17 October 2013
Bluff collapse events: new videos from the USA and Canada
Posted by Dave Petley
Two new videos have emerged on the web in the last few days showing coastal bluff collapse events:
1. Port Townsend in Washington State
This excellent video on Youtube shows the collapse of a north-facing bluff in soft glacial till. There is a full description of the site and the event on excellent the Observations of Washington State Landscapes, Geology, Geography, History and Land Use blog by Dan McShane:
The video catches the initial collapse event, which happened on 13th October at about 6 pm, really well, with fractures opening as the main block detaches, as this screenshot shows:
2. Wreck Beach on the Campus of UBC in Canada
A similar, though most gradual event, also occurred on the bluffs above the famous Wreck Beach in Canada, which lies on the campus of UBC on the edge of Vancouver. I am not sure if the embed will work here – if not then there is a video report of the event with an interview with John Clague here:
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And a nice video of the collapse event here (and please be assured that the video is less racy than it might appear from the title!):
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Thanks to Peter Weisinger for highlighting this one to me.
Both these landslides are in the same soil units; dense sands prone to seepage erosion, capped by very dense basal till.
Somewhat ironically, the largest school of geological engineering in Canada is less than 300m from the second landslide.
Also of note, though it was dry at the time, there were a few rather large storms about two weeks prior. Also, the university adjacent to the slide has been recently constructing several sustainable buildings, all of which channel storm water runoff into groundwater recharge.