Cold-water geyser

Mechanism

In cold-water geysers, the supply of CO₂-laden water lies confined in an aquifer, in which water and CO₂ are trapped by less permeable overlying strata. The more familiar hot-water geysers derive the energy for their eruptions from the proximity to (relatively) near-surface magma. In contrast, whereas cold water geysers might also derive their supply of CO₂ from magmatic sources, by definition of "cold-water", they do not also obtain sufficient heat to provide steam pressure, and their eruptions are propelled only by the pressure of dissolved CO₂. The magnitude and frequency of such eruptions depend on various factors such as plumbing depth, CO₂ concentrations and refresh rate, aquifer water yield, etc.

The water and its load of CO₂ powering a cold-water geyser can escape the rock strata overlying its aquifer only through weak segments of rock, like faults, joints, or drilled wells. A borehole drilled for a well, for example, can unexpectedly provide an escape route for the pressurized water and CO₂ to reach the surface. The column of water rising through the rock exerts enough pressure on the gaseous CO₂ so that it remains in the water as dissolved gas or small bubbles. When the pressure decreases due to the widening of a fissure, the CO₂ bubbles expand, and that expansion displaces the water above and causes the eruption.