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Internal/External Forces of the Earth Inner Structure of the Earth 1. Inner Core—dense and solid 2. Outer Core—Molten or liquid • Both are mostly hot and made of hot metal (iron) 3. Mantle—thick layer of rock (1800 miles thick); mostly solid, but has pockets of magma (melted rock) 4. Crust—very thin layer; rocky surface Natural forces interact with the crust, creating landforms on the surface of the earth. · Below the oceans, the crust is about 5 miles thick. Below the continents it averages 22 miles in thickness. Inner Structure of the Earth Internal Forces that Shape Landforms 1. Volcanoes—form when magma inside the earth breaks through the crust. Lava flows and may produce a large, cone-shaped mountain 2. Fault—a break in the earth’s crust. Movement along a fault can send out shock waves, causing an earthquake. The Plate Tectonic Theory 1. The lithosphere—the earth’s crust and upper layer of the mantle—are broken into a number of large, moving plates. 2. The plates slide very slowly over a hot, pliable layer of mantle. 3. The earth’s oceans and continents ride atop of the plates. 1.The Ring of Fire is a circle of volcanic mountains surrounding the Pacific Ocean 2.Hot Spots are hot regions deep within the mantle that produce magma, which rises to the surface. Volcanic island chains form as oceanic plates drift over the hot spot. Example: Hawaiian Islands. What Happens When Plates Meet? Converging (Collision) Zone They collide and push slowly against each other and form a collision or converging zone. •If 2 oceanic plates collide, 1 slides under the other. Islands often form this way. •If 2 continental plates collide, mountains are formed. Example: Himalayas Continental Crush (Collide) SPREADING ZONE Plates pull away from each other and form a spreading zone. These areas are likely to have earthquakes, volcanoes, and rift valleys (a large split along the crest of a mountain). Spreading Zone They meet, or CONVERGE and form a subduction zone. *If an oceanic plate collides with a continental plate, the heavier oceanic plate will slide under the lighter, continental plate. This results in volcanic mountain building and earthquakes. Subduction Fault At a FAULT, the plates will grind or slide past each other rather than colliding. Example: San Andres Fault.