Friday, June 15, 2018

View and Notes on Racehorse Slide

I had a nice view of the Racehorse Slide (cool-oblique-lidar-image-of-racehorse) (first-description-of-racehorse-slide)on a recent trip up the Nooksack River valley. If the clouds and rain are not low, the slide area can readily be seen. 

2018 view of slide

2015 view of slide

I marked up the next picture with the arrow indicating the area of the block that detached and slid as down into the lower Racehorse Creek canyon in 2009. The headwall area of the older and much larger slide that spilled out across the Nooksack River valley is marked with a dashed line. Note that additional logging has taken place between 2015 and 2018 along the southwest side (right in the picture) of slide.

Logging had taken place on and adjacent to the 2009 slide shortly before the failure took place. As can be seen in the photograph above additional logging has been taking place along the older large slide headscarp and along a block that has remained attached on to the right of the slide. That block is located on the south side of the slide. 

lidar showing large slide area and deposit

The impacts of logging on large deep-seated landslides is uncertain. It certainly is not positive, but a direct connection between logging and reactivation of deep-seated bedrock landslides has not been firmly established. The 2009 slide was certainly coincidental with the logging that had taken place, but it also took place during a very intense rain on snow event that was likely on the order of a 25 to 50 year event. Estimating the water input difference between the slope harvested and not harvested  might be an informative exercise. I am not aware if anyone has tried this. The land in question is managed by the State DNR.   

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