Role of Holocene Relative Sea Level and Wave-Induced Strength Decay in Tropical Soft-Cliff Retreat

Abstract:

The reported retreat rates of tropical soft cliffs, among the highest worldwide, highlight a complex influence of nearshore morphodynamics and geological history. Here, we explore two processes operating at different scales that exert control on tropical soft-cliff retreat along the tectonically active Southern Caribbean Coast of Colombia. First, we modify the Soft Cliff and Platform Erosion (SCAPE) model to account for rock strength decay by including a time-varying calibration term. This modification represents the potential effect of wave-induced cliff flexing. We also apply the sea-level equation solver SELEN v4.0 to calculate the relative sea-level history at several locations along the Southern Caribbean coastline. We focus on quantifying the role of glacio-isostatic adjustment (particularly hydro-isostasy) in the Late Holocene relative sea-level variability. Preliminary results show that soft cliffs in the southern region of the Caribbean coast of Colombia exhibit ~3 meters of relative sea-level fall since ~6 ka BP. Given the upheaval of marine terraces by neotectonic processes in the region (including mud diapirism), we argue that sea level has been falling since the Late Holocene and soft cliffs were inactive. Thus, recent soft-cliff retreat, likely controlled by wave-related strength decay, relates to human activities that modify nearshore morphodynamics. Understanding these mechanisms becomes paramount for developing rational solutions to soft-cliff erosion along these tropical coastlines.