Glaciations in response to climate variations preconditioned by evolving topography

Previously glaciated landscapes tend to have large areas concentrated at the same elevation; here it is shown that small climate changes can trigger massive glacial expansions for these landscapes, explaining long-term patterns of erosion in the Quaternary period. Glaciation prompts dramatic response to climate change Large parts of the Earth's surface were glaciated during the Quaternary cold periods of the past 2.5 million years, and these events have left their mark on the mountain topography we see today. Post-glacial landscapes tend to feature large areas concentrated at the same elevation, but the effect of this on subsequent glaciations was unknown. Vivi Pedersen and David Egholm use numerical simulation of glaciation and case studies of alpine topography of the Sierra Nevada, Spain, where there was little glacial activity in the Quaternary, and the Bitterroot Range in Idaho, which was significantly modified by glaciers during the Quaternary. The results show that prior glaciations transform a system from one in which climate exerts a near-linear influence on glacial extent to one in which a small change in climate can result in massive glacial expansion. This helps to explain the long-term patterns of erosion in the Quaternary period. Landscapes modified by glacial erosion show a distinct distribution of surface area with elevation 1 , 2 , 3 (hypsometry). In particular, the height of these regions is influenced by climatic gradients controlling the altitude where glacial and periglacial processes are the most active, and as a result, surface area is focused just below the snowline altitude 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 . Yet the effect of this distinct glacial hypsometric signature on glacial extent and therefore on continued glacial erosion has not previously been examined. Here we show how this topographic configuration influences the climatic sensitivity of Alpine glaciers, and how the development of a glacial hypsometric distribution influences the intensity of glaciations on timescales of more than a few glacial cycles. We find that the relationship between variations in climate and the resulting variation in areal extent of glaciation changes drastically with the degree of glacial modification in the landscape. First, in landscapes with novel glaciations, a nearly linear relationship between climate and glacial area exists. Second, in previously glaciated landscapes with extensive area at a similar elevation, highly nonlinear and rapid gl