Geology Class
Lava
Molten rock expelled by a volcano during an eruption. When first expelled from a volcanic vent, it is a liquid at temperatures from 700 °C to 1,200 °C. It can flow great distances before cooling and solidifying.
Tectonic Plates
Tectonic plates are large plates of rock that make up the foundation of the earth's crust and the shape of the continents. The tectonic plates comprise the bottom of the crust and the top of the earth's mantle. There are ten major plates on the earth and many more minor ones. They float on a plastic-like part of the earth's mantle called the asthenosphere.
Lithosphere
The lithosphere, Greek for “rocky sphere,” is the outermost shell of the Earth. The term is also used to refer to the outermost rocky shell of other solid planets. It is a relatively thin layer, 50-100 km thick under the oceans, 150 km thick on the continents.
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms (and for fluids only), viscosity is "thickness".
Subduction Zone
A subduction zone is a convergent boundary where two tectonic plates collide. Plates are large, dense masses in the crust of the earth, the lithosphere, that float on top of liquefied rock in the asthenosphere. They are constantly shifting and moving, so when they subduct, one pushes beneath the other. Subduction zones create geologic formations such as mountain ranges, ocean trenches, and island arcs, as well as phenomena like earthquakes and volcanoes.
Divergent Plate Boundaries
At the mid-oceanic ridges, two tectonic plates diverge from one another. New oceanic crust is being formed by hot molten rock slowly cooling and solidifying.
Volcanic Winter
A volcanic winter is the reduction in temperature caused by volcanic ash and droplets of sulfuric acid obscuring the sun and lowering the albedo (increasing the Earth's reflectivity), during a large particularly explosive type of volcanic eruption. Long-term cooling effects are primarily dependent upon injection of sulfide compounds in aerosol forms into the upper atmosphere—the stratosphere—the highest, least active levels of the lower atmosphere where little precipitation occurs, requiring a lengthy time to wash the aerosols out of the region.