17 November 2016
Hapuku River: a major landslide dam after the earthquake in New Zealand
With each passing day the impact of the Kaikoura earthquake becomes more clear. Whilst human losses in this sparsely populated area were low, the major legacy appears to be the landslides, of which there are very many. Resources are becoming available that provide detail, I would highlight the following as being particularly interesting:
- Canterbury Maps have put online a GIS map that provides details of their reconnaissance flights, and a large set of georeferenced photographs of the impacts, mostly landslides.
- The ESA has placed online a Sentinel satellite image that, though cloudy, allows many of the landslides to be seen. The implication from this image is that landsliding is very extensive.
- The Research Group on Engineering Geology in Greece has posted a provisional landslide map, again using the Sentinel image. This is not complete because of the cloud cover, but it starts to give an indication of what an extraordinary event this has been in landslide terms. I think we can now safely say that this is the largest landslide events since the 2008 Wenchuan earthquake in China:
The landslide dam on the Hapuku River
At the moment the site that is causing the greatest concern is a landslide dam on the Hapuku River, which has completely blocked the flow and is about 150 m high. This landslide was witnessed and photographed by a local resident, Neil Protheroe. The Civil Defence has been circulating this photograph of the dam, and has advised those living downstream to relocate.
There is a set of images on the Canterbury Government web server that I highlighted above, of which these are two:
The dam appears to be tall, narrow and, at least on the surface, comparatively fine grained. The concern about the threats posed by this river blockage are not misplaced. More detailed analysis is urgently required, and will undoubtedly be underway.