Silence preceds the eruption. Then the ground beneath you rumbles, shaking loose dust and debris from the cavernous ceiling above. Rocks come rattling down the cavern walls. A groan issues from the earth itself, forecasting the explosion to come. And just as the rumbling reaches its zenith, the geyser erupts, issuing a steaming hot pillar of water into the air hundreds of feet and splashing against the cavern ceiling. It rains down in a mist.