Abstract

In the early 1990s we studied six features identified as liquefaction-induced lateral-spread landslides in Box Elder County, including the Madsen Spur landslide. Most of these landslides occurred about 12,000 to 13,000 ¹⁴C yr B.P. in Lake Bonneville gravels, when the lake was at an elevation of 1,353 meters (4,440 ft) and receding. Our field work, aerial-photo mapping, and subsequent discussions with previous investigators lead us to conclude that liquefaction was not necessary for the occurrence of the six landslides. We cannot discount the possibility that liquefaction may have occurred in the gravel deposits saturated by Lake Bonneville, but the morphology of these landslides, especially the Madsen Spur landslide, and steepness of slopes on which they formed are such that movement could have occurred in the absence of liquefaction. For most of these landslides, including the Madsen Spur landslide, the possibility of renewed, non-liquefaction-induced failure, especially during large-magnitude earthquakes or significant wet periods in northern Utah, exists and may present a hazard to nearby development.