Canterbury Earthquake: Rockfalls on Banks Peninsula

Our home is on the lower slopes of the Port Hills, which form the northeastern side of Banks Peninsula. The shock waves from the September 4 earthquake travelled about 30km across the sedimentary shingles of the Canterbury Plains before striking the volcanic rock of Banks Peninsula.

My impressions are that house damage on the hills is modest, although over in Cashmere some older houses have lost their chimneys. Most houses where I live, at Kennedys Bush,  have concrete foundations with timber framing plus plaster cladding.   These houses have stayed firmly attached to the underlying rock. However, one nearby hill suburb, Westmorland, is partly built on loessial (wind blown) soils that lack structure. I have yet to hear how they have got on, but a lack of stories is probably a good sign.

Nevertheless, there have been rockfalls. Halswell Quarry Park (no longer an active quarry) suffered some significant falls, including onto one of the picnic areas (see photo). I know that some of this came from an aftershock rather than the main event, but how much was from the aftershock I do not know. Above the Summit Road there have been a few falls, but mainly down the southern side, most of which is not visible from the road itself.

 On Sunday I was walking along the Crater Rim Track on the south side of Cass Peak, and there have been big falls there, with rocks ranging from about 30kg up to many tonnes having torn down the hillside towards Governor’s Bay. There are additional rocks loosened and just waiting still to go, and I did not dawdle in getting out of there. On the northern side of Cass Peak a rock of several tonnes landed directly on the Summit Road and would have made a great photo, but by the time I got back there today with a camera, much to my surprise, a grader had been there before me. And that typifies much of what is happening here: the clean up is occurring at an amazing rate.

Halswell Quarry Park Picnic Area

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Halswell Quarry Park

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Rockfall on road descending to Gebbies Pass

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About Keith Woodford

Keith Woodford is an independent consultant, based in New Zealand, who works internationally on agri-food systems and rural development projects. He holds honorary positions as Professor of Agri-Food Systems at Lincoln University, New Zealand, and as Senior Research Fellow at the Contemporary China Research Centre at Victoria University, Wellington.
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