Massive mudslides in Kaikōura Canyon destroy seabed life

Huge mudslides from November’s earthquakes have wiped out all organisms living in the seabed of the Kaikōura Canyon.

Huge mudslides from November’s earthquakes have wiped out all organisms living in the seabed of the Kaikōura Canyon.

Less than three months after the November earthquake, NIWA scientists have undertaken two research trips to the canyon this year and discovered mudslides have occurred at its head, sending mud and debris into the canyon’s central channel.

While the structure of the canyon itself has remained intact, the mudslides have left no evidence of seabed life.

NIWA marine geologist Dr Joshu Mountjoy led a team on a week-long investigation in January funded by the Natural Hazards Research Platform. His project had two aims: to map the offshore faults ruptured when the earthquake happened, and to investigate changes to the slopes at the head of the Kaikōura Canyon.

Dr Mountjoy compared maps of the canyon rim made in 2013 with what he saw last month.

“In 2013 everything at the head of the canyon was smooth and draped in mud. Our new data shows that the earthquake resulted in a huge slipping event. Almost every part of the upper slope had mud removed from it.”

Landslides "massive"

The maps made last month reveal the features of the upper slopes of the canyon in far greater detail, with large valleys and ridges once filled with mud, now completely cleared.

Dr Mountjoy said the amount of debris that cascaded through the canyon was massive.

“Some individual landslides are more than three times the size of the landslides that damaged the road to the north of Kaikōura.”

The combination of all the landslides are likely to be the source of a huge current detected by NIWA scientists shortly after the earthquake.

The rim of the canyon is very close to the road south of Kaikōura Peninsula and has been studied in an ongoing project between NIWA and ECAN because of the risk posed by potential tsunami. Dr Mountjoy said that preliminary analysis of the data indicates that the likelihood of a damaging tsunami being generated from landslides in the canyon has not increased due to the earthquake, and may be lower than previously thought.

Dr Mountjoy’s project was followed by a second survey funded by the Ministry for Primary Industries (MPI) and led by NIWA marine ecologist Dr Dave Bowden, which used cameras to survey the seafloor further into the arm of the canyon.

The work, undertaken from NIWA’s research vessel Tangaroa, was completed at the end of an MPI survey of biodiversity on the seabed across the Chatham Rise. MPI was keen to take advantage of the Tangaroa’s proximity to the Kaikōura Canyon, and deploy cameras to see if there was any earthquake damage to this renowned biodiversity hotspot.

Biodiversity led to marine reserve status

Ten years ago scientists from NIWA and the US surveying the same area found the canyon had one of the highest volumes of organisms living in the mud known anywhere in the world.

“It was about 100 times higher than anything reported anywhere else for that kind of seabed. There was an extraordinary amount of life living in the bottom of the canyon which we think was a consequence of the very high marine productivity of the whole region.”

The results of that survey contributed to the area becoming a marine reserve.

Dr Bowden said comparing the two surveys was extraordinary.

“We surveyed exactly the same area we did in 2006 and, while fish were still found in the area, this time didn’t record evidence of a single organism living on or in the seabed over a stretch of nearly six kilometres of seabed . Nothing. It was quite sobering, and a catastrophic event for the ecology of the canyon.”

Previously the seabed was covered with burrows, tracks, pits and mounds made by seabed animals but it is now smooth and barren. While fish and whales were still observed in the area, the consequences for these predators is not yet known.

However, Dr Bowden says the change in the canyon now opens the way for some important research.

“We suspect that events like this might happen every few hundred years in the Kaikōura Canyon. It will be very interesting to follow what happens from here, and I will be highly surprised if it doesn’t regenerate.”

Emergency research package for Kaikoura

MPI Fisheries Science Manager Dr Shelton Harley said it will be important to understand how deep sea effects on productivity in the canyon affect the foodweb.

 “It is clear that this earthquake has impacted on different parts of the marine ecosystem in different ways.

“There are few people who weren’t shocked by the photos of exposed paua beds along the coast, but we know that there are other potential less obvious impacts that we need to understand.

“MPI will work with NIWA, DOC, local iwi, and the Kaikōura Marine Guardians to determine how best to monitor these ongoing impacts in the Kaikōura Canyon.

“MPI is administering a $2 million emergency research package for the Kaikōura region covering a wide range of marine fauna of critical importance to the ecosystem and local community. This research will cover rock lobster, paua, blue cod, sperm whales, fur seals, Hutton’s shearwaters and a range of intertidal and subtidal rocky reef animals and seaweeds. The results of this research will enable MPI to build a far better picture of the long term effects and the most appropriate actions to manage sustainably for the future.”

New bathymetric data shows that the earthquake resulted in a huge slipping event. Almost every part of the upper slope had mud removed from it and significant innundation has covered much of the canyon floors. [Infographic: NIWA]