Earthquake’s Unseen Impact - Mapping the seafloor off Kaikoura

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Shortly after the November 2016 Kaikōura earthquake NIWA’s Dr Joshu Mountjoy led a team of scientists to the Kaikōura coast area to investigate how the magnitude 7.8 quake had affected the sea floor and nearby canyon system.

The Natural Hazards Research Platform funded project had two aims: To map the offshore faults ruptured when the earthquake happened, and to investigate submarine landslides at the head of the Kaikōura Canyon.

Using multibeam and seismic echosounder technology to map the area, Dr Mountjoy was able to quickly compare imagery of the canyon rim made in 2013 with the new data captured after the earthquake.

The recorded changes to many areas of the sea floor around Kaikōura dwarf what has been observed on land. While the structure of the canyon itself has remained intact, huge undersea mudslides failed down into the canyon system destroying the rich canyon floor ecosystem.

“In 2013 everything at the head of the canyon was smooth and draped in mud. The new data from this survey show that the earthquake resulted in widespread landslides. Almost every part of the upper slope had mud removed from it. Videos show that this mud has also wiped out most of the life on the canyon floor.”

Following this initial survey Dr Mountjoy has been leading an effort to analyse additional data collected with RV Tangaroa in the deeper parts of the canyon and the 1500 km-long Hikurangi Channel.

“What we now know is that this event is the first direct documented example of “canyon-flushing”. Hundreds of millions of cubic metres of mud have cascaded down the canyon, eroding the seafloor and transporting sediment at least 700 km down the channel. This event will change how the international community understands deep sea sediment transport and submarine canyon development.”

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