| A | B |
|---|
| batholith | a large mass of igneous rock that formed when magma intruded at depth, became crystallized, and subsequently was exposed by erosion; Batholiths have a surface exposure greater than 100 square kilometers. |
| caldera | a large depression typically caused by collapse or ejection of the summit area of a volcano |
| cinder cone | a small volcano built primarily of pyroclastic material ejected from a single vent |
| composite cone | a volcano composed of both lava flows and pyroclastic material |
| crater | the depression at the summit of a volcano or that which is produced by a meteorite impact |
| decompression melting | melting due to a drop in confining pressure that occurs as rock rises |
| dike | a tabular-shaped intrusive igneous feature that occurs when magma is injected into fractures in the surrounding rock, cutting across preexisting rock layers |
| geothermal gradient | the gradual increase in temperature with depth in the crust; The average is 30°C per kilometer in the upper crust. |
| intraplate volcanism | igneous activity that occurs within a tectonic plate away from plate boundaries |
| laccolith | a massive igneous body intruded between preexisting strata |
| pluton | an intrusive igneous structure that results from the cooling and hardening of magma beneath the surface of Earth |
| pyroclastic material | the volcanic rock ejected during an eruption, including ash, bombs, and blocks |
| shield volcano | a broad, gently sloping volcano built from fluid basaltic lavas |
| sill | a tabular igneous body formed when magma is injected along sedimentary bedding surfaces |
| vent | an opening in the surface of Earth through which molten rock and gases are released |
| viscosity | a measure of a fluid’s resistance to flow |
| volcano | a mountain formed of lava and/or pyroclastic material |
