Quantifying flow and stress in ice mélange, the world’s largest granular material

Significance Ice mélange, a granular collection of broken icebergs ranging from tens of meters to hundreds of meters in size, sits in front of many of the Earth’s most active tidewater glaciers. In addition to influencing heat and mass transport in the ocean, the jam-packed mélange provides a geophysical living laboratory to test principles developed for small-scale granular materials such as sand. By characterizing both flow and mechanical stress using field measurements, laboratory experiments, and numerical modeling, we show that ice mélange is a quasi-2D, creeping granular fluid which constantly jams and unjams as it advances through the fjord. Most importantly, our results show how ice mélange can act as a “granular ice shelf” which buttresses even the largest icebergs that calve into the ocean.