22 November 2015
Vasquez Canyon: a new landslide in Santa Clarita, California
Posted by Dave Petley
Vasquez Canyon landslide
A significant landslide has developed in the last few days in Vasquez Canyon, in Santa Clarita in California. The landslide, which appears to be progressive and has no obvious recent trigger, has caused extensive buckling of the road, which has been closed over a three kilometre stretch. This image, from the Santa Clarita Valley Signal, provides quite a good general view of the situation beyond the road:
The landslide, from the Santa Clarita Valley Signal
.
The landslide has caused impressive damage to the highway:
Vasquez Canyon road from KTLA5
.
.
interestingly, the media are suggesting that this buckling has occurred because the road is moving upwards. Whilst this might sound a little odd, this excellent drone footage suggests that this might the case:
.
This is a still from the drone footage of the landslides, showing the damage to the highway:
Vasquez Canyon Road via Youtube
.
This is Google Earth imagery of this section of the road, dated April 2015 – i.e. seven months ago:
Vasquez Canyon Road via Google Earth
.
There are clearly some signs of instability in this image, and note the other landslides in the image. The section of road that has failed is in a box cut, so it would appear that unloading of the slope may be a key factor in the landslide. And interestingly, this imagery from two years ago (May 2013) suggests significant movement at that time as well:
Vasquez Canyon road in 2013 from Google Earth
.
And finally, this is Google Street View imagery of the road, taken in 2011:
Vasquez Canyon road via Google street view
.
The extensive deformation in the road was clear even then – indeed the road shows longitudinal cracks along this entire section. Thus, although this landslide looks very sudden, it has been developing over a prolonged period.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Classic rotational slide toeing out in the roadway. Cut the road right through it. Someone has even photoshopped in a “Graboid” from the movie thriller “Tremors” into a photo on the net!
Go here for a recently updated (2014) 30′ x 60′ geologic map of the region:
ftp://ftp.consrv.ca.gov/pub/dmg/rgmp/Prelim_geo_pdf/losangeles_100k_v2.0_Map.pdf
Bedrock is indicated as upper Miocene “lacustrine bottomset facies” of the Mint Canyon Formation (Tmcl on the map). Looks like a pretty punky weathered slitstone/claystone. Slide City in the aerial photos!
That 2nd-oldest scarp that you can see in the drone video and in the gmaps images isn’t present yet in the oblique “birds-eye” layer on bing maps.
The bedding attitudes as indicated on the geologic map Jim Falls linked to and visible in the southern road cut in Google Street View, are unfavorable. This is a likely reason why the slip plane extends north of the ridge crest.
Would be helpful if someone can produce a 3D structural map.
The geo map also shows several dikes near the toe of the slope. I can’t tell if they are conformable or not, or if they would be near the slide body.
From Google Earth, it the area on the north side of the ridge and south side of Puckett Mtwy is much more green than the surroundings, suggesting more water at that location. Whether or not the water is following the bedding down from the ridge to the east, or as sheet flow down Puckett Mtwy and then ponding at the location just north of the slide, I cannot tell.
We visited the site today. If you can send me your email, I’ll send you a few more photos. The slide is still active. Mine is [email protected]