Divergence, convergence, and path dependency of paraglacial adjustment of alpine lateral moraine slopes

Titelangaben

Draebing, Daniel ; Eichel, Jana:
Divergence, convergence, and path dependency of paraglacial adjustment of alpine lateral moraine slopes.
In: Land Degradation & Development. Bd. 29 (2018) Heft 6 . - S. 1979-1990.
ISSN 1099-145X
DOI: https://doi.org/10.1002/ldr.2983

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Abstract

Abstract Lateral moraines represent important sediment storages and are one of the most dynamic areas within glacier forelands. Following glacier retreat, lateral moraine slopes adjust as their material is reworked by paraglacial processes. Previous research focused primarily on the role of gullying, however, path-dependent slope adjustment and divergent adjustment of lateral moraine slopes are poorly understood. We report data from geomorphic and vegetation mapping, electrical resistivity tomography, soil moisture measurements, and soil texture analysis acquired in the Turtmann glacier foreland in the Swiss Alps where periglacial processes are abundant. We demonstrate that paraglacial slope adjustment shows divergent, convergent, and path-dependent behaviour. Steep proximal moraine slopes are first eroded by gullying processes. When moraine slopes reach a threshold angle of 30°, the importance of solifluction increases, and solifluction processes subsequently rework debris flow deposits. In contrast, more gently inclined distal slopes are below the threshold angle immediately following glacier retreat and biogeomorphic feedbacks result in an earlier onset of solifluction processes. We identified two different types of turf-banked solifluction lobes based on their temporal development and genesis. Lobe Type 1 develops on distal moraine slopes and reworks glacial till, whereas Lobe Type 2 evolves from debris flow deposits at the footslopes of the lateral moraines. Both lobe types can only be differentiated using actual shape. Overprinting by subsequent geomorphic processes can result in equifinal and convergent forms such as solifluction sheets from the Last Glaciation. Our study provides an actualistic example of how paraglacial solifluction in 90 to 150 years rapidly reworks glacial sediments.