Kaikōura Canyon

Sperm whales can be seen close to the coast south of Goose Bay, because the deep water of the Kaikōura Canyon is only one kilometre (0.62 mi) off the shoreline in this area.

An estimated 850 million tonnes of sediment had flowed into deeper water, and a turbidity current travelled more than 600 km (370 mi) along the Hikurangi Channel.

It is thought to be the sink for the coastal sediment transport system that carries large amounts of erosional debris northwards up the coast from the rivers draining the tectonically active mountains of the South Island.

[5] Mixing of these currents leads to the formation of offshore eddies, and some turbulence reaching to the depths of the Hikurangi Trough and Kaikōura Canyon.

Sediment consisting of fine sand and silt is continually deposited at the head of the Kaikōura Canyon, and by 2006 it was estimated that a total volume of 0.24 cubic kilometres (0.058 cu mi) had accumulated.

Studies identified that a near-field tsunami caused by the displacement of this sediment in a submarine landslide could pose a significant threat to the surrounding area, especially coastal infrastructure such as roads and houses.

Marine sediments can be seen to overlie an historical Māori occupation site on Seddon's Ridge, near South Bay, adjacent to the Kaikōura peninsula.

[13] Rapidly accumulating sandy sediment on a steep slope in an active tectonic region is likely to be susceptible to failure during moderately large earthquakes.

Strong ground shaking associated with rupture on nearby faults can be expected to reduce the shear strength of the sandy sediment deposit at the canyon head and may trigger mass failures.

[14] Prior to 2016, there had been no large seismic events centred close to Kaikōura since written records of the area began in about 1840 AD, but lichen-dating of rock-falls suggests that there may have been a major earthquake in the vicinity 175 years ago.

Consequently, the initial motion of a debris avalanche in the gully, and the resulting tsunami, is towards the shore of South Bay and the southern side of the Kaikōura Peninsula.

[16][17] In September 2017, a NIWA expedition found that marine life in the canyon was recovering faster than expected, and observed high densities of sea cucumbers and urchins in some areas.

[18] In 2019, results of tsunami modelling studies were reported, seeking to explain the 7-metre (23 ft) runup that was observed locally in Kaikōura following the earthquake.