Runoff Impact on Active Geomorphosites in Unconsolidated Substrate. A Comparison Between Landforms in Glacial and Marine Clay Sediments: Two Case Studies from the Swiss Alps and the Italian Apennines

摘要

The cultural value of geomorphological heritage (i.e., geomorphosites) is universally recognised and at the same time the interest on its mutability, as a consequence of both natural-climate and human pressure, is growing. In some cases a sudden increase in the velocity of processes can cause irreversible modifications threatening the survival of sites as well as their scientific value in terms of integrity. The focus of this paper is put on two types of geomorphosites (active geomorphosites and evolving passive geomorphosites), in which it is possible to observe and quantify the geomorphological processes varying mainly as a response to climate change. The study cases are runoff-derived landforms on unconsolidated deposits in two morphoclimatic contexts: 'calanchi' on marine originated clays in the Italian Apennines in Mediterranean climatic context (Crete d'Arbia and Radicofani, Tuscany) and earth pyramids formed in glacial deposits in continental Alpine environment (Pyramides d'Euseigne, Canton Valais, Switzerland). In both sites, human activities have strongly contributed to landscape evolution. To investigate erosion rates, dendrogeomorphological analysis (i.e. stress indicators and root exposure analysis) were combined with traditional quantitative geomorphological techniques. Analysis of the roots exposure, well correlated with the climatic data (denudation rates are higher during wet period), show that denudation rates are lower at Pyramides d'Euseigne due to the different texture of the deposits. Unfortunately, at the moment, a comparison between the two sites based on geomorphological monitoring data is not possible due to the different time interval of analysis, and only conclusions on denudation rates coming from roots exposure are allowed. Both geomorphosites have a high scientific value (representativeness and educational exemplarity) and are characterised by dynamicity. Providing data for modelling the sites evolution and possible decrease of their scientific value, caused by proceeding of the process itself, may be particularly significant.