Phreatic
Phreaticis a term used inhydrologyto refer to aquifers, inspeleologyto refer to cave passages, and involcanologyto refer to a type of volcanic eruption.
Hydrology
[edit]The termphreatic(the word originates from theGreekphrear,phreat-meaning "well" or "spring" ) is used in hydrology and theearth sciencesto refer to matters relating to ground water (anaquifer) below thewater table.The term 'phreatic surface' indicates the location where thepore water pressureis under atmospheric conditions (i.e. thepressure headis zero). This surface normally coincides with thewater table.The slope of the phreatic surface is assumed to indicate the direction of ground water movement in anunconfined aquifer.
Thephreatic zone,below the phreatic surface where rock and soil is saturated with water, is the counterpart of thevadose zone,or unsaturated zone, above. Unconfinedaquifersare also referred to as phreatic aquifers because their upper boundary is provided by the phreatic surface.
Speleology
[edit]Inspeleogenesis,a division of speleology, 'phreatic action' formscavepassages by dissolving the limestone in all directions,[1]as opposed to 'vadoseaction', whereby a stream running in a cave passage erodes a trench in the floor.[2]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 notsaturatedwithcalcium carbonateorcalcium magnesium carbonate.A cave passage formed in this way is characteristically circular or oval in cross-section as limestone is dissolved on all surfaces.[3]
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
[edit]A phreatic eruption or steam-blast eruption occurs when magma heats ground or surface water.
Biology
[edit]Animals living within the phreatic zone of groundwater aquifers can be referred to asphreatobites.[4]They are usuallyisopodoramphipodcrustaceans such as species ofStygobromus,though there is also a genus of snails (Phreatodrobia) andPhreatobiusare a genus ofcatfishliving within flooded leaf litter. Alternative descriptions for such animals includestygobite,[5]troglobiteor Interstitial animals, as they live in waterbetweenthe particles of the floodedsubstrate.They usually exhibittroglomorphism,with a loss of colour and eyesight, like the familiarblind cavefishwhich may also be referred to as 'phreatic fish'.
Such animals can often be found inwells,where human pursuit of water has dug down into their habitat.
See also
[edit]- Phreatic zone– Zone in an aquifer below the water table
- Vadose zone– Unsaturated aquifer above the water table
- Water content– Quantity of water contained in a material
- Category: Aquifer articles
References
[edit]- ^New Mexico: Bureau of Mines & Mining Bulletin 117 (Part I: Discussion of Deposits and Events)
- ^"Glossary of Cave-Related Terms".Upper Cumberland Grotto Home Cave.Retrieved13 November2010.
- ^John A. Webb & Stanley Lithco (September 2001).Use of water chemistry to identify flow conduits in the porous Gambier Limestone, southeast Australia(PDF).7th Conference on Limestone Hydrology and Fissured Media. France: Universite de Franche-Comte, Sciences & Techniques de l'Environnement. pp. 333–336.ISBN2-905226-14-5.Retrieved13 November2010.
Passages are usually narrow vertical fissures, but phreatic tubes, circular or oval in cross-section, are present in some caves...
[permanent dead link] - ^"Glossary: Phreatobite".Speleogenesis.UIS Commission on Karst Hydrogeology and Speleogenesis.
- ^"Glossary: Stygobite".Speleogenesis.UIS Commission on Karst Hydrogeology and Speleogenesis.
External links
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