Drones will take to the skies above Auckland to reveal the threat landslides pose to many parts of the city.
Big deluges like those that came with cyclones Fehi and Gita are known to trigger big slips around our largest city - but activity like removing trees, steep roadside cuttings and leaking pipes can also raise the risk.
Not all landslides involved fearsome avalanches of rock and debris, but were sometimes "small and slow-moving" masses, University of Auckland researcher Dr Martin Brook said.
These still had the potential to wipe out a person's backyard, threatening their home and its value.
In a new EQC-funded study, Brook and his team will use drones to take a closer look at how land is moving on 10 slopes in different parts of Auckland.
"We know we have areas like Avondale, parts of the North Shore, East Coast Bays, Orakei Basin and others places where the water builds up under the soil."
On these slopes, the water soaked into the soil, but could hit a barrier layer, like clay or hard rock, and couldn't soak further down.
"As it rains, the water pressure within the spaces between individual soil particles keeps building up," Brook said.
"Eventually, the soaked soil will start to move down the slope, creating a landslide and gradually taking anything built on it with it."
Detailed images captured by the drones will be fed into software that creates 3D models of the ground.
Those models will then be compared to laser-generated Lidar data, revealing how much the ground has shifted.
"Because our system of getting the data is so much cheaper, we can also take readings four times a year and get a good sense of how fast the ground on a slope is moving."
The scans could also be cross-checked by taking regular photos that compared the ground to a fixed point like a fence or lamp post.
"All of this gives us a really good idea of how a slope is moving, and this is important data for people wanting to use the land."
Further, it meant council officers, developers and homeowners could take action before a landslide could happen.
"We have Auckland Council geotechnical scientists on the research team," Brook said.
"They'll be looking at the data itself, and also at the techniques we've used to get the data to see if it's something they might want to use more widely around the city."
EQC resilience general manager Dr Hugh Cowan said landslide research was important for New Zealand.
"Most years, EQC gets more claims for landslide damage than any other natural hazard," said Cowan, adding the new insights would be particularly crucial for those areas that may be opened up for future housing development.
The study comes as experts at GNS Science have launched a five-year, $8 million investigation into New Zealand's wider landslide risk.
That work will shed new light on how long a landscape takes to "heal" after a major event such as magnitude 7.8 Kaikoura Earthquake.
The November 2016 quake generated tens of thousands of landslides across an area stretching 10,000sq km, including the major slips that covered State Highway 2 and nearly 200 which blocked large, steep valleys.
Understanding how big quakes from major faults such as the Wellington Fault and the South Island's Alpine Fault could trigger landslides could help roading planners design safer routes.
Drones and science
• GNS Science technicians have already used a high-end hobby drone to help map and monitor our most active volcano, White Island. It's also been used to survey river terraces and geothermal systems around the North Island.
• Drones have been used in a Surf Life Saving New Zealand pilot study looking at how rip currents work.
• Otago University scientists deployed drones to capture detailed images of Southern right whales during an expedition to the wild and windy subantarctic islands.
• AUT scientists have flown drones over the freezing landscapes of Antarctica, the hot deserts of Namibia, and the wilderness of New Zealand for conservation surveys.