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THE BEAR RIVER LANDSLIDE COMPLEX, PRESTON, IDAHO: GEOLOGIC CONSIDERATIONS AND HISTORICAL PERSPECTIVES
Proceedings of the Symposium on Engineering Geology and Soils Engineering (1987)
  • James P. McCalpin
Abstract
The Bear River Landslide Complex is a series of earth movements in northern Cache Valley, north of Preston, Idaho. The landslides occur in unconsolidated sediments of the Pleistocene Bear River Delta which formed where the river entered Lakes Bonneville and Provo. The Lake Bonneville delta deposits are up to 490 feet (150 m) thick and consist of a lower alluvial coarse sand and gravel unit, a middle delta front fine sand and silt unit, and an upper pro-delta clay up to 50 feet (15 m) thick. The interbedded character of the fine sands, silts, and clays, together with abrupt lateral facies changes, produce numerous confined and perched aquifers. The complex exhibits widely variable types of failure, movement rates and magnitudes. The majority of movements are properly classified as complex, and are slump-earth flows. Earth falls, slumps, rotational slides, and earth flows are also common. The laterally variable nature of the deltaic sediments and resultant inhomogeneous· groundwater flow patterns produce the variability of movements within the complex. The first order cause of the earth movements is the incision of the unconsolidated deltaic sediments by the Bear River, which has created steep unstable slopes along the margins of the river valley. The second order cause of the landslides is high groundwater levels created by a combination of normal infiltration and artificially-created recharge due to irrigation of farmland on the delta surface. Periods of abnormally high precipitation serve to further increase the saturation level of the sediments, and decrease stability in the area of the landslide complex. The period of high precipitation in 1980-1983 resulted in extensive landslide activity in 1981-1984, which seriously threatens the route of U. S. Highway 91 north of Preston.
Keywords
  • landslides,
  • Idaho,
  • Lake Bonneville
Disciplines
Publication Date
1987
Citation Information
James P. McCalpin. "THE BEAR RIVER LANDSLIDE COMPLEX, PRESTON, IDAHO: GEOLOGIC CONSIDERATIONS AND HISTORICAL PERSPECTIVES" Proceedings of the Symposium on Engineering Geology and Soils Engineering Vol. 23 (1987)
Available at: http://works.bepress.com/james_mccalpin/6/