Transcript Volcano
What is a Volcano? Volcano - A Volcano is an opening in the Earth’s surface through which molten material or volcanic gases are erupted. A volcano can either be a classic volcanic cone….. Mt. St. Helens, pre-1980 Mount Ranier a crack in the ground, through which lava erupts…… Or a simple volcanic vent. How Magma Rises Where are volcanoes located? Major Volcanoes Around the World Volcanic Settings How and Where Volcanoes Form Volcanic activity takes place primarily at subduction boundaries, 1. Water in the subducted rock is released into the asthenosphere. 4. Some of the magma reaches Earth’s surface, and volcanoes form on the overriding continental plate. Oceanic lithosphere Asthenosphere 2. The water lowers the melting temperatures of materials in the asthenosphere, leading to magma formation. Continental lithosphere 3. The magma is less dense than its surroundings, so it rises. OceanContinental Subduction Pacific Northwest Volcanoes OceanOcean Subduction OceanOcean Subduction Diverging Boundary Volcano Hot Spot Volcano How and Where Volcanoes Form Magma and volcanoes also form at hot spots. Kauai Direction of Plate Movement Oahu Molokai Lanai Maui Hawaii The Hawaiian Islands formed over a hot spot. Major Hotspots of the World Plate Tectonics and Magma Generation Tectonic Settings and Volcanic Activity Volcanoes are classified as either Active, Extinct or Dormant Active Mt. Ranier Dormat Vesuvius Extinct Magma and Erupted Materials Parameters of volcanism: 1.Viscosity 2.Chemistry of Magma 3.Gases within the magma 4.Water content of magma Magma and Erupted Materials Magma and Erupted Materials VOCABULARY viscosity lava pahoehoe aa pillow lava pyroclastic material pyroclastic flow Viscosity: Viscosity is a measure of how thick (viscous) and sticky a liquid is. Types of Magma Felsic Magma Characteristics: -light in color -high viscosity: means it is very thick and flows very slowly. -Associated with composite type volcanoes and continential hotspots -Found along continental-ocean subduction boundaries. Mafic Magma Characteristics: -dark in color -low viscosity: means it is thinner and flows much faster -Associated with shield volcanoes, rift zones, and oceanic hotspots -Found at divergent boundaries and oceanic hotspots Gases in Magma Water Vapor CarbonDioxide Carbon Monoxide SulfurDioxide HydrogenSulfide Types of Lava Pahoehoe Lava Aa Lava Aa Lava Pillow Lava Types of Lava Fragments Ash Ash Layers Pyroclastic Rock- Tephra Pyroclastic Rock- Pumice Cinder Bombs Blocks Blocks Volcanic Blocks Pyroclastic Flows There are three types of volcanic cones: Cinder – explosive eruptions, small but • ______ steep slopes, pyroclastics. Shield – non-explosive eruptions, fluid • _______ basaltic lava, gentle broad slopes. Composite – alternating between lava and • _________ pyroclastics, explosive and non-explosive eruptions, steep and tall. Volcano Types Volcanoes Volcanic Landforms VOCABULARY shield volcano cinder cone composite volcano lahar caldera lava plateau 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. Shield Volcano Shield and Composite Volcanoes Volcanoes Volcanic Landforms 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 Volcanoes Volcanic Landforms Composite volcanoes are formed by layers of pyroclastic materials and lava that have erupted in the past. Composite Volcano Composite volcanoes Debris Avalanche and Eruption of Mount St. Helens, Washington 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. Lava Plateau Volcanoes Volcanic Landforms A caldera is a large crater-shaped basin that forms when the top of a volcano collapses. Formation of Crater Lake EFFUSIVE ERUPTIONS • Generally at hots spots, spreading centers • Mantle comes directly to surface • Hot lava; low viscosity, very mafic, flows easily, gases escape easily • Forms shields, flood basalts 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