21 July 2015
Semirara: an interesting coal mine landslide video
Posted by Dave Petley
Last week a landslide occurred in a coalmine on the island of Semirara in the Philippines, killing nine miners. Semirara is a strange place, as satellite images show:
A huge portion of the northern part of the island has been mined out. This is a mine that appears to be very prone to landslides – the image below shows an earlier collapse for example:
There is an excellent gallery of images of the landslide last week on the ABS CBN website, from which this image is taken:
The ABS CBN report suggests that this is a very large landslide – 374,000 cubic metres. The failure appears to be a rotational slip with quite a high level of mobility at the toe. The report also indicates that the slope was being monitored with prisms (i.e. optical surveying), so it is quite surprising that such high levels of loss occurred. I would be very interested to see the data.
Anyway, there is a video version of the news report on the Youtube website. This includes a section of video that I have not seen before – it starts about 20 seconds into the report – that shows an earlier (smaller) landslide in the same mine:
This is quite interesting in terms of the way that it starts as a comparatively small cliff collapse but then fragments on impact to transition into a high mobility flow. It is understandable that the effects are so dramatic when people get in the way of these landslides.