Volcanoes (Ch 5) 09:36 Volcanic dome Steep-sided mass if felsic (silicic lava often forming plugs- commonly gas-rich and explosive (eg dome currently developing in Mt St Helens) Central vent eruptions Eruptions from pipe-like conduit (central vent) produces volcanic cones, typically with craters at summit Pyroclastic eruptions Volcanic vents that discharge pyroclastic materials Caldera Large “collapse” structure developed after violent eruption & loss of large volumes of magma- commonly with resurgent dome. (E.g. Crater Lake Oregon) Fissure eruptions Lava flowing from a long fracture (most commonly at mid-ocean ridge) Flood basalts Large volumes of basaltic lava issues from a fissure- e.g. Columbia river basalts or Laki, Iceland Ash flow deposis Pyroclastic materials of felsic magma- extremely dangerous! Lahar Mud flows of wet volcanic material typically pyroclastic Geysers & Fumaroles (hot springs) Emissions of heated water & steam, and deposition of sulfur or travertine Global pattern of volcanism Most volcanoes are found near plate boundaries- 500-600 active volcanoes 15% of volcanoes are at extensional boundaries (eg mid-ocean ridges)
Volcanoes (Ch 5) 09:36 Generates extensive hydrothermal activity that Effectively transports heat from Earth’s interior Alters ocean crust to ultimately carry water to subduction zones and released to contribute to melting Leaches metals and other elements to change ocean chemistry, generate metal deposits, and supply nutrients to a peculiar biological community 5% of volcanoes are found within plates (e.g. intraplate volcanoes such as in the Hawaiian islands) Basaltic lavas are found in divergent rift zones and intraplate volcanoes Basalt + andesite develop at ocean/ocean plate converging plate boundaries Basalt + andesite + rhyolite lavas develop at ocean/continental converging plate boundaries Volcanic Hazards & Eruptions Hazards associated with volcanic eruptions Supervolcanic eruptions Massive eruption that effects the local and world environment Volcanic ash & hot poisonous gases May bury or poison people Undersea eruptions or volcanic flank collapses cause tsunamis Ash erupted into the stratosphere may threaten air traffic Monitoring and predicting eruptions It is getting better with improved technology, but still needs great improvements
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