The Deep Creek Mudflow of April 16,1979, Uintah County, Utah, USA

On April 16, 1979, about 12 acres (5 ha) of gently sloping alluvial pasture near Vernal, Utah, liquefied, caved into a tributary of Deep Creek, and flowed down- stream. The event lasted about 5 hours, involved an estimated 300,000 yards (230,000 m) of earth, and resulted in a dendritically branched arroyo system one-half mile long and up to 21 feet (6.4 m) deep. The liquefying layer appears to have been sand with interbedded gravel. Liquefaction appears to have been initiated by high pore pressure caused by unusually high groundwater levels. Although the ground was unusually wet, there is no evidence to suggest that groundwater conditions were unique. This event and the resultant landform indicate that liquefaction-sapping is a viable process for rapid arroyo formation.