Alaska Had Biggest Landslide in Decades— and No One Saw

If millions of tons of rock slide down an Alaskan mountain and no one is around to hear it, does it make a sound? Regardless, it certainly creates enough of a ruckus to get picked up by a sophisticated seismic monitoring network, Alaska Dispatch News reports. The Oct. 17 Icy Bay landslide into Taan Fiord, which took about a minute, was North America's biggest since the 1980 collapse of Mount St. Helens, according to ADN. It caused a local tsunami (up to 100 feet high) that could have been dangerous if people had actually been around. Alaska's southeast is the "world's hotspot for these huge rockslides," geology and geophysics professor Colin Stark told a meeting of the American Geophysical Union earlier this month.

Scientists discovered the slide, which had a magnitude of 4.9, via its "seismic signature," the AP reports. The monitoring network includes hundreds of seismographs and atmospheric sensors. "We're reading the data … in a way that lets us detect the landslides and figure out where they are," Stark says. Also in October, there was a 45 million ton slide at Mount Steele in the Yukon; and in February 2014, 68 million tons of debris tumbled down Alaska's Mount La Perouse, ADN reports. Scientists say fragile rock from developing mountains and retreating glaciers in the region result in a faster erosion rate and more slides, per ABC. Some are concerned that the retreating Columbia Glacier along Alaska's south coast may cause a destructive slide closer to towns. (After ground ice gave way, a Canadian lake fell off a cliff.)