A hot spring, also known as a hydrothermal spring or geothermal spring, is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma or by circulation through the Earths crust. There is no universally accepted definition of a hot spring, but it can be defined as any spring heated by geothermal activity, a spring with water temperatures above its surroundings, a natural spring with water temperature above human body temperature, or a natural spring of water whose temperature is greater than 21°C (70°F) . Hot springs can vary in temperature and characteristics, and they can be found in both volcanic and non-volcanic areas.

Some key features of hot springs include:

• Temperature: Hot springs have water temperatures that are substantially higher than the air temperature of the surrounding region. The temperature of hot springs can vary widely, from just above human body temperature to superheated water that can result in injury or death.

• Formation: Hot springs are developed when hot water is forced back up through fissures and cracks by the combination of extreme temperatures and high pressure deep under the Earth.

• Thermophilic microorganisms: Many of the colors in hot springs are caused by heat-loving microorganisms, such as certain types of bacteria, archaea, and algae. These microorganisms derive their energy from various chemicals and metals and can grow in huge colonies called mats that form the colorful scums and slimes on the sides of hot springs.

Hot springs are popular tourist destinations because they are believed to have medicinal, therapeutic, and overall healing powers. Some hot springs are safe for bathing, while others are too hot and dangerous for human contact. Warm springs are natural swimming areas that are temperate for getting in but arent hot enough to be considered a hot spring.