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Processes on Arid-Region Alluvial Fans

1967; University of Chicago Press; Volume: 75; Issue: 4 Linguagem: Inglês

10.1086/627271

1537-5269

Roger LeB. Hooke,

Soil erosion and sediment transport

Alluvial fans were studied in the field, largely in the desert regions of California, and in the laboratory. Field study consisted of detailed mapping of parts of four fans and reconnaissance work on over one hundred additional fans. Features mapped included the nature and age of deposits, material size, and channel pattern. In the laboratory small alluvial fans were built of mud and sand transported through a channel into a 5-foot by 5-foot box under controlled conditions. Material is transported to fans by debris flows or water flows that follow a main channel. This channel is generally incised at the fanhead, because there water is able to transport on a lower slope the material deposited earlier by debris flows. The main channel emerges onto the surface near a midfan point, herein called the "intersection point." On laboratory fans most deposition above the intersection point is by debris flows that exceed the depth of the incised channel. Fluvial deposition dominates below the intersection point. This depositional relation probably also occurs on natural fans. On fans deficient in fine material large discharges may infiltrate completely before reaching the toe of the fan. Coarse debris is then deposited as lobate masses, herein called "sieve deposits." In many respects sieve deposits resemble debris-flow deposits, but they lack primary fine material, and fresh lobes are highly permeable.