24 September 2015
Pemberton Portage Road landslide
On Sunday 20th September, heavy rainfall induced a landslide in the town of Birken, north of Pemberton in British Columbia, western Canada. This landslide, which has become known as the Pemberton Portage Road landslide, appears to be an impressive flow type slide that caused damage to a house, a highway, railway lines and power infrastructure. Fortunately no-one was injured in the landslide, but of course the owners of the house are the real losers as it appears that, in common with many domestic insurance policies, landslides are excluded from their cover.
Yesterday BC Transportation tweeted this very impressive image of the landslide:-
The landslide itself is interesting. It appears to have started in the steep upper catchment, although the initial failure event is far from clear. It may well be a very small failure or even a temporary blockage in the channel. It then appears to have transitioned into a classic channelised debris flow. The middle part of the landslide track seems to show large amounts of erosion, suggesting that the landslide was entraining material to increase its volume.Deposition may well be controlled by a gradient change in the underlying topography. If you look carefully on the right side of the deposit the house that was destroyed can be seen, as shown in the CBC image below. Note that this is a two storey house, so the lower half of the house is completely buried:-
The best impression of the type of debris involved in the Pemberton Portage Road landslide can be gained from this short video of the immediate aftermath of the landslide, uploaded to Youtube by BC Transportation:-
Clearly this is not a mudflow per se (as the various articles are describing it), but technically it is a channelised debris flow.
There is now a fundraising campaign for the family – details are available on the Kelowna Now website. It is easy to forget the long term impacts of these types of landslides. There does seem to be a need to reconsider the lack of domestic insurance cover for mass movements in most countries.
Similar events that may be of interest:
- The 2011 Umyeonsan debris flows in South Korea
- Aerial images of the Izu-Oshima debris flows in Japan
- The June 2008 Lantau debris flow in Hong Kong
Another landslide in the Pemberton area (but somewhat larger!):
Thanks to Mika McKinnon for highlighting this landslide to me.