30 September 2015

Rockfall and landslide damage in the Port Hills from the Christchurch earthquake sequence

Posted by Dave Petley

Rockfall damage in the Port Hills

The media in New Zealand are reporting that, almost five years after the earthquakes, demolition has started on houses in the Port Hills area of Christchurch that were damaged by the 2010-1 earthquake sequence.  Stuff.co.nz reports that:

“The first of a four-phase series of demolitions on the Port Hills has started.  The Canterbury Earthquake Recovery Authority (Cera) is demolishing 16 red-zoned houses at Moncks Bay.  Port Hills operations manager Brenden Winder said two properties at the top of the bay had already been cleared with two further properties at the bottom now being worked on. Demolition has begun on two red-zoned houses at Moncks Bay, Christchurch.Winder said potential rock fall, cliff collapse and landslips had made demolishing houses on the Port Hills significantly more difficult than in flatter areas.  “Every property we deal with has a degree of risk associated and generally that’s very high.  “It’s steep in there, access is constrained, there’s cliffs around, there’s broken retaining walls, there’s rockfall up above it and broken houses.”

The damage to some houses in the Port Hills area was profound.  These are some of the photographs that I took after the earthquakes:

Port Hills

An example of a large-scale cliff collapse during the earthquake. Note the proximity of the boulders to the houses below

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Port Hills

Some sections of cliff underwent extremely extensive failure.

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Port Hills

At the foot of the cliff problems ranged from large rockfall events to highly mobile individual boulders. The lightweight structures that are common in New Zealand provided little resistance to rapidly moving boulders in some cases.

Port Hills

Buildings at the top of the cliff were also extensively damaged as the slopes moved below the foundations of the property

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Port Hills

In some cases, the failure of large sections of cliff left properties in an extremely precarious position.

Port Hills

Movements in the loess capping at the clifftop generated extensive damage, causing the loss of some historic, beautiful properties.

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