A REGIONAL-SCALE ROCK GLACIER INVENTORY IN TRENTINO(ITALIAN ALPS)

A number of rock glacier inventories were implemented in the framework of PermaNET (Permafrost long-term monitoring network), a project part of the European Territorial Cooperation and co-funded by the European Regional Development Fund (ERDF) in the scope of the Alpine Space Programme (www.alpine-space.eu). Rock glaciers are regarded as one of the most prominent permafrost-related landforms in the alpine territories. A new statistical model and a permafrost distribution map for the entire Alps are partly based on the rock glacier inventories carried out within the project and, in this framework, a new inventory was completed also in the province of Trento. This region is located in the southern part of the Alps and 20% of its territory lies above an altitude of 2000 m a.s.l. The rock glacier inventory is based on analyses carried out in a GIS using a recent (2006) orthophoto (resolution of 0.5m) and a DEM (grid resolution of 2m). First, the rock glaciers were identified using i) the orthophotos and ii) an hillshade derived from the DEM. Then, the outline of the landforms were digitized in the GIS as polygon shapes. The characteristics of the rock glaciers were included in an attribute table linked to the shapes. Our database consist of several descriptive parameters, including that of the Permafrost Evidences Database (PED) of the PermaNET project. However, in agreement with other project partner (e.g. ARPA Valle d'Aosta), we used a number of supplementary parameters, in order to achieve a more complete description of the landforms. The database was partially filled in during the landform digitalization, but most of the information (particularly the morphometric parameters) were obtained from analyses performed in the GIS. In summary, a first group of descriptive parameters of each rock glacier include: location (mountain group and coordinates), altitude (mean and range), slope, length, width, perimeter and area. Other parameters describe additional characteristics, such as: geometry (lobate or tongue shape); general morphology (simple, complex); surface morphology (presence of longitudinal and transverse ridges and furrows and/or hollows and pits); lithology of the feeding area; debris source (talus, till); degree of vegetation coverage, relationships with the local vegetation boundaries and with the glaciers/perennial snowfields located above the rock glacier. Particular attention was paid to the definition of the activity status of the rock glaciers, that were classified as intact (active and inactive landforms containing frozen material) or relict (landforms without frozen material). The assessment was based on i) several evidences visible in the orthophotos and in the DEM, ii) direct field observations carried out in our previous works and iii) field data (i.e. topographic surveys). We used particularly restrictive criteria for classifying the activity status of the rock glaciers from the orthophotos, and this may have resulted in a slightly lower percentage of intact landforms compared to other inventories. Our inventory includes a total of 705 rock glaciers, 134 (19%) classified as intact, the others as relict. They are located at an average altitude 2280 m a.s.l., with a considerable distinction between relict (average altitude of 2190 m a.s.l.) and intact (average altitude of 2660 m a.s.l.) landforms. 50.3% of the rock glaciers face towards N, NE and NW, while 35.2% face towards S, SE and SW. The landforms density (n of rock glacier/km2) is notably different in the various mountain groups of the province, and this seems to be related to the different lithologies that characterize the region. The average surface of the rock glaciers is about 4.7 hectares (0.047 km2). The total area covered by the rock glaciers (33.3 km2) is 1.2% of the entire area of the province located above 1500 m a.s.l., indicating as these landforms are prominent in the periglacial environment of this region