GEOL 110 Volcanoes
GEOL 110 Volcanoes GEOL 110
Long Beach State
Popular in Natural Disasters
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This 4 page Class Notes was uploaded by Elizabeth Rubio on Friday February 26, 2016. The Class Notes belongs to GEOL 110 at California State University Long Beach taught by Ewa Burchard in Spring 2016. Since its upload, it has received 33 views. For similar materials see Natural Disasters in Geology at California State University Long Beach.
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Date Created: 02/26/16
2292016 Volcanoes cont. ch5 Volcanic Explosivity Index measures the height and weight of a volcano explosion (Table 3.2 [in instructor's own powerpoint] or 5.2 in your powerpoint) Volcano Types, Formation, and Eruptive Behavior, cont. Shield Volcanoes – Largest volcanoes in the world • Thin lava flows build up volcano with gentle slopes • Wider than they are tall • Still among tallest mountains on Earth (measured from bases) – Associated with basaltic magma • Low viscosity, low volatile content • Gently flowing lava with nonexplosive eruptions • Develop a cladera, if magma is below the chamber – Common at hot spots in the oceanic lithosphere and divergent plate boundaries, continental rifts • Hawaiian Islands, Iceland, and in the East African Rift • Examples: Mauna Loa and Kilauea in Hawaii Volcano Types, Formation, and Eruptive Behavior, cont. Cinder Cones – Cone shaped with summit crater • Built from an accumulation of tephra Small pieces of black or red lava Formed when lava meets groundwater – Associated with basaltic eruptions • Low to intermediate explosivity • Also called scoria cones – Common on larger volcanoes, normal faults, or along cracks and fissures • Examples: SP Crater in AZ, Parícutin in Mexico, Eldfell in Iceland Continental Caldera – Large summit depression • Collapse of the land surface or volcanic edifice – Associated with rhyolite eruptions • Violent explosions • ultraPlinian extrude a great deal of pyroclastic debris on mainly ash • Largest known as the supervolcanic type – Very rare • Examples: Mount Mazama (Crater Lake), Yellowstone caldera Geographic Regions at Risk from Volcanoes Direct volcanic risk – Ring of Fire: surrounds Pacific Ocean basin – Hot spots: Hawai’i and Yellowstone Park – Midocean ridges: Iceland – Rift valleys: East Africa • Indirect volcanic risk – Ash fall and ash clouds: all locations in path Effects of Volcanoes 50 to 60 volcanoes erupt each year worldwide – In the United States, 2 to 3 per year, mostly in Alaska – Most eruptions are in sparsely populated regions – 500 million people live close to volcanoes • Japan, Mexico, Philippines, and Indonesia and several U.S. cities are vulnerable • Primary Effects – Lava flows, ash fall, pyroclastic flows, lateral blasts, and release of volcanic gases • Secondary Effects – Debris flows, mudflows, landslides or debris avalanches, floods, fires, and tsunamis – Global cooling of the atmosphere in a large eruption Lava Flows • One of most familiar products of volcanic activity – Results when magma reaches the surface through crater or from a vent – Three types: basaltic, andesitic, rhyolitic • Basaltic is the most abundant – Can form lava tubes • Can move slowly or more rapidly – Basaltic lavas are the most rapid at 15–35 km/h (10–30 mph) – Pahoehoe lavas are smooth and ropey – AA are blocky flows – Move slow enough for people to get out of the way Pyroclastic Activity Explosive volcanism that blasts magma and rocks from a vent – Known as tephra • Fine dust to sandsized ash (less than 2mm) • Small gravelsized lapilli (2 to 64 mm) • Large angular blocks and smoothsurfaced bombs (greater than 64mm) – Falls cool and lightly like snow or hat, fast, and heavy like a freight train • Accumulation forms a pyroclastic deposit Ash Fall – Explosive fragmentation of magma during an eruption – Can cover hundreds or thousands of square kilometers – Direct hazards • Vegetation may be destroyed • Surface water may be contaminated by sediment – Fine particles clog the gills of fish and kill other aquatic life – Ash accumulation on roofs may cause structural damage – Irritation of the respiratory system and eyes – Engines of jet aircraft may “flame out” Linkages between Volcanoes and Other Natural Hazards Fire – Hot lava may ignite plants and structures • Earthquakes – Usually accompany or precede volcanic activity • Landslides – Mud Flows, ash flows, and landslides are common secondary effects • Climate change – Debris can reflect sunlight causing global cooling Natural Service Functions of Volcanoes Volcanic soils – Good for coffee, maize, pineapples, sugar cane, and grapes • Geothermal power – Can create energy for nearby urban areas • Mineral resources – Gold, silver, etc. and nonmetallic rocks – Used for soap, building stone, aggregate for roads, railroads, etc. Recreation – Health spas and hot springs – Hiking, snow sports, and education – Kilauea National Park • Creation of new land – Hawaiian Islands • Humans do not affect the frequency or severity of eruptions • Minimization of loss of life and property damage is best action Forecasting Unlikely to accurately forecast the majority of volcanic activity in the near future – Need experience with actual eruptions – Better able to predict eruptions in Hawaiian Islands • Forecasting uses information gained by – Monitoring seismic activity – Monitoring thermal, magnetic, and hydrologic conditions – Monitoring the land surface to detect tilting or swelling of the volcano – Monitoring volcanic gas emissions – Studying the geologic history of a particular volcano or volcanic center
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