By Sid Perkins
Just after dusk on Aug. 14, at an amphitheater in Mount Rainier National Park’s Cougar Rock campground, a deep grumbling sound began to drown out a park ranger who was regaling visitors with an interpretive lecture about the park’s natural wonders. The rumble quickly grew to a freight-train-like roar. That’s when the ranger ran to a creek near the amphitheater and saw a large flow of mud and debris surging down the normally placid channel.
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![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2001/11/794.jpg?resize=98%2C150&ssl=1)
“It rumbled up on the ridge until about 10:30 [p.m.],” says Jill Hawk, chief ranger at the national park. Although the campground was never threatened, large pulses of rocky mud continued to sweep down the mountainside for more than 5 hours that evening, and smaller clumps followed for the next 5 days. It was a natural wonder all right.