19 April 2011

Rockfalls and landslides from the February 2011 earthquake in Christchurch

Posted by dr-dave

The 22nd February earthquake in Christchurch triggered extensive landslides and rockfalls in the Port Hills area to the east of the city.   These mass movements resulted in at least five fatalities, and many homes were damaged.  Unfortunately, these mass movements represent a serious long term threat in many areas – in the aftermath of the earthquake several hundred houses had to be evacuated.  The science response to the landslide problem was led by GNS Science under the Geonet programme, assisted by partners from the public and private sectors.  They have produced an excellent poster describing these activities that is available for download here.  The file size is about 1.7 MB.

Perhaps the most interesting data on the poster is a map of the distribution of the different mass movement types:

For reference the image below shows the same area from Google Earth:

The Google Earth image helps to show the way that the mass movements are concentrated on the steepest slopes, especially the active and abandoned coastal cliffs.  There is a very helpful report written by Graham Hancox of GNS describing the helicopter reconnaissance flight that they undertook in the aftermath of the earthquake.  Note this is a pdf file, though does not appear to be labeled as such.  Firefox couldn’t download it, but Internet Explore had no problems).  There are some stunning aerial shots in there, of which I reproduce just two here:

These are remarkable images, which are being backed up with a very comprehensive data collection and hazard analysis exercise.  The GNS blog has a short but excellent post outlining some of the work that is being undertaken to understand and mitigate the legacy rockfall hazard, in which with my former PhD student Chris Massey is playing a key role.  We will all await the formal reports and scientific papers from this work with great interest.