ESS 106 Lecture 05 June 2013

Supereruptions volcanic explosivity index vei of 8

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Unformatted text preview: in spurts –  Times of growth separated by long periods of NO growth –  Built up incrementally. Collapse. Build again. The Lowdown: Hazards •  LAHARS from Mt Rainier constitute the greatest volcano hazard in the Cascade range –  USGS Special report 98-428 Supervolcanoes! Supereruptions •  Volcanic explosivity index (VEI) of 8 •  Short-term, explosive events that eject magma with a mass of 1015kg – which is 11 trillion tons of magma! •  Produce pyroclastic deposits with volumes of 1000 km3 •  A supervolcano is a volcano that has produced at least one explosive supereruption •  Destructive capacity far greater then smaller explosive eruptions how much stuff erupted or greater 545 mi3 Yellows tone 2.1 Ma Prehistoric Eruptions 57 mi3 145 mi3 240 mi3 Yellows tone 1.3 Ma Long V alley Yello wstone 0.76 Ma 0.54 Ma 2.4 mi3 12 mi3 Krakatau Tambora 1883 1815 19th Century Eruptions 0.1 mi3 1.2 mi3 MSH Pinatubo 1980 1991 20th Century Eruptions Supereruption look like large calderas (holes in the ground) usually with a lake in the middle of them Supereruption ! Caldera Caldera-forming Supereruptions Post eruption cinder cone Aniakchak Caldera in the Aleutian Range, Alaska 10 km in Diameter Crater Lake (Mount Mazama) •  “Crater” formed 7,000 years ago during catastrophic eruption ~1900 ft at its deepest (deepest lake in North America) •  Wizard Island is a post-caldera dome within the caldera Wizard Island Cinder cone and lava flows Calderas on Mars Calderas on Mars Olympus Mons largest volcano in the solar system Calderas on Mars Olympus Mons Calderas Comparison of Olympus Mons, Everest, and Maxwell Montes (tallest mountain on venus) Olympus Mons summit caldera Post-caldera-forming eruptive activity •  •  •  Possible formation of lake generally a given because of the depression that results Erosion (over the next 1000 s of years) Uplift of caldera floor (resurgence; over the next 10 s of thousands of years) Resurgent Dome •  Up-warped caldera floor due to reintrusion of magma beneath the caldera Toba, Sumatra 74,000 years ago Post-caldera-forming eruptive activity •  Effusive eruptions –  –  •  Dome eruptions Lava flows Smaller explosive eruptions –  –  Ash fall Pyroclastic flows The Valles Caldera, Jemez Mountains, northern New Mexico Yellowstone National Par...
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