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Mt St Helens, 1982

Strato volcano. Mt St Helens, 1982. Global Volcano Distribution (active & dormant). Volcanism on the Earth: I. Some important Terms: magma : molten (or partially molten) rock and dissolved gas volcanoes: vents in the crust where magma reaches the surface

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Mt St Helens, 1982

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  1. Strato volcano Mt St Helens, 1982

  2. Global Volcano Distribution (active & dormant)

  3. Volcanism on the Earth: I • Some important Terms: • magma: molten (or partially molten) rock and dissolved gas • volcanoes: vents in the crust where magma reaches the surface • lava: magma and condensed H2O ejected from a volcano as liquid • pyroclastics: magma ejected as solids – ash, pumice, bombs, cinders…

  4. Types of Volcanic Eruptions • pyroclastic falls: airborne ash and rock fragments • pyroclastic flows: avalanches of heated rock and gas mixtures • lahars: mudflows made of ash and rainwater • lava flow compositions: basalt, andesite, rhyolite • basaltic flow styles : pahoehoe (billowy) & aa (blocky) • strato volcano • shield volcano • fissure eruption • pyroclastic cone Types of Volcano Edifices

  5. Historically Important Eruptions • Vesuviusce79 - ash fall destroyed Pompeii • 1815 Tambora -- pyroclastic flow ~ 300,000 fatalities • 1883 Krakatau -- pyroclastic flow + tsunami • 1902 Pelee -- famous pyroclastic flow • 1980 St. Helens • 1991 Pinatubo -- largest eruption of 20th century; global climate effects; forecasted

  6. Volcano Explosive Index (VEI)

  7. Historical Example by VEI VEI Volume (km^3) Eruption 0 Effusive Masaya (Nicaragua), 1570 >0.00001 Poás (Costa Rica), 1991 2 >0.001 Ruapehu (New Zealand), 1971 3 >0.01 Nevado del Ruiz (Colombia), 1985 4 >0.1 Pelée (West Indies), 1902 >1 Mount St. Helens (United States), 1980 >10 Krakatau (Indonesia), 1883 >100 Tambora (Indonesia), 1815 >1000 Yellowstone (United States), Pleistocene

  8. Pyroclastic Cone: Paricutin, Mexico (1947)

  9. Volcanic Caldera: Crater Lake, OR

  10. Shield Volcano: Mauna Kea, Hawaii (last eruption: 4000 bce)

  11. Caldera with pyroclastic cones: Haleakala, Maui (last eruption: 1700 ce)

  12. Shield Volcano: Mauna Loa, Hawaii (last eruption 1800 ce)

  13. Shield Volcano: Kilauea Summit, Hawaii (active)

  14. Loihi Seamount, Hawaii (70 km SE of Kilauea)

  15. Basaltic Lava Flows, Kilauea eruption temperature ~ 1200 C Low silica, low viscosity low crystal content relatively low gas content (not explosive) pahoehoe (gas poor) aa (somewhat higher gas content)

  16. Lava flow: Volcano Mayon, Phillippines

  17. Pyroclastic Flows Ash clouds rise above a pyroclastic flow traveling down the flank of Mayon Volcano, Philippines, September 12, 1984

  18. Pyroclastic Flows Pyroclastic flows in 1997 sweep across the flank of Soufrière Volcano on Montserrat.

  19. Pyroclastic Fall: Erosional dissection of an ash deposit from the 1991 Pinatubo eruption, Philippines

  20. Lahars: volcanic mudflows St Helens Pinatubo

  21. Famous Active Volcanoes I Stromboli Vesuvius (1944) Etna (2002)

  22. Explosive Volcanoes, Eruption Columns, and Plumes

  23. Explosive Volcanoes, Eruption Columns and Plumes • Eruption Column Anatomy • Plume Types • Iceland Eruption • Historical Catastrophic Eruptions • Volcanic Aerosols and Climate

  24. Anatomy of an Explosive Volcanic Eruption Neutral buoyancy level Umbrella Turbulent Gravity Current Turbulent convective plume Pumice & ash fallout Jet phase Surface vent conduit Fragmentation & ex-solution Magma chamber Silicate liquids & solids + volatiles (CO2, H2O, SO2…)

  25. Famous Active Volcanoes II Hekla (2000) Krakatoa Arenal Paricutin (1947)

  26. Melting in the Mantle magma genesis by decompression (pressure reduction) melting Decompression melting

  27. Subduction Zone - Island Arc Volcanism • Volcanoes located ~ 200 km behind deep sea trench • Andesite (silica-rich) composition • Often explosive • Magma produced by subducted volatiles (melting point reduction) • Examples (abundant): Cascade Volcanoes, Aleutians, Andean & Central American Volcanoes…

  28. Hotspots: long-lived mid-plate volcanic centers • tracks defined by island chains • regular age progression • tracks indicate plate motion • nearly stationary mantle heat source (thermal plume) • examples: Hawaii (best), Yellowstone, Iceland… • mostly basaltic volcanism • decompression melting starting ~ 100 km depth

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