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105_05-volcanoes_part_1 - Volcanism and Volcanoes Volcanoes...

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Unformatted text preview: Volcanism and Volcanoes Volcanoes and Volcanism Lava Lava is produced when magma reaches Earth’s surface Explosive Explosive eruptions can produce rapidly cooled rock pyroclasts fragments called pyroclasts – Size range from dust (ash) to boulders (blocks and volcanic bombs) Chapter 5 Calm Calm oozing of magma out of lava the ground produces lava flows Lava Lava flows and pyroclasts pile up to form volcanoes Volcanoes and Volcanism Volcano Volcano – Landform created by eruption of lava Quiet Quiet (Hawaii) Explosive Explosive (Krakatau, Mt. St. Helens) Mt Vesuvius, Bay of Naples, Italy Volcanism Volcanism – Geologic processes involved in eruptions of lava, gases and pyroclastic material Form extrusive rocks from cooling of lava Bay of Naples, from space. Vesuvius – Naples, Italy Vesuvius 1 Vesuvius – Naples, Italy Pompeii, buried by AD 79 eruption of Vesuvius (in background), and excavated by archeologists. 2 Vesuvius A.D.79 eruption Volcanic Landforms Volcanic Volcanic craters – Bowl or circular shaped depression around the vent Materials extruded during eruption Gases Gases Liquids Liquids Solids Solids Volcanic Gases Volcanic Volcanic Gases – 1% - 9% of most magmas are gases – 50-80% water vapor, CO2, N2, S and others 50– Gases contained in rising magma expand and can contribute to violent explosions Explosiveness of volcanoes Controlled by two factors: - Amount of gas in the lava - How easily this gas can escape the lava 3 Explosiveness of volcanoes Viscosity! - resistance to flow Explosiveness of volcanoes Mafic lava: low viscosity, hot, gases escape easy - lava flow (Hawaii) Felsic lava: high viscosity, colder, pressure builds up - explosive (St. Helens) Lava Flows Pahoehoe Pahoehoe Lava Flows – Fast moving; fluid, ropy – Gas bubbles – Paths are predictable – Rarely a danger to human life – Two types are recognized from Hawaiian flows: pahoehoe and aa Night view, Kilauea lava flows. Kilauea Iki lava lake 4 Lava Flows Aa Aa – Slow moving; blocky, chunky – Low gas content Lava tube 5 Lava tunnel, Hawaii. View into lava tube with flowing lava inside. El Malpais National Monument, NM El Malpais National Monument, NM Summer 1998 El Malpais National Monument, NM El Malpais National Monument, NM Summer 1998 Summer 1998 6 El Malpais National Monument, NM El Malpais National Monument, NM Summer 1998 Summer 1998 El Malpais National Monument, NM Lava Flows Basalt layers cool and contract after solidifying. Vertical cracks develop as the rock contracts, forming six-sided columns called columnar jointing. Summer 1998 Columnar jointing Columnar jointing Close Encounters of the Third Kind Devil’s Tower, Wyoming 7 Columnar jointing Columnar jointing Columnar jointing Columnar jointing Lava Flows Pillow Pillow lava – Lava erupts under water Pillow lavas exposed in Iceland’s Eldgia fissure area 8 ...
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