Le grandi frane pleistoceniche di Marziai e dei Collesei di Anzù e loro effetti sull’evoluzione geomorfologica e paleoidrografica della Valle del Piave nel Canale di Quero (Prealpi Venete)

The present study, which regards the Piave Valley from Busche to Quero, has allowed the identification of two large landslides of Quaternary age. Those gravitational phenomena, which caused the formation of the Marziai Lake, had remarkable geomorphological effects on river courses, effects ignored by previous researchers. Different methods were employed in the research. The field survey allowed the construction of a detailed geomorphological map. The geophysical investigation, together with several drillings, allowed the identification of the bedrock and of the Quaternary deposits which are buried within the three valleys that surround the Mt. Miesna. Through a palinological analysis it was possible to reconstruct the environment of the Quero Canyon during the Upper Pleistocene - Holocene and to have evidence that the gravitational phenomena occurred in the first phase of the alpine deglaciation. Two lakes have been identified upstream of the Quero end moraine system: the Quero Lake, caused by a bedrock outcrop in the valley bottom, and the Marziai Lake, caused by Marziai and Collesei di Anzù landslides. Considering the remarkable size of the Marziai Lake (about 20 kilometres in length) there is evidence of high sedimentation rates since the basin was completely filled, likely, between 17,000 and 15,000 years B.P. Finally, the base level represented by the accumulation of the Marziai landslide had remarkable effects on the evolution of the Piave River in the Vallone Bellunese and in the Quero Canyon.