4 September 2009
As I reported a couple of days ago, the Mw=7.0 earthquake in Indonesia on Wednesday triggered a substantive landslide in the village of Cikangkareng in West Java. This landslide buried ten houses, a mosque and an amusement (video game) arcade with the loss of about 57 lives. AP have today released images of the landslide that are quite interesting. In particular this one:
Why is this interesting? Well, first lets note that we should ignore the red colour on the face of the scarp – this is a mantle of tropical soil that have come down from the crown of the slide (you can see the red soil at the very top of the landslide – this is of course typical of a tropical area). More important is the structure behind the mantle of soil debris. Here it is clear that the rocks are horizontally-bedded (or at least nearly so). Such a large failure in horizontally-bedded rocks is certainly not unprecedented, but is slightly surprising. The debris is very coarse-grained and has travelled quite a long way, which is also interesting.
Often, failures like this are associated with some process that has caused undercutting of the toe – for example wave erosion. Clearly there are no waves here – I wonder if there had been any activity to quarry stone from the slope, perhaps as a building material?
I am reminded of the Manshiet Nasser landslide in Cairo a year ago:
In that case the key cause was probably quarrying at the foot of the slope.