A debris flow calendar derived from sediments of lake Lago di Braies (N. Italy) R. Irmler ⁎ , G. Daut, R. Mäusbacher Friedrich–Schiller-University Jena, Physical Geography, Institute of Geography, Löbdergraben 32, D-07743 Jena, Germany Received 1 October 2004; received in revised form 24 August 2005; accepted 3 January 2006 Available online 14 February 2006 Abstract In this study lake sediments were used for developing a high resolution calendar of past debris flow events. Debris flows frequently occur in the high-alpine catchment of the lake Lago di Braies (N. Italy). While the coarse grained material accumulates on the debris flow cones, the fine grained material is flushed into the lake. This material forms characteristic layers in the lake sediments, which are different from the typical annual lamination. By analysing thin sections of sediment, debris flow events of the last 2250 years were reconstructed with an annual resolution. Since debris flow frequency varies strongly, periods with high and low frequencies can be distinguished. However, neither a debris flow magnitude–frequency relationship nor a strong reaction of debris flow activity to past climate changes was identifiable in this study. © 2006 Elsevier B.V. All rights reserved. Keywords: Lake sediments; Geochronology; Debris flow frequency; Debris flow magnitude; Lago di Braies 1. Introduction Natural hazards like debris flows concern scientists more and more in view of climate change and/or human impact. Thereby, the frequency and magnitude of debris flow events (Zimmermann et al., 1997a; Van Steijn, 1996; Jakob and Bovis, 1996) are of especial interest. Information for debris flow events can be obtained by studying archives such as historical data (Zimmermann et al., 1997b; Jakob and Bovis, 1996; Coe et al., 2003), by 14 C-dating of buried soils (Curry, 2000; Patzelt, 1994), dendrochronology (Hupp, 1984; Strunk, 1989, 1995; Gärtner et al., 2003) or lichenometry (Winchester and Harrison, 1994; Innes, 1983, 1997). The disadvan- tage of these approaches is their limited time span and/or coarse temporal resolution. The first high resolution debris flow calendar of the catchment area of lake Lago di Braies was derived by dendrogeomorphologic methods (Strunk, 1995), and covers a period of 450 years. However this calendar has a resolution of ± 3 years and a biased frequency due to the limited life span of trees. The debris flow calendar presented in this paper re- presents the first high resolution calendar reconstructed from lake sediments (Irmler, 2003), whereby the dating was done by varve counting. The use of lake sediments for reconstructing debris flow calendars was done by Jonasson et al. (1997). They assigned a thick minero- genic layer in a X-radiograph of a sediment core of lake Ulvådalsvattnet (Norway) to a large debris flow event observed in 1960. A more extensive study was done by Kotarba and Baumgart-Kotarba (1997) with sediments of lake Czarny Staw Gąsienicowy in the High Tatra mountains of Poland. However, the sedimentation Geomorphology 77 (2006) 69 – 78 www.elsevier.com/locate/geomorph ⁎ Corresponding author. Tel.: +49 3641 948827; fax: +49 3641 948812. E-mail address: ralf.irmler@uni-jena.de (R. Irmler). 0169-555X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2006.01.013