Permafrost landform dynamics in high mountain environments: a multi-sensoral approach to assess rockglacier evolution

Abstract

Permafrost, defined as lithospheric material whose temperature remains below 0 °C for two or more consecutive years, occurs in many high mountain regions of the European Alps. Observed and projected high rates of changes of atmospheric, earth surface and subsurface conditions in these regions will influence the state of permafrost and, therefore, inflict a strong impact on processes and landforms controlled by permafrost conditions. This may, in turn, become potentially hazardous to critical infrastructure as well as human habitat and economic sectors. Rockglaciers – common landforms in alpine periglacial regions that develop due to creeping of perennially frozen, unconsolidated material – serve as important indicators to describe the impacts of a warming climate on high mountain permafrost: Their short-term and long-term evolution represents the only feature of high mountain permafrost to be visually observable and can therefore be assessed by a variety of scientific surveying and monitoring methods. This dissertation aims to contribute to an improved understanding of rockglacier evolution combining kinematic and sediment controls by using multi-sensoral remote sensing data. The foundation of this approach are multi-temporal digital elevation models derived from airborne and terrestrial remote sensing techniques. In order to apply them reliably in high mountain environments for the assessment and quantification of landform structures and processes, this dissertation conducts a comprehensive accuracy assessment of multiple remote sensing products. These multi-temporal digital elevation models are subsequently used to quantify sediment production, transport dynamics and changes therein in high mountain periglacial systems. A cascading, systemic model is developed in order to describe and quantify sediment transfer rates and derive energy fluxes in such systems. Periglacial slopes are characterized by rockglaciers, ice-cored moraines and/or solifluction lobes and are often closely connected to glacial and gravitational landforms. All of these landforms are considered to be significant indicators for changes in climate forcing. This thesis develops a surveying strategy which is applied to quantify headwall recession, surface dynamics and rockglacier creep and facilitates the analysis of rockglacier dynamics in relation to their setting in a geomorphological process chain. Geomorphic work and sediment transfer rates are calculated to characterize and compare the potential energy of geomorphological systems and hold the opportunity to detect and quantify changes within these systems over time. The findings on backweathering rates, sediment production and rockglacier kinematics are integrated into a numerical flow model based on the conservation of mass within the debris process chain in order to assess the temporal and spatial evolution of rockglacier surfaces. The implementation of the flow model generates observed rockglacier geometries and rheologies which rely on long-term field measurements on sediment and landform dynamics.. The modeling helps to understand the driving forces of the dynamic changes of rockglaciers and demonstrates the effects of sediment supply and temperature variations on the morphological and rheological evolution of rockglaciers. Further, it elaborates to which degree these variations can account for signs of degradation and may serve as a tool to determine the state of alpine rockglaciers and their potential state of degradation which is indispensable for a comprehensive natural hazard management. This thesis presents a holistic and comprehensive approach to assess permafrost landform dynamics in high mountains. Starting with data generation and evaluation, moving to its application and quantification in the field, and resulting in an approach to model process and landform dynamics, this dissertation presents a novel, multi-sensoral approach to assess rockglacier evolution.