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GGR378H5 (17)
Lecture 7

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Barbara Murck

Lecture 7 Volcanic Hazards • Science of Volcanoes – Volcanic materials – Tectonic environments – Types of volcanoes & eruptions • Volcanic Hazards & Impacts • Predicting Eruptions – Monitoring – Early warning & evacuation • Magma – Molten rock under the ground – + rock fragments, crystals, dissolved gas • Lava – Molten rock that flows onto the surface • Volcano – Vent through which molten rock and gas escape • Volcanic rock – Solidifies quickly above ground • Plutonic rock (feeder system) – Solidifies slowly under ground • Gases – Dissolved in magma – Can greatly affect behaviour – Water + carbon dioxide = 98% • Pyroclastics: broken-up volcanic particles – Ash: extremely fine – Tephra: slightly coarser – Bombs: larger, up to car-size – Glass: lava cools, crystallizes very quickly Types of Volcanoes and Eruptions • Shield volcanoes – Shallow slopes – Low-viscosity basaltic lava flows – Non-explosive “Hawaiian”-type eruptions – Divergent plate boundary rift zones and intraplate “hot spots” Types of Volcanoes and Eruptions • Fissure eruptions – Basaltic lava – Very fluid, low-viscosity – Divergent rifts • Laki Eruption (Iceland), 1783 – 8-month eruption from Laki fissure and Grímsvötn volcano – 14 km of basaltic lava and clouds of poisonous hydrofluoric acid – Killed over 50% of Iceland’s livestock, leading to famine that killed 25% of the population – Eruption killed over two million people globally – Drop in temperatures due to the sulphur aerosols, caused crop failure, drought • Stratovolcanoes – Steep slopes – Layered pyroclastic deposits – Explosive “Vesuvian” or “Plinian” eruptions – Large caldera (summit crater) – Convergent boundary – subduction zones • Examples: Pacific “Ring of Fire” volcanoes – Mt. St. Helens, Pinatubo, Vesuvius, etc. Volcanic Hazards & Impacts • Primary: – Lava flows – Gas emissions – Glowing avalanches – Ash falls – Volcanic earthquakes • Secondary: – Volcanic mudflows – Landslides – Tsunami – Fires – Local atmospheric effects – Impacts on water and vegetation • Tertiary: – Long-term climatic effects – Permanent terrain changes
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