Attrition (weathering)

Attrition is a form of coastal or river erosion, when the bed load is eroded by itself. Rocks are hit together as they travel downstream, suspended in the river, and are broken up into smaller rocks. This process also makes them rounder and smoother. Attrition can also occur in glaciated regions, where it can be traced to the moving ice and its embedded boulders over surface sediments.

Pebbles are more affected by attrition further downstream, as the rivers' velocity tends to be higher, and therefore its competence (ability to carry sediment) is increased. This means that the load rubs against itself more and with more force when suspended in the river, thus increasing erosion by attrition, though there is a point after transport over a certain distance that pebbles reach a size that is relatively immune to further attrition. Grain-size distribution of sediments produced by attrition can also be controlled by the size range of clasts within the source rock.

Attrition can also be mistaken for sorting, which indicates the distribution of grain size of sediments.

ources

*Strasbourg, Universite, Institut de Geographie, Laboratoire, "Etudes de geomorphologie dynamique sur le Var inferieur", Geologische Rundschau, vol.43, no.2, pp.371-383, 1955
*Bird, Eric C F, "Lateral grading of beach sediments; a commentary", Journal of Coastal Research, vol.12, no.3, pp.774-785, 1996

another way is by balloons falling from the sky, killing all small birds, and sometimes even larger creatures such as humans