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| A subsurface rock or sediment unit that is porous and permeable. To be an aquifer it must have these traits to a high enough degree that it stores and transmits useful quantities of water. |
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| The volume of pore space in a rock, sediment or soil. Usually expressed as a percentage. This pore space can include openings between grains, fracture openings and caverns. |
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evapotranspiration [image] |
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| All methods of water moving from a liquid to water vapor in nature. Includes both evaporation and transpiration. |
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artesian formation [image] |
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| Water added to an aquifer or other water body. An aquifer is recharged by precipitation in an area where the aquifer has a porous connection to the surface. |
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| A budget of the incoming and outgoing water from a region, including rainfall, evaporation, runoff, and seepage; often used to estimate |
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| A budget of the incoming and outgoing water from a region, including rainfall, evaporation, runoff, and seepage; often used to estimate |
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A thick hydrosphere is thought to exist around the Jovian moon Europa. The outer layer of this hydrosphere is almost entirely frozen, but current models predict that there is an ocean up to 100 km in depth underneath the ice. This ocean remains in a liquid form due to tidal flexing of the moon in its orbit around Jupiter. |
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| A layer of rock, sediment or soil that does not allow water to pass through. This could be caused by a lack of pore space or pore spaces that are so small that water molecules have difficulty passing through |
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| The Earth's water is always in movement, and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth. Since the water cycle is truly a "cycle," there is no beginning or end. |
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| The water table is the level at which the ground water pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the ground water in a given vicinity. It usually coincides with the phreatic surface, but can be many feet above it. As water infiltrates through pore spaces in the soil, it first passes through the zone of aeration, where the soil is unsaturated. At increasing depths water fills in more spaces, until the zone of saturation is reached. The relatively horizontal plane atop this zone constitutes the water table. |
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| A measure of how well a material can transmit water. Materials such as gravel, that transmit water quickly, have high values of permeability. Materials such as shale, that transmit water poorly, have low values. Permeability is primarily determined by the size of the pore spaces and their degree of interconnection. Permeability measures are expressed in units of velocity, such as centimeters per second, and assume a gradient of one vertical foot of drop per linear foot. |
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