From active to stable: Paraglacial transition of Alpine lateral moraine slopes

Abstract

Many retreating Alpine valley glaciers leave large lateral moraines behind. Reworking of these landforms by geomorphic processes is one of the most important paraglacial processes in many Alpine environments. Although several studies investigated moraine reworking by gullying processes, it is not well known what happens when gullying ceases and why and when lateral moraine slopes become stable. This study improves the understanding of the paraglacial transition from active to stable Alpine lateral moraine slopes by assessing potential influencing factors, indicators for completed paraglacial adjustment, and its spatiotemporal patterns using a combination of geomorphic and ecologic data. A geomorphic and ecologic permanent plot survey and geomorphic mapping were carried out on three lateral moraine complexes in the Turtmann glacier foreland (Switzerland). Subsequently, permanent plot data were analysed using multivariate statistics. Our study suggests that ecosystem engineering by colonizing plant species, slope geomorphometry, and material properties are important factors influencing the paraglacial transition from active to stable slopes. Geomorphic processes are often absent once vertical vegetation layers and soil horizons develop, showing that mature vegetation and advanced soil development are valuable indicators for slope stability and completed paraglacial adjustment. In a conceptual model, we describe the paraglacial transition of Alpine lateral moraine slopes as a temporal sequence in which gullying (Stage I), solifluction (Stage II), and finally stabilization (Stage III) follow one after another. In space, paraglacial adjustment is heterogeneous, and resulting patterns can be explained by the identified influencing factors.

Effects of climate change on high Alpine mountain environments: Evolution of mountaineering routes in the Mont Blanc massif (Western Alps) over half a century

“…A paraglacial period starts as a direct reaction to deglaciation and ends when all glacial sediments have been removed or stabilized (Church and Ryder 1972;Ballantyne 2002). In this study, paraglacial processes refer mainly to the erosion of moraines through rockfall and landslides (McColl 2012;Deline et al 2015;Draebing and Eichel 2018;Eichel, Draebing, and Meyer 2018;Ravanel et al 2018), illustrated by the gullying of the inner flank of lateral moraines due to very steep slopes, up to 80° (Lukas et al 2012).…”

Spatiotemporal soil development in the Pindari proglacial area (Indian Central Himalaya)

“…The slopes of the middle section in proximity to the 1906 moraines fit Stage II, where solifluction dominates (Eichel et al, 2018). The development of soil-cover is mainly disturbed by cryogenic and erosional processes, which result in discontinuous soil cover as indicated by patchy vegetation.…”

“…The instability of the slopes of the lateral moraine ridges is related to their relative heights and inclinations ( Fig. 6), which are about one-third greater than those in the European Alps (Egli, 2006;Eichel et al, 2018). Soils do not develop on steep slopes with highly active, destructive, geomorphic processes.…”

“…Sequences of soil types and properties, with increasing distance from the ice front, represent temporal developments in selected stable landforms (Egli et al, 2001(Egli et al, , 2006. However, recent studies in the European Alps have shown a complex interplay of landform morphodynamics and soil-cover formation in proglacial areas (Burga et al, 2010;Temme and Lange, 2015;Eichel et al, 2018;Temme, 2019).…”

“…These studies analysed soil development from a chronosequence viewpoint, with investigations being made of time and vegetation succession on stable landforms. However, proglacial areas in mountain valleys are dynamic and heterogenous environments where landforms, in conjunction with hillslope processes and fluvial erosion, may enhance or reduce soil development (Burga et al, 2010;Temme and Lange, 2014;Klaar et al, 2015;Eichel et al, 2018). As a result, chronosequence studies cannot demonstrate the important relations between topography and soil development (Carrivick and Heckmann, 2017).…”