11 July 2017

Ngauranga Gorge: a landslide caught on video causes chaos in Wellington, New Zealand

Posted by Dave Petley

Ngauranga Gorge: a landslide caught on video causes chaos in Wellington, New Zealand

The most important road in and out of the capital of New Zealand, Wellington, is State Highway 1, which passes through Nguaranga Gorge as it crosses the hills on the edge of the city. This afternoon, a landslide occurred on the walls of the gorge, with the debris ending up on three lanes of the carriageway.  The rockslide came down when the road was busy, but fortunately did not strike any vehicles.  The landslide was captured on the dashcam videos of two vehicles travelling through Ngauranga Gorge at the time.  This vehicle had a near miss:

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The other video was recorded from a vehicle travelling in the opposite direction. WordPress no longer allows simple embedding of videos, so I cannot post this one, but you can view it here.  The same news report has a nice image of the aftermath of the landslide:

Ngauranga Gorge

The landslide on the Ngauranga Gorge outside Wellington on 11th July 2017. Image via Stuff.co.nz, Kent Petersen

 

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This looks to be a comparatively small landslide, but it nonetheless caused very considerable traffic disruption.  The stability of the Ngauranga Gorge has long been a concern, in particular in relation to a potential Wellington Fault earthquake.  As an article from earlier this year noted:

New Zealand Transport Agency Wellington highways manager Neil Walker said the agency was investigating the stability of the Ngauranga Gorge, and expected to complete stabilisation improvements within two years.

I noted  hazards associated with steep slopes in Wellington, in particular in the event of an earthquake, in a post earlier this year.  The problems posed by the Ngauranga Gorge can be seen in this image from Google Earth, which looks down the road towards the city.  At the foot of the hill, on the margin of the bay, is the trace of the active Wellington Fault.  The gorge slopes would be likely to suffer various nearfield effects that make the behaviour somewhat unpredictable.

Ngauranga Gorge

Google Earth image of the Ngauranga Gorge, showing the steep slopes from which the landslide orginated

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It is interesting that this slide came down in good weather.