Do landslides happen around your own corner?

Saturday morning, March 22, 2014: 
Deadly landslide happened in ... no, not in China or India, ... in Oso, Washington, USA.

42 people died. One is still missing.


What happened in Oso, WA so recently?

50 miles north of Seattle on a Saturday morning on the 22nd of March, 10 million cubic yards of debris came down a slope. The landslide had a velocity of 60 miles/hour! There was no chance of running away. 45 houses were destroyed. The total damage amounts in millions of US Dollars. At the very same location in Oso, landslides happened in 1951, 1967, 1988, and 2006. None as devastating as the most recent one. The ground was fluidized due to heavy rainfall and slid as a mass of mud downwards.
End of May, after the completion of the mudslide debris removal, the State Route 530 reopened again. But there is still a lot to clean up... 

See here for maps of the affected area.

Slide Area of Oso Landslide, Washington State, March 2014

Landslides happen more often than you think, and they may occur just where you live!


What is a landslide?

A landslide is a downward falling or sliding of a mass of mud, soil, detritus, or rock on a steep slope.


Where does a landslide may occur?

• One way to figure out where landslides may occur, is to look at ancient landslides. Ancient landslides may reactivate.
• Another point is existing rivers or streams. Rivers tend to bend from left to right to left to go their way down to the ocean. The water of a river is faster on the outside of a curve than on the inside, which could lead to elutions or scours of adjacent land on the outside. When the foot of a slope is missing, the slope may get unstable and slides downwards.
• A third - and may be by homeowners unpopular - point is the clearing of steep slopes from high trees. A homeowner may want to have a marvelous view over the valley, but the same slope is stolen the roots. Roots of trees and bushes stabilize a slope and transport water from the ground into the air. In case of heavy rainfall, a slope without its stabilization is meant to slide.
• Another point to look at is water pipes and drainage lines. Water should be collected above a slope. Concentrated water outlets, e.g. from a street above a slope, over time may be a trigger and the slope may get washed away. 
• Broken water or sewer lines may be a trigger, too. The water flows concentrated down the slope and may weaken it. To counteract, every water pipe in the ground should be tested in spring time to make sure it is not broken.

What questions should be asked in case of a landslide?

1. Why did it occur?
2. How to mitigate immediately?
3. Is the rest going down, too?

How to control a landslide?

• Water collection! The collection and transfer of any kind of water is a critical point.
• Vegetation of a slope! The roots of vegetation hold the slope itself and water is taken from the ground into the air.
• Ancient landslides? A reactivation of an ancient landslide may occur. Mapping of "inventory" and susceptibilities are necessary to analyze ancient landslides.

The most recent landslide in the US:

The most recent landslide is still sliding. It is in Fort Washington, Maryland. The slow downward movement of the land mass cuts off water, sewer, and electricity lines, which affects 28 homes and their residents.


(I thank Dr. Scott Burns - Prof. of Geology at Portland State University and GIGSO - Oregon State University Geo-Institute Graduate Student Organization for the guest lecture about landslides at Oregon State University on May 28, 2014.)