Icebergs C19A

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An Iceberg is a floating mass of freshwater ice that has broken from the seaward end of a glacier or a polar ice sheet. Icebergs are typically found in open seas, especially around Greenland and Antarctica. 

 

They form mostly during the spring and summer, when warmer weather increases the rate of calving (separation) of icebergs at the boundaries of the Greenland and Antarctic ice sheets and smaller outlying
glaciers. In the Northern Hemisphere, for example, about 10,000 icebergs are produced each year from the West Greenland glaciers, and an average of 375 flow
south of Newfoundland into the North Atlantic shipping lanes, where they are a
hazard to navigation. 

Arctic icebergs vary in size from the size of a large piano, called growlers, to the dimensions of a 10-story building. Icebergs about the size of a small house are called bergy its. 

Many icebergs in the Arctic are about 45 meters tall and 180 meters long.

 

US
Coast Guard C130 airplane flying over a large iceberg

US Coast Guard International Ice Patrol Image

 Icebergs of the Antarctic not only are far more abundant but are of enormous dimensions compared with those in the Arctic. Ninety-three percent of the world's mass of icebergs is found surrounding the Antarctic.

Usually 1/8th of an iceberg is
above the waterline. That part consists of snow, which is not very compact. The
ice in the cold core is very compact (and thus relatively heavy) and keeps
7/8ths of the iceberg under water. The temperature in the core is constant:
between -15 and -20 degr. Centigrade. An iceberg that has tumbled over several
times, has lost is light snow layers and so the iceberg gets relatively heavier
then before (with the snow) and because of the greater compactness, only 1/10th
rises above the surface.

 

International Ice Patrol (IIP)
Frequently Asked Questions

Where do North Atlantic icebergs come from?

The principal origin of those icebergs that reach the North Atlantic Ocean are the 100 or so major tidewater glaciers of West Greenland. 

Map
from Worldatlas.com

Between 10,000 to 15,000 icebergs
are calved each year, primarily from 20 major glaciers between the Jacobshaven
and Humboldt Glaciers. Since icebergs originate from Glaciers, they are
composed of fresh water. As described in the other FAQs, 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:
1,000 B.C. Snow/Firn
950 B.C. Ice/Glacier
-- Glacier movement
1998 A.D. Calving
2001 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 that
have accumulated on top of it. Therefore, icebergs are composed of fresh water.
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. Once waterborne, icebergs are driven by strong subsurface currents, the core's of which a relocated at a depth of approximately fifty meters (This occurs because 7/8 of an icebergs mass rests below the waterline). Therefore, deeper currents have greater surface area to push against compared to winds or wind generated surface currents. This is why it is not uncommon to see icebergs heading directly into strong winds. 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. At most it will take two months to melt unlike icebergs stuck in parts of Baffin Bay where it can take upwards of four years for a berg to melt.

How many icebergs last long enough to reach the Atlantic shipping lanes (south of 48 N)?

The mean number of icebergs passing south of 48 N is 473 icebergs with a standard deviation of 492 icebergs. Therefore, yearly totals are highly variable and are subject to highly variable climatic factors

Where is iceberg alley?

The area we call "Iceberg Alley" is located about 250 miles east and southeast of the island of Newfoundland, Canada. Iceberg Alley is usually considered to be that portion of
the Labrador Current, that flows southward from Flemish Pass, along the eastern
edge of the Grand Banks of Newfoundland, to the Tail of the Banks. This area
extends approximately from 48 to 43 degrees North Latitude at 48 degrees West
longitude. Icebergs and sea ice flowing south from Iceberg Alley created the
Titanic disaster of 1912. This is the area of the ocean we patrol and monitor
most carefully.

What are the shapes and sizes of icebergs?

ICEBERG SHAPE CLASSIFICATION

TABULAR: An iceberg with steep
sides and flat top having a length-to-height ratio greater than 5:1. Many show
horizontal banding.

NON-TABULAR: Describes all icebergs that are not tabular shaped as described above. This category is further
subdivided to include the specific shapes described below. If no other
description applies, the iceberg is simply referred to as a non-tabular.

Non-Tabular Iceberg Shape
Classifications

DOME: An iceberg with a rounded
top

PINNACLE: An iceberg with one or
more spires

WEDGE: An iceberg having a steep
vertical side on one end and sloping on the other

DRY-DOCK: An iceberg that has
eroded so a slot or channel is formed

BLOCKY: An iceberg with a flat top
and steep vertical sides

What are the most dangerous icebergs?

All icebergs are dangerous to shipping but depending on its 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 to a vessel. 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 CATEGORY % OF TOTAL
Growler 5.6%
Small 15.3%
Medium 15.3%
Large 12.5%
Very Large 2.8%
General 48.5%
(Size Unknown)

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.
Keep in mind we are talking about an iceberg's mass. Due to irregular iceberg
shapes, icebergs may have varying heights out of the water, but mass is
relatively consistent. The following provides further background information:

Buoyancy

Buoyancy is the upward force exerted on an object immersed in a fluid. Of course, water is the most common fluid, but buoyancy also applies to hot air balloons (where the fluid is the surrounding air) and many other situations. What's the basic idea?

Archimedes figured out that the key to buoyancy is how much volume the object displaces compared to its weight. Archimedes Principle of buoyancy states that the upward force on an object in a fluid is equal to the weight of the fluid that is displaced. If this buoyant force is less than the weight of the object itself, the object will be left with a net downward force and will sink. If the object floats, it floats enough that the buoyant force exactly balances its weight.

For solid, uniform objects like an iceberg, this boils down to the object's mass density, its mass divided by its volume, usually represented by the Greek letter . For something like a boat hull, which is hollow, not uniform, you have to just look at the total weight and the volume of displaced water.

Icebergs of the Antarctic

Map
from Worldatlas.com

 

 

Iceberg names are derived from the Antarctic quadrant in which they were originally sighted. The quadrants are divided counter-clockwise in the following manner:

A = 0-90W (Bellinghausen/Weddell Sea)

B = 90W-180 (Amundsen/Eastern Ross Sea)

C = 180-90E (Western Ross Sea/Wilkesland)

D = 90E-0 (Amery/Eastern Weddell Sea)

When an iceberg is first sighted, The National Ice Center documents its point of origin. The letter of the quadrant, along with a sequential number is assigned to the iceberg. 

 

 

http://www.natice.noaa.gov

 

The National Ice Center is a tri-agency operational center represented by the United States Navy (Department of Defense); the National Oceanic and Atmospheric Administration Department of Commerce); and the United States Coast Guard (Department of Transportation). The National Ice Center mission is to provide world-wide operational ice analyses for the armed forces of the United States and allied nations, U.S. government agencies, and the private sector.

 Iceberg B-15J Calves Iceberg Named B-15S

 

MODIS image of B-15J AND B-15S 

 

February 02, 2007, Washington, DC-- The National Ice Center (NIC) was informed by the Antarctic Meteorological Research Center that iceberg B-15J (Figure 1) has calved a new iceberg that meets criteria for naming and tracking by the NIC. The new iceberg will be named B-15S. This iceberg marks the 18th calving event of icebergs belonging to the B-15 series. B-15S is located at 76 03' 11" South, 168 08' 35" East, near Franklin Island in the Central Ross Sea. Iceberg B-15S measures 10 nautical miles on its longest axis and 2 nautical miles on its widest axis.

The National Ice Center is a tri-agency operational center represented by the United States Navy (Department of Defense), the National Oceanic and Atmospheric Administration (Department of Commerce), and the United States Coast Guard (Department of Homeland Security). The National Ice Center mission is to provide the highest quality strategic and tactical ice services tailored to meet the operational requirements of U.S. national interests and to provide specialized meteorological and oceanographic services to United States government agencies.

National Ice Center Naval Ice Center Liaison Branch

Iceberg Video