Transcript volcanoesx
Volcanoes and Plate Tectonics • A volcano is a weak spot in the crust where molten material, or magma, comes to the surface. • Magma is a molten mixture of rock-forming substances, gases, and water vapor from the mantle. • When magma reaches the surface, it is called lava. Volcanoes and Plate Tectonics • After lava has cooled, it forms solid rock. • The lava released during volcanic activity builds up Earth's surface. • Volcanic activity is a constructive force that adds new rock to existing land and forms new islands Location of Volcanoes • Volcanic belts form along the boundaries of Earth's plates. • At plate boundaries, huge pieces of the lithosphere diverge (pull apart) or converge (push together). • Here, the lithosphere is weak and fractured, allowing magma to reach the surface. Location of Volcanoes Location of Volcanoes • Most volcanoes occur along diverging plate boundaries, such as the mid-ocean ridge, or in subduction zones around the edges of oceans. • But some volcanoes form at “hot spots” far from the boundaries of continental or oceanic plates. Such as Hawaii • One major volcanic belt is the Ring of Fire, formed by the many volcanoes that rim the Pacific Ocean. Volcanoes at Diverging Plate Boundaries • Volcanoes form along the mid-ocean ridge, which marks a diverging plate boundary. • Along the ridge, lava pours out of cracks in the ocean floor. • Only in a few places, as in Iceland and the Azores Islands in the Atlantic Ocean, do the volcanoes of the mid-ocean ridge rise above the ocean's surface. Volcanoes at Converging Boundaries • Many volcanoes form near the plate boundaries where some oceanic crust returns to the mantle. • Subduction causes slabs of oceanic crust to sink through a deep-ocean trench into the mantle. • The crust melts and forms magma, which then rises back toward the surface. • When the magma from the melted crust erupts as lava, volcanoes are formed. Convergent and Divergent Plate Boundaries If two Ocean Plate collide • Many volcanoes occur on islands, near boundaries where two oceanic plates collide. • The older, denser plate dives under the other plate, creating a deep-ocean trench. • There it begins to melt, forming magma. • The magma seeps upward through cracks in the crust. • Eventually, the magma breaks through the ocean floor, creating volcanoes. If Two Ocean Plate Collide • The resulting volcanoes create a string of islands called an island arc. • The curve of an island arc echoes the curve of its deep-ocean trench. • Major island arcs include Japan, New Zealand, Indonesia, the Caribbean islands, the Philippines, and the Aleutians. If a continental and Ocean Plate Collide • Subduction also occurs where the edge of a continental plate collides with an oceanic plate. • Collisions between oceanic and continental plates produced both the volcanoes of the Andes mountains on the west coast of South America and the volcanoes of the Pacific Northwest in the United States. Hot Spot Volcanoes • Some volcanoes result from “hot spots” in Earth's mantle. • A hot spot is an area where magma from deep within the mantle melts through the crust like a blow torch. • Hot spots often lie in the middle of continental or oceanic plates far from any plate boundaries Inside a Volcano Hot Spot Volcanoes Types of Volcanoes