Questions About Heat Flow and Geothermal Energy at Yellowstone
How hot is Yellowstone?
Yellowstone is a plateau high in the Rocky Mountains, and is snowbound for over six months per year. The mean annual temperature is 2.2°C, barely above the freezing point of water. However, Yellowstone is also an active geothermal area with hot springs emerging at ~92°C (the boiling point of water at Yellowstone's mean altitude) and steam vents reported as high as 135°C. Only about 0.3% of the park's terrain is thermal ground, so most places are no hotter than anywhere else in the Rockies.
In some of Yellowstone's thermal areas, heat flow is over 100 watts per square meter, about 50 times that of Yellowstone's average and ~2000 times that of average North American terrain. This enormous heat flow is derived from the molten rock or magma in the crust beneath the caldera, which ultimately is generated by the Yellowstone Hot Spot, a partly molten region of the Earth's mantle hundreds of kilometers beneath the surface.
What is heat flow?
The term "heat flow" refers to the heat that is transmitted from the hot interior of Earth to the surface in a specified time across a specified area.
How is heat released in Yellowstone?Earth's heat is released in Yellowstone by two main processes, conduction and convection:
- Conduction is the movement of heat from hotter material to colder material. A common example of conduction is when heat from a stove is transferred through the bottom of a coffee pot to the liquid inside. Conduction in Yellowstone helps transfer heat from deep within Earth to shallower depths. Of the heat released from the ground at Yellowstone, about 25% is by conduction.
- Convection is heat transported by hot material in motion, such as hot water or magma. Convection happens inside a coffee pot when heat is carried to the top of the liquid in the pot by hot water that rises buoyantly from the heated bottom because it is less dense than overlying cooler water. As the water boils, the rise of the hotter water and the compensating fall of cooler water from the top forms what is called a convection cell. Convection of molten rock helps carry heat up through the Yellowstone caldera. Near the surface, convection of hot ground water drives geysers, hot springs, and fumaroles. Convection accounts for roughly 75% of the heat released from the ground at Yellowstone.
Can we use the heat from Yellowstone for energy?
Geothermal energy, heat energy from the earth's interior, is used to generate electricity in a variety of places throughout the world. Although Yellowstone and its surroundings are a significant geothermal resource, the Park itself is off limits to development. Because geothermal developments often cause a decrease in flow of nearby hot springs and other geothermal features, it is questionable whether anyone could get permission to develop geothermal energy in the region outside the park.
There are other natural heat sources in the United States that are being used for geothermal energy. Typically, hot water or steam is tapped from a deep reservoir through a geothermal drillhole. The fluid is then expanded through a turbine to generate electricity. In California, there are about 4 to 5 GW of electricity generated at power plants at The Geysers, Salton Sea, Coso, Casa Diablo and other geothermal systems. This is enough to provide energy for several million people. There are also power plants in Nevada, Utah, and Hawaii. Geothermal power is also used in many others countries. The Geothermal Education Office has a good website with lots of information about geothermal energy, its uses, and the output of different geothermal systems. The U. S. Geological Survey also has an educational and well-illustrated booklet on geothermal energy.