Yellowstone Hot Springs and Geysers 101

When water falls as snow or rain on the Yellowstone Plateau , it slowly percolates through layers of porous rock. Sinking to a depth of nearly 3300 meters (10000 feet), it comes in contact with the hot rocks of the magma chamber under the surface. The water is cooked and becomes superheated (200°C or 400°F) while remaining in its liquid state due to the pressure pushing down on it from rocks and water.
Because the superheated water is less dense, it starts its journey back to the surface, where it forms a hot spring when pressure and heat energy which gets released slowly.

Yellowstone Hot Spring | Location on map

While in underground, some of this silica contained in the water deposits on the walls of the underground “plumbing system” forming a pressure-tight seal. This seal locks in the hot water and breaks when the pressure gets high enough, producing a geyser. The most famous geyser in Yellowstone is undoubtedly the Old Faithful and is one of the most predictable geysers, shooting boiling water to a height of 44 to 56 meter more or less every 90 minutes.

Old Faithful, Yellowstone N.P. | Location on map