The Utah Thistle Landslide of 1983: A Historical Perspective

In April 1983, an ancient landslide mass in Spanish Fork Canyon, Utah, re-mobilized, creating a landslide dam in the canyon over 200 ft (61 m) high in less than 30 days. The landslide buried a significant highway corridor, a major railroad line, and dammed the Spanish Fork River, inundating the town of Thistle, permanently displacing all of its residents, and destroying all structures in the town. Losses caused by the landslide resulted in Utah’s first Presidential Disaster Declaration and the designation of the Thistle Landslide as the most economically damaging landslide in US history up to that time. Numerous studies characterized the geological, geotechnical, and hydrological conditions associated with the slide and discussed factors that may have initiated it, without broad agreement on the cause. At least two lawsuits ensued, one of which concluded that a century of excavations at the toe of the ancient slide mass by the railroad aggravated stability and allowed a period of extreme precipitation to trigger the movement. The court awarded damages to the displaced residents. This paper discusses the background, circumstances, and impacts of the Thistle Landslide and summarizes the disagreements over the causes of this damaging event.