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Figures for your volcano presentation. Plate Boundaries. All Boundaries Together. Divergent Boundaries. Plates away New crust MORs (mid-oceanic ridges) Cont. vs. Ocean Sed. Basin. Convergent Boundaries. Plates together Subduction Melting Volcanic islands Volcanic mountains
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Divergent Boundaries • Plates away • New crust • MORs (mid-oceanic ridges) • Cont. vs. Ocean • Sed. Basin
Convergent Boundaries • Plates together • Subduction • Melting • Volcanic islands • Volcanic mountains • Fold belt mountains • Sed. Basin
Shield Volcano Hot Spot Theory • Volcanoes form over hot spots of magma. Note the direction of plate movement. The active, new volcanoes on the Island of Hawaii (Mauna Loa) are largest; and the islands of Kauai and Oahu that have moved past the hot spot are inactive and eroding away..
Basaltic Magma Rhyolitic Magma Andesitic Magma Silica Content Least (~50%) Intermediate (~60%) Most (~70%) Gas Content Least Intermediate Most Viscosity Least viscous Intermediate Most viscous Type of Eruption Rarely explosive Usually explosive Sometimes explosive Melting Temp. Highest Intermediate Lowest Location Subduction boundaries Rifts, oceanic hot spots Continental hot spots Minerals and erupted materials • Basaltic magma has the least amount of silica, so it has low viscosity and flows easily. • Andesitic and ryholitic magmas have more silica, so they have high viscosity and are more resistant to flow. extrusive igneous rocks = fine grained texture