San Pedro landslide - a slow build up to a dramatic event

San Pedro is on the Palos Verdes peninsula just south of Los Angeles - and in Sunday 20th November 2011 a slow-moving landslide which had been moving at a few 10s of mms per day for several months suddenly failed dramatically in a few minutes. A 200m stretch of the main Paseo del Mar road slid away from the clifftops, dropping some 30m.  It's a beautiful hilly area, with upmarket housing and fantastic coastal views.  It's also a hotspot for landslides, as evidenced by the excellent California Geological Survey landslide map produced in 2007 which you can access at:
ftp://ftp.consrv.ca.gov/pub/dmg/pubs/lsim/LSIM_PalosVerdes.pdf
Be patient as it is a large file and takes some time to download.  if you read the text on the right hand side of the map you'll find out more about why the area is prone to landslides.  The essential reasons are:

1. The peninsula is underpinned by Miocene rocks, including shale.  Many of the landslides are located on the easily erodible shale.
2. The peninsula is crossed by the Palos Verdes fault and folded into a complex anticlinal structure.

Human activities have also been blamed for the high occurrence of landslides here. Not only building extensively on the clifftops, but also mis-managing drainage systems and, one factor quoted in the local news as being responsible for the most recent event - cold war underground missile silos are allegedly found in the area.  On Sunday 20th November 2011 it was a horrendously rainy day in Los Angeles - over 20mm of rain fell in a few hours.  

You can explore the coast on Google Maps below - the site of the 20th November 2011 landslide is at the centre of the view - but if you head N and W up the coast you can see vast numbers of houses and impermeable concrete structures along the clifftops.  Surely asking for trouble?


View Larger Map

Think about how would describe the causes of this landslide, using Mike Crozier's predisposing, triggering and maintaining factors framework. Was the rainstorm on November 20th the trigger? Or not?

Paraglacial processes shaped the Lake District

..well, partly at least!  This paper by Peter Wilson nicely documents five rock slope failures in the Lake District and, based on quite detailed fieldwork (don't get bogged down in the details), suggests that they are of paraglacial origin.  My lecture on 'Climate, climate change and geomorphology' introduced the concept of paraglaciation, and this paper should help to bring it to life.  When you look at the paper, think about the sources of evidence Wilson uses and what other evidence would be really useful to test whether or not the rock slope failures actually WERE a result of paraglaciation.  You can access a pdf of the paper at:

http://www.science.ulster.ac.uk/ae/docs/Peters%20papers/Wasdale.pdf

Landslides in action

There are lots of good resources about landslides and other mass movements available on the web.  The best is the Landslides Blog by Prof Dave Petley, University of Durham.http://blogs.agu.org/landslideblog/

He updates it regularly and it contains some excellent examples and explanations of mass movements and their impacts from around the world.

There's also a good You Tube video of a recent dramatic cliff collapse in Cornwall which is well worth looking at http://youtu.be/ZVjr4mii3cE