Transcript
DAVE PETLEY: Generally speaking, although not always, the landslide blockage is loose and broken up material. So as the water starts to flow over the top it erodes the landslide away. The water gets released very very quickly, and it picks up all the debris from landslides, generating what is essentially a huge debris flow that then travels all the way down the river channel. And that's really destructive, because the volumes of water can be quite large. And the amount of sediment that it is carrying is very destructive. So in the past we've seen really damaging floods from these sort of landslide dams. The question in this case is of course going to be, what is the potential for that happening and over what time scale? How many of these things are there, and who is downstream? This is a problem that needs attention. It might well be that... although there is the potential to generate significant floods here, in fact the number of people who would be affected is relatively low. But it feels to me that that sort of assessment needs to be done fairly urgently.
JOHNNY BLADES: This Hela and Southern Highlands region, generally is the earth quite loose and unstable? Obviously, there's been a lot of rain up there lately as well...
DP: Yeah this is an area that hasn't been studied in a huge amount of detail. But because there was a large mining project to the west (of the epicentre) at Ok Tedi which suffered an enormous landslide a couple of decades ago, some detailed mapping has been done of the landslides in these mountains. What we found is that this is a landscape which is absolutely dominated by landslides, both in terms of ongoing processes - so in an earthquake or heavy rainfall you would expect to see landslides - but also a legacy of lots of landslides sitting all over the landscape which would be reactivated in these sorts of events. So in a way it's not a surprise to see large numbers of landslides in this sort of significant earthquake.
JB: This is all going to require a lot of assessment, mapping and all that sort of stuff which will require a lot of resources for a country like PNG.
DP: Yeah. There's sort of two elements to this, I think. The first element is really as a matter of absolute urgency, we need to try to get an assessment of what is up there. So, how many of these landslide dams are there? How tall are they? How wide are they? And how much water are they starting to accumulate? This is obviously an area that suffers really heavy rainfall. I read for Ok Tedi further to the west that there's up to ten metres of rainfall per year. So potentially these landslide dams can fill with water really fast. So that's the first element. There is a real need just to get a handle on what is there and how dangerous might that be. And then the second element that we need to do is, if there are landslide dams that are dangerous, is either to move everyone out of the way of them before they breach, or to try and get heavy equipment in to drain them out. Now obviously draining them is a real challenge. In the aftermath of the 2008 earthquake in China, the Chinese authorities dealt with about 200 of these successfully, although in one case they had to evacuate a million people downstream when they breached it. But they had enormous resources at hand. I doubt that Papua New Guinea has that level of resource, so outside assistance is going to be needed. In this area of PNG obviously road access is even worse, and so if it does come to pass that there is a need to manage some of these landslide dams, that's going to be very challenging indeed.
JB: Are you picking up on any signals of any particular bad landslides and so forth around the LNG Project in Hela and Southern Highlands?
DP: That's a really interesting question. Those pipelines are designed... the alignment is designed to try to minimise the effects of landslides. but some of the landslides here look so large that obviously if the pipeline is in the way there is potential for the pipeline to be damaged. The pipelines themselves also cross active faults. And we're only starting to get the (satellite) imagery now that give us an indication of which faults have ruptured. And again the pipelines are designed to be able to take some faulting-related defamation. The imagery at the moment isn't good enough for us to be able to tell whether the pipelines themselves are damaged. And there doesn't seem to be very much information coming out at the moment from the owner/operators of the pipelines. So it's a bit of an unknown, to be honest.
