A landslide in Alaska last month may have been the biggest ever in North America—and it almost went completely unnoticed. A pilot happened to fly over the remote valley beneath Lituya Mountain in Glacier Bay National Park this week and snap pictures of the aftermath, the AP reports. A cliff collapsed on June 11, sending rock and ice pouring into the valley, in an event so momentous it registered as a 3.4-magnitude earthquake.
The slide was estimated to be 5 1/2 miles long and half a mile wide. "I don't know of any that are any bigger," one research geomorphologist says, adding that anyone standing in front of the slide would have been flattened by the air blast alone. Scientists say several things could have contributed to the slide, including weakening rock, melting snowpack and, you guessed it, climate change. "We are seeing an increase in rock slides ... throughout the world because of permafrost degradation," the geomorphologist says.