More than 300 new landslides found on Raoul Island after major earthquakes

It was the earthquakes that resulted in tsunami alerts and massive evacuations for those living in coastal areas across the country.

But it appears that the earthquakes that occurred in the early hours three weeks ago, on Friday, March 5, also resulted in a different kind of natural phenomenon.

More than 300 landslides have been found on Raoul Island, in the Kermadec Islands, near where a magnitude 8.1 earthquake occurred that morning.

That big shaking came after a 7.1 magnitude earthquake off the North Island around 2.30 that morning, followed by a 7.4 magnitude earthquake just over four hours later.

GeoNet, a collaboration between the Earthquake Commission and GNS Science, has revealed stunning images showing how much the island had changed after staff visited the area after the earthquakes.

“Our team of experts found that the island was dotted with more than 300 new landslides.”

With the help of the New Zealand Defense Force, staff members were able to map the various landslides using satellite imagery, oblique photographs, and pre-earthquake imagery.

“Coastal slopes generally have high portability of stimulated landslides and the majority of mapped landslides occurred on these slopes,” said a statement.

“This is because they generally have a steeper angle and higher locally sloped relief.”

Staff also discovered that larger landslides had occurred on the rim of the volcanic crater; which corresponded to areas of “high probability of simulated landslides”.

Landslides like two neck-deep rugby fields in the rocks

GNS Science geologists Chris Massey, Brenda Rosser and Biljana Lukovic said the “most spectacular” landslides occurred around Blue Lake and along the island’s rugged coastline.

Some of the largest identified had up to 20,000 m3.

“Think of two neck-deep rugby fields in the rocks,” they said.

The other relatively smaller landslides were around 100m3 to 200m3 and most were made up of avalanches and rock and soil falls.

“There was a significant landslide at Bells Beach, where about 400 meters of coastal cliffs collapsed, leaving a column of sediment in the ocean.”

Major earthquakes earlier this month were described as a “swarm” and caused much of the North Island, including Northland, parts of the Bay of Plenty and the East Coast, to be hit by a tsunami watch.

Many cities were also evacuated and the National Emergency Management Agency issued a series of warnings that day.