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Chapter 7, section 1 What is a volcano? X Magma→ Volcanoes and Plate Tectonics A volcano is a structure on the surface of our planet where molten rock,fragments, and gas erupt through the crust rock, Magma- liquid melted rock located inside the Earth Volcanism- the process that involves the movement of magma to or towards earth’s surface Large areas of magma form where rock has melted. The magma pushes toward the crust because it is less dense than the surrounding rock As it moves upwards rock that the magma contacts melts as well Sometimes the magma breaks through the surface of Earth Lava- magma that erupts onto Earth’s surface Vent- the opening through which the magma flows onto Earth’s surface Volcanoes around the world → There are over 600 volcanoes that have erupted in the last 50 years Just like earthquakes, volcanoes mainly occur at plate boundaries Major volcanic zones → 1) Subduction zone- occur at convergent plate boundaries where a oceanic plate moves underneath another plate (oceanic or continental) o When the plate moves underneath into the hot asthenosphere water from the subducting plate mixes with the rock and it Volcanism → X melts, forming magma o A major volcanic zone is around is around the Pacific Ring of Fire o Oceanic-oceanic → island arcs form in the ocean o Oceanic-continental → volcanoes form on land 2) Mid-ocean ridges- occur at divergent plate boundaries as plates pull apart and moves upward. As the magma reaches the crust it cools, and forms new lithospheric crust (creating new ocean floor) o These volcanoes mostly go unnoticed because they are under water. The exception is Iceland, a country located directly on a mid-ocean ridge X 3) Hot spots- an area where a plume of magma within the asthenosphere touches the lithospheric plate and melts the rock above it X o Does NOT occur at a plate boundary! They occur in the middle of a plate o The hot spot remains stationary, it is the plate that moves slowly over the hot spot. A new volcano is made where the plate is melted by the hot spot. o Most hot spots occur in the ocean, creating islands, although this is not always true o Examples: 1) Hawaiian islands- there are over 80 volcanoes created from a hot spot The first island was created over 5.5 million years ago 2) Yellowstone- located in the U.S., hydrothermal features have been created by a hot spot. Yellowstone may turn into a supervolcano one day X X