Introduction

This paper presents the results of an inventory of rockglaciers in the Italian Alps which represents one of themain objectives of the last ten years of research con-ducted by the Glaciological Section of the NationalGroup on Physical Geography and Geomorphology.The recently published inventory (Guglielmin andSmiraglia, 1997) groups together data and analyses onabout 1600 of these landforms. Some preliminaryresults have already been presented at previousPermafrost Conferences (Carton et al., 1988; Belloni etal., 1993). Rock glaciers are widely distributed in high-altitude and high-latitude environments. Scientificinterest in these landforms pivots around a variety ofelements: their geometry, the type of ice found internal-ly, their genesis, movement and above all, their climaticand paleo-climatic significance. In addition to these ele-ments of interest, there are others of a more practicaland applied nature, as well as those related to currentclimatic trend. In fact, further increases in temperaturecould heighten the melting of the ice inside rock glaci-ers, causing debris flows that could reach catastrophicproportions and create instability problems for build-ings and structures. Therefore, having an inventoryavailable is essential - an inventory that is as completeas possible and that also supplies information on thedistribution and characteristic of these landforms.

Methods

Rock glaciers were identified by interpretation ofcolour and black and white aerial photographs at va-

rious scales (1:20,000 -1:56,000). To check the dataobtained from this work, numerous site visits weremade.

The rock glaciers were classified from the morphody-namic point of view following Barsch (1988) as active orinactive forms, with two additional categories of uncer-tain activity and complex rock glaciers. For each rockglacier, relationships with glacial landforms or differentice bodies located slightly above or adjacent to it wererecorded as well as its morphological setting (cirque,slope etc.).

The rock glaciers were then drawn on small-scale(1:25,000-10,000) regional and national maps in order tocompute morphometric parameters such as: maximumlength, width, minimum altitude of the front (MAF),maximum altitude of the head of rock glacier (MARH)and aspect. The width and length were measured in thenormal direction and parallel to the direction of themain flow of the rock glacier, respectively. Aspect isdivided into 16 classes from N to NNW. The lithologyof the rock wall that feeds each rock glaciers was deter-mined from geological maps.

Data treatments

The average slope of the rock glacier surface was cal-culated as the tangent of the ratio of the difference inheight (head elevation minus the minimum altitude) tothe maximum length of the rock glacier.

Abstract

An inventory of rock glaciers in the Italian Alps has recently been compiled. It contains data on 1594 rockglaciers. The rock glaciers were identified by aerial photo interpretation and some field surveys. Two hundredand ninety-seven (19%) of these landforms were considered active and 914 (59%) inactive. The total area occu-pied by these rock glaciers in the Italian Alps is about 220 km2 and the total volume of permafrost estimated onthe basis of geophysical investigations carried out in the Upper Valtellina is at least 109 m3. The rock glaciersare concentrated mainly in the central part of the Alps with a maximum density of features of 1 per 9 km2 in theAtesine Alps. Rock glacier distribution is affected by lithology, glacial history and climatic conditions (especial-ly insolation and precipitation regime).

M. Guglielmin, C. Smiraglia 375

THE ROCK GLACIER INVENTORY OF THE ITALIAN ALPS

M. Guglielmin1, C. Smiraglia2

1. Via Matteotti 22 20035 Lissone Italy e-mail: cannone.guglielmin@galactica.it

2. Earth Department, Milan University, Via Mangiagalli 34, Milan Italye-mail: Claudio.Smiraglia@unimi.it

The area was calculated as the product of the maxi-mum length multiplied by the width. This is, therefore,an over-estimation of area, because the real shape ofrock glaciers cannot be considered really rectangular.

The ratio of length to width that permits the separa-tion of tongue-shaped and lobate rock glaciers was alsocalculated (Wahrhaftig and Cox , 1959).

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Figure 1. An example of an Inventory of Italian Alps Rock Glacier map.

The density of rock glaciers was calculated for theareas above an altitude of 1000 m a s.l. for each of thenine traditional geographical sectors of the Italian Alps:Maritime, Cottian, Graian, Pennine, Lepontine,Rhaetian, Atesine, Dolomite and Carnic Alps.

Statistical analyses discussed below refer to rock gla-ciers for which all the data were available.

In addition, cluster analysis using the CANOCO pro-gram (Ter Braak, 1987) was performed to elucidate thecomplex, multiple interactions that constrain rock glaci-er occurrence.

The main characteristics of the rock glaciersin the italian alps: results and discussion

A total of 1594 rock glaciers were identified in theItalian Alps. The mean density of these landforms isequal to 6 per 100 km2 but ranges between 2 per 100km2 in Dolomite Alps to 1 per 9 km2 in Atesine Alps.The rock glaciers are concentrated in areas, generallywhere peaks are less than 3500 m a.s.l.

An example of the Italian rock glacier inventory mapsis shown in Figure 1.

Almost 60% of rock glaciers were classified as inac-tive, whereas only 19% are active (Figure 2a). As con-cerns the morphological locations, the greatest numberof rock glaciers are located in cirques and on slopes butthis varies considerably among the different Alpine sec-tors (Figure 2b). Rock glaciers are located mainly onslopes in the Graian, Pennine and Lepontine Alps,whereas the cirque locations are more important in theother sectors.

M. Guglielmin, C. Smiraglia 377

Figure 2. Main characteristics of Italian rock glaciers: (a) classificationbased on degree of morphodynamic activity; (b) morphological location; (c)relationships with glacial landforms and ice bodies; (d) relationships withlithology.

Table 1. Geographical distribution of rock glacierin the sectors of Italian Alps

1) Number of rock glaciers per sector ; 2) MAF of active rockglaciers; 3) MAF of inactive rock glaciers; 4) total surface area(ha); 5) estimated permafrost volume (*10,000 m3); 6) densityof rock glacier expressed as area (km2) for 1 rock glacier.

Figure 2c shows the topographic relationshipsobserved between rock glaciers and different types ofice bodies and morainic forms. Only 27% of rock glaci-ers are clearly close to these features, and within thisgroup, semi-permanent snow banks and moraines arethe most important.

Over 80% of the rock glaciers have sources in meta-morphic rocks (Figure 2d). This high percentage is dueto the rock types that are characteristic of the ItalianAlps, as metamorphic rocks clearly prevail. However,as previously demonstrated for several sectors of theItalian Alps (Guglielmin, 1997), by comparing surfaceareas of the same dimension, the density of rock gla-ciers is at least doubled for metamorphic rocks com-pared to carbonate rocks.

More than two-thirds of the rocks glaciers yielded alength: width ratio greater than 1 and can be defined astongue-shaped. This ratio was almost equal to 1 only inthe Pennine Alps and thus lobate rock glaciers prevailthere.

As concerns rock glacier morphometry, one may notethat over two-thirds of the rock glaciers have lengthsranging between 100 and 600 m, with a mean of 448 m.A substantial 85% of these landforms have widths ran-ging between 50 and 500 m, with a mean of 281 m. Theprevailing slope is between 10 and 35¡ with a meanslightly exceeding 22¡.

Table 1 contains information on altitude, that is, themeans for the minimum altitudes reached by the frontsof active and inactive rock glaciers in the various sec-tors of the Italian Alps. The mean minimum altitude foractive rock glacier fronts proved to be 2564 m, with amaximum for the Graian Alps and a minimum for theLepontine Alps.

The total surface covered by rock glaciers extendsover 22000 ha of the Italian Alps; almost a half of this isconcentrated in the Rhaetian Alps.

The volume of the permafrost existing in the activerock glaciers in the Italian Alps is estimated to be 109 m3 assuming a mean thickness of 12 m (Guglielmin,1997).

Figure 3 shows the plots of axes (X1 and X2) obtainedby principal component analysis (PCA) using a datamatrix of MAF, MARH, aspect, slope, length and widthof active and inactive rock glaciers, respectively. Theslope and aspect lie near the origin of the principalcomponent axes and are less discriminant factors thanMAF, MARH and length or width. Above all it shouldbe noted that MARH-MAF and slope-aspect areinversely related.

The prevalent aspect proved to be northern (for 21%of the rock glaciers), followed by a NW aspect (14%). If

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Figure 3. Results of Principal Component Analysis (PCA) of the main parameters of active and inactive rock glaciers.

only the active rock glaciers are taken into considera-tion, the percentage of rock glaciers facing the northernsectors (NNW to NNE) increases, reaching 34% (ofwhich 26% facing northward).

Additional aspect-related information can be found inFigure 4, which shows the distribution of MARH andMAF with respect to the orientation of both active andinactive rock glaciers. The distribution of active rockglaciers apparently reflects insolation and also the ge-neral pattern of snow distribution.

Actually, snow distribution reflects the main atmos-pheric circulation that is characterized by cold and,usually dry, winds blowing from N and E duringJanuary and February and by wet winds from the Wand S during late autumn and early spring. This kind ofcirculation increases the snow accumulation on slopesfacing south which are less subject to permafrost aggra-

dation. The less pronounced increase in altitude resul-ting for inactive rock glaciers that face south, suggeststhat the climatic conditions were once governed by anatmospheric circulation that was quite different fromtodayÕs.

The pattern of distribution of MAF and MARH withrespect to orientation of the rock glaciers in cirques andon slopes (Figures 5a and 5b) is almost the same; in anycase, the values for rock glaciers located inside cirquesare generally, lower than those for rock glaciers locatedon the slopes. This is due to the more prolonged snowcover, which limits the effects of higher summer tem-peratures, the lower insolation recorded in the cirquesand heavy avalanche accumulation.

Considering the available climatic data on large-scale(Ministero Lavori Pubblici, 1966; TCI, 1986) theLepontine and the Carnic Alps are characterized byhigher mean summer air temperatures and by a greateramount of total and winter precipitation. On the otherhand, the Graie and Atesine Alps and partially thePennine and Rhaetian Alps have lower temperaturesand precipitation. According to Haeberli (1985), the firsttwo sectors should be the less favorable for permafrostformation and aggradation, while the second groupshould be more favorable. In fact, one can note that thehighest rock glacier densities are found in the Atesineand Rhaetian Alps. Yet, the lowest MAF values for inac-tive landforms were found in the Lepontine and CarnicAlps (and in the case of Lepontine Alps, also for activerock glaciers) and the highest MAF and MARH values

M. Guglielmin, C. Smiraglia 379

Table 2. Differences of MAF and MARH betweenactive and inactive rock glaciers

Figure 4. Relationships between aspect and MAF and MARH. Note the different trends for active and inactive landforms.

for active and inactive landforms proved to be for theGraian Alps and the Cottian Alps (Figures 6a and 6b).These results suggest that the rock glaciers identified inLepontine and Carnic Alps, might be ice-cored rockglaciers or debris-covered glaciers. High values forMARH and MAF in the Cottian, Graian and AtesineAlps cannot be explained in climatic terms. In fact inthese areas, which are the most favorable in terms ofthermal and precipitation regimes, insolation is reducedbecause many mountains exceed 3500 m a.s.l near therock glacier sites. The distribution of the rock glaciers inthese areas probably reflects a more widespread andcomplex history of relationships between rock glaciers

and glaciers, where morphology also plays a veryimportant role.

Table 2 shows the differences between the MAF andMARH of active and inactive landforms. Assuming thatthe inactive rock glaciers really are Òclimaticaly inac-tiveÓ (Barsch, 1997), and that they are of the same age(which it is not possible to demonstrate), this trend of (MAF) can be explained as due to an increase in meanannual air temperature, and possibly to an increase, ofsmaller proportion in precipitation where the actualvalues are relatively low.

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Figure 5. The effect of morphological location of rock glaciers on MARH and MAF with respect to orientation. The plots show (a) the values of rock glacierslocated in cirques and (b) those located on slopes.

Conclusions

From the different statistical analyses carried out andthe geographical distribution of the rock glaciers identi-fied in the Italian inventory, three main factors seemedto influence the distribution of these features and theirevolution over time:

1) relationships with climate, and, above all the pre-cipitation regime and insolation conditions;

2) relationships with glacier development and diffe-rent kinds of ice bodies;

3) lithology of the source areas of the rock glaciers.

The influence of precipitation regime and, above all,the insolation conditions appear to be clear consideringthe MAF and MARH distribution with respect to themorphological locations (cirques, slope) and the orien-tations of rock glaciers sites.

The geographic distribution of rock glaciers in theItalian Alps seems to reflect also the different glacialhystory of the alpine sectors; in some sectors the altitu-dinal distribution of the rock glaciers suggest a differentorigins (ice-cored rock glaciers or debris covered glaciers) for some of these forms.

M. Guglielmin, C. Smiraglia 381

Figure 6. Altitudinal distribution of active and inactive rock glaciers with respect to aspect and geographical location. Plot (a) shows the MARH pattern andplot (b) shows the MAF pattern. Numbers from 1 to 9 follow in the same order as that used for the sectors in Table 1 (Maritime to Carnic).

The lithology of the rock glacier source areas is animportant factor in terms of distribution because thedensity of rock glaciers under the same climatic condi-tions doubles when the rock glaciers are nourished bymetamorphic rocks.

This is probably because these types of rocks havemore favorable thermal properties and/or a more abun-dant production of rock debris.

Acknowledgments

We would like to thanks the researchers who helpedin identifying the rock glaciers: C. Baroni, N. Cannone,A. Carton, G.B. Castiglioni, V. Maggi, G. Mastronuzzi,

U. Mattana, M. Meneghel, M. Onorati, C. Ottone, G.Palmentola, B. Parisi, M. Pelfini, G.B. Pellegrini, M.Petruzzelli, A. Ribolini, P. Sans�, U. Sauro, C. Tellini, V.Toniello, C. Vanuzzo, C. Voltolini. The efforts of G.Palmentola and G. Orombelli which permitted this pro-ject to be implemented and of F. Dramis for his com-ments are especially deserving of our appreciation.

The paper was published with a MURST 40% fund.

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