Scientists study canyon for tsunami potential

Last updated 11:46 26/02/2014

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Scientists will be working off the east coast of the South Island this week investigating the potential for a landslide tsunami in the head of the Kaikoura Canyon.

The Kaikoura Canyon is up to 2000 metres deep and comes within 500 metres of the coast south of Kaikoura, closer than any other New Zealand submarine canyon. It is in an active seismic region, with faults such as the nearby Hope Fault capable of producing large earthquakes.

This is the second stage of a three-stage project. Last year Niwa scientists mapped the shallow reaches of the canyon between Oaro and Goose Bay by collecting seismic data.

The Kaikoura Canyon investigation is part of a programme with Environment Canterbury (ECan) to understand the hazard posed to the Canterbury coastline from tsunamis.

Based on the imaging results from last year, the project is now being followed up by fieldwork from Niwa's research vessel Ikatere to assess the strength of sediment layers at the canyon head.

This will be done using a freefall cone penetrometer test. Niwa marine geologist and project leader Dr Joshu Mountjoy said this involved lowering a lance into the seafloor to measure the strength of the seafloor up to five metres below the seabed. The data is downloaded once the instrument is retrieved.

The results will be used to understand how, when and where landslides can occur. Determining the strength of the sediment layers will enable the scientists to figure out what changes are needed to make it slide. If the layer is weak it will slide easily, but denser layers are likely to be stronger and more stable.

"Our work last year showed us that several different types of landslides can occur here, and we need to understand what will happen to the rock and sediment during an earthquake."

Understanding more about the hazard potential in the canyon will enable coastal communities to be better prepared for natural hazards.

"It is very important to understand how big these tsunamis can be, and where and when they might occur," Dr Mountjoy said. "This fieldwork will fill in a significant piece of the puzzle and will enable us to undertake sophisticated numerical modelling to better understand the landslide tsunami potential."

The work this week will take place close to the shore between Peketa and Oaro, and well out of the oil prospecting permit area where Anadarko's seismic vessel is undertaking its survey.

The third stage of the project will be tsunami modelling, which, once complete, will mean the team can inform the public of tsunami hazard and consider the risk, Dr Mountjoy said.

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- The Marlborough Express

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