Yellowstone Net names fountain and cone geysers as the two principal types; geysers are hot springs that erupt periodically. Fountain geysers shoot water out in various directions through a pool. However, cone geysers shoot water out in a fairly narrow jet, usually from a cone-like formation.
Yellowstone Net lists geysers among the four basic types of thermal features in the park, along with hot springs, fumaroles and mudpots. It also mentions that Yellowstone contains the majority of the world's geysers, with more than 500 of the 10,000 thermal features classified as geysers. Upper, Midway, Lower, Norris, West Thumb, Shoshone and Heart Lake geyser basins feature the highest concentration of geysers in the park. Yellowstone Net explains that the eruptions result when the superheated water below the ground becomes trapped in channels leading to the surface. The bottoms of the channels contain the hottest temperatures, but the deep water doesn't vaporize because of the weight of the water above. This causes bubbles of steam to travel upward and collect in the channel’s tight spots until they essentially become clogged, which leads to the confined bubbles lifting the water above, causing the geyser to overflow. The pressure then decreases until the sudden violent boiling travels the column, producing a tremendous volume of steam that forces the water out of the vent in a superheated mass – hence an eruption.