Bubbling upward,the steam expands as it near the top of the water column.At a critical point, the confined bubbles actually lift the water above, causing the geysers to splash or overflow.this decreases pressure on the system, and violent boiling results.Tremendous amounts of steam force water out of the vent, and an eruption begins.Water is expelled faster than it can enter the geyser's plumbing system, and the heat and pressure gradually decrease.The eruption stops when the water reservoir is depleted or when the system cool.