Analisi della propensione all'innesco di debris flow applicata alla stabilità dei depositi glaciali nelle aree recentemente deglacializzate della Valle di Rhemes (Italia) = Analysis of debris-flow initiation hazard - application to the glacial debris in recently deglaciated areas (after LIA) of Rhemes Valley (Italy)

In this work I have tried to apply the Bonnest-Staub method (2001) “A methodology for the mapping and analysis of debris-flow initiation hazard – application to the Bragousse torrent (France)” to the glacial debris in recently deglaciated areas (after LIA) of Rhȇmes Valley (Italy). This valley is the result of carving by the scouring of an ancient glacier during Pleistocene. The glacier was a tributary to the Great Balteo Glacier that streamed along the main dale of Aosta Valley. Of the Rhȇmes Glacier remain only fourteen minor flaps. During the Little Ice Age these glaciers covered over the 20% of the Rhȇmes Valley, now, after the current deglaciation, only the 8%. The Little Ice Age was a period of cooling of the Northern Hemisphere that occurred from 1350 to 1850. During this period the amount of cooling was much less than Pleistocene glaciations and it wasn’t a globally-synchronous event. Several causes have contributed to increase the cooling of the Nord Atlantic areas: cyclical lows in solar radiation; heightened of volcanic activity; changes in the ocean circulation; and decrease in the human population. During the XIX century the rise of the temperatures leads the glacier to reduced, marking the end of the Little Ice Age. The retreat left behind large amount of unstable debris which could be originating a debris flow. Debris flows are viscous flow of saturated materials at high velocity, concentrated in channels. These streams have a high concentration of solid, comparable to those of landslide and their dynamics may be considered at interface between mechanical and hydraulic flow. The triggering factor is intense rainfall or snowmelt which brings the loose material to a state of almost complete saturation. Five criteria were chosen to define the debris flow hazard: (1) slope angle; (2) nature of geological formation and hydrogeological characteristics; (3) slope erodability and instability; (4) grain size; (5) available volumes of superficial deposits present in the source area. Using ArcGis instruments and the result of GlaRiskAlp project, the five indices are determinate for each glacial deposits of the Rhȇmes Valley. The global index of debris-flow initiation hazard is obtained by adding each index. The results are summarized on a specific ID card for each glacier.