Chapter 17 & 18 Section 1 PDF

12/30/2024 Chapter 17 Section 1 Chapter 18 Section 1 What are the lines of evidence that led Wegener to suggest that Earth’s continents have moved?...

12/30/2024 Chapter 17 Section 1 Chapter 18 Section 1 What are the lines of evidence that led Wegener to suggest that Earth’s continents have moved? 1  12/30/2024 How do plate tectonics influence the formation of volcanoes? Early Observations With the exception of events such as earthquakes, volcanic eruptions, and landslides, most of Earth’s surface appears to remain relatively unchanged during the course of a human lifetime. Copyright © McGraw-Hill Education Drifting Continents 2  12/30/2024 Early Observations On the geologic time scale, however, Earth’s surface has changed dramatically. Copyright © McGraw-Hill Education Drifting Continents Early Observations In the late 1500s, Abraham Ortelius, a Dutch cartographer, noticed the apparent fit of continents on either side of the Atlantic Ocean. He proposed that North America and South America had been separated from Europe and Africa by earthquakes and floods. Copyright © McGraw-Hill Education Drifting Continents 3  12/30/2024 Early Observations The first time that the idea of moving continents was proposed as a scientific hypothesis was in the early 1900s. In 1912, German meteorologist Alfred Wegener presented his ideas about continental movement to the scientific community. Copyright © McGraw-Hill Education Drifting Continents Continental Drift Wegener developed a hypothesis that he called continental drift. He proposed that Earth’s continents had once been joined in a single landmass, a supercontinent called Pangaea, that broke apart about 200 mya and sent the continents adrift. Copyright © McGraw-Hill Education Drifting Continents 4  12/30/2024 Continental Drift Evidence from rock formations Wegener observed that many layers of rocks in the Appalachian Mountains in the United States were identical to layers of rocks in similar mountains in Greenland and Europe. These similar groups of rocks, older than 200 million years, supported Wegener’s idea that the continents had once been joined. Copyright © McGraw-Hill Education Drifting Continents Continental Drift Evidence from fossils Wegener gathered evidence of the existence of Pangaea from fossils. Similar fossils of animals and plants that once lived on or near land had been found on widely separated continents. Copyright © McGraw-Hill Education Drifting Continents 5  12/30/2024 Continental Drift Climatic evidence Fossils of the plant Glossopteris had been found on many parts of Earth, including South America, Antarctica, and India. Wegener reasoned that the area separating these fossils was too large to have had a single climate. Copyright © McGraw-Hill Education Drifting Continents Continental Drift Climatic evidence Wegener argued that because Glossopteris grew in temperate climates, the places where the fossils had been found had been closer to the equator. This led him to conclude that the rocks containing these fossil ferns had once been joined. Copyright © McGraw-Hill Education Drifting Continents 6  12/30/2024 Continental Drift Climatic evidence Glacial deposits nearly 300 million years old on several continents led Wegener to propose that these landmasses might have once been joined and covered with ice. The extent of the ice is shown in white. Copyright © McGraw-Hill Education Drifting Continents A Rejected Notion Although Wegener had compiled an impressive collection of data, the hypothesis of continental drift was not accepted by the scientific community. Two unanswered questions: What forces could cause the movement? How continents could move through solids? It was not until the early 1960s, when new technology revealed more evidence about how continents move, that scientists began to reconsider Wegener’s ideas. Copyright © McGraw-Hill Education Drifting Continents 7  12/30/2024 Zones of Volcanism Volcanism describes all the processes associated with the discharge of magma, hot fluids, and gases. Copyright © McGraw-Hill Education Volcanoes Zones of Volcanism Most volcanoes form at plate boundaries. The majority form at convergent boundaries and divergent boundaries. Copyright © McGraw-Hill Education Volcanoes 8  12/30/2024 Zones of Volcanism 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. Copyright © McGraw-Hill Education Volcanoes Zones of Volcanism Convergent volcanism Most volcanoes located on land result from oceanic-continental subduction. These volcanoes are characterized by explosive eruptions. Copyright © McGraw-Hill Education Volcanoes 9  12/30/2024 Zones of Volcanism 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. Copyright © McGraw-Hill Education Volcanoes Zones of Volcanism 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 10  12/30/2024 Zones of Volcanism 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 Zones of Volcanism 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 11  12/30/2024 Zones of Volcanism 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 Zones of Volcanism 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 12  12/30/2024 Zones of Volcanism 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 Zones of Volcanism 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 13  12/30/2024 Zones of Volcanism 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 Zones of Volcanism 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. Copyright © McGraw-Hill Education Volcanoes 14  12/30/2024 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 15  12/30/2024 Types of Volcanoes The appearance of a volcano depends on two factors: The type of material that forms the volcano The type of eruptions that occur. Copyright © McGraw-Hill Education Volcanoes Types of 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 16  12/30/2024 Types of 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 Types of 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 Volcanoes 17  12/30/2024 Tectonic Cookies Video: Volcanologist Cookies and plate boundaries Copyright © McGraw-Hill Education Volcanoes 18