27 April 2021
Great Whale River: a very large, low-angled landslide in Canada on 22 April 2021
On 22 April 2021 a very large landslide occurred on the Great Whale River, upstream from the upstream of the villages of Kuujjuaraapik and Whapmagoostui in Quebec, Canada. Nunatsiaq News has this dramatic image of the landslide:-
The landslide is located at 55.298, -77.638. It is clearly visible on the Planet Labs image taken on 23 April 2021:-
The slide is large – from the crown to the channel it is about 1.6 km, and from the crown to the toe it is about 4 km.
The landslide is not thought to pose a direct threat to the communities downstream, fortunately, although there is some risk to users of the river as break-up of the ice is now unpredictable.
The news reports describes this as having occurred in an area of clay. The form of the landslide suggests that it could be a quick clay / sensitive clay failure. CBC has a splendid video shot from a helicopter that flew the length of the landslide. This is a still from that video:-
The video suggests that the downstream deposit is highly liquid mud with rafts of trees. Note that many are still standing upright. This is indicative of a quick clay landslide. The landslide itself appears to be quite deep-seated, probably reflecting a thick clay deposit. This implies that the volume of the landslide on the Great Whale River is likely to be in the millions of cubic metres.
There is little information as to the likely trigger at this point, but large landslides often occur in the spring as melt occurs.
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/