Geological Significance of the Perrot Spring in Mont Avic Natural Park (NW Alps)

Abstract

Alpine areas shaped in a normally fissured bedrock do not typically contain important groundwater aquifers. In contrast, a wide Quaternary cover in mountainous areas, especially of landslide deposits, can make large aquifers promising for water withdrawals. A geological study of the central sector of the Chalamy Valley, a right tributary of the main Dora Baltea River (Aosta Valley) in which the Perrot Spring is located, was carried out, with the aim of providing a preliminary assessment of hydrogeological significance. The main interest of this investigation is, in addition to the high discharge of the Perrot Spring, its location within Mont Avic Natural Park, which is a very busy area with walkers, cyclists, visitors, and scholars. The geological survey shows a thick body of sandy silty glaciolacustrine sediments, consequent to the barrage of the Chalamy Valley from the glacier hosted in the main Aosta Valley. These sediments, outcropping in the north-facing slope of the Chalamy Valley, are involved in significant gullies and covered by a thick landslide accumulation located in the northern slope of the Bec de Nona, formed by very heterometric sediments. A wide detachment scarp is shaped in serpentinite characterized by evident fracture systems. The preliminary hydrogeological significance for the Perrot Spring, located at the boundary between glaciolacustrine and landslide sediments, was proposed. In detail, the thick landslide cover, characterized by high permeability, represents an important aquifer with a relatively fast groundwater flow to the spring. The underlying glaciolacustrine sediments of the low band of the slope, typically with very low permeability, favor the concentration of groundwater near the boundary with landslide sediments and the spring supply.

Analysis of the Recharge Area of the Perrot Spring (Aosta Valley) Using a Hydrochemical and Isotopic Approach

“…The most abundant fine Quaternary unconsolidated, very thick (up to 240 m) sediments diffusely cover the metamorphic bedrock on the wide valley floor, where they crop out in large badlands. They consist of overlapped subglacial, ice-marginal, glaciolacustrine and landslide deposits [52] (Figure 2). The subglacial over consolidated sediments (30 m thick) consist of abundant sandy-silty matrix, containing subordinate clasts, that were deposited at the base of the Chalamy Glacier.…”