Abstract
Abstract. Mediterranean Alpine populations are particularly exposed to natural hazards like floods and earthquakes because of both the close Mediterranean humidity source and the seismically active Alpine region. Knowledge of long-term variability in flood and earthquake occurrences is of high value since it can be useful to improve risk assessment and mitigation. In this context, we explore the potential of a lake-sediment sequence from Lago Inferiore de Laures in Valle d'Aosta (Northern Italy) as a long-term record of past floods and earthquakes. The high-resolution sedimentological study revealed 76 event layers over the last ca. 270 years; 8 are interpreted as most probably induced by earthquakes and 68 by flood events. Comparison to historical seismic data suggests that the recorded earthquakes are strong (epicentral Medvedev–Sponheuer–Kárník (MSK) intensity of VI–IX) and/or close to the lake (distance of 25–120 km). Compared to other lake-sediment sequences, Lago Inferiore de Laures sediments appear to be regionally the most sensitive to earthquake shaking, offering a great potential to reconstruct the past regional seismicity further back in time. Comparison to historical and palaeoflood records suggests that the flood signal reconstructed from Lago Inferiore de Laures sediments represents the regional and (multi-)decadal variability of summer–autumn floods well, in connection to Mediterranean mesoscale precipitation events. Overall, our results reveal the high potential of Lago Inferiore de Laures sediments to extend the regional earthquake and flood catalogues far back in time.
Highlights
Natural hazards are of particular concern for societies as they cause widespread loss of life, damage to infrastructure and economic deprivation (e.g. Munich Re Group, 2003)
According to several studies providing a comprehensive overview of event layers (e.g. Mulder and Cochonat, 1996; Gani, 2004; Van Daele et al, 2015; Wilhelm et al, 2016b), the 77 beds represent short-term depositional events and they correspond to 74 graded beds (GBs), 1 matrix-supported bed (MSB), 1 homogeneous bed (HB) and 1 deformed layer (Fig. 3)
GBs are associated with turbidity currents triggered by either flood events or mass movements (e.g. Sturm and Matter, 1978; Shiki et al, 2000; Arnaud et al, 2002; Mulder and Chapron, 2011; Wilhelm et al, 2012b)
Summary
Natural hazards (e.g. earthquakes, floods, landslides) are of particular concern for societies as they cause widespread loss of life, damage to infrastructure and economic deprivation (e.g. Munich Re Group, 2003) The frequency of both geological (i.e. earthquakes) and hydrological (i.e. floods) events varies in time mainly as a function of tectonic processes and climatic regimes, respectively. Such long-term changes need to be taken into account for more accurate risk assessments. Downstream, lakes may act as sediment traps, resulting in the deposition of a coarser-grained layer that will be preserved in time
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