Expert: Erosion on satellite photo not a factor in slide

Expert: Erosion on satellite photo not a factor in slide

Credit: KING

Expert: Erosion on satellite photo not a factor in slide

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by CHRIS INGALLS / KING 5 News

Bio | Email | Follow: @cjingalls

KING5.com

Posted on March 28, 2014 at 5:47 PM

Updated Friday, Mar 28 at 8:46 PM

Does a Google satellite photo show damage to the slope that gave way causing Saturday’s Oso landslide?

A University of Washington professor says, after talking with the people who built a retaining wall at the base of the slope, he no longer thinks it was a factor in the slide.

“I’m probably pretty confident now that it was not a contributing factor,” geologist Dave Montgomery told KING 5 on Friday.

The day before, Montgomery said that the image could show evidence that the Stillaguamish river was undermining the slope.

The image, photographed by a Google Earth satellite in July of 2013, clearly shows the log “revetment," a retaining wall built by the Stillaguamish Tribe to keep sediments from the unstable hillside from harming salmon runs in the river.

At the northwest end of the wooden wall there is a jumble of logs and a crescent shape gap where the river appears to have cut into the slope.

On Thursday, Montgomery said this could have been evidence that the river was undermining the slope.  But he cautioned at the time that he would need to have a better understanding of the log wall project to be certain.

Montgomery said on Friday that a conversation with the tribe’s environmental manager Pat Stevenson convinced him that the wall structure was mostly sound and that the erosion seen in the satellite photo is not significant.

Many experts agree that heavy rain and loose soil under the slope are the primary cause of the massive landslide.

Scientists are also looking at whether the river beneath the slope and logging above it could have contributed to the instability.

Those factors have long been responsible for the history of slides in the area.
 

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