Auckland floods: Big downpours likely to have caused thousands of new landslides, slips - expert

People in storm-hit regions are being urged to keep away from steep slopes and cliffs, as an expert predicts the extreme weather has caused thousands of fresh landslides and slips.

Torrential downpours over recent days have brought widespread slips and flooding across the upper North Island, with 34 roads closed – down from 80 – as at Wednesday afternoon.

In some of the most serious incidents, Remuera resident Dave Lennard was killed when a landslide crashed into his Shore Rd home on Friday night, knocking it off its foundations.

On Saturday night, several homes in Tauranga’s Egret Ave were destroyed as a slip came down amid heavy rain, while, this afternoon, another landslide that collapsed a seaside bach at Auckland’s Manukau Heads left three people injured.

Three people are injured - one critically - after a building collapsed in Orua Bay Beach at Manukau Heads this afternoon. Photo / Michael Craig

GNS Science engineering geologist Andrea Wolter said reports of landsliding had been received from as far afield as the Bay of Islands to south of Taupō.

“So far, we have identified 240 sites from traditional and social media, with some sites including multiple landslides,” she said.

“We are actively still gathering information.”

These included many landslides with Auckland – particularly in West and Central Auckland, and coastal cliff areas – as well as in Bay of Plenty.

“Coromandel is likely also badly impacted.”

Associate Professor Martin Brook, of the University of Auckland’s School of Environment, expected the wet weather would have caused thousands of new landslides and slips across the upper north.

The picture would become clearer with new satellite imagery, he said.

“In Auckland, from what I’ve seen there appears to be a lot of failures on vegetated slopes.”

Severe rainfall has caused extensive flooding and destabilised slopes around Auckland and Waikato. There’s potential for more landslides in the coming days with rain forecast this week. We have information and links for those in affected areas here: https://t.co/Mcdcqd3XMX pic.twitter.com/KUNfnV37HK

— GeoNet (@geonet) January 31, 2023

Across the upper North Island more generally, he was expecting to see many shallow “translational failures” – or the failure of a slope along a weak zone of soil – along with widespread damage to pastures in rural areas.

“While some of these failures might be in the middle of fields, once the soil is gone, it doesn’t come back for a generation or two.”

Wolter noted it had already been a wet summer before the latest events, and pre-existing ground conditions “certainly wouldn’t have helped”.

More rain could further destabilise slopes that had already slipped, and ground cracking and slumping – warning signs of landsliding – had been reported across affected regions.

“Landslides can also occur without warning, [such as on] sunny days after the rain.”

We're experiencing more flooding, slips, underslips, and debris on state highways as the severe weather continues. If you're in a North Island region affected by the rain, don't travel unless you have to. pic.twitter.com/Shzo37psbz

— Waka Kotahi NZ Transport Agency news (@WakaKotahi_news) January 31, 2023

She encouraged people to stay up to date with current weather warnings and emergency management information – and to stay away from steep slopes and cliffs if possible.

“If you notice doors and windows not closing, or cracks in cladding, paved areas, or the ground - particularly on slopes - advise council.”

Aucklanders were also being advised to keep away from walking tracks on conservation land, as local Department of Conservation staff assessed damage.

People can report slips and landslides - with as much detail as possible about the time, size, location and type - to landslides@gns.cri.nz.