Retreat of the Turtmanngletscher and succession of Larix decidua Mill. since the LIA using geomorphological mapping and dendrochronological analysis

This thesis examines the landscape evolution of the southern Turtmann Valley, in Switzerland, focusing on the retreat of the Turtmanngletscher since the Little Ice Age (LIA). Through a combination of geomorphological mapping, glacier extent reconstructions and dendrochronological analysis of Larix decidua Mill., the study investigates processes shaping the landscape and the tree establishment in the proglacial area. The methods used included geomorphological mapping through aerial images and different maps and mapping of glacier extents through historical maps and aerial images, both in a GIS environment. Further methods were tree-ring width measurements with a correlation analysis on the relationship of the tree-ring width and temperature resp. precipitation, and the approach of a chronosequence by the determination of the minimum age of the sampled L. decidua Mill. The resulting geomorphological map presents the interactions between different processes in an alpine valley following deglaciation in the late Holocene. The findings reveal that the Turtmanngletscher reached its maximum extent in the mid-19th century followed by a period of retreat with minor readvances in the 1920s and 1980s. While geomorphological mapping clearly identified the frontal “LIA” moraine at the focus site, dendrochronological dating of these landforms was limited, as tree establishment in the area occurred only after significant glacier retreat. Geomorphic processes, such as gravitational and periglacial disturbances, were found to delay tree establishment in parts of the proglacial area following the Turtmanngletscher's retreat from its maximum extent during the LIA. Tree growth patterns of L. decidua Mill. were found to correlate with temperature, while precipitation had less impact. As a final result, the response of tree growth to climatic conditions could be used to validate glacier extent mapping. In conclusion, this thesis contributes to understanding the landscape evolution of the southern Turtmann valley as a post-glacial landscape by highlighting the connection of geomorphology, climate and succession of larch trees.