Aerial view of Black Sand Basin. NPS photo.

Access to Yellowstone National Park’s Black Sand Basin will be temporarily closed until at least the Memorial Day weekend while maintenance crews replace and reroute a section of boardwalk that has been damaged by the area’s thermal features.

The closure will include the entire boardwalk around the basin as well as the associated public parking area. Trails leading into the basin will also be signed and marked to protect visitors. It is unsafe and illegal to enter a closed thermal area in the park.

Black Sand Basin, a popular geothermal area located in the park’s Upper Geyser Basin near Old Faithful, has more than 300 feet of boardwalk that safely guides visitors through attractions such as Sunset Lake and Rainbow Pool. However, as the “plumbing” underneath Yellowstone’s thermal features constantly changes, so too must the boardwalks that are carefully and strategically placed over their surfaces.

Approximately 120 feet of Black Sand Basin boardwalk that has been damaged by extremely hot, acidic thermal waters will be rebuilt and rerouted using a combination of untreated Douglas Fir wood decking and treated composite framing materials. An additional 200 feet of deck planking on the remaining boardwalk throughout the basin will also be replaced in stages, with half being completed during this project and the remaining half completed the following summer.

Wooden boardwalks in Yellowstone -- of which the park has more than 14 miles, or almost 74,000 feet! -- can last up to 30 years, depending upon conditions such as weather exposure, thermal feature influence and wear and tear by the hundreds of thousands of visitor feet that cross over them every day. ADA-approved ramps and other accessible features are also incorporated into outdated boardwalks when repairs are due.

Black Sand Basin’s boardwalk is nearly 22 years old, making it a prime candidate for repair. And whether they’re made of wood or experimental recycled composite plastic, as in the case of the Old Faithful boardwalk, their careful placement serves not only as a reminder of the respect due to the forces of Mother Nature, but of the constant flux of Yellowstone’s geologic personality.

Using thermal mapping technologies, park geologists monitor the best areas to place boardwalks that keep visitors safe, but still provide the most up-close and personal experience possible with the thermal feature.

“We use cutting edge technology and work collaboratively with park maintenance crews, landscape architects and law enforcement to protect not only our visitors, but also Yellowstone’s wonderfully dynamic geothermal processes that move and change daily right before our eyes,” said Yellowstone chief geologist Henry Heasler. “So rather than build a permanent boardwalk around a spring or geyser, we continually move it, shape it, replace and re-route it, so that the springs can move where they wish and visitors can still follow them along.”

Yellowstone will announce when the basin will re-open in late May.