Pleneau Island & Icebergs

Near Pleneau Island, there is a shallow place in the bay where floating icebergs often become grounded, and so it is a wonderful "collection" of icebergs that are easy to view by Zodiac raft.  Skimming between these towering structures, we often felt as though we were in an art gallery, as the wind and waves had carved each iceberg into ever more beautiful shapes.

Why are icebergs such weird shapes?
We were told that icebergs, once they have "calved" off of the main ice sheet, will float with only about 20% of their surface above water.  Air is a better insulator than water, so the underwater part melts faster than the top part, and at some point, the iceberg rolls over, exposing the underwater towers and crevices.  This process can repeat several times, leading to some absolutely amazing shapes.

Why are icebergs blue? There was some extremely lively debate among our onboard scientists (both amateur and professional!), as to just why the icebergs are such an amazing color of blue.  After talking to several of them, my understanding of the general consensus is the following:  The Antarctic ice sheet is extremely thick -- miles thick in places -- and the weight of all of the ice causes the ice in the lower parts of the sheet to become amazingly compressed.  This extremely dense ice has all of the air squeezed out of it, sort of like snowflakes that have been mashed into the smallest possible space, and thereby lost all of the air bubbles in their crystalline matrix.  Ice without air in it, is naturally blue in color.  Less dense ice, however, has more air in it, and therefore reflects light differently, hence the lack of blue.  The blue can also be enhanced when there's a part of the iceberg that's just below the water... In some places, it looked exactly like a swimming pool.  Unheated, of course.  ;)

  Pleneau Iceberg


Icebergs near Cuverville Island

Page last updated: March 12, 1999

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