You dip your toe into a tranquil pool of water, expecting it to be refreshingly cool. It is not, however - the water is hot, warmer than the ambient temperature of the air and even than your body temperature. Even in winter, when the banks of the pool are covered in ice and snow, the water within is steaming. Sometimes, hot water bubbles forth, making the water turbulent. What natural forces cause this strange phenomenon?
What Is a Hot Spring?
A hot spring, also called a thermal spring or geothermal spring, is a naturally occurring spring of water, hotter than 98 degrees Fahrenheit (36.7 degrees Celsius) when it flows from the ground. The water in a hot spring is warmed by contact with hot rocks beneath the Earth's surface, rocks that have been heated by nearby magma.
These phenomena generally form near areas of volcanic activity. However, they can form in non-volcanic areas as well, if geological features allow groundwater to sink deep enough that it can be heated by rocks near the Earth's mantle.
They may flow slowly, seeping into a still pool, or quickly, forming a small river. Some hot springs release great amounts of pressure, expelling water similar to a geyser.
When the water in a hot spring mixes with dirt or clay before it reaches the surface, the spring is called a mud pot. Mud pots are often highly acidic, bubbling pools. When minerals in the mixture cause the mud to be brightly colored, it is called a paint pot. Mud pots and paint pots can be found in the United States and Europe.
The Ecology of Hot Springs
Some animals take advantage of the warmth of natural hot springs in order to survive cold winter temperatures. In Japan, for example, troops of monkeys called macaques or snow monkeys live in a very cold area, where snow is present for much of the year. They have been observed entering and bathing in the hot springs, even in spa areas frequented by humans.
Some are also home to thermophiles - tiny prokaryotic, single celled organisms similar to bacteria that thrive in hot water. These thermophiles, also called extremophiles, may cause the water to be stained in striking colors.
Recently, scientists identified microscopic organisms known as Archaea living deep within a hot spring in Idaho. The scientists found that these organisms are able to survive without access to oxygen or carbon, and have given scientists reason to believe organisms can live in conditions that are typically thought of as hostile to life on other planets and moons.
Are Hot Springs Dangerous to Humans?
Many hot springs have become tourists attractions. In Japan, for example, spas are built around the natural springs - called onsen - so that people can relax in the warm water. Some people feel that the warmth, along with the high mineral content of the water, is good for one's health. People with skin conditions, muscular problems, or joint pain often visit hot springs for this reason.
There are, however, springs so hot that contact with the water could result in burns or even death. Volcanic hot springs, such as those in Yellowstone National Park in the United States, may heat water past the boiling point. Some springs also contain naturally occurring chemicals that are harmful to humans.
Well-known Hot Springs around the world
Hot springs are located in various places all over the world, from snowy mountains to the tropics. The following are some of the most unique hot springs.
- Grand Prismatic Spring. This hot spring is located in Yellowstone National Park. It is the largest hot spring in the world - it is 300 feet (91 meters) wide and 160 feet (49 meters) deep. The spring is called prismatic because it seems to display all the colors of the rainbow - deep blue in its center, changing to green, yellow, orange and red near its banks. This coloration is caused by the presence of algae and thermophile bacteria.
- Blood Pond. This spring is located in Japan, and the water is bright red in color, resembling blood. The redness is caused literally by rust, as there are high concentrations of iron in the water.
- Jigokudani. Located in Japan's Nagano Prefecture, this spring is nestled in an area of volcanic activity. It is famous for the snow monkeys that bathe in the hot springs.
- Pamukkale. The word pamukkale means "cotton castle" in the Turkish language. It describes the white, cascading deposits of travertine that beautify this hot spring.
- Hammam Debagh. Located in Algeria, the water from this spring cascades over a cliff. White mineral deposits along the cliff face resemble waterfalls. The water from Hammam Debagh is hot enough to boil an egg.
- Hot Springs, Arkansas This city in southwest Arkansas was built around a number of hot springs, where bath houses were built to provide supposed health benefits. Today, eight bath houses still remain and one of these, the Buckstaff, continues to operate.