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Ch.9 study stack
volcanoes and other igneous activity
| Term | Definition |
|---|---|
| aa flow | a type of lava flow that has a jagged, blocky surface. |
| batholith | a large mass of igneous rock that formed when magma was emplaced at depth, crystallized, and subsequently exposed by erosion. |
| caldera | a large depression typically caused by collapse or ejection of the summit area of a volcano. |
| cinder cone | a rather small volcano built primarily of pyroclastics ejected from a single vent. |
| columnar joint | a pattern of cracks that form during cooling of molten rock to generate columns that are generally six-sided. |
| composite cone | a volcano composed of both lava flows and pyroclastic material. |
| concordant | a term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock. |
| conduit | a pipelike opening through which magma moves toward Earth's surface. it terminates at a surface opening called a vent. |
| continental volcanic arc | mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. |
| crater | the depression at the summit of a volcano, or that which is produced by a meterorite impact. |
| decompression melting | melting that occurs as rock ascends due to a drop in confining pressure. |
| dike | a tabular-shaped intrusive igneous feature that cuts through the surrounding rock. |
| discordant | a term used to describe plutons that cut across existing rock structures, such as bedding planes. |
| eruption column | buoyant plumes of hot, ash-laden gases that can extend thousands of meters into the atmosphere. |
| fissure | a crack in rock along which there is a distinct separation. |
| fissure eruption | an eruption in which lava is extruded from narrow fractures or cracks in the crust. |
| flood basalt | flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses or hundreds of meters. |
| geothermal gradient | the gradual increase in temperature with depth in the crust. the average is 30 degrees C per kilometer in the upper crust. |
| hot spot | a concentration of heat in the mantle capable of producing magma, which in turn extrudes onto Earth's surface. the intraplate volcanism that produced the hawaiian islands is an example. |
| intraplate volcanism | igneous activity that occurs within a tectonic plate away from plate boundaries. |
| intrusions | a structure that results from the emplacement and crystallization of magma beneath the surface of earth. |
| island arc | a chain of volcanic islands generally located a few hundred kilometers from a trench where active subduction of one oceanic slab beneath another is occuring. |
| laccolith | a massive igneous body intruded between preexisting strata. |
| lahar | mudflows on the slopes of volcanoes that result when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels. |
| lava tube | tunnel in hardened lava that acts as a horizontal conduit for lava flowing from a volcanic vent. lava tubes allow fluid lavas to advance great distances. |
| mantle plume | a mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity. these plumes of solid yet mobile material may originate as deep as the core-mantle boundary. |
| massive | an igneous pluton that is not tabular in shape. |
| nuee ardente | incandescent volcanic debris buoyed up by hot gases that moves downslope in an avalanche fashion. |
| pahoehoe flow | a lava flow with a smooth-to-ropey surface. |
| partial melting | the process by which most igneous rocks melt. since individual minerals have different melting points, most igneous rocks melt over a temp range of a few 100 degrees. if the liquid is squeezed out after some melting occurs, a higher silica content results |
| pipe | a vertical conduit through which magmatic materials have passed. |
| plutons | a structure that results from the emplacement and crystallization of magma beneath the surface of Earth. |
| pumice | forms during explosive eruptions of viscous magmas having an intermediate (andestic) or felsic (rhyolitic) composition. |
| pyroclastic flow | a highly heated mixture, largely of ash and pumice fragments, traveling down the flanks of a volcano or along the surface of the ground. |
| pyroclastic material | the volcanic rock ejected during an eruption, including ash, bombs, and blocks. |
| scoria | hardened lava that has retained the vesicles produced by escaping gases. |
| scoria cone | a rather small volcano built primarily of pyroclastics ejected from a single vent. |
| shield volcano | a broad, gently sloping volcano built from fluid basaltic lavas. |
| sill | a tabular igneous body that was intruded parallel to the layering of preexisting rock. |
| stock | a pluton similar to but smaller than a batholith. |
| stratovolcano | a volcano composed of both lava flows and pyroclastic material. |
| tabular | Term used to describe a feature such as an igneous pluton having two dimensions that are much longer than the third. A pluton that is thin in one dimension. |
| vent | A conduit that connects a magma chamber to a volcanic crater. |
| viscosity | A measure of a fluid's resistance to flow. factors affecting flow. Temperature, composition(high silica vs. low silica), and disolved gases (volatiles) |
| volatiles | Gaseous components of magma dissolved in the melt. Volatiles will readily vaporize (form a gas) at surface pressures. |
| volcanic island arc | a chain of volcanic islands generally located a few hundred kilometers from a trench where active subduction of one oceanic slab beneath another is occuring. |
| volcanic neck | An isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano. |
| volcano | A mountain formed of lava, and/or pyroclastics. |
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