Phreatic

Phreatic

The term phreatic is used in Earth sciences to refer to matters relating to ground water below the static water table (the word originates from the Greek "phrear", "phreat-" meaning "well" or "spring"). The term phreatic surface is where the hydrostatic pressure of groundwater or soil moisture is atmospheric (or pressure head is zero). This surface normally coincides with the water table.

The phreatic zone is the layer(s) of soil or rock below the water table in which voids are permanently saturated with groundwater, as opposed to the higher "vadose zone" in which the pore spaces are not completely filled with water.

Phreatic action forms cave 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. Phreatic action usually takes place when the passage is below the water table (although it may happen if the passage is full of water and not saturated with calcium carbonate or calcium magnesium carbonate). A cave passage formed in this way is characteristically circular 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.

Phreatic eruptions are certain types of extremely violent volcanic eruptions resulting from the interaction of ground water and magma.

See also

*Aquifer
*Phreatic explosion
*Phreatic surface
*Phreatic zone
*Water content


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Look at other dictionaries:

  • Phreatic — Phre*at ic, a. [F. phr[ e]atique, from Gr. ?, ?, a well.] (Geol.) Subterranean; applied to sources supplying wells. [1913 Webster] …   The Collaborative International Dictionary of English

  • phreatic — [frē at′ik] adj. Geol. of, having to do with, or being groundwater …   English World dictionary

  • phreatic — /free at ik/, adj. Geol. 1. noting or pertaining to ground water. 2. noting or pertaining to explosive volcanic activity involving steam derived from ground water: a phreatic explosion. [1890 95; < Gk phreat (s. of phréar) artificial well + IC] * …   Universalium

  • phreatic cave —    1. Cave conceived and developed by dissolution, usually below the water table, where all voids are water filled within the phreas. Phreatic caves may include loops deep below the water table, particularly in dipping limestone with widely… …   Lexicon of Cave and Karst Terminology

  • Phreatic eruption — A Phreatic eruption, also called an ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma (anywhere from 600 °C to 1,170 °C (1110–2140 °F)) causes near instantaneous… …   Wikipedia

  • phreatic eruption — ALASKA VOLCANO OBSERVATORY GLOSSARY An explosive volcanic eruption caused when water and heated volcanic rocks interact to produce a violent expulsion of steam and pulverized rocks. Magma is not involved. GLOSSARY OF VOLCANIC TERMS A steam… …   Glossary of volcanic terms

  • Phreatic zone — The phreatic zone (from Ancient Greek phrear, phreat a well ), or zone of saturation, is the area in an aquifer, below the water table, in which relatively all pores and fractures are saturated with water. The phreatic zone may fluctuate with… …   Wikipedia

  • phreatic water —    That part of the underground water in a karst limestone which lies within the zone of permanently saturated rock the phreatic zone. Caves formed within this zone are known as phreatic caves [19].    See phreas …   Lexicon of Cave and Karst Terminology

  • phreatic lift —    An active or abandoned phreatic conduit that carries or carried water upwards in a downstream direction [9] …   Lexicon of Cave and Karst Terminology

  • phreatic zone —    1. Those parts of the earth’s crust in which all voids are filled with water under pressure greater than atmospheric [22].    2. That part of the earth’s crust beneath the regional water table in which all voids, large and small, are ideally… …   Lexicon of Cave and Karst Terminology

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