GEYSER PERIODICITY AND THE RESPONSE OF GEYSERS TO DEFORMATION

Numerical simulations of multiphase fluid and heat transport through a porous medium define combinations of rock properties and boundary con ditions which lead to geyser-like periodic discharge. Within the rathe r narrow range of conditions that allow geyser-like behavior, eruption frequency and discharge are highly sensitive to the intrinsic permeab ilities of the geyser conduit and the surrounding rock matrix, to the relative permeability functions assumed, and to pressure gradients in the matrix. In theory, heat pipes (concomitant upward flow of steam an d downward flow of liquid) can exist under similar conditions, but our simulations suggest that the periodic solution is more stable. Simula ted time series of geyser discharge are chaotic, but integrated quanti ties such as eruption frequency and mass discharge per eruption are fr ee of chaos. These results may explain the observed sensitivity of nat ural geysers to small strains such as those caused by remote earthquak es, if ground motion is sufficient to induce permeability changes. Cha nges in geyser behavior caused by minor preseismic deformation, period ic surface loading, and Earth tides are more difficult to explain in t he context of our current model.