Citation: Dolce, S.; Forno, M.G.; Gattiglio, M.; Gianotti, F. The Lac Fallère Area as an Example of the Interplay between Deep-Seated Gravitational Slope Deformation and Glacial Shaping (Aosta Valley, NW Italy). GeoHazards 2024, 5, 38–63. https://doi.org/10.3390/ geohazards5010003 Academic Editors: Davide Tiranti and Tiago Miguel Ferreira Received: 27 October 2023 Revised: 29 December 2023 Accepted: 31 December 2023 Published: 11 January 2024 Copyright: © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). GeoHazards Article The Lac Fallère Area as an Example of the Interplay between Deep-Seated Gravitational Slope Deformation and Glacial Shaping (Aosta Valley, NW Italy) Stefano Dolce , Maria Gabriella Forno * , Marco Gattiglio and Franco Gianotti Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy; stefano.dolce996@edu.unito.it (S.D.); marco.gattiglio@unito.it (M.G.); franco.gianotti@unito.it (F.G.) * Correspondence: gabriella.forno@unito.it Abstract: The Lac Fallère area in the upper Clusellaz Valley (tributary of the middle Aosta Valley) is shaped in micaschist and gneiss (Mont Fort Unit, Middle Penninic) and in calcschist and marble (Aouilletta Unit, Combin Zone). Lac Fallère exhibits an elongated shape and is hosted in a WSW– ENE-trending depression, according to the slope direction. This lake also shows a semi-submerged WSW–ENE rocky ridge that longitudinally divides the lake. This evidence, in addition to the extremely fractured rocks, indicates a wide, deep-seated gravitational slope deformation (DSGSD), even if this area is not yet included within the regional landslide inventory of the Aosta Valley Region. The Lac Fallère area also shows reliefs involved in glacial erosion (roches moutonnée), an extensive cover of subglacial sediments, and many moraines essentially referred to as Lateglacial. The DSGSD evolution in a glacial environment produced, as observed in other areas, effects on the facies of Quaternary sediments and the formation of a lot of wide moraines. Glacial slope sectors and lateral moraines displaced by minor scarps and counterscarps, and glaciers using trenches forming several arched moraines, suggest an interplay between glacial and gravitational processes, which share part of their evolution history. Keywords: Aosta Valley; glacial landforms; DSGSD; LGM; Lateglacial 1. Introduction The various and complex relationship between glacial and deep-seated gravitational processes in a high-mountain environment is the subject of this study. This issue represents a poorly investigated topic due to a greater interest in the genetic mechanisms and kinematics of the deep-seated gravitational slope deformations (DSGSDs) [1–9], chronology [10–14], and current activity [15–18]; however it offers an interesting and innovative tool in the field of landscape genetics [19–22]. DSGSDs act over very long timescales [23–26] comparable, for example, to the extension of the Lateglacial period [18,27], which favours a possible interaction between glacial and gravitational processes. Unlike most landslides, DSGSDs are characterised by slow movements of the rock mass [28–34]. Moreover, slopes affected by DSGSDs retain the original cover of glacial and gravitative deposits, even if these are partly buried by debris or extensively deformed, resedimented, and reshaped. The retreat of glaciers causes a debuttressing phenomenon that changes the stress state of the rock mass through progressive release of stress accumu- lated when the area was covered by ice mass [35]. The consequent propagation of joints in the rocky mass predisposes the slope to rapid gravitational readjustment or slow release of accumulated residual stresses [36–40]. In the context of a DSGSD, it is not uncommon for a glacial landform to be fragmented into slabs by one or more minor scarps (e.g., in the Pointe Leysser DSGSD) [41], while the preservation of a gravitationally displaced moraine is unusual (e.g., Rodoretto DSGSD GeoHazards 2024, 5, 38–63. https://doi.org/10.3390/geohazards5010003 https://www.mdpi.com/journal/geohazards