essential questions how do plate tectonics influence the formation of volcanoes? where are the major...

Essential Questions

• How do plate tectonics influence the formation of volcanoes?

• Where are the major zones of volcanism?

• What are the parts of a volcano?

• How do volcanic landforms differ?

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Review

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• volcanism• hot spot• flood basalt• fissure• conduit• vent• crater• caldera • shield volcano• cinder cone• composite volcano

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Vocabulary

Volcanoes

• Volcanism describes all the processes associated with the discharge of magma, hot fluids, ash and gases.

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Zones of Volcanism

• Most volcanoes form at plate boundaries. The majority form at convergent boundaries and divergent boundaries.

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Convergent volcanism

• In an oceanic-continental subduction zone, the denser oceanic plate slides under the continental plate into the hot mantle. Parts of the mantle above the subducting plate melt and magma rises, eventually leading to the formation of a volcano.

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Convergent volcanism

• Most volcanoes located on land result from oceanic-continental subduction. These volcanoes are characterized by explosive eruptions.

Santiaguito Dome, Guatemala

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Two major belts

• The volcanoes associated with convergent plate boundaries form two major belts. The larger belt, the Circum-Pacific Belt, is also called the Pacific Ring of Fire. The outline of the belt corresponds to the outline of the Pacific Plate.

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Two major belts

• The smaller belt is the Mediterranean Belt. Its general outlines correspond to the boundaries between the Eurasian, African, and Arabian plates.

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Divergent volcanism

• Eruptions at divergent boundaries tend to be nonexplosive. At the divergent boundary on the ocean floor, eruptions often form huge piles of lava called pillow lava.

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Hot spots

• Some volcanoes form far from plate boundaries over hot spots.

• A hot spot is an unusually hot area in Earth’s mantle where high-temperature plumes of mantle material rise toward the surface.

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Hot spots

• The Hawaiian islands are located over a plume of magma. The hot spot formed by the magma plume remains stationary while the Pacific Plate slowly moves northwest.

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Hot spots

• The volcanoes on the oldest Hawaiian island, Kauai, are inactive because the island no longer sits above the stationary hot spot. The world’s most active volcano, Kilauea, on the Big Island of Hawaii, is currently located over the hot spot.

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Hot spots

• Chains of volcanoes that form over stationary hot spots provide information about plate motions. The rate and direction of plate motion can be calculated from the positions of these volcanoes.

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Hot spots

• The Hawaiian islands are at one end of the Hawaiian-Emperor volcanic chain. The oldest seamount, Meiji, is at the other end of the chain and is about 80 million years old.

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Hot spots

• Flood basalts form when lava flows out of long cracks in Earth’s crust. These cracks are called fissures.

• The Columbia River basalts, located in the northwestern United States, were formed this way.

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Hot spots

• About 65 mya in India, a huge flood basalt eruption created an enormous plateau called the Deccan Traps. The volume of basalt in the Deccan Traps is estimated to be about 512,000 km3.

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Anatomy of a Volcano

• Lava reaches the surface by traveling through a tubelike structure called a conduit.

• The lava then emerges through an opening called a vent.

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Anatomy of a Volcano

• Over time, layers of solidified lava can accumulate to form a mountain known as a volcano. At the top of a volcano, around the vent, is a bowl-shaped depression called a crater.

• Volcanic craters are usually less than 1 km in diameter. Larger depressions, called calderas, can be up to 100 km in diameter.

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Types of Volcanoes

• The appearance of a volcano depends on two factors: the type of material that forms the volcano and the type of eruptions that occur.

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Shield volcanoes

• A shield volcano is a mountain with broad, gently sloping sides and a nearly circular base.

• Shield volcanoes form when layers of lava accumulate during nonexplosive eruptions. They are the largest type of volcano.

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Cinder cones

• When eruptions eject small pieces of lava into the air, cinder cones form as this material, called tephra, falls back to Earth and piles up around the vent.

• Cinder cones have steep sides and are the smallest type of volcano.

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Composite volcanoes

• Composite volcanoes are formed of layers of ash and hardened chunks of lava from violent eruptions alternating with layers of lava that oozed downslope before solidifying.

• These volcanoes are generally cone-shaped with concave slopes.

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ReviewEssential Questions

• How do plate tectonics influence the formation of volcanoes?

• Where are the major zones of volcanism?

• What are the parts of a volcano?

• How do volcanic landforms differ?

Vocabulary

• volcanism• hot spot• flood basalt• fissure

• conduit• vent• crater• caldera

Volcanoes

• shield volcano• cinder cone• composite

volcano