Earthquake Commission IQ

Risk

Slow to Fast

Abbotsford is a suburb in south-west Dunedin. The gently sloping hill on which Abbotsford was built began to exhibit signs of strain in 1968, but it wasn't until 1979 that geologists were called in to investigate. Initally slow, the final movement of the seven hectare block was swift, taking about 15 minutes to move 50 metres. There was a loud rumbling sound as the ground fell apart and 69 houses were destroyed. 600 residents escaped without any deaths. A 1951 study had found the hill to be unstable and unsuitable for homes but it was subdivided and settled.

Fast

After intense rain in the catchments behind the small township of Matata in the Bay of Plenty, landslips and debris flows almost buried the town with soil, boulders and felled trees. Matata was extensively damaged with the cost to EQC totalling more than $8 million. The landslips and associated floods destroyed 27 homes and damaged a further 87 properties. Fortunately there were no serious injuries or deaths. Geologists say it appears to be a recurring 500 year event with smaller slides in between times

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Shallow, rain-caused

Rainstorms over the southern North Island caused extensive shallow landsliding over about 8000 km² of Manawatu-Wanganui hill country. Hillsides without trees slid most in the rain. 30 - 50 percent of hillsides in pasture were affected, but only eight percent of those covered in native scrub or pine plantations succumbed. Trees less than 10-years-old offered little protection against the rain and consequent sliding.

Slow

West of the Taihape township is a landslide that first moved up to 11,000 years ago. 45 hectares of land is on the move, supporting approximately 209 houses and a school. Instability was first noticed in 1971. Movement of the slip is very slow. GNS Science is monitoring the slip and EQC and the Rangitikei District Council have undertaken remedial works to minimise risk to people and property.

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