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Yellowstone Caldera

Geological Places

Yellowstone National Park is a remarkable geological wonderland located primarily in the U.S. state of Wyoming, with parts extending into Montana and Idaho.

It is known for its geothermal features, including geysers, hot springs, and other unique geological formations.

Geological Activity

Yellowstone’s geological features are a result of its location atop a supervolcano, and within the Yellowstone Caldera. This caldera is a massive volcanic depression formed from past volcanic eruptions and collapse events.

Hotspot Volcanism

The park’s geothermal and volcanic activity is closely linked to a hotspot in the Earth’s mantle. This hotspot, like the Hawai’i Volcanoes, has led to a series of volcanic eruptions and the thermal features seen in the park today.


One of the most famous aspects of Yellowstone is its geysers, including the iconic Old Faithful. Geysers erupt due to the buildup of steam and pressure in underground chambers, caused by heated groundwater interacting with magma deep within the Earth’s crust.

Old Faithful got its name by being regular in it’s eruptions. An eruption happens on average every 91 minutes. The geyser releases between 3,700 and 8,400 gallons of boiling hot water, in a column reaching about 145 feet.

Hot Springs

Yellowstone’s many colorful hot springs are formed by geothermally heated water rising to the surface more slowly than in the geysers, into small basins. The spring water contains minerals that promote bacteria and algal growth that gives rise to the vibrant colors seen in the pools, with each color corresponding to different microbial communities. These communities are made up of thermophiles, organisms that can, and often only, live in the extreme heat of the pools.

Mud Pots

Mud pots are another geothermal feature in Yellowstone. These bubbling pools of mud are formed when hot water interacts with clay-rich sediments, creating a mixture that appears to boil due to the escaping gases. This is similar to watching soup boiling slowly on the stove.


Fumaroles are steam vents that release gases and steam directly into the atmosphere. These vents result from the intense heat of the volcanic activity and the interaction between water and hot rocks. They lack enough water to be called a geyser but are similar otherwise.

Yellowstone Caldera

The Yellowstone caldera spanning a significant portion of the park, is a remnant of past volcanic eruptions. These massive eruptions had a profound impact on the surrounding landscape and even affected global climates.

The last eruption was about 6 to 700,000 years ago and covered much of North America with a layer of ash. Evidence of three eruptions have been found, about two million and 1 million years ago. The volcano is quite old, as volcanoes go, so is not currently expected to erupt again. That, of course is subject to change.

Lava Flows and Geology

The park’s geological history includes lava flows, volcanic rocks, and the formation of the Grand  Canyon of the Yellowstone River, which was carved by the river’s erosional action.

The park’s geothermal activity leads to extensive hydrothermal alteration of rocks, creating unique landscapes such as terraces of mineral deposits around hot springs.

Earthquake Activity

Yellowstone experiences frequent earthquakes due to the movement of magma beneath the surface. While most earthquakes are minor reflecting ongoing geological processes within the park. There are around 2,000 earthquakes in Yellowstone each year. Yellowstone is a highly visited park. Many millions of visitors enter the volcanic caldera each year. Park closures are infrequent, but crowding is not. Check with the park website to plan any visit. And don’t pet the fluffy cows.