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The term phreatic is used in Earth sciences to refer to matters relating to ground water below the static water table
Water table

The water table is the level at which the ground water pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the Groundwater in a given vicinity....
 (the word originates from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 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
Pressure head

Pressure head is a term used in fluid mechanics to represent the internal energy of a fluid due to the pressure exerted on its container. It may also be called static pressure head or simply static head ....
 is zero). This surface normally coincides with the water table
Water table

The water table is the level at which the ground water pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the Groundwater in a given vicinity....
.

The phreatic zone is the layer(s) of soil or rock below the water table
Water table

The water table is the level at which the ground water pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the Groundwater in a given vicinity....
 in which voids are permanently saturated with groundwater
Groundwater

Groundwater is water located beneath the ground surface in soil porosity spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water....
, as opposed to the higher vadose zone
Vadose zone

The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the phreatic or zone of saturation ....
 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.






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The term phreatic is used in Earth sciences to refer to matters relating to ground water below the static water table
Water table

The water table is the level at which the ground water pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the Groundwater in a given vicinity....
 (the word originates from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 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
Pressure head

Pressure head is a term used in fluid mechanics to represent the internal energy of a fluid due to the pressure exerted on its container. It may also be called static pressure head or simply static head ....
 is zero). This surface normally coincides with the water table
Water table

The water table is the level at which the ground water pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the Groundwater in a given vicinity....
.

The phreatic zone is the layer(s) of soil or rock below the water table
Water table

The water table is the level at which the ground water pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the Groundwater in a given vicinity....
 in which voids are permanently saturated with groundwater
Groundwater

Groundwater is water located beneath the ground surface in soil porosity spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water....
, as opposed to the higher vadose zone
Vadose zone

The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the phreatic or zone of saturation ....
 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 eruption
Phreatic eruption

A Phreatic eruption, also called an ultravulcanian eruption, occurs when rising magma makes contact with ground water or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam resulting in an explosion of steam, water, ash, rock, and volcanic bombs....
s are certain types of extremely violent volcanic eruption
Volcano

A volcano is an opening, or rupture, in a planet's surface or Crust , which allows hot, molten rock, ash, and gases to escape from below the surface....
s resulting from the interaction of ground water and magma
Magma

Magma is molten Rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles....
.

See also

  • Aquifer
    Aquifer

    An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well....
  • Phreatic explosion
  • Phreatic surface
  • Phreatic zone
    Phreatic zone

    The phreatic zone , 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....
  • Water content
    Water content

    Water content or moisture content is the quantity of water contained in a material, such as soil , Rock , ceramics, or wood on a volumetric or gravimetric basis....