Icebergs are huge chunks of ice which break off from glaciers in a process called calving. Most icebergs in the Northern Hemisphere break off from glaciers in Greenland, while icebergs in the Southern Hemisphere calve from Antarctica.
Drifting Chunk of Ice
After three decades of being grounded, the world's biggest iceberg starts to drift towards the equator. The block of ice, called A23a, is 1,312 feet (400 meters) thick and has an area of 1,540 square miles (3,989 square kilometers), more than twice the size of Greater London.
The tooth-shaped iceberg broke off from the Filchner Ice Shelf in August 1986 and grounded in the southern Weddell Sea in November 1991. There have been many large icebergs which detached from Antarctica and floated away, but A23a had only drifted a couple of hundred miles since the break off. Its lack of movement was due to being stuck on the seafloor which made it less vulnerable to fragmentation.
Remote sensing expert Dr. Andrew Fleming from the British Antarctic Survey first spotted the signs of movement from A23a back in 2020. He noted that A23a had been grounded since 1986, but it eventually decreased in size, allowing it to lose grip and start moving. Since then, it has been carried northwards by wind and ocean currents.
A satellite image taken on November 15 reveals that it is currently situated at the tip of the Antarctic Peninsula. It is expected to reach the Antarctic Circumpolar Current, a loop of ocean water which flows around the continent. It could get grounded again near the island of South Georgia located further north in the southern Atlantic Ocean.
Icebergs 'ground' on the ocean floor when their keel, the part a bit below the water's surface, is deeper than the water's depth. Once they break off from glaciers, they could reach the open ocean, where they are likely to break into smaller pieces due to rougher waters. Objects as big as this chunk of ice need to be constantly tracked since they can pose a threat to ships and wildlife.
Experts wonder if there were any changes in the temperature of shelf water which could have provoked the movement of the iceberg. They also fear that if A23a becomes grounded in South Georgia, it could disrupt the feeding routines of the creatures such as seals and seabirds. On the other hand, the ice chunk could melt and provide nutrients for organisms living at the bottom of the ocean.
What Causes Ice Calving?
The term "ice calving" covers the wide range of processes through which chunks of ice are discharged to the oceans from the margin of ice shelves. Also known as glacier calving, this process has been crucial in the mass loss of the world's ice sheets.
There are many suspected causes of ice calving. One of these is longitudinal stretching which controls the formation of crevasses or deep open cracks in glaciers. When crevasses penetrate the full thickness of ice, glacier calving may occur. Calving can also happen due to waterline melting, a process that undercuts the subaerial ice and leads to collapse.
Calving is a normal part of a glacier-fed ice shelf, even those that involve massive chunks. However, scientists believe that glaciers are set to retreat and calve more due to climate change. As the Earth's surface temperatures increase due to global warming, more icebergs are calving from melting ice caps. Ironically, global warming has sped up the formation of icebergs while also increasing the rate at which they melt into the sea.
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