Presentation on theme: "Volcanism Volcanic Features Location and Types of Volcanic Activity"— Presentation transcript:
1Volcanism Volcanic Features Location and Types of Volcanic Activity Effusive Eruptions Explosive Eruptions Volcano Forecasting and Planning
2How and Where Volcanoes Form VOCABULARYvolcanoVolcanic activity takes place primarily at subduction boundaries,hot spot4. 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 lithosphereContinental lithosphereAsthenosphere3. 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.
3How and Where Volcanoes Form VOCABULARYvolcanoMagma and volcanoes also form at hot spots.hot spotKauaiOahuDirection of Plate MovementThe Hawaiian Islands formed over a hot spot.MolokaiLanaiMauiHawaii
4How Magma RisesTo view this animation, click “View” and then “Slide Show” on the top navigation bar.
8Magma 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:ViscosityChemistry of MagmaGases within the magmaWater content of magma
9Magma and Erupted Materials Viscosity: Viscosity is a measure of how thick (viscous) and sticky a liquid is.VOCABULARYviscositylavapahoehoeaapillow lavapyroclastic materialpyroclastic flow
10Lava Flows Lava Flow - A 'stream' of molten rock 'aa' lava flow - jagged, rubbly, broken surface 'pahoehoe' lava flow - smooth, ropy surface
11Magma and Erupted Materials Silica ContentMelting Temp.Gas ContentViscosityType of EruptionLocationLeast (~50%)Basaltic MagmaLeastLeast viscousRarely explosiveHighestRifts, oceanic hot spotsRhyolitic MagmaMost (~70%)MostMost viscousUsually explosiveLowestContinental hot spotsAndesiticMagmaIntermediate (~60%)IntermediateSometimes explosiveSubduction boundaries
12Volcanic LandformsA 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.
13Tectonic Settings and Volcanic Activity To view this animation, click “View” and then “Slide Show” on the top navigation bar.
14Igneous __________- classified by shape, size, and orientation IntrusionsIgneous __________- classified by shape, size, and orientation
15There 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.ShieldComposite
16Volcano TypesTo view this animation, click “View” and then “Slide Show” on the top navigation bar.
17Volcanic Landforms Volcanoes VOCABULARYA volcano’s shape and structure depend on how it erupts and what materials are released.shield volcanocinder conecomposite volcanoShield volcanoes are formed by basaltic lava that flows long distances before hardening.laharcalderaShield Volcanolava plateau
19Volcanic 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
20Volcanic Landforms Volcanoes Composite volcanoes are formed by layers of pyroclastic materials and lava that have erupted in the past.Composite Volcano
22Debris Avalanche and Eruption of Mount St. Helens, Washington To view this animation, click “View” and then “Slide Show” on the top navigation bar.
23Nuee 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 than20,000 people in the town of St. Pierre were killed.
24Volcanic Landforms Volcanoes A caldera is a large crater-shaped basin that forms when the top of a volcano collapses.
25Formation of Crater Lake To view this animation, click “View” and then “Slide Show” on the top navigation bar.
26EFFUSIVE ERUPTIONS Generally at hots spots, spreading centers Mantly comes directly to surfaceHot lava; low viscosity, very mafic, flows easily, gases escape easilyForms shields, flood basalts
27EXPLOSIVE 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 explosionsForms composite volcanoes, cinder cones, calderas, aerial bombs, nuee ardente gas flows, very destructive
28:Summary Volcanoes A. Magma Formation B. At Subduction Boundaries C. At Divergent BoundariesD. Over Hot SpotsII. Magma and Erupted MaterialsIII. Volcanic LandformsA. Types of MagmaA. Shield VolcanoesB. Lava FlowsB. Cinder Cones1. Lava Flows on LandC. Composite Volcanoes2. Underwater Lava FlowsD. CalderasC. Ash and Rock FragmentsE. Lava Plateaus