Zion National Park's Weeping Rock closed indefinitely after report suggests future danger

A rockfall in late August dumped 435,712 cubic feet of debris onto Weeping Rock trail and nearby trails at Zion National Park and a new report from the Utah Geological Survey finds similar rockfalls could happen at any time in the area.

“With annual visitation exceeding 4.3 million in 2018, the likelihood of geologic hazards affecting park visitors and infrastructure continues to rise,” the survey states.

The rockfall occurred around 5:30 p.m. on Aug. 24, 2019, injuring three visitors. A piece of Navajo sandstone weighing over 31,000 tons, broke off Cable Mountain, about 3,000 feet above Weeping Rock. The rockfall caused an avalanche of debris to fall on the Weeping Rock trailhead parking lot, the trail itself, Hidden Canyon trail, East Rim trail, with some rocks flowing across the Zion Canyon Scenic Drive to the Virgin River.

Researchers conducting the survey found no definite cause for this particular incident but indicated that triggers of rockfalls include precipitation, snowmelt, seismic events and "thermal cycling." Since this rockfall happened on a warm day at the end of August, geologists say thermal cycling is most likely the reason behind the rockfall.

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"As the day warms up, [rock slabs] separate from the rockface wall, and when it cools it contracts back down. It's millimeters but over time that can cause more fractures," Ben Erickson, a geologist that worked on the survey, said.

The survey found various rock slabs in the same area that could potentially fall along Cable Mountain cliff face. Many are "unstable" and could fall at any point.

Funding for the survey conducted by the Utah Geological Survey came partially from the park's nonprofit partner, the Zion Forever Project.

Indefinite closures

Park officials have said that the trails affected by this rockfall will be closed to hikers indefinitely. Cass Bromley, the chief of resource management and research for the park, said the area is still experiencing lots of movement from precipitation and colder weather. She said the park is "letting winter and water do its work."

Zion was formed through centuries of rockfalls and flooding. Balancing the natural processes with keeping the public safe is a priority for the park, according to Bromley.

“This is a place where geology happens,” Bromley said. “Canyon carving isn’t a past tense thing.”

When the rockfall occurred in August, Hidden Canyon was closed at the time of the rockfall, which the survey states "undeniably saved lives."

Record-setting numbers, despite closed trails

Park visitation numbers have been climbing in recent years, and there is no sign of stopping. In the last 10 years, yearly park visitor numbers have more than doubled. But how many people is too many people?

"There are definitely limits to how many people can be in an area and still enjoy the area and get what they're trying to get from Zion," Eugenne Moisa, a park spokesperson said.

I can't figure out how to embed the original graphic that has the increase in visitors of the past few years.

With the high number of visitors coming to the park, especially during the peak summer months, managing the crowds has been on the minds of park officials. Creative solutions to handling the crowds are in the works — like tracking real-time visitor numbers and updating the visitor use management plan for the park.

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But several trails remain closed, pushing the high number of visitors into a smaller area of the park. Here are the trails that are currently closed:

Weeping Rock trail

Hidden Canyon trail

Observation Point trail (East Rim from Weeping Rock)

Lower Emerald Pools trail is closed until spring 2020

Staying safe

Erickson said that there's no way to definitively say the area is "completely safe," given the nature of the canyon. According to the survey, "rockfall is the most frequent mass wasting process in Zion National Park."

The survey recommends the park estimate the rockfall risks in the area, then avoid building structures and limit access to hazardous rockfall areas as much as possible. Additionally, the survey said the park can accept the risk of the rockfalls and make an effort to make individuals aware of the hazard, for example by using signage.

Bromley said the park is going through the data provided in the survey before making a final decision on how the park will go forward with making the vulnerable area accessible.

But educating the public about the canyon nature of the canyon, and its constant shifting can help make people aware of the dangers of the park, Erickson said.

"I enjoy looking at [the canyon] and experiencing it. But I'm also aware of the potential danger I'm getting into," Erickson, who spent time in the park working on the survey, said. "You can't be afraid of the canyon, but you can be aware of the risk."

Lexi Peery is the environment, politics and development reporter for The Spectrum & Daily News, a USA TODAY Network newsroom based in southern Utah. You can reach her at lpeery@thespectrum.com and follow her on Twitter @LexiFP.