THE MORPHOLOGY OF STRIATIONS PRODUCED DURING LABORATORY EXPERIMENTS OF SUBGLACIAL ABRASION

During the erosional process of subglacial abrasion, rock fragments entrained in the basal ice wear down underlying bedrock and produce linear scratch-like features called striations. The presence and orientation of striations have been used to determine the past extent and ice flow direction of glaciers and ice sheets. Additionally, the morphology of striations can provide insights into subglacial mechanics, but this area of research has been underdeveloped due to the lack of theoretical and empirical understanding of the relationship between subglacial forces and striation morphology. Here, we present results on the morphology of striations produced during two cryogenic ring shear experiments. The experiments simulate the sliding of temperate ice containing granite rock fragments over a flat marble bed under glaciologically realistic conditions. The ice was slid at a steady velocity under a constant normal load. We continuously monitored basal drag and vertical ice velocity. Following the experiments, we used a high-resolution white light profilometer to scan the striated bed surface and produce digital elevation models of the morphology for over 400 striations. We focus on examining the change in striation depth and width with longitudinal distance, and group striations into three categories following previous work. In our experiments, the most common striation type we observe is “carrot-shaped” in which striation depth quickly reaches a maximum and then gradually decreases. We interpret these striations to represent that rock fragments rapidly indent into the bed but gradually plow themselves out. We compare our striation morphology data with the basal drag record from our experiments to understand how debris-bed contact forces evolve during the experiment as rock fragments indent and striate the bed. Our results provide evidence of the mechanical interactions between rock fragments and the glacier bed. Additionally, our results have implications for understanding the influence of debris-bed contact forces on glacial slip, improving mechanistic models of the subglacial abrasion process, and they provide a comparison for field-based studies of glacial striations and other erosional features.