Mud Volcano Trail

Yellowstone itself is a volcano, and one of its most spectacular eruptions occurred 640,000 years ago. During the eruption, the land collapsed and left a large depression in the earth—the Yellowstone Caldera. This caldera filled with lava flows over hundreds and thousands of years creating the volcanic plateau that comprises much of the central part of the park.

Here at Mud Volcano you are close to one of the resurgent domes. The hills you see east of here comprise Sour Creek Dome. Resurgent domes are areas of active ground deformation, where the land moves up or down with the fluctuation of the magma chamber below. Scientists monitor these domes closely for information about ongoing volcanic activity.

Not surprisingly, many of the park’s geysers, hot springs, mudpots, and fumaroles are also found near or within the caldera.

Details

Duration

1-2 Hours

This is a 0.6-mile (1 km) loop trail of boardwalks and pavement that begins and ends at the same parking lot, though at different trailheads.

Activity

Hiking

Easy, though there are a couple of steep sections.

Pets Allowed

No

Activity Fee

No

Entrance fees may apply, see Fees & Passes information.

Location

Mud Volcano

This trail is located 6 miles (10 km) north of Fishing Bridge.

Reservations

No

Season

Year Round

This area is accessible during the spring, summer, and fall when the main park road is open. In the winter, snowcoach tours may be able to taking tours to this area, though the trails will be covered in snow and ice.

Time of Day

Any Time

Accessibility Information

The southern part of the trail is paved, but it does have a steep grade to the top of the hill. The northern end of the loop has stairs going partway up the hillside. The smaller loop around Mud Volcano and Dragon's Mouth Spring meets federal guidelines for wheelchair accessibility, though there are stairs leading up to a viewing platform at Dragon's Mouth Spring.

Thermophiles in the mudpot create the sulfuric acid needed to break down the surrounding rock.

NPS/Diane Renkin

Area Facts

• One of the most acidic features in the park, Sulphur Caldron, is located here.
• The pungent odor of rotten eggs is caused by hydrogen sulfide gas.
• Near the greatest uplift and sinking of the caldera floor.
• Many faults converge here and earthquakes are common.

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.

Protect Yourself and Protect the Features

Hot Water • Thin Crust

Hydrothermal features are fragile rarities of nature. Yellowstone preserves the largest collection of hydrothermal features on the planet. You have an unparalleled opportunity to view hot springs, geysers, mudpots, and fumaroles in a natural setting. In order to protect these rarities for future enjoyment, please:

• Stay on boardwalks or trails in hydrothermal areas that are officially marked and maintained; for your safety and to protect fragile formations.
• Keep all objects out of features. Rocks, sticks, coins, and other objects can choke off water circulation and end all feature activity.
• Smoking is prohibited in Yellowstone’s hydrothermal areas.
• For their safety, do not bring pets into Yellowstone’s hydrothermal areas.
• It is illegal to pick flowers or collect rocks or other objects. You may not collect any natural or cultural objects or remove, deface, or destroy any plant, animal, or mineral in Yellowstone National Park.
• Never approach or feed wildlife. Bears and other wildlife may appear in areas frequented by people—on trails, on boardwalks, and along roads. Do not approach animals and remain at least 100 yards (92 meters) away from bears and wolves, and 25 yards (23 meters) away from all other wildlife.
• Toxic gases such as hydrogen sulfide and carbon dioxide have been measured in some hydrothermal features. If you feel sick, leave the location immediately.

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.