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And factors controlling their profiles shield

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Unformatted text preview: the volume of magma involved in eruptions 10 A few basic types of volcanic landforms and factors controlling their profiles Shield Composite Cone (Stratovolcano) Cinder Cone Profile of volcano related to viscosity of lava (runny, low viscosity lava long produces ____, thin flows whereas stiffer, high viscosity lava produces short _____, thick flows) Angle of repose of pyroclastic material also influences profile (coarse-grained tephra (especially angular “cinders”) form steeper slopes than finer-grained ash) Types of Volcanoes: Shield volcano (e.g. in Hawaii, formed at hotspot) Enormous Size Gentle slope Lots of lava Mauna Kea (dormant) Small chance of erupting again (hasn’t erupted in past 3,500 yrs.) Mauna Loa (active) 4 Broad, low-profile shape of shield volcanoes reflects gentle relatively quiet outpouring of low viscosity, basaltic lava Effusive (quiet) eruptions Gentle enough to become tourist attractions! Napua crater Kilauea volcano Hawaii Basaltic lavas flows, low viscosity, effusive Two main types of basalt lava in Hawaii: Pahoehoe, Aa Pahoehoe (ropy and smooth) Aa (rough and rubbly) Composite Cone (Stratovolcano) (form at convergent plate boundaries) • Large (up to 1000’s m high, kilometres wide at base) core • Classic ____ shape • Composed of inter-bedded lava flows and pyroclastic debris • Intermediate to felsic composition lava (therefore explosive) • If more felsic, a volcanic dome may develop at crater 5 Types of Volcanoes: Composite cones (Stratovolcanoes) Mt. Fujiyama (Japan) Mt. St. Helens (Cascades, U.S.A.) 5 Before May 18, 1980 eruption After May 18, 1980 eruption Types of Volcanoes: Cinder cones (Stratovolcanoes) • Rather small with steep slopes • Mostly fragments of ________ rock basaltic (ejected due to high volatile content) • All Tephra (cinders and ash) • Often on flanks of larger volcanoes • Can be fast growing Types of Volcanoes: Calderas In the most violent eruptions (e.g. where felsic magma is generated by melting of continental crust above hot spot, and in some cases, in convergent ,settings). the top of the volcano _caves in ____ __ Hu...
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