Some interesting icebergs facts from the book of Dr. Stephen Bruneau, Icebergs of Newfoundland and Labrador, available from Flanker Press.
- The 90% of icebergs seen off Newfoundland and Labrador come from the
glaciers of western Greenland. The rest come from glaciers on islands in
Canada’s Arctic area.
- Icebergs are edges of glaciers that have broken off and slipped into the ocean. Glaciers form on land by snow building up over thousands of years. Each layer of snow compresses those below until 60 to 70 metres down, glacial ice forms. Glaciers then “flow“ or “creep“ towards the ocean under their own weight, and eventually slip into the ocean. The glaciers of western Greenland flow at speeds of up to seven kilometres a year, among the fastest moving in the world. After slipping into the ocean, the bergs float in frosty Arctic bays melting slowly, if at all, until passing through the Davis Strait and into the Labrador Current which carries them south into Iceberg Alley. Once they head south, they rarely last more than one year.
- Every year about 40,000 medium – to large-sized icebergs break off, or calve, from Greenland glaciers. Only about 400-800 make it as far south as St. John’s, but these numbers can vary greatly from year to year. The chances of seeing icebergs in a particular area depend on the number of bergs, wind direction, ocean currents and temperatures, and the amount of sea ice, or pack ice. Sea ice protects icebergs from the battering of waves and helps them last longer. Years of little sea ice cover are often years of few icebergs along Newfoundland’s coast. Also, there may be areas where you can’t see any, but 100 kilometres up the coast there might be dozens, so be prepared to travel around. And remember that icebergs are constantly on the move.
- As glaciers creep over land, meltwater fills crevasses and later freezes, creating clear, bubble-free ice. This shows up as bluish streaks in icebergs because of the light scattering characteristics of pure ice. Sometimes airborne dust from volcanic eruptions, or the wind, falls on a glacier and becomes trapped inside, forming a noticeably darkened brown or black layer. But because most volcanoes are south of glaciers and winds from the south rarely mix with Arctic air masses, there are very few pollutants in the ice.
- Icebergs don’t have a consistent speed. There are many factors that contribute to the speed of an iceberg, like size, shape, ocean currents, waves, and wind. These forces also contribute to the berg’s irregular path, which is equal to two to three times the distance it would travel if it were heading in a straight line. The average drift speed is around 0.7 km/h, although speeds greater than 3.6 km/h have been recorded.
Almost 90% of an iceberg is underwater, hence the phrase “tip of the iceberg.” Its maximum width under water is 20-30% larger than you can see at the surface. The average depth, or draught of an iceberg, is slightly less than its apparent length above water.
- Icebergs can vary greatly in size, ranging from very large – greater than 10 million tonnes and hundreds of metres long – to large, medium, and small bergs. The smallest are termed “bergy bits,” which are the size of a small house, and “growlers,” which are the size of a grand piano. These smaller pieces are hazardous to ships because radar may not pick them up as they bob up and down among the waves. The average weight for a Grand Banks-area iceberg is 100,000-200,000 tonnes – about the size of a cubic 15-storey building.
- In the Northern Hemisphere, the largest iceberg on record was encountered in 1882 near Baffin Island. It was 13 km long, 6 km wide, and was about 20 m above water. It weighed over 9 billion tonnes – enough for everyone in the world to drink a litre of water a day for more than 4 years. Icebergs from Antarctica can be many times larger. In 1987 an iceberg, with an area of 6,350 sq. km, calved from the Ross Ice Shelf. It weighed about 1.4 trillion tonnes and could have provided everyone in the world with 240 tonnes of pure drinking water.
- It’s about 10% as strong as concrete. This may not seem very hard, but it’s a lot harder than ice you make in your freezer. A ship colliding with an iceberg almost certainly means disaster due to the enormous momentum involved and potentially massive contact region. The ice can literally generate hundreds of tonnes of force on a ship’s hull, causing it to buckle, dent, crumple, and even tear apart.
- Icebergs often “ground“ or reach the seabed and get stuck. This happens when fluctuating tidal currents or strong winds bring icebergs close to shore or onto shallow areas like reefs. At times, icebergs “scour“ the ocean floor, creating irregular troughs that can be several kilometres long and up to half a metre deep. The famous Grand Banks fishing grounds, off Newfoundland’s south coast, have been crisscrossed with these marks for many years.