s to 1000’s of m in diameter). Why? .... Buoyancy . Hot magma is less dense than cool country rock Convergent Plate Boundaries 35 km M e ltin g Plutons rise at convergent plate boundaries too…. … but they have to burn their way up. This is not an easy trip to the surface. Subduction Hot Spots
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2 Properties of Magma/Lava 1. Magma derived from just below the lithosphere (e.g., 100 km down) is hot (2000 ° C) and very fluid ( low viscosity ) 2. Lava erupted at divergent plate boundaries and oceanic hotspots has made it to the surface of the Earth quickly and is still hot (up to 1800 ° C) and fluid ( low viscosity ). 3. Lava erupted at convergent plate boundaries and continental hotspots has made it to the surface of the Earth very slowly. It is cooler (as low as 800 ° C) and very contaminated by country rock and water (
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This note was uploaded on 02/04/2012 for the course GLY 111 taught by Professor Haywick during the Fall '11 term at S. Alabama.

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111-pp7 - UNIVERSITY OF SOUTH ALABAMA Last Time 1 GY 111...

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