Sidle was cautious about predicting a rockfall-driven apocalypse in a warming Yosemite, but didn’t rule out more rockfall activity. “We’ll have to wait and see.” All three geologists were careful to point out that there’s no conclusive data yet to prove rockslides are getting more frequent in Yosemite. “It could be that the effects cancel out,” said Glazner. On the one hand, fewer freezing nights could reduce the number of rockslides caused by freeze-thaw cycles on the other hand, a warmer and wetter climate could increase the number of slides caused by heat-based rock expansion and water weight. It’s hard to tell what the cumulative effect of a changing climate will be on the frequency of rockslides. As hurricanes and other storms become less frequent and more intense, the water weight from large storms could also trigger more rockfalls. According to Glazner, the sheer weight of water can sometimes be too much for a rock formation, and cause sections to break off. We’ll have to wait and see.”Ĭlimate change could also impact the wetting and drying cycles that may trigger rockslides. “It could be that the effects cancel out. In colder places like the Alps, melting glaciers and permafrost have been linked to an expected uptick in rockslides. According to Allen Glazner, a professor of geology at the University of North Carolina at Chapel Hill, this kind of melting “has really no effect on what’s happening in Yosemite.” But there are still glaciers in the Sierra Nevada, and they’ve ben retreating for a century. Rising global temperatures are also melting the glaciers and permafrost that support rock formations. As temperatures rise worldwide, those hot, sunny days will become more frequent, which could mean more rockslides. The more the temperature rises and falls between day and night, or summer and winter, the more rock will expand and then contract, causing cracks to propagate through it. Like sticky wood doors in the summer, rock expands ever so slightly when it’s heated. Then, in 2016, Yosemite’s park geologist published a paper in Nature Geoscience that found most rockslides in Yosemite happen on hot, sunny days, not in freezing temperatures. The idea was that water seeped into cracks during winter rainstorms, then expanded when it froze-the same process that forms potholes. Putnam said that, until recently, most geologists thought freeze-thaw cycles, also called frost wedging, caused the majority of rockfalls. Roy Sidle, a professor of geography at the University of the Sunshine Coast, said in an email that those triggers fall into four major categories: “freeze-thaw action, wetting and drying, temperature changes, and (of course) human disturbances (even rock climbing).” Rockslides happen in rock with existing weaknesses, like large cracks, after they become unstable as a result of a trigger.
But despite their frequency, there is a possibility that warming temperatures and an unstable climate could cause even more rockfalls at Yosemite and worldwide. Rockfalls are par for the course at Yosemite, where the National Park Service estimates 80 events happen every year. In fact, he said, the quick succession of rockfalls “perfectly shows how a small rockfall happens and then-boom-that causes another rockfall, and another.” Thursday’s released a volume of rock larger than 10,000 cubic meters, about four Olympic swimming pools’ worth of rock.Īccording to Roger Putnam, a climber and geologist at Moorpark College, these rockslides were not unusual from a geologic standpoint.
Wednesday’s rockslide killed one person, the first rockfall-related fatality in the park since 1999. Last Wednesday and Thursday, there were two major rockfall events at Yosemite’s El Capitan, a rock formation extremely popular with climbers.
0 kommentar(er)
