Where to find alluvial fans

The rushing water carries alluvium to a flat plain , where the stream leaves its channel to spread out. Alluvium is deposited as the stream fans out, creating the familiar triangle-shaped feature. The narrow point of the alluvial fan is called its apex , while the wide triangle is the fan's apron. Alluvial fans can be tiny, with an apron of just a few centimeters spreading out from the trickle of a drainpipe. They can also be enormous. Over time, water flowing down the Koshi River in Nepal, for example, has built up an alluvial fan more than 15, square kilometers almost 5, square miles wide.

This "megafan" carries alluvium from the Himalaya Mountains. A bajada is the convergence, or blending, of many alluvial fans. Bajadas are common in dry climate s, such as the canyons of the American Southwest. Bajadas can be narrow, from the flow of two or three streams of water, or they can be wide, where dozens of alluvial fans converge.

Alluvial fans and bajadas are often found in desert s, where flash flood s wash alluvium down from nearby hills. They can also be found in wetter climates, where streams are more common. Alluvial fans are even found underwater. A subaqueous fan is created as an underwater current deposits alluvium from a submarine hill or glacier. Sometimes, fans are formed without the aid of water. These are called colluvial fan s.

Colluvial fans are created by mass wasting. Mass wasting is simply the downward movement of rock, soil, or other material. Alluvium is material transported by water, while colluvium is material transported by mass wasting. Landslide s are an instance of mass wasting that often create colluvial fans. A debris cone is a type of alluvial fan with a steep slope , closer to the shape of a half-cone than a flat fan.

Debris cones can be created by the slow accumulation of alluvium over many centuries. They can also form as boulder s and other large materials gather during landslides, floods, or other instances of mass wasting. Alluvial fans can be very diverse habitat s. Shrub s such as rabbitbrush and greasewood, or even trees such as ash or willow, are common in the area of alluvial fans. These plants have very deep root s, which can access the water that helped create the alluvial fan, but has now sunken far below it.

It loses its capacity to carry as much alluvium and deposits the excess in sandbars throughout the channels. Over time, the channel migrates back and forth, creating fan-shaped deposits known as alluvial fans. The narrowest point of an alluvial fan—closest to the mountain front—is known as the apex; the broader part is called the apron.

Alluvium deposited closer to the apex tends to be coarser than the material that makes up the apron. Alluvial fans are more likely to form in deserts because there is plenty of loose alluvium and not much vegetation to prevent stream channels from shifting. In the lower left of the image, the Tente River flows through a narrow channel in the foothills of the Dzungarian Alatau range.

Where the Tente emerges from the hills near Lake Alakol, it spreads out and becomes a braided stream. Alluvial fans in arid areas are often used for agriculture because they are relatively flat and provide groundwater for irrigation. This fan is no exception. The blocky green pattern across the apron are fields or pasture land. The straight feature cutting through Beskol and along the northeastern portion of the fan are railroad tracks.

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Timetables, fares, FAQs and all the information you need to get around Dunedin. An alluvial fan is a build up of river or stream sediments which form a sloping landform, shaped like an open fan or a segment of a cone. Flooding on alluvial fans can be damaging as the fans have steeper gradients than river floodplains.