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105_05-volcanoes_part_2 - Pyroclastic material Particles...

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Unformatted text preview: Pyroclastic material Particles Particles that are produced by explosive magma, collectively called Tephra: Pyroclastic material Tephra: Tephra: – Dust 1/1000 1/1000 mm – Ash < 2 mm mm – Cinders 2-64 mm – Bombs > 64 mm 64 Rabaul volcano in New Guinea, from space Volcanic Landforms Volcanic Volcanic bombs Calderas Calderas – Collapsed structure around the crater – Forms when the magma chamber is empty and the roof collapses into it 1 Volcanic Landforms Shield Shield Volcanoes – Low, rounded profiles; slope angles 2-10°; 2-10° composed of numerous flows of mafic composition and little explosive activity – Largest of all volcanoes Mauna Loa: shield volcano Mauna Loa, Hawaii Mauna Loa: shield volcano K’ilauea: shield volcano Volcanic Landforms Cinder Cinder Cones – Composed of pyroclastic materials that accumulate around the vent; steep slopes (33°) (33° – Usually short-lived and may represent final eruptive stages short- Volcanic Landforms Cinder Cinder Cones 2 Volcanic Landforms Composite Composite Volcanoes (Stratovolcano) – Composed of alternating layers of pyroclastics and lava flows – High viscosity magma: Composition is intermediate, with andesite common – Eruptions are infrequent, violent, and may involve lahars Volcanic Landforms Composite Composite Volcanoes (Stratovolcano) Composite cones: Lauca National Park, Chile Pomerape Parinacota Volcanic Landforms Lahars Lahars – Volcanic mudflows – Often occur on steep sided stratovolcanoes – Can cause extensive damage and be very dangerous March 1982 – Mount St Helens lahar 3 Volcanic Landforms Lava Lava Domes – High-viscosity, felsic magmas move slowly upward to form Highsteepsteep-sided lava domes – Sudden collapse or explosive eruption may cause a nuée ardent to move rapidly downslope, incinerating everything in its path Volcanic Landforms Lava Lava dome Lava dome Trapped gases escape Volcanic Landforms Volcanic Volcanic dome Trapped gases explode Pyroclastic flow Pyroclastic Flows High High gas content Fast Fast moving, ~ 100 mph Hot, Hot, 800°C Also Also known as nuées ardentes (glowing cloud) 4 ...
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