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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 ...
In (semi)arid regions, therefore, alluvial fans are often used for irrigation of agricultural crops. The fans reveal much greenery in the harsh desert-like environment. Irrigation methods in alluvial fans differ according to the hydrological regime of the river, the shape of the fan, and the natural resources available to maintain human life.
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.
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]
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.
This can be demonstrated at home. Partly fill a circular bowl or cup with water and sprinkle a little sand, rice or sugar into the water. Set the water in circular motion with a hand or spoon. The secondary flow will quickly sweep the solid particles into a neat pile in the center of the bowl or cup.
A subaqueous fan is a fan-shaped deposit formed beneath water (similar to deltas or terrestrial alluvial fans), that is commonly related to glaciers [1] and crater lakes. [ 2 ] Subaqueous fan deposits are generally described as coarse to fine gravel and/or sand , with variable texture and sorting.
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.