Fly Geyser. View of the continually erupting Fly Geyser in the Black Rock Desert, Nevada, USA. Geysers are eruptions of underground water through holes in the ground. The calcite travertine cones are artificial, having formed around pipes put into the ground by an abortive mining operation. Similarly the surrounding pools, which contain green, algae-covered terraces (foreground), were formed by dredging. In this area, hot volcanic rock heats the base of a column of subsurface water forming steam. As steam takes up a larger volume than water, the water above is pushed out at the surface. The reduced pressure on the water remaining underground causes it to boil and erupt.