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New Zealand’s new coastline

New Zealand’s new coastline Anna Redmund
08 Dec
2016
The 7.8 magnitude earthquake that hit New Zealand in November has caused the seafloor around Kaikoura to rise a full two metres out of the water

At Kaikoura, on the northeast coast of New Zealand’s south island, what used to be the seabed has now become a wall of stone two metres high. Laced with seaweed and the purplish layers of rock, the raised platform is the raw product of the category 7.8 earthquake that struck the region on 13 November.

Image: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey and Sentinel data from the European Space AgencyImage: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey and Sentinel data from the European Space Agency

‘The change happened in seconds,’ says Dr Joshu Mountjoy, a marine geologist at New Zealand’s National Institute of Water and Atmospheric Research, ‘with a fault rupture speed of approximately two kilometres per second.’ Locals reported that the sound of water rushing off the new beach was louder than the earthquake itself, as gallons of seawater were suddenly displaced by the tectonic movement. Meanwhile, visitors to the coast noticed sea creatures such as crayfish and pāua snails still crawling among the rocks – surprised, perhaps, by the sudden change of scene. ‘There has been a very big impact on the coastal ecosystem,’ says Mountjoy. The local fishing industry is expected to be severely impacted and there have been a number of landslides and rockfalls along the shore.

crab rise(Image: Anna Redmund)

The dramatic change, known as coastal uplift, occurred when at least four different faults broke at once. Although uplift in New Zealand is normal for large earthquakes near the coast, the Kaikoura quake offers geologists a chance to observe how several different faults can join together in a large earthquake. ‘The effect on the landscape is huge,’ says Mountjoy. ‘Scientists will be learning from this earthquake for many years to come.’

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