Plate Tectonics, Earthquakes, and Volcanoes Study Guide

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Convection Cell
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unequal heating and cooling of the air often makes a pattern of rising air, sinking air, and winds
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Continental Crust
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The portion of the earth’s crust that primarily contains granite, is less dense than oceanic crust, and is 20-50 km thick
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Lithosphere
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the solid part of the earth consisting of the crust and outer mantle
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Asthenosphere
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The solid, plastic layer of the mantle beneath the lithosphere; made of mantle rock that flows very slowly, which allows tectonic plates to move on top of it
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oceanic crust
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A crust primarily composed of basalt that is located under the ocean.
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Seismic Waves
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vibrations that travel through Earth carrying the energy released during an earthquake
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Apparent polar wander
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the fact that the magnetic minerlas preserved in rocks point to a different north pole for different geologic periods
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Continental Drift
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the gradual movement and formation of continents (as described by plate tectonics)
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Abyssal Plains
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a smooth, nearly flat region of the deep ocean floor
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Mid-ocean ridge
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an undersea mountain chain where new ocean floor is produced; a divergent plate boundary
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Trench
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a long steep-sided depression in the ocean floor
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Seafloor Spreading
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The process that creates new sea floor as plates move away from each other at the mid-ocean ridges
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Convergent plate boundary
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A tectonic plate boundary where two plates collide or where one plate gets subducted.
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Transform plate boundary
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Boundary between two plates that are sliding past each other.
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Subduction zone
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the region where an oceanic plate sinks down into the asthenosphere at a convergent boundary, usually between continental and oceanic plates
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Transform fault
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Area where the earth’s lithospheric plates move in opposite but parallel directions along a fracture (fault) in the lithosphere.
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Primary waves
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1st wave, P, travels the fastest, back-and-forth waves, move through solids, liquids, and gases
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Secondary waves
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slower than P waves, transverse motion (up and down), can move through solids only
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Love waves
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Surface waves that shear the ground in a horizontal direction. Can only travel through solids. Third to arrive.
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Rayleigh waves
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Surface waves that travel in a backward-rotating, elliptical motion, causing both vertical and horizontal ground movement. Can travel through solid, liquid, and gas. Fourth to arrive. Dangerous.
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Body waves
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seismic waves that travel through the Earth’s interior
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Surface waves
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seismic waves that travel along the Earth’s surface
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Epicenter
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the point on the Earth’s surface directly above the focus of an earthquake
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Elastic rebound theory
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theory that rocks that are strained past a certain point will fracture and spring back to their original shape
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Mercalli intensity scale
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a 12 point scale to determine the earthquake intensity by determining the damage
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Richter scale
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a logarithmic scale of 1 to 10 used to express the energy released by an earthquake
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Seismograph
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a measuring instrument for detecting and measuring the intensity and direction and duration of movements of the ground (as an earthquake)
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Seismometer
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Instrument used to measure horizontal or vertical motion during an earthquake.
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Fissure
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a long narrow depression in a surface
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Mantle Plume
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A buoyant mass of hot rock rising through Earth’s mantle. As it nears the surface of Earth, some of the plume melts and erupts at the surface forming a \”hot spot.\”
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Magma
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molten rock in the earth’s crust
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Lava
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magma that reaches Earth’s surface
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Active volcano
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One that is erupting or shows signs that it may erupt in the near future.
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Dormant volcano
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A volcano that has not erupted for a long time, but may erupt again one day.
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Effusive volcano
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a volcano with a gentle and low viscosity
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Extinct volcano
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A volcano that has not erupted for thousands of years and probably will not erupt again.
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Pyroclast
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A volcanic rock fragment ejected into the air during an eruption.
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Viscosity
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resistance of a liquid to sheer forces (and hence to flow)
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Magma chamber
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the pocket beneath a volcano where magma collects
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Caldera
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a large crater caused by the violent explosion of a volcano that collapses into itself
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Cinder cone
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a steep, cone-shaped hill or small mountain made of volcanic ash, cinders, and bombs piled up around a volcano’s opening.
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Composite or stratovolcano
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a steep-sided volcano formed by an alternating series of lava flows and pyroclastic eruptions and marked by repeated eruption
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Supervolcano
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massive volcano with eruptions that are rare but incredibly powerful. Thousands of cubic kilometers of matter can be ejected in the form of dust and ash that can cool the world’s climate for years.
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Shield volcano
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A low, flat, gently sloping volcano built from many flows of fluid, low-viscosity basaltic lava

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