Multi-decadal dating of surface slope movements in forested DSGSD areas of the European Alps: detecting precipitation triggering factors

ABSTRACT

An integrated approach including dendrometric and dendrogeomorphological analysis, geotechnical monitoring and numerical modeling was established on a reactivating landslide in a forested Deep-Seated Gravitational Slope Deformation (DSGSD) area in Valtellina, Italy, in order to define the distribution of surface displacements in space and time as well as to identify the triggering factors (i.e. precipitation and a recent road tunneling). By means of a normalized difference eccentricity index (EI), we dated with annual resolution the surface displacements occurred over the period 1980–2016: the instability signals spread from the upper portion of the landslide (C) in 1980s to the middle section (B) especially in the 2000s, when they also occurred in the lowest portion (A). Mean Absolute EI (MAEI index) highlighted the intensity of the displacement signals, whereas changes in the MAEI series (dMAEI index) allowed to find correspondences between precipitation input and tree-ring eccentricity. A diagnostic test applied to these correspondences showed an overall accuracy of 0.74 and allowed to determine the precipitation threshold values acting as triggering factors. Topographic monitoring networks in 2016 revealed displacements <1 mm in the upper portion of the landslide, whereas the middle and lowest portion displacements were ranging 1–10 mm. The inclinometric probes confirmed the same trend for in-depth displacements, pointing out multiple sliding surfaces. A numerical stress-strain model, integrating information both from the instrumental and the dendrochronological approaches, provided information on the slope dynamics and its controlling factors, including groundwater flow conditions and the recent tunneling, thus allowing a comprehensive assessment of the geomorphological hazard.

KEYWORDS:

• Dendrogeomorphology
• geotechnical monitoring
• numerical modeling

Acknowledgements

The Authors wish to thank the Major and Municipality of Valdisotto (Sondrio) for the allowance to use the collected data for scientific purposes and the tree sampling permissions delivered to carry the study. This work has besides benefited from the framework of the COMP-HUB Initiative, funded by the ‘Departments of Excellence’ program of the Italian Ministry for Education, University and Research (MIUR, 2018–2022). Distinct contributions: G. Leonelli was responsible of the sampling design, the data analysis for the dendrochronological parts, the spatio-temporal reconstructions of landslide movements, he contributed to the geomorphological map and co-wrote most of the paper. A. Chelli was responsible of the geomorphological characterization of the area, he made the geomorphological map and co-wrote some parts of the paper. M. Consonni and C. Lorenzo implemented the geotechnic monitoring and were responsible of data acquisition and co-wrote some parts of the paper. P. Gattinoni supervised and coordinated the research group and was responsible of data analysis for the geotechnical parts and the numerical modeling; she co-wrote the paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Italian Ministry for Education, University and Research (MIUR, 2018-2022): [grant number COMP-HUB Initiative, funded by the ‘Departments of Excellence’].

Notes on contributors

G. Leonelli

G. Leonelli, graduated in Natural Sciences, PhD in Earth and Environmental Sciences, he is Associate Professor of Physical Geography and Geomorphology at University of Parma. His research activities deal with the reconstruction of geomorphological dynamics, geomorphological cartography and climate change impacts.

A. Chelli

A. Chelli, graduated in Geological Sciences, PhD in Geomorphology, he is Associate Professor of Physical Geography and Geomorphology at University of Parma. The research interests include the study of deep-seated landslides and the geomorphological mapping.

M. Consonni

M. Consonni, Expert collaborator at Tethys s.r.l. since 2009. He has experience in support, coordination and technical supervision of projects and on-site investigations in the field of environmental remediation, hydrogeological risk assessment, slope stability and groundwater resource management.

C. Lorenzo

C. Lorenzo, Environmental Engineer working since 2001 in the fields of Hydrogeology, Geology, Geomorphology, GIS, Civil and Environmental Engineering. Tethys Associate with expertise in technical consultancy concerning geological, geotechnical and environmental issues for civil and monitoring network design, GIS advanced spatial analysis, landslide evaluation and hydrogeological risk assessment.

P. Gattinoni

P. Gattinoni, graduated in Environmental and Land Planning Engineering, PhD in Applied Geology, she is Associate Professor of Applied Geology at Politecnico di Milano. Her research activities mainly deal with the geological and hydrogeological issues involved in civil and environmental engineering.