Images

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

A debris flow is a form of rapid mass movement in which a combination of loose soil, rock, organic matter, air, and water mobilizes as a slurry that flows downslope. Debris flows include <50% fines.

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

Lateral spreads are distinctive because they usually occur on very gentle slopes or flat terrain. The dominant mode of movement is lateral extension accompanied by shear or tensile fractures.

Toppling failures are distinguished by the forward rotation of a unit or units about some pivotal point, below or low in the unit, under the actions of gravity and forces exerted by adjacent units or by fluids in cracks.

Rotational slide: This is a slide in which the surface of rupture is curved concavely upward and the slide movement is roughly rotational about an axis that is parallel to the ground surface and transverse across the slide.

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.

Landslides near the 2017 Thomas fire burn area that initiated during a series of atmospheric river events in December 2022 and January 2023.  

University of Puerto Rico-Mayagüez students Estefania Vicens, Tania Figueroa, Anishka Ruiz, Cesar Rodriguez, and Kimberly Maisonet stand next to completed landslide monitoring station at Yauco, Puerto Rico, part of the Landslide Monitoring Network.

Estefania Vicens, Tania Figueroa, Kimberly Trahan, Victor Ortega stand next to completed Mayagüez monitoring station, part of the Puerto Rico Landslide Monitoring Network

Completed landslide monitoring station at Ponce, Puerto Rico among the palms. One of the sites in the Puerto Rico Landslide Monitoring Network.

Example of a landslide that initiated within the footprint of the 2019 Cave Fire during the 9 January 2023 rainstorm. The landslide source area is shown in the upper left of this image. The debris-flow runout path is shown in the center and lower right of this image.

San Lorenzo, Puerto Rico landslide lonitoring site. The San Lorenzo monitoring station is located in a moderately vegetated area underlain by Cretaceous volcaniclastic rock. 

Debris-flow deposits downstream of the 2022 Pipeline Fire burn scar, north of Flagstaff, Arizona.

The June 28, 2022, Chaos Canyon debris slide with main features labeled. Horizontal distance from the middle of headscarp to the middle of toe is about 585 m. North is towards the right side of the photograph.

View looking down the debris slide to the pool of mud accumulating behind the ridge of dirty, snow boulders. North is towards the left of the photograph.