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Changes to Earth’s Surface Chapter 9 Vocabulary • • • • • • • • • Landform Weathering Erosion Deposition Landslide Volcano Fault Earthquake Epicenter Landforms • Natural features that cover Earth’s surface are landforms. • Landforms can be different sizes and shapes. • For example, a mountain is a landform. Landforms • Plains are flat landforms on low ground. Landforms • Plateaus are flat landforms on high ground. Landforms • Valley, canyons, and peninsulas are also landforms. Landforms Valley Peninsula Weathering • When rocks are broken into smaller pieces, the process is called weathering. • http://www.youtube.co m/watch?v=lyysL02ZvQ 8 Erosion • When water, ice, gravity, and wind work together to move weathered pieces of rock, this process is called erosion. Deposition • When rock, soil, organic matter, or other material are laid down on Earth’s surface is called deposition. • It often adds to and creates landforms. Landslide • When a large amount of rock and soil is rapidly moving downhill, this is a landslide. How do weathered materials move? • Materials that are from rock by weathering can be carried to a new place, where they become part of another landform. • Water, ice, gravity, and wind work together to move weathered pieces of rock. This process is called erosion. Effects of Erosion • Moving water erodes, or carries away, materials from landforms. • Rain picks up loose material from the surfaces of rocks. As the rain runs into streams, it takes the loose, weathered material with it. Effects of Erosion • Water running downhill wears away rocks and soil. After many years, the grooves that the water carves in the land become canyons or valleys. Effects of Erosion • Waves from the ocean constantly change the shape of a shoreline. How can Earth’s surface change rapidly? • Volcanoes and earthquakes cause large, rapid changes to Earth’s surface. Volcanoes • A volcano is a landform that can cause a rapid change to Earth’s surface. • At 80 to 160 km (50 – 100 miles) underground, very hot rock, called magma is partially melted into liquid. Volcanoes • A volcano forms at a weak spot in Earth’s crust where magma is forced upward because of gas and it reaches the surface. • When the magma boils onto the surface, the volcano erupts. • When magma flows out of the volcano, it is known as lava. Volcanoes • Sometimes the pressure builds up, so the gases in the magma explode. Hot rocks, gases, and ash burst into the air from openings called vents. • Sometimes volcanoes explode, and sometimes the magma oozes out. Active Volcanoes • An active volcano has frequent eruptions or shows signs of future eruptions. • In Hawaii, the island Kilauea began erupting in 1983 and is continuing to erupt today, so it is an active volcano. Dormant Volcanoes • A volcano that has not erupted in a long time is dormant. • Mount Rainier in the Cascade Mountains in Washington has not erupted in about 150 years. However, scientists consider it dangerous because if the magma inside the mountain were to heat up, it would explode. Extinct Volcanoes • Volcanoes are classified as extinct if scientists do not think it will erupt again. • Mount Keyna in Africa is extinct. • There are extinct volcanoes all over the world. Effects of Eruptions • Volcanic eruptions can create a lot of rock and ash. • Volcanoes can cause major, rapid changes to Earth’s surface. • For example. Mount St. Helens used to be 9,600 ft high, but in May 1980, it erupted and it created an area 3,300 feet where the mountain exploded! The ash from the explosion went more than 15 miles into the air! Before and After Mount St. Helens Before 1980 Eruption Mount St. Helens After Eruption Question Time! 1. What is magma? Magma is very hot, partially liquid rock found under Earth’s crust. 2. What causes a volcano to erupt? A volcano erupts because of a build up of hot gas pressure and magma and the Earth’s crust is weak, so the magma comes to the surface the the volcano erupts. 3. What is an active volcano? An active volcano has frequent eruptions or shows signs of future eruptions. Earth’s Moving Plates • Earth’s outer layer, or crust, rests on top of another layer called the upper mantle. • These two layers, together, are divided into very large pieces called plates. • The plates move all the time. Most volcanoes are along or near the places where plates come together. The Plates The Cause of Earthquakes • A fault is a break or crack in rocks where Earth’s crust can move. The Cause of Earthquakes • Sometimes rocks along the fault get stuck, but the plates continue their slow movement. • If they pressure becomes strong enough, the rocks can break and the plates move suddenly. The sudden movement that causes Earth’s crust to shake is an earthquake. The Cause of Earthquakes • Earthquakes often cause major, rapid changes to Earth’s surface. The Cause of Earthquakes • The place underground where the plates start to move and earthquake beings is called the focus. • The point on Earth’s surface above that area (the focus) is the epicenter. The Cause of Earthquakes • Earthquakes are cause by plates sliding along each other and they give off lots of energy. • The energy moves in the form of vibrations, or waves. • So people may feel the earthquake from far away, but the damage it causes is usually greatest near the epicenter. Effects of Earthquakes • Earthquakes can cause tsunamis. • In 2004, an earthquake under the ocean off the west coast of Indonesia cause tsunamis that traveled throughout the Indian ocean. The tsunamis affected at least 11 countries. Effects of Earthquakes • Earthquakes can cause damage to buildings, roads, and bridges. • In 1906 an earthquake occurred in San Francisco. It caused gas lines to break which created a fire that burned for three days! Effects of Volcanoes • Volcanoes can cause damage to cities and can change our environment. • In 1815, Mount Tambora in southeast Asia erupted. The ash from the volcano filled the sky. • Less sunlight could reach Earth. • Snow fell in northeaster United States in June. • People called it they “year without a summer.” Question Time! 1. What are some large-scale effects of volcanoes and earthquakes? Some large scale effects of volcanoes are that volcanic ash can reduce the amount of sunlight reaching Earth’s surface, causing cooler temperatures. Earthquakes can cause tsunamis. 2. What is one cause and effect of an earthquake? Cause: a sudden movement of Earth’s plates shakes Earth’s crust layer. Effect: There are sudden changes in Earth’s surface. 3. Why would it be important to locate the epicenter of an earthquake? The epicenter is directly above the earthquake’s focus. The largest amount of damage may occur at the epicenter.