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? Copyright © McGraw-Hill Education Volcanoes

Review convergent New volcanism hot spot flood basalt fissure conduit vent crater caldera shield volcano cinder cone composite volcano Copyright © McGraw-Hill Education Vocabulary Volcanoes

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

Volcanoes Copyright © McGraw-Hill Education Zones of Volcanism Most volcanoes form at plate boundaries. The majority form at convergent boundaries and divergent boundaries.

Volcanoes Copyright © McGraw-Hill Education 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.

Volcanoes Copyright © McGraw-Hill Education Convergent volcanism Most volcanoes located on land result from oceanic- continental subduction. These volcanoes are characterized by explosive eruptions. Santiaguito Dome, Guatemala

Volcanoes Copyright © McGraw-Hill Education 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.

Volcanoes Copyright © McGraw-Hill Education Two major belts The smaller belt is the Mediterranean Belt. Its general outlines correspond to the boundaries between the Eurasian, African, and Arabian plates.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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 km 3.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Volcanoes 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.

Copyright © McGraw-Hill Education Review 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? Vocabulary volcanism hot spot flood basalt fissure conduit vent crater caldera Volcanoes shield volcano cinder cone composite volcano