Abstract

Sandy beaches are characterised by high temporal and spatial variability, resulting in environmental gradients between beaches based on morphodynamic differences. This variability is less well known when beaches are affected by abrupt and highly energetic perturbations such as earthquakes and tsunamis. Here, we analysed the changes in the morphodynamic characteristics of six beaches in south-central Chile. Morphodynamic variables were analysed seasonally, and as a function of changes caused by a mega-earthquake and subsequent tsunami on 27 February 2010 (Mw = 8.8). The results indicate that Dichato and Lenga have reflective morphodynamic states, while Cobquecura, Mela, Perales and Puda have intermediate states. The canonical analysis of principal coordinates (CAP) biplot of the first two components showed that the second component (CAP2) related Dichato and Mela significantly to mean grain size, frequency of effluent line crossing, swash frequency, breaking wave frequency and swash speed; while Cobquecura, Perales, Puda and Lenga were related to beach slope, height of breaking wave and swash frequency. Beaches generally showed coarse sand during winter and lower textural range in summer, but with high seasonal variability of mean grain size. The mega-earthquake and subsequent tsunami that hit the study area in February 2010 led to short-term changes in morphodynamics, mainly beach slope and granulometry, but beaches tended to regain conditions similar to those prior to the earthquake, showing an apparent high resilience to this strong natural perturbation.