"Our best evidence is that the crustal magma chamber is filling with molten rock. But we have no idea how long this process goes on before there either is an eruption or the inflow of molten rock stops and the caldera deflates again," added Smith. Volcanic activity in Yellowstone heats up underground water which create geysers of superheated water, and is responsible for the creation and continuous eruption of Old Faithful.
There is a volcano in Yellowstone.