Abstract

The North Ogden landslide is a prehistoric, liquefaction-induced landslide complex in northern Weber County, Utah. Although first identified as a possible earthquake-induced lateral-spread landslide in 1980 and mapped as such in 1990 by the U.S. Geological Survey, little follow-up work aimed at discerning the age, failure history, or hazard potential of this landslide has been conducted. We mapped surficial geology and geomorphology, and excavated trenches on the feature, to better understand its movement history.

Geomorphic mapping indicates that the North Ogden landslide is a complex landslide that has failed by both lateral spreading and flow failure. This theory is supported by stratigraphic evidence illustrated in two trenches excavated on the landslide. Radiocarbon dating of the modem and buried soils in one of the trenches shows that the landslide complex has experienced at least three, but possibly four or more liquefaction events during the Holocene; movement of the landslide complex may have accompanied each of these events. At least one liquefaction event, evidenced by sand-injection features in one trench, occurred in late Holocene time. These liquefaction events can be loosely correlated with the Holocene paleoseismic record of the Weber segment of the Wasatch fault zone. Current soil and ground-water conditions on and surrounding the North Ogden landslide complex indicate that the feature, or portions of it, may reactivate in future moderate to large earthquakes on the Wasatch or other nearby faults.