Tsunamis: destructive, fast-moving large waves caused mainly by earthquakes Crest and trough, wave height and wavelength, shoreline friction Water molecules tend to move up and down in place and not move with the wave. Waves are caused by wind on the ocean’s surface. Tides are caused by gravitational forces of the sun and moon there are two tides daily. Surface currents: large circular streams kept in motion by prevailing winds and rotation of the earth Gulf Stream (North Atlantic), Kuroshio (North Pacific) Subsurface currents are caused by upwelling from prevailing offshore winds (Peru, Chile) and density differences (Antarctica) the upwelling pushes up nutrients from the ocean floor. Evidence for long-term movement of plates includes fit of continents and matches of rock types, fossils, and structures ocean floor age and topography ancient climate zones locations of earthquakes, volcanoes, and mountain ranges magnetic directions in ancient rocks.As plates move over these hot spots, they cause chains of volcanoes and island chains like the Hawaiian Islands. Volcanoes usually occur where plates are pulling apart or coming together, but some occur at holes (hot spots) in the crust away from plate boundaries.Severity of ground shaking is measured on the Richter scale Earthquakes cause waves (vibrations) which have:įocus, the point below the surface where the quake beginsĮpicenter, the point on the surface above the focus Earthquakes usually occur where stress has been built up by plates moving in opposite directions against each other. Plates move at speeds ranging from 1 to 4 inches (5-10 centimeters) per year.
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Plates move because molten rock rises and falls under the crust causing slowly flowing currents under the plates. The surface of earth is made up of rigid plates that are in constant motion. Inner core: solid iron and nickel, 800 miles thick, about 7,000 degrees C The continents were once joined (Pangaea).Ĭrust: surface layer of mainly basalt or granite, 5 to 25 miles thick Mantle: 1,800 miles thick, rock of intermediate density, moves very slowly Outer core: liquid iron and nickel After the sun was formed,matter cooled creating the planets.
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The present features of earth come from its ongoing history. The surface of the earth is in constant movement.