Definition of phreatic in US English:



  • 1Relating to or denoting underground water in the zone of saturation (beneath the water table).

    Compare with vadose
    • ‘Gravitational sediments can enter a cave system in the form of entrance talus material, colluvium, roof fall, or phreatic infiltrates.’
    • ‘In the case of the Kendrick Formation, however, the system was closed by early compaction of surrounding clays, and diagenesis apparently occurred in a marine phreatic environment.’
    • ‘In 1990 John Cordingley found that the sump had disappeared and that the passage continued along a tube to a step up into a small phreatic rift.’
    • ‘For example, they may occur in the continental realm above the water table - the vadose zone; or in the permanently shallow saturated zone - the phreatic zone, in either freshwater or marine conditions.’
    • ‘Conversely, grainstone fabrics of the upper sequences show the development of bladed and equant calcite cement around oolites, indicative of a primary cementation in a freshwater phreatic environment.’
    1. 1.1 (of a volcanic eruption) caused by the heating and expansion of groundwater.
      • ‘This type of eruption, called a phreatic eruption, is characterized by a volcanic crater that goes beneath the level of the surrounding landscape and is encircled by a wide, low ring of volcanic debris.’
      • ‘That in 4390 was large and complex, with eruptions at the central vent and radial fissures on the flank, submarine and phreatic eruptions, and pyroclastic flows.’
      • ‘Eruptions after 26 October 1986 were phreatic steam explosions, not direct expressions of magma.’
      • ‘This eruption began in July 1995 with phreatic explosions following 3 years of precursory seismic activity.’
      • ‘The characteristic tuffs of the Balder Formation originate from phreatic eruptions from the incipient continental rift zone between Eurasia and Greenland to the west.’


Late 19th century: from Greek phrear, phreat- ‘a well’ + -ic.