Muriwai: the complex story of a fatal landslide in New Zealand

In New Zealand, the clean up after the heavy rainfall of recent weeks, and in particular the impacts of Cyclone Gabrielle, continues. The number of landslides is very high – Auckland Council estimates that there have been 3,000 to 5,000 landslides in that region alone, with about 1,000 causing damage to properties and infrastructure.  The ground remains saturated, and some rain has continued to fall, so the risk of slope failures continues.

Landslides killed at least two people.  In one event, at Muriwai, a slope failure killed a volunteer member of the fire and rescue service, Dave van Zwanenberg, and left another critically injured.  The NZ Herald has an excellent article about this landslide, and others in the Auckland area.  It quotes an old friend of mine, Tim Davies of the University of Canterbury, who has noted that the recent events will probably have changed the landslide risk profile of Auckland permanently:

“…the slips this week might have destabilised adjacent areas and made them more likely to fail in future storms.”

I think this is likely to be correct.

Meanwhile, the Muriwai landslide event is also explored in an article on Stuff.  Martin Brook of the School of Environment, University of Auckland has noted that the track of the landslide partially coincides with another landslide that occurred in 1965, killing two people.  Back in 2013, the same outlet ran a story about this earlier landslide.  Rather presciently, the 2013 article quotes Kay Allen, a resident of Muriwai at the time of the 1965 landslide, on seeing a small slip in the same area:

“The Mt Somers resident was horrified to see yet another landslide above Domain Cres in Muriwai.

“I don’t want to see history repeating itself,” Ms Allen says … “We walked down to the slip to have a look – it’s nowhere near as big but it’s in the same place and the ground looks unstable.”

The Waitemata County Council declared back then that the sections in the path of the slip would never be built on.

“There are now houses on all those sections,” Ms Allen says, decades later.

Newstalk has a gallery of photographs of the aftermath of the landslides at Muriwai, which includes this aerial image of the site of the fatal failure:-

The aftermath of the landslides at Muriwai. Image by George Heard via Newstalk.

.

Meanwhile, Stuff has another gallery of images from this area, which illustrates the scale of the problems.  Recovery is going to be a slow and expensive process.