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Icebergs can tell a story of their life so far.
The colour of the ice, the degree of whiteness or blueness
gives an indication of how much air there was in the layer of
snow that has that colour when the snow fell on the glacier
that the iceberg was calved from. The whiter they are the more
air, the bluer, the less air.
The direction of these
thin dark lines however show that they were not laid down as
snowfall. Their dark blue colour shows that the water they are
frozen from contained no air - i.e. that it was actually liquid
water.
So what is the story behind this? As glaciers
flow over the underlying rock they sometimes go over a bump
which causes a crevasse to form, a crack from the bottom of
the glacier to the top. During the summer there can be be some
significant melting of the glacier causing water to flow down
crevasses and other cracks or simply to fill them with water.
The water then freezes and the glacier continues on to the end
with the evidence of the water-filled crack literally frozen
in time.
Picture copyright Paul Ward 2009.
Pentax digital equipment.
