Deep-seated gravitational slope deformations as possible suitable locations for prehistoric human settlements: An example from the Italian Western Alps

Abstract

a b s t r a c tThe Plan di Modzon is a mountain area (2300 m) located in the Verrogne Valley, NW of Aosta (Western Alps). It occurs along the contact between the Middle Penninic (micaschist and gneiss from the Gran San Bernardo Nappe) and the overlying upper units of the Piedmont Zone (carbonate calcschist alternating with marble).This area, largely shaped by Pleistocene glaciers, was involved in a wide deep-seated gravitational slope deformation (Pointe Leysser DSGSD) on the western extension of the Becca France doubled ridges. Several ridges that were affected by glacial erosion, discontinuously covered by glacial sediments, are present throughout the area. Extremely fractured rocks and various gravitational forms (minor scarps and trenches) mark the DSGSD.Several archaeological sites (MF1eMF9) have recently been found between 2242 and 2292 m asl. They have revealed artifacts of rock crystal (hyaline quartz) referred to the Sauveterrian stage of the Mesolithic. An ensemble of other archaeological evidence is referred to the Copper Age. The investigation in progress specifically concerns the systematic excavation of sites MF1 and MF3.Some concomitant morphological factors have created very favorable conditions for prehistoric settlements in the Plan di Modzon area, including the exceptionally wide valley floor directly perched on the main Dora Baltea Valley, in consequence of the Verrogne Glacier diversion promoted by the P. Leysser DSGSD. Easy and direct accessibility to this area is provided by the gently-dipping slope of the Dora Baltea Valley affected by the DSGSD. The ridged and grooved morphology as the result of the glacial and gravitational interaction, offered wide surfaces free from geological hazards (debris flow and avalanche processes). The DSGSD is, therefore, one of the primary causes of the archaeological settlement of this area, contributing to create a morphology adapted to prehistoric settlements.

Human settlement pressure drives slow-moving landslide exposure

“…We surmise that patterns of settlement footprints on slow-moving landslides reflect an interaction between human decisions to retain geographical benefits amid landslide-prone areas [13,14], establish settlements in settings limited by steep terrain [22,23,19,3], and avoid flood exposure [21,37,20]. Our model indicates the fraction of landslides inhabited across IPCC regions grows with the urbanization, except in WCA (Fig.…”

“…In steep terrain, many slopes that appear amenable to human settlements may host slow-moving landslides [22,23,24]. These landslides are mass movements of coherent soil and rock moving along discrete shear zones [5,11] and can involve entire continuously deforming hillslopes [24,10].…”

Alpine gullies system evolution: erosion drivers and control factors. Two examples from the western Italian Alps

“…A particular feature is constituted by the presence of travertines locally outcropping and related to water infiltration caused by the DSGSD dynamics (Forno et al, 2016). According to Forno et al (2013Forno et al ( , 2016 and Pini et al (2013), the preservation of Quaternary deposits is favoured in such areas by the irregularities of the slope, mainly elongated ridges, which favour deposition.…”

The Lac Fallère Area as an Example of the Interplay between Deep-Seated Gravitational Slope Deformation and Glacial Shaping (Aosta Valley, NW Italy)

“…An early onset was highlighted for the Pointe Leysser DSGSD in the Mont Fallère area, following the Dora Baltea Glacier withdrawal, which triggered the collapse of the south-facing side of the Dora Baltea Valley in the Saint-Pierre, Saint-Nicolas, and Sarre municipalities [59][60][61].…”