04 Sep 2023
 | 04 Sep 2023
Status: this preprint is open for discussion.

Evolution of the Frébouge polygenetic cone during the Holocene (Val Ferret, Mont Blanc Massif)

Catharina Dieleman, Philip Deline, Susan Ivy Ochs, Patricia Hug, Jordan Aaron, Marcus Christl, and Naki Akçar

Abstract. Proglacial settings in the Alps are typically polygenetic, often characterized by a complex and discontinuous interplay between glacial, fluvial, and gravitational processes. These processes yield high volume of sediments, which usually exceeds the transportation capacity. The excessive proglacial sediment load leads to accumulation on slopes, and thus, to subsequent failures such as debris flows. Such failures can occur unexpectedly and harm the villages and infrastructure in the vicinity of proglacial environments. The northern slopes of the Ferret and Veny valleys in the Mont Blanc Massif are home to several polygenetic cones and are a stunning field laboratory for the exploration of the interplay between the glacial, fluvial, and gravitational processes. This study investigates one of the active and well-preserved polygenetic cones in these valleys, namely the Frébouge cone, to disentangle the geomorphic processes that contributed to its formation, and to reconstruct its evolution. To achieve these goals, detailed field, and remote mapping, 10Be surface exposure dating of different geomorphic features, and runout modelling with DAN3D® were applied. The geomorphological map revealed complex interactions of glacial, fluvial, debris flow, and rock and snow avalanche processes. The established chronology indicates two major fluxes of debris flows, the first one at ca. 2 ka, and the second at ca. 1 ka. In addition, a rock mass with a maximum volume of to 12 Mm3 collapsed in the upper reaches of the cone at 1.3 ± 0.1 ka and overran the cone, travelling more than 100 m up onto the opposite valley slope. Afterwards, the Frébouge Glacier overrode the cone several times leaving moraines and till, reaching its maximum extent ca. 300 years ago. This study underscores the untwisting of the complex interaction of surface processes in the Alpine valleys, which are prone to hit the urban areas and infrastructure.

Catharina Dieleman et al.

Status: open (until 05 Nov 2023)

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Catharina Dieleman et al.

Catharina Dieleman et al.


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Short summary
Valleys in the Alps are shaped by glaciers, rivers, mass movements, and slope processes. An understanding of such processes is of great importance in hazard mitigation. We focused on the evolution of the Frébouge cone, which is composed of glacial, debris flow, rock avalanche, and snow avalanche deposits. Debris flows started to form the cone prior to ca. 2 ka ago. In addition, the cone was overrun by a 10 Mm3 large rock avalanche at 1.3 ± 0.1 ka and by the Frébouge glacier at 300 ± 40 a.