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Linking detrital layers in the varved sediment record of Lake Mondsee to flood events during the last 30 years

Lucas Kämpf1, Tina Swierczynski1, Philip Müller2, Andreas Güntner2, Bruno Merz2, Peter Dulski1, Achim Brauer1
1 Sektion 5.2 Klimadynamik und Landschaftsentwicklung, Helmholtz-Zentrum Potsdam Deutsches Geoforschungszentrum GFZ
2 Sektion 5.4 Hydrologie, Helmholtz-Zentrum Potsdam Deutsches Geoforschungszentrum GFZ

V 6.3 in Quartäre Landschaftsentwicklung - ein Schlüssel zum Verständnis aktueller Georisiken

19.09.2012, 14:50-15:10, H8

 

Establishing long flood time series from geoarchives has become a main issue of modern palaeoclimatic research in order to decipher links between climate variability and flood occurrence. Lakes are particularly valuable archives because they form ideal traps in the landscape, continuously recording land surface processes in the catchment including extreme events.

Discrete detrital layers intercalated in the varved sediments of Lake Mondsee coincide with historical flood events and therefore present a potential flood archive covering the mid to late Holocene (Swierczynski et al., 2012). Comparing instrumental flood series with the sediment archive revealed that selected extreme floods especially those occurred from autumn to early spring did not result in a discrete layer. Therefore, we aim an advanced interpretation of the flood layer record by investigating patterns of spatial sediment distribution and relating sedimentary processes during past flood events.

A succession of 15 detrital layers ranging in thickness from 0.05 to 10 mm was detected in 20 short cores by applying microscopic and µ-XRF scanning techniques. All detrital layers were seasonally dated according to their position within the varve sequence and have been compared with instrumental flood series from AD 1977 to 2005. Two thirds of all event layers can be linked to spring and summer floods following heavy precipitation events. 80% of the most intense floods lead to the formation of a detrital layer. In contrast, 30% of floods in winter and early spring caused by snow melt and rain-on-snow events are reflected in the sediment record.

The event deposits exhibit a clear proximal-distal pattern indicated by most frequent and thickest layers (0.5-10.0 mm) in cores close to the inlet of the main tributary to Lake Mondsee (0.8 km apart), and thinner layers (0.05-0.8 mm) in the long master core sequence (3.0 km). However, the distribution of detrital layers follows a seasonal pattern: 75% of the eight summer flood layers deposited near the delta are recorded in the lake centre (ca. 1.5 km off the river inlet) and 40% at the master coring site. In winter and early spring, only one of the four detrital layers is distributed over the entire lake floor.

We assume that detrital layer formation is effectively dependent on seasonal variability in (1) run-off generation and sediment dynamics within the catchment, (2) density differences between lake and river water and (3) internal lake currents. Therefore, a comprehensive monitoring network in Lake Mondsee and its catchment is in progress giving new insights into the chain of hydrological and sedimentary processes from the head-catchments to the lake.

 

References:

Swierczynski.,T., Brauer, A., Lauterbach, S., Martin-Puertas, C., Dulski, P., von Grafenstein., U., Rohr, C. (accepted): A 1600-year seasonally resolved record of decadal scale flood variability from the Austrian pre-Alps. Geology.



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Letzte Änderung 25.07.2012