EXPERIMENTAL METHOD TO CONSTRAIN ENERGY DISSIPATION DURING SUBGLACIAL ABRASION

Subglacial abrasion is a dominant erosive process and the expression of clast-bed contact forces for hard-bedded glaciers in temperate environments. Consequently, this mechanism may be an important energy sink and thus should be considered when estimating the gravitational energy balance for these glaciers. However, few attempts have been made to estimate its contribution to the energy balance, and extant data relies heavily on imprecise field measurements that attain only order of magnitude approximations.

To address this deficiency, we designed a laboratory experiment to measure the amount of sliding energy consumed in the generation of new surface area (i.e. abrasion). Using a direct shear apparatus, a slab of ice (10 cm x 10 cm x 1.6 cm) laden with granitic rock fragments (approximately 33% by volume) was slid across a stationary limestone slab at velocity of 14.4 m/day for a distance of 7.2 mm. A normal stress of 823.2 kPa was applied vertically to the sample chamber, and the temperature was held near the pressure melting point. Resultant striations were scanned using a white light interferometer at 15 mm line spacing with 31 nm vertical accuracy, and the grainsize distribution of the gouge particulate was analyzed via laser diffraction method (LDM) in order to ascertain the total change in surface area.

Results indicate that for our experimental setup, the energy dissipated through abrasion accounts for approximately 30% of the total mechanical work done during sliding. Furthermore, the maximum recorded shear traction was approximately 357 kPa with a corresponding frictional coefficient m = 0.43, indicating that frictional resistance to sliding can be substantial for glaciers with a similar bedload. These results corroborate previous estimates for abrasion energy and underscore the necessity to incorporate debris-bed friction into existing sliding models.