At -69.184611, -68.124276 (just east of the Bugge Islands) there is a triangular ice shelf. On satellite images (as seen on Google/Bing maps) you can see it is riddled with --for lack of a clearer description-- chunks of ice that are either ribbed or smooth.

triangular shelf

What are these chunks? And how are they formed?

I think both types of chunks might be created by the glaciers flowing toward the coast; as seen at -69.214204, -67.055682 (mostly ribbed):

ribbed chunks

and at -69.315307, -67.625613 (mostly smooth):

smooth chunks

But how is there a difference between the two?


1 Answer 1


What you see are ice bergs frozen into a sheet of sea ice. The "chunks" are the ice bergs. Ice shelves are fed by two sources, ice from the interior of the ice sheet and ice formed by compaction of snow accumulating on the shelf itself. This means that a shelf can have very different dynamic regimes. Parts of shelves where ice is mostly formed locally will tend to be smooth whereas shelves feed by ice discharging from the interior can exhibit crevassing. It is very common to have ice streams or more rapidly flowing sectors carrying ice from the interior to the shelf and the position and width of these are often determined by subglacial topography (valleys and ridges where larger flow occurs in the valleys). At the margins of such more rapid sectors velocities drop from maybe hundreds of meters per year to a few or tens of meters per year. This cases severe shearing resulting in formation of cracks/crevasses.

When the ice eventually calves into the ocean as ice bergs, the ice will exhibit different patterns depending from what sectors it originates. The crevassed parts will result in the "ridged" features you see. Essentially, the ridges and furrows are traces of crevasse patterns. In your mid-picture you also see the calving front on the right hand side and it is evident that the ice there is heavily crevassed. It also exhibits flow striping (stripes in the direction of flow, usually perpendicular to the ice front) which indicates rapid flow.


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