Long-term morphodynamics and paraglacial adjustment on LIA lateral moraines in the Eastern Alps

Kurzfassung/Abstract

With progressing glacier melting since the end of the Little Ice Age (LIA), lateral moraines have been exposed, often showing high slope angles and unconsolidated material. Subsequently, lateral moraines are reworked by geomorphological processes such as debris flows, slides or fluvial erosion which lead to a shift of sediment downslope and with that to a paraglacial adjustment of the slopes over time.
Previous studies investigating paraglacial adjustment were mostly conducted at a single point in time and the time since deglaciation was substituted by selecting moraine sections at different distances from the recent glacier terminus. These studies mostly detected a decline of erosion rates over decades after deglaciation. One of the aims in this work was to investigate which trends of morphodynamics we can detect when observing lateral moraines over decades. For that purpose, the morphodynamics on lateral moraines in 10 glacier forefields in the Eastern Alps were analysed by using several datasets of archival aerial images reaching back to the 1950s. These images were the base for the calculation of DEMs and DEMs of difference (DoD). Beside the development of the morphodynamics, we studied possible influence factors on the morphodynamics, such as the melting of dead ice, the slope angle, time since deglaciation and the altitude a.s.l.
Our analyses show declining erosion rates over time for most of the moraine slopes. However, especially on gullied slopes the dynamics stay high and on some slopes we also detected stagnating or increasing erosion rates. Concerning the influence factors, the results indicate that the initial slope angle at the time of deglaciation has a significant influence on the later morphodynamics, whereas the time since deglaciation does not show such a strong influence. These observations raise concerns whether analyses based on the comparison of lateral moraine sections with different distances to the glacier terminus can provide sound evidence concerning their process of stabilization.