| A | B |
|---|
| theory of plate tectonics | the crust of the Earth is broken into plates that move around due to convection currents in the mantle |
| theory of continental drift | Wegner's theory that the continents were once together based on rocks, fossils and the fit of the continents like a puzzle |
| convergent boundaries | two plates coming together; ex. Pacific Ring of Fire |
| divergent boundaries | two plates moving apart; ex. Mid-Ocean Ridge in the Atlantic |
| transform boundaries | two plates sliding past each other; ex. San Andreas Fault in California |
| shield volcano | basaltic lava accumulates during non-explosive eruptions |
| cinder cone volcano | magma is ejected high into the air and falls back to Earth, piling around the vent |
| composite volcano | magma that is alternatingly spit out and gently rolling out with other volcanic fragments |
| viscosity | how fluid flows |
| basaltic magma | low viscosity, low dissolved gas, low silica, quiet reactions |
| andesitic magma | high silica, medium viscosity, medium reactions |
| rhyolitic magma | high silica, high viscosity, high levels of dissolved gases, explosive eruptions |
| earthquake | when rock fragments move, they release energy in the form of seismic waves |
| focus | where an earthquake occurs |
| epicenter | the point on the surface that is directly above the focus |
| seismograph | an instrument that records seismic waves |
| subduction | process by which one tectonic plate slips beneath another |
| hot spot | unusually hot area in the Earth's mantle that is stationary for long periods of time |
| caldera | large crater, up to 50 km in diameter, that forms when the side of a volcano collapses into the magma chamber during or after an eruption |
| crater | bowl-shaped depression that forms around the central vent at the summit of a volcano |
| fault | fracture in the Earth's crust that occurs when stress is applied too quickly or stress is too great |
| 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 |
| secondary wave | seismic wave that causes rock particles to move at right angles to the direction of the wave |
| stress | forces per unit area that act on a material--compression, tension, and shear |
| strain | deformation of materials in response to stress |
| surface wave | seismic wave that moves in two directions as it passes through rocks, causing the ground to move both up and down and side to side |
| seismogram | record produced by a seismometer that can provide individual tracking of each type of seismic wave |
| seismometer | instrument used to measure horizontal or vertical motion during an earthquake |
| magnitude | measure of the energy released during an earthquake, which can be described using the Richter Scale |
| modified Mercalli scale | measures earthquake intensity on a scale of I-XII; the higher the number, the greater the damage the earthquake has caused |
| Richter scale | numerical scale used to measure the magnitude of an earthquake |
