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Volcanoes And Plate Tectonics objectives • F.3.1.1. Identify where most of Earth’s volcano regions are located and explain why they are found in these areas. • F.3.1.2. Explain how a hotspot volcano forms and give an example of one. Definitions • A volcano is a weak spot in Earth’s crust where magma is able to come through and reach the surface. • Magma is a combination of molten (melted) rock, gases and water. • Once it reaches the surface it is called lava. This does not mean the substance has changed, it hasn’t. It just means it has reached the surface. • Lava cools to from new rock. Volcanoes and plate boundaries • Volcanoes most often form along plate boundaries. There are exceptions but usually they are found where plates meet. • The Ring of Fire is a long belt of volcanoes that stretch all the way around the Pacific Ocean. Ring of fire Most volcanoes form along Convergent Boundaries Divergent Boundaries Divergent boundaries • Many volcanoes form along mid ocean ridges under water and along rift valleys on land. Can you name a famous mid ocean ridge? • The Mid Atlantic Ridge Divergent boundaries • Divergent boundaries on land are called rift valleys. Convergent Boundaries • Many volcanoes form along convergent plate boundaries where the older, more dense plate is being subducted back into the mantle. Oceanic to oceanic • Where an older, more dense oceanic plate subducts under a newer less dense plate, the rock can melt to produce magma. The less dense magma and superheated water vapor become less dense than the surrounding rock. What will this less dense material do? • Rise through the crust. Oceanic to oceanic • This type of subduction can often produce an Island Arc. Island arc Island arc Oceanic to continental Oceanic to continental This type of convergence created the Andes Mountains in South American and the volcanic mountains in the Pacific Northwest of the United States. Mt. St. Helens During Mt. St. Helens Before Eruption After Eruption Hot spot volcanoes • Hot Spot Volcanoes form above a hot spot in the mantle where convection currents bring superheated magma from the core to the surface. Hot spot volcanoes Hawaii Hawaii Hawaii Hawaii From space Hawaii Bathymetry f.3.1.1. • Where do most volcanoes form? • Most of Earth’s volcanoes form along convergent and divergent plate boundaries. F.3.1.1. • Why do they form along plate boundaries? • These are places where the crust opens up to allow magma up or where melting rock and super heated water create buoyant pressure from below. f.3.1.1. • What is the ring of fire? • It is a volcano belt that surrounds the Pacific Plate. f.3.1.2 • Some scientists believe this to be a hot plume of the molten metal from the outer core rising through the mantle. f.3.1.2. • A plume of hotter material rises through convection currents to just beneath the crust and causes a breach to form in the crust that allows magma to push through to the surface. Spongy Job Kids