Flow-Modelling of Firn-Covered Cold Glaciers

Cold high altitude mountain glaciers represent an important archive of the regional climate history. In this project, the flow properties of compressible cold firn is investigated. In addition, and closely related to the flow properties, a numerical model coupling the flow, densification, stress and temperature fields of high altitude glaciers covered with a firn layer of subtantial thickness is developed.

This project aims supporting the dating and the interpretation of physical properties of ice cores drilled at Colle Gnifetti (Monte Rosa, Swiss Alps) and Fieschersattel (Bernese Alps) by the group of Prof. H. Gäggeler (University of Berne).

The research work is divided into two parts, which are closely connected and interdependent. One part includes field experiments measuring borehole deformation in firn and evaluates the obtained deformation rates in terms of a constitutive relation between firn deformation and stress. The second part concerns numerical modelling, where the equations for ice flow, firn compaction and ice temperature must be solved with an appropriate flow law. In return, the modelling results will be used for the interpretation of the measured deformation rates of boreholes by providing the necessary stress conditions in the vicinity of the borehole.

A newly designed and built caliper-inclinometer was used for the logging of the boreholes. By repeated tracking vertical positions of markings in these boreholes with the caliper probe, the vertical strain-rate (including firn compaction) could be calculated. Assuming a temporally constant vertical density profile, the depth dependent thinning-rate of annual layers can be determined. This information is important for reconstructing past annual accumulation rates. These measurements were carried out immediately after drilling and then repeated two to three times after several months. In addition, surface velocities, ice temperatures and firn compactions were measured at several points on the investigated glaciers.