Landslides are a common occurrence, a function of geology, seismic activity, erosion caused by heavy rainfall, changes in temperature, changes in groundwater, wildfire, and other natural events
But human activities can trigger landslides as well: commercial and residential development, logging, mining, road-building, and water diversions among them.
That may have been the case in this weekend’s landslide in Jackson, Wyo., and in an earlier, massive slide in Oso, Wash., that killed at least 39 people with four more still unaccounted for.
President Obama is scheduled to visit the rural Washington State community on Tuesday. He’ll meet with victims, first responders, and recovery workers who continue to look for remains of the missing where a huge mudslide crossed the North Fork of the Stillaguamish River and roared through the town of Oso.
The Wyoming slide has been happening – so far, at least – in slow motion over the past two weeks.
It has sheared one hillside home in half, and it threatens more homes and businesses in its potential path. A road and parking lot have ruptured, and the residents of 42 houses and apartments have been ordered to evacuate.
Experts are unsure how long the hill will continue to move, although they don’t expect it to come thundering down like the mudslide in Washington.
"Is it weeks, is it longer? I really don't know," landslide specialist George Machan said at a town meeting Friday. "I think it's really unpredictable how long it might take. I don't expect it to end in a day."
Both natural and human causes may have combined to start the slide.
Authorities are looking into whether recent construction at the foot of East Gros Ventre Butte made the slope unstable. They say there could be a variety of other causes, including prior construction at the site.
The area has been graded for roads and businesses in recent years, including a new Walgreens. That could have weakened the hillside and set the stage for its collapse.
Meanwhile, warmer weather and a wet winter that put more water into the ground, likely acted as a lubricant for unstable rocks and soil, which happens throughout the Rocky Mountain region.
"As more people move into more mountainous environments, the opportunities for interactions between human infrastructure and people, and landslides, increase,” said David Montgomery, a geology professor at the University of Washington in Seattle. "When you add it up, it's actually a major geological hazard.”
Oso, Washington, in the Pacific Northwest is a rural area with a much small population than Jackson, heavily forested and with more rainfall. Residents include retirees, vacation-home owners, those who commute to nearby towns, and loggers.
Questions are being raised about logging there and how it might have contributed to the slide.
The hillside in and around the slide area, which slopes steeply down toward the river, has seen much clear-cut logging over the years.
Landslides have followed logging in that area at least four times.
"There was cutting in the 1940s; it failed in the '50s. There was cutting in 1960, then it failed in the mid-'60s. There was cutting in '88; it failed in '91. There was cutting in 2005, and it failed in 2006 and in 2014,” geomorphologist Paul Kennard told KUOW radio station in Seattle.
Media reporting since the slide on March 22 reveals that authorities knew about but failed to fully heed the warnings of scientists that such a disaster was a real threat.
Authorities considered – but then rejected – a suggestion that they buy out home and business owners whose properties lay just across the Stillaguamish River from a steep hill that had fallen away several times before. The Seattle Times newspaper reported that Snohomish County officials analyzed the situation, finding that the costs of a buyout “would be significant, but would remove the risk to human life and structures.”
Instead, they decided to build a wall intended to stabilize the slope, leaving existing structures in place and allowing more to be built.
Robin Youngblood, who was saved by helicopter after her home was destroyed, said she hopes to speak with the President when he visits Tuesday, if only to convey that laws need to change to ensure homes aren’t built in such risky areas, or that residents are warned when they are.
“People need to be given exact knowledge of whatever dangers they may be facing,” she said. “Nobody should have been living there.”
This report includes material from the Associated Press.