16 December 2007

La Honda landslide

Posted by Dave Petley

A dat off from the American Geophysical Union meeting saw my colleague Nick Rosser and I take a trip over to La Honda in the Santa Cruz mountains to take a look at the La Honda landslide. The Google Earth image (shwon on the right), though not perfect, shows the damage quite well. Not in particular the offsets on the road and upslope (on the right) the tension cracks that run across the slope. This landslide has already resulted in the destruction of about nine homes.

Our visit on Thursday occurred as works are underway, seemingly to construct some drains to reduce the pore pressures. This work seems essential as the degree of damage on the ground is now high. The image below shows the level of damage, looking down onto the road from the top of the backscarp. Note the broken road on the left – I have tried to label the key features. The displaced section is in the stand of trees in the centre of the image – maybe 15-20 m downslope.

Click on the image for an enlarged view

Installing drains seems prudent, and one can only hope that it proves to be successful. Stabilising such an active slide is undoubtedly a real challenge.