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Volcanoes and Plate Tectonics What is a volcano? Volcanoes are weak spots in the crust where magma rises to the surface. Location of Volcanoes Volcanic belts form along the plate boundaries. Volcanoes Fire occur in belts like the Ring of Location of Volcanoes Most volcanoes occur along diverging plate boundaries or in subduction zones. Volcanoes at Diverging Plate Boundaries Volcanoes form at the mid-ocean ridge underwater Volcanoes at Converging Plate Boundaries Volcanoes form in subduction zones - Two oceanic plates collide - An oceanic plate and continental plate collide Volcanoes at Converging Boundaries If subduction zone involves two pieces of oceanic crust, volcanoes are created These volcanoes create a string of islands called an island arc If Volcanoes at Converging Boundaries subduction zone involves oceanic and continental crust, volcanoes are created on land. Hot Spot Volcanoes Hot spot is an area where magma melts through the crust like a blow torch Hot spots are not often at plate boundaries Hot Spot Volcanoes Hot spots volcanoes can be created in the ocean floor Hawaii Hot Spot Volcanoes Hot spots can form under continents Yellowstone National Park Inside A Volcano Draw the picture Label the parts Add the central vent, the side vent, and the pipe A Volcanic Eruption Did you know that dissolved gases are trapped in magma? These dissolved gases are under great pressure. When the volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent. Two Types of Volcanic Eruptions Explosive eruptions: magma is high in silica and thick and sticky. This magma builds up in the pipe and plugs it like a cork. When enough pressure builds, it explodes. Quiet eruptions: magma is hot or low in silica and thin and runny. The gases in the magma bubble out gently. This type formed the Hawaiian Islands. Volcano Hazards Both types can cause tremendous damage. Quiet eruptions allow lava to flow from vents, setting fire to everything in its path. Explosive eruptions allow volcanoes to belch out hot rock and ash that produces fast-moving clouds that rush down the side of the volcano called pyroclastic flow. Stages of Volcanic Activity Active: a volcano that is erupting or has shown signs that it may erupt in the near future Dormant (sleeping): a volcano that may awaken in the future Extinct: a volcano that is unlikely to ever erupt again.