30 May 2019
High resolution Planet Labs SkySat image of the Joffre Peak landslides
This is a beautiful image, capturing the track of the landslide in full. Note that there are some distortions in the source area, an artifact of the processing of an oblique image to a vertical view. Of course there are better ways to capture imagery of very steep slopes than the use of satellite images. But, importantly, the track is fully imaged.
Perhaps the most interesting aspect of this image is the mid track section of the Joffre Peak landslides site:-
In my earlier post I noted that there was little evidence of super-elevation in the lower bend of the landslide track (super-elevation occurs when fast-moving landslides travel around sharp corners; the landslide debris travel up the valley wall, much as a racing car moves to the top of a banked level of track). My interpretation of the image is that the landslide does appear to have undergone significant super-elevation around the first bend (in which it changed from a track towards the northeast to one towards the east). The evidence for this is the stripped slope, brown in colour and thus probably soil and weathered bedrock and rather than landslide debris. The landslide has stripped the trees from the slope.
There is a small amount of super-elevation in the first part of the second bend (where the track changes from eastwards to northwards), but much less than upstream.
The implication is that the Joffre Peak landslides were moving rapidly in the upper portion of the track, but more slowly when they hit the second bend. Immediately after the second bend there is a large area of deposition. Interestingly, there is also a considerable amount of deposition in the upper portions of the track.
Once again the high resolution imagery provides very clear insight into the landslide processes.
Reference and acknowledgement
Planet Team (2019). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. Thanks to Robert Simmon of Planet Labs for obtaining and processing the image.