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Volcanism Volcanic Features Location and Types of Volcanic Activity
Effusive Eruptions Explosive Eruptions Volcano Forecasting and Planning
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How and Where Volcanoes Form
VOCABULARY volcano Volcanic activity takes place primarily at subduction boundaries, hot spot 4. Some of the magma reaches Earth’s surface, and volcanoes form on the overriding continental plate. 1. Water in the subducted rock is released into the asthenosphere. Oceanic lithosphere Continental lithosphere Asthenosphere 3. The magma is less dense than its surroundings, so it rises. 2. The water lowers the melting temperatures of materials in the asthenosphere, leading to magma formation.
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How and Where Volcanoes Form
VOCABULARY volcano Magma and volcanoes also form at hot spots. hot spot Kauai Oahu Direction of Plate Movement The Hawaiian Islands formed over a hot spot. Molokai Lanai Maui Hawaii
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How Magma Rises To view this animation, click “View” and then “Slide Show” on the top navigation bar.
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Volcanic Settings
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Plate Tectonics and Magma Generation
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Major Volcanoes Around the World
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Magma and Erupted Materials
Gases escape easily from basaltic magma, generating relatively quiet eruptions. Hardened basaltic lava flows on land are characterized as pahoehoe or aa; if the lava cools underwater, it is characterized as pillow lava. Parameters of volcanism: Viscosity Chemistry of Magma Gases within the magma Water content of magma
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Magma and Erupted Materials
Viscosity: Viscosity is a measure of how thick (viscous) and sticky a liquid is. VOCABULARY viscosity lava pahoehoe aa pillow lava pyroclastic material pyroclastic flow
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Lava Flows Lava Flow - A 'stream' of molten rock
'aa' lava flow - jagged, rubbly, broken surface 'pahoehoe' lava flow - smooth, ropy surface
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Magma and Erupted Materials
Silica Content Melting Temp. Gas Content Viscosity Type of Eruption Location Least (~50%) Basaltic Magma Least Least viscous Rarely explosive Highest Rifts, oceanic hot spots Rhyolitic Magma Most (~70%) Most Most viscous Usually explosive Lowest Continental hot spots AndesiticMagma Intermediate (~60%) Intermediate Sometimes explosive Subduction boundaries
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Volcanic Landforms A volcano’s shape and structure depend on how it erupts and what materials are released. Shield volcanoes are formed by basaltic lava that flows long distances before hardening.
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Tectonic Settings and Volcanic Activity
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Igneous __________- classified by shape, size, and orientation
Intrusions Igneous __________- classified by shape, size, and orientation
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There are three types of volcanic cones:
Cinder ______ – explosive eruptions, small but steep slopes, pyroclastics. _______ – non-explosive eruptions, fluid basaltic lava, gentle broad slopes. _________ – alternating between lava and pyroclastics, explosive and non-explosive eruptions, steep and tall. Shield Composite
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Volcano Types To view this animation, click “View” and then “Slide Show” on the top navigation bar.
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Volcanic Landforms Volcanoes
VOCABULARY A volcano’s shape and structure depend on how it erupts and what materials are released. shield volcano cinder cone composite volcano Shield volcanoes are formed by basaltic lava that flows long distances before hardening. lahar caldera Shield Volcano lava plateau
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Shield and Composite Volcanoes
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Volcanic Landforms Volcanoes
Cinder cones are formed when molten lava is thrown into the air from a vent and breaks into drops. These drops harden into cinders that form a steep cone around the vent. Cinder Cone
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Volcanic Landforms Volcanoes
Composite volcanoes are formed by layers of pyroclastic materials and lava that have erupted in the past. Composite Volcano
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Composite volcanoes
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Debris Avalanche and Eruption of Mount St. Helens, Washington
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Nuee ardente: pyroclastic flow, of searing superheated gas and incandescent volcanic ash and dust
Mount Pelee, on the Carribean island of Martinique, 1902 eruption. All but 2 of the more than 20,000 people in the town of St. Pierre were killed.
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Volcanic Landforms Volcanoes
A caldera is a large crater-shaped basin that forms when the top of a volcano collapses.
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Formation of Crater Lake
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EFFUSIVE ERUPTIONS Generally at hots spots, spreading centers
Mantly comes directly to surface Hot lava; low viscosity, very mafic, flows easily, gases escape easily Forms shields, flood basalts
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EXPLOSIVE ERUPTIONS Found at subduction zones
Magma low temp (800 degrees C), high viscosity, does not flow easilty, more felsic mineralogy, gases trapped, hard to predict explosions Forms composite volcanoes, cinder cones, calderas, aerial bombs, nuee ardente gas flows, very destructive
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:Summary Volcanoes A. Magma Formation B. At Subduction Boundaries
C. At Divergent Boundaries D. Over Hot Spots II. Magma and Erupted Materials III. Volcanic Landforms A. Types of Magma A. Shield Volcanoes B. Lava Flows B. Cinder Cones 1. Lava Flows on Land C. Composite Volcanoes 2. Underwater Lava Flows D. Calderas C. Ash and Rock Fragments E. Lava Plateaus
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