Investigating morphodynamics on Little Ice Age lateral moraines in the Italian Alps using archival aerial photogrammetry and airborne LiDAR data

Abstract

The rapid glacier recession in the European Alps exposes large amounts of unconsolidated sediment. Several processes are involved in the reworking of this sediment on steep lateral moraines, e.g. small slides on the upper slopes, sheet erosion by snow gliding, fluvial erosion and debris flows. To gain deeper insight into the dependence of the morphodynamics on lateral moraines on the time since deglaciation, we analysed erosion rates and geomorphological processes occurring at different distances from the present-day glacier termini. Moreover, we assessed the significance of parameters like slope gradient, altitude a.s.l. and the presence of dead ice for the morphodynamics. We used historical (1959) as well as contemporary (2016) aerial images and airborne laserscanning data (2006) to derive orthophotos, 3D point clouds (SfM) and Digital Elevation Models of Difference (DoD). These models cover the entire lateral moraine sections of two glaciers in South Tyrol, Italy, but detailed analysis was restricted to five test areas which deglaciated at different times. We were able to detect areas with decreasing geomorphological activity showing an erosion rate below 1 cm per year mainly on moraine sections remote from the contemporary glacier tongue. Simultaneously, moraine sections with continuous high levels of morphodynamics or even increasing activity were observed. The latter show heavy gullying on the upper slopes with erosion rates of 5.9–10.1 cm per year and no indications of decreasing rework rates could be found. We suppose a strong influence of degrading debris-covered dead ice, which all these slope experienced over many years after glacier melting. However, moisture availability and the slope angles, amongst others, also affect the geomorphological processes forming the moraine slopes. Thus, our results are only partly consistent with the literature, because we found areas with decreasing activity, as assumed in the paraglacial adjustment model, as well as moraine sections where no stabilization can be observed to date.