The Pacific Northwest’s landscape is precarious and ever-shifting. Mount Rainier provides no shortage of proof. Evan Bush reports for the Seattle Times A glacial outburst at about 6:50 p.m. Monday at the mountain’s South Tahoma Glacier sent debris and boulders as big as pickup trucks flowing down the mountain, said Mount Rainier National Park geologist Scott Beason. The debris flow registered on seismic monitors and ran for more than 8 miles, Beason said. Beason suspects warm, sunny weather filled the glacier with melt, rearranged the “internal plumbing” at the glacier’s base, caused water to blast a new channel through the glacier, and then flooded glacial melt into Tahoma Creek. “The event lasted an hour and had four separate surges,” Beason said of the outburst flooding. “The outlet channel definitely shifted. It picked up a lot of loose material just below the glacier and carried it downstream and mobilized it into a debris flow.”  As the world warms and Mount Rainier’s glaciers thin and retreat over time, these massive debris flows have become a common occurrence on the mountain’s south side. The park is building systems to forecast massive debris flows and send alerts to park staff when they’re triggered, Beason said. Read the full story Not receiving our free updates?