There was a massive rockslide at Lake Powell in Arizona, where part of the canyon wall collapsed yesterday. The reservoir is in severe drought as a result of the warming climate.
KSL writes on boater Miley Carter who shared a stunning video of the rockslide.
Carter said the slide happened near the Warm Creek Bay entrance around noon Monday.
Lake Powell water levels hit a historic low this year, instigating a plan from the Colorado River Authority of Utah to move 500,000 acre-feet of water from Flaming Gorge to the suffering reservoir.
It's unclear what caused the rockslide on Monday.
Rockslide porn.
Geologists at the Utah Geological Survey, in an interview with local channel Fox13, weighed in on the rockfall:
"We've got these large cliffs throughout the Colorado Plateau, and rockfalls like this happen," the geologist said. "Actually, quite frequently — it's just not often we happen to get it on video."
He added that "quite frequently" in geologic terms is once every 1-10 years.
Knudsen says the rock responds to the pressure caused by changing lake levels.
"We know the presence of the lake itself has probably accelerated rockfall, and particularly when you have fluctuations in lake levels, it can at times trigger accelerated rockfalls," he said.
The water forces itself into the rock's open spaces when the lake fills, affecting the rock with a force called positive pore pressure.
When the lake level drops, the water pulls out, creating a suction-like effect called negative pore pressure.
Both forms of pressure can destabilize the rock.
Along with pore pressures, natural waves and boat wakes add to the erosive impact of the lake.
From the Introduction:
Salt Lake City (June 15, 2020) – Stunning landscapes and a variety of recreational opportunities centered on Lake Powell attract nearly 4.4 million visitors annually to Glen Canyon National Recreation Area; however, the active geologic processes that shaped this rugged landscape can create hazardous conditions for visitors, employees, and infrastructure. To assist the National Park Service to manage and mitigate natural hazards, the Utah Geological Survey (UGS) completed a geologic-hazard investigation of two high-use sections of the recreation area: a 297-square-mile area near the Bullfrog and Halls Crossing Marinas, and a 117-square-mile area centered on the Wahweap and Antelope Point Marinas near the Utah-Arizona border. Results of this investigation include detailed geologic-hazard mapping that covers flooding and debris flows, rockfalls, landslides, soil erosion, and other problem soil and rock hazards, surface faulting, earthquake-induced liquefaction, and indoor radioactive gas (radon) potential.