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Rias are elongated inlets, arms of the sea, that penetrate in the continental zone. These forms are understood as sea flooded river valleys since the German researcher von Richthofen introduced the term into the scientific literature in 1886. Many authors have dealt with this rocky coast macroform, and most of them highlight their fluvial origin. Nevertheless, a detailed study of the different Galician rías shows the lack of fluvial deposits or forms inside them. This fact force to reconsider the contribution of fluvial and marine factors in shaping the coast, as well as the age of these forms. With regard to this last topic, many studies show the relevance of the falling sea level in rias formation during the last glacial period, but these approaches does not take into account that inside of rías there are Eemian interglacial dated forms and deposits. A careful revision on the rías'literature and the shaping processes and agents (i.e., lithology, joint degree, or the existing of forms and deposits) lead to the conclusion that rias are polygenic forms where the tectonic structure define its morphological pattern. The fluvial dynamics, initiated in the Cenozoic, triggered the valleys incision; and the marine processes were the main agent to shaping the actual character and form of this rock coast macroforms; therefore the fluvial contribution should be understood as a secondary process. [ABSTRACT FROM AUTHOR]

This work exposes some features of the landscape that enable us to determine neotectonic activity in the internal sector of the cordillera (35°30'S - 70°15'W). Through field observations, there were recognized lacustrine deposits characterized by laminated sands, silts, and clays, which records the sedimentation in a paleolake during a stage of the Last Glacial Maximum. The age of the deposits is inferred from their position in relation to a frontal moraine attributed to the last glaciation. Based on a sedimentary profile in the lacustrine deposits, there are described soft-sediment deformation structures and tectonic faults, one of them named El Seguro fault, presents 4 m of displacement measured along the fault plane, and an inverse movement. Morphological features indicate a seismic trigger, proposing the activity of the fault as a possible source. The frequency and distribution of >0.1 km2 mass movement deposits and their location close to the active structures allow us to identify an accumulation of landslides around them. Although many factors have favored these movements as lithology, steep slopes and pos-glacial relief, their position in the landscape suggest that seismic activity accelerated the development of large mass movements. Finally, it is proposed that tectonic activity has taken place during the Pleistocene-Holocene inclusive, with earthquakes of magnitude Ms =6, so that El Seguro fault could be an active fault at present. [ABSTRACT FROM AUTHOR]