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Geology exam 2
Ch. 16, 17, 19
| Term | Definition |
|---|---|
| Natural hazard | A natural feature of the environment that can cause injury to living organisms and/or damage to buildings and the landscape. |
| Rock glacier | A slow-moving mixture of rock fragments and ice. |
| Landslide | A sudden movement of rock and debris down a nonvertical slope. |
| Avalanche | A turbulent cloud of debris mixed with air that rushes down a steep hill slope at high velocity; the debris can be rock and/or snow. |
| Creep | The gradual downslope movement of regolith. |
| Mass movement (mass wasting) | The gravitationally caused downslope transport of rock, regolith, snow, or ice. |
| Solifluction | The type of creep characteristic of tundra regions; during the summer, the uppermost layer of permafrost melts, and the soggy, weak layer of ground then flows slowly downslope in overlapping sheets. |
| Substrate | A general term for material just below the ground surface. |
| Failure surface | A weak surface that forms the base of a landslide. |
| Slump | Downslope movement in which a mass of regolith detaches from its substrate along a spoon-shaped, sliding surface and slips downward semicoherently. |
| Mudflow (mudslide) | A downslope movement of mud at slow to moderate speed. |
| Debris flow | A downslope movement of mud mixed with larger rock fragments. |
| Head scarp | The distinct step along the upslope edge of a slump where the regolith detached. |
| Lahar | A thick slurry formed when volcanic ash and debris mix with water, either in rivers or from rain or melting snow and ice on the flank of a volcano. |
| Debris slide | A sudden downslope movement of material consisting only of regolith. |
| Rockslide | A sudden downslope movement of rock. |
| Talus | A sloping apron of fallen rock along the base of a cliff. |
| Turbidity current | A submarine avalanche of sediment and water that speeds down a submarine slope. |
| Submarine slump | The underwater downslope movement of a semicoherent block of sediment along a weak mud detachment. |
| Slope failure | The downslope movement of material on an unstable slope. |
| Angle of repose | The angle of the steepest slope that a pile of uncemented material can attain without collapsing from the pull of gravity. |
| Quick clay | Clay that behaves like a solid when still (because of surface tension holding the water-coated clay flakes together) but that flows like a liquid when shaken. |
| Undercutting | Excavation at the base of a slope that results in the formation of an overhang. |
| Liquefaction | The process by which saturated, unconsolidated sediments are transformed into a substance that acts like a liquid as a result of ground shaking. |
| Landslide-potential map | A map on which regions are ranked according to the likelihood that a mass movement will occur. |
| Riprap | Loose boulders or concrete piled together along a beach to absorb wave energy before it strikes a cliff face. |
| Stream | A ribbon of water that flows in a channel. |
| Channel | A trough dug into the ground surface by flowing water. |
| Flood | An event during which the volume of water in a stream becomes so great that it covers areas outside the stream's normal channel. |
| Headwaters | The beginning point of a stream. |
| Mouth | The outlet of a stream where it discharges into another stream, a lake, or a sea. |
| Sheetwash | A film of water less than a few mm thick that covers the ground surface during heavy rains. |
| Headward erosion | The process by which a stream channel lengthens up its slope as the flow of water increases. |
| Downcutting | The process in which water flowing through a channel cuts into the substrate and deepens the channel relative to its surroundings. |
| Tributary | A smaller stream that flows into a larger stream. |
| Drainage network | An array of interconnecting streams that together drain an area. |
| Trunk stream | The single larger stream into which an array of tributaries flow. |
| Drainage divide | A highland or ridge that separates one watershed from another. |
| Continental divide | A highland separating drainage that flows into one ocean from drainage that flows into another. |
| Watershed | The region that collects water that feeds into a given drainage network. |
| Permanent stream | A stream that flows year-round because its bed lies below the water table, or because more water is supplied from upstream than can infiltrate the ground. |
| Ephemeral stream | A stream whose bed lies above the water table, so that the stream flows only when the rate at which water enters the stream from rainfall or meltwater exceeds the rate at which water infiltrates the ground below. |
| Discharge | The volume of water in a conduit or channel passing a point in 1 second. |
| Pothole | A bowl-shaped depression carved into the floor of a stream by a long-lived whirlpool carrying sand or gravel. |
| Scouring | A process by which running water removes loose fragments of sediment from a streambed. |
| Turbulence | The chaotic twisting, swirling motion in flowing fluid. |
| Thalweg | The deepest part of a stream's channel. |
| Abrasion | The process in which one material (such as sand-laden water) grinds away at another (such as a stream channel's floor and walls). |
| Dissolved load | Ions dissolved in a stream's water. |
| Bed load | Large particles, such as sand, pebbles, or cobbles, that bounce or roll along a streambed. |
| Delta | A wedge of sediment formed at a river mouth when the running water of the stream enters standing water, the current slows, the stream loses competence, and sediment settles out. |
| Suspended load | Tiny solid grains carried along by a stream without settling to the floor of the channel. |
| Competence | The maximum particle size a stream can carry. |
| Bar | (1) A sheet or elongate lens or mound of alluvium; |
| Longitudinal profile | A cross-sectional image showing the variation in elevation along the length of a river. |
| Point bar | A wedge-shaped deposit of sediment on the inside bank of a meander. |
| Alluvium | Sorted sediment deposited by a stream. |
| Stream gradient | The slope of a stream's channel in the downstream direction. |
| Capacity | The total quantity of sediment a stream can carry. |
| Base level | Uplift of basement rock by faults that penetrate deep into the continental crust. |
| Graded stream | A stream that has attained an equilibrium longitudinal profile in which the sediment input into an area equals sediment removal. |
| Rapid | A reach of a stream in which water becomes particularly turbulent; as a consequence, waves develop on the surface of the stream. |
| Canyon | A trough or valley with steeply sloping walls, cut into the land by a stream. |
| Valley | A trough with sloping walls, cut into the land by a stream. |
| Stream terrace | When a stream downcuts through the alluvium of a floodplain so that a new, lower floodplain develops and the original floodplain becomes a step-like platform. |
| Meandering stream | A reach of stream containing many meanders (snakelike curves). |
| Braided stream | A sediment-choked stream consisting of entwined subchannels. |
| Meander | A snake-like curve along a stream's course. |
| Alluvial fan | A gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions. |
| Oxbow lake | A meander that has been cut off yet remains filled with water. |
| Natural levee | A pair of low ridges that appear on either side of a stream and develop as a result of the accumulation of sediment deposited naturally during flooding. |
| Floodplain | The flat land on either side of a stream that becomes covered with water during a flood. |
| Distributary | The fan of small streams formed where a river spreads out over its delta. |
| Stream piracy | A process that happens when headward erosion by one stream causes the stream to intersect the course of another stream and capture its flow. |
| Drainage reversal | When the overall direction of flow in a drainage network becomes the opposite of what it once had been. |
| Stream rejuvenation | The renewed downcutting of a stream into a floodplain or peneplain, caused by a relative drop of the base level. |
| Superposed stream | A stream whose geometry has been laid down on a rock structure and is not controlled by the structure. |
| Antecedent stream | A stream that cuts across an uplifted mountain range; the stream must have existed before the range uplifted and must then have been able to downcut as fast as the land was rising. |
| Seasonal flood | Floods that appear almost every year during seasons when rainfall is heavy or when winter snows start to melt. |
| Flash flood | A flood that occurs during unusually intense rainfall or as the result of a dam collapse, during which the floodwaters rise very fast. |
| Floodway | A mapped region likely to be flooded, in which people avoid constructing buildings. |
| Annual probability | The likelihood that a flood of a given size or larger will happen at a specified locality during any given year. |
| Recurrence interval | The average time between successive geologic events. |
| Flood-hazard map | A representation of a portion of the Earth's surface that is designed to show how the danger of flooding varies with location. |
| Sinkhole | A circular depression in the land that forms when an underground cavern collapses. |
| Groundwater | Water that resides under the surface of the Earth, mostly in pores or cracks of rock or sediment. |
| Pore | A small, open space within sediment or rock. |
| Porosity | The total volume of empty space (pore space) in a material, usually expressed as a percentage. |
| Permeability | The degree to which a material allows fluids to pass through it via an interconnected network of pores and cracks. |
| Aquitard | Sediment or rock that does not transmit water easily and therefore retards the motion of the water. |
| Aquifer | Sediment or rock that transmits water easily. |
| Water table | The boundary, approximately parallel to the Earth's surface, that separates substrate in which groundwater fills the pores from substrate in which air fills the pores. |
| Capillary fringe | The thin subsurface layer in which water molecules seep up from the water table by capillary action to fill pores. |
| Soil moisture | Underground water that wets the surface of the mineral grains and organic material making up soil, but lies above the water table. |
| Perched water table | A quantity of groundwater that lies above the regional water table because an underlying lens of impermeable rock or sediment prevents the water from sinking down to the regional water table. |
| Discharge area | A location where groundwater flows back up to the surface and may emerge at springs. |
| Recharge area | A location where water enters the ground and infiltrates down to the water table. |
| Hydraulic head | The potential energy available to drive the flow of a given volume of groundwater at a location; it can be measured as an elevation above a reference. |
| Spring | A natural outlet from which groundwater flows up onto the ground surface. |
| Darcy's law | A mathematical equation stating that a volume of water, passing through a specified area of material at a given time, depends on the material's permeability and hydraulic gradient. |
| Hard water | Groundwater that contains dissolved calcium and magnesium, usually after passing through limestone or dolomite. |
| Hydraulic gradient | The slope of the water table. |
| Artesian spring | A location where the ground surface intersects a natural fracture (joint) that taps a confined aquifer in which the pressure can drive the water to the surface. |
| Oasis | A verdant region surrounded by desert, occurring at a place where natural springs provide water at the surface. |
| Cone of depression | The downward-pointing, cone-shaped surface of the water table in a location where the water table is experiencing drawdown because of pumping at a well. |
| Artesian well | A well in which water rises on its own. |
| Hot spring | A spring that emits water ranging in temperature from about 30°C to 104°C. |
| Geothermal region | A region of current or recent volcanism in which magma or very hot rock heats up groundwater, which may discharge at the surface in the form of hot springs and/or geysers. |
| Geyser | A fountain of steam and hot water that erupts periodically from a vent in the ground in a geothermal region. |
| Contaminant plume | A cloud of contaminated groundwater that moves away from the source of the contamination. |
| Groundwater contamination | Addition of chemicals or microbes (e.g., from agricultural and industrial activities, and landfills or septic tanks) to the groundwater supply. |
| Speleothem | A formation that grows in a limestone cave by the accumulation of travertine precipitated from water solutions dripping in a cave or flowing down the wall of a cave. |
| Stalactite | An icicle-like cone that grows from the ceiling of a cave as dripping water precipitates limestone. |
| Stalagmite | An upward-pointing cone of limestone that grows when drips of water hit the floor of a cave. |
| Disappearing stream | A stream that intersects a crack or sinkhole leading to an underground cavern, so that the water disappears into the subsurface and becomes an underground stream. |
Created by:
jabflat
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