''Phreatic'' is a term used in
hydrology
Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is calle ...
to refer to aquifers, in
speleology to refer to cave passages, and in
volcanology
Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma and related geological, geophysical and geochemical phenomena (volcanism). The term ''volcanology'' is derived from the Latin word ''vulcan''. Vulcan was the anci ...
to refer to a type of volcanic eruption.
Hydrology
The term phreatic (the word originates from the
Greek , meaning "well" or "spring") is used in hydrology and the
earth sciences to refer to matters relating to ground water (an
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
) below the
water table
The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated.
T ...
. The term 'phreatic surface' indicates the location where the
pore water pressure
Pore water pressure (sometimes abbreviated to pwp) refers to the pressure of groundwater held within a soil or rock, in gaps between particles ( pores). Pore water pressures below the phreatic level of the groundwater are measured with piezometers. ...
is under atmospheric conditions (i.e. the
pressure head is zero). This surface normally coincides with the
water table
The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated.
T ...
. The slope of the phreatic surface is assumed to indicate the direction of ground water movement in an
unconfined aquifer.
The
phreatic zone, below the phreatic surface where rock and soil is saturated with water, is the counterpart of the
vadose zone
The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is fr ...
, or unsaturated zone, above. Unconfined
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
s are also referred to as phreatic aquifers because their upper boundary is provided by the phreatic surface.
Speleology
In
speleogenesis, a division of speleology, 'phreatic action' forms
cave
A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...
passages by dissolving the limestone in all directions, as opposed to '
vadose action', whereby a stream running in a cave passage erodes a trench in the floor. It occurs when the passage is full of water, and therefore normally only when it is below the water table, and only if the water is not
saturated
Saturation, saturated, unsaturation or unsaturated may refer to:
Chemistry
* Saturation, a property of organic compounds referring to carbon-carbon bonds
** Saturated and unsaturated compounds
**Degree of unsaturation
** Saturated fat or fatty ac ...
with
calcium carbonate or
calcium magnesium carbonate
Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomiti ...
. A cave passage formed in this way is characteristically circular or oval in cross-section as limestone is dissolved on all surfaces.
Many cave passages are formed by a combination of phreatic followed by vadose action. Such passages form a keyhole cross section: a round-shaped section at the top and a rectangular trench at the bottom.
Volcanology
A phreatic eruption or steam-blast eruption occurs when magma heats ground or surface water.
See also
*
Phreatic zone
*
Vadose zone
The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is fr ...
*
Water content
*
Index: Aquifer articles
References
External links
Aquifers
Cave geology
Hydrology
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