Natural post-tsunami recovery of the Mataquito River mouth, after the 2010 Chilean tsunami

Abstract

The ensuing tsunami from the Mw=8.8 2010 Chilean earthquake was one of the most destructive events on Chilean history (Fritz et al. 2011). It caused not only major damage and loss of infrastructure on several locations, but also drastic morphological changes on coastal environments (Cienfuegos et al., 2010). The large scale and magnitude of the change could be considered effectively as system resets. This situation presented a unique opportunity to witness the natural recovery of some coastal landforms such as sand spits. The Mataquito River mouth, located just in front of the rupture area where most of the earthquake energy was released (Lay et al. 2010), is an example of a natural coastal system heavily affected by the 2010 tsunami: its 8 km-long sand spit almost completely disappeared under the combined action of tsunami waves and the relatively large land subsidence (Vargas et al. 2011). After the earthquake and tsunami, we have monitored the coastal evolution of the river mouth using different techniques such as site surveys, airborne and satellite images, to characterize qualitatively and identify the main processes driving the formation and recovery of the sand spit by waves and wind. This was complemented with forcing information like wind, waves and river discharge in order to better understand the system dynamics. Our observations evidenced a massive accretion and a surprisingly fast coastal recovery . In fact, most of the original configuration of the spit was reformed in less than 18 months. On the contrary, Duao beach, located 15 km north of Mataquito, experienced a dramatic erosion probably by land subsidence and consequent beach response to incoming wave climate.In this work we discuss on the role of waves, longshore currents, river hydrology and land subsidence in determining the rapid coastal evolution experienced in the Mataquito area. Moreover, this ongoing research will adress whether morphological changes are definitive or not.