Phreatic

Phreatic is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption.

==Hydrology== The term phreatic (the word originates from the Greek , meaning "well" or "spring") is used in hydrology and the earth sciences to refer to matters relating to groundwater (an aquifer) below the water table. The term 'phreatic surface' indicates the location where the pore water pressure is under atmospheric conditions (i.e., the pressure head is zero). This surface usually coincides with the water table. The slope of the phreatic surface is assumed to indicate the direction of groundwater movement in an unconfined aquifer.