Tropical Barrier Islands of Colombia's Pacific Coast

Sixty-two barrier islands on the Pacific Coast of Colombia are reported and described. The islands, covered by tropical rainforest and backed by mangrove forests, line the seaward margin of a narrow, extensive, deltaic plain formed from rivers draining the northwestern Andes. The islands are of interest because of a combination of factors including: their position on a leading-edge coast which contributes to relative sea-level rise through long-term subsidence; short-term seismic subsidence and tsunamis; their tropical setting where deltaic sedimentation and heavy vegetative cover influence island dynamics in terms of subsidence, river channel switching and quality and quantity of sand supply, the possible shortterm influence of El Niño events; and the lack of human influence on island dynamics. Five genetic island groups are identified: two groups associated with straight stretches of coastal lowland and three delta lobe groups (Rio San Juan, Rio Patia, and Rio Mira deltas). A few of the islands formed due to spit detachment. Initially the islands were probably transgressive, then became regressive for an indeterminate period before recent reinitiation of a transgressive phase, and severe island front erosion. Many of the islands are sand starved due to sediment supply loss when distributary switching occurred, or because they are in areas with little sand in the associated mangrove substrate and no fluvial sand supply. The recognition of the barrier island nature of this coast provides a new management tool to guide coastal hazard mitigation and future development. Future stratigraphic studies may provide a basis to identify the frequency of short-term events such as El Niño and tsunamis and to establish recent sea level history for specific island groups. /// En la costa del Pacifico colombiano sesenta y dos islas barrera han sido reportadas y descritas. Las islas, con una densa cobertura de bosque tropical y antecediendo una extensa planicie de manglar, definen el borde costero de un angosto y extenso prisma deltáico, formado por los ríos que drenan esta parte de los Andes. Las islas son interesantes por varias razones entre las que se incluyen: su posición en una margen costera tectónicamente activa, que a través de subsidencia a largo plazo produce aumentos relativos del nivel del mar; subsidencia sismica a escalas de tiempo más cortas; tsunamis; su ubicación en un ambiente tropical, donde la sedimentación deltáica y la densa cobertura de vegetación