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Science Bowl-Geology
| Question | Answer |
|---|---|
| aa | A lava flow that solidifies with a spiny, rubbly surface |
| ablation or wastage | the loss of glacial ice or snow by melting, evaporation, or breaking off into icebergs |
| abrasion | grinding away of rock by friction and impact during transportation |
| absolute age or numerical age | age given in years or some other unit of time |
| abyssal fan | great fan-shaped deposit of sediment on the deep sea-floor at the base of many submarine canyons |
| abyssal plain | very flat sediment-covered region of the deep-sea floor; usually at the base of the continental rise |
| accreted terrane | terrane that did not form at its present site on a continent |
| accretionary wedge (subduction complex) | a wedge of thrust-faulted and folded sediment scraped off a subducting plate by the overlaying plate |
| accumulation stage | stage in the evolution of major mountain belts characterized by the accumulation of great thicknesses (several kilometers) of sedimentary of volcanic rocks |
| active continental margin | a margin consisting of a continental shelf, a continental slope, and an oceanic trench |
| actualism | the principle that the same processes and natural laws that operated in the past are those we can actually observe or infer from observations as operating at present. uniformitarianism has the same meaning as actualism for most geologists |
| advancing glacier | glacier with a positive budget so that accumulation results in the lower edges being pushed outward and downward |
| aftershock | small earthquake that follows a main shock |
| a horizon or zone of leaching | the top layer of soil, characterized by the downward movement of water |
| alkali soil | soil containing such a great quantity of sodium salts precipitated by evaporating ground water that it is generally unfit for plant growth |
| alluvial fan | large fan-shaped pile of sediment that usually forms where a stream's velocity decreases as it emerges from a narrow canyon onto a flat plain at the foot of a mountain range |
| alpine glaciation | glaciation of a mountainous area |
| amphibole group | mineral group in which all members are double-chain silicates |
| amphibolite | amphibole (hornblende), plagioclase schist |
| andesite | fine-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar with the rest being ferromagnesium minerals |
| angle of dip | a vertical angle measured downward from the horizontal plane to an inclined plane |
| angular | sharp-edged; lacking rounded edges or corners |
| angular unconformity | unconformity in which younger srata overlie an erosion surface on tilted or folded layered rock |
| anorthosite | crystalline rock composed almost entirely of calcium-rich plagioclase fledspar |
| antecedent stream | stream that maintains its original course despite later deformation of the land |
| anticline | an arched fold in which the rock layers usually dip away from the axis of the fold |
| aquifer | a body of saturated rock or sediment through which water can more readily |
| arch (sea arch) | bridge of rock left above an opening eroded in a headland of waves |
| Archean Eon | the oldest eon of Earth's history |
| arete | a sharp ridge that seperated adjacent glacially curved valleys |
| arid region | an area with less that 25 cm of rain per year |
| arkose | a sandstone in which more that 25% of the grains are feldspar |
| artesian well | well where water rises above the aquifer |
| artificial recharge | ground-water recharge increases by engineering techniques |
| aseismic ridge | submarine ridge with which no earthquakes are associated |
| volcanic ash | fine pyroclasts (less that 4 mm) |
| assimilation | process where very hot magma melts country rock and assimilates the newly molten material |
| asthenosphere | region made up of mantle beneath the lithosphere; behaves plastically |
| atoll | circular reef surrounding a deeper lagoon |
| augite | mineral of the pyroxene group found in mafic igneous rocks |
| aureole | zone of contact metamorphism adjacent to a pluton |
| axial plane | plane containing all of the hinge lines of a fold |
| backarc spreading | type of sea-floor spreading that: moves an island arc away from a continent, tears an island arc in two, or splits the edge of a continent, forming a new sea floor |
| backshore | upper part of the beach, landward of the high-water line |
| bajada | broad, gently sloping, depositional surface formed at the base of a mountain range in a dry region by the coalescing of individual alluvial fans |
| bar | ridge of sediment, usually sand or gravel, that has been deposited in the middle or along the banks of a streamby a decrease in stream velocity |
| barchan | crescent shaped dune with the horns of the crescent pointing downwind |
| barrier island | ridge of sand paralleling the shoreline and extending above sea level |
| barrier reef | reef seperated from the shoreline by the deeper water of a lagoon |
| basal sliding | movement in which the entire glacier slides along as a single body on its base over the underlying rock |
| basalt | fine grained mafic, igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium rich plagioclase feldspar |
| base level | a theoretical downward limit for steam erosion of the Earth's surface |
| batholith | large discordant pluton with an outcropping area greater than 100 square kilometers |
| bauxite | principal ore of Al (Al2O3 * n H20) |
| baymouth bar | ridge of sediment that cuts a bay off from the ocean |
| beach | strip of sediment, usually sand but sometimes pebbles, boulders, or mud, that extends from the low-water line inland to a cliff or zone of permanent vegetation |
| beach face | section of beach exposed to wave action |
| bedding | arrangement of layers or beds of rock |
| bedding plane | nearly flat surface separating two beds of sedimentary rock |
| bed load | heavy or large sediment particles in a stream that travel near or on the stream bed |
| bedrock | solid rock that underlies the soil |
| Benioff zone | distinct earthquake zone that begins at an oceanic trench and slopes landward and downward into Earth at an angle of 30 or 60 degrees |
| bergschrund | the crevasse that develops where a glacier is pulling away from a cirque wall |
| berm | platform of wave-deposited sediment that is flat or slopes slightly landward |
| B horizon or zone of accumulation | soil layer characterized by accumulation of material leached downward from the A horizon above |
| biochemical | precipitated by the action of organisms |
| bioclastic limestone | limestone consisting of fragments of shells, corals, and algae |
| biotite | iron/magnesium-bearing mica |
| block | large, angular pyroclast |
| blowout | depression on the land surface caused by wind erosion |
| body wave | seismic wave that travels through Earth's interior |
| bomb | large spindle or lens shaped pyroclast |
| bottomset bed | delta deposit formed from the finest silt and clay, which are carried far out to sea by river flow or by sediments sliding downhill on the sea floor |
| boulder | sediment particle with a diameter greater than 256 mm |
| Bowen's reaction series | sequence in which minerals crystallize from a cooling basaltic magma |
| braided stream | stream that flows in a network of many interconnected rivulets around numerous bars |
| breaker | wave that has become so steep that the crest of the wave topples forward, moving faster than the main body of the wave |
| breakwater | offshore structure built to absorb the force of large breaking waves and provide quiet water near shore |
| brittle strain | cracking or rupturing of a body under stress |
| butte | narrow pinnacle of resistant rock with a flat top and very steep sides |
| calcareous | containing calcium carbonate |
| calcite | mineral with the formula CaCO3 |
| caldera | A volcanic depression much larger than the original crater |
| capacity (of stream) | the total load that a stream can carry |
| capillary action | the drawing of water upward into small openings as a result of surface tension |
| capillary fringe | a thin zone near the water table in which capillary action causes water to rise above the zone of saturation |
| carbonaceous chondrite | stony meteorite containing chondrules and composed mostly of serpentine and large quantities of organic materials |
| carbonic acid | has formula H2CO3 and is a weak acid common in rain and surface waters |
| cave or cavern | naturally formed underground chamber |
| cement | the solid material that precipitates in the pore space of sediments, binding the grains together to form solid rock |
| cementation | the chemical precipitation of material in the spaces between sediment grains, binding the grains together into a hard rock |
| Cenozoic Era | the most recent of the eras (follows Mesozoic) |
| chain silicate structure | silicate structure in which two of each tetrahedron's oxygen ions are shared with adjacent tetrahedrons, resulting in a chain |
| chalk | very fine-grained bioclastic limestone |
| channel (Mars) | feature on the surface of the planet Mars that closely resembles certain types of streams or channels on Earth |
| chaotic terrain (Mars) | patch of jumbled and broken angular slabs and blocks on the surface of Mars |
| chemical sedimentary rock | rock composed of material precipitated directly from solution |
| chemical weathering | decomposition of rock resulting from exposure to water and atmospheric gases |
| chert | hard, compact, fine-grained sedimentary rock formed almost entirely of siica |
| chill zone | in an intrusion, the finer-grained rock adjacent to a contact with country rock |
| chondrule | round silicate grain within some stony meteorites |
| C horizon | soil layer composed of incompletely weathered parent material |
| cinder (volcanic) | pyroclast approximately the size of a sand grain. Sometimes defined between 4 and 32 mm |
| cinder cone | volcano constructed of loose rock fragments ejected from a central vent |
| circum-Pacific belt | major belt around the edge of the Pacific ocean on which most composite volcanoes are located and where many Earthquakes occur |
| cirque | steep-sided, amphitheater-like hollow carved into a mountain at the head of a glacial valley |
| clastic sedimentary rock | sedimentary rock composed composed of fragments of preexisting rock |
| clastic texture | arrangement of rock fragments bound into a rigid network by cement |
| clay | sediment composed of particles with a diameter of 1/256 nm or less |
| clay mineral | hydrous aluminum silicate that occurs as a platy grain of microscopic size with a sheet silicate structure |
| clay mineral group | collective term for several clay minerals |
| cleavage | ability of rock to break along preferred planes |
| coal | sedimentary rock formed from the consolidation of plant material. Rich in carbon, usually black, and burns readily |
| coarse-grained rock | rock in which most of the grains are larger than 1 mm for igneous and 2 mm for sedimentary |
| coast | land near the sea, including the beach and a strip of land inland from the beach |
| coastal straightening | the gradual straightening of an irregular shoreline by wave erosion of headlands and wave deposition in bays |
| cobble | a sediment particle with a diameter of 64 to 256 mm |
| column | a dripstone feature formed when a stalactite downward and a stalactite growing upward meet and join |
| columnar structure or columnar jointing | volcanic rock in parallel, usually vertical columns, mostly 6-sided |
| comet | small object in space, no more than a few kilometers in diameter. composed of frozen methane, frozen ammonia, and water ice, with small solid particles and dust imbedded in the ices |
| compaction | loss in overall volume and pore space of a rock as the particles are packed closer together by the weight of overlying material |
| competence | largest particle that a stream can carry |
| composite volcano or stratovolcano | volcano constructed of alternating layers of pyroclastics and rock solidified from lava flows |
| compressive directed pressure | directed pressure that tends to compress some portions of a body more than other portions |
| compressive stress | stress due to a force pushing together on a body |
| conchoidal fracture | curved fracture surfaces |
| concordant | parallel to layering or earlier developed planar structures |
| concretion | hard, rounded mass that develops when a considerable amount of cementing material precipitates locally in a rock, often around an organic nucleus |
| cone of depression | depression of the water table formed around a well when water is pumped out; it is shaped like an inverted cone |
| confined aquifer or artesian aquifer | aquifer completely filled with pressurized water and separated from the land surface by a relatively impermeable confining bed (such as shale) |
| confining pressure (also called geostatic or lithostatic pressure) | pressure applied equally on all surfaces of a body |
| conglomerate | coarse-grained sedimentary rock (grains coarser than 2 mm) formed by the cementation of rounded gravel |
| consolidation | any process that forms firm, coherent rock from sediment or from liquid |
| contact | boundary surface between two different types or ages of rocks |
| contact (thermal) metamorphism | metamorphism under conditions in which high temperature is the dominant factor |
| continental crust | thick, granitic crust under continents |
| continental drift | concept suggesting that continents move over the Earth's surface |
| continental glaciation | covering of a large region of a continent by a sheet of glacial ice |
| continental rise | wedge of sediment that extends from the lower part of the continental slope to the deep sea floor |
| continental shelf | submarine platform at the edge of a continent, inclined very gently seaward generally at an angle of less than 1 degree |
| continental slope | relatively steep slop extending from a depth of 100 to 200 m at the edge of the continental shelf down oceanic depths |
| contour current | bottom current that flows parallel to the slopes of the continental margin (along the contour rather than down the slope) |
| contour line | line on a topographic map connecting points of equal elevation |
| convection (current) | very slow circulation of a substance driven by differences in temperature and density within that substance |
| convergent plate boudary | boundary between two plates that are moving toward each other |
| conquina | limestone consisting of coarse shells |
| core | central zone of the Earth |
| correlation | determining time equivalency of rock units (rock units may be correlated within a region, a continent, and even between continents) |
| country rock | any rock that was older than and intruded by igneous rock |
| crater (volcano) | basinlike depression over a vent at the summit of a volcanic cone |
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