DBPapers
DOI: 10.5593/SGEM2014/B12/S2.029

CONTROL OF FANS DOMINATED BY LANSLIDE ON THE QUATERNARY SEQUENCE IN ALPINE VALLEYS (VALTELLINA, NORTHERN ITALY)

E. De Finis, A. Bini
Wednesday 1 October 2014 by Libadmin2014

References: 14th International Multidisciplinary Scientific GeoConference SGEM 2014, www.sgem.org, SGEM2014 Conference Proceedings, ISBN 978-619-7105-08-7 / ISSN 1314-2704, June 19-25, 2014, Book 1, Vol. 2, 219-226 pp

ABSTRACT
Alpine fans characterize so greatly some Alpine valley floors (i.e. Valtellina, Val Venosta) as to have contributed to modelling the profile, since the end of the Last Glaciation. They were considered anomalous with reference to the considerable ratio between area of fan and area of basin, so the definition of new category of catastrophic slope failure outcome was suggested for them. These morphologies can be classified therefore like fans dominated by landslide, differentiated from classical debris-flow or alluvial fans. These fans, characterized by steep slopes and small catchment basin with the head surrounded by imposing scarps, have often diverted and sometimes blocked the main stream, with the formation of landslide dams. The process of silting concerning the landslide dams has contributed to construct, inside the same valley, one or a series of morphological steps, that can be different even for a hundred metres in height. This research improved the classification of the landslide dams, proposed by Costa [1] with the introduction of a new tipology. This allowed also to reconstruct, through stratigraphic data, part of the geomorphological setting of the Quaternary Sequence in the Alpine valley floor of Valtellina between the fans of Ponte in Valtellina and Migiondo (Valtellina, Northern Italy). The surveys, carried out along 50 km of this part of the valley floor, indicate the presence of fine-deposits. They can be correlated each other for example upstream of the fans of Ponte, like also upstream of the fan of Sernio. This fact indicates the presence of ancient lakes, created as a result of the formation of cones dominated by landslide.

Keywords: alluvial fans, landslide dam, debris flow, Alpine valley floor.