Mass transport processes in the submarine slopes of the archipelago of San Andres, Providencia and Santa Catalina (western Caribbean): implications for tsunami generation

Javier Idárraga-Garcia

Universidad del Norte, Departamento de Física y Geociencias, Barranquilla, Colombia

Lateral collapses are common phenomenon in many volcanic edifices, such those reported for many volcanic islands around the world and the archipelago of San Andres, Providencia and Santa Catalina (ASAPSC) in northwestern Colombian Caribbean is not the exception. These processes represent major oceanic events and can result in massive tsunami generation. The detailed analysis of multibeam bathymetry allowed to differentiate at least four zones of the seabed that exhibit hummocky-type morphology, representing deposits of debris avalanches. Deposits of these characteristics were identified on the southern flank of Albuquerque, northwestern flanks of Este-Sureste and Roncador, and western flank of San Andres islands, which areas varying between 22.2 and 93.8 km2. These features are interpreted as the result of large-scale lateral collapses of the islands upper flanks. The sources of these avalanches are located in the island shelf break where 6–14 km-wide amphitheater-like headwalls are observed. Furthermore, some scarps identified at some guyot summits (e.g., Sue, Turmeque and Macondo) might represent planes of weakness through which large collapses could be generated in the future. Also, a series of large-scale seafloor waveforms on the submarine flanks of Serrana, Bajo Nuevo, Quitasueño, Roncador and Este-Sureste islands are identified and described for the first time, which have wavelengths of 250–800 m and wave heights of 10–90 m. It is suggested that these bedforms originated from slope failures triggered in the upper parts of the flanks. Although specific studies should be undertaken in the ASAPSC area to characterize in detail the gravity-driven instability processes and their deposits (e.g., thicknesses, morphologies, sediment volume per event, and probable ages), the results presented in this study suggests that tsunamis triggered by underwater landslides and collapses of ancient volcanic buildings may have occurred in the recent geological past and may occur in the future. At present, there is little doubt that the threat posed by tsunamis triggered by ocean-island flank landslides is both real and significant. In this sense, and considering that the impact of underwater landslides-related tsunamis is generally local, or more rarely regional (in the case of extreme events), the mentioned above implies a new hazard to the emerged areas of the ASAPSC and to the coastal zones of western Caribbean.

  • Javier Idárraga-Garcia