Logo Universitat Bremen
Die Inhalte dieser Seite sind leider nicht auf Deutsch verfügbar.
Seitenpfad:
  • INTERCOAST
  • Latest News
  • Archiv
  • News 2014
  • Investigation of the landsliding and tsunami potential in Kaikoura and Haumuri Canyon, New Zealand – a collaborative fieldwork of NIWA, University of Canterbury and INTERCOAST by Franziska Hellmich

Investigation of the landsliding and tsunami potential in Kaikoura and Haumuri Canyon, New Zealand – a collaborative fieldwork of NIWA, University of Canterbury and INTERCOAST by Franziska Hellmich

The offshore area in the south of the Kaikoura Peninsula on the South Island of New Zealand is known for a range of canyons in close proximity to the coastline. From shallow water depths of around 30 m the continental shelf plunges down to water depths of more than 200 m in steep incisions such as the Kaikoura Canyon and the Haumuri Canyon.

In a previous study Lewis & Barnes (1999) investigated the local sediment transport regime and proposed an area of loosely accumulated sediment at the head of Kaikoura Canyon. A tsunami model by Walters et al. (2006) showed that in an event of an earthquake a failure of this sediment deposit would induce an up to 13 m high tsunami which would cause severe harm to the adjacent coastal areas and their inhabitants and infrastructure. This tsunami hazard has led to a joint project of the National Institute of Water & Atmospheric Research Ltd. (NIWA) and the Environment Canterbury Regional Council (ECAN) which in three phases should validate the findings of the previous workers.

In the first phase Dr. Joshu Mountjoy from NIWA collected new multibeam bathymetry data, multi-channel boomer seismic reflection data and short sediment cores of the area around the two canyon heads (Mountjoy et al., 2013). This new data could not support the previously proposed sediment accumulation at Kaikoura Canyon head, but showed several landslide scars at both canyon heads and further slope failure potential.

For the second phase in-situ measurements of the sediment shear strength, an important parameter for assessing the likelihood of failure during an earthquake, were planned to complement the earlier findings of Dr. Joshu Mountjoy and to give a more accurate picture of the sediment and its physical properties around and in the canyon slopes. Dynamic cone penetration testing (CPT) is the perfect method for gaining the requested data. For a dynamic CPT measurement a dart like lance is lowered through the water column at winch speed or in free-fall mode until it hits the seafloor and penetrates it by its own momentum. Upon penetration the resistance of the sediment against the conical tip, the sleeve fraction along the CPT lance shaft, pore water pressure and acceleration/deceleration are measured and later used for calculating the sediment shear strength. In collaboration with the working group Marine Geotechnics of Prof. Dr. Achim Kopf the MARUM free-fall CPT for shallow water depths was used during this field campaign. The fieldwork was conducted by INTERCOAST PhD student Franziska Hellmich, who will also process the data which was gained.
In the week of 24th – 28th February 2014 the field campaign for the second phase of NIWA’s project took place. More than 100 CPT deployments along transects through landslide scars where taken in controlled and true free-fall mode. After first test deployments and swapping the rope from a hydraulic to an electric winch, which could be run in free-fall mode, an extra weight was added to the rope 15 m above the CPT lance to ensure that after impact of the lance on the seafloor rope kept paying out of the winch to allow the part of rope between lance and extra weight to go slack. By these means any upwards movements by the ship due to swell and waves will not affect the penetration process of the CPT lance and thus will not be shown in the data. According to mud traces on the lance shaft the deepest penentration is expected to be around three meters. Additionally, 18 gravity cores of up to 1.3 m length have been taken. Several geotechnical/geomechanical laboratory tests, including grain size analysis and triaxial shear tests, will be conducted on the sediment by University of Canterbury PhD student Arul Arumugam. Results of both the CPT data and the laboratory tests will be compared and in the end, together with the findings of the first phase of the project, will give a full picture of the sediment distribution and its physical properties in the area of Kaikoura and Haumuri Canyon. In the third phase of the project, NIWA will implement these results into a new tsunami model for the Kaikoura area.

I, Franziska, had a really great time during the fieldwork (I would even say it was the best week of my New Zealand research stay!), which especially is because of the fantastic crew we were all together. Thanks Joshu Mountjoy and NIWA for this collaboration! A big thank you for their help also has to go to Andrew James, the “skipper” of the NIWA research vessel IKATERE and Sam Harrison, the deck hand or winch guy as he liked to call himself. Thanks Arul for help with the field work. And thanks Marion for letting me surf your couch in Christchurch, I had a fabulous time with you.
Lewis, K. B., & Barnes, P. M. (1999). Kaikoura Canyon, New Zealand: active conduit from near-shore sediment zones to trench-axis channel. Marine Geology, 162(1), 39–69. doi:10.1016/S0025-3227(99)00075-4

Mountjoy, J., Lane, E., Orpin, A., Woelz, S., Pallentin, A., & Arnold, J. R. (2013). Kaikoura Landslide Tsunami Hazard - Investigation and analysis of potentially unstable sediment at the head of Kaikoura Canyon (pp. 1–54). Wellington, New Zealand.

Walters, R., Barnes, P., Lewis, K., Goff, J. R., Fleming, J. (2006). Locally generated tsunami along the Kaikoura coastal margin: Part 2. Submarine landslides. New Zealand Journal of Marine and Freshwater Research, 40, 1, p. 17-28.Locally generated tsunami along the Kaikoura coastal margin: Part 2. Submarine landslides. New Zealand Journal of Marine and Freshwater Research, 40, 1, p. 17-28.



For further information please contact:

Franziska Hellmich, PhD student, University of Bremen

Dr. Joshu Mountjoy, NIWA

Dr. Marion Gadsby, ECAN ( [Bitte aktivieren Sie Javascript] )

CPT lance ready for deployment

Extra weight for best deployment set-up

whale watching after a successful day of work

Detailed map of CPT and corer deployments

The crew (L-R): Sam Harrison, Arul Arumugam, Andrew James, Joshu Mountjoy, Franziska Hellmich

The field research even appeared in the newspaper...