Craig Pass Closed for the Season; Mammoth to Norris Closed Sept. 14-30
The road linking West Thumb and Old Faithful is closed for the season—traffic should detour through West Thumb, Lake, and Canyon. The road from Mammoth to Norris is closed for two weeks—traffic should detour over Dunraven Pass. More »
How Geysers Work
For geyser to occur there must be heat, water, and a plumbing system. A magma chamber provides the heat, which radiates into surrounding rock. Water from rain and snow works its way underground through fractures in the rock.
As the water reaches hot rock it begins to rise back to the surface, passing through rhyolite, which is former volcanic ash or lava rich in silica. The hot water dissolves the silica and carries it upward to line rock crevices. This forms a constriction that holds in the mounting pressure, creating a geyser's plumbing system.
As superheated water nears the surface, its pressure drops, and the water flashes into steam as a geyser. Hot springs have unconstricted plumbing systems.
Did You Know?
You cannot fish from Fishing Bridge. Until 1973 this was a very popular fishing location since the bridge crossed the Yellowstone River above a cutthroat trout spawning area. It is now a popular place to observe fish.