Reinhard Starnberger

Geophysical, topographic and stratigraphic analyses of perialpine kettles and implications for postglacial mire formation

ABSTRACT Kettle holes are common ice decay features in formerly glaciated areas. They are highly variable in size and geometry and may form in a variety of glacial and glaciofluvial landforms. Kettle holes are either dry or exist as wetlands or lakes, only rarely transforming into kettle-hole mires. This study investigates Late Pleistocene kettles in the area of the LGM Salzach Glacier Lobe in the North Alpine Foreland. Kettles are here specifically well preserved and concentrate along the former glacier lobe terminus, where they could develop within large elevated areas protected from pro and postglacial sediment redistribution also showing minor anthropogenic overprint. Highest kettle concentrations were observed within a narrow swath along the distal lobe dominated by terminal moraines, ice wastage and outwash deposits, whereas they are almost absent in the centre of the former glacier lobe. Based on a new dataset on regional kettle distribution and a study of comparable wetland environments, we show that kettle lake formation is a specific but rare phenomenon, which is closely related to the preceding dynamics at the glacier lobe and the glacial depositional environment. By applying geophysical surveys (electrical resistivity tomography, ground-penetrating radar), topographic as well as stratigraphic investigations (DEM analysis, core-drilling and radiocarbon dating), we explore the postglacial evolution of the Jackenmoos kettle and propose a modified model of peat formation in kettle-hole mires, mainly as a function of the centripetal growth of a floating mat covering a central subsurface water body.