How the undersea Kaikoura Canyon would appear if exposed. More than 100 million dumptruck loads of sediment was flushed through it in the 2016 earthquake. Image / Animated Research/Taylormade media
How the undersea Kaikoura Canyon would appear if exposed. More than 100 million dumptruck loads of sediment was flushed through it in the 2016 earthquake. Image / Animated Research/Taylormade media
More than 100 million dumptruck loads of mud and sand gushed through a huge undersea canyon during the Kaikoura earthquake, wiping out life living in it.
The monster 7.8 quake revealed to scientists how hundreds of tonnes of sediment is washed through the deep, life-rich Kaikoura Canyon in big events on average every 140 years.
The 850 tonnes of muck that billowed from the canyon head in the November 2016 episode also proved one of the largest "canyon-flushing" events ever documented.
But the displacement wasn't enough to trigger a devastating tsunami hitting the coast - something that had been earlier feared.
A 3D rendering of the Kaikoura Canyon. Image / NIWA
The Kaikoura Canyon is a huge structure which comes within 500m of the coast just south of the tourist town, and feeds sediment into the 1500km-long Hikurangi Channel, running east of New Zealand.
Its depths provide an incredibly productive ecosystem for many of Kaikoura's world-famous deep-diving species, among them sperm whales, humpback whales, Southern right whales, orca and several dolphin species.
The pre-earthquake morphology of the canyon rim. Image / NIWA
These larger animals appeared to fare well in the disaster - unlike the plethora of organisms living in the seafloor mud.
Only a decade ago, the volume of life in the canyon's sediment had been found to be the highest observed anywhere in the world - but this deep sea community was obliterated by the undersea avalanche barrelled through.
The post-earthquake morphology of the canyon rim. Image / NIWA
The deluge then travelled along the deep-sea Hikurangi Channel and its banks, where scientists took samples of the sediment-flow deposits, known as turbidites, up to 680km northeast of Kaikoura.
In 2013, everything at the head of the canyon was smooth and draped in mud, but investigations two months after the earthquake revealed that the mud from almost every part of the upper slope had been stripped away.
"The event has completely changed much of the canyon floor, eroding into rock and moving dunes of gravel through the lower canyon," Niwa marine geologist Dr Joshu Mountjoy said.
"We knew that events like this could happen from telecommunication cable breaks during earthquakes that can cause major interruptions to international communication.
This image shows the amount of erosion and deposition on the Kaikoura Canyon floor. Image / NIWA
"But we have never had data to show us what impact these events have on the canyons themselves."
Other findings in a study led by Mountjoy, and published today in the major journal Science Advances, revealed how the floor of the two main reaches of the canyon had deepened by up to 50m.
This suggested that submarine canyons could cut their way into rock much faster than previously thought, and similar quake-driven events were calculated to reoccur on average every 140 years.
"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," Mountjoy said.
The material removed included seven million tonnes of carbon that was now available to nourish deep sea communities.
The Kaikoura Canyon boasts one of the most productive ecosystems on the planet. Image / How the undersea Kaikoura Canyon would appear if exposed. More than 100 million dumptruck loads of sediment was flushed through it in the 2016 earthquake. Image / Animated Research/Taylormade media
An earlier Niwa-led study found how the biodiversity hotspot was now showing signs of recovery, with evidence of juvenile animals that once dominated the head of the canyon beginning to colonise the seafloor.
Other studies since the earthquake have revealed it was the most complex quake ever recorded, rupturing more than 21 on and offshore faults along more than 100km, producing widespread coastal uplift, vertical ground movement and numerous landslides.
