Water Resources of the United States

PROJECT ALERT NOTICE (WA) Oso landslide, update

Date: Thu, 27 Mar 2014 20:29:48 EDT

Summary: There have been no significant changes since yesterday: the North Fork Stillaguamish River continues to flow across the natural dam that formed due to a large landslide and the water continues to gradually erode a larger channel.

The North Fork Stillaguamish River, Washington, continues to flow across the natural dam that formed due to a large landslide and the water continues to gradually erode a larger channel; i.e., there are no significant changes since yesterday.

The USGS published a report today by Ralph Haugerud, titled "Preliminary interpretation of pre-2014 landslide deposits in the vicinity of Oso, Washington." The report is available at the new Oso Landslide webpage, http://wa.water.usgs.gov/data/oso.html.

USGS scientific and public affairs personnel continue to be on site to assist as needed. Multiple discharge and suspended-sediment concentration measurements were made.

Miscellaneous information:
1. The level of the lake behind the natural dam dropped about 2 feet since yesterday;
2. Turbidity of water downstream from the natural dam is high but steady, confirming controlled erosion of the natural dam;
3. Heavy rains are expected Friday through Sunday, which will accelerate erosion of the natural dam;
4. Catastrophic failure of the natural dam is considered unlikely but conditions will be monitored closely.

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