|
|
 |
Pacific Coast: Mira River delta
The Mira River delta plain (Fig. 43) is a Plio-Quaternary accretionary prism that encompasses about 1600 km2. The delta is limited to the east by hills and terraces of semi-consolidated sediment, and to the north by the extensive mangrove and freshwater swamps bordering southern Tumaco Bay. Morphological evidence suggests that the Mira delta prograded progressively from Tumaco Bay to the southwest. The older delta is recognized by an extensive system of arcuate beach ridges landward of the more recent deposits of sandy barrier spits and mangrove swamps that characterize the present depocenter (Arango and Ponce 1982, Correa y González 1988). The straight, E-W segment of the lower river course (Fig. 43) also suggests structural control of the position of the river.
Figure 43. Radar image showing the recent Mira River delta surficial features, including the extensive arcuate beach-ridge system, the recent sets of spits, mangrove swamps, and the present river mouth. Reproduced by permission of Instituto Geográfico Agustín Codazzi (IGAC) and INTERA Information Technologies (STAR-1 radar). |
The northwest Mira delta shore (Figs. 44 and 45) is a wave-dominated environment characterized by narrow, erosive barrier islands backed by mangrove and transitional swamps (Martínez et al. 1995). Northeastern barrier islands and sandy intertidal shoals and bars migrate continuously to the southwestern part of Tumaco Bay. These features represent the least stable shores of the entire Pacific coast.
Figure 44. Shoreline features of the northwestern Mira River delta. Central part of the Bocagrande barrier island, frequently overwashed and breached during extreme storms. Photo by A. Tovar. |
Figure 45. Erosional scarp on the Bocagrande Island beaches. Photo by A. Tovar. |
continue to Gorgona Island
|
