University of Utah Department of Geology & Geophysics

Helicopters might be weakening Utah’s arches and towers, U. study finds

By Carter Williams, KSL.com | Posted - Dec. 26, 2019 at 9:20 p.m.


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SALT LAKE CITY — Are helicopter flights damaging Utah’s arches and other red rock features?

Perhaps not immediately, but a new University of Utah study presented at the American Geophysical Union Fall Meeting in San Francisco earlier this month found that helicopters are creating vibrations in Utah’s natural features that are upwards of 100 times stronger than they normally would experience.

While those vibrations aren’t “instantaneously damaging,” researchers say it’s concerning when you consider there are thousands of helicopter flights over Utah’s national parks each year. They say the number of flights might be weakening the natural land features.

Riley Finnegan, a University of Utah graduate student and a co-author of the study, presented the findings during a press conference posted online Dec. 12. She explained that the results centered around something called infrasound, or a really low-frequency sound. A common blade helicopter produces 13 hertz, which she said a human couldn’t perceive but can, they found, measure at “quite high powers.”

“This infrasound has been able to cause different arches and towers to resonate at vibrations that are 100 times stronger than they typically do,” Finnegan said. “Some studies have shown that towers can vibrate at potentially damaging levels.”

For their experiment, Finnegan and two other U. researchers traveled to a handful of Utah’s different arches, towers and hoodoos mostly on land owned by the Bureau of Land Management. She said the Native American Consultation Committee originally posed the question whether multiple helicopter flights were damaging Rainbow Bridge National Monument, but the group expanded its focus to cover other features.

An undated photo of Rainbow Bridge National Monument in the Lake Powell area of southern Utah. (Photo: University of Utah Department of Geology & Geophysics)

While there, they measured the infrasound from a Bell 206 helicopter and the impact it had on the different features by using broadband seismometers and nodal geophones that tracked the movement of five sandstone arches and six sandstone towers, according to the study’s abstract.

Finnegan said they found a helicopter’s speed, distance from the features, number of blades and its angle can result in different infrasound, while the size, shape and material of an arch can factor in how much a rock feature is affected.

She used Two Bridges, an arch in southern Utah, as an example in the presentation. In that case, the helicopter flew about 2,000 feet above the feature.

“Yet we see an increase of vibrations of 100 times, which is quite a lot for the helicopter being so far away,” she said.

The group’s abstract says these vibrations don’t cause immediate harm, but there is still cause for concern.

“The geographic reach of helicopters is virtually unlimited and many well-known landforms experience regular overflights, validating concerns that sustained exposure to anthropogenic airborne energy may result in adverse structural degradation of culturally significant landforms over time,” the group wrote in its abstract.

The group’s findings are just the most recent discovery in researching the natural and manmade movement of Utah’s red rock region. They published a paper in the Bulletin of the Seismological Society of America that showed how Castleton Tower in Grand County naturally sways in August.

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The study presented in December shows more of the impact humans may have on the region. Finnegan said the results mean a lot for Utah, where the features are a “very culturally valuable resource."

“We have over 6,000 documented around the state and an entire national park dedicated to how great these features are,” she said. “Additionally, Native American groups in the southwest desert region consider arches sacred, so we want to make sure we aren’t inadvertently affecting the health of these really precious features.”

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Carter Williams

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