Quakes set off multiple landslides on Raoul Island
They were the earthquakes that resulted in tsunami warnings and mass evacuations for those living on coastal areas around the country.
But it seems the quakes that hit in the early hours three weeks ago — on Friday, March 5 — also resulted in a different kind of natural phenomena.
More than 300 landslides have been found on Raoul Island, in the Kermadec Islands, near where an 8.1 magnitude quake struck that morning.
That big shake, which was 80km from Raoul Island, came after a 7.1 magnitude quake off the North Island about 2.30 that morning, followed by a 7.4 magnitude quake just over four hours later.
Geonet, a collaboration between the Earthquake Commission and GNS Science, has revealed stunning images showing just how much the island had changed after staff visited following the quakes.
“Our team of experts discovered that the island was scattered with more than 300 new landslides,” Geonet said.
With the help of the New Zealand Defence Force, staff members were able to map out the various landslides using satellite imagery, oblique photographs and pre-earthquake imagery.
“The coastal slopes generally have a high stimulated landslide portability and most of the mapped landslides occurred on these slopes,” a Geonet statement said.
“This is because they are generally steeper in angle and higher in local slope relief.”
The Geonet staff also found that larger landslides had happened on the volcanic crater rim on the island; which corresponded to areas of “high simulated landslide probability”.
GNS Science geologists Chris Massey, Brenda Rosser and Biljana Lukovic said the “most spectacular” landslides happened around Blue Lake and along the rugged coastline on the island.
Some of the larger ones identified were up to about 20,000 cubic metres..
“Think two rugby fields neckdeep in rocks,” the geologists reported.
The other relatively smaller landslides ranged between about 100 cubic metres and 200 cubic metres and most were made up of rock and soil avalanches and falls, the scientists said.
“There was a significant slip at Bells Beach — where about 400m of coastal cliffs collapsed, leaving a plume of sediment in the ocean.”
The major quakes this month were described as a “swarm” and resulted in much of the North Island — including Northland, parts of the Bay of Plenty and the East Coast — being affected by a tsunami warning.
Many towns were also evacuated as a result of the tsunami danger and the National Emergency Management Agency issued a series of warnings that day.