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Unformatted text preview: crust. melting Generally non-explosive (fluid mafic lava quietly extruded from pipes) Mafic Volcanic Flows • Solidify at surface and deform – Pahoehoe, Aa, Blocky Hotspot Volcanoes (intraplate enviroments) …But if contaminated by melting of continental crust (producing felsic magma), have the highest destructive potential Classification of Volcanic Cones Volcanic Cones • • • • Shield volcanoes (at hot spots) Composite (stratovolcanoes)(convergent boundaries) Cinder cones (non-specific), but mafic source Calderas Photograph by M. Williams, National Park Service, 1977 USGS/Cascades Volcano Observatory photo Volcanic Cones and Calderas Morphology reflects eruptive style • Mafic lavas – shield shield • Mafic explosive – cinder cone cinder • Intermediate/felsic mixed – stratovolcano stratovolcano • Felsic - caldera caldera Photograph by M. Williams, National Park Service, 1977 USGS/Cascades Volcano Observatory photo Volcanic Cones Shield volcanoes (closely associated with hotspots) • Broad, slightly domed-shaped (e.g. Mauna Loa, Hawaii) • Composed primarily of mafic lava • Generally cover large areas • Produced by mild eruptions of large volumes of lava • Lava solidifies at surface and deforms • Ropy lava: Pahoehoe; Rough blocky lava: Aa Pahoehoe Aa Volcanic Structures and Eruptive Styles • Composite cones (stratovolcanoes) • Most are located in convergent settings, adjacent to the Pacific Ocean (Ring of Fire) • Large, symmetrical volcano (hundreds of metres high & several kilometres wide at base) • Composed of interbedded lava flows and layers of pyroclastic debris Volcanic Structures and Eruptive Styles • Cinder Cones (scoria cones) • Built from ejected lava (mainly pea to walnut-size fragments) • Steep slope angle • Rather small size • Paricutin in Mexico is a famous example Volcanic Cones A size comparison of the three types of volcanic cones Calderas • Can form as steep-walled collapse depressions at the summits of stratovolcanoes in convergent settings (Crater Lake, Oregon) • Size exceeds 1 km in diameter • Collapse pits – less than 1 km across • Slow upheaval or resurgence of floor of caldera may follow eruption Calderas Highly explosive behavio...
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This note was uploaded on 02/13/2014 for the course EARTH SCI ES2200 taught by Professor Camtsujita during the Fall '13 term at Western University (Ontario) - Also known as University of Western Ontario.

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