Earth Science Chapter 17-20 Vocabulary

Viscosity?

A substance's internal resistance to flow.

Modified Mercalli Scale?

Measures eathquake intensity on a scale from 1 to X11; the higher the number, the greater the damage the earthquake has caused.

Rickter Scale?

Numerical scale used to measure the magnitude of an earthquake's, using values based on the size of the earthquake's largest seismic waves.

Vent?

Opening in Earth's crust through which lava erupts and flows out out onto the surface.

Fault?

Fracture or system of fractures in Earth's crust that occurs when stress is applied too quickly or stress is too great;can form as a result of horizontal compression, horizontal shear or horizontal tension.

Magnitude?

Measure of the energy released during an earthquake, which can be described using the Ritcher scale.

Seismic Gap?

Place along an active fault that has not experienced an earthquake for a long time.

Secondary Wave?

Seismic wave that causes rock particles to move at right angles to the direction of the wave.

Surface Wave?

Seismic wave that moves in two directions as it passes through rocks, causing the ground to move both up and down and from side to side.

Primary Wave?

Seismic wave that squeezes and pulls rocks in the same direction that the wave travels, causing rock particles to move back and forth.

Pangaea?

Ancient landmass made up of all the continents that began to break apart around 200 million years ago.

Crater?

Bowl-shaped depression, usually less than 1 km in diameter, that forms around the central vent at the summit of a volcano.

Shield Volcano?

Broad volcano with gently sloping sides built by nonexplosive eruptions of basaltic lava that accumulates in layers.

Magnetic reversal?

Changes in Earth's magnetic field over geologic time, recorded in ocean-floor rocks and continental basalt flows.

Magnetometer?

Device used to map the ocean floor that detects small changes in magnetic fields.

Seafloor Spreading?

Hess's theory that new ocean crust is formed at mid-ocean ridges and destroyed at deep sea trenches; occur in a continuous cycle of magma intrusion and spreading.

Seismometer?

Instrument used to measure horizontal or vertical motion during an earthquake.

Pluton?

Intrusive igneous rock bodies, including batholithsm stocks, sills, and dikes , formed through mountain-building processes and oceanic-oceanic collisions; can be exposed at Earth's surface due to uplift and erosion.

Caldera?

Large crater, up to 50 km in diameter, that can form when the summit or side of a volcano collapses into the magma chamber during or after an eruption.

Tsunami?

Large, powerful, ocean wave generated by the vertical motions of the seafloor during an earthquake; in shallow water, can form huge, fast-moving breakers exceeding 30 m in height that can damage coastal areas.

Composite Volcano?

Large, sloping volcano built by violent eruptions of volcanic fragments and lava that accumulate in alternating layers.

Rift Valley?

Long, narrow depression that forms when continental crust begins to separate at a divergent boundary.

Divergent Boundary?

Place where two of Earth's tectonic plates are moving apart; is associated with volcanic, earthquakes, and high heat flow, and is found primarily on the seafloor.

Convergent Boundary?

Place where two of Earth's tectonic plates are moving toward each other; is associated with trenches, island arcs, and folded mountains.

Transform Boundary?

Place where two tectonic plates slide horizontally past each another that is characterized by long faults and shallow earthquakes.

Focus?

Point of the initial fault rupture where an earthquake originates that usually lies at least several kilometers beneath Earth's surface.

Epicenter?

Point on Earth's surface directly above the focus of an Earthquake.

Subduction?

Process by which one tectonic plate slips beneath another tectonic plate.

Seismogram?

Record produced by a seismometer that can provide individual tracking of each type of seismic wave.

Tephra?

Rock fragments, classified by size, that are thrown into the air during a volcanic eruption and fall to the ground.

Theory of Plate Tectonics?

States that Earth's crust and upper mantle are broken into plates, which are huge rock slabs that move in different directions and at different rates over Earth's surface.

Cinder-cone Volcano?

Steep-sided, generally small volcano that is built by the accumulation of tephra around 30,000 K at its top.

Paleomagnetism?

Study's of Earth's magnetic record using data gathered from iron-bearing minerals in rocks that have recorded the orientation of Earth's magnetic field at the time of their formation.

Pyroclastic Flow?

Swift-moving, potentially deadly clouds of gas, ash, and other volcanic material produced by violent eruptions.

Slab Pull?

Tectonic process associated with convection currents in Earth's mantle that occurs as the weight of the subducting plate pulls the trailing lithosphere into a subduction zone.

Ridge Push?

Tectonic process associated with convection currents in Earth's mantle that occurs when the weight of an elevated ridge pushes an oceanic plate toward a subduction zone.

Hot Spot?

Unusually hot area in Earth's mantle that is stationary for long periods of time, where high temperature plumes of mantle material rise toward the surface.

Continental Drift?

Wegener's hypothesis that Earth's continents were joined as a single landmass, called Pangaea, that broke apart about 200 million years ago and slowly moved to their present positions.