Sequential satellite imagery and modeling are used to investigate crevasse patterns at the head of Ice Stream B tributary B1b. The crevasses, informally called the "chromosomes", form at the upstream limit to B1b's northern shear margin and chaotic crevasse zone. We find that the onset to crevasse formation, and by inference the onset to streaming flow, has migrated upstream over time at a mean rate of 230(16) m a−1. A possible cause for that migration is changes in net basal friction due to changes in basal water production rate and storage.
The Journal of Glaciology is published six times per year. It accepts submissions from any discipline related to the study of snow and ice. All articles are peer reviewed. The Journal is included in the ISI Science Citation Index.