Introduction

Geothermal features can be observed in areas of active volcanism, or areas that have inactive volcanoes. Subsurface magma heats groundwater, creating steam and hot water. The hot, less dense water rises through fissures and cracks in the ground. When it reaches the surface, features such as geysers, fumaroles, hot springs, and mud pits are created.

Geothermal features have great benefits. Geothermal processes create heat and electricity that provide power and hot water to cities in Iceland, New Zealand, Italy and Northern California. As well as being used for energy sources, geothermal waters can also contain minerals and elements such as sulfur, gold, silver, and mercury that can be recovered and used.

Geothermal/Hydrothermal Features

• Hot springs are heated by geothermal heat—heat from the Earth's interior. In volcanic areas, water may come into contact with very hot rock heated by magma. Hot springs in active volcanic zones may produce superheated water, so hot that immersion can result in injury or death. In non-volcanic areas, the temperature of rocks within the Earth also increases with depth—this temperature increase is known as the Geothermal Gradient. If water percolates deeply enough into the crust, it comes into contact with hot rocks and can circulate to the surface to form hot springs.
• Geysers are the most well known geothermal feature. Each geyser has unique characteristics due to complex internal plumbing. Generally, geysers require that large amounts of groundwater fill underground cavities in an area of volcanic activity. The water in these deep cavities is heated by nearby magma. Suddenly, some of the water flashes into steam and expands rapidly. The overlying water column is forced violently from the vent in an explosion of hot water and steam. This cycle can be repeated regularly. Old Faithful is a geyser in Yellowstone National Park that has erupted once every 65 minutes for hundreds of years!
• Fumaroles are also geothermal features that depend on the interactions of released volcanic gases and the local groundwater system. These occur in areas where a magma conduit passes through the water table. The magma can be liquid or recently solidified, but still hot. The heat from the magma causes water to become steam. As the steam rises it carries volcanic gases such as hydrogen sulfide (H2S) to the surface. This mixture of steam and gas is erupted from vents and fissures in the ground. Due to this chemical activity, fumaroles can be very dangerous. Associated chemical reactions can color the surrounding rocks. Areas with fumarole features are sometimes called "dying volcanoes" because they occur near the end stages of volcanic activity as the magma deep underground solidifies and cools.
• Mudpots are surface features that occur when limited amounts of geothermal water is mixed with mud and clay. Acid and bacteria in the water can dissolve surrounding rock forming viscous pools of bubbling mud.

Featured Video—Yellowstone Geysers

Energy

Geothermal Energy is one component of Renewable Energy and is often considered to be a clean source for heat and generation of electricity. In the National Park System, the infrastructure and drilling required for utility-scale geothermal energy development can be at odds with the primary preservation and recreation mission of the NPS. Many park units are also specifically named in the Geothermal Steam Act and receive additional monitoring and protection.

Stories From Around the NPS

Earth scientists from many disciplines are working to improve the Park Service's ability to gather, analyze, and use geoscience information.

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