The Many Guises of Ice

If you thought that ice was a fairly straightforward substance, and chiefly of use for cooling a gin and tonic, then Antarctica will be a revelation. You quickly realize that it comes in an astonishing array of shapes and sizes. These are the most common you will encounter:

• Brash ice refers to accumulations of floating fragments not more than six feet across.
• Fast ice gathers at the edges of the continent, remains stationary for several years and can attain thicknesses of several yards.
• Frazil ice is created by ice crystals that have been agitated by wave motion. It looks like slush and has a depth of up to 10 feet.
• Grease ice forms in open water by accumulating ice crystals. It looks like an oil slick and has a sheen and low reflectivity that provide its name.
• Pack ice is made up of thin plates of ice that form around the continent in winter, so named by the explorer Captain James Cook in 1774.
• Pancake ice is roughly circular pieces of floating ice formed by accretions of brash and/or frazil ice.

Icebergs are formed when pieces break off from the Antarctic ice sheet, ice shelves or glaciers. Any piece of ice that rises 15 feet or more above the surface of the ocean is classified as an iceberg. Pieces that rise between five and 15 feet are called bergy bits; those less than five feet and more than one foot are called growlers. There are two principal types of iceberg: tabular, so named for their flat, table-like tops — the largest calved off the Ross Ice Shelf in 2000 and measured 185 by 23 miles — and non-tabular, which come in irregular shapes. When the latter become top-heavy from their immersed portions melting away, they flip over, revealing fantastic ice sculptures.