No abstract

The regressive barrier (strandplain) of Tongoy is a complex system of coastal landforms, composed of foredunes, beach ridges and semipermanent streams that together have shaped the actual lagoons. This research aims to contribute to the knowledge of these features in the tectonic active western continental margin of South America and analyzes their evolution in the development of the regressive barrier of Tongoy Bay. A geomorphological survey was conducted, between the Pleistocene marine terraces and the modern shoreline; aerial photographs from different years were used, observing changes over the barrier surface, estuaries and lagoons. From the identified forms it is concluded that the barrier corresponds to an accretion system, which together with the development of beach ridges has evolved into a regressive barrier system. It is still possible to find abandoned lagoons behind the present lagoons. Currently, accretion conditions are demonstrated by the preservation of foredunes and embryonic dunes.

RESUMENEl terremoto y tsunami de 2010 generó cambios en la morfología y dinámica sedimentaria del litoral de Pichilemu, Chile central, evidenciado a través del retroceso y erosión de las playas arenosas y dunas. Se identifi caron los patrones de modifi cación a través del análisis de imágenes satelitales anteriores y posteriores al terremoto/tsunami mencionado, comparando con registros geomorfológicos del año 2004. Se realizó trabajo de terreno para la observación de formas esenciales y medición de perfi les de playa representativos de la dinámica de las ensenadas estructurales (headland bay beach); se analizó la variabilidad del tipo de playa dominada por olas. Los resultados indican que existe erosión litoral y un cambio en el balance sedimentario asociado a la subsidencia de la costa, como también, que transcurridos cuatro años del evento extremo, luego de la fase erosiva, se observa un cambio tendiente hacia la progradación del litoral arenoso siguiendo el patrón dinámico típico de sistemas de ensenadas estructurales.Palabras Clave: Ensenada; tsunami; microdunas; cambios en la playa ABSTRACTThe earthquake and tsunami of 2010, triggered changes in the geomorphological and sedimentary dynamics along the coast of Pichilemu, in central Chile. These changes were evidenced through the retreat and erosion of sandy beaches and coastal sand dunes. Modifi cation patterns were identifi ed through analysis of satellite images prior to and after the earthquake/tsunami, and compared with records from geomorphological fi eldwork carried out in 2004 that measured essential features of representative beach profi les in the headland bay beaches. The variability of beaches dominated by waves was analyzed. The results indicate that there is coastal erosion and a change in the sedimentary balance associated with the subsidence of the coast, and that four years after the earthquake/tsunami, after the erosive phase, a change in tendency towards progradation of sandy coastlines in the headland bay beaches can be observed

A geomorphological analysis of the Comau Fjord was carried out to identify geohazards that are a product of current landform dynamics and processes. The geological setting of the area includes fractured metamorphic and volcanic rocks forming steep hillslopes in an active tectonic context due to the Liquiñe-Ofqui Fault Zone (LOFZ). Geomorphological and hazard mapping was performed using aerial photographs, GIS geoprocessing and fieldwork in January and May 2016 and February 2017. The susceptibility of landsliding was statistically assessed and validated with the inventory of landslides completed during fieldwork. The triggering of geohazards such as landslides and fluvial floods in the study area is associated with high annual precipitation (>5000 mm annually) with a concentration of rainfall that has increased in the last 50 years. Geohazard mapping demonstrated the potential for rock and earth falls, debris flows and river floods, as well as the potential impact of these geohazards on the area's intensive aquaculture industry and a main national highway projected for the eastern flank of the fjord. In a geographical scenario of environmental and territorial change, the present and future human occupation of Comau Fjord's coast constitutes potential hazard and risk conditions for aquaculture infrastructure and highway users.

The Chilean coast is controlled by the tectonics and structure, generating an irregular coastal landscape, with bays, marine terraces, sandy and gravel beaches, sand dune fields and Andean slopes, forming some mega cliffs that are attacked by waves. The Chilean coastline is shaped by headland bay beaches, with a dynamic coast modeled by south-western winds and south–north longshore current. We analyzed the case of the Coquimbo mega headland bay beach, which consists of four headland bay beaches. A methodological study was carried out on the morphometric parameters of the shoreline and the types of beaches dominated by waves along with geomorphological analysis of the coastal zone. We observed a mass transfer process from south to north. The northern sections of the bays are the places with the densest sand dune fields. This concentration of dunes occurs in each bay individually and in the mega bay as well. The sedimentary supply comes from Andean catchments to the shoreline and is transported and reworked by the longshore current to the northern area, where a huge sand field dune has developed, 120 km away from the mouth of Limarí River, the most southern catchment in the study area. In the mega bay, the current trend is a continuous sedimentary supply, despite the semi-arid conditions and the extreme drought that has affected the area since 2011. The study area is also a popular destination in Chile for beach tourism and is a place of interest for the mining industry.