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 ...
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.
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 .
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.
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.
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.
Areas where more particles are dropped are called alluvial or flood plains, and the dropped particles are called alluvium. Even small streams make alluvial deposits, but it is in floodplains and deltas of large rivers that large, geologically-significant alluvial deposits are found. The amount of matter carried by a large river is enormous.