Yellowstone is well known for its many geysers, hot springs and other thermal features. In fact, more than half of all the thermal features in the world are located within the park. Some are bigger than others. Some, like Old Faithful, are named; others are not.
Geysers and hot springs are both fed by groundwater from rain and melted snow that seeps through cracks in the surface and is collected in porous rock underground. The water comes into contact with heat from magma chambers below Yellowstone, which warms the water and sends it back up towards the surface via networks of subterranean “plumbing.”
The big difference between a geyser and a hot spring is that a geyser has an obstruction in its hydrothermal plumbing near the surface. In hot springs, water is allowed to circulate to the surface and move freely, giving off steam and heat. In geysers, constrictions keep the boiling water underground. Steam pushes water upward towards the surface, causing a drop in pressure and a subsequent eruption.
Old Faithful is the most famous geyser at Yellowstone, and few thermals can match the beauty of the Grand Prismatic Spring, but there are plenty of amazing geyers, hot springs and other features in the park. The terraced, calcified limestone at Mammoth Hot Springs resembles a cave turned inside out. Curious mudpots bubble and gurgle, and fumaroles vent steam and gas from the earth at scalding temperatures that can reach 280 degrees Fahrenheit. Grand Geyser erupts in explosive bursts, and Steamboat, the largest geyser in the world, spouts water up to 400 feet in the air.