A clearcutting operation in the very same place this mudslide took place caused another slide in 2007. The vegetation had not fully grown back. What effect does clearcutting trees have on the environment?
Clear cutting and its effects on landslides
Over the years, many case studies have proven that the mass removal of large trees and vegetation has a had a drastic increase on the probability of landslides occurring (Heiken, 1997). These studies have laid out several mechanisms of clear cutting that have contributed to the increase:
Large trees provide strong root structures that penetrate fragile cracks in the underlying bedrock and anchor the soil.
Old growth trees natural have large leaf surface areas which cause much water transfer. The water is drawn up from the soil and eventually transpired back to the atmosphere.
Forests create a canopy of foliage high up in the air to help dissipate rain fall over large areas.
Heavy logging machinery damages precious topsoil and decreases its ability to absorb water.
Logging slash (leftover tree limbs) or debris blocks natural drainage basins.
Anytime large amounts of vegetation are removed from an area the delicate root systems eventually die off which leaves the soil vulnerable to over saturation.
Above image source: http://landslides.usgs.gov/html_files/landslides/slides/landslideimages.ht
A study done by Richard Meehan was conducted in 1991 and a few of his conclusions were as followed: "The frequency of mass erosion [landslides, debris flows, earthflows, etc] is strongly linked to the type and intensity of land treatment in the basin. Although most mass movements are associated with roads and their drainage systems, many originate on open slopes after logging has raised soil water tables and decreased root strength." [Meehan, 1991 page 194] He also stated that: "The increase in mass movement due to clear cutting varies widely, ranging from 2-4 times in Oregon and Washington...to 31 times in the Queen Charlotte Islands... An increase of 6.6 times...is probably closer to the norm."
(Excellent video explanation here : www.youtube.com/watch?v=3y9RQKgEgTs&feature=youtu.be
Oso Landslide Very Similar To 2007 Event
In 2011, PCVA filed several lawsuits against timber companies and the State Department of Natural Resources (“DNR”) to recover for similar damages caused by negligent timber practices. Experts retained by PCVA agree that landslides and mudslides occur when timber is harvested on steep slopes in areas of unstable land, heavy rainfall, and defective drainage.
Such negligent timber practices were the result of a mudslide that destroyed the Ranch House BBQ restaurant in 2007. There, DNR agreed to settle the lawsuit for $800,000. Thankfully, the case involved only property and business damages, and not personal injury or wrongful death. More can be read about the settlement here [http://www.theolympian.com/2010/04/23/1216014/state-to-pay-ranch-house.html].
PCVA is currently awaiting an important decision from the Washington State Supreme Court in the several cases filed in 2011. The decision will have an impact on where lawsuits for property damages can be filed. Oral arguments were heard in the spring of 2013 and a should be released shortly.
Washington law is clear that those who manage timber owe landowners a duty of care to prevent foreseeable damage to property and person. The recent mudslides along Highway 530 near OSO in Snohomish County underscore exactly how negligent timber practices can lead to catastrophe. PCVA extends their deepest condolences to those families impacted by the recent mudslides.
Emergency responders and volunteers were to resume search operations Tuesday morning and attempt to narrow down the number of people unaccounted for following Saturday's massive mudslide in a rural part of Washington state, north of Seattle.
Late Monday, authorities announced that the official death toll had increased to 14 after searchers discovered six more bodies in the rubble.
The main focus of the search operations has been to pin down the exact number of people unaccounted for after the disaster. Snohomish County Emergency Management Director John Pennington told reporters late Monday that officials were working off a potential list of 176 people, but he stressed that authorities believed that included many duplicate names.
"I believe very strongly  is not a number we're going to see in fatalities," Pennington said. "I believe it's going to drop dramatically." However, other authorities said they have not been able to determine whether there were multiple calls about the same missing person.
The 1-square-mile mudslide struck Saturday morning near the town of Oso in Snohomish County. Authorities have described the search for additional survivors to be "grim" as crews battle uneven ground and rising waters. Monday’s search included specially trained dogs, firefighters, law enforcement, aircraft and search-and-rescue teams. Heavy equipment from the Washington State Department of Transportation helped to move trees, boulders and earth.
"I’m very disappointed to tell you that we didn’t find any sign of any survivors, and we found no survivors today,” Snohomish County Fire District 21 Chief Travis Hots Monday evening.
Pennington gave his own somber diagnosis, saying ""Most of us in these communities do not believe we'll find anyone alive." However, Pennington then added "I'm a man of faith and I believe in miracles."