9 March 2011
Just when you think you have seen every conceivable type of landslide, one occurs that makes you catch your breath. A few weeks ago I included in two posts (here and here) rather sketchy details of a large landslide that occurred on 17th Feb in an open cast coal mine at Collolar in Turkey, which sadly killed ten employees of the site.
Two kind correspondants have provided updates. First, Caner Zanbak posted a number of links on the original post, including some images and also a thesis in which modelling of stability of the site was undertaken. Second, Einar Bjorgo posted a link to a UNOSAT satellite image analyis of the failure. This analysis can be downloaded as a pdf. This is the key satellite image from the latter source:
Wow! There are several key things to note here:
- There are two landslides: intriguingly there are collapses on opposing walls of the quarry.
- The size: note the scale bar at the foot of the image – the main landslide is c.300 m wide at the wall of the quarry and almost a kilometre in length. The text accompanying the image above indicates that the area covered by the two landslides is about 2.73 square kilometres.
- The images suggest that Landslide B occurred first as the toe appears to have been covered by debris from Landslide A. Understanding the sequence here is really important. I wonder if landslide B triggered landslide A in some way, whether they were both triggered by the same phenomenon, or that they were independent events.
- The accompanying text in the UNOSAT document suggests that Landslide A was rotational. I suspect that this is not strictly the case – to me it looks more like a translational failure with a considerable amount of flow. However, the transverse ridges (basically the bands that run across the landslide subparallel to the quarry wall) suggest that the slide was retrogressive (i.e. that it failed in stages consisting of sections of the backscarp slipping one after the other). Each of these successive quarry wall failures may well have involved rotation.
The best publicly available aerial image of the slide that I have been able to find is this one, from here:
Landslide A is on the left side of the image. The retrogressive nature of the failures is clear, as is the the flow style of movement. Landslide B is on the right – there may be an element of rotation here, but it is hard to tell. The challenge of clearing up the debris is manifest.