''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 drainage basin sustainability. A practitioner of hydrology is called a hydro ...

to refer to aquifers, in

speleology Speleology () is the scientific study of caves and other karst features, as well as their chemical composition, composition, structure, physical property, physical properties, history, ecology, and the processes by which they form (speleogenes ...

to refer to cave passages, and in

volcanology Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma and related geology, geological, geophysical and geochemistry, geochemical phenomena (volcanism). The term ''volcanology'' is derived from the Latin language, Latin ...

to refer to a type of volcanic eruption.

Hydrology

The term phreatic (the word originates from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

, meaning "well" or "spring") is used in hydrology and the

earth sciences Earth science or geoscience includes all fields of natural science related to the planet Earth. This is a branch of science dealing with the physical, chemical, and biological complex constitutions and synergistic linkages of Earth's four spheres ...

to refer to matters relating to groundwater (an

aquifer An aquifer is an underground layer of water-bearing material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...

) below the

water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...

. 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 (geology), rock, in gaps between particles (soil pore, pores). Pore water pressures below the phreatic level of the groundwater are ...

is under atmospheric conditions (i.e., the

pressure head In fluid mechanics, pressure head is the height of a liquid column that corresponds to a particular pressure exerted by the liquid column on the base of its container. It may also be called static pressure head or simply static head (but not ''sta ...

is zero). This surface usually coincides with the

. The slope of the phreatic surface is assumed to indicate the direction of groundwater movement in an

unconfined aquifer An aquifer is an underground layer of water-bearing material, consisting of permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The study of water flow in aquifers ...

. The

phreatic zone The phreatic zone, saturated zone, or zone of saturation, is the part of an aquifer, below the water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractur ...

, below the phreatic surface where rock and soil are saturated with water, is the counterpart of the

vadose zone The vadose zone (from the Latin word for "shallow"), 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 ...

, or unsaturated zone, above. Unconfined

s are also called phreatic aquifers because the phreatic surface provides their upper boundary.

Speleology

speleogenesis Speleogenesis is the origin and development of caves, the primary process that determines essential features of the hydrogeology of karst and guides its evolution. It often deals with the development of caves through limestone, caused by the prese ...

, a division of speleology, 'phreatic action' forms

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

passages by dissolving the limestone in all directions, as opposed to '

vadose The vadose zone (from the Latin word for "shallow"), 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 ...

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 with

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

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 (see Dolomite (rock)). An alternative name sometimes ...

. 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 action 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 or steam-blast eruption occurs when magma heats ground or surface water.

Biology

Phreatobite Phreatobites are animals living within the phreatic zone of groundwater aquifers. They are usually isopod or amphipod crustaceans such as species of '' Stygobromus'', though there is also a genus of snails ('' Phreatodrobia'') and '' Phreatobius'' ...

s'' are animals living within the phreatic zone of groundwater aquifers. ''

Phreatophyte A phreatophyte is a deep-rooted plant that obtains a significant portion of the water that it needs from the phreatic zone (zone of saturation) or the capillary fringe above the phreatic zone. Phreatophytes are plants that are supplied with sur ...

s'' are deep-rooted plants that obtain a significant portion of the water that it needs from the phreatic zone or near it.

References

External links