What is the difference between a geyser and a hot spring?

Water is ejected explosively in a geyser. 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.