Scientists will be working off the east coast of the South Island next week investigating the potential for a landslide tsunami in the head of the Kaikoura Canyon.
The Kaikoura Canyon is up to 2000 metres deep in places 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.
Last year NIWA scientists successfully mapped the shallow reaches of the canyon between Oaro and Goose Bay. The Kaikoura Canyon investigation is part of an ongoing programme with Environment Canterbury to understand the hazard posed to the Canterbury coastline from tsunamis.
That 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.
NIWA marine geologist and project leader Dr Joshu Mountjoy says the seafloor drops off steeply into the Kaikoura Canyon.
"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," Dr Mountjoy said.
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.
Understanding more about the hazard potential in the canyon will enable vulnerable coastal communities to build resilience and 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."
Dr Mountjoy will be joined on the research vessel by doctorate students from the University of Canterbury and the University of Bremen in Germany. The team will use a new coring system to retrieve sediment from a range of water depths for testing in the engineering laboratory at the University of Canterbury.
A state-of-the-art free-fall Dynamic Cone Penetration (CPT) system from the Marine Geotechnics department at the University of Bremen will be used to measure the strength of the sediment. The CPT is also used to see if there is any pressure within the sediment that might weaken the slopes and make it easier for landslides to occur.
"Geotechnical measurements will allow us to use numerical modelling to determine the response of the shallow seabed to future earthquakes," Dr Mountjoy said.
The Kaikoura District Council, Civil Defence and Environment Canterbury are holding a Community Preparedness/Tsunami Information roadshow on March 19 and 20 in Kaikoura, Clarence and Goose Bay.
