Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
EXTRUSIVE IGNEOUS ROCKS Volcanoes and Volcanic Rocks Igneous Rock Names and Compositions • Composition • Intrusive Rock Name Name • • • • Ultramafic Mafic Intermediate Silicic (felsic) • • • • Peridotite Gabbro Diorite Granite • Volcanic Rock Name • • • • (Komatiite) Basalt Andesite Rhyolite Magma and Lava • Magma is the term for any molten silicate material, whether below the surface or on top. • Volcanic rocks are erupted on the surface. – Volcanic rocks are fine-grained (<1 mm) • Lava is the term for a magma on the surface. 1 Most Volcanoes are at Plate Boundaries Geologic Settings 2 Basaltic Eruptions • Low Viscosity • High Temperature (1000 - 1200ºC) • Normally Quiescent Lava Flows – Aa - early, low temperature, blocky flow – Pahoehoe - later high temperature ropy flow – Pillow Lavas - underwater flow • Edifice – Shields – Cinder cones Pahoehoe, Hawaii (Basalt) Aa, Hawaii (Basalt) 3 Pillow Lava, Kauai (Basalt) Nyiragongo, Congo (Zaire) 4 Goma, Congo (Zaire) Skjaldbreidur Shield, (Basalt) Cinder Cone, Pu’uo’o, Hawaii (Basalt) 5 Cinder Cone + Caldera, (Basalt) Basaltic Eruptions • Low Viscosity • High Temperature (1000 - 1200ºC) • Normally Quiescent Lava Flows – Aa - early, low temperature, blocky flow – Pahoehoe - later high temperature ropy flow – Pillow Lavas - underwater flow • Edifice – Shields – Cinder cones Most Volcanoes are at Plate Boundaries 6 Andesite Eruptions • • • • • Higher viscosity (higher polymerization ) Lower temperature More water, more explosive Subduction zone volcanism Flows – Viscous lava flows – Pyroclastic flows • Edifice – Composite Cones Geologic Settings Andesite Flow, Mt Shasta 7 Composite Cone, Mt. Fuji Composite Cone, Mt. Daisen Composite Cone, Mt. St Helens 8 9 Andesite Eruptions • • • • • Higher viscosity (higher polymerization ) Lower temperature More water, more explosive Subduction zone volcanism Flows – Viscous lava flows – Pyroclastic flows • Edifice – Composite Cones 10 Rhyolite Eruptions • Very high viscosity • Low temperature (600 - 800ºC) • Massive Pyroclastic eruptions – Air fall (pumice) – Ash Flow (Nuée Ardente) Tuff – Obsidian Flows • Edifice – Caldera (5 - 25 km) – Resurgent dome Rhyolite Eruptions • Associated Phenomena – Hot Springs – Geysers – Fumaroles • Geologic Setting – Continental Margins and Interiors – Subduction Zones Geologic Settings 11 Pumice = Glass foam Ash-Flow Tuff with AirFall Units Ash-Flow Tuff Unit Non-Welded Top Welded Core Vitrophyre Non-welded base 12 Silicic Tuff Units (Jemez, NM) Obsidian Flow Non-welded Air-Fall Units Sulfur Fumarole, Nysseros Caldera with Cinder Cone Crater Lake, OR 13 Geyser Old Faithful (Yellowstone) Rhyolite Eruptions • Very high viscosity • Low temperature (600 - 800ºC) • Massive Pyroclastic eruptions – Air fall (pumice) – Ash Flow (Nuée Ardente) Tuff – Obsidian Flows • Edifice – Caldera (5 - 25 km) – Resurgent dome 14 Andesite Eruptions • • • • • Higher viscosity (higher polymerization ) Lower temperature More water, more explosive Subduction zone volcanism Flows – Viscous lava flows – Pyroclastic flows • Edifice – Composite Cones Basaltic Eruptions • Low Viscosity • High Temperature (1000 - 1200ºC) • Normally Quiescent Lava Flows – Aa - early, low temperature, blocky flow – Pahoehoe - later high temperature ropy flow – Pillow Lavas - underwater flow • Edifice – Shields – Cinder cones Geologic Settings 15 Most Volcanoes are at Plate Boundaries 16