Dynamic jamming in iceberg-choked fjords

We investigated the behaviour of icebergs in a narrow fjord at the terminus of a glacier in Greenland. At the terminus, where the glacier slides into the sea, large chunks (up to hundreds of meters in height and width) of this glacier break off at irregular intervals during summer time. During such an event, the calving iceberg pushes against the densely packed icebergs  that are floating in the fjord. By analysing ground-radar images taken during these events we have shown that the collection of floating icebergs can be viewed as a granular material close to the jamming point. Dynamic jamming fronts can be observed that travel more than 10 km down the fjord, at speeds of about 1 m/s. These observations give us valuable information about the packing density of the icebergs, which will eventually provide us with a better understanding of the rheology of this ice melange and its resisting force to iceberg calving from the glacier.


Satellite image of the Ilulissat Icefjord and the terminus of Jakobshavn Isbrae (Greenland).

[1] I.R. Peters, J.M. Amundson, R. Cassotto, M. Fahnestock, K.N. Darnell, M. Truffer, and W.W. Zhang, Dynamic jamming of iceberg-choked fjords, Geophys. Res. Lett. 42 (2015) [pdf]