13 July 2012

A (probably) fatal landslide in Johnsons Landing, Kootenay Lake, BC Canada yesterday

Posted by Dave Petley

A large landslide hit the community of Johnsons Landing in British Columbia yesterday, leaving a reported four people missing.  The landslide is thought to have engulfed three houses, of which one was fortunately unoccupied. A number of news outlets in Canada have good initial reports about the event, including:

The best images are this one from CBC News:


And in particular this one from TMTV News:


The landslide appears to have been a highly mobile flow type of event, but with quite an interesting and unusual morphology in the toe region.  On a provisional inspection (and very tentatively) it appears that after an initial failure the landslide debris followed an existing channel and then spilled over the bank and down the slope, with some of the debris remaining in the channel (see the lower left of the upper image).  I think that this is the area on the Google Earth imagery, but again this is pure speculation at this stage:

A slightly intriguing aspect of this event is that the weather at the time of the event is reported to have been sunny and warm (although there has been a lot of rain recently).  Even more intriguing is the fact that just a few minutes before the landslide, at 10:22 am local time, the USGS recorded a small earthquake in BC that they are describing as a quarry blast.  Initially I wondered whether this might be the seismic signature of this event.  However, the location is reported to be about 275 km from Johnsons Landing, although I am not sufficiently au fait with seismic data to be able to state the likely location error.  Just to be clear though, it is highly unlikely that the recorded seismic event was the trigger for the landslide, and there is a high chance that it iscompletely unrelated.  I would be interested to hear the views of those with more experience of seismic data than me.