Geopix UK - Sedimentation

Transport and Deposition

If rivers have enough energy, discharge and speed, they can transport a vast 'load' of material, as

bed load which moves by
- rolling or traction
- saltation

suspended load
compare the clear water with the murky water as two rivers meet

solution load (which cannot be seen)

It is useful to consider the following scenario:

when fragments fall into a river they are large and angular, with sharp edges and corners.
during transport, the fragments become rounder and smaller due to attrition.

The greater the length of transport, the rounder and smaller the fragments become.

The fragment is said to be rounded if the corners and edges are smoothed off:
it doesn't have to be spherical to be rounded.

When the current slackens, the heavier particles are deposited while the lighter ones are carried further downstream. In this way, the sediment is sorted into different grades. Only the lightest will be transported as far as the sea.

Sorting is the degree to which the grains in a sediment are grouped according to size.
Transport tends to increase the degree of sorting, especially if wind is involved.

Desert sands are well sorted.

Boulder clay, on the other hand, where all the fragments are frozen into the ice and therefore do not come into contact with each other, is unsorted, or poorly sorted.
The fragments remain angular.