Six homes have temporarily been evacuated after a landslide partially blocked the Cedar River in Mapple Valley, Kent County, Washington State, at about 10.30 am local time on Saturday 10 May 2013. The landslide dislodged a triangular section of hillside, roughly 100 m high and 100 m wide at the base, depositing a large volume of rocks and mud, plus several mature trees, into the river. The floodwater invaded the gardens of seven properties, and is thought to have caused flood damage to six houses. The river has now resumed flowing, but the section around the landslide is still closed to the public due to concerns about the stability of the slope, and a number of further trees which are hanging precariously over the river.
The 10 May 2014 Maple Valley landslide. King County Sheriff's Department.
Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall, although King County has not reported any exceptional rainfall this week, so it it likely that on this occasion the landslip has been caused by the action of the river undermining the slope by washing away sediments from its base.
The approximate location of the 10 May 2014 Maple Valley landslide. Google Maps.
See also...
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