GeoExtreme 2025: Palos Verdes Field Trip with Tim Stark

Palos Verdes Peninsula Landslides w/Tim Stark

Title: Engineering on the Edge: History, Hazards, and Innovation at the Portuguese Bend Landslide

Overview:
This technical field tour invites geotechnical engineers, geologists, researchers, and policy professionals to examine the Portuguese Bend Landslide, one of the most complex and historically significant landslide systems in North America. Situated on the Palos Verdes Peninsula, the landslide has been active for over 70 years, triggered by mid-20th century development activities. This tour highlights both the evolving scientific understanding and the municipal response to living atop a moving landscape.

Historical Emphasis:

The Portuguese Bend Landslide began accelerating in 1956 following residential grading and road construction that may have altered surface and subsurface hydrology. Since then, the area has seen continuous movement of up to 5 feet per year, with significant impacts on homes, infrastructure, and public policy.

Landslide movement was accelerated by heavy rains over the past few years.  The moving portions of the landslide had doubled in area (600+ acres) and locally accelerated movement to 50 foot per year.  The City with the help of its technical consultants have found ways to decelerate this dramatic movement by keeping water from entering the landslide complex while draining up to 1 million gallons per day from under the deep slip planes.

The site has served as a living laboratory for decades of research, legal precedent, and engineering experimentation. This tour will trace the history of the landslide from its initiation to present-day monitoring and management efforts.

Tour Objectives:

1. Analyze the historical development and progression of the landslide over the past seven decades.
2. Examine the geological and hydrological conditions underlying the slope failure.
3. Understand engineering mitigation techniques, both historical and current.
4. Evaluate the policy and planning implications of long-term ground movement.

Itinerary Highlights:

1. 1. Historical Timeline & Geologic Context
      A detailed overview of the landslide’s history since the initial failure in the 1950s. Presenters will walk participants through the key phases of movement, litigation, and land use response, framed within the geologic setting of the Altamira Shale and bentonite shear layers.
   2. On-Site Field Observations
      Guided visits to deformation hotspots along Palos Verdes Drive South. Participants will observe road realignments, displaced utilities, cracked foundations, and sheared ground surfaces. Discussion will include the legacy of early engineering responses and the physical evidence of long-term displacement.
   3. Monitoring and Instrumentation Systems
      Review of the monitoring program developed over decades, including subsurface instrumentation and recent advancements in surveys. Participants will be briefed on historical movement data to understand velocity trends and acceleration events.
   4. Engineering Interventions & Lessons Learned
      Presentations by consulting engineers on historical and current attempts at slope stabilization, drainage improvements, and adaptive infrastructure design. Emphasis will be placed on what has—and has not—worked over time.
   5. Discussion & Forward-Looking Perspectives
      Open discussion on how historical understanding informs future slope stability projects, urban planning in hazard zones, and academic research directions.

Duration: 5-6 hours, 9am-2/3pm

Lunch: Provided

Intended Audience: Engineers, geoscientists, academic researchers, policy makers, and urban planners

Presenters:

• • Neven Matasovic, Geo-Logic
  • Travis Deane, Shannon & Wilson
  • Tim Stark, PhD PE

Safety & Access: Even though limited to publicly-accessible areas, terrain tour may include walking over unstable and uneven areas. Attendees should wear appropriate field gear. Tour route may be adjusted due to current landslide (reserve) conditions and/or weather.