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March 24, 2021

Recent landslide activity along California’s Pacific coast in the region known as Big Sur has provided graphic examples of the power and impacts of natural hazard events.

While these events highlight the importance of USGS earth science to society, they also demonstrate the crucial role USGS web managers play in ensuring our science teams coordinate communications that convey hazards information to our various audiences.

A view from the sky of a winding coastal road that runs along steep, rocky cliffs, with a section washed out and collapsed.
The storm that hit California’s coast between January 26 and 28, 2021, blew out a portion of Highway 1 near Big Sur. On January 29, a USGS reconnaissance flight snapped this dramatic photo above the Rat Creek drainage showing the debris flow. (Public domain.)

Landslides in this area are inevitable, partly due to the tectonic setting and partly because drainage and coastal erosion processes have created steep slopes and narrow canyons. All combined, the area is characterized by slope failures that continually erode and alter sediment supply along the coast. Effects from wildfire, drought and heavy rainfall events contribute to the dynamic nature of this region, demonstrating the interplay of geologic evolution and natural hazard events. USGS research of these processes—from reconstructing the past history of earthquakes on the nearby San Andreas Fault, to studying how the offshore San Gregorio-Hosgri fault has shaped this mountainous central coast region, to monitoring landslide activity, to analyzing the geologic record in offshore coastal sediments—helps build scientific understanding of the regional geologic setting.

In addition to geologic research, the USGS helps monitor these conditions in support of infrastructure and public safety for emergency managers at state and local levels. Through the Landslide Hazards Program (LHP), our scientists conduct research to improve the understanding of factors and mechanisms that control the locations, timing, extent, and speed of large, potentially catastrophic landslides. This includes assessing debris flows that are commonly related to areas burned by wildfire. LHP research includes conducting landslide hazard assessments, landslide investigations and forecasts, and providing technical assistance to respond to landslide emergencies. In the case of Big Sur, the LHP works with experts at the Coastal and Marine Hazards and Resources Program (CMHRP) to use remote-sensing technologies—such as aerial photography, satellite imagery, structure-from-motion (SfM) photogrammetry, and lidar (laser-based surveying)—to measure coastal changes along the Big Sur coastline. The incredibly visual material provides valuable data for scientists and is also used to help inform the public.

Take a look at the Big Sur Landslides Special Topic webpage and learn more.

An illustration shows how aerial photographs are taken around a landslide in order to use them in computer models.
USGS photographs taken from a contracted small airplane are used to build three-dimensional representations of the hillslopes of Big Sur, California, as shown here for the Mud Creek landslide site in 2017.  Blue symbols show the locations of individual photos obtained on the flight, and the gray area shows the hillslope landscape created from the photos using Structure-from-Motion (SfM) photogrammetry. (Public domain.)

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