The geothermal areas of Yellowstone include several geyser basins in Yellowstone National Park as well as other geothermal features such as hot springs, mud pots, and fumaroles. The number of thermal features in Yellowstone is estimated at 10,000 and 200 to 250 geysers erupt in Yellowstone each year, making it the place with the highest concentration of active geysers in the world, thanks to its location in an ancient active caldera. Many of these features build up sinter, geyserite, or travertine deposits around and within them.