13 January 2014
Dart Valley Landslide
In the last two weeks there has been some interest in New Zealand in a landslide that blocked the Dart Valley on South Island on 4th January, creating a large lake. Initially there was some concern that this landslide dam might suffer a breach event, but fortunately the water overtopped the landslide deposit without a major failure. The landslide is a well-known feature (GNS have a long-standing image of it on their website), situated in the Te Koroka / slip stream area, and located at -44.587,168.332. It is easily identifiable on Google Earth from an image in August 2011:
The January 2014 movement event is just the most recent of a succession of landslides at this site – it has even been written up in a GNS Science report (Thomas and Cox 2009), although sadly I cannot find this online. Several news stories have good images of the landslide during this recent event, including this one from The Press:
The lake that developed reached a maximum length of over 3 km and is over 20 m deep. Aerial imagery suggests that this is quite an impressive feature:
The major impacts of the landslide has been the inundation of a hiking track along the valley, which has now been rerouted, and temporary suspension of jet-boating downstream. The landslide dam is not considered to pose a major risk. However, the silt generated by the erosion of the landslide has also caused the colour of the water in Lake Wakatipu to change to a blue-green colour.
Thomas, J.S. and Cox, S,C. 2009. 42 years Evolution of Slip Stream Landslide and Fan, Dart River, New Zealand. GNS Science Report Sr 09/43, 32 pp.