re: Video: Mudslide obliterates town near Nepal/China border

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Why do you build next to a major river?

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The fact that it wasn't just water, but a giant debris flow makes it even more terrifying. It isn't uncommon to see smaller debris flows in canyons and washes, they happen out west every monsoon season, but this scale is just almost impossible to comprehend. Entire buildings were in that debris flow along with the soil, rock, trees, and half that mountainside. Unreal.

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And another poster is correct, the flood caused the earthquake; not the other way around.

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In September 2023, an unusual seismic signal raced around the world, zipping from eastern Greenland to Antarctica in less than 1 hour. The seismic waves continued to radiate worldwide for 9 days, ringing Earth like a giant bell.

Now, scientists have tracked these mysterious signals to their source—a colossal landslide in a remote Greenland fjord that sparked tsunami waves up to 200 meters tall, the team reports today in Science. Like sloshing water in a bathtub, the tsunami resonated within the narrow valley, beating against the channel walls and creating the globetrotting seismic waves like “a big musical instrument,” says Stephen Hicks, an author of the new study and seismologist at University College London.

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Although researchers quickly spotted the strange signal, they were initially baffled as to its cause. The waves were surprisingly uniform, monochromatic in frequency—far different from the jumble of waves generated by the jolt of an earthquake. The waves were also very long, repeating every 90 seconds. Similar long-period waves are often created by volcanoes, such as the ones generated in 2018 by the largest underwater eruption ever recorded. But these signals usually last for minutes or hours, not days.

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He and his colleagues backtracked the seismic signals, but could only trace them to a large area in eastern Greenland. So they reached out to local scientists, who told them sea level gauges had recorded a large tsunami in the Dickson Fjord, an uninhabited valley near the signal’s source. Further detective work using satellite images and drone videos revealed the perfect storm of events that set the world shaking: A rockslide high above the valley pummeled a glacier that fed into the side of the fjord. Some 25 million cubic meters of rock and ice—nearly 10 Giza pyramids’ worth—careened down the glacial gully and plunged into the waters below.

When the researchers later visited the site, they found a dark band of sediments on the glacier’s face left by the tallest waves—evidence that they initially reached more than twice as high as the Statue of Liberty. The sloshing water scoured vegetation from the fjord’s shores, leaving them barren, Hicks says.

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