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What Motions Occur at Plate Boundaries? WHAT ARE THE THREE MAJOR PLATE BOUNDARIES? DIVERGENT BOUNDARIES Plates move away from each other as magma rises in convection cells Only occurs along midocean ridges Seafloor spreading will create new oceanic crust Age of the rocks increase as distance from the ridge increases Extreme Ecosystems – Hydrothermal Vents HYDROTHERMAL VENT COMMUNITIES CONVERGENT BOUNDARIES Two plates Colliding where convection cells are sinking. What happens when the plates collide is determined by the types of crust that are colliding OCEANIC CRUST CONTINENTAL CRUST Density = 3.0 g/ml Basalt – mafic /denser Thinner Younger Density = 2.7 g/ml Granite – Felsic/less dense Thicker – mountains Older CONVERGENT: OCEANIC VS CONTINENTAL Oceanic Crust is Denser (Basalt / Mafic) so it sinks under the Less Dense Continental Crust (Granite/Felsic) Subduction Zone with deep focus earthquakes. Trench forms –deepest parts of the ocean Mountains – form on the surface as the continental crust crumbles into the oceanic crust Yellowstone hotspot X X earthquake focus X X X Which one is Denser? What do Denser Objects Do? EX: WEST COAST OF SOUTH AMERICA Turn to pg 5 of the Handy Dandy ESRT Feature found below the Surface – Peru Chile Trench Surface feature – Andes Mountains ANDES MOUNTAINS CONVERGENT: CONTINENTAL VS CONTINENTAL Once all the oceanic crust has been subducted the continental crusts collide Both crustal plates have the same density and they crumble into each other and move up creating the tallest mountains (neither is subducted). Earthquakes – due to friction btn the continents ***Not as deep as those on subduction zones Ex: Himalayans-Created by India colliding into Asia Himalayan formation 2 CONVERGENT: OCEANIC VS OCEANIC Deepest Trenches form Ex: Mariana’s Trench – Deepest section of the ocean (Pacific Plate Colliding into the Phillippine Plate) Tonga Trench Erupting Video of Underwater Eruption TRANSFORM BOUNDARIES Plates slide past each other small transform boundaries occur along other types of boundaries. San Andreas fault (California) is the longest transform boundary LET’S REVIEW Lets review all the boundaries Quiz challenge