The Rattlesnake Ridge slope failure adjacent to Union Gap is turning into a well documented slide. The slope movement has continued to progress with the slide moving towards the rock quarry. As the slide has progressed, the fractures have become more developed - particularly the fractures that extend across the slope break and down onto the steep river gap slope.
This drone video is the best I have seen at showing this feature.
The Washington State Department of Transportation has a blog dedicated to the slide and the Washington State Department of Natural Resources has a page describing the slide as well with good figures for describing the feature
https://wsdotblog.blogspot.com/2018/01/crews-monitoring-land-movement-on.html
https://www.dnr.wa.gov/rattlesnake-hills-landslide
Diagram of slide by DNR
A set of pictures of the slide is provided at
https://www.flickr.com/photos/wastatednr/sets/72157692053372215
The documentation of this large translational slide involving basalt lava flows sliding over an old interbed soil has been fascinating to follow. But the way this slide is moving and intersects the slope of the river gap has created a remarkable and unique perspective.
The following two pictures by Tom Ring with the Yakama Nation are -- well incredible. The slope of the river gap intersects the lower failure plain of the slide. As the slide has moved the fractures have traced the base of the failure along the steep sidewall of Union Gap.
One of the big questions about this slide will be how the edge of the slide shown in the two pictures above will behave as it progresses from left to right. How much will the edge of the slide disaggregate and tumble down the steep essentially angle of repose slope?
The DNR and WDOT recognizes that there is some uncertainty, but overall seem to be taking a proactive and precautionary approach.
This drone video is the best I have seen at showing this feature.
The Washington State Department of Transportation has a blog dedicated to the slide and the Washington State Department of Natural Resources has a page describing the slide as well with good figures for describing the feature
https://wsdotblog.blogspot.com/2018/01/crews-monitoring-land-movement-on.html
https://www.dnr.wa.gov/rattlesnake-hills-landslide
Diagram of slide by DNR
A set of pictures of the slide is provided at
https://www.flickr.com/photos/wastatednr/sets/72157692053372215
The documentation of this large translational slide involving basalt lava flows sliding over an old interbed soil has been fascinating to follow. But the way this slide is moving and intersects the slope of the river gap has created a remarkable and unique perspective.
The following two pictures by Tom Ring with the Yakama Nation are -- well incredible. The slope of the river gap intersects the lower failure plain of the slide. As the slide has moved the fractures have traced the base of the failure along the steep sidewall of Union Gap.
Click the picture to expand and note the dark line angling across the slope that traces the base of the slide that is moving from left to right
Closer view of the base of the slide area.
The DNR and WDOT recognizes that there is some uncertainty, but overall seem to be taking a proactive and precautionary approach.
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