Alaska has long been known for sizable geological events -- particularly the 1964 magnitude-9.2 Good Friday earthquake, the second-largest ever recorded, and the 1912 eruption of Novarupta, the largest volcanic eruption of the 20th century. Earlier this month, Alaska added to the list another notable event on a massive scale, an immense landslide that tumbled loose in Southeast Alaska, perhaps the largest natural landslide on Earth since 2010.
NASA managed to capture satellite photos of the landslide, which broke free from Mount La Perouse a 10,728-foot peak in the Fairweather Range in Glacier Bay National Park, on Feb. 16, releasing an estimated 68 million metric tons of debris. The scale of the slide, which stretched nearly five miles over snow-covered terrain, was visible from space. From the NASA Earth Observatory blog:
The sediment slid in a southeasterly direction, stretching across 7.4 kilometers (4.6 miles) and mixing with ice and snow in the process. The slide was triggered by the collapse of a near-vertical mountain face at an elevation of 2,800 meters (9,200 feet), according to Columbia University seismologist Colin Stark.
Stark first became aware that a landslide may have occurred when a rapid-detection tool that sifts through data collected by a global earthquake monitoring network picked up a signal indicative of a fairly significant event. The earthquake sensors detect seismic waves—vibrations that radiate through Earth’s crust because of sudden movements of rock, ice, magma, or debris.
The landslide was far bigger than the 2012 Lituya Mountain slide in Alaska, which measured about 20 million metric tons. Stark and Columbia University colleague Goran Ekstrom also detected that slide with their newly developed monitoring system. An approximately 30 million metric ton slide occurred last August in Wrangell-St. Elias National Park.
When news broke last week of the massive landslide -- at a then-unknown location in a remote part of Southeast Alaska -- Haines-based pilot Drake Olson decided to go looking for it. On Friday, he found it, on the slope of Mount La Perouse. Olson shared photos of the slide -- which was already covered with a slight dusting of snow -- with the American Geophysical Union’s Landslide Blog. As the blog notes, the new slide is less than 10 kilometers from the location of the 2012 Lituya Mountain slide. In addition to the striking photos from the air, Olson was also able to land near the slide’s “toe” and take some photos of the debris up close. To see the photos, visit the AGU’s blog post.
NASA's Landsat-8 satellite passed over the slide the day after Olson discovered the debris field and was able to photograph the slide, offering a stark contrast to the previously pristine-white snowscape observed in the area in May 2013.