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VOLCANOES Lava & Magma Lava vs. Magma…What’s the difference? Lava- magma that flows into Earth’s surface; the rock that forms when magma cools & solidifies. Magma- liquid rock produced under the Earth’s surface. Major Volcanic Zones 1. Subduction Zone- one tectonic plate moves under another. -deep trenches form -island arcs form 2. Mid-Ocean Ridges- plates pulling apart from one another. -Produces the most magma from underwater volcanoes. -Mid-Atlantic Ridge and Iceland are examples. 3. Hot Spots- happen with the interior of plates. -example = Hawaiian islands -made by mantle plumes Where volcanoes form Hot Spots Mid Ocean Ridges Subduction Zones Hot Spots Types of Magma 1. Mafic -made up of magnesium and iron -dark in color -oceanic and continental crust 2. Felsic -made up of silicates -lighter in color -continental crust Types of Eruptions 1. Quiet Eruptions -mafic magma -oceanic volcanoes (Hawaii) -low viscosity 2. Explosive Eruptions -felsic magma -continental volcanoes -high viscosity -throw off large amounts of pyroclastic material STRUCTURE • Tephra (pyroclastics) – ash and rock ejected from a volcano. •Vent – conduit or pathway for magma. • Strata – layers of rock. • Magma chamber – storage place for magma. LAVA LAVA Pahoehoe AA Pillow Lava Tephra (pyroclastic material) Volcanic Ash – the small stuff Volcanic Ash is small, but it is the most deadly. Volcanic Blocks Volcanic Bombs Types of Volcanoes 1. Shield – Broad at the base, gently sloping sides, quiet eruptions, largest volcanoes. (Exp- Hawaiian Islands.) 2. Cinder Cone – Explosive eruptions, very steep slopes, only a few 100 meters high. 3. Composite of Stratovolcano – Explosive eruptions, pyroclastic flows can be deadly, very large volcanoes. (Exp- Mt. St. Helens, Mt. Pinatubo) TYPES OF VOLCANOES CINDER CONE CINDER CONE SHIELD VOLCANO Mauna Kea, Hawaii SHIELD COMPOSITE VOLCANO Mt. Fuji Craters & Calderas Crater- opening of the volcano where magma and or pyroclastic material is released. Caldera- when the magma chamber of a volcano empties and collapses on itself. CRATER CRATER CALDERA Crater Lake in Oregon Mt. Mazama EXTRATERRESTRIAL VOLCANOES VOLCANOES FOUND ON MARS, IO (MOON OF JUPITER), OUR OWN MOON MARS – OLYMPUS MONS, 28 KM ABOVE THE SURFACE, 600 KM ACROSS, CALDERA IS 70 KM ACROSS. IO – ACTIVE VOLCANOES ON SURFACE (FIRST PLANETARY BODY TO HAVE ACTIVE VOLCANOES) MOUNT ST. HELENS MT. ETNA Predicting Volcanic Eruptions -changes in earthquake activity around an earthquake. -increase in pressure of the surrounding rocks. -temperature changes -fracturing of rock -sections of the volcano may bulge