As Kathryn Vollinger prepares to climb Castleton Tower, a 120-meter-tall sandstone formation in the desert near Moab, Utah, an outdoor guide evaluates her gear. rope? Check. Helmets and seat belts? Check. Climbing frame? Check. On that day in March 2018, Wallinger’s list also included an unusual piece of equipment: a seismograph. This excursion is not just for fun. It’s also for science.
Castleton Tower and its counterparts may still appear. But these towering geological structures are in constant motion, vibrating with earthquakes, human activity and even distant ocean waves. The same goes for fins, which are irregularly shaped rock formations rather than cylindrical or rectangular towers, says Riley Finnegan, a geophysicist at the University of Utah in Salt Lake City.
Seismographs measure the degree to which towers and fins vibrate naturally.The data is key to assessing the stability of the formation and can even help researchers look for possible signs in the rock seismic activity in the distant past (SN: March 15, 2006).
These insights are important not only to scientists, but also to Native Americans, including the Eastern Shoshone, Hopi, Navajo, Southern Paiute, Ute and Zuni. Many of the features located on the traditional lands of these groups have cultural and religious significance, Finnegan said.
Finnegan’s team worked with Vollinger for nearly five years to assemble The first dataset on the dynamic physical properties of 14 towers and finsthe researchers reported on February 16 in Seismic Research LettersFinnegan said the project would not have been possible without an experienced climber like Vollinger.
Collecting data is a huge challenge. Climbing the toughest formations safely requires climbing chops, strength, stamina, and a lot of planning. “I was willing to take such a big risk in order to install these seismometers,” Vollinger said. “It adds another element when you haul extra gear.”
Vollinger and her climbing partner, husband Nathan Richman, had to make sure the wall was vertical enough to avoid dragging equipment. Dragging “may knock off loose rocks,” she said. Once Wallinger reaches the top of a formation — after one to six hours of climbing — she reads a book or chats with her husband while the seismometer collects data. Then they dragged back the instruments and other gear.
Back at the University of Utah, Finnegan and colleagues analyzed the data and found that the structure’s lowest natural frequency, called the fundamental frequency, ranged from 0.8 to 15 hertz. In other words, the towers swing about 1 to 15 times per second.
The team also used computer models to study the way formations bend and twist at a given frequency. These simulations help provide a more complete understanding of how physics affects the behavior of towers and fins, Finnegan said.
What’s more, inputting the formation’s height, density, cross-sectional area, and other material properties into the model, the formation’s fundamental frequency can be predicted.
Findings ‘strengthen our understanding of height and width dependencies’ [fundamental frequencies] said Ramon Arrowsmith, a geologist at Arizona State University who was not involved in the work. Finnegan and her colleagues have shown that “the geometry is sufficient to really discuss the dominant frequencies of strut behavior.”
Ultimately, such a model could eliminate the need for climbers to deploy seismometers to measure frequencies. If future scientists need seismic measurements, Arrowsmith envisions robots putting seismometers in place and drones flying over to collect data. But for now, Wallinger will continue to expand the scientific use of these formations.