ERTH 2415 Lecture Notes - Pyroclastic Flow
11 Apr 2012
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Hot spot: magma composition: andesitic to rhyolitic, high viscosity, high volatile content, very large volume, largest explosive volcanic eruptions, two different phenomena, volcano collapse - or - Caldera-type eruptions: volcano collapse, collapse of existing stratovolcano into partially emptied magma chamber. Follows a plinian-type eruption that opened void space below the volcano. Piston-like action of collapsing volcano cause very large volume of magma to flow outward as pumicerich sheets: cataclysmic explosion, explosion blows the existing volcano apart completely. Krakatoa, indonesia: subduction of australian plate under. Had been quiet for 200 years: 26-27 august 1883: series of explosions. Final cataclysmic explosion completely destroyed volcano: walls of volcano ruptured, ocean water invaded magma chamber, explosion due super hot steam. Size of explosion 100 megatons (20 kilotons at hiroshima) Explosion heard on 1/3 of earth"s surface. More importantly: ocean-bottom telegraph cables transmitted the news around the world. Hot enough to cause burn-related fatalities 40 km away. Reached 2,500 km downwind after several days.
