Search results
Results from the WOW.Com Content Network
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.
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.
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.
The shape of alluvial fans is mostly influenced tectonically. An alluvial fan can be completely changed due to orogenic thrusting. [4] 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.
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 .