Quake left us with a slip hazard
the shape of the Earth and its surface characteristics – to study the detailed topography after Gita.
That would be compared with LiDAR from before and immediately after the earthquake.
‘‘That will tell us where the sediment has come from, where it’s ended up, how thick it is,’’ Dellow said. ‘‘We will be able to trace that sediment through the landscape.’’
In October 2017, GNS started a five-year, $8.2 million project under the Ministry of Business, Innovation and Employment’s Endeavour programme to develop predictive tools for managing the risks from landslide and sediment hazards generated by earthquakes and post-earthquake rain and aftershocks.
‘‘Evidence from previous earthquakes in New Zealand and overseas suggests that the frequency of landsliding after a large earthquake is significantly higher than before the event. This is because strong earthquakes cause slope cracking and generate a lot of landslide debris,’’ the project outline said.
‘‘The debris generated by the Kaiko¯ura Earthquake, when mobilised, will create new hazards, including further landslides, landslide dams and dam failures, rapid aggradation, and increased river channel instability, as the debris cascades from hill slope to sea.
‘‘These hazards may persist for decades and therefore represent a prolonged risk that must be considered by the impacted communities and stakeholders.’’
NZ Transport Agency earthquake recovery manager Tim Crow said about 300,000 cubic metres of material needed to be cleared from 60 highway sites on either side of Kaiko¯ura after Gita. The largest at Okiwi Bay, north of Kaiko¯ura, had around 200,000cu m of material.
South of Kaiko¯ura at Rosy
Morn – where two houses filled with debris – about 5000 cu mof material had washed down the hill.
The amount of damage caused by Gita to the highway through Kaiko¯ura was the most by a storm or cyclone since 1975, when former cyclone Alison brought down 83 slips north and south of the town.
Dellow said researchers would be looking closely at the damage caused by Alison, compared to that of Gita.
Last Thursday, scientists also flew over the largest of the landslide dams resulting from the Kaiko¯ura Earthquake – on the Hapuku River – to see what impact Gita had on it.
The dam was among about only 10 remaining of the original 196 landslide dams created by the earthquake, Dellow said. The surviving dams were slowly getting smaller. Hapuku hadn’t failed catastrophically and was episodically declining in size.
The Kaiko¯ura Earthquake generated tens of thousands of landslides in a 10,000-squarekilometre area of North Canterbury and Marlborough. The most intense landslide damage was concentrated in a 3500sq km area around the areas of fault rupture.
More than 200,000 cubic metres of debris came down across State Highway 1 at a single site near Okiwi Bay, north of Kaiko¯ura.