Integrated Emergency Management System
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ICE AND ICEBERGS Norm Catto Memorial University of Newfoundland, St. John’s, NL, Canada
Definition An iceberg is a floating mass of ice. Discussion Ice poses hazards to mariners in three ways: as floating sea ice, icebergs, and riming. Floating ice and icebergs continue to pose hazards, despite advances in meteorological and ice forecasting, radar, and communication. Since the sinking of Titanic in 1912, more than 500 ice–ship collisions have occurred in the North Atlantic. Worldwide, 5–10 collisions occur annually. Sea ice Floating sea ice poses a hazard to ship traffic in several shipping lanes, including the North Atlantic, Arctic, and Southern Oceans. Sea ice is composed of freshwater, formed from surface freezing in coastal areas and embayments, ice lifted by waves and tides from beaches, and pieces which break off (calve) from glaciers and ice shelves that reach tidewater. Sea ice gradually accumulates throughout the winter. Although some areas of the Arctic and Antarctic support multiyear ice, which have survived the previous summer, ice which poses a hazard to mariners is dominantly single-year. The hazard is thus at its greatest from midwinter towards the end of winter and early spring, where the maximum amount of ice has accumulated and has moved toward the shipping lanes. Sea ice transported by currents flowing toward the Equator, notably the Labrador Current off eastern Canada, may extend more than 1,000 km seaward. In this area,
the maximum southern extent typically is reached in early March, with ice extending to 44 N. Sea ice in this area may require the services of icebreakers to keep shipping lanes clear. Sea ice typically recedes from the northern tip of Labrador, Cape Chidley, in early July, opening Hudson Strait for navigation by vessels plying the Churchill (Manitoba, Canada)–Europe grain shipping route. The autumn sea ice expands southward to close off Hudson Strait to navigation in September. For northern and Arctic coastal communities, the development of sea ice is critical for winter transportation and subsistence hunting. Unexpected variations in ice thickness, or breakup due to strong wave action, can pose hazards for travelers. Climate warming has resulted in inconsistencies in the timing, persistence, and thickness of sea ice in many Arctic areas. Open leads (polyna; ashkui) present in coastal areas can also pose hazards for travelers, although they are also suitable areas for harvesting fish and marine mammals.
Icebergs Icebergs are composed of freshwater generated from calving of glaciers, which reach tidewater in the Arctic and Antarctic, in addition to isolated glaciers in mountainous coastal areas. Icebergs are concentrated by the major ocean surface currents. In southernmost Davis Strait, one of the major areas of iceberg concentration, iceberg numbers have varied between 1,800 and 2,000 annually since 1990. Traveling with velocities of 1–4 km/h, icebergs can persist for several years from the point of calving, and reach latitudes of 40 N or S. However, icebergs melt rapidly
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