VENY VALLEY (ITALY) FIELD TRIP - A GEOLOGICAL AND GEOMORPHOLOGICAL OBSERVATION OF THE VALLEY

Every year, Italian Young Geomorphologists (AIGeo) organizes a conference and field trip, dedicated to the young Geomorphologists. In this VIII Italian young geomorphologists’ day geomorphologists came from Italy, Europe, and also from out of Europe.

Veny Valley Field trip (from my diary): 

On 28 June a Field trip for Veny valley (Mont Blanc Massif) has been organized. We arrived there one day in advance that was on the evening of 27th June. We saw plain to mountain geomorphology through this journey that was from Milan to Courmayeur. A single resort (Refugio Monte Binaco) was there on the elevation of 1,976 meters from there we were able to see the glacier view of Mount Blanc Massif and different peaks. On the next day, our field trip. 

Plate - 1: We arrived at Refugio Monte Binaco resort in the lap of Veny Valley, Italy (Photo credit: Mahato, R.K., 2019)

The field trip area is located on the Italian side of the Mont Blanc Massif (NW-Alps), close to the French and Swiss borders (See plate 1). The highest elevation of the massif is 4,808 m a.s.l., and many of its fractured granite faces, peaks and crests stand well above 3,000 m. 

Fig. 1: Mt. Blanc Massif and their different geological horizons  

The itinerary (Fig. 1) offers spectacular panoramic views over the Mont Blanc Massif and numerous insights into the Miage, Brenva and other minor glaciers of Val Veny.

started after taking breakfast at 8.30 am. During the entire field trip, we never feel tired because of the variety of different fluvioglacial geomorphological landscapes. Prof. M/s. Irene and her team always took care during difficult pathways especially on glacier pathways. The route starts at the "Rifugio Monte Bianco" hut, an ideal place to introduce the geoglacial and geomorphological setting of the area, and we observed the terminal moraines of both the Brenva and Miage glaciers. The ascent to the "Sentiero Balcone" trail of the Val Veny allows to admire the major peaks of the Italian side of the Mont Blanc, the glacial cirques and minor glaciers  that characterize the massif, and the numerous traces of slope instability. At the top of the trail, we enjoyed a splendid view of the Miage Glacier: from the three frontal lobes within the Val Veny, to the main debris covered tongue through the deep Miage valley, up to the confluence of the glaciers with the upper basins. 

Plate - 2:Veny Valley field trip's members; organized by VIII Italian Young Geomorphologists' Days (Photo credit: Mahato, R.K., 2019)

After a few hours of walking, we arrived on the highest point of the pathway that was almost 2,365 meters. We took some rest and finished our lunch here. Prof. Marco and Francesco grasp us about the geomorphology of terminal moraines of Brenva and Miage glaciers. Then we went down descend the trail towards the Plan Combal, where the moraines of the Miage amphitheater block the Val Veny, here we saw the glacial margin and different moraine deposits and lakes. From the Plan Combal, we moved along the valley bottom, between the lateral moraine of the southern lobe of the Miage Glacier and the Dora di Veny River. Through this walk, we saw the avalanche deposits, landslides, and debris flow, down to the fluvioglacial plain of the Visaille. After this, we directly moved to Bus for going to Milan city. 

Geological and Geomorphological framework of the Veny Valley: From a geological point of view, the Mont Blanc Massif is a granite batholite of the Hercynian age, strongly deformed by the Alpine orogeny (Plate 1).

In the Val Veny area, a series of tectonic contacts testify to the convergence and collision movements between the European and African (Adriatic) plates. These deformations brought units of different paleogeographic origin into contact: Helvetic (Monte Bianco), Ultrahelvetic (Mont Chetif), External Pennidic (Sion-Courmayeur Zone).

The field trip itinerary runs along the Pennidic Front, an important tectonic discontinuty along which the Pennidic Units overthrust the underlying Ultrahelvetic Units. In the Val Veny area (Fig. 2), Helvetic and Ultrahelvetic units are mostly represented by granites and clay - carbonatic schists, while the Penninic Domain includes quartzite, dolomite, limestone breccias and schist (e.g., De Giusti et al., 2003). The structural setting of the area is characterized by NW - dipping units separated by large subvertical Variscan N200-striking faults, and Alpine N450-striking faults with mylonitic zones.

Fig. 2: Geological map of the fieldtrip area in Veny Vally (from De Giusti et al., 2003). The colored and numbered areas represent the geological units of the Veny Valley; the black lines represent the main tectonic contacts (surfacing: continuous line; buried: dotted line).

Legend: 

0 Geomorphology and Quaternary (light colours, ubiquitous): g) glaciers; dg) glacier deposits; fl) alluvial and fluvioglacial deposits; dt) gravitational deposits.

0 Helvetic units (red and green colors, numbers 1-4, northwestern sector of the map): 1) Non-differentiated sedimentary cover (Aalenian-Albian); 2) Carbonaceous - arenaceous schists (Upper Carboniferous); 3) Mont Blanc Granite; 4) Pre-granite basement: paragneiss with amphibolite intercalations.

0 Ultrahelvetic units (Units of M. Chetif; red and green colors, numbers 5-8, central belt): 5) Sedimentary covers (Liassic limestones); 6) Porphyroids and metagranites; 7) Calcschists, argillaceous schists and limestone (Upper Dogger-Malm); 8) Carniole, limestones and dolomites (middle - upper Trias).

0 External Pennidic Units (Zone Sion - Courmayeur; blue and green colors, numbers 9 -12, southeastern sector of the map): 9) Flysch with conglomerate intercalations (Cretaceous); 10) Pre-cretaceous substrate: neritic Lias; Triassic evaporites, carniole, dolomites and limestones; 11) quartzites and conglomerates (Permian - Sciticic); 12) Black schist and micaceous sandstone (Upper Carboniferous). 

The past and present geological history of the Mont Blanc massif controls the relief energy and the geomorphological structure of Val Veny. Due to the continuing collision of the Eurasian and Adriatic tectonic plates, the massif is uplifting at few mm/year (Lemonite et al., 2000). As a result, the Mont Blanc is the highest massif in the Alps: Many of its peaks exceed 4,000 meters in elevation.

The summits of the massif host the accumulation basins of the main glaciers of the western Alps. The greater extension of glaciers on the northern (French) side of the massif (Fig. 3) clearly shows the disadvantageous conditions for glacialism on the southern (Italian) side, in terms of slope exposure, elevation distribution and local climate characteristics (mainly related to the types and amount of precipitation).

Fig. 3: Map of glacier distribution in the Mont Blanc Massif. Note the uneven extent and altimetric distribution of the glaciers on the two sides of the France - Italy border (Data source: Glariskalp project, Alcotra Program 2007-2013, www.glariskalp.eu).

The Val Veny develops on the Italian side of the Mont Blanc Massif, starting from the Col de la Seigne (2,516 m a.s.l.). It is the westernmost tributary valley of the Aosta Valley, and extends as far as the Valdigne to Courmayeur, where the Dora di Veny joins the Dora di Ferret. The confluence takes place near Entreves (literally "between the waters"), where the Dora Baltea originates. 

FIELDTRIP ITINERARY NOTES:

The Start: Rifugio Monte Bianco: 

The ininerary starts at the Rifugio Monte Bianco - CAI Uget. From this point it is possible to observe both the fronts of Brenva and Miage glaciers, the striking walls of the Mont Blanc Massif, and the gentler morphology of the opposite side of the valley, where most of the excursion have been taken place. 

Fig. 4: Our Field trip tracking route in Veny Valley 

The asymmetry, the different morphologies and elevations of the two sides of the Veny Valley depend mostly on the geological and structural characteristics of the the area (Fig. 2). The steep walls, the sharp peaks and the glacial cirques (like the relict Fauteuil des Alleemands-Combalet glacial cirque) that characterize the high (over 4,000 m a.s.l.) northern slope of the Veny Valley are carved in the granites and gneiss composing the bedrock of the Mont Blanc. Rare outcrops of the Ultrahelvetic schists are present at the base of the slopes. Here, the bedrock walls leave to landforms and deposits of different nature (landslide, talus cones, fluvial and avalanche deposits).

Plate - 3: The asymmetry, the different morphologies and slopes with glacier remains during pathway walking (Photo credit: Mahato, R.K., 2019)

The southern side of the Veny Valley is less high (the peaks do not exceed 3000 m) and is characterized by a gentler morphology and less steep slopes. Here, schists and other metasedimentary rocks outcrops; these are more subject to erosion than those on the opposite side of the valley. Free - flowing and channelled waters, snow avalanches, debris flows are the current morphogenetic agents that dominate these slopes and produce erosion, canyons, talus cones. Teh valley bottom of Veny Valley is largely occupies by alluvial and fluvioglacial deposits, and by landforms and deposits of present and Pleistocene glacial origin.

From the Monte Bianco, Se went up the slope along the ski slope and then we followed the trial no. 6, until we reach Col Checruit. 

Fig. no. 5: An view from NE of Veny Valley, with its Typical U-shaped transverse profile and the glaciers at the base of the south-western sector of Mont Blanc (orthophoto from 2006 overlaying digital elevation model, with location numbering described below; Luigi Perotti).

Stop at Col Checrouit - Rifugio Maison Vieille:

Once climbed up the southern slope of Veny Valley, we reached the Col Checrouit, a saddle placed on the watershed with Valdigne. In this morphological depression are located the chalets of the Aretu and the Maison Vieille refuge (1,956 m a.s.l.), a welcoming resting place along the Tour du Mont Blanc, exactly the junction between the path n.6 and n.2 - corresponding to the "Balcone della Val Veny" path.

Plate - : Ice sheet deposited over the slope of the Aretu (Photo credit: Mahato, R.K., 2019)

Here, we recognized two important factors that have conditioned the geomorphology of the areas:

1. The morpho-structural impact of the Pennidic Front: the contact between the Pennidic Units and the underlaying Units develops at the Col Checrouit towards E-W;

2. The Pleistocene glacialism: This in its maximum expansions caused the transfluence of the Veny Valley glacier by modelling the Col Checrouit adn isolating the Mont Chetif peak, a sort of nunatak in front of the Mont Blanc during the Last Glacial Maximum (Fig. 6).

Fig. no. 6: The paleogeographic interpretation of the Mont-Blanc area during the "Wurm glacial maximum" (Coutterand and Buoncristiani, 2006). The white arrows highlight the glacial flow lines; the red rectangle marks the fieldtrip area, the red circle marks the Mont Chetif; equidistance of contour lines is 100 m.

The Checrouit lake and the "anomalies" of the southern slope of Veny Valley:

We followed the Balcony path towards the West. In the first section, we focused on the "anamalous" forms of the southern slope of the Veny Valley and on its geomorphological processes.

First of all, the Checrouit lake, withoud tributaries and emissaries, is a circular depression developed by dissolution of carbonate rocks. Similar karst phenomena are responsible for numerous other closed depressions present along the slope, in correspondence of lithotypes susceptible to karst processes. 

Plate - 4: The Checrouit lake and karst phenomena on beside lithological structures (Photo credit: Mahato, R.K., 2019)

Plate - 5: Main scarps on the southern slope of Mont Rouge de Peuterey revealing the link between slope stability phenomena and lithological and structural setting of the area (Photo credit: Mahato, R.K., 2019).

Anong the Balcony path, we recognized other landforms (depressions, trenches, counter slopes) generated by a particular types of slope instability: deep gravitational slope deformation. This phenomenon has been locally recognized and interpreted as the effect of deep dissolution, due to the presence of soluble rocks, such as limestones, schists and conglomerated of the Pennidic and Ultrahelvetic system, breccias and carniole along the tectonic contacts between the Helvetic (Mont Blanc), Ultrahelvetic and Pennidic Units (Fig. 7). 

Fig. no. 7: Geomorphological features of the southern slope of Veny Valley. Not the irregular transverse profile, characterized by linear erosion, counter slope erosion, and depressions. Phenomena of slope instability are linked to deep dissolution of soluble rocks along the deformation zone in correspondence of the Pennidic Front, the main tectonic contact of the Veny Valley.

Plate - 6: We can see the whole Veny Valley from the balcony path (Photo credit: Mahato, R.K., 2019). 

View of the Miage Glacier: 

The Miage Glacier is the main glacier of the Italian side of the Mont Blanc and the third larger Italian Glacier (13 km2 area, 11 km length). A thick and continuous debris cover characterizes this glacier the Miage a "debris-covered glacier" or a "black glacier".

Plate - 7: View of the Miage Glacier with its distinctive features: the three frontal lobes of the glacial mass, the Miage Lake and the moraine amphitheatre, the long and straight debris - covered tongue that runs through the deep glacial valley, the confluence with the glaciers coming from the upper basin (Photo credit: Mahato, R.K., 2019)

The debris cover has an irregular topography due to differential ablation, and is fed by instability phenomena (landslides, debris flows, rockfalls) that originate from the surrounding steep slopes.

Stop at the Miage Lake (2700 m a.s.l.): Once reached the top of 800 AD and LIA moraines, we seen in the front of the remnants of the Miage Lake.

It is a typical glacial contact lake, located where the glacier changes direction (towards the east), and with its banks partly constituted by the lateral moraines, partly by the ice cliff (more than 30 meters high from the water surface). It has always been known for frequent events of ice collapse (calving) and rapid emptying.

From here, We observed the three or four small residual basins, the ice wall of the Miage, and the moraines that enclose the basin; among these stands a high debris wall with a pyramid-shape, on which the previous lake levels are visible. The filling and the geometry of the basins are in continuous and rapid transformation (See Fig. no. 7)

Plate - 8: The glacial Miage Lake located in the beneath of the glacier (Photo credit: Mahato, R.K., 2019)

Between the Miage moraines and the southeastern slope of Veny Valley (1885 m a.s.l.): 

We started our descent and looked where the Miage moraines dam Plan Combal. Here the path follows the valley bottom, between the lateral moraine of the Miage right lobe and the Dora di Veny: a hazardous position for tourists and hikers, as potentially subject to instability phenomena related to glacier and river dynamics. 

A little further down the Ponte del Combal, we observed the effects of the frequent avalanche dynamics that characterize the south - eastern side of the Veny Valley. Sandy sediments and large boulders hae been mobilzed adn deposited by major avalanche events, such as those occured in the spring 2012 and 2013. 

Plate - 9: The deposits of moraine by Miage glacier in the top left hand side we can see a hill of moraine where road system is going beside Dora river valley (Photo credit: Mahato, R.K., 2019)

Plate - 10: Limestone and dolomite deposits beds created a rough situation here where river eroded the bed sediments and made a cliff type of landscape (Photo credit: Mahato, R.K., 2019)

Following the road, we observed reddish landslide deposits overlaying the moraine deposits. Looking south, we identified the source area of the landslide, characterized by steep walls of breccias, gypsum, carbonites, dolomites and limestone. these are soluble lithotypes and therefore more prone to instability, due to the undercutting action of the Dora river. 

Further downstream of the landslide, we observed other instability phenomena, here related to the Miage moraine. Holes and incisions are visible on the road tarmac: these have been caused by various rock falls originated from the top of the right lateral moraine. The moraine became unstable due to significant changes in the glacier, in particular after a marked expansion phase. During this period, the glacier increased its mass, exceeding in height the lateral moraines of several meters, causing the instability of the moraine deposits. 

We descend along the tarmac road, which continues beyond the gate that limits vehicle access to the Alta Veny Valley. From here, we reached the Visaille plain, where the fieldtrip ends. 

References:

Coutterand S. & Buoncristiani J.F. - Paleogeographie du Dernier Maximum Glaciaire du Pleistocene Recent de la Region du Massif du Mont Blanc, France. Quaternaire, 17, (1), 35-43, 2006.

De Giusti F., Dal Piaz G.V., Massironi M., Schiavo A. - Carta geotettonica della Valle d'Aosta. Mem. Sci. Geol., 55, 129-149, 2003.

Deline P. - Change in surface debris cover on Mont Blanc massif glaciers after the Little Ice Age termination. The Holocene, 15, 302-309, 2005.

Deline, P., Orombelli, G. - Glacier fluctuations in the western Alps during the Neoglacial as indicated by the Miage morainic amphitheatre (Mont Blanc massif, Italy). Boreas, 34 (4): 456-467, 2005.

Diolaiuti G., Citterio M., Carnielli T., D'Agata C., Kirkbride M., Smiraglia C. - Rates, processes and morphology of fresh - water calving at Miage Glacier (Italian Alps). Hydrological processes, 20. 2233 - 2244, 2006.

Lemine M., De Graciansky P.C., Tricart P.. - De I'ocean a la chaine de montagnes: tectonique des plaques dans les Alpes. Editions scientifiques GB, p. 208, 2000.

Mortara G., Sorzana P.F. - Situazioni di rischio idrogeologico connesse all'espansione recente del ghiacciaio del Miage ed all'instabilita dei versanti in alta Val Veni (Massiccio del Monte Bianco). Rev. Valdoraine Hist. Nat., 41, 111-118, 1987. 

Veny Valley field trip, 2019