The Guiana Coast of northeastern South America, backed by mangrove swamps and fronted by migrating mudflats and associated subtidal mudbanks, has developed during the Holocene as a prograding mud wedge from Amazon-derived sediment. A hypothesis is offered for the periodic stabilization of shifting mudflats, a process that has been recognized previously as the mechanism for initiation of new land growth. The hypothesis assumes that solar semiannual and 18.6-yr tidal components allow abnormal exposures of coastal mudflats and conditions that are favorable for establishment of Avicennia mangroves. Once colonized, mangrove roots displace muds upward, thus decreasing the frequency of tidal inundation and increasing the ability of vegetation to trap and hold muds. Based on estimated rates of root growth and forecasted tide records for the coast of Surinam, land elevation will increase by 25 cm in 10 yr and frequency of tidal inundation above 2.45 m (8.0 ft) will decrease from 106 to 2 per year during the same period.

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