Amazing Striped Icebergs - University of Missouri–St：惊人的条纹冰山-密苏里堪萨斯大学–ST. ….ppt

Icebergs: General Information ? An iceberg is a large piece of ice from freshwater that has broken off from a snow- formed glacier or ice shelf and is floating in open water. It may subsequently e frozen into pack ice. Alternatively, it may come to rest on the seabed in shallower water, causing ice scour (also known as ice gouging) or ing an ice island . Icebergs Cont. ? Because the density of pure ice is about 920 kg/m 3 , and that of sea water about 1025 kg/m 3 , typically only one-tenth of the volume of an iceberg is above water. The shape of the underwater portion can be difficult to judge by looking at the portion above the surface. This has led to the expression "tip of the iceberg", for a problem or difficulty that is only a small manifestation of a larger problem. Most of the iceberg is under water. How Big is Big ? Though usually confined by winds and currents to move close to the coast, the largest icebergs recorded have been calved, or broken off, from the Ross Ice Shelf of Antarctica. Iceberg B-15, photographed by satellite in 2000, measured 295 km long and 37 km wide (183-23 mi), with a surface area of 11,000 km 2 (4,250 mi 2 ). The mass was estimated around three billion tons. B-parison ? Rhode Island: – Area 1,545 sq. mi. – Length: 48 miles – Width: 37 miles ? B-15: – Surface area 4,250 sq. mi. – Length: 183 miles – Width: 23 miles ? Comparison: – B-15 was almost three times the size (surface area) of Rhode Island. Amazing Striped Icebergs ? the photographs were taken by Norwegian sailor Oyvind Tangen from aboard a research vessel. The iceberg photographs were snapped in an area several hundred miles north of the Antarctic. As the message explains, blue stripes are formed as iceberg layers melt and refreeze quickly, while green stripes are created by the freezing of algae-rich sea water. Other colored stripes, such as black, brown and yellow, were created by sediment collected by the ice as it moved down a hillsi