By Professor Dave Petley*
The landslide a week ago in Papua New Guinea continues to generate a great deal of noise in that part of the world. The confirmed death toll is now 25 people, but that number is expected to rise. However, given the size of the landslide, I wonder whether it is really possible to recover all of the victims. Only four bodies have been recovered to date.
There are now some better images of the landslide available online. This one, from the Australian, appears to show the head-scarp area.
The article suggests that the landslide occurred at the site of a limestone quarry (of which more below). Certainly the rock would appear to be limestone with quite a thick soil layer. The very planar rear scarp would suggest a large, unfavourable joint as the release plane. The block at the top on the left is still sitting on this joint and may be unstable. The joint either has a very weathered surface and/or is draped by soil from above.
It is interesting to see the way in which the lower part of the landslide has bifurcated down two drainage paths – unusual but not at all unprecedented. Of more interest is the apparently large lateral margin scarp on the far side of the landslide, below the trees, which suggests that the landslide has removed a considerable volume of material on that side. It is hard to tell, but this does not seem to be replicated on the nearside. To me this suggests quite a complex landslide process (although this does not mean that the triggering process itself was complex). This does suggest that if a meaningful investigation of this landslide is to be undertaken then it will need someone who really knows how to interpret landslide processes. It is not likely to be straightforward in any way.
At the time of the landslide there were suggestions that it was linked to the LNG pipeline being built through the area by ExxonMobil. It now appears that the hillslope was a limestone quarry associated with the project, which fits with my observations of the area at the crown of the landslide. There is a pdf online here,with an Esso Highlands logo, entited “TUMBI QUARRY (QA1) Resettlement Action Plan”, which states that “Tumbi Quarry, known as QA1, is required for aggregate to be used by the Project in the Komo area. The Project will be leasing the quarry from Hides Gas Development Corporation (HGDC) for an estimated two year period, depending on aggregate requirements of the Project, after which the quarry will be returned to HGDC.”
The LNG watch blog has a post by Dr Kristian Laslett of Ulster University, which notes that the site had been blasted in the days leading up to the landslide. This seems to be supported by various news reports, although of course there is no proof either way. It seems entirely plausible, though not certain, that the landslide could have been triggered by blasting. There are many previous examples of landslides being triggered by quarries.
It seems to me that an investigation of this event is urgently required. However, the investigation does need to be undertaken by an open-minded, independent and very experienced team as the landslide is complex. IF the quarry was the cause or trigger for the landslide, and if it was providing rock for the Exxon-Mobil project, then this is surely somewhat significant.
Given the focus on the Deepwater Horizon accident a couple of years ago, I am amazed that the mainstream media are not pursuing this story with some alacrity. One would also hope that Exxon-Mobil will fund a proper investigation of this, and that they will look again at any other quarries that are providing rock for the pipeline project.
* Wilson Professor of Hazard and Risk in the Department of Geography at Durham University, United Kingdom. Originally posted on The Landslide Blog.