Icebergs in the Northern Hemisphere: FAQ

Source: The International Ice Patrol

Where do North Atlantic icebergs come from?


iceberg

The principal origin of those icebergs that reach the North Atlantic Ocean are the 100 or so major tidewater glaciers of West Greenland. Between 10,000 to 15,000 icebergs are calved each year, primarily from 20 major glaciers between the Jacobshaven and Humboldt Glaciers.

Glaciers are formed by thousands of years of snowfall accumulation which eventually is compressed into ice. It is estimated that these glaciers account for 85% of the icebergs which reach the Grand Banks of Newfoundland. Other sources of icebergs are the East Greenland glaciers, which produce about half the amount of icebergs as the West Greenland glaciers, but account for only 10% of the icebergs reaching the Grand Banks. The remaining 5% are thought to come from glaciers and ice shelves of northern Ellesmere Island.

What is the life cycle of an iceberg?

The life cycle of a typical iceberg found in the North Atlantic today might look something like this:

Time LineIceberg development
1,000 B.C.Snow/Firn
950 B.C.Ice/Glacier
Glacier movement
1993 A.D.Calving
1996 A.D.Iceberg melt

Snow falls on the ice cap of Greenland. Then over the course of several months it changes into firn, which is basically a granular snow. Several decades later it is compressed into very dense ice by the weight of the firn and snow. Driven by the enormous weight of the ice cap above, the ice begins to flow seaward through openings in the fringe of the mountains (thinking of it like water leaking out of a cracked bowl may help). This force moves the rivers of ice known as glaciers up to sixty-five feet a day, eventually pushing the ice to Greenland's western coast.

At the glacier's terminus or end, huge slabs of ice are weakened and then broken by the action of the rising and falling tides. This process is called calving and results in an iceberg's birth. By the time these mountains of ice enter Baffin Bay they have seen nearly 3,000 years pass.

In order for an iceberg to reach the North Atlantic the currents typically take it from Baffin Bay through the Davis Strait and Labrador Sea. This is a long trip and most icebergs never make it. Most icebergs melt well before entering the Atlantic Ocean. One estimate is that of the 15,000 to 30,000 icebergs produced annually by the glaciers of Greenland only one percent (150 to 300) ever make it to the Atlantic Ocean. When an iceberg does happen to reach the Atlantic its long and traveled life quickly comes to an end melting rapidly in the warm waters.

What are the sizes and shapes of icebergs?

Iceberg size classification
Size categoryHeight (ft.)Height (m)Length (ft.)Length (m)
Growlerless than 3less than 1Less than 16less than 5
Bergy Bit3–131–415–465–14
Small14–505–1547–20015–60
Medium51–15016–45201–40061–122
Large151–24046–75401–670123–213
Very LargeOver 240Over 75Over 670Over 213
Iceberg shape classification
Shape categoryDescription
TabularSteep sides with flat top. Very solid. Length-height ratio less than 5:1
Non-TabularThis category covers all icebergs that are not tabular-shaped as described above. This includes bergs that are dome-shaped, sloping, blocky, and pinnacle.

Iceberg Shapes

Tabular: A flat-topped iceberg. Most show horizontal banding.

Blocky: A flat-topped iceberg with steep vertical sides.

Drydocked: An iceberg which is eroded and a U-shaped slot is formed. Pinnacled: An iceberg with a central spire, with one or more spires.

Wedged: An iceberg which is flat on top and with steep vertical sides on one end and sloping on the other.

What are the most dangerous icebergs?

All icebergs are dangerous to shipping but depending on size, shape, and location some icebergs can be more troublesome than others. Obviously, icebergs nearest the Atlantic shipping lanes are of greatest concern to mariners. Large icebergs, because of their great mass, can inflict the most damage on a ship. However, they are usually easy to detect on a ship's radar and therefore can be avoided.

On the other hand, the smaller an iceberg, the harder it is for ships to detect and avoid. For example, many growlers or bergy bits are mostly submerged and are about the size a small vessel. These "hidden" icebergs can cause a significant amount of damage.

Lastly, an iceberg's shape is a factor. A smoothed iceberg can be more difficult to detect.

What is the typical size of an iceberg in the North Atlantic Ocean?

Size distribution of icebergs in the
IIP operation area for
1994 ice season
Size category% of total
Growler5.6%
Small15.3%
Medium15.3%
Large12.5%
Very Large2.8%
General (Size Unknown)48.5%

What is the largest iceberg ever recorded?

The largest icebergs (also referred to as ice islands) originate from the vast ice shelves surrounding Antarctica. The largest-known iceberg was from this region. It was roughly the size of the state of Rhode Island.

The tallest known iceberg in the North Atlantic was 550 feet high. Extending out of the water to almost the height of the Washington Monument, it is the tallest iceberg recorded to date.

Besides the North Atlantic, where else might icebergs be found?

Icebergs are also commonly found around the ice shelves of Antarctica and a very small number of icebergs calve into the ocean in Alaska and in Siberia or south of Franz Joseph Land in the Barents Sea.

How much of an iceberg is below the water?

About 7/8ths of an iceberg is below the water line. This figure is approximate. Although icebergs are similar, not all are the same. Varying factors are iceberg density, water density etc. Due to irregular iceberg shapes, icebergs may have varying heights out of the water.

How large was the iceberg that sank the Titanic?

The exact size of the iceberg will probably never be known, but according to early newspaper reports the height and length of the iceberg was approximated at 50 to 100 feet high and 200 to 400 feet long.

Where did the RMS Titanic actually hit the iceberg?

The RMS Titanic hit an iceberg on the evening of 14 April, 1912, and sank early in the morning of 15 April, 1912. Titanic's CQD or SOS (distress call) position was 41-56 degrees North and 50-14 degrees West. Titanic's final resting position, over 2000 meters below the surface of the North Atlantic Ocean, is 41-44 degrees North and 49-56 degrees West.

In 1912, navigation at sea could be very imprecise. Obviously, today we have satellite navigation. Back then they used celestial navigation and dead reckoning. The night they struck the berg, there was no moon. In order to accurately compute your position using the stars or the moon, you need to be able to see the horizon through a sextant. Captain Smith may have tried to do this, but he would have been guessing as to the exact sighting of the horizon.

He may have just used what is called the dead reckoned position. Their last accurate fix was probably at twilight when a distinct horizon is available and the stars were visible (we know the sky was clear that night). That means they had to rely on their recordings of ship course and speed to compute their position from their last accurate position (which was probably 5 hours old).

What Captain Smith probably did was use a combination of the two methods. He probably split the difference between a celestial fix and a dead reckoned position. This is only conjecture.

See also Titanic Facts.


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