File:Thermal image of Topsoil Spring (8 June 2016).jpg

English: The temperature scale is in degrees Fahrenheit.

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Hot springs are sites where groundwater emerges at the Earth’s surface (or on the seafloor). Hot spring water has to be higher in temperature than the human body (an admittedly arbitrary definition): over 98° Fahrenheit or over 37° Celsius. Geysers are hot springs that episodically erupt columns of water. The highest concentration of geysers and hot springs anywhere is at the Yellowstone Hotspot Volcano in northwestern Wyoming, USA.

Topsoil Spring is a small hot spring, about 1.3 x 1.6 meters in size, located in the Grand Group of Yellowstone’s Upper Geyser Basin. It is usually quiet, with a calm water surface. Yellowish-colored microbial mats can be present on the shallow floor of the spring. When the water is hotter, the microbial mats are absent. Occasionally, the pool’s water level is so low that only the central, funnel-shaped vent area is submerged. Topsoil’s activity includes roiling and overflowing (“eruptions”), with occasional subterranean thumping. Eruptions a few inches to 1 foot high have also been reported (Bryan, 2008, The Geysers of Yellowstone, Fourth Edition, p. 78).