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How do icebergs lose their salt?
Category: Earth Science
Published: August 14, 2013
By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and physics professor at West Texas A&M University
Icebergs do not have any salt to begin with. Icebergs are not pieces of frozen ocean water. Rather, icebergs are frozen chunks of fresh water that began their life on land. It all starts when snow falls in a region of land that is too cold for the snow to melt. Over time, the non-salty snow builds up on the ground. Without temperatures warm enough to melt the snow, it piles up so high that it starts to crush under its own weight. The crushing force of gravity fuses the non-salty snow crystals into a giant slab of non-salty ice known as a glacier. This process is very slow and takes a long time. Gravity not only pulls the snow down into the ice, it also pulls the ice downhill. Often "downhill" means "towards the ocean". Very slowly, the giant slab of ice slides downhill to the ocean. Once it reaches the ocean, it just keeps going like a train with no brakes. A glacier is so big that just the very edge of it slides out over the ocean. Because ice floats on water, the edge of a glacier has no problem just sitting there, floating on the ocean.
But eventually, the glacier slides too far out over the ocean, stretches from the movement, and cracks on the edges. Warm temperatures can also speed up the cracking process. Once the crack is deep enough, pieces of the glacier break away and drift out into the open ocean. A new iceberg is born. Note that this explanation may make it sound like a one time event. In reality, each glacier is continually forming, flowing, and cracking. One end of a glacier up in the mountains is forming from the new snow, while at the same time, the other end is cracking over the ocean and making icebergs. Because the glacier is very deep, the iceberg chunks that break off are very tall. The word "iceberg" literally means "ice mountain" in Germanic languages, signifying their height. In contrast, frozen ocean water forms thin flat sheets called pack ice. In summary, non-salty snow turns into non-salty glacier ice on land, which breaks into non-salty icebergs over the ocean.