Vasquez Canyon Road in Santa Clarita, California has undergone a dramatic change in just a few hours. The 3-km stretch between Lost Creek Road and Vasquez Way, Santa Clarita Valley’s few east-west connectors, is closed until further notice. But it is providing a learning experience for geology students.
There was no earthquake, rain or other weather event that appeared to trigger this sudden destruction of the roadway. Engineers are investigating the cause which is suspected to be related to a slow mass movement of soil under the road (called mass wasting in geologic terminology), which can be thought of as a progressive landslide. The Landslide Blog by Dave Petley at the University of East Anglia, U.K. provides us some expert commentary on the roadway. Using past imagery from Google Earth, Dr. Petley noted signs of instability of the roadway appeared several months ago:
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.
Cracks in the roadway were noticed in 2011. Dr. Petley concludes that this event has been going on, albeit slowly, for a while, perhaps since the road was first built.
The dramatic destruction did appear rather quickly on November 19. Here is a tweet from Los Angeles Public Works Department:
— LA Co Public Works (@LAPublicWorks) November 20, 2015
The movement continued into the night. Local geological experts say the subsurface material here is permeable so water could have been a factor. But I checked weather records for November in Santa Clarita. There was only slight precipitation on November 2 (0.05 in) and November 15 (0.02 in).
Drone footage shows the extent of the damage and the
This portion of the road was created by cutting into the slope and depositing that material on the downslope. It’s a common method but it can be problematic if done on a slope that is inherently unstable. Officials have characterized it as “essentially a catastrophic failure”. The road will have to be completely rebuilt in this stretch. Let’s hope they take into account the potential instability THIS time. Such events highlight the importance of complete geologic assessment of an area prior to disturbance. But, it’s not always clear what will happen when the landscape is re-sculpted by humans. Nature sometimes reclaims itself.
Yes, the references to Tremors (giant worms and Kevin Bacon) are following fast and furious from the news.
Please RT: Crews fenced off Vasquez Canyon Rd landslide area. Mountain is still sliding & is unsafe. Stay away! pic.twitter.com/KnyC2Qqle1
— LA Co Public Works (@LAPublicWorks) November 25, 2015