Measuring the tempo of Utah's red rock towers

You won't see them move, no matter how closely you watch. You won't hear their vibrations, even with your ear pressed to their cool sandstone.

But new research shows that the red rock towers found in southern Utah and throughout the Colorado Plateau are in constant motion, vibrating with signature rhythms as unique as their dramatic profiles against the depth of the blue desert sky.

The study is published in Seismological Research Letters and was funded by the U.S. National Science Foundation. "Geomorphologists study how the landscape changes over time," says Justin Lawrence, a program director in NSF's Division of Earth Sciences. "This study is an example of this fascinating field of inquiry."

University of Utah researchers know that rock towers and arches shimmy, twist and sway in response to far-off earthquakes, wind and even ocean waves. Their latest research compiles a first-of-its-kind dataset to show that the dynamic properties, the frequencies at which the rocks vibrate, and the ways they deform during vibration can be predicted using the same math that describes how beams in built structures resonate.

Knowing these properties is crucial to understanding the seismic stability of a rock tower and its susceptibility to hazardous vibrations. But it has been tough to get the needed data, partly because getting to the base of the towers often requires traveling through treacherous terrain -- and then someone must climb the towers to place a seismometer at the top.

Now, however, with the help of experienced climbers, researchers have measured the dynamic properties of 14 rock towers in Utah, creating a unique dataset with a variety of heights and tower shapes.

"This ability to make predictions about a tower's fundamental frequency using just the tower's width, height, and material properties is powerful because that means someone doesn't necessarily have to climb a 300-foot tower with a seismometer to get this information," says lead author Riley Finnegan. Knowing these properties is important for assessments related to the seismic stability of a tower or potential vibration damage, according to Finnegan.

"Some of the most rewarding times I have had in the field are times when I'm able to listen and imagine these towers in motion," says Jeff Moore, senior author on the paper. "We can't see or hear or feel their motion, but it is very real and is always happening. For me, this new perspective creates a renewed and intimate connection with the landscape."