''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 call ...

to refer to aquifers, in

speleology Speleology is the scientific study of caves and other karst features, as well as their make-up, structure, physical properties, history, life forms, and the processes by which they form ( speleogenesis) and change over time (speleomorphology) ...

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 an ...

to refer to a type of volcanic eruption.

Hydrology

The term phreatic (the word originates from the

Greek Greek may refer to: Greece 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 ...

, 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 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 characteris ...

) 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 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 normally coincides with the

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

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 ...

. The

phreatic zone The phreatic zone, saturated zone, or zone of saturation, is the part of an aquifer, below the water table, in which relatively all pores and fractures are saturated with water. Above the water table is the unsaturated or vadose zone The v ...

, 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 f ...

, or unsaturated zone, above. Unconfined

s are also referred to as phreatic aquifers because their upper boundary is provided by the phreatic surface.

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 presenc ...

, 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 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 ...

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 or calcium magnesium carbonate. 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.

References

External links

Aquifers Cave geology Hydrology {{geology-stub

Hydrology

Speleology

Volcanology

See also

References

External links