Landslides or moraines? A new geomorphological map of the area of Mt. Cimone (the highest peak of the Northern Apennines, Italy)

D. Castaldini, P. Coratza & M. Panizza Dipartimento di Scienze della Terra, University of Modena and Reggio Emilia, Modena, Italy

ABSTRACT: The extent of the study area is about 20 km2 and its elevation ranges from about 1300 m a.s.l. to 2165 m a.s.l. With its typical pyramid-like shape, Mt. Cimone rises isolated and shifted to the north with respect to the Apennine watershed. From a geological point of view it is ascribable to the overthrust. The landforms and deposits of the study area may be mainly defined according to the following groups of morphogenetic factors and processes: glacial landforms and deposits, cryogenetic and nivation landforms and deposits, structural landforms, slope landforms and deposits due to gravity; landforms and deposits due to running water, anthropogenic landforms; they are shown in a new geomorphological map at the 1:10,000 scale. The presence of glaciers in the Mt. Cimone area, during the last glacial expansion, is witnessed by small cirques and vast moraine deposits modeled in the shape of ridges. Post-glacial slope landforms and deposits due to periglacial processes and gravity are very common. The landslides are of various types and essentially inactive. Worthy of note for their dimensions are some mass movements on the eastern sector of the study area. In the Mt. Cimone area small perennial or temporary lakes of structural, glacial and artificial origin are found. Finally, anthropogenetic landforms mainly linked to winter tourism, which has been particularly accentuated in the past decades, are widespread. The novelty of this work is that many zones mapped as landslide or debris slope deposits in previous papers, have been here considered as moraine deposits. The trenches, concavities and reverse slopes which locally characterize watersheds and slopes and which have been not considered in former papers, have been interpreted for the first time as the surface expression of "Deep-seated Gravitational Slope Deformations". The extent of the glacial features in the area is much wider than it was believed before. Moreover all the landslides are of post-glacial age as they involve or covers the glacial deposits. Therefore the main, or at least one of the most important, triggering factor of the Mt. Cimone mass movements, could be the glacial debuttressing.

1 FOREWORD

This paper describes a new geomorphological map implemented in the area of Mt. Cimone which is located in the high Apennines of Modena Province, Italy (Fig. 1). The study area extent is about 20 km2 and its elevation range from about 1300 m a.s.l. to the top of the Mt. Cimone, which attains the altitude of 2165 m a.s.l.

Mt. Cimone (once named Mt. Alpone) is the highest peak of the Northern Apennines. This area is one of the most important summer and winter tourism resorts of the entire Apennines; along its slopes many ski lifts have been constructed and 50 km ski runs developed.

The data collected during this research allowed to make a revision of the geomorphological features of this sector of the Apennines, in particular as concern the slope and glacial landforms and deposits.

Figure 1. Location of the Mt. Cimone area, high sector of Modena Apennines (*).

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2 GEOGRAPHICAL AND GEOLOGICAL SETTING

The Mt. Cimone area is located in the Frignano Park, which was established in 1988 by the Emilia-Romagna Region.

The climate is considerably influenced by the altitude and location near the watershed between the Adriatic and Tyrrhenian sides of the Apennines (Servizio Meteorologico Regione Emilia-Romagna 1995). Below 1000 m a.s.l., the average annual temperature is about 10 °C, whereas above this elevation it progressively decreases to 6 °C. Annual precipitation ranges from 1250 mm in the lower part to over 2000 mm in the upper part. The ground is snow-covered for about 100 days a year.

The general geological features of the Modena Apennines are illustrated by Bettelli et al. (1989), whereas detailed geological information can be found in the Geological Maps of the Emilia - Romagna Region at the 1:25,000 and 1:10,000 scale (Regione Emilia-Romagna – Servizio Geologico, Sismico e dei Suoli 2007).

With its typical pyramid-like shape, Mt. Cimone rises isolated and shifted to the north with respect to the watershed; it can be recognised from a distance of several km. The particular uplift of this mountain is ascribable to the overthrust of an overturned outlier of Mt. Modino Complex (constituted by Arenarie di Mt. Modino with the underlying Argilliti di Fiumalbo Formations), on top of the Sequence of Mt. Cervarola Sandstones. The flat area at the northern foot of Mt. Cimone (Pian Cavallaro), has a tectonic origin since it corresponds to a contact surface between the two Units which is covered by surface deposits. The Mt. Modino Complex (Upper Oligocene-Lower Miocene?), in its lower portion, is composed of multi-coloured shales, marlstones, silty marlstones and siltstones (belonging to the Argilliti di Fiumalbo Formation), followed by thick layers of mid-coarse to fine grained sandstone, with intercalations of marly clays (belonging to the Arenarie di Mt. Modino Formation). The Mt. Cervarola Sandstones (Lower-Middle Miocene) are fine-grained, greyish arenaceous-pelitic turbidites.

The influence of the structural characteristics on the morphology is also evident in correspondence of the main scarps and ridges.

3 PREVIOUS GEOMORPHOLOGICAL STUDIES AND GEOMORPHOLOGICAL SETTING

The geomorphological studies in this sector of the Northern Apennines have mainly dealt with landforms linked to glacialism. The first investigations on glacialism began at the end of the 19th century. For instance, De Stefani (1887) and

Sacco (1893) described moraine deposits, valley lakes and glacial cirques. On the other hand, Pantanelli (1886) tried to explain the Apennine morphogenesis by means of simple slope processes, even though he admitted the existence of striated pebbles and landforms of uncertain origin.

In the first half of the 20th century many authors produced other mainly qualitative contributes (e.g. Sestini 1936, Losacco 1949). Some decades later, Losacco (1982) carried out an updated and accurate overview of glacial traces in the Northern Apennines.

Since the late 1970s many authors reported glacial deposits in the North - Western sector of the Northern Apennines whose location, morphology, lithology and weathering rate could be explained only by previous glaciations (Federici, 1977, 1980, Gruppo Ricerca Geomorfologia C.N.R. 1982, Federici & Tellini 1983). In the previous papers, the glacial traces of the Northern Apennines were always attributed to a single glaciation event, corresponding to the Alpine Würm. Jaurand (1999) reviewed the knowledge of the glacialism in the Apennines by trying to attain a more accurate outline of both the last glacial period (maximum of the recent Würm and retreat phases) and the traces of more ancient glaciations.

The lack of traces of glacial periods older than the Würm in the high Modena Apennines may be due to different causes (cfr. Panizza 1978, Losacco 1982).

Very recently Panizza (in press) proposed to ascribe the term "Tagliole" to the last glacial expansion occurring in this sector of the Apennines.

In the high Modena Apennines the evidence of glacial traces is represented by both erosional (glacial cirques, overdeepened hollows, roches moutonnées) and depositional forms (moraines, moraine ridges), containing locally small lakes or impoundments. According to Castaldini et al. (2002) the most common origin (about 65%) of the lakes of the high Emilia-Romagna Apennines is due to glacial morphology.

Landforms resulting from periglacial processes (e.g. block fields, block streams, avalanche cones etc.) and from the action of surface running water (e.g. gullies, alluvial and colluvial fans etc.) are also quite common.

The most typical slope landforms are scree slopes, talus cones and landslides. Anthropogenetic landforms mainly linked to winter tourism, which has been particularly accentuated in the past decades, are rather widespread in some areas.

Among the papers of the past decades containing geomorphological data on the Mt. Cimone area, Carton (1977) studied the geomorphological features of the Lake della Ninfa and Panizza et al. (1978) assumed that some big landslides in the northern

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zone of Mt. Cimone could have been controlled by neotectonic discontinuities.

Carton & Panizza (1988) published the geomorphological map (1:25,000 scale) of the torrents Fellicarolo and Ospitale which comprise the eastern side of the Mt. Cimone area. Bertacchini et al. (1999) described the main features of the Mt. Cimone area within the framework of an inventory of the geological heritage of the Province of Modena. Castaldini et al. (2003) illustrated the geomorphological characteristics of the Mt. Cimone area, also with a geomorphological map, of the northern and eastern slopes, at the 1.40,000 scale.

4 GEOMORPHOLOGICAL MAP

The detailed morphological features of the study area are illustrated in a geomorphological map, produced from bibliographic research, analysis of aerial photographs and satellite images from various periods and field survey. In implementing this map the legends used for recent geomorphological maps were applied (e.g. Castaldini et al. 1998, Pasuto et al. 2005). The map was implemented in colours; in Figure 2 is shown a black and white sketch of the "Ruina del Cimone" zone on the eastern slope of Mt. Cimone (Fig. 2).

The ages shown on the geomorphological map result from bibliographic data and field survey, since no chronological determination was conducted on deposits and related landforms. From a morphodynamic standpoint, landforms and deposits are considered as active, dormant, or inactive. Obviously, structural and anthropogenetic landforms were excluded from these distinctions.

This document is the first geomorphological map at a large scale (1:10,000 scale) which covers the entire area of Mt. Cimone. The landforms and deposits have been defined mainly according to the following systems or groups of morphogenetic factors and processes: structural landforms, landforms and deposits due to running water, slope landforms and deposits due to gravity; glacial landforms and deposits, cryogenetic and nivation landforms and deposits, anthropogenetic landforms.

In particular, by examining the main features of the area, the influence of the structural characteristics on the slope morphology is particularly evident in the scarps visible in the upper part of the area. On the eastern face of Mt. Cimone, a cirque-like form, that some authors interpreted as due to glacial origin (e.g. Losacco 1982, Carton & Panizza 1988), is observable. On the contrary we mapped that feature as a landslide scarp.

In fact, the zone at the foot of this slope, named "Buca del Cimone", is characterised by a large landslide deposit. In detail, the large arenaceous block on which the terminal station of a skilift was

built, is a large landslide body resulting from a rock block slide along a rotational surface which took place in an unknown period. Anyhow, as the landslide debris cover moraine deposits, it is clear that the mass movement occurred in the post-glacial period. Moreover, at the present level of knowledge, it is not possible to establish whether the long ridge stretching NE of Mt. Cimone ("Cresta del Gallo") was originally the rim of a cirque or not since vast post-glacial slope movements have practically hidden the original morphology.

Anyhow the presence of glaciers is witnessed by small cirques and moraine deposits modeled, in the shape of ridges, at the feet of all the mountain slopes. Many of the glacial forms, probably located at the higher altitudes, could have been obliterated or cancelled by erosional processes linked to the intense uplift occurring from the Middle-Upper Pleistocene to date (Bartolini 1999). Also landforms derived from cryogenetic and nivation processes, such as avalanche cones, protalus ramparts, block fields are widespread at the higher altitudes.

Slope landforms and deposits due to gravity and, in particular, scree slopes, talus heaps and landslides are very common in this area. The landslides are of various types: rotational and/or roto-translational slides, block slides, flows, complex. All the landslide phenomena are inactive except the landslide, due to flow, on which is located the Botanic Garden "Esperia".

The landslides activity is testified by cracks which affect the house for visitors of the Botanic Garden. Worthy of note for its dimensions is the landslide to the east slope of Cresta del Gallo ridge; inside its body the Lake della Ninfa is found. By the older authors, this deposit is in fact the result of several landslide episodes originated from a single large block slide. According to Panizza et al. (1978) this detachment of rock has been controlled by two neotectonic discontinuities. It has been assumed that this landslide might have been triggered in concomitance with a seismic shock during the Holocene. Other huge mass movements, probably controlled by the same neotectonic movements, are located on the western slope of the Mt. Cervarola.

Lake della Ninfa, at an altitude of 1500 m a.s.l., is a very popular tourist resort of the Modena Apennines. Originally, this little lake was just a pond. In order to make the Lake della Ninfa more attractive for tourists, many years ago the palustrine vegetation that used to grow from its bottom was removed together with the thin silty-clay layer that waterproofed it. Unfortunately, owing to this intervention, also the impoundment got depleted. In order to get round this irreparable damage, the floor of the basin was tarred. Notwithstanding this, the loss of water was still high; therefore, in 2002, the basin was artificially depleted and the floor was once more waterproofed.

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Figure 2. Geomorphological sketch of the "Ruina del Cimone" zone on the eastern slope of Mt. Cimone. Legend: 1) Sandstones; 2) Shales, marlstones and siltstones; 3) Lake Il Terzo; 4) Edge of glacial cirque; 5) Moraine ridge; 6) Moraine deposit; 7) Block stream; 8) Gully and stream; 9) Gorge; 10) Colluvial deposit; 11) Lacustrine deposit; 12) Edge of landslides scarp; 13) Talus cone; 14) Talus heap; 15) Rotational and/or roto-translational slide; 15) Landslide due to flow; 17) Complex slide; 18) Block slide. In the immediate surroundings of Lake della Ninfa, other genetically similar depressions are found; they are small impoundments seasonally fed by snowmelt. In the area of Mt. Cimone other small lakes of various origin, at altitudes ranges from about 1300 m a.s.l. to 1800 m a.s.l. are found; they are structural (L. dei Bagni), glacial (L. Il Terzo), or artificial lakes used for the production of artificial snow (L. Le Polle, L. Lamaccione, L. dei Farsini, L. Piaggia Silvestro). Other forms and deposits linked to the action of surface running water are mainly represented by gullies, small V-shaped valleys, alluvial and colluvial fans.

Finally, anthropogenetic landforms mainly linked to the winter tourism, which has been particularly accentuated in the past decades, are widespread. Its expansion has in fact determined, several cases of excavation and landfill areas, of construction of large parking areas which in many places have altered the original morphology. Moreover, the construction of ski tracks has produced the deforestation of the north sector of Mt. Cimone, thus exposing some areas to rillwash erosion.

5 FINAL REMARKS

The novelty of this work, beside the fact that it is the first geomorphological map which covers the entire sector of Mt. Cimone, is that many zones mapped as landslide or talus heap in previous works, have been here considered as moraine deposits.

In particular, the large scale and very recent Geological Maps of the Emilia - Romagna Region (Regione Emilia-Romagna – Servizio Geologico, Sismico e dei Suoli 2007) indicate as moraines only few deposits in the eastern sector of the Mt. Cimone area. In the new geomorphological map glacial features (edge of cirques, moraine deposits and moraine ridges) have been mapped also in the western, northern and southern sectors of the Mt. Cimone area. Moreover, the presence of moraine deposits in the eastern sector is considered wider than it was believed. The new interpretation has been made mainly on the base of the geomorphological studies and, in some cases, of

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very recent opened slope cuts carried out for ski tracks.

In the following will be described a couple of examples concerning these new interpretation.

On the eastern slope of Mt. Cimone is located the "Ruina del Cimone" zone. Worthy of note is that the place name "Ruina" is very common in the Emilia - Romagna Apennines; it means "ruin", "disaster" and it is always used to indicate areas affected by historical landslides. The "Ruina del Cimone" zone has been mapped as landslide by previous authors. The upper sector of this zone is constituted by big boulders and debris organized in parallel ridges which become shaped in a concave arc in the lower part. These kind of features have been interpreted,, in high altitude mountains, as due to slope or periglacial processes (for a discussion see Fort, 2003). In the present work these boulders and debris, considering their textural characteristics and their combination in the landscape, have been mapped as moraine deposits and ridges (Figs 2, 3). The concave landforms at the top of the slope have been considered as an edge of glacial cirque instead of a landslide scar. The lowest sector of the "Ruina del Cimone" zone has been confirmed as a landslide.

Figure 3. Panoramic view of the moraine ridges of the "Ruina del Cimone" zone, considered as landslide by previous authors.

A quite similar case has been found in a zone

located in the south western sector of Mt. Cimone; also this zone, considering that the debris shows a parallel and linear distribution and the presence of clear glacial features at the bottom of the slope, has been mapped as moraine deposits instead of landslides deposits, as indicated by Regione Emilia-Romagna – Servizio Geologico, Sismico e dei Suoli (2007).

Other interesting features are the double ridges, trenches, concavities and reverse slopes which locally characterize watersheds and slopes and which have been not considered in former papers. These features have been found on the watershed which connect, from SE towards NW, the peaks Mt.

La Piazza, Mt. Cimoncino, Mt. Cimone, Il Balzone, Alpicella del Cimone, on the Cresta del Gallo ridge and on the east slope of Mt. Cervarola. These morphological features have been interpreted as the surface expression of "Deep-seated Gravitational Slope Deformations" (DGSDs) (Fig. 4).

Figure 4. Double ridge and trenches in the north west ridge of the Mt. Cimone: geomorphological features of "Deep-seated Gravitational Slope Deformations".

Similar features have been described and mapped

in the Abetone area (Caredio et al. 1996, Castaldini et al. 1998) and in the Upper Tagliole Valley (Castaldini et al. in press); both areas are located near the watershed of the Northern Apennines, and are about 10 km far from Mt. Cimone.

In the Abetone area the favorable conditions for the development of these phenomena were identified in the structural conditions, remarkable thicknesses of competent rock types, high relief energy, meteo-climatic conditions, seismic intensity and deglaciation. It could be interesting to carry out the inventory and the detailed study of these particular morphological features connected to mass movements which characterize the upper parts of the Northern Apennines.

Important remarks coming out from the present work is that the extent of the glacial features in the Mt. Cimone area is much wider than it was believed before. Moreover all the landslides, also of huge extent, are of post-glacial age as they involve or covers the glacial deposits.

Therefore the main, or at least one of the most important, triggering factor of the Mt. Cimone mass movements, could be the slope debuttressing due to the significant ice loss (glacial debuttressing) as it has been detected in the Northern Apennines (Abdrakhmatov et al. 2004), in the Italian Alps (Panizza 1973, Eisbacher & Clague 1984) as well as in other mountainous areas of the world (Evans & Clague 1994; Hewitt et al. 2008).

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ACKNOWLEDGEMENTS Federici, P. R. & Tellini, C. 1983. La geomorfologia dell'alta Val Parma (Appennino settentrionale). Riv. Geogr. Ital. 90: 393-428. The research was carried out with the financial support of

CERG (Centre Européen sur les Risques Géomorphologiques, Strasbourg, France) and Frignano Park and within the framework of the European Project "Mountain Risks". The Authors are grateful to M. Fort, University Paris-Diderot, for her critical review of the paper.

Fort, M. 2003. Are high altitude, lava stream like, debris mixtures all rock glaciers? A perspective from the Western Himalaya. Zeitschrift für Geomorphologie. Supplement band 130, 11-29.

Gruppo Ricerca Geomorfologia C.N.R. 1982. Geomorfologia del territorio di Febbio tra il M. Cusna e il F. Secchia (Appennino Emiliano). Geogr. Fis. Dinam. Quat. 5: 286-360.

Hewitt, K. Clague, J.J. & Orwin J.F. 2008. Legacies of catastrophic rock slope failures in mountain landscapes. Earth-Science Reviews. 87, 1-38.

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