Naturally-Occurring Surface-Shock Starburst Instabilities

For decades, a curious fluid dynamic instability at the Matanuska Glacier in Alaska has puzzled local glaciologists and tourists alike. Throughout the ablation season, the meltwater that flows from the toe of the glacier is in large parts covered by a thin, black, particulate layer that bursts apart in a distinctive, radially symmetric starburst pattern when touched by hand. In this work, we analyze field videos of these naturally-occurring starbursts that we collected over two summer seasons at Matanuska, as well as a related cracking instability that occurs in particularly dense, muddy areas. We find that these phenomena only occur in response to surfactant perturbations to the surface, such as from introducing skin oil or soap. We further analyze meltwater samples collected from the glacier using contact angle measurements and SEM of extracted particles. Our data indicate that the glacier starbursts are a naturally-occurring example of surfactant shock-driven jamming and fracture. We further discuss other starburst instabilities that we believe may be driven by closely related physics.