DENUDATIONAL PROCESSESAND RELIEF DEVELOPMENTIN MOUNTAIN VALLEYS INWESTERN NORWAY:: A HOLOCENE TO CONTEMPORARY TIME PERSPECTIVE

Abstract

The evolution of mountain landscapes is controlled by the interactions between tectonic, climate and geomorphic surface processes through time. The rates at which mountain landscapes change today are a response of both, their long-term landscape history including past tectonic and glacial activity and the contemporary imprint of current tectonic activity, climate change and anthropogenic influences.

Large areas of the Norwegian mountainous fjord landscapes are occupied by hillslopes that reflect the influence of glacial inheritance from the Last Glacial Maximum (LGM). This thesis deals with the analysis of denudational slope processes and relief development in mountain valleys in western Norway from the end of the LGM until today. Particular attention is given to (i) the complexity of hillslope development since the LGM in glacially formed valleys and (ii) the assessment of the controls, rates and spatial-temporal variability of relevant denudational slope processes operating under Holocene to contemporary environmental conditions in western Norway.

The core research was conducted in two steep, parabolic-shaped and glacier-fed tributary valleys, Erdalen and Bødalen, located on the western side of the Jostedalsbreen ice cap in western Norway. A process-based approach with a main emphasis on field work and geomorphic process analysis (including process monitoring) was continuously applied throughout this thesis.

The primary results of this research revealed that the Holocene to contemporary relief development with its associated denudational slope processes in mountain valleys in western Norway is primarily controlled by the imprint of its glacial history. Apart from that, a significant influence of the Little Ice Age (LIA) glacier advance on hillslope morphometry was discovered, causing higher intensities of post-LIA denudation on hillslope systems affected by the LIA glacier advance as compared to non-affected hillslope systems. Distinct differences are found between single headwater systems of Erdalen and Bødalen (i) regarding the absolute and relative importance of different contemporary slope processes as well as (ii) with respect to the importance of sediment delivery from headwater systems for the sedimentary budgets of the entire drainage basin systems. The detected differences are seen as a direct consequence of the varying glacially inherited valley morphometries which determine hillslope storage capacity, the average process transport distances and the level of hillslope-channel coupling. The intensity of slope-channel connectivity is different in Erdalen and Bødalen but appears to be altogether rather low. Both mountain valleys represent supply-limited systems.

A comparison to geomorphic process rates published for other cold climate environments situated at high latitudes of the northern hemisphere permits the statement that the general intensity of present-day denudational processes in Erdalen and Bødalen is in a comparable range of magnitude. Denudational slope processes have caused a valley widening in Erdalen and Bødalen. However, the Holocene modification of the inherited glacial relief is considered to be minor.