Monday, January 26, 2009

Photos of the Day

From last year's Daily Mail (U.K.):

source of all: March 18, 2008, Daily Mail

According to the Daily Mail:
These stunning banded icebergs -- formed over hundreds, if not thousands, of years -- were pictured floating in the waters of the Antarctic.

Some of the stripes formed when layers of the iceberg melted and refroze.

Others were created from the dust and soil picked up when the ice sheet that gave birth to the iceberg was sliding down an Antarctic hillside. . .

Most of those in the Antarctic were formed from snow falling on the giant ice sheet that covers the continent.

Over time, the snow is compressed to form more ice, which slides slowly towards the sea.

There it either breaks off into the water, or forms an ice shelf.

Most appear white as a result of the tiny bubbles trapped within them which scatter light in every direction.

However, if the bubbles are squeezed out, or if part of the iceberg melts and quickly refreezes, it can appear blue.

Blue stripes are often created when a crevice in the ice sheet fills up with meltwater and freezes so quickly that no bubbles form.

When an iceberg falls into the sea, a layer of salty seawater can freeze to the underside. If this is rich in algae, it can form a green stripe.

Brown, black and yellow lines are caused by sediment, picked up when the ice sheet grinds downhill towards the sea.
The London Times added:
Keith Makinson, of the British Antarctic Survey, said that icebergs that seemed to show stripes were quite common in southern waters, but it was the first time that he had seen brown stripes. They are believed to be created when ice crystals form under the water and, in a process described as “inverted snow”, rise to stick to the bottom of the ice shelf. As the ice crystals form a new layer at the bottom of the ice shelf, which later fragments to float away as icebergs, tiny particles of organic matter are trapped.

Parts of dead marine creatures such as krill form much of the trapped material and have the effect of creating coloured stripes, mainly blues and greens, in icebergs. Dr Makinson said that the brown stripes in this example were likely to have been formed from sediment washing underneath the ice shelf.
Other related photos here.

(via reader OBH, Snopes)

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