Limestone is the dominant underlying rock here instead of rhyolite, which is dominant in the park's other major hydrothermal areas.
... more » This area is one of the world's best examples of travertine-depositing hot springs. It's also one of the park's most dynamic hydrothermal areas; its features constantly change.
Inactive terraces underlie most of this area, including the hotel and Albright Visitor Center. Maximum water temperature is 163°F/73°C.
For hundreds of years, Shoshone and Bannock people collected minerals from Mammoth Hot Springs for white paint. These minerals contribute to the beautiful terrace structures, along with heat, a natural "plumbing" system, water, and limestone.
The volcanic heat source for Mammoth Hot Springs remains somewhat of a mystery. Scientists have proposed a number of sources, including the large magma chamber underlying the Yellowstone Caldera, or perhaps a smaller heat source closer to Mammoth.
At Mammoth, a network of fractures and fissures form the plumbing system that allows hot water from underground to reach the surface. The water comes from rain and snow falling on the surrounding mountains and seeping deep into the earth where it is heated. Small earthquakes may keep the plumbing open.
Limestone, deposited here millions of years ago when a vast sea covered this area, provides the final ingredient. Hot water with dissolved carbon dioxide makes a solution of weak carbonic acid. As the solution rises through rock, it dissolves calcium carbonate, the primary compound in limestone. At the surface, the calcium carbonate is deposited in the form of travertine, the rock that forms the terraces of Mammoth Hot Springs.
Thermophiles (heat-loving microorganisms) create tapestries of color where hot water flows among the terraces. Colorless and yellow thermophiles grow in the hottest water; orange, brown, and green thermophiles thrive in cooler waters. Colors also change with the seasons.
These terraces are like living sculptures, shaped by the volume of water, the slope of the ground, and objects in the water's path. They change constantly, and sometimes overnight—but the overall activity of the entire area and the volume of water discharge remain relatively constant.
Here, as in few other places on earth, rock forms before your eyes.
You can reach these terraces from boardwalks at their base or from Upper Terrace Drive. Some sections of boardwalk are wheelchair-accessible; the rest of the area has stairs or steep grades due to the terrain.
Upper Terrace Drive:
The entrance to the Upper Terrace Drive is two miles (3.2 km) south of the Albright Visitor Center on the Grand Loop Road. This one-way scenic drive winds for 1.5 miles (2.4 km) among hot springs and travertine formations.
Trailers, buses, and motor homes are prohibited on the drive due to limited parking and a narrow, winding roadway. Park these vehicles in the lot beside the Grand Loop Road, then enjoy the Upper Terraces on foot. Please stay on the road and boardwalks.
The information in this guide was taken from the Mammoth Hot Springs Area Trail Guide, which is available at the trailhead. Other sources of information include http://mms.nps.gov/yell/features/mammothtour/index.htm and http://www.yellowstonenationalpark.com/mammoth.htm