Wall of Rock Collapses Into Historically Low Lake Powell

The rock slide was “pretty incredible,” Carter said. “Saw something like I had never seen before….I feel like the video didn’t do that big tidal wave justice. It was huge.”

Lake Powell has been a site of extreme events lately, thanks mostly to the historically low water levels in the lake. As of Thursday, the lake stood at 3,532 feet (1,076.6 meters) above sea level, according to readings provided by the U.S. Bureau of Reclamation. That’s a slight uptick from early last month, when it sank to a record low of 3,522.7 feet (1,073.7 meters). But it’s still 29 feet (8.8 meters) lower than this same weekend in 2021 and almost 75 feet (22.8 meters) lower than Memorial Day weekend in 2020.

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These record-low numbers are the result of a one-two punch of the West’s strained water system and its worst drought in 1,200 years. The extremely low water levels have rendered the parched lake almost unrecognizable in places, and officials have had to make tough decisions to keep water levels high enough for the lake to keep generating electricity—which can only happen if the reservoir’s level is at or above 3,490 feet (1,063.8 meters). (Fortunately, no human remains have been found at Lake Powell, as they have at Lake Mead—yet.)

This particular rock slide might be another unusual event attributed to the drought. Rock slides can be triggered by a lot of different factors, from storms to earthquakes, but they can also be helped by water levels declining in a lake, as pressure changes when water falls and removes support from cliffs that may have been stabilized by water saturation.

“The saturation and then drying with the falling water levels kind of contributed to that thing falling over,” Joe Cook, a research geologist with the Arizona Geological Survey, told KTVK of the Memorial Day collapse. “It might have fallen over anyway but having a reservoir there may have sped up the process.”

Cook added that it’s relatively rare occurrence for humans to see a slide, which he called a “rock topple,” like the one that Carter caught on camera.

“There’s probably a whole bunch of these things that are ready to go but they could happen in 100 years, 1,000 years,” Cook said. “We don’t really know.”

Officials have not released an official cause for the rock slide, and other experts pointed out that it’s difficult to determine specific causes for any one event.

“We see increased rockfalls during intense precipitation events and earthquakes, but apparently none of those conditions existed at the time of the rockfall in the video, so its trigger remains unknown,” Tyler Knudsen, a senior geologist with the Utah Geological Survey, told CNN. “Water-level decline certainly could have been the trigger, but, again, we can’t say for sure at this point. We do know that the creation of Lake Powell and its historical water-level fluctuations have contributed to elevated rockfall generation.

“Is it possible that some cliffs that are now being dewatered for the first time in over 40 years are generating more rockfalls? Yes, it’s possible,” Knudsen added. “Record low water levels are likely contributing to recent rockfalls along Lake Powell’s receding shores, but it’s difficult to definitively link a particular rockfall solely to declining water levels.”