Question | Answer |
Asthenosphere | plasticlike layer of Earth on which the lithospheric plates float and move around. |
Cinder cone volcano | steep-sided, loosely packed volcano formed when tephra falls to the ground. |
Composite volcano | volcano built by alternating explosive and quiet eruptions that produce layers of tephra and lava; found mostly where Earth's plates come together and one plate sinks below the other. |
Continental drift | Wegener's hypothesis that all continents were once connected in a single large landmass that broke apart about 200 million years ago and drifted slowly to their current positions. |
Convection current | current in Earth's mantle that transfers heat in Earth's interior and is the driving force for plate tectonics. |
Crater | steep-walled depression around a volcano's vent. |
Earthquake | vibrations produced when rocks break along a fault. |
Epicenter | point on Earth's surface directly above an earthquake's focus. |
Hot spot | the result of an unusually hot area at the boundary between Earth's mantle and core that forms volcanos when melted rock s forced upward and breaks through the crust. |
Lithosphere | rigid layer of Earth about 100 km thick, made of the crust and a part of the upper mantle. |
Pangaea | large, ancient landmass that was composed of all the continents foined together. |
plate tectonics | theory that Earth's crust and upper mantle are broken into plates that float and move around on a plasticlike layer of the mantle. |
plate | a large section of Earth's oceanic or continental crust and rigid upper mantle that moves around on the asthenosphere. |
primary wave | seismic wave that moves rock particles back-and-forth in the same direction that the wave travels. |
Seafloor spreading | Hess's theory that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge. |
Secondary wave | seismic wave that moves rock particles at right angles to the direction of the wave. |
Seismograph | instrument used to register earthquake waves and record the time that each arrived. |
Shield volcano | broad, gently sloping volcano formed by quiet eruptions of basaltic lava. |
surface wave | seismic wave that moves rock particles up-and-down in a backward rolling motion and side-to-side in a swaying motion. |
tephra | bits of rock or solidified lava dropped from the air during a explosive volcanic eruption; ranges in size from volcanic ash to volcanic bombs. |
Vent | opening where magma is forced up and flows out onto Earth's surface as lave, forming a volcano. |
Volcano | opening in Earth's surface that erupts sulfurous gases, ash, and lava; can form at Earth's plate boundaries, where plates move apart or together, and at hot spots. |