Thing to Do

Mud Volcano Trail

Yellowstone National Park

People walk down a boardwalk towards a large plume of steam.

NPS / Addy Falgoust

Yellowstone National Park

Swirls of black, gray, and white in a bubbling mudpot.
Thermophiles in the mudpot create the sulfuric acid needed to break down the surrounding rock.

NPS/Diane Renkin

Makings of a Mudpot

The fascinating and mysterious mud features found here are some of the most acidic in the park. This acidity plays a part in making them different from most hot springs and geysers. Hydrogen sulfide gas is present deep in the earth at Mud Volcano. Some microorganisms use this gas as an energy source. They help convert the gas to sulfuric acid, which breaks down rock to clay. Hydrogen sulfide, steam, carbon dioxide, and other gases explode through the layers of mud in dramatic or delightful ways.

In contrast, the more alkaline waters in most of Yellowstone’s geyser basins react with underground rock to line subsurface cracks with silica, creating the natural “plumbing” systems of geysers and hot springs.

Sights, Smells, and Sounds

Listen to the sounds, notice the smell, and observe the colors of the Mud Volcano area. Much of what you sense comes from sulfur. It is present in many forms: hydrogen sulfide creates the area’s infamous aroma, microbes convert the hydrogen sulfide into an acid that dissolves rocks and soil, and sulfur minerals paint the features in hues of yellow and shades of gray.

Hydrothermal Area Wildlife

As you walk from feature to feature, look for wildlife. You may see marmots, Clark’s nutcrackers, mule deer, and elk. In the spring, grizzly bears feed on winter-killed animals.

Be especially alert for bison. Bison and their young frequent this area in large groups and will travel on the walkways if they choose. If you encounter a bison, be sure to stay 25 yards or more away from them, even if that means you must return the way you came. These magnificent animals appear tame and slow but are actually wild and quick.

During any time of year, do not approach—and never feed—bison, coyotes, birds, or other animals. Wild animals are dangerous and unpredictable.

Lightning strikes Electric Peak as a dark storm rolls over the mountain.
Yellowstone Backcountry Situation Report

Current conditions for Yellowstone National Park trails and campsites.

Bison walking along the road.
Safety in Yellowstone

Prepare yourself to safely enjoy wildlife, hydrothermal areas, and other features of Yellowstone National Park.

A bear biologist deploys bear spray during a demonstration.
Bear Spray

Read about this highly effective bear deterrent.

Hikers standing on the rocky top of Avalanche Peak with Yellowstone Lake in the background.
Yellowstone Day Hikes

Lace up your boots and explore some of the over 1,000 miles of trails in Yellowstone National Park.

Hikers rest and look out at Yellowstone Lake from atop a mountaintop.
Lake Area Day Hikes

Explore trails that traverse a variety of Yellowstone ecosystems and provide stunning views of Yellowstone Lake.

Last updated: December 6, 2024