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Abstract

Many volcano summits host craters that are partially overlapping. The formation of such nested craters has been commonly interpreted as vent migration. Here, we present an additional mechanism that may explain the geometry of nested craters at volcanoes. Láscar Volcano, the most active volcano of the Central Volcanic Zone in the Chilean Andes, hosts ENE-WSW trending summit craters that are partially overlapping (nested). Details on the evolution and interaction between the different craters remain unclear. To create a robust dataset, Terrestrial Laser Scanner (TLS) data were collected at the summit of Láscar in 2013. The resulting topographic data set, consisting of more than 15 million data points with centimetre sampling, allows visualising almost the complete eastern edifice of the volcano's summit. From the TLS data, a Digital Elevation Model (DEM) and a slope map were generated allowing us to create a lineament map and quantify the observed morphological and structural features. To further improve our understanding of the processes responsible for the formation of the craters and geomorphology, we designed sandbox analogue models. Results suggest that one of the craters is a ‘parasite’ crater, formed as a consequence of ongoing activity in the adjacent crater. Our data suggest that the nested craters have all been modified since the last major eruption in 1993, by near surface effects associated with cooling, compaction and gravitational sliding of the crater floor infill. As the active crater deepens, the adjacent inactive crater extends and partially slumps towards the active one. Understanding the structural development of these nested craters is relevant for assessing potential future eruption sites, thus making Láscar a dynamic target for a detailed morphology study. These findings may similarly be applied to other volcanoes, where nested craters have developed.