Oso, Washington landslide was the deadliest landslide in the history of the US. Researchers claim that the landslide was not a fluke. The region has experienced many major landslides and their can be many more on their way.
In March 2014, a major landslide occurred in Oso, Washington which killed more than 40 people and destroyed dozens of homes. It was considered the deadliest landslide in US history.
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Now, new research from the University of Washington claims that the 2014 devastating landslide that ripped through the region in the west of Washington was not a fluke. The region has experienced major landslides before, in fact, the area around Oso has collapsed every 500 years on average while slammed by much-high magnitude landslides once every 140 years. And these major landslides could happen again.
“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,” said co-author Sean LaHusen from Washington University. “We found that that’s not the case – in fact, landslides have been continuing in recent history.”
Oso is an area well known for unstable hills and mud sliding but here in this study, researchers have focused on the pattern on which landslides occur in the region. The findings could also have implications for determining future patterns of landslides in the state.
“This was well known as an area of hillslope instability, but the question was: ‘Were the larger slides thousands of years old, or hundreds of years old?’ Now we can say that many of them are hundreds of years old.” Alison Duvall, one of the authors of the study said.
Researchers have used a new method to find the sequence of all the previous landslides in the region. They looked for the branches or trees that have been uprooted during the landslides and used radiocarbon dating to establish the period when such devastating events took place.
Large landslides leave imprints on trees and branches and they can help reveal the particular order in which these catastrophic events followed each other.
“When you have a large, catastrophic landslide, it can often uproot living trees which kills them and also encapsulates them in the landslide mass,” said Duvall. “If you can find them in the landslide mass, you can assume that they were killed by the landslide, and thus you can date when the landslide occurred.”
To get landslide deposits, researchers searched the area along 3.7-mile stretch of the north fork of the Stillaguamish River and managed to unearth wood remains from various periods. Results from several debris samples showed that the Rowan landslide, which was one of the freakish landslides in the history of the region, took place 300 to 694 years ago. The Headache Creek landslide occurred somewhere around 6,000 years ago.
“This is the first time this calibrated surface dating method has been used for landslide chronologies, and it seems to work really well,” said Sean LaHusen. “It can provide some information about how often these events recur, which is the first step toward a regional risk analysis.”
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Research suggested that Oso landslide was not unusual or uncommon event. Such major landslides have occurred in the past and may be many more are about to come. By analyzing previous major landslides, researchers can predict which places in the region are most vulnerable to massive landslide and how they can minimize the damage which is caused by those landslides.