Massive Landslide at Oso Site Took Place 500 Years Ago
On analyzing the woody debris of the huge Rowan Landslide and using radioactive dating technique, geologists at the University of Washington have found that the massive nearby slide happened around 500 years ago. Researchers managed to unearth samples of wood buried in the Rowan landslide, just downstream of the Oso site, and the Headache Creek landslide, just upriver of the 2014 slide. The two slides areas were stretched at a distance of 3.7-mile (6-kilometer) stretch of the north fork of the Stillaguamish River. Till now, it was believed that the massive landslide took place thousands of years ago, but the new study published online Dec. 22 in the journal Geology shows it happened only 500 years before.
Sean LaHusen, a UW doctoral student in Earth and space sciences, said “The soil in this area is all glacial material, so one hypothesis is the material could have fallen apart in a series of large landslides soon after the ice retreated, thousands of years ago”. With the help of new method to date all the previous landslides at a particular location, researchers found that the slopes in the area around Oso have collapsed on average once every 500 years. They found that the slopes in the area around Oso have collapsed at a higher rate of about once every 140 years over the past 2,000 years. Their findings found that the Headache Creek landslide took place within a couple hundred years of 6,000 years old.
Alison Duvall, a UW assistant professor of Earth and space sciences, said it was a big confusion that whether the area of hillslope instability thousands of years old or hundreds of years old. But, now we can surely say that many of them were hundreds of years old. In March 2014, the large, fast-moving mudslide that buried much of Oso, Washington was the deadliest landslide in U.S. history. Duvall said that large, catastrophic landslide has the potential to uproot living trees, killing and encapsulating them in the landslide mass.
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