Landslides

RECENT POSTS

Water From Above and Below Likely Culprit in SoCal Landslide

Rain, irrigation and residential development contributed to November’s San Pedro Slide

USGS & Don Knabbe

Options for fixing the San Pedro Slide in southwestern Los Angeles range from several million to 62 million dollars.

It’s a long and inconclusive list of usual suspects that appear in the final draft report [PDF] released by the City of Los Angeles this week. The Department of Public Works tapped the Glendale geotechnical consulting firm Shannon and Wilson to investigate the slide that sent a 600-foot section of seaside roadway toward the Pacific last November.

My radio report and blog post back in April explained the slippery mix of water and soft sediment that permeates the Palos Verdes Peninsula, and what happens when too much water gets between those unstable layers of earth.

Shannon and Wilson’s report lists the following as “contributors” to the slide: irrigation — both residential and watering done inside the White Point Nature Preserve adjacent to the slide — coastal bluff erosion, precipitation, road construction and underground utilities. Just above the Preserve is a 13.2-acre complex of U.S. Air Force housing, and watering from those homes could be “influencing groundwater” near the slide. Continue reading

Storms and Rising Seas Present New Threats to Unstable SoCal Peninsula

The geologic features of the Palos Verdes Peninsula make it a hotspot for landslides

Bureau of Engineering / City of Los Angeles

November's sea cliff failure took out 600+ feet of roadway and sidewalks.

The latest Palos Verdes Peninsula slide may calve, and the main slide mass is likely to keep “moving oceanward.” That’s according to a preliminary draft of a geotechnical study commissioned by the City of Los Angeles in early winter, but that’s the extent of the news for now. The same report says based on the studies completed to date, the risk of landslide movement behind last November’s slide — landward into a nature preserve and beyond a new chain link fence — is low.

That’s just the latest from an area southwest of downtown L.A. that has been generating geological news for decades. According to a landslides map by the California Geological Survey, the PV Peninsula boasts 175 slides, 49 of them active.

Continue reading