The term phreatic (the word originates from the Greek phrear, phreat- 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.
A cave passage formed in this way is characteristically circular or oval in cross-section as limestone is dissolved on all surfaces.
Such passages form a keyhole cross-section: a round-shaped section at the top and a rectangular trench at the bottom.
A phreatic or steam-blast eruption occurs when magma heats ground or surface water.
Phreatophytes are deep-rooted plants that obtain a significant portion of the water that it needs from the phreatic zone or near it.