Search and rescue operations continue under difficult conditions after a massive landslide careened through a neighborhood four miles east of the small town of Oso, Washington on Saturday morning. Officials have recovered the bodies of 16 victims while the number missing has increased to 176 though some names may be duplicates. Snohomish County District 21 Fire Chief Travis Hots said rescuers believe they have found another eight bodies, which would bring the current fatalities to 24.

The rain-soaked hillside collapsed, sending millions of tons of mud, trees and debris across the valley floor, damming the North Fork of the Stillaguamish River and blocking State Route 530. This disaster, which hit the former fishing and logging town 55 miles northeast of Seattle, may rank as far deadlier than the 2005 landslide that killed 10 people in the beach community of La Conchita, California. In the United States, mudslides and landslides result in an average of 25 to 50 deaths a year, according to the Centers for Disease Control and Prevention (CDC).

The area has experienced heavy rainfall over the past weeks, with up to 200 percent of normal rainfall. Nearly 15 inches of rain has, according to state geologists, created a saturated ground prone toward sliding. Additionally, an earthquake occurring right behind the site of the landslide and measuring 1.1 was recorded on March 10.

The debris from the mudslide covered nearly a mile, bulldozing and burying nearly 50 homes from the Steelhead neighborhood. A state geologist stated that the slide was the largest he had ever seen. The slide deposited a layer of mud, soil and rock debris 1,500 feet (460m) long by 4,400 feet (1,300m) wide. It was measured at 30 to 40 feet (9.1 to 12.2m) deep.

Governor Jay Inslee has declared a state of emergency for the area and has mobilized the National Guard. President Obama signed an emergency declaration Tuesday freeing up federal money for aid.

Fire Chief Hots explained the dangerous conditions facing rescue efforts. Due to the instability of the mudflow and debris, he said, “Some of my guys could only go 50 feet in five minutes.” He added, “Our crews are up against an enormous challenge. It’s like quicksand out there.” Emergency responders have had to be rescued themselves after being sucked into the mud.

A flood watch was due to be lifted Tuesday night as concerns were eased that the new course cut by the Stillaguamish River could unleash the mudflow created lake. However, forecasts calls for four inches of more rain in the next few days, both creating more difficulties for the searchers and posing the hazard of flooding for the already devastated area. This has dimmed the potential for rescue, with recovery being instituted instead.

The hill that collapsed on Saturday had a history of instability, with a landslide occurring as recently as 2006. Reports of multiple geologic surveys warning of the instability have begun to emerge. Since the 1950s, geologists have been warning of dangers from a massive slide on the hill above Oso.

A 1967 slide damaged or flooded 25 homes and dammed the river. No one was killed or injured then. The most prescient warning came from a 1999 report for the US Army Corps of Engineers. Written by Geomorphology expert Daniel Miller and his wife, Lynne Miller, the report warned of “the potential for a large catastrophic failure.”

Speaking to the Seattle Times, Miller stated, “We’ve known it would happen at some point, we just didn’t know when.”

Miller has been studying reports on the hill going back over decades. In contrast to Snohomish County Emergency Manager John Pennington’s statement that, “It was considered very safe,” and that, “This was a completely unforeseen slide.” Miller stated to the Seattle Times, “We’ve known that it’s been failing. It’s not unknown that this hazard exists.”

Residents of the area were not aware of the Army Corps of Engineers study, and a Corps spokeswoman said zoning was a “local issue” and “that we don’t have the jurisdiction to do anything.”

Part of the area had also reportedly been logged in the 1980s, which may have contributed to the weakening of the hillside. Moreover, the Stillaguamish River constantly erodes the base of the hillside.

According to one article, residents of the area referred to the hill as “slide hill.” At the time of the 2006 slide, five homes were permitted and built below the slide-prone hill with others permitted in 2009 and 2013.

Since his original statement on the “safety” of the area, Emergency Manager Pennington is now claiming that residents were very aware of the dangers of a slide. The media has picked up on this theme, with headlines declaring, “residents knew of high risks.” Despite the heavy rains, the Washington Post reported, there were no mudslide warnings issued to area residents.