Chapter 2 Lesson 3 How Do Movements Of The Earth’s Crust Change Landforms? S5E1A: Students will identify features caused by destructive/constructive processes Vocabulary Preview Plate: a section of Earth’s crust and mantle that fits together with other sections like puzzle pieces Earthquake: a shaking of the Earth’s surface, caused by movement of rock in the crust Epicenter: the point on Earth’s surface directly above the focus of an earthquake Fault: a crack in the Earth’s surface Vocabulary Preview Magma: melted rock that is beneath Earth’s surface Lava: molten rock that flows from a volcano onto Earth’s surface Volcano: a mountain that forms as molten rock flows through a crack onto Earth’s surface Earth’s Structure Imagine you’re a miner digging for gold or gems. You dig deep into Earth, maybe 1 or 2 miles down. But even at this depth, you’ve barely scratched Earth’s surface. You’d need to dig down about 4,000 miles to reach the center of the Earth. What do you think you’d find at the center? Earth’s Structure You would think maybe you would find rock, but you wouldn’t. Earth has 4 layers-crust, mantle, outer core, and the inner core. If you could dig a hole to the center of the Earth, you’d find that the layers are different from one another. The thin crust is solid rock. The mantle also has a thin crust. But some rock within the mantle is soft, like melted candy. The deeper you’d go, the hotter things would get. The outer core is liquid, but it’s iron, not rock. The inner core is also metal, but its solid due to intense pressure. Layers of the Earth Crust 5-70 km (3-43 mi The crust is the surface layer of Earth.Mantle 2885 km (1790 mi) The mantle has two parts: the upper mantle and the lower mantle. Most of the mantle is solid rock, but some mantle rock is soft. Outer Core 2270 km (1410 mi) The hot outer core is liquid iron.Inner Core 1210 km (750 mi) Inner core is iron and nickel. Even though the core is very hot, great pressure at the center of Earth keeps the inner core solid. Earth’s Structure Earth’s crust and uppermost mantle are divided into sections, called plates. Plates are blocks of crust and upper mantle rock that fits together like puzzle pieces. Look at the map on the next slide. There are 10 major plates. Most of North America, Greenland, and part of the Atlantic Ocean are on the North American Plate. Part of California and most of the Pacific Ocean are on the Pacific Plate. Earth’s Structure Plates “float” on the softer rock of the mantle. As the rock flows, plates move. Because plates fit together so closely, the movement of one plate affect the other plates. At different places, plates move toward each other, away from each other, or alongside each other. These plate movements cause many changes in Earth’s surface. Earth’s Structure Earthquakes Suppose you press your palms together as hard as you can. If one hand slips, energy is released suddenly and your hands move past each other. When two of Earth’s plates move suddenly past each other, energy is also released and the ground shakes. An earthquake is movement of the ground caused by a sudden release of energy in the Earth’s crust. Earthquakes The place within the crust where energy is released during an earthquake is called the focus. The release of energy may hardly be noticed, or it may cause a lot of damage. The greatest damage is likely to occur directly above the focus. The point on Earth’s surface directly above the focus is called the epicenter. An earthquake occurs when Earth’s crust moves and releases energy. The energy of an earthquake spreads out like ripples on a pond. Places farther from the epicenter are likely to experience less damage than places near the epicenter. Earthquakes Earthquakes are caused by three different types of plate movement. Plates pushing together, plates sliding past each other, and plates pulling apart all produce earthquakes. Most earthquakes occur along a fault, or break in the Earth’s crust. Some faults occur in the middle of plates, but most are found near the edge of plates. Faults develop as plate movements bend and crack the crust. Earthquakes Earthquakes caused by plates or pieces of crust pushing together or sliding past each other are usually very strong. Earthquakes caused by plates or pieces of crust pulling apart are usually weak. Scientists classify earthquakes by estimating their magnitude, or amount of energy being released. This is reported using a scale of magnitude. Earthquakes This scale is called the Richter Scale. An earthquake measuring 2.0 on the scale is too small to be felt. There are millions of earthquakes like this every year. An earthquake measuring 6.0 or higher on the Richter Scale can cause a great deal of damage. Each increase of 1 on the Richter Scale is an increase in strength of about 32 times. About 20 earthquakes of magnitude 6.0 or greater occur each year. Major Earthquakes Read the information in the table. Then, on a world map, mark the areas where these major earthquakes occurred. Using the information in the text below, estimate how many times stronger the 1964 Alaska earthquake was than the 1976 China earthquake. An earthquake in Seattle in 2001 measured 6.8 on the Richter scale and caused a lot of damage. The pattern of the rocks after an earthquake clearly show the San Andreas Fault. The map shows the location of this fault Volcanoes You know that there are places in Earth’s mantle where solid rock melts. Melted, or molten, rock beneath Earth’s surface is known as magma. Magma forms in places where plates push against each other or pull away from each other. Magma is less dense than solid rock, so it’s pushed upward through the mantle and crust. Volcanoes As magma travels upward, it sometimes reaches an opening, or vent, in the crust. Magma that has flowed out of a vent is called lava. Lava is molten rock that reaches Earth’s surface. As more and more lava flows from a vent, a volcano begins to form. A volcano is a mountain made of lava, ash, or other materials from eruptions. Volcanoes Lava may ooze slowly out of a vent or it may explode from a vent with tremendous force. The 1883 eruption of Krakatoa in Indonesia blew lava 17 miles into the air! Krakatoa before 1883 Krakatoa after 1883 Volcanoes Some volcanoes form above an especially hot column of magma. This column is called a hot spot. A hot spot can melt a hole through the crust as the magma rises to the surface. As a plate moves slowly over a hot spot, volcanoes form in new locations. Eventually, a hot spot can produce a chain of volcanoes. This is how the Hawaiian Islands were formed. Volcanoes Composite, Shielded, Cinder Cone Volcanoes How Mountains Form Mountains are the tallest landforms on Earth. They form where the crust is crumpled and pushed upward by the movements of plates. Many mountains form where plates come together. The edge of the denser plate is forced into the mantle, while the dense plate is pushed up. How Mountains Form The Appalachian Mountains are mostly the result of normal faults folding and thrusting upwards. The Valley and Ridge region, and the Blue Mountains, on the other hand, were built up by a series of reverse faults that force large sheets of rock to pile up. The diagrams show two different ways that faults can move. How Mountains Form Mountains may also form in the middle of a plate. Suppose you hold a cracker and push down on the opposite edges. The cracker would soon break, with jagged, broken edges in the center moving up. This is how the Grand Teton Mountains in Wyoming, formed. How Mountains Form Millions of years ago, surrounding plates put tremendous pressure on the edges of the N. American plate. The pressure snapped a block of rock in the middle of the plate. The rock rose up from the land around it, forming mountains. Cloudland Canyon State Park in northern Georgia was produced by the movement of faults. The layers of rock in this mountain in Montana are the result of reverse faults. In a normal fault, the rock layers above the fault move down In a reverse fault, the rock layers above the fault move up. How Mountains Form Plates that move apart leave gaps between them. When this happens, mantle rock moves in to fill the gaps. Magma builds up along plate boundaries, forming a ridge.