Assessing the impact of Quaternary glaciations on the topography of Sierra de Gredos (central Spain)
Keywords: relief, glacial erosion, basins, cross-sections, relief production, Sierra de Gredos, Spain
AbstractIt is well known that glacial erosion modifies the topography by increasing the local relief, producing cirques and U-shaped valleys. During the Last Glacial Maximum (LGM) the glaciers that flowed down from the top of Sierra de Gredos, central Spain, modified the preexisting landscape forming cirques and causing the apparent deepening of valleys. Both, glacial advances and related landforms are well documented for Sierra de Gredos; however, quantitative estimates of how glacial erosion has modified the topography of the range have not been provided yet. We compare the means of relief, normalized steepness index (ksn), and elevation of basins as well as the width, form ratio (FR) and relief of ridge-toridge cross-sections of valleys to evaluate the impact of glacial erosion on the topography of the sierra. The idea that the relief production is high in fully glaciated basins contrasts with our results, which indicate that local relief is greater in the southern flank where glacial erosion was moderate and confined to cirques and where the rates of rock uplift are particularly high. Also, the maxima of local relief occur below the LGM equilibrium line of altitude (ELA). We postulate that in Sierra de Gredos, glacial erosion lowered the ridgelines and the bottom of valleys inhibiting the relief production. The high local relief on the southern flank is explained by the incision of bedrock rivers responding to high tectonic uplift rates. The glacial advances during the LGM may have increased the stream discharge, promoting the sediment evacuation and enhancing the bedrock incision.