The Kaikoura quake triggered an undersea 'canyon flushing' event that wiped out an entire ecosystem, new research has found.
Around 100 million dump trucks' worth of mud and sand was sent flowing down through the undersea Kaikoura Canyon when the magnitude 7.8 quake struck on November 14, 2016.
In a matter of hours around 850 million tonnes of sediment was displaced as far away as 680km along the Hikuranga Channel, about 200km off the east coast of the North Island.
"The event has completely changed much of the canyon floor, eroding into rock and moving dunes of gravel through the lower canyon," said lead author Dr Joshu Mountjoy of NIWA.
In two places, the canyon is now 50m deeper than before.
Photographs taken before and after the quake show the extent of the damage.
"The seafloor of the Kaikoura canyon has some of the highest productivity of any ocean floor ecosystem in the world, and you can see that it's been completely destroyed as a result of the canyon flushing," Dr Jamie Howarth of Victoria University's School of Geography, Environment and Earth Sciences told Newshub.
Photos taken two months later show life already starting to come back. In addition to the millions of tonnes of sand and mud, 7 million tonnes of carbon was also redistributed along the channel, nourishment that will help the ecosystem recover.
"The event has completely changed much of the canyon floor, eroding into rock and moving dunes of gravel through the lower canyon," said Dr Mountjoy.
"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."
It's estimated the Kaikoura Canyon experiences such a flushing every 140 years or so, but this is the first time it's been witnessed happening.
"They're quite rare, but their also very high magnitude - they're exceptionally large. One of the interesting things we've been able to do in this study is actually determine how often they occur, and the fact that earthquake... play a fundamental role in triggering these events."
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During the study the team, made of scientists from NIWA, GNS Science, Victoria University, Auckland University and abroad, took samples of sediment deposits made during the flushing.
"That allows us to get at the frequency with which large earthquakes occur, and also potentially where they're occurring and how much of the plate boundary is rupturing in a given earthquake. The really neat thing about this Kaikoura event is... we've actually observed an example of an earthquake forming one of these deposits."
Dr Howarth says the ongoing research into the Kaikoura quake will give scientists valuable information on how Kiwis could prepare for the next big one.
"As sobering as the effects of the earthquake have been for New Zealand in general, the scientific opportunity that it's generated has been significant. Hopefully those learnings will feed back into understanding of seismic hazards along the Hikurangi margin and ultimately help make New Zealand a more resilient place."
The study's findings were published in journal Science Advances.