Waves of incision from Cataract Canyon help carve Canyonlands | Natalie M. Tanksi
Those that float the Colorado River through Canyonlands have likely observed that, as you approach the confluence of the Green River and Colorado River and continue downstream, the canyon walls are arched upward and falling apart. Big chunks of rock fall into the river, creating a choke point to form the rapids of Cataract Canyon.
This change in canyon character has been attributed to a complex dance between the deepening canyon and a thick, underlying layer of salt (the Pennsylvanian Paradox Formation). As the river flow cuts the canyon, it has allowed the relatively buoyant salt to push upwards. This causes the canyon walls above to bend, crack, and fall apart. The shifting salt layer and fallen rocks can make the river steeper and act like a natural dam, slowing down the water upstream and creating a backwater effect in Meander and Stillwater Canyons (Lake Cataract).
Natalie and her team’s research project has an initial goal of understanding when this process (the feedback between canyon cutting and “salt tectonics”) began. Did it begin recently because of stormy weather as we exited our last ice age (about 12,000 years ago)? Or has it been happening for a much longer time?
Natalie’s team figured this out by studying the history of Meander Canyon’s formation by mapping and dating paleo river deposits. These ancient sediments can tell us at what time in the geologic past the canyon bottom was at certain elevations. Knowing this, the team learned how quickly the river cut through Meander Canyon over time and where this cutting happened.
Their study documents two episodes of rapid canyon erosion in the last 350,000 years. This rapid erosion seems to have started from Cataract Canyon and moved upstream, suggesting that: (1) the unsteady canyon cutting has been caused by the dynamic, shifting salt tectonics occurring downstream, and (2) the salt-tectonic situation of Cataract Canyon has been going on for just about the same length of time (350,000 years).
They also found that the current backfilling through Meander Canyon began sometime after 60,000 years ago. Knowing when and why these waves of incision happened is an important piece of the puzzle of how our canyons formed.
Adapted from a summary by Natalie M. Tanski
🤓 Read the full paper in Geology here! (paywall)
