Researchers at University of Washington (UW) undertook a new study to prove that the Oso landslide that occurred in Washington on March 22, 2014, was not merely a coincidence. The landslide was astonishingly huge in terms of size and intensity. It seems that this deadliest ever landslide, which swallowed up an area around the North York of the Stillaguamish River, is a recurring event.

The study, published online by the journal Geology, has revealed that such major landslides have been hitting this valley since last 2,000 years at an average interval of every 140 years. According to Sean LaHusen, a UW doctoral student and lead author on the paper, said this particular valley is highly dynamic. He added that landslides in this valley will not stop.

Geologists used a laser scanning technique called lidar to examine the maps of this area by stripping away vegetation. The technique was able to detect the tracks made by earlier landslides up and down the valley, along a 3.7-mile stretch of river. The time period of these two dozen landslides was estimated by analyzing landslide deposits. Radiocarbon dating was done for several trees or bits of wood buried in the slide.

Landslides have been frequently occurring in this area since last 15,000 years. “We know that the ingredients are there for unstable hill slopes, regardless of what we do”, she said. “But knowing this place is so unstable, we ought to take a careful look at our land-use practices”, said Alison Duvall, a UW geologist and co-author.