Landslides and Landslide dams caused by the Kaikoura Earthquake

After the Kaikoura Earthquake, the GNS landslide and paleoseismology teams were quick to take to the air on the 14th November to find evidence of the earthquake effects in the landscape. The team were fascinated by the sights they saw from the helicopter. The effects were widespread over an area of 7,000 km2 with estimates that there has been between 80,000 to 100,000 landslides triggered by the earthquake and subsequent aftershocks.

Along the coastline damage became apparent south from Cape Campbell, becoming more intense south of the Clarence River, with several large (100,000 – 500,000 m3) landslides disrupting both SH1 and SIMT railway (e.g. Ohau Point and Waipapa Bay areas). South of Kaikoura, on the steep slopes near Twin Tunnels, damage was similar to areas north of Kaikoura, again covering and or disrupting both SH1 and SIMT. 

Landslide Dams

Since Tuesday, GNS has been working to compile a complete inventory of landslide dams in the area affected by landslides after the earthquake. This work has two parts. The first involves using remotely sensed imagery to locate landslide dammed lakes in inland areas. The second involves a systematic search of vulnerable areas. 

A satellite image from WorldView-2 image was received and processed. This image covers part of the area north of Kaikoura and has identified 12 landslide dams. Only one was known prior to processing this image.

GNS has also started systematically flying landslide affected areas to visually identify landslide dammed lakes. The southeast flank of the Seaward Kaikouras, was flown on the 16th November and seven landslide dams were found. These flights will continue over the next three or four days. The purpose of these flights is to systematically cover affected areas where no data is currently available. The second purpose is to photograph the landslide dams to allow assessment of the hazard at each site.

As the data comes in it is being forwarded to NIWA to undertake dam-break modelling, which will help determine what will happen if the dam-breaks. From this people and assets at risk can be identified.  

 

Safety around Landslides

Please take precautions and stay away from regions of landslides and landslide dams. Avoid rivers or streams that have been blocked by landslides. Stay away from steep cliffs and slopes in the Kaikoura and Marlborough region. 

Director of the Ministry of Civil Defence and Emergency Management, Sarah Stuart-Black, advises that people in those areas to be especially vigilant and to keep clear of river valleys and outlets. Landslide dams can break quickly, and release large volumes of water and sediment as a flood wave. Homes at potential risk have been advised to evacuate.

For more information from the Ministry of Civil Defence and Emergency Management, go to http://www.civildefence.govt.nz/.

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