Volcanoes & Plate Tectonics CH 6 Prentice Hall p.178-181

What is a Volcano? A weak spot in the crust where molten material, or magma comes to the surface. Volcanic Activity is a constructive force that adds new rock to existing land or forms new islands.

Volcano Menu Stages of Volcanoes Lava Crater Vent Volcano Erupts Lava Flow Pipe Magma Rising Magma Chamber Magma 3

Magma / Lava Magma- a mixture of rock forming substances, gases and water vapor from the mantle. Lava- Magma that reaches the surface. Cools and forms solid rock. Volcano Menu 4

Magma Rises Magma is a liquid- therefore it is less dense than surrounding solid material. Flows upward into any cracks in the rocks above. Rises until it reaches the surface or becomes trapped beneath layers or rocks. Volcano Menu 5

Volcano Erupts Dissolved gases trapped in magma are under tremendous pressure. The gasses dissolved in magma rush out, carrying magma with them. Volcano Menu 6

Crater Lava collects in the crater, the bowl-shaped area that forms around the volcano’s vent. Volcano Menu 7

Vent The point on the surface where magma and gas leave the volcanoes pipe. Volcano Menu 8

Pipe A narrow, almost vertical crack in the crust through which magma rises to the surface. Volcano Menu 9

Magma Chamber A large underground pocket of magma that forms from magma rising to the surface. Volcano Menu 10

Lava flow The river of lava that pours down a volcano over the land. Volcano Menu 11

Stages of a Volcano Active: Dormant: Extinct: A live volcano that is erupting or shows signs that it may erupt in the future. Dormant: A sleeping volcano. It may awake in the future and become active. Extinct: A dead volcano. It is unlikely to erupt again. 12

Location of Volcanoes Most occur along diverging boundaries such as the mid-ocean ridge or in subduction zones. 13

Location of Volcanoes About 600 active volcanoes on land, more lie beneath the sea. Occur in belts that extend across continents and oceans. Ring of Fire-formed by the many volcanoes that rim the Pacific Ocean 14

Divergent Boundaries Form along the mid-ocean ridge. Ridge a long underwater rift valley. Lava pours out of the cracks in the ocean floor. Iceland- is a volcano on the mid-ocean ridge that has reached the surface. 15

Convergent Boundaries Plates collide Denser plate subducts towards the mantle. Forms a deep-ocean trench The crust melts and forms magma that rises. Rising magma erupts through a volcano on the surface. 16

Convergent Boundaries Ocean/Ocean Denser ocean plate subducts Forms a deep sea trench Forms an island arc of volcanoes. Japan New Zealand Aleutians 17

Convergent Boundaries Continent to Ocean Dense ocean plate subducts Forms a deep sea trench Forms volcanoes on the land. Mt. St Helens Andes Mountains-S. America. 18

Hot Spot Volcanoes An area where magma from deep within the mantle melts through the crust like a blow torch. Lie in the middle of plates. Hawaii- formed in the middle of the Pacific Ocean plate. Yellowstone- formed under the continent. The plate travels over the hot spot. Created a chain of islands to form Hawaii 19

Hot Spot Volcanoes 20