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16/3/2018 — Environment and Society
Quake upheavals moved mud great distances

Scientists now say that a massive underwater landslide caused by the devastating 2016 Kaikoura earthquake moved more than 100 million dump trucks of mud and sand over hundreds of kilometres.

GNS Science has given detailed accounts about the damage and the impact the quake had on the landscape and seascape in the Kaikoura region.

Now the website newstalkzb reports that the landslide, known as canyon flushing, was one of the largest ever documented and took place just off the Canterbury coast in the Kaikoura Canyon.

Scientists, publishing a paper in the Science Advances journal last week, found at least 850 tonnes of sediment billowed down from the top of the canyon.

It wiped out all organisms living in the seabed before travelling along the deepsea Hikurangi Channel to distances up to 680 kilometres north-east of Kaikoura.

Lead author of the report Joshu Mountjoy reportedly said the canyon head had been smooth and draped in mud in 2013. However, investigations two months after the 2016 earthquake revealed mud had been stripped away from almost every part of the upper slope.

“The event has completely changed much of the canyon floor, eroding into rock and moving dunes of gravel through the lower canyon,” he said.

"We knew that events like this could happen from telecommunication cable breaks during earthquakes - however, we have never had data to show us what impact these events have on the canyons themselves.”

Newstalkzb said scientists found parts of the canyon had deepened by up to 50 metres because of sediment cutting into the sea floor.

The website reported scientists claiming similar events triggered by large earthquakes were likely to occur in the Kaikoura Canyon every 140 years on average. The mass upheaval also released 7 Mt of carbon, now available to nourish deep sea communities.

This report comes after a NIWA study last September found the canyon's former biodiversity hotspot decimated by the earthquake was now showing signs of recovery and re-colonisation by animals.

Other studies since 2016 have also revealed the quake was the most complex one ever recorded, with more than 21 on-and-offshore faults rupturing across more than 100 km.

This led to widespread coastal uplift and numerous landslides.

In the past week the earthquake monitoring website GeoNet has reported a series of light to moderate earthquakes hitting the Kaikoura region, with two recorded on Wednesday - the strongest on Wednesday evening being magnitude 3.8 at a depth of 17 km, and 10 km west of Kaikoura.

Early morning on Thursday last week there was a M 4.7 quake at 9 km depth categorised as “moderate” which was 20 km west of Kaikoura.

Sources: newstalkzb.co.nz, nzresources.com; geonet.org.nz; gns.cri.nz, niwa.co.nz

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