19 October 2015
First announcement: a giant rock avalanche on the flanks of Mount Steele in the Yukon last week
Posted by Dave Petley
Mount Steele Rock Avalanche
On 12th October at 02:02:32 UT a giant rock avalanche occurred on the flanks of Mount Steele in the Yukon area of Northwest Canada. The landslide was detected by Colin Stark and Goram Ekstrom of Columbia University using the global seismic network, and I am posting this news with their kind permission. Since the landslide occurred the availability of cloud-free satellite imagery has allowed the location to be identified.
The landslide is large – I will give the full details from the seismic inversion tomorrow – but Stark and Ekstrom estimate a mass of about 60 million tonnes, which yields a volume of about 24 million cubic metres. The crown of the landslide is at an elevation of about 3350 m, the total vertical distance is about 2200 m to the toe, with a runout over the Steele Glacier of about 3700 m.
Colin Stark has provided this Landsat 8 image of the landslide, draped into a digital elevation model. As can be seen below the landslide detached from the flank of Steele SE, a sub-peak of Mount Steele:
This is an image of the same location on Mount Steele before the landslide, also from Landsat 8 via Colin Stark:
Note the location of the landslide as indicated through analysis of the Landslide Force History (LFH) seismic data. This was within 7 km of the actual location of the Mount Steele rock avalanche, which is impressively close. The seismic data suggests that this rock avalanche had a peak velocity of about 60 m / sec, which is about 220 km/h. An interesting aspect of this landslide is the smooth morphology of the slope that failed compared to those around it, as seen in the above image. I am unsure as to whether this is significant.
I will provide more detail about, and further images showing, this landslide tomorrow.