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The coastal development of the Guianas is dominated by extensive, shoreface-attached and alongshore westward migrating mudbanks. The behaviour of these mudbanks is mainly determined by a combination of the large supply of Amazon-borne silt and clay and the trade wind generated wave action. In the front zone of the mudbanks, fluid mud is formed. As a result, the incoming waves are strongly attenuated and deposition is favoured. At their rear side, compacted clay deposits are eroded by waves. The mudbanks, migrating in this manner, are the driving mechanism in the development of the smallest coastal unit, which consists of a mudbank and the eastward adjacent interbank area. Eisma et al. [Neth. J. Sea Res. 28 (1991) 181] has demonstrated that the frequency of the northeast trade wind, which blows towards the coast of the Guianas, in the windy season (January till April), shows a systematic change in time. For the period 1953–1986, there is evidence that the frequency of winds coming from directions between 50° and 80° (roughly east–northeast) increases. The same applies to the wind velocity from that direction. In the last 10 years a reversal of these trends appears to occur. For a more or less east–west directed coastal section, e.g. the coastline of Suriname, a more easterly direction of the northeast trade wind results in an increased longshore wave energy flux in the coastal waters. This causes an increase in length of the mudbanks, at the detriment of the usually eroding interbank parts of the coast. This is evidenced by the large-scale coastal development during the related period, demonstrating an increasing length of the mudbanks and consequently an increasing net accretion. It is hypothesised that this development will reverse if the new trends in wind direction and velocity develop further. At the geological scale, it is considered that a coincidence of a systematic increase of more northerly directed wind frequencies and a fall in sea level are responsible for the two erosive interruptions in the generally accreting coastal plain during the Young Holocene Period. |
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