blackberryanna.blogg.se - Formation of a meander

Over time the meander becomes more pronounced and the ‘neck’ of the meander becomes smaller. Video on formation of meanders and ox-bow lakes

On the inside of the bend the velocity is much slower and consequently, deposition occurs creating a slip-off slope. The faster water travels around the outside of the bend, eroding the banks through abrasion and hydraulic action.

They are formed by a combination of erosion and deposition. Erosion is now mainly lateral and it has widened the river. In the middle section the river has more energy and a high volume of water. Landforms resulting from erosion and deposition This process happens repeatedly which means that the waterfall gradually retreats upstream creating a gorge. Over time this creates an overhang which eventually, due to gravity, collapses under its own weight. A plunge pool is created and processes such as abrasion and hydraulic action cause further erosion of the soft, less resistant, rock. As the river flows over the hard rock onto soft rock, the soft rock will be more easily eroded. When a river flows over alternating layers of hard/soft rocks waterfalls can be formed. Interlocking spurs are created when the river has to flow around an obstruction for example, hard rock. This means that abrasion can continue to steepen the valley and the river cuts further downwards. Freeze-thaw weathering and other processes create loose material on the valley sides which are then washed into the river from the steep valley sides during times of heavy rainfall, adding to the material being carried by the river. This causes the most distinctive river feature, the V-shaped valley. In the upper course of the river, the river cuts rapidly downwards, as the main direction of erosion is verticall. In the upper course erosion is the dominant process creating V-shaped valleys, interlocking spurs and waterfalls. Each of these sections have different dominant processes resulting in different features.

The term is sometimes used synonymously with slip-0ff slopes although the term slip-off slope is used to refer to the cross section and the term point bar is used to refer to the aerial view.Rivers have an upper, middle and lower course.

They show the former positions of a meander during its downstream migration.

They are crescent-shaped and located on the inside of a stream bend of meanders.

A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope.

The lateral erosion of the meanders and their migration widen the flood plain.

This causes meander to migrate down the valley.

The greater erosion of the concave bank occurs just downstream of the axis of the meander bend, because the course of the maximum velocity zone in the channel does not reflect the meander shape.

Over time a small river beach or runoff slope builds up on the inner bend.

This increased friction further reduces the velocity (thus further reducing energy), encouraging further deposition.

the inner bend water is slow flowing, due to it being a low energy zone, deposition occurs resulting in a shallower channel.

The lateral erosion results in undercutting of the river bank and the formation of a steep sided river cliff these cliffs are also known as bluffs.

There also vertical erosion which deepens the channel, which reduces friction and increases in energy results in further erosion.

It erodes this bank laterally by attrition and hydraulic action.

Water flows fastest on the outer bend (concave bank) of the river where the channel is deeper and there is less friction.