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River deposition landforms geography
River or fluvial processes occur by erosion, transport, and deposition. In this explanation, we will be looking at deposition. Don't know what a river deposition landform is? Fear not, as all is about to be revealed!
In geographical terms, deposition is when materials are deposited, i.e. left behind because the water or wind can no longer carry them.
Deposition in a river happens when the current is no longer strong enough to carry materials, also known as sediments. Gravity will do its work, and those sediments and materials will be deposited or left behind. Heavier sediments, such as boulders, will be deposited first, as they need more velocity (i.e. stronger currents) to carry them onwards. Finer sediments, such as silt, are much lighter and therefore don't need a lot of speed to keep them going. These finer sediments will be deposited last.
The difference in sediment weight and when and where they are deposited can be clearly seen in the landscape. Boulders are found along the beds of mountain streams; fine silts are located close to a river's mouth.
River deposition landforms features
Before we dive in and look at the different types of river landforms, let's explore some of the typical features of river deposition landforms.
- A river needs to slow down in order to deposit sediments. This material that gets left behind from this slowing down of river flow is what builds river landforms.
- During periods of drought, when discharge is low, there will be more deposits of sediments.
- Deposition landforms often occur in the middle and lower courses of the river. This is because the river bed is wider and deeper at these points, so energy is much lower, allowing deposition to occur. These areas are much flatter than the upper course and only slope gently.
What are some of the reasons a river slows down, you ask? Well, the reasons include the following:
- Falling river volumes - for example, during a drought or following a flood.
- The eroded materials increase - the buildup will slow down the river's current.
- The water is or becomes shallower - if evaporation is higher or there is less rainfall.
- The river reaches its mouth - the river reaches flatter land, so gravity isn't pulling the river down the steeper slopes.
River deposition Landforms types
There are several types of river deposition landforms, so let's look at them now.
| Type | Explanation |
| Alluvial fan | Alluvium is gravel, sand, and other small(er) material deposited by flowing water. When water is confined in a channel, it can then freely spread out and infiltrate the surface, depositing sediments; you will see that it has a cone shape. It literally fans out, hence the name. Alluvial fans are found in the river's middle course at the foot of a slope or mountain. |
| Delta | Deltas, flat, low-lying deposits of sediments, can be found at a river's mouth. In order to become a delta, the sediment must enter water that moves slower or is stagnant, which often is where a river enters an ocean, sea, lake, reservoir, or estuary. A delta is often shaped like a triangle.
|
| Meanders | Meanders are loopy! These rivers curve along their route in a loop-like pattern rather than going in a straight line. These curves mean that the water flows at different speeds. The water flows faster on the outer banks, causing erosion, and slower on the inner banks, causing deposition. The result is a steep cliff on the outer bank and a nice, gentle slip-off slope on the inner bank.
|
| Oxbow lakes | Erosion causes the outer banks to grow wider and create bigger loops. In due course, the deposition can cut off that meander (loop) from the rest of the river, creating an oxbow lake. Oxbow lakes often have the rough shape of a horseshoe.
Fun Fact: Oxbow lakes are still water lakes, meaning no current flows through the water. Therefore, over time, the lake will silt up and become a bog or swamp before evaporating entirely at some point. In the end, the only thing left is what we call a 'meander scar', a visual reference that once there was a meander (that became an oxbow lake). |
| Floodplains | When a river floods, the water-covered area is called a floodplain. The flow of water slows down, and the energy is taken out of the river - this means the material is deposited. Over time, the floodplain builds up and becomes higher.
|
| Levees | A floodplain will seriously reduce the water's velocity by causing friction. Now, the water will deposit sediments there, with coarser, heavier materials deposited first, creating a raised bank, known as a levee (sometimes spelt levées), at the river's edge. These levees are defences against potential floods, depending on their height.
|
| Braided channels | A braided channel or river is a river that is divided into smaller channels. These dividers are created by eyots, temporary (sometimes permanent) islands created by sediment deposition. Braided channels often form in rivers with a steep profile, are rich in sediments, and have regularly fluctuating discharge, the latter being most often due to seasonal variations.
|
| Estuary & mudflats | You will find an estuary where the open mouth of the river meets the sea. In this area, the river is tidal, and the sea retreats the water volume, reducing the water in the estuary. Less water means silt deposits form, which, in turn, form mudflats. The latter is a sheltered coastal area where tides and rivers deposit mud.
|
Table 1
Meanders and Oxbow lakes
Above, we mentioned meanders and oxbow lakes as being deposition landforms. However, in reality, meanders and oxbow lakes are caused by both deposition and erosion.
Once upon a time, there was a little river. Erosion on the outer bank and deposition on the inner bank caused the little river to get a little bend. Continuous erosion and deposition caused the little bend to become a big(ger) bend, working harmoniously to create a meander. And they lived happily ever....no wait, the story isn't over yet!
Remember the little bend becoming a bigger bend? Well, when the river erodes through a meander's neck, an oxbow lake is born. Silty deposition builds up over time, and then the meander and oxbow lake go their separate way.
This a perfect example of two opposites working together to create such a wonderful tale!
River deposition landforms diagram
You have learned about several different river deposition landforms, but you know what they say "a picture is worth a thousand words". The diagram below shows you some, not all, of the landforms mentioned in this article.
River deposition landforms example
Now that you have read about several river deposition landforms, let's look at an example, as those are always helpful.
The Rhône river and delta
For this example, we first move to the Swiss Alps, where the Rhône river begins as meltwater of the Rhône Glacier. The water flows west and south through Lake Geneva before flowing southeast through France before it discharges into the Mediterranean Sea. Near the river's mouth, in Arles, the Rhône river is split into the Great Rhône (le Grande Rhône in French) and the Little Rhône (le Petit Rhône in French). The delta that is created forms the Camargue region.
Fig. 11 - Rhône river and delta, ending in the Mediterranean Sea
At the mouth of the Rhône, you will find the Mediterranean Sea, which has a very small tidal range, meaning that there are no currents that transport the deposits there. Furthermore, the Mediterranean Sea is salty, and clay and mud particles will stick together due to the salt water, and these particles do not float in the river's flow. This means that deposition at the river's mouth is rapid.
Now, the formation of the delta did not happen overnight. First, sandbanks are created in the river's original mouth causing the river to be divided. If this process is repeated over time, the delta ends up with many streams or channels branching off; these stream branches/channels are called distributaries. Each separate channel will create its own set of levees, impacting the human and physical environment.
Fig. 12 - Rhône river delta at its mouth
You may have to identify a landform from a photo or a map, so familiarise yourself with what they look like.
River Deposition Landforms - Key takeaways
- Deposition in a river happens when the current is no longer strong enough to carry materials, also known as sediments. The sediment will be dropped and left behind, creating different types of deposition landforms.
- There are different types of river deposition landforms:
- Alluvial fan
- Delta
- Meander
- Oxbow lake
- Floodplain
- Levees
- Braided channels
- Estuaries & mudflats.
- Some landforms, such as meanders and oxbow lakes, are created by a combination of erosion and deposition.
- An example of a river deposition landform is the Rhône river and delta.
References
- Fig. 1: Yukon Delta, Alaska (https://search-production.openverse.engineering/image/e2e93435-c74e-4e34-988f-a54c75f6d9fa) by NASA Earth Observatory (https://www.flickr.com/photos/68824346@N02) Licensed by CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/)
- Fig. 3: Oxbow lake in Lippental, Germany (https://de.wikipedia.org/wiki/Datei:Lippetal,_Lippborg_--_2014_--_8727.jpg) by Dietmar Reich (https://www.wikidata.org/wiki/Q34788025) Licensed by CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en)
- Fig. 5: Floodplain on the Isles of Wight after a massive flood (https://en.wikipedia.org/wiki/File:Floodislewight.jpg) by Oikos-team (no profile) Licensed by CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en)
- Fig. 7: Rakaia River in Canterbury, South Island, New Zealand, an example of a braided river (https://en.wikipedia.org/wiki/File:Rakaia_River_NZ_aerial_braided.jpg) by Andrew Cooper (https://commons.wikimedia.org/wiki/User:Andrew_Cooper) Licensed by CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en)
- Fig. 8: River Exe estuary in Exeter, UK (https://en.wikipedia.org/wiki/File:Exe_estuary_from_balloon.jpg) by steverenouk (https://www.flickr.com/people/94466642@N00) Licensed by (CC BY-SA 2.0 https://creativecommons.org/licenses/by-sa/2.0/deed.en)
- Fig. 11: Rhône river and delta, ending in the Mediterranean Sea (https://en.wikipedia.org/wiki/File:Rhone_drainage_basin.png) by NordNordWest (https://commons.wikimedia.org/wiki/User:NordNordWest) Licensed by CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en)
- Fig. 12: Rhône river delta at its mouth (https://en.wikipedia.org/wiki/File:Rhone_River_SPOT_1296.jpg) by Cnes - Spot Image (https://commons.wikimedia.org/wiki/User:Spot_Image) Licensed by CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en)
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Frequently Asked Questions about River Deposition Landforms
What are the depositional landforms of rivers?
Deposition in a river happens when the river's current is no longer strong enough to carry materials, known as sediments, any further. These sediments will eventually be deposited, i.e. dropped and left behind, where they will create landforms.
What is an example of river deposition?
An example of river deposition is the River Severn estuary
What are the features of river deposition landforms?
River deposition landforms usually occur in the middle and lower courses of the river and feature an accumulation of sediment which often forms a mound.
What are five landforms formed by river deposition?
Flood plains, levees, deltas, meanders, and oxbow lakes
How can river deposition change a landform?
Deposition of sediments can transform any landform. An example is: deposits can turn a meander into an oxbow lake. Further deposition by silt then causes the oxbow lake to become a bog or swamp. This example shows how deposition can change one (small) section of a river into two different landforms over time.
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