A massive slide of rock and ice tumbled down a mountain in the wilderness of Canada's Yukon Territory this month, but the event would likely have gone unnoticed had it not been for a seismic-instrument network, satellite imagery from NASA and a pair of scientists at Columbia University.
The Oct. 11 avalanche sent about 45 million metric tons of debris down the southeast flank of 16,644-foot Mount Steele, Canada's fifth-tallest peak and part of the St. Elias range that straddles the Alaska-Canada border region, NASA said.
There was no earthquake or other obvious event that set off the slide, NASA said. Instead, it was its own seismic event, detected by Colin Stark and Göran Ekström, scientists at Columbia's Lamont-Doherty Earth Observatory. They noticed that within that day's global seismic-monitoring data that there was the type of long-wave event indicating a massive landslide, NASA said.
The data examined by Stark and Ekström determined that the event happened near Mount Steele, but it could not pinpoint the exact location. Instead, it identified a 500-square-kilometer area where the avalanche occurred.
Confirmation -- and a precise location -- came Oct. 13 from imagery provided by NASA's Landsat 8 satellite. The captured image showed avalanche debris had spilled from Mount Steele onto Steele Glacier.
The imagery also showed remnants of an even bigger slide, a 2007 event that dumped 105 million metric tons of debris onto Steele Glacier.
Stark and Ekström made a similar discovery last year when they used seismic data to find a slide that sent an estimated 68 million metric tons down the side of Mount La Perouse in Southeast Alaska.