Every land mass on Earth has miles of coast at the interface between the hydrosphere and the lithosphere. Natural forces such as wind, waves and currents are constantly shaping the coastal regions. In addition several other factors result in changes to coasts. Amongst these are winter storms, hurricanes, typhoons and tsunamis which result in major coastal changes over very short time periods. These are referred to as catastrophic events because of the extensive damage that is caused and the unpredictable nature of the event. Humankind has been struggling to control the destructive forces associated with the everyday erosion of the coast, as well as the catastrophic events.
The natural factors that influence the coast are: (1) the sand sources and sinks, (2) changes in relative sea level, (3) geological characteristics of the shore, (4) sand size, density and shape, (5) sand-sharing systems of beaches, dunes and offshore bars, (6) effects of waves, currents, tides and wind, (7) bathymetry of the offshore sea bottom. Other coastal erosion factors include: (1) effects of human impact, such as construction of artificial structures, (2) mining of beach sand, (3) offshore dredging, or building of dams or rivers, (4) loss of sediment offshore, onshore, alongshore and by attrition, (5) reduction in sediment supply due to deceleration cliff erosion, (6) reduction in sediment supply from the sea floor, (7) increased storminess in coastal areas or changes in angle of wave approach, (8) increase in beach saturation due to a higher water table or increased precipitation. In many areas, coastal erosion is a growing problem, driven by natural processes which are exacerbated by the upstream construction of dams and the development of other forms of coastal infrastructure such as artificial lagoons and the clearing of mangrove systems. In the longer term, climate change is also a major threat to critical coastal ecosystems such as the Nile, the Niger and other low-lying deltas and oceanic islands, particularly in the Indian Ocean, which may be inundated by rising sea levels.