Old Faithful, one of the world’s most famous geysers, received its name due to its predictive eruptions. However, the formation of a geyser is more interesting than any geyser’s eruption pattern.
A geyser is a hole, commonly referred to as a vent, in the surface of the Earth that occasionally emits a vertical column of hot water and/or steam.
Four conditions are required for a geyser to form: Subsurface presence of volcanic temperatures, ample source of groundwater, a reservoir of subterranean water fissures, or tubes, which provide access to the surface through the vent.
Normal Steam Conditions
Above ground steam is produced as water evaporates at boiling temperatures (100 F); thereby, consuming much more space than originally occupied. However, as groundwater seeps below the surface it becomes trapped and cannot expand.
Subsurface Water in a Geyser
Eventually, the subsurface water reaches a volcanic source and the water becomes superheated. The water cannot expand; therefore, producing extremely high-pressure beneath the Earth’s surface.
Blowing the Geyser
Below surface, the superheated water enters a ground fissure. The high-pressure then shoots the water out of a vent; thus, producing a massive column-like eruption of steam and water at the surface.