Chapter 18Chapter 18VolcanoesVolcanoes

Section OneSection OneVolcanoes and Plate TectonicsVolcanoes and Plate Tectonics

VocabularyVocabulary

Volcano:Volcano:– A weak spot in the crust where magma has come to A weak spot in the crust where magma has come to

the surface.the surface.

Magma:Magma:– The molten mixture of rock-forming substances, The molten mixture of rock-forming substances,

gases, and water from the mantle.gases, and water from the mantle.

Island Arc:Island Arc:– A string of islands formed by the volcanoes along a A string of islands formed by the volcanoes along a

deep ocean trench.deep ocean trench.

VocabularyVocabulary

Lava:Lava:– Liquid magma that reaches the surface; also Liquid magma that reaches the surface; also

the rock formed when liquid lava hardens.the rock formed when liquid lava hardens.

Ring of Fire:Ring of Fire:– A major belt of volcanoes that rims the Pacific A major belt of volcanoes that rims the Pacific

Ocean.Ocean.

Hot Spot:Hot Spot:– An area where magma from deep within the An area where magma from deep within the

mantle melts through the crust above it.mantle melts through the crust above it.

Location of VolcanoesLocation of Volcanoes

Location of VolcanoesLocation of Volcanoes

Complete the concept map.Complete the concept map.

occur at

Location of VolcanoesLocation of VolcanoesMid-Ocean RidgeMid-Ocean Ridge

Volcanoes at Diverging Plate Volcanoes at Diverging Plate BoundariesBoundaries

Describe how volcanoes form along the Describe how volcanoes form along the mid-ocean ridge.mid-ocean ridge.– Volcanoes form when lava pours out of cracks Volcanoes form when lava pours out of cracks

in the ocean floor.in the ocean floor.

True or False: Most volcanoes of the mid-True or False: Most volcanoes of the mid-ocean ridge rise above the ocean’s ocean ridge rise above the ocean’s surface.surface.

Volcanoes at Converging Volcanoes at Converging BoundariesBoundaries

True or False: Many volcanoes form near True or False: Many volcanoes form near converging plate boundaries where oceanic converging plate boundaries where oceanic crust returns to the mantle.crust returns to the mantle.

How does subduction at converging plate How does subduction at converging plate boundaries lead to the formation of volcanoes?boundaries lead to the formation of volcanoes?– Subduction causes slabs of oceanic crust to sink Subduction causes slabs of oceanic crust to sink

through a deep-ocean trench into the mantle, where it through a deep-ocean trench into the mantle, where it forms magma that rises back toward the surface. forms magma that rises back toward the surface. When the magma erupts, volcanoes are formed.When the magma erupts, volcanoes are formed.

Volcanoes at Converging Volcanoes at Converging BoundariesBoundaries

What are three major island arcs?What are three major island arcs?– Three major island arcs include Japan, New Three major island arcs include Japan, New

Zealand, Indonesia, the Caribbean Islands, Zealand, Indonesia, the Caribbean Islands, the Philippines, and the Aleutians.the Philippines, and the Aleutians.

Hot spot VolcanoesHot spot Volcanoes

How did the Hawaiian Islands from? How did the Hawaiian Islands from? – The Hawaiian Islands formed as the Pacific The Hawaiian Islands formed as the Pacific

plate drifted over a hot spot.plate drifted over a hot spot.

True or False: Hot spots form only under True or False: Hot spots form only under oceanic crust.oceanic crust.