16. The Historical, Geomorphological Evolution of the Colombian Littoral Zones (Eighteenth Century to Present)

The complex geological framework of Colombia is reflected on its Caribbean and Pacific coasts by the highly contrasting nature of their littoral types, ranging from low-relief deltaic barrier islands and mangrove swamps to steep-rocky reliefs cut by plunging cliffs and wide erosional shore platforms. Relative sea-level changes during the Quaternary and the Holocene are evidenced by morphological features of ancient coastline positions, including emerged marine terraces with coral reefs, cliffs, stacks, and raised beach ridges deposits.

An overview of the historical evolution of the Colombian littorals since the end of the eighteenth century evidences a high morphological instability indicated by coastline changes of hundreds of meters and corresponding land losses or gains of tens of km². These evolutions reflect noticeable variations in the littoral’s sediment budgets, much of them triggered or greatly influenced by human actions. Along the 1700 km-length, micro-tidal Caribbean shores, critical areas are found between the Magdalena delta and the Urabá Gulf, a developed, highly tectonic coastal fringe influenced by mud diapirism and by man-induced changes on its hydrological and sedimentological regimes. Along the meso-macro tidal, 1300 km-length, less populated and engineered Pacific coast (but highly intervened by deforestation and mining), most critical cases are shown by the breaching of its major barrier islands, due to natural factors including coseismic subsidence, tsunamis, and positive sea-level anomalies during El Niño events.