Retrogressive Breach Failure in a Tropical Sandy Spit: A Case Study in Puntarenitas, Costa Rica

Abstract

On Thursday, February 8th, 2024, a subaqueous slope failure occurred adjacent to the sand spit terminus at Puntarenitas, Puerto Jiménez, Costa Rica, whereby sediments were mobilized from a nearshore area encompassing approximately 410 m² of beach front. Investigation procedures included salinity, temperature, and density profiling at multiple stations, complemented by underwater videography. Additionally, photogrammetric mosaics were generated through Unmanned Aerial Vehicle (UAV) surveys, and a bathymetric map was constructed using echosounder data. The failure event was characterized by a primary headscarp and three secondary scarps exhibiting a succession of a stepped-like configuration that extended into the subaqueous zone. The submarine failure surface displayed a concave convergent morphology with a proximal sediment accumulation adjacent to the landslide. Morphological and kinematic analysis of the event indicates that it represents a Retrogressive Breach Failure mechanism. These processes are relatively rare yet recurrent at specific locations, as was corroborated through satellite imagery analysis, thereby constituting a natural hazard requiring measures to prevent future risk generations.