Collaborative Research: Investigating jamming in iceberg-choked fjords with field observations, laboratory experiments, and numerical models

Nontechnical: This award is jointly funded by the Condensed Matter Physics Program and the Office of Multidisciplinary Activities in Math and Physical Sciences and the Artic Natural Sciences Program in Geosciences. The polar regions of our planet are home to many dynamic physical processes. Although the word "glacier" may invoke connotations of stoic and slow-moving mountains of ice whose changes are indistinguishable to the eye, this is not always the case. Among the most active regions of glaciological activity are the massive coastal fjords in Greenland. Rivers of ice which are 5-10 km wide and up to 1 km deep are rapidly flowing towards the ocean. At the end of these glaciers, where the ice meets the sea, icebergs are constantly breaking off or "calving" into the ocean. Approximately 30-50% of all ice discharged into the ocean occurs through calving, as opposed to other mechanisms such as melting. Unfortunately, the physical processes which control calving are not well understood. One possible influence is the presence of an ice mélange, which is a floating layer of icebergs and sea ice extending many kilometers away from the front of the glacier. The mélange is essentially a large-scale, quasi-two dimensional granular material, which can potentially have a large impact on calving rates and our ability to detect iceberg calving. This collaborative project aims to determine the correct physical description of ice mélange mechanics, as well as its influences on iceberg calving. This is accomplished through an interdisciplinary combination of satellite imagery, small-scale laboratory experiments, and theoretical modeling. By bringing together ideas in condensed matter physics to study large-scale glaciological processes, the project sheds new light on the underlying mechanisms which shape the polar regions of our planet. Technical: The primary goal of this project is to characterize the rheology of ice mélange, a closely-packed granular material composed of icebergs and sea ice that is found in fjords throughout Greenland. Ice mélange is unique among granular materials in that it contains exceptionally large clasts (10s to 100s of meters in scale in all directions), is constrained to flow in a quasi-two-dimensional setting, and floats in its own melt. Seasonal variations in ice mélange motion and extent are well-correlated with seasonal variations in iceberg calving rates, suggesting that ice mélange is an important control on outlet glacier and ice sheet stability. The dynamics, energetics, and oceanographic consequences of ice mélange are essentially unexplored. The research team's aim is to study ice mélange by combining analysis of field observations with laboratory experiments and numerical modeling. Satellite imagery, along with previously collected time lapse photography and terrestrial radar data, is analyzed to produce ice mélange velocity fields and quantify iceberg-size distributions. This work provides new insights into ice mélange kinematics and composition, and serves as a benchmark for laboratory and numerical modeling experiments. In addition, experiments are conducted in which synthetic icebergs in a water tank are pushed by a model terminus. These experiments study jamming of particles that model icebergs during and between calving events to investigate stress transmission through ice mélange. Finally, numerical experiments are performed in which ice mélange is simulated using discrete particle and continuum models adapted from previous work on granular materials. The model rheology can be adjusted to find a description of ice mélange that is consistent with field observations and laboratory experiments.