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

Abstract

Denudation processes affecting mountain slopes may vary according to different factors (e.g., lithology and structural setting of bedrock, climate, relief features), which may be very diverse at the local scale. Gully complex systems, characterised by morphological features similar to those developing in other climate contexts (i.e., pseudo-badlands) are also becoming common at higher altitudes and latitudes. The *Revised manuscript with no changes marked Click here to view linked References selected study cases of Gran Gorgia (Susa Valley) and Saint Nicolas (Aosta Valley), in the Western Italian Alps, are sites of geomorphological interest as they are specifically relevant for their scientific features. The aims of this work are (i) reconstructing the morphometric evolution of gullies edges and vegetation colonisation in specific years by means of multitemporal spatial analysis on variation of surface areas affected by erosion; (ii) performing dendrogeomorphological analysis to spatially reconstruct, with a more continuous record through time, the effects of denudation processes affecting trees colonising the different regions of the gullies and the erosion rates by using dendrogeomorphological indicators (i.e., compression wood, traumatic resin ducts) and exposed roots and (iii) performing geopedological investigations aimed at deriving data on aggradation/degradation episodes along the slopes surrounding such hot-spots of erosion through time. Multidisciplinary analyses regarding the study sites allowed for detailing of erosional history of the studied slopes detecting the prevailing drivers of their evolution. According to the results and considering the common climate and bedrock conditions, the structural background seems to have more influence on slope evolution at the Saint Nicolas site, while superficial geomorphic processes seem to be more relevant at the Gran Gorgia site. Because the sites have already been recognised as part of geoheritage by local authorities, the data obtained in the present research on their genesis, evolution, and local drivers affecting the rates of denudation (i.e., scientific relevance of the site) suggests that description of the sites for dissemination purposes should include links to the entire slope history.

Role of land set-up systems on soil (physicochemical) conditions

“…In a scenario affected by changes of climate and soil use and management, soils of mountain areas require specific attention as they are the most vulnerable to changes. In fact, mountain slope denudation processes are variable in intensity depending mainly on soil features, bedrock structural setting, climate, and relief (Bollati et al, 2019). Further, mountain soils management shows several limitations due to difficult climatic and topographic conditions, and the main obstacles to sustainable agriculture are conservation of soil chemical and physical fertility, and the occurrence of steep slopes and problematic land accessibility, which indirectly affect land conservation especially when marginal areas become prone to slope failures and erosion enhances after abandonment (Curtaz et al, 2015).…”

Controlling Factors of Badland Morphological Changes in the Emilia Apennines (Northern Italy)

“…Therefore, images dated to 1954 and 1981, with non-comparable scales, were excluded from the mapping. Considering this source data, with a resolution of 0.5 m, the expected error is of ±2% [11,103]. Subsequently, the area (A) of each drainage basin and its bare surface was calculated and uploaded into a geodatabase, and the percentages of surface variations throughout the investigated periods were calculated with respect to the initial surface area size in order to compare their evolution and perform the succeeding morphometric analysis.…”

“…The morphogenesis and evolution of badlands are complex and still under debate. Among the controlling factors suggested in the literature, those indicated as fundamental are as follows: (i) The lithology [3,4] and physical, chemical and mineralogical properties (e.g., sediment size, clay mineralogy, Atterberg's limits, porosity and pore water chemistry) [5,6]; (ii) climatic factors such as strong seasonal humid/arid contrasts favoured by south-facing slopes [6][7][8][9][10][11]; (iii) the landscape morphology/topography, particularly the slope gradient, orientation and exposure [12]; (iv) anthropic activities such as deforestation for land reclamation, land levelling, cropland abandonment, extensive agriculture and pasture [13,14]. Moreover, badland areas are often characterised by scarce or absent vegetation cover [15][16][17][18][19], related to unfavourable climate conditions, and by the occurrence of mass wasting processes such as slides, earthflows, mudflows and creeping [8,14,20,21].…”

“…In Italy, badlands are spread widely and discontinuously in areas of the Apennines mountain chain and Sicily, where Plio-Pleistocene marine clayey and marly terrains outcrop [81]. In the Italian literature, the investigation of badland landforms and landscapes-their identification, characterisation, and temporal and spatial variation-dates back to the beginning of the last century and is mainly concentrated on central and southern parts of Italy [2,6,[11][12][13][14]17,23,28,49,55,67,.…”

Reconsidering the compound effect of geomorphology, vegetation, and climate change on paleopedogenesis in sensitive environments (Northern Apennines, Italy)

“…Soil evolution in active landscapes, such as mountain environments, is mainly influenced and controlled by topography (Zanini et al, 2015). Slope dynamics and instability influence soil formation, development, and preservation: conditions of slope instability can dramatically impact on soil formation and conservation in both short and long terms (Bollati et al, 2019;Coltorti et al, 2019). Areas characterized by steep slopes are affected by frequent and, often, rapid mass movements related to gravity and water-driven processes, which are able to substantially disrupt the relief and modify the old surfaces and dismantling previous soils and paleosols (Dewolf and Bourrié, 2008).…”