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Alluvial fans have also been found on Mars and Titan, showing that fluvial processes have occurred on other worlds. Some of the largest alluvial fans are found along the Himalaya mountain front on the Indo-Gangetic plain. A shift of the feeder channel (a nodal avulsion) can lead to catastrophic flooding, as occurred on the Kosi River fan in 2008.
They can be thought of as an underwater version of alluvial fans and can vary dramatically in size, with widths from several kilometres to several thousands of kilometres. [1] The largest is the Bengal Fan, followed by the Indus Fan, but major fans are also found at the outlet of the Amazon, Congo, Mississippi and elsewhere. [2] [3] [4]
In this arid environment, alluvial fans form at the mouth of these streams. Very large alluvial fans merged to form continuous alluvial slopes called bajadas along the Panamint Range. [33] The faster uplift along the Black Mountains formed much smaller alluvial fans because older fans are buried under playa sediments before they can grow too large.
Erosional submarine canyons slope downward and lead to alluvial fan valleys with increasing depth. [2] It is in this zone that sediment is deposited, forming the continental rise. Alluvial fans such as the Bengal Fan , which stretches 3,000 kilometers (1,900 miles), make up one of the largest sedimentary structures in the world. [ 1 ]
An alluvial megafan is a large cone or fan-shaped deposit built up by complex deposition patterns of stream flows originating from a single source point known as an apex. Megafans differ from alluvial fans in their sheer size. Due to their larger size, they may be formed by different geomorphic processes.
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]
The valley and alluvial fan provide evidence for geologically recent (Amazonian-aged) fluvial activity [2] [3] and sustained water flow [4] on Mars. Recent high-resolution orbital images of Peace Vallis and its watershed also suggest that at least one glacial episode affected Gale crater. [ 5 ]
They are also found on fluvial (stream-dominated) alluvial fans. [17] Extensive braided river systems are found in Alaska, Canada, New Zealand's South Island, and the Himalayas, which all contain young, rapidly eroding mountains. The enormous Brahmaputra river in Northeastern India is a classic example of a braided river. [18]