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Transcript
Volcanoes Frequency and Quantity There are ~ 550 historically active volcanoes About 60 erupt annually The majority are 1) at the edge of continents and 2) underwater Dormant volcanic cone in Japan Mid ocean ridges Mid ocean ridge Mid ocean ridge Rift valley plate plate magma Mid ocean ridges Are continuous underwater mountain ranges Are formed by rising magma Cause sea floor spreading Form a rift valley between spreading plates Pillow lava at mid ocean ridge Land based volcanoes Mt St Helens one day before eruption Mt St Helens 4 months after eruption Another before… …and 2 years later Land based volcanoes Are more dangerous than underwater types Form island chains like the Aleutian islands off Alaska The Ring of Fire The ring of fire The Ring of Fire Where the earth’s crustal plates meet, one plate will often slide under another As one plate slides under another, it heats up, mixes with water and the rock melts to form magma This less dense magma then rises to feed volcanoes A volcano at the edge of a continent Mid ocean ridge Sinking plate ? Melted rock forming magma Rift valleys and volcanoes Outward spreading Valley forms here Rift valleys Are formed by plates moving away from each other A valley forms by crust sinking between the diverging plates East Africa has a large rift valley with volcano formation The African Rift Valley Africa’s rift valley Rift valley Kenya’s Rift valley Hot Spots Hawaiian Islands – hot spot Volcanoes National Park Hot Spots A hot spot is a fixed source of abundant rising magma As a plate moves over the hot spot, magma forms undersea volcanoes; some of which rise above the ocean surface forming island chains Loihi Seamount A new volcanic cone is forming near Hawaii It’s top is 1000 m (3000 feet) below the water surface, and it will break the surface in the next 10,000 to 100,000 years. Big Island of Hawaii Loihi Map Projections How do you project a 3D object on a 2D map? Mercator Projection Mercator Projection Winkel Tripel Projection Maps of the Earth Cartography is the science and art of graphically representing a defined geographical area by means of a map. First off, the earth is round and maps are flat Map projections are ways of flattening a round earth into a useful picture; the resulting picture is distorted There is always distortion and compromises in accurately making a map