15 Mar 2018

Underwater mudslide deepens Kaikōura sea-canyon

5:23 pm on 15 March 2018

Scientists have found the massive underwater mudslide caused by the Kaikōura earthquake carved out parts of the nearby sea-canyon by up to 50 metres in places.

A NIWA model of the Kaikōura Canyon.

A NIWA model of the Kaikōura Canyon. Photo: NIWA

The Kaikōura sea-canyon has one of the highest volumes of seabed organisms anywhere in the world and is about the same size as the Grand Canyon.

In a paper published today in scientific journal, Science Advances, NIWA marine geologist Joshu Mountjoy said the quake triggered more than 100 million dumptrucks of mud and sand to flow through the canyon.

Dr Mountjoy said that made it one of the largest "canyon flushing" events ever documented.

Their findings that the floor of the two main reaches of the canyon had deepened by up to 50 metres indicated submarine canyons cut their way into rock much faster than previously thought.

"This study unequivocally demonstrates that earthquake-triggered canyon flushing is the primary process that carves out submarine canyons and delivers coastal sediment to the deep ocean."

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

These events, triggered by large earthquakes, occurred about every 140 years.

A survey shortly after the quake found the mudslides had wiped out all organisms living on the seabed, he said.

But there were now signs of recovery, with evidence of juvenile animals that once dominated the head of the canyon beginning to colonise the seafloor.

Animations of the changes in the Kaikōura canyon can be viewed here, here and here.

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