It is the process of friction caused by scuffing, scratching, wearing down, marring, and rubbing away of materials. The intensity of abrasion depends on the hardness, concentration, velocity and mass of the moving particles. Abrasion generally occurs four ways.[1][2] Glaciation slowly grinds rocks picked up by ice against rock surfaces.[3] Solid objects transported in river channels make abrasive surface contact with the bed and walls.