Images

Text "Landslide Basics" on green background, infographic made for landslide basics page

Flooding and debris flows during rain events following the 2024 South Fork Fire near Ruidoso, New Mexico.  

A road sign in the 2024 South Fork Fire, Lincoln National Forest, New Mexico warns of flooding and debris flow hazards.  Partially burned trees are visible on the hillslope in the image background.  Mud and other debris moved down the slope and were deposited along the road, near the base of the sign.

Fast-moving, highly destructive debris flows triggered by intense rainfall are one of the most dangerous post-fire hazards. The risk of floods and debris flows after fires increases due to vegetation loss and soil exposure. Cases of sudden and deadly debris flow are well documented along the western United States, particularly in Southern California.

Timelapse photography of vegetation recovery following the 2020 CZU Lightning Complex in the Santa Cruz Mountains of northern California. This two-year image sequence begins four and a half months after the wildfire was contained. Time between photographs is approximately two weeks.

Timelapse photography of vegetation recovery following the 2020 CZU Lightning Complex in the Santa Cruz Mountains of northern California. This two-year image sequence begins four and a half months after the wildfire was contained. Time between photographs is approximately two weeks.

A landslide monitoring station within the footprint of the 2016 Fish Fire in the San Gabriel Mountains of southern California.  The station collects surface and subsurface data to monitor and detect changes in local hillslope hydrologic conditions.  

The USGS Postfire Landslide Monitoring Station “Maria Ygnacio” is located within the Los Padres National Forest in the Santa Ynez Mountains of southern California. The site consists of surface and subsurface instrumentation that is monitoring the hillslope shown in this image.

University of Puerto Rico, Mayagüez and USGS scientists working on the Añasco monitoring station

Situated on a vegetated hillslope surrounded by cattle, is the Añasco monitoring station. A fence was built around the station to keep the grazing cattle from damaging any of the station components

Stephen Hughes, Gabriel Colón, and Ednet López stand on hillslope next to completed landslide monitoring station at Añasco, Puerto Rico

Steep, rugged terrain in the area burned by the 2009 Station Fire, Angeles National Forest, California. This photo was taken approximately 14 years after the wildfire, and the vegetation has fully recovered.  Note the steep slopes in the background of the image.

Screenshot from the U.S. Landslide Inventory web application, an openly accessible, centralized map of existing information on landslide occurrence across the entire U.S

Charlie Miles performing field work on the Alaskan Gyre at the Prince William Sound, Alaska

TYPES OF LANDSLIDES

Creep is the imperceptibly slow, steady, downward movement of slope-forming soil or rock. Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure.

Debris avalanche: This is a variety of very rapid to extremely rapid debris flow.

Rockfalls are abrupt movements of masses of geologic materials, such as rocks and boulders, which become detached from steep slopes or cliffs. Separation occurs along discontinuities such as fractures, joints, and bedding planes, and movement occurs by free-fall, bouncing, and rolling.

Earthflows have a characteristic "hourglass" shape. The slope material liquefies and runs out, forming a bowl or depression at the head. The flow itself is elongated and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions. However, dry flows of granular material are also possible.

A block slide is a translational slide in which the moving mass consists of a single unit or a few closely related units that move downslope as a relatively coherent mass.

Translational slide: In this type of slide, the landslide mass moves along a roughly planar surface with little rotation or backward tilting.