Stories

Icebergs

By Dr. Stephen E. Bruneau Ph.D., P.Eng

Where do icebergs come from?

A majority of the icebergs in the North Atlantic come from about 100 iceberg producing glaciers along the Greenland coast while a few originate in the Eastern Canadian Arctic Islands. The glaciers of western Greenland, where 90% of Newfoundland's icebergs originate, are amongst the fastest moving in the world, up to 7 km per year. The icebergs we see off Newfoundland are carried south in the cold Labrador current.

How many icebergs are there?

Approximately 40,000 medium to large sized icebergs calve annually in Greenland and about 1 to 2% (400-800) of those make it as far south as 48o north latitude (St. John's). The numbers vary greatly from year to year and seasonally as most are seen off Newfoundland in the spring and early summer.

How old are icebergs?

The icebergs that reach the east coast of Newfoundland probably calved from a glacier more than a year before. They often spend a year or more in cold arctic bays melting slowly (or not at all in winter) until eventually passing through the Davis Strait and into the Labrador current. Rarely do icebergs last more than one year south of this point. The glacial ice that icebergs are made of may be more that 15,000 years old!

How do icebergs form?

Glaciers form on land as a result of a net accumulation of snow over thousands of years. Successive layers compress earlier accumulations until, at depths below 60 to 70 meters, glacial ice is formed. Glaciers "flow" or "creep" outward under their own weight like a viscous fluid. When the edge of a glacier advances into the ocean the pieces that break off are what we call icebergs.

How fast do icebergs move?

The average drift speed of icebergs off the north east coast of Newfoundland is around 0.2 m/s (0.7km/h). Iceberg drift speed is actually influenced by many factors including iceberg size and shape, currents, waves and wind. Speeds greater than 1 m/s (3.6 km/h) have been observed, as have stationary non-grounded bergs. Icebergs often take quite eccentric paths so that the distance travelled by a berg may be two or three times the straight line distance over a week or so.

Where do icebergs go?

Before some icebergs completely deteriorate they may travel many thousands of kilometers. Originating at around 75o north latitude in Baffin Bay, an iceberg may travel up to 4,000 km south to around 40° north latitude (800 km south of St. John's). Extremely unusual sightings in Bermuda and Ireland have occurred well outside of this normal limit.

Why are icebergs mostly white?

Icebergs are mostly white because the ice is full of tiny air bubbles. The bubble surfaces reflect white light giving the iceberg an overall white appearance. Ice that is bubble free has a blue tint which is due to the same light phenomenon that tints the sky.

What causes streaks and colours in icebergs?

The blueish streaks of clear, bubble free ice often seen in icebergs results from the refreezing of meltwater which fills crevasses formed in the glacier as it creeps over land. The ice is blue because of the natural light scattering characteristics of pure ice. Occasionally airborne dust or dirt eroded from land ends up on the glacier surface eventually forming a noticeably darkened brown or black layer (in any orientation) within the ice of a floating iceberg.

How much of an iceberg is below water?

The "tip of the iceberg" expression can be explained as follows: Icebergs float because the density of ice (around 900 kg per cubic meter) is lower than that of seawater (around 1025 kg per cubic meter). The ratio of these densities tells us that 7/8 of the iceberg's mass must be below water. Usually icebergs are 20% to 30% longer under the water than above and not quite as deep as they are long at the waterline.

How do icebergs break up?

Simply put, icebergs melt. In the process they often calve and fracture into many pieces which can create trails or halos of smaller floating pieces. Usually icebergs melt the fastest at the waterline by the action of waves . The Waterline "notch" which forms induces calving of overhanging and submerged blocks. Melt and breakup rates change with water and at temperature. For instance a large berg may take 90 days to fully deteriorate in water temperatures around 0o whereas the same berg may only last 11 days in 10o water.

How much do icebergs weigh?

Icebergs off the coast of Newfoundland and Labrador range in size from massive tabular and blocky bergs in excess of several million tonnes to small bergs weighing 1% of this. Categories of iceberg sizes which are used for recording iceberg statistics range from very large (greater than 10 million tonnes and hundreds of meters long) to large, medium and small bergs and on to bergy bits then growlers, which are grand piano size pieces. Note that the average iceberg weight for the Grand Banks area is one to two hundred thousand tonnes, and is about the size of a cubic 15 storey building.

How cold are icebergs?

The interior temperature of icebergs off the coast of Newfoundland and Labrador is in the range of -15o to -20o C. Only at the surface does the temperature increase to 0o C (the melting point). Oddly, icebergs in warm water appear colder than those in cold water because the fast melting steepens the internal temperature gradient exposing the cold interior.

What shapes do icebergs come in?

A fantastic variety of shapes result from the deterioration process of icebergs. Despite the fact that no two icebergs are the same, there are certain categories of shapes that are used for iceberg observation. Often the terms; tabular, blocky, wedge, dome, pinnacle, and drydock are used.

What should I watch for when looking at an iceberg?

For those who wish to look beyond the beauty of icebergs there are many things to look for which can make iceberg watching more interesting. Besides estimating the iceberg's size and shape there are many features which may be noted. Coloured streaks, caves and tunnels, old and new waterline notches, even objects such as boulders or birds are seen on icebergs. Even more spectacular is the occasion of an iceberg calving and rolling which can often be heard from a good distance. An observers checklist is included with this website.

How close can you get to an iceberg?

It is dangerous to approach an iceberg because it can calve or roll creating a huge disturbance in the water which can upset a boat. There is no rule for safe space because certain icebergs may have long underwater rams which pose an even greater threat to an unwary vessel. Usually a minimum distance of the iceberg length should be kept though at this distance safety cannot be guaranteed. It is even more dangerous to attempt to get on an iceberg. Falling ice is a threat and a rolling berg can dump you in the very cold water before collapsing over on top of you.

Can you tow an iceberg?

Towing icebergs was first demonstrated in 1971 in Newfoundland. It is now a common practice in the management of icebergs for the offshore oil industry. Towing may not be the best term however, as often massive icebergs are merely deflected slightly from their paths. The tow is arranged by a vessel navigating around a berg while paying out a floating tow line. A junction is made so that the berg is lasooed and then tow tension is applied carefully to avoid rolling the berg or pulling the line over the top.

What is the largest iceberg recorded?

The largest Northern Hemisphere iceberg on record was encountered near Baffin Island in 1882. It was 13 km long, 6 km wide and had a freeboard (height above water) of about 20 m. The mass of that iceberg was in excess of 9 billion tonnes - enough water for everyone, in the world to drink a litre a day for over 4 years. Despite this staggering statistic, icebergs from Antarctica may be many times larger than this. In 1987 an iceberg with an area of 6350 square kilometers broke from the Ross ice shelf. That berg had a mass of around 1.4 trillion tonnes and could have supplied everyone in the world with 240 tonnes of pure drinking water.

How pure is iceberg ice?

Since glacier ice is formed from falling snow and snow results from condensed water vapor in the atmosphere, the water from icebergs is quite pure. Sometimes airborne dust from volcanic eruptions or from the wind (thousands of years ago) is deposited on the surface of a glacier and gradually becomes trapped within the ice so that traces are found in icebergs. But there are not likely to be many pollutants!

Are icebergs unstable?

Often icebergs are very unstable. The highly random shape and non-uniform melting and breakup of an iceberg leads to frequent shifts in orientation. Tabular bergs are generally the most stable whereas domed and wedge shaped bergs may roll completely over in seconds without any apparent provocation.

How hard is iceberg ice?

The crushing strength of ice is around 1% that of steel or 10% that of concrete. Though this may not sound very hard, a ship collision with an iceberg would surely end in disaster. The enormous momentum involved and potentially huge contact area with the ice can generate hundreds of tonnes of force on the hull which would cause it to dent and crumple.

Do icebergs hit the bottom?

Yes. Icebergs often "ground" or contact the seabed and get stuck. This is a frequent occurrence along the coast where icebergs are brought into shore by irregular tidal currents or strong winds. Sometimes icebergs "scour" the seabed creating irregular troughs that may be several kilometers in length. The edges of the Grand Banks are criss-crossed with old and new iceberg scour marks.

Are icebergs salty?

No. Icebergs are comprised of pure fresh water. There may be some dust embedded in the ice and salt water may be on the surface but it does not penetrate the ice. Iceberg ice is quite safe to consume.

Does iceberg ice last longer than fresh ice?

In short, the answer is no. When a piece of iceberg ice and a piece of freshwater ice are the same size, shape and temperature they will melt at around the some rate. A small experiment in which this was demonstrated actually showed that a block of tap water ice outlasted a similar iceberg ice block by 10 minutes over 30 hours.