Coasts and the Coastal Processes Coast s can be active (i.e., plate boundaries) or passive Following are examples of coastal erosion by waves: (i.e., non-tectonic), and erosiona l – stream erosion, wind abrasion and glacial activity (e.g., fjords), or – erosion by waves and currents (e.g., effects of surging, plunging and spilling breakers) and The example below is that of a delta: depositiona l (i.e., beaches, deltas etc). Deltas are of three types: (a) river-dominated (e.g., Mississippi, Danube, Po); (b) wave-dominated (e.g., Nile, Niger, São Francisco); and (c) tide-dominated (e.g., Colorado, Ganges- Brahmaputra, Mekong). Longshore current and littoral drift Wave interference creates a “longshore current” parallel to the shoreline (i.e., along the shore). This longshore current straightens the shoreline, and carries the sand in littoral drift that it may dump in a submarine canyon or use for creating a barrier island and the like features. W ave refraction along a straight coast B e a c h W ave refraction along a straight coast B e a c h W ave touches bottom here and slow s dow n 1940 1963 X X N Shown on the left, for instance, are two pictures of Sandy Beach (shown by the cross here), NJ, one taken in 1940 and the other in 1963. They show that the longshore current here flows to the north — notice how littoral drift has built a barrier island here. These two cartoons below show how longshore current straightens the shoreline by eroding the headlands and filling the bays by this eroded material As shown on the right, berms form above the highest wave activity, beachface (or the backshore) always lies above water, and foreshore or tidal terrace is only exposed at the low tides. Beaches Beach bearing coasts have backshore, foreshore and offshore regions that are defined mainly by the tidal heights and shore geometry and thus have tidal flats or tidal terraces.