Late Neolithic Mondsee Culture in Austria: living on lakes and living with flood risk?
Abstract. Neolithic and Bronze Age lake-dwellings in the European Alps became recently protected under the UNESCO World Heritage. However, only little is known about the cultural history of the related pre-historic communities, their adaptation strategies to environmental changes and particularly about the almost synchronous decline of many of these settlements around the transition from the Late Neolithic to the Early Bronze Age. For example, there is an ongoing debate whether the abandonment of Late Neolithic lake-dwellings at Lake Mondsee (Upper Austria) was caused by unfavourable climate conditions or a single catastrophic event. Within the varved sediments of Lake Mondsee we investigated the occurrence of intercalated detrital layers from major floods and debris flows to unravel extreme surface runoff recurrence during the Neolithic settlement phase. A combination of detailed sediment microfacies analysis and μXRF element scanning allows distinguishing debris flow and flood deposits. A total of 60 flood and 12 debris flow event layers was detected between 4000 and 7000 varve yr BP. Compared to the centennial- to millennial-scale average, a period of increased runoff event frequency can be identified between 4450 and 5900 varve yr BP. Enhanced flood frequency is accompanied by predominantly siliciclastic sediment supply between 5000 and 5500 varve yr BP and enhanced dolomitic sediment supply between 4500 and 5000 varve yr BP, revealing a change from regional floods to more local runoff events. Interestingly, during the interval of highest flood frequency a change in the location and the construction technique of the Neolithic lake-dwellings at Lake Mondsee can be observed. While lake-dwellings of the first settlement phase (ca. 5750–5200 cal. yr BP) were constructed on wetlands, later constructions (ca. 5400–4650 cal. yr BP) were built on piles upon the water, possibly indicating an adaptation to either increased flood risk or a general increase of the lake-level. However, also other than climatic factors (e.g. socio-economic changes) must have influenced the decline of the Mondsee Culture because flood activity generally decreased since 4450 varve yr BP, but no new lake-dwellings have been established thereafter.