The 2014 Oso mudslide swept down Skaglund Hill, just east of Oso, Washington on March 22, 2014, killing at least 14 people and causing the disappearance of many more.
At about 11 a.m., the mudslide flowed across the North Fork of the Stillaguamish River, through a neighborhood of some 30 homes, and crossed Highway 530, damming the river and completely blocking the highway.
More than 100 first responders from Snohomish and surrounding counties were dispatched to assist with medical aid and search-and-rescue efforts.
The hill has a history of instability, and experienced up to 200 percent normal rainfall over the previous 45 days.
The mile-wide slide was described by witnesses as a “fast-moving wall of mud” containing trees and other debris cutting through homes directly beneath the hill.
One survivor assisted by bystanders was a six-month old baby pulled out of the mud and taken for medical treatment.
A firefighter interviewed by the Seattle Times newspaper stated, “When the slide hit the river, it was like a tsunami.”
The slide blocked the North Fork of the Stillaguamish River which backed up eastward toward the nearby town of Darrington. By that evening, officials were concerned that the mud and debris dam could fail, causing downstream flooding. As of 23 March 2014, the river began flowing through a hole in the mud dam. As of 24 March 2014, a flash flood watch issued by the National Weather Service remained in effect. However, the river was flowing past the dam and the upstream pool depth had stabilized.
Highway 530 was closed indefinitely and an alternative route around the slide was being prepared by the Washington State Department of Transportation.
Late in the evening of March 22, 2014, Washington state Lieutenant Governor Brad Owen declared a state of emergency in Snohomish County. State Governor Jay Inslee toured the area by air the following day before joining county officials at a news conference.
As of March 24, 2014, 14 people were confirmed dead and there were 176 reports of people missing or unaccounted for.