Investigation of a Recent Landslide in Fort Smith, Arkansas

D. Mayo, University of Arkansas at Fort Smith, Fort Smith, Arkansas
M.J. Thomas, University of Arkansas at Fort Smith, Fort Smith, Arkansas
A. Burns, University of Arkansas at Fort Smith, Fort Smith, Arkansas
J. Pruitt, University of Arkansas at Fort Smith, Fort Smith, Arkansas
P. Karr, University of Arkansas at Fort Smith, Fort Smith, Arkansas

Keywords

site characterization, topographic profiles, slope failure, slide material, rupture surface

Abstract

A morphologically youthful slope failure, herein referred to as the Landfill Landslide, was identified in a remote section of the City of Fort Smith Landfill, and permission was obtained to investigate. The slide on a deforested, NW-facing 27% slope beneath a linear head scarp about 200 meters long. One end of the head scarp curves abruptly downhill and transforms into a distinct lateral scarp greater than 100 meters long. The surface of the slide is about 24,000 m2 (6 acres) in area and is easily distinguished from adjacent intact slopes by its hummocky morphology and transverse ridges and valleys. The slide is interpreted as a translational failure of poorly sorted fill placed above a shale-rich part of the McAlester Formation (a member of the Desmoinesian Krebs Group). The fill was derived primarily from a now largely destroyed service road cut into colluvium near the top of the slope. The slide mass, exposed in the walls of two deep gullies, is composed of angular fragments of the underlying McAlester Formation in a moist, clay-rich matrix. The UAFS Unmanned Aerial Systems program obtained permits, created a flight plan and acquired 791 images over the landslide with a drone-born RGB camera. DroneDeploy software was used to stitch the images together and produce a topographic map and profiles. Analysis of the profiles indicates that approximately 60,000 m3 of slide material moved downslope about 7.5 meters over a failure surface about 2.5 meters deep. Historical Google Earth images indicate that most of the slide movement occurred between 2006 and 2016. Weather records show that Fort Smith’s average annual precipitation of 42 inches was exceeded during 12 of the 16 years from 2006 to 2021, with the 2015 total of 74 inches the highest on record since 1887. We conclude that the Landfill Landslide was triggered by a combination of tree removal, redistribution of mass during road construction, and abnormally high rainfall on thick clayrich colluvium.

Recommended Citation

Mayo, D.; Thomas, M.J.; Burns, A.; Pruitt, J.; and Karr, P. (2023) "Investigation of a Recent Landslide in Fort Smith, Arkansas," Journal of the Arkansas Academy of Science: Vol. 77, Article 3.
Available at: https://scholarworks.uark.edu/jaas/vol77/iss1/3

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