A key requirement that enables a geyser to erupt is a material called geyserite found in rocks nearby the geyser. Geyserite—mostly silicon dioxide (SiO2), is dissolved from the rocks and gets deposited on the walls of the geyser's plumbing system and on the surface. The deposits make the channels carrying the water up to the surface pressure-tight. This allows the pressure to be carried all the way to the top and not be leaked out into the loose gravel or soil that are normally under the geyser fields.