Fig. 7
Schematic sedimentological model proposed for the evolution of the northwestern part of Lake Lauerz within the last 200 years. Note the approximate location of the profiles, furthermore the coring positions of the delta cores are indicated on map d. Modern shoreline is indicated on all maps with a dashed line. Bathymetrical contours are hypothetical. a Pre-1806 ad stage: the shoreline of Lake Lauerz is characterized by a very shallow arm extending into the swamps of Sägel in the west. The river mouth of the Steiner Aa is prograding at 3 m year−1 in a southwestern direction. b 1806 ad rock avalanche: the accumulation of rockslide debris (dark gray with blocky signature) on the mechanically weak swamp deposits (medium gray) leads to a gravity spreading-induced mobilization of swamp material and eroded lake sediment into the lake basin and reduces the lake’s superficial area by roughly 1/7 of its original size. As a secondary effect, the process triggers the formation of impulse waves of 15 m amplitude. The indicated formation of fold-and-thrust belt structures is hypothetical. However, similar processes were described for the subaqueous realm by Schnellmann et al. (2005). c Pre-1934 ad stage: delta sediment (LU D2; light gray) is deposited on top of the mobilized swamp (LU D3; medium gray). The Steiner Aa is constantly prograding in a southwestern direction. d 1934–2006 ad: during a major flood in 1934 ad, the estuary of the Steiner Aa is relocated westwards, corresponding to the sharp transition from LU D2 (light gray) to LU D1 (dark gray). This event marks the onset of a new progradation direction of the delta, which is associated with the ongoing separation of the shallow northwestern bay from the rest of the lake