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:

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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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.

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

Movements in the loess capping at the clifftop generated extensive damage, causing the loss of some historic, beautiful properties.
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Other posts that might be of interest:
- Rockfall risk assessment reports for the Port Hills, Christchurch, New Zealand
- The latest events in the Christchurch earthquake sequence
- Landslides from the Christchurch earthquakes part 5: landslides that involve sliding
- Landslides from the Christchurch earthquakes part 4: large-scale cliff collapses
- Images of landslides from the Christchurch earthquakes part 3: topographic amplification at the cliff tops
- Images of landslides from the Christchurch earthquakes part 2: evil dancing boulders
- Images of landslides from the Christchurch earthquakes part 1: boulder damage to a house
- Rockfalls from M=6.3 aftershock in Christchurch, New Zealand
- Rockfalls from the 2011 Christchurch earthquake