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Alluvial fans are common in the geologic record, such as in the Triassic basins of eastern North America and the New Red Sandstone of south Devon. Such fan deposits likely contain the largest accumulations of gravel in the geologic record. Alluvial fans have also been found on Mars and Titan, showing that fluvial processes have occurred on ...
Alluvial fans, also called inland deltas, occur at the foot of mountain ranges and mark the presence of river floods.They contain considerable groundwater reservoirs that are replenished each year by infiltration of the water from the river branches into the usually permeable underground, thus creating rich aquifers.
Straight-type channels can be found at alluvial fans. Braided rivers, which form in (tectonically active) areas that have a larger sedimentary load than the discharge of the river and a high gradient. Meandering rivers, which form a sinuous path in a usually low-gradient plain toward the end of a fluvial system.
Fanglomerates are poorly sorted, matrix-rich conglomerates that originated as debris flows on alluvial fans and likely contain the largest accumulations of gravel in the geologic record. [ 4 ] Breccias are similar to conglomerates, but have clasts that have angular (rather than rounded) shapes.
They make up significant percentages of many alluvial fans and debris cones along steep mountain fronts. Fully exposed deposits commonly have lobate forms with boulder-rich snouts, and the lateral margins of debris-flow deposits and paths are commonly marked by the presence of boulder-rich lateral levees .
An alluvial fan could have been deposited and formed outside of a mountain range, however, thrusting of the mountain belt could cause the alluvial fan to become broken up by the new mountain forming. Thus, the alluvial fan would be split with the fan on either side of the new mountain range development and could change the steepness of the fan. [1]
Alluvial fans usually form at the base of mountains, where high-velocity rivers or streams meet a relatively flat area and lose the energy needed to carry large quantities of sediment, which ultimately spreads out in all available directions. They tend to be larger and more obvious in arid regions.
Processes of vesicular horizon development and desert pavement formation on basalt flows of the Cima Volcanic Field and alluvial fans of the Avawatz Mountains Piedmont, Mojave Desert, California. Doctoral thesis, University of California, Riverside. Goudie, A.S. 2008. The history and nature of wind erosion in deserts. Annual Review of Earth and ...