Old Faithful, of course, is probably the most famous geothermic event in the world.
Located in Yellowstone National Park, Wyoming, Old Faithful is a cone geyser that gets its name from its regular eruptions, which occur every 60 to 90 minutes.
In spite of its name, the interval between Old Faithful's eruptions has actually changed over time. Since the earliest accounts from Western explorers in the 1870s, the time between each eruption has increased.
Old Faithful, Wyoming. Photo credit: Joelh085/Creative Commons