ST. GEORGE — Officials at Zion National Park are continuing to monitor the area above the Weeping Rock shuttle stop in the main canyon where a massive rockslide injured three people and left several others momentarily stranded in August 2019.
At approximately 5:30 p.m. on Aug. 24, 2019, a large slab of Navajo Sandstone detached from Cable Mountain nearly 2,000 vertical feet above the Weeping Rock parking lot, according to a Jan. 10 post on the Zion National Park Facebook page.
The rockfall indefinitely closed several popular hiking trails including Weeping Rock trail, Hidden Canyon trail and Observation Point trail.
Utah Geological Survey geologists recently completed an investigation of the rockfall site, classifying the slide as a small rock avalanche due to its flow-like qualities and its calculated volume.
The investigation into the slide concluded the mass of the slide was approximately 31,000 tons, and the estimated volume of the slide was 435,712 cubic feet (12,338 cubic meters).
That volume of material would fill up a football field 7.5 feet deep, the park’s post said.
Though the investigation into the slide didn’t conclude that there were any specific triggering events, it did point to thermal cycling as one probable factor in the cause of the rockfall.
“Zion Canyon is a dynamic place where geology is in action,” according to a Jan. 18 post on the park’s Facebook page regarding the rockfall.
With the investigation concluded, many are eager to know when and if the park will begin cleanup efforts and reopen the trails.
Zion National Park’s chief of resources and research Cass Bromley said the park is continuing to monitor the slide area and are figuring out what cleanup efforts will look like if and when they happen.
Currently, park officials are allowing nature — rain, snowmelt and gravity — to move some of the material down the steep slope where the slide occurred, Bromley said.
It is the same nature that shaped Zion Canyon, the Jan. 18 post said.
Monitoring will continue through the winter and spring, Bromley said, as materials move and shift, exposing some parts of the trails while burying others. For now, the trails will remain indefinitely closed.
Bromley said the park hasn’t seen any noticeable decline in visitation due to the trail closures, but that they have noticed a shift in the dispersing of visitors as they head toward trails that remain open.
In addition to the trails affected by the August 2019 rockfall, the Lower Emerald Pools trail on the canyon’s west side is closed for repairs until spring.
The Utah Geological Survey investigation was funded by the Zion National Park Forever Project which is the nonprofit partner of Zion National Park.
“When the fall had initially occurred, it became apparent that deeper research was going to be needed to understand the impact,” Zachary Almaguer, marketing and communications manager for the Zion Forever Project, said.
As the park’s nonprofit partner, the forever project is guided by the needs of the park, and in this case, funding the geological survey, Almaguer said.
Going forward, he said the Zion Forever Project will allow the park to lead them as they continue to provide support and funding for the critical rockslide area.
“Once they have determined what the resolution will be, and the solution will be going forward, we will support them in that,” Almaguer said.
While Zion’s dynamic geology is continually changing, Almaguer said it is the goal of the forever project to support critical programs that maintain the margin of excellence visitors expect when they enter the park.
The entire Utah Geological Survey’s report can be read here.
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