Volcanoes_3 - EOSC 114 Guillaume Carazzo Earthquakes...

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Unformatted text preview: EOSC 114 / Guillaume Carazzo Earthquakes Volcanoes Landslides Storms Waves Impacts Recap Last session we examined: where volcanoes occur different types of volcanoes the relative risk between types of volcanoes Volcanoes Lecture 1 Lecture 2 Lecture 3 Lecture 4 Lecture 5 - Volcano Basics - Types of volcanoes - Volcanic hazards I - Volcanic hazards II - Volcano monitoring and predicting eruptions Outline 1 / Size of an eruption 2 / Hazards: lava + airfall Learning Goals Estimating the SIZE of eruptions. Compare different types of eruption and their hazards: LAVAS PYROCLASTIC FALL PYROCLASTIC FLOWS (and next class) LAHARS (next class) Volcanoes, volcanism and hazards Molten magma rises within the Earth and is erupted either: quietly (lavas) ,or violently (pyroclastics) Eruption Size VEI scale many every year several every decade several every 1,000 yrs 1 or 2 every 1,000,000 yrs The Volcanic Explosivity Index VEI- 5 Plinian, Mt St Helens VEI 3 Vulcanian Montserrat VEI 1 Hawaiian VEI 6 Ultra-Plinian Mt Pinatubo, Phillippines VEI 8 - Imagine 100 Pinatubos erupting at the same time Ash from VEI 8 eruption VANCOUVER TORONTO YELLOWSTONE N.P. LOS ANGELES NEW ORLEANS http://www.cotf.edu/ete/movies/caldera.mov Location map of some these super-eruptions VEI 7 VEI 8 VEI 7 VEI 8 VEI 8 Hazards: 1. Lava flows This is a basalt lava flow in a channel Due to its low silica content (mafic) and high temperature, it has a low viscosity Yet lava usually flows fairly slowly 0.0130km/h 1a. Pahoehoe lava Not very large volume and often channelised Can flow fast Figure 3.49 This is a Hawaiian term for smooth, ropy lava It generally exhibits fluid-like textures 1b. Aa lava This type of lava is quite blocky on the surface, and comparatively cool Yet below the surface, the lava is fairly massive and much hotter Large volume Fairly slow moving Figure 3.50 Lava flows- move slowly and (usually) don't kill people Heimaey, Iceland 1974 Figure 3.65 But are very hard to stop Cooling by sea water Lava flows- move slowly and (usually) don't kill people Heimaey, Iceland 1974 HOWEVER can cause millions $$ of damage (property) In Goma (Republic of Congo, Africa) a 2002 basalt lava eruption killed 2000 people, made 400,000 homeless fires, water supply destroyed, fuel-tanks exploded. But are very hard to stop Cooling by sea water eruption in northern BC killed 2000 TSEAX basalt lava First Nation people around 1750 AD flooding, famine, Canada's worst poison gases. Figure 3.65 natural disaster La Runion (April 2007) 1c. Fire fountaining Sometimes basaltic lava can contain lots of gas Then, small explosive eruptions form fire fountains As partially liquid drops fall back to the ground, they may coalesce to form a lava flow Spindle bombs A key eruption: Paricutin 1943 (Mexico) 2. Pyroclastic falls (ash fall) During explosive volcanic eruptions, ash falls downwind of the volcano In the case of very large eruptions, the ash may be deposited over a vast area http://www.youtube.com/watch?v=Uo01vhGnn6E&feature=related Figure 3.42 Magma fragments and freezes to form pyroclastic ash When a volcano erupts liquid magma with gas dissolved in it suddenly decompresses, gas bubbles rapidly expand blowing up the liquid magma, which freezes in mid air to form ash particles Remember the Menthos experiment ! Mt. Pinatubo (1991) Ash and lapilli Obsidian HAZARDS to people: Breathing in ash can be deadly Total darkness very scary Roofs collapse most dangerous problem, most fatalities are people trying to shelter HAZARDS to aircraft: Engines suck in ash and STOP not good Windshields are scratched and break Turbulence Satellites now watch for ash clouds B747, 257 passengers - The aircraft flew into a plume from a volcanic eruption at 37,000 feet (12 km) during the night. All engines failed and the windshield lost transparency because of pitting. The first engine was restarted at 12,000 feet (4 km), followed by the other three and the plane landed safely at Jakarta Pinatubo 15 June 91 1989 Redoubt Eruption B747, 231 passengers - All engines failed 4min. of powerless descent over mountain terrain A key eruption: Mt Vesuvius AD 79 Pompei before the disaster: 20,000 inhabitants A witness... Pompei Pliny the Younger Pliny the Elder August 24th, 1pm An umbrella pine (...) rose to a great height on a sort of trunk and then split off branches (Pliny the Younger, Epistulae VI . 16) Pompei People have been killed by another phenomenon... Ash fall deposit Next Class... Next session we will: Look at other types of eruption hazard Pyroclastic Flows Lahars, Sector collapse (volcanic landslides), Toxic gas. Hazard maps Monitoring ...
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