Below are some interesting answers to many frequently asked questions on icebergs.
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While most of the icebergs found in the North Atlantic come from the glaciers along the coast of Greenland, a handful begin in the eastern Canadian Arctic Islands. However, it is from the glaciers of western Greenland where 90% of Newfoundland's icebergs come from, and with speeds of up to 7 km a year, these are amongst the fastest moving in the world. The icebergs that we see off the coast of Newfoundland are carried south in the cold Labrador current. Most find their way down through Iceberg Alley.
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Every year, roughly 40,000 medium to large sized icebergs break off, or calve, from Greenland glaciers. Of these, around 400 to 800 make it as far south as St. John's, Newfoundland and Labrador. However, these numbers vary greatly both seasonally and year to year. Off the coast of Newfoundland, the majority are seen in the spring and early summer.
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The icebergs that pass by the east coast of Newfoundland have usually calved from a glacier about a year or more before you spot them. They usually spend the year in frosty arctic bays melting slowly, if at all, until slipping through the Davis Strait and into the Labrador current. Unfortunately, once they head south, they rarely last more than one year. However, this does not mean that icebergs are roughly a year old – one must take into consideration the fact that the glacial ice that icebergs are made of may be more than 10,000 years old!
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Icebergs are edges of a glacier that have broken off and slipped into the ocean. Glaciers form on land as an effect of snow building up over thousands of years. Each layer compresses the later until, 60 to 70 meters down, glacial ice is formed. Similar to the flow of a thick liquid, glaciers then "flow" or "creep" towards the ocean under their own weight, and eventually slip in.
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Off the northeast coast of Newfoundland, the average drift speed of an iceberg is around 0.2 m/s (0.7 kph). Icebergs do not have a consistent speed, but rather are influenced by a variety of factors including the size and shape of the iceberg, ocean currents, waves, and wind, just to name a few. Speeds greater than 1 m/s (3.6 kph) have been recorded, as have fixed non-grounded bergs. Due to these factors, icebergs often take unconventional and irregular paths. Therefore the distance travelled by a berg may be two or three times the straight line distance over a week or so.
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Before icebergs deteriorate completely, some may have traveled several thousands of kilometres. Originating in Baffin Bay, an iceberg may trek up to 4000 km south – ending up around 800 km south of St. John's. However, very rare sightings in Bermuda and Ireland have occurred.
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Due to the tiny air bubbles contained within the ice, icebergs are mainly white. The surface of the bubble reflects white light, thus giving the iceberg an overall white appearance. Ice that is bubble-free has a blue tint. This is the same lighting effect that tints the sky.
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As the glacier crept over land, meltwater filled the crevasses. This water later froze and created clear, bubble free ice, and the illusion of bluish streaks through the iceberg. Why blue? Because of the natural light scattering characteristics of pure ice. Occasionally, airborne dust and dirt land on the glacier surface forming a noticeably darkened brown or black layer within the ice.
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Icebergs float because the density of ice is approximately 900 kilograms per cubic meter, which is lower than that of seawater (around 1025 kilograms per cubic meter). The relation of these densities tells us that 7/8 of the iceberg's bulk should be below water. Generally, icebergs protrude underwater, meaning that they are 20 to 30% longer than they appear from the surface. Also, the average depth, or draught of an iceberg is slightly less than its apparent length above water. Knowing this, the "tip of the iceberg" expression can be easily explained.
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Basically, icebergs melt. During that process, they often calve and fracture into multiple pieces, creating trails or halos of smaller floating ice pieces. Due to the action of the waves, icebergs usually melt the quickest at the waterline. The waterline "notch" that forms induces the calving of overhanging and submerged blocks. Of course, the melt and breakup rates change with water and air temperature. For example, a large iceberg may last 90 days in water temperatures around 0°C, whereas the same berg may only last 11 days in 10°C water!
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From immense tabular and blocky bergs over several million tonnes to small bergs weighing 1% of this, icebergs off the coast of Newfoundland and Labrador can vary greatly in size. For recording iceberg statistics, categories of iceberg sizes range from very large – greater than 10 million tonnes and hundreds of meters long – to large, medium and small bergs. They can be further broken down into "bergy bits" and "growlers", which are the size of a grand piano. Just to give you an idea of the icebergs in our area, the average weight for the Grand Banks area is one to two hundred thousand tonnes (about the size of a cubic 15 storey building).
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Growler
Height: ~1 meter
Width: <5 meters |
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Bergy Bit
Height: 1-4 meters
Width: 5-15 meters |
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Small
Height: 5-15 meters
Width: 15-60 meters |
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Medium
Height: 16-45 meters
Width: 60-120 meters |
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Large
Height: 46-75 meters
Width: 120-220 meters |
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X-Large
Height: >75 meters
Width: >220 meters |
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Icebergs found off the coast of Newfoundland and Labrador have an interior temperature of approximately -15° to -20°C. Only at the surface does the temperature increase to 0°C, which is the melting point of water. Strangely, icebergs in warm water appear colder than those in cold water due to the fact that the exterior melts at a quicker rate, therby exposing the colder interior.
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A vast array of shapes result from the melting and breaking of icebergs. Despite the fact that no two icebergs are exactly the same, there are certain categories of shapes that are used for observation, along with the terms tabular, blocky, wedge, dome, pinnacle, and drydock.
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Tabular |
A flat-topped iceberg with a width five times greater than its height. Most have some horizontal banding. |
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Blocky |
A flat-topped iceberg with steep sides. |
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Wedged |
A flat surfaced iceberg with steep surfaces on one side and gradually sloping on the other, thus forming a wedge. |
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Dome |
An iceberg that is smooth with a rounded top. |
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Pinnacle |
An iceberg with at least one main spiral or pyramid on it. |
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Dry Dock |
An iceberg with a U-shaped slot at or near water level, and at least two pinnacles or columns. |
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Aside from an iceberg’s shape and size, there are many other features which can be noted. Colour streaks, caves and tunnels, waterline notches, and even objects such as large rocks and seabirds may be spotted on an iceberg. If you pay attention, you may notice an iceberg about to calve or roll, which is a spectacular event both to witness and hear.
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Since it is possible for an iceberg to calve or roll at any time, it is extremely dangerous to approach an iceberg at any distance. The calving or rolling creates a huge disturbance in the water, which can easily upset a boat, especially a smaller one. There is no “rule-of-thumb” for a safe distance as icebergs have varying shapes, and may have long underwater rams which pose a threat to all vessels. Generally, a minimum distance of the iceberg length should be kept, though safety can never be guaranteed. Furthermore, any attempt to explore an iceberg is extremely dangerous. Due to their instability, falling ice or a rolling berg could throw you into the frigid water before collapsing on top of you.
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Iceberg towing was first demonstrated in Newfoundland in 1971. It is now a regular practice in the offshore oil industry for iceberg management. However, towing an iceberg may not be the best term as huge icebergs are often only slightly moved from their original paths. The tow is arranged by a vessel navigating around a berg while laying out a floating tow line. A junction is made so that the berg is lassoed, and then tow tension is slowly and carefully applied to avoid any chance of rolling the berg or pulling the line over the top.
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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. The weight of the iceberg was over 9 billion tonnes - enough for everyone in the world to drink a litre of water a day for more than 4 years. Even though this is an astounding statistic, icebergs from Antarctica may be many times larger than this. Take, for example, in 1987 when an iceberg with an area of 6350 square kilometres calved from the Ross ice shelf. That berg had a weight of roughly 1.4 trillion tonnes and could have provided everyone in the world with 240 tonnes of pure drinking water.
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The water from icebergs is actually quite pure, since glacier ice is created from falling snow, and snow results from condensed water vapour in the environment. Sometimes airborne dust from volcanic eruptions or from the wind is deposited on the surface of a glacier. Over thousands of years the dust slowly becomes trapped inside the ice, leaving traces buried inside. However, due to the location of the glaciers, you will not find many pollutants in the ice or meltwater!
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Icebergs are often very unstable. The random shape combined with the varying degrees of melting and breakup leads to regular shifts in orientation. Generally, the most stable icebergs are tabular, while domed and wedge shaped bergs may roll completely over in seconds without any evident reason.
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The crushing strength of ice is around 1% that of steel or 10% that of concrete. Although this may not seem very hard, a ship colliding with an iceberg almost certainly ends in disaster, due to the enormous momentum involved and potentially massive contact region. The ice can literally generate hundreds of tonnes of force on a ships hull, which can cause it to buckle, dent, crumple, and even tear apart.
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Yes, icebergs often "ground" or reach the seabed and get stuck. This is a normal occurrence along the coast where icebergs are brought closer to shore by fluctuating tidal currents or strong winds. At times, icebergs "scour" the ocean floor, creating irregular troughs that can be several kilometres in length and up to half a meter deep. The Grand Banks are criss-crossed with iceberg scour marks, both recent and decades old.
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Icebergs are created from pure fresh water and snow, so they are not salty. There may be some dust found within the ice or salt water on the surface, but it will not go through the ice. Iceberg ice is completely safe to consume.
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Generally, iceberg ice does not last any longer than fresh ice. When the two pieces of ice are the same size, shape, and temperature, they will melt at approximately the same rate. However, a small experiment in which this was established actually showed that over 30 hours, a chunk of tap water ice can outlast a similar iceberg chunk by 10 minutes.
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Information above provided by Dr. Steven E. Bruneau
Illustrations for “The Size of Icebergs” and “Shapes of Icebergs” are courtesy of www.icebergfinder.com.
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Iceberg
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