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Science----Chapter 4 lesson 2- Earthquakes and Volcanoes Test Friday, December 9, 2016 1. 2. 3. 4. Volcano-an opening in Earth’s crust through which lava may flow. Focus- the point where an earthquake starts. Lava- hot, melted rock that reaches Earth’s surface. Hot spot- a stationary location in Earth’s mantle where magma melts through a tectonic plate. 5. Epicenter- the point on Earth’s surface directly above the focus of an earthquake. 6. Earthquake- a sudden shaking of Earth’s crust Notes 1. Scientists can predict whether a volcano will erupt because the volcano may give off smoke or steam, or there may be earthquakes just before an eruption. 2. Walls and buildings may crumble during an earthquake because of the ground trembling. 3. In this lesson, we learned that the shifting of a tectonic plate or plates might make the ground move. 4. Earthquake waves travel through the layers of Earth. 5. Two scales used to measure earthquakes are the Richter scale and the Mercalli scale. 6. The Richter scale measures magnitude at the epicenter. It rates earthquakes from weakest to strongest, starting from 1. 7. The Mercalli scale is based on observed effects, not on mathematics. The Mercalli scale rates earthquakes in Roman numerals from 1 to XII, XII being the most severe. 8. The Mercalli scale is less reliable than the Richter scale. 9. When a volcano forms underwater as soon as the lava emerges from the vent, the lava is cooled by the water and forms rock. 10 .If an underwater volcano kept erupting again and again the mound of lava would grow taller and taller. Three stages of volcanoes 1. Active volcanoes are currently erupting or have recently erupted. 2. Dormant volcanoes are volcanoes that have not erupted for some time. 3. Extinct or dead volcanoes have stopped erupting. Three ways volcanoes are formed 1. Shield volcanoes are built by thinner, fluid lava that spreads over a large area. These mountains have a broad base and gently sloping sides. 2. Cinder cone volcanoes are built by thick lava that is thrown high into the air and falls as chucks or cinders. These mountains form as a cone shape with a narrow base and steep sides. 3. Composite volcanoes are built by layers of ash and cinders sandwiched between layers of hardened lava. The shape on one side of a cone formed by a composite volcano usually looks the same as the shape on the opposite side.