| Term | Definition |
|---|
| aquiclude | A relatively impermeable bed that bounds an aquifer above or below and acts as a barrier to the flow of groundwater. |
| aquifer | A bed that stores and transmits groundwater in sufficient quantity to supply wells. |
| artesian flow | A water flow produced by the greater pressure of groundwater in a confined aquifer than in an unconfined aquifer. |
| Darcy's law | A summary of the relationsips among the volume of water flowing through an aquifer in a certain time, the vertical drop of the flow, the flow distance, and the permeability of the aquifer. |
| discharge | 1) the volume of groundwater leaving an aquifer in a given time. 2)The volume of water that passes a given point in a given time as it flows through a channel of a certain width and depth. |
| groundwater | The mass of water stored beneath Earth's surface. |
| groundwater table | The boundary between the unsaturated zone and the saturated zone. |
| hydraulic gradient | The ratio between the difference in elevation of the groundwater table at two points and the flow distance that the water travels between those two points. |
| hydrologoic cycle | The cyclyical movement of water from the ocean to the atmosphere by evaporation, to the surface through rain, to strams through runoff and groundwater, and back to the ocean. |
| hydrology | The science that studies the movements and characteristics of water on and under Earth's surface. |
| hydrothermal water | Hot water in the crust. |
| infiltration | The movement of groundwater or hydrothermal water into rock or soil through pores and joints. |
| karst topography | An irregular hilly terrain characterized by sink holes, caverns, and a lack of surface streams; formed in regions of high rainfall with extensively jointed limestone formations and an appreciable hydraulic gradient. |
| meteoric water | Rain, snow, or other forms of water derived from the atmosphere. |
| permeability | The ability of a solid to allow fluids to pass through it. |
| potable water | Water that tastes agreeable and is not dangerous to health. |
| rain shadow | An area of low rainfall on the leeward slope of a mountain range. |
| recharge | The infiltration of water into any subsurface formation, often by rain or snow meltwater form the surface. |
| relative humidity | The amount of water vapor in the air, expressed as a percentage of the total amount of water the air could hold at that temperature if saturated. Whe nteh relative humidity is 50 percent and the temperature is 15 C, for example, the amount of moistrue in the air is one-half the maximum amount the air could hold at 15 C. |
| reservoir | 1) A place in which water is stored, including the oceans; glaciers and polar ice; groundwater; lakes and rivers; the atmosphere; and the biosphere. 2) A geochemical reservoir: a place of residence for elements in a geochemical cycle. |
| runoff | The sum of all rainwater that flows over the surface, including the fraction that may temporarily infiltrate near-surface formations and then flow back to the surface. |
| saturated zone | The level in the groundwater table in which the pores of the soil or rock are completely filled with water. |
| sinkhole | A small, steep depression in the land surface above a cavernous limestone formation. |
| unsaturated zone | The level in the groundwater table in which the pores of the soil or rock are not completely filled with water. |
| ablation | The total amount of ice that a glacier loses each year. |
| accumulation | The amount of snow added to a glacier annually. |
| basal slip | The sliding of a glacier along its base. |
| cirque | An amphitheater-like hollow, usually shaped like half of an inverted cone, formed at the head of a glacial valley by the plucking and tearing action of ice. |
| continental glacier | A thick, extremely slow moving sheet of ice that covers a large part of the continent. |
| crevasse | A large vertical crack in the surface of a glacier caused by the movement of brittle surface ice as it is dragged along by the plastic flow of the ice below. |
| drift | All material of glacial origin found anywhere on land or at sea. |
| drumlin | A large streamlined hill of till and bedrock that parallels the direction if ice movement in a continental glacier terrain. |
| esker | A long, narrow, winding ridge of sand and gravel found in the middle of a ground moraine. |
| fjord | A former glacial valley with steep walls and a U-shaped profile, now occupied by the sea. |
| glacier | A large mass of ice on land that shows evidence of being in motion or of once having moved. |
| hanging valley | A valley left by a melted tributary glacier that enters a larger glacial valley above its base, high up on the valley wall. |
| iceberg calving | The process by which pieces of ice break off and from icebergs when a glacier reaches a shoreline. |
| ice shelf | Sheets of ice floating on hte ocean that are attached to a continental glacier on land; common on the periphery of Antarctica. |
| ice stream | A current of ice in a continental glacier that flows faster than the surrounding ice. |
| kettle | A hollow or undrained depression that often has steep sides and may be occupied by ponds or lakes; formed in glacial deposits when outwash was deposited around a residual block of ice that later melted. |
| moraine | An accumulation of rocky, sandy, and clayey material carried by glacial ice and deposited as till. |
| outwash | Drift that has been caught up and modified, sorted, and distributed by meltwater streams. |
| permafrost | A permanently frozen aggregate of ice and soil occuring in very cold regions. Any rock or soil remaining at or below 0 C for two or more years. |
| plastic flow | The total of all the small movements of the ice crystals that make up a glacier, resulting in a large movement of the whole mass of ice. |
| striation | A scratch or groove left on bedrock and boulders by overriding ice, showing the direction of glacial motion. |
| surge | A sudden period of fast movement of a valley glacier, sometimes occurring after a long period of little movement and lasting several years. |
| till | An unstratified and poorly sorted sediment contianing all sizes of fragments from clay to boulders and deposited by glacial action. |
| tillite | Ancient lithified till. |
| U-shaped valley | A deep valley with steep upper walls that grade into a flat floor; the typical shape of a valley eroded by a glacier. |
| valley glacier | A river of ice that forms in the cold heights of mountain ranges where snow accumulates, usually in preexisting valleys, and flows down the bedrock valleys. |
| varve | A pair of alternating coars and fine layers formed in one year by the seasonal freezing of a lake surface. |
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