Icebergs are not frozen sea water. They form when the edge of a glacier reaches the sea and the ice breaks off in huge chunks and floats away.

Glacial ice is made up of snow that has fallen over thousands of years. The stripes and different colored layers in the ice (that become more apparent when it is split into icebergs) represent different periods of snowfall.

The layers can tell us about the weather conditions under which the snow fell.

If it was very cold, then a light open layer of snow would fall, trapping air within the ice crystals. This creates a paler or white layer.

The darker, bluer layers come from snow that fell in relatively warm (maybe even wet) conditions, when little or no air was trapped in the snow.

The weight of the snow build-up turns the snow in the lower layers to ice, both compressing the layers and the air trapped within them. When the ice enters the water as an iceberg, this air is released as the berg melts - often creating popping or hissing sounds.

PICTURE: Ice layers in an iceberg that is frozen in sea ice. Yes, that little spot at the bottom is a person, and keep in mind that about 85% of that berg is below the waterline!