ABRASION

ABRASION (from the Latin word abrasio, meaning scraping; EN: abrasion; The rocky stack (kekur) with the windowDE: Abrasion; FR: abrasion; ES: abrasion; RU: абразия) is the process of the mechanical destruction and the removal of the rocks in the coastal zone of the water bodies (oceans, seas, lakes, reservoirs) by the waves and the surf, and by the impact of the clastic material, which is moving and suspended in the water.

The specific forms of the relief, which are created as the result of the abrasion: abrasion scarps (cliffs), wave-cut niches, stacks (kekur or otpryadysh in Russian), underwater abrasion terraces or platforms (benches), etc. This process is often named as the mechanical abrasion, unlike the heat abrasion (thermal abrasion), that is the destruction of the coasts which are composed of the permafrost rocks and ice, and unlike the chemical abrasion (the destruction of the coast as the result of the chemical action of the water). The less resistant are the rocks, the more is the inclination of the slope area of the adjacent bottom of the water body, and the greater is the power of the waves, the greater is the rate of the abrasion.

The abrasion is the most intensive in the surf zone. The length of the abrasion areas on the shores of the water bodies around the globe is 400 million kilometres (51% of the total length). On average, 3.45 billion of the cubic metres of the clastic material per year arrive from the cliffs into the water, and yet 7.4 billion cubic metres per year more from the benches. The sand, pebbles, gravel, and the larger clastic material, which are created at the time of the abrasion, form the underwater accumulative terrace, which is attached to the bench, and the accumulative coastal and underwater landforms (sand spits, siltings, etc.), The rocky slope, which has been created by the abrasionwhich are asThe rocky slope, which has been created by the abrasionsociated with the coastal and marine placers and deposits of the construction materials.

At the time of the development of the coastal deposits of the gravel and sand, it is necessary to coordinate the scale of their extraction with the rate of the supply of the clastic material. The sediments of the abrasion origin, which are suspended in the water, migrate along the shoreline, or are carried by the currents away from the coastal zone, and deposited in the deeper parts of the water bodies.