“…How,ever, the same general considerations apply. Superhydrostatic pressures in shallow steam zones have been observed at The Geysers (up to approximately 150% of hydrostatic at 150 m depth) [Allen and Day, 1927], Matsukawa (M. Hanano, unpublished data, 1986), Mud Volcanoes, Yellowstone (approximately 125% of hydrostatic at 106 m depth) [White et al, 1971], and Svartsengi, Iceland, where a "steam cap" is forming in response to exploitation [Gudrnundsson and Thorhallsson, 1986]. The stability of the "liquid over steam" configuration at the top of the vapor-dominated zone has been considered something of an enigma, though Schubert and Straus [1980] showed that this configuration will be stable in a medium with a uniform low permeability (< 4 x 10-• ?…”