Satellites revealing new view of lingering landslide risk after 2023′s extreme summer

Several people were injured in the collapse of a Manukau Heads bach during last year's Auckland Anniversary weekend deluge. Photo / Michael Craig

Last year’s extreme summer caused 50,000 slips in Auckland alone: now, scientists are turning to satellites to gauge landslide risk in the places hit hardest.

Wreaking an estimated $250 million in damage each year, landslides are considered more dangerous than earthquakes - as shown by the hundreds of properties condemned after last summer’s storms.

In some of the most serious incidents, Remuera resident Dave Lennard was killed when a landslide crashed into his Shore Rd home, while several people were injured inside a collapsed Manukau Heads bach.

In a just-launched project, researchers are returning to the hardest-hit sites to investigate whether the land gave any warning signs before slipping - and what could happen in future.

“Until these problems are addressed, it’s difficult for people to return to their homes, rebuild, or return to any semblance of normal life,” said University of Auckland geologist Associate Professor Martin Brook, who’s leading the EQC-funded effort.

Rather than taking the traditional approach of ground-motion sensors on land, Brook’s team will draw on satellite-based InSar technology capable of detecting millimetre-level changes from space.

“InSar can give us a much better understanding of landslide hazards at a street or even individual land parcel level, without stepping foot on the ground.”

Last year’s extreme summer caused 50,000 slips in Auckland alone. Photo / Brett Phibbs

That data has been collected from the Sentinel-1 satellite, launched by the European Space Agency in 2014 as part of its Copernicus Programme.

By comparing detailed satellite images taken over the same geographic areas before and directly after the storms, Brook hoped to glean fresh insights into what caused the ground to slip.

“It could tell us if slopes which seem to have stabilised are still moving, and if they are showing any increased movement.”

The results would be eventually shared with EQC and local councils, as well as in published research and public meetings.

Auckland Council engineering resilience head Ross Roberts said his team had mapped some 50,000 landslides since last summer’s events, which was five times more than he’d initially anticipated.

Roberts said the council had been using InSar itself: a technology he said remained limited by the fact it often couldn’t pick sudden, storm-triggered landslides - as mainly happened in Auckland.

“They happen in pretty much an instant, and then a few seconds later, they’ve stopped.”

Nevertheless, Roberts said Brook’s study would add to the council’s evidence base - all of which would eventually inform changes in local planning policy.

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.