Possible pre-failure ground deformation at the St-Jude quick clay landslide in Canada

Sadly, it has been confirmed that the family reported missing in the landslide at Saint-Jude in Canada yesterday were killed in the basement of their house.  Interestingly, the area of road on the north side of the slide looks like this (this view is looking north, effectively standing on the slide looking across at ground that did not move):

Note the two large, very recent tarmac repairs extending right across the road.  The nearer of the two is very suspicious given its shape.  There are also other hairline cracks in the road - right in the foreground for example.  This one may have a small amount of displacement across it (the line is slightly offset) although this may well be just an artifact of the image.  However, compare the two repairs with the Montreal Gazette aerial view of the slide - in this case looking from the north towards the south (i.e. in the opposite direction to the Google Earth image:

 The larger of the two repairs is clearly visible in the image, which means that the lateral margin (edge) of the landslide is almost exactly where the other repair is located.  It may well be that slide was creeping prior to final collapse, although this is clearly no more than speculation at this time.

I am glad to see that the media reports are now calling this a landslide rather than a sinkhole!

Possible flowslide (not a sinkhole) in St Jude, Canada

The Canadian media is reporting the case of a "sinkhole" that developed in St Jude, 77 km to the north of Montreal, last night.  The sinkhole included a family house, with four people inside.  At the moment these occupants are reported to be missing. 

The Montreal Gazette has a photo gallery of the site.  One of the photos is this one:

Based upon this image this does not look like a sinkhole but instead to be a quick clay slide, probably in Leda Clay.  Such slides are not uncommon in this area.  I have covered a previous example in Norway on this blog.  The famous Rissa quick clay landslide in Norway is available as a video here if you want an idea of the extreme end of this type of failure.Quick clay slides often occur on very low angled slopes, and can be triggered through ground disturbance which causes the clay to restructure, allowing it to flow.

At the moment I am unsure of the exact location of this event, but St Jude is at 45.77 N, 72.99 W.

Hat-tip to Peter Weisinger for highlighting this one.

Norwegian landslide - is this a quick clay slide?

Most people would probably not think of Norway as being hazard prone, but it does have two particular landslide issues. The first is that occasional large-scale failures occur on the walls of fjords. Given the height of these rock walls, these failures can be large and energetic, and sometimes trigger small scale tsunamis. The other is a strange type of failure known as a quick clay slide. Perhaps the best way to explain a quick clay slide is to direct readers towards the original landslide viseo, which shows the Rissa slide. This is described at the site below, which also contains the video in two parts:

http://www.ce.washington.edu/~geotech/courses/cee522/RissaLandslide/rissa.html

Do take a look - the film is amazing. quick clay slides occur in marine clays that have an unstable structure. Disturbance of that structure can cause a massive reduction in strength, which then destabilises the slope allowing failure on even low slope angles. In the case of Rissa, a small excavation for the foundations of a barn was enough to trigger the failure.

Today, reports have emerged of a landslide at Namsos in Norway that has destroyed ten or so houses. Fortunately there have been no fatalities. Various pictures of the landslide are available - these two particularly caught my eye (from here and here - click on the image for a better view in a new window. The people are homeowners I think):




Familiar? It is clear that this is a landslide occurred in clay on a pretty low angle slope on the edge of a lake. What's more, the newspaper reports (e.g. this one) suggest that "It happened near a road construction site, and NRK said it could be related to blasting or excavation." I don't know for certain that this is a quick clay landslide, but I have my suspicions, especially when I look at this image of the site (from here):


There are a some other pretty good images around too, mostly focusing on the aftermath. For example, this one (from here) shows the displaced houses:

Whilst this one (from here) shows just what a low angle slope the failure occurred on. Presumably the road works in the foreground are the proposed cause of the problems:


Quick clay landslides are pretty rare (I have never seen one) if rather dramatic.