Erosion rates and erosion patterns of Neogene to Quaternary stratovolcanoes in the Western Cordillera of the Central Andes: An SRTM DEM based analysis

Abstract

Erosion patterns and rates of 33 stratovolcanoes in the arid to hyperarid Central Andean Volcanic Zone (14 S to 27 S) have been constrained by morphometric modelling. All selected volcanoes belong to the short-lived, symmetrical, circular andesitic stratocone type, with ages spanning 14 Ma to recent. Starting from the initial, youthful volcano morphology of this type, represented in our study by Parinacota volcano, and comparing reconstructed volumes of progressively eroded volcanoes, such a time span allows us to infer long-term erosion rates. Typical erosion rates of <10 to 20 m/Ma have been obtained for the Altiplano-Puna Plateau. Lowest erosion rates typify the hyperarid Puna plateau (7-9 m/Ma), while somewhat higher values (13-22 m/Ma) are recorded for volcanoes in the more humid South Peru, suggesting climatic control on differences in erosion rates. By contrast, much higher short-term erosion rates of 112 to 66 m/Ma, decreasing with age, are found for young (Late Quaternary) volcanoes, which indicates that juvenile volcanoes erode more rapidly due to their unconsolidated cover and steeper slopes; surface denudation slows down to approximately one tenth of this after a few Ma An inverse correlation is observed between the degree of denudation (defined as volume removed by erosion/original volume) and edifice height from base to top after erosion. This relationship is independent of climate and original edifice elevation. The degree of denudation vs. volcano age provides a rough morphometric tool to constrain the time elapsed since the extinction of volcanic activity. This method can, however, only be applied to the volcanoes of the Altiplano (i.e. under uniform, long-term arid climate) with an uncertainty of similar to 1 Ma Finally, an erosional pathway is suggested for volcanoes of the Altiplano-Puna preserving a peculiar "edelweiss" valley pattern related to glaciations. This pattern may have overprinted previous drainages and resulted in a discontinuous height reduction of the degrading stratovolcanoes. (C) 2011 Elsevier B.V. All rights reserved.