Iceberg

For other uses, see Iceberg (disambiguation).

An iceberg in Greenland off Cape York

Aerial view of icebergs and glaciers at Cape York, Greenland

An iceberg is a large piece of ice from freshwater that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice. Alternatively, it may come to rest on the seabed in shallower water, causing ice scour (also known as ice gouging) or becoming an ice island.

Etymology

The word "iceberg" is a partial loan translation from Dutch ijsberg, literally meaning ice mountain, cognate to Danish Isbjerg, German Eisberg, Low Saxon Iesbarg and Swedish Isberg.

Overview

Iceberg calved from the Ross Ice Shelf

Because the density of pure ice is about 920 kg/m³, and that of sea water about 1025 kg/m³, typically only one-ninth of the volume of an iceberg is above water. The shape of the underwater portion can be difficult to judge by looking at the portion above the surface. This has led to the expression "tip of the iceberg", for a problem or difficulty that is only a small manifestation of a larger problem.

Icebergs generally range from 1 to 75 metres (3.3 to 246 ft) above sea level and weigh 100,000 to 200,000 metric tons (110,000 to 220,000 short tons). The largest known iceberg in the North Atlantic was 168 metres (551 ft) above sea level, reported by the USCG icebreaker East Wind in 1958, making it the height of a 55-storey building. These icebergs originate from the glaciers of western Greenland, and may have an interior temperature of -15 to -20 °C (5 to -4 °F).

Though usually confined by winds and currents to move close to the coast, the largest icebergs recorded have been calved, or broken off, from the Ross Ice Shelf of Antarctica. Iceberg B-15, photographed by satellite in 2000, measured 295 by 37 kilometres (183 by 23 mi), with a surface area of 11,000 square kilometres (4,200 sq mi). The mass was estimated around three billion tonnes. The largest iceberg on record was an Antarctic tabular iceberg of over 31,000 square kilometres (12,000 sq mi) [335 by 97 kilometres (208 by 60 mi)] sighted 150 miles (240 km) west of Scott Island, in the South Pacific Ocean, by the USS Glacier on November 12, 1956. This iceberg was larger than Belgium.

When an iceberg melts, it makes a fizzing sound called "Bergie Seltzer". This sound is made when compressed air bubbles trapped in the iceberg pop. The bubbles come from air trapped in snow layers that later became glacial ice.

A photomontage visualising what the whole of an iceberg might look like

Classification

Size

Names for various sizes of iceberg are not universal, but usually follow a similar pattern. The size classification in the table below is used by the International Ice Patrol:

Size Category	Height	Length
Growler	Less than 1 metre (3.3 ft)	Less than 5 metres (16 ft)
Bergy Bit	1–5 metres (3.3–16 ft)	5–15 metres (16–49 ft)
Small	5–15 metres (16–49 ft)	15–60 metres (49–200 ft)
Medium	15–45 metres (49–148 ft)	60–120 metres (200–390 ft)
Large	45–75 metres (148–246 ft)	120–200 metres (390–660 ft)
Very Large	Over 75 metres (246 ft)	Over 200 metres (660 ft)

Recent large icebergs

• Iceberg B-15 11,000 km² (4,200 sq mi), 2000
• Iceberg A-38, about 6,900 km² (2,700 sq mi), 1998
• Iceberg B-15A, 3,100 km² (1,200 sq mi), broke off 2003
• Iceberg C-19, 5,500 km² (2,100 sq mi), 2002
• Iceberg B-9, 5,390 km² (2,080 sq mi), 1987
• Iceberg D-16, 310 km² (120 sq mi), 2006
• Ice sheet, 260 km² (100 sq mi), broken off of Petermann Glacier in northern Greenland on Aug 5, 2010, considered to be largest Arctic iceberg since 1962. About a month later, this iceberg split into two pieces upon crashing into Joe Island in the Nares Strait next to Greenland. In June 2011, large fragments of the Petermann Ice Islands were observed off the Labrador coast.
• Iceberg B-17B 140 km² (54 sq mi), 1999, shipping alert issued December 2009.

Shape

In addition to size classification, icebergs can also be classified on the basis of their shape. The two basic types of iceberg forms are tabular and non-tabular. Tabular icebergs have steep sides and a flat top, much like a plateau, with a length-to-height ratio of more than 5:1. This type of iceberg can be quite large, as in the case of Pobeda Ice Island. Antarctic icebergs formed by breaking off from an ice shelf, such as the Ross Ice Shelf or Filchner-Ronne Ice Shelf, are typically tabular. The largest icebergs in the world are formed this way.

The calving of Iceberg A-38 off Ronne Ice Shelf

Non-tabular icebergs have different shapes, and include:

• Dome: An iceberg with a rounded top.
• Pinnacle: An iceberg with one or more spires.
• Wedge: An iceberg with a steep edge on one side and a slope on the opposite side.
• Dry-Dock: An iceberg that has eroded to form a slot or channel.
• Blocky: An iceberg with steep, vertical sides and a flat top. It differs from tabular icebergs in that its shape is more like a block than a flat sheet.

Monitoring

Icebergs are monitored worldwide by the U.S. National Ice Center (NIC), established in 1995, which produces analyses and forecasts of Arctic, Antarctic, Great Lakes and Chesapeake Bay ice conditions. More than 95% of the data used in its sea ice analyses are derived from the remote sensors on polar-orbiting satellites that survey these remote regions of the Earth.

Iceberg A22A in the South Atlantic Ocean

The NIC is the only organization that names and tracks all Antarctic Icebergs. It assigns each iceberg larger than 10 nautical miles (19 km) along at least one axis a name composed of a letter indicating its point of origin and a running number. The letters used are as follows:

• A – longitude 0° to 90° W (Bellingshausen Sea, Weddell Sea)
• B – longitude 90° W to 180° (Amundsen Sea, Eastern Ross Sea)
• C – longitude 90° E to 180° (Western Ross Sea, Wilkes Land)
• D – longitude 0° to 90° E (Amery Ice Shelf, Eastern Weddell Sea)

Iceberg B15 calved from the Ross Ice Shelf in 2000 and initially had an area of 11,000 square kilometres (4,200 sq mi). It broke apart in November 2002. The largest remaining piece of it, Iceberg B-15A, with an area of 3,000 square kilometres (1,200 sq mi), was still the largest iceberg on Earth until it ran aground and split into several pieces October 27, 2005. It has been determined that the cause of the breakup was an ocean swell generated by an Alaskan storm 6 days earlier and 13,500 kilometres (8,400 mi) away.

History

In the 20th century, several scientific bodies were established to study and monitor the icebergs. The International Ice Patrol, formed in 1914 in response to the Titanic disaster, monitors iceberg dangers near the Grand Banks of Newfoundland and provides the "limits of all known ice" in that vicinity to the maritime community.

Technology history

The iceberg suspected of sinking the RMS Titanic; a smudge of red paint much like the Titanic's stripe was seen near the base.

Before April 1912 there was no system in place to track icebergs to guard ships against collisions. The sinking of the RMS Titanic, which caused the deaths of 1,514 of its 2,223 passengers, created the demand for a system to observe icebergs. For the remainder of the ice season of that year, the United States Navy patrolled the waters and monitored ice flow. In November 1913, the International Conference on the Safety of Life at Sea met in London to devise a more permanent system of observing icebergs. Within three months the participating maritime nations had formed the International Ice Patrol (IIP). The goal of the IIP was to collect data on meteorology and oceanography in order to measure currents, ice-flow, ocean temperature, and salinity levels. They published their first records in 1921, which allowed for a year-by-year comparison of iceberg movement.

New technologies monitor icebergs. Aerial surveillance of the seas in the early 1930s allowed for the development of charter systems that could accurately detail the ocean currents and iceberg locations. In 1945, experiments tested the effectiveness of radar in detecting icebergs. A decade later, oceanographic monitoring outposts were established for the purpose of collecting data; these outposts continue to serve in environmental study. A computer was first installed on a ship for the purpose of oceanographic monitoring in 1964, which allowed for a faster evaluation of data. By the 1970s, icebreaking ships were equipped with automatic transmissions of satellite photographs of ice in Antarctica. Systems for optical satellites had been developed, but were still limited by weather conditions. In the 1980s, drifting buoys were used in Antarctic waters for oceanographic and climate research. They are equipped with sensors that measure ocean temperature and currents. Side-Looking Airborne Radar (SLAR) made it possible to acquire images regardless of weather conditions. On November 4, 1995, Canada launched RADARSAT-1. Developed by the Canadian Space Agency, it provides images of Earth for both scientific and commercial purposes. This system was the first to use Synthetic Aperture Radar (SAR), which sends microwave energy to the ocean surface and records the reflections to track icebergs. The European Space Agency launched ENVISAT (an observation satellite that orbits the Earth's poles) on March 1, 2002. ENVISAT employs Advanced Synthetic Aperture Radar (ASAR) technology, which can detect changes in surface height accurately. The Canadian Space Agency launched RADARSAT-2 in December in the year of 2007, which uses SAR and multipolarization modes and follows the same orbit path as RADARSAT-1.

An iceberg in Greenland

One important iceberg in history was the one that hit the RMS Titanic on the 14th of April 1912. It struck the right side of the Titanic, leaving shards of ice on the deck near the bow. Icebergs had been reported by other ships in the vicinity in the days leading up to the accident and yet the crew of the Titanic only saw the one that sunk them when they were almost on top of it. The night was clear and there was no moon out to illuminate the iceberg. The seas were unusually calm and the lack of wave action and spray around the waterline of the iceberg made it practically invisible that night. The sinking of the Titanic resulted in the death of 1,517 of the 2,200 passengers who were on board. An RMS Titanic survivor said "When the dawn rose I was stunned to see that we were surrounded by a veritable mountain range of icebergs. In the dark, they had been completely invisible. But in the rising dawn, they were everywhere. For objects so lethal, they were also majestic. And almost beautiful, in a horrid way." After the sinking of the Titanic, rules were introduced to ensure there were enough lifeboats to accommodate all passengers and crew of sea-going vessels. Monitoring of ice fields also began, in an attempt to prevent a repeat of the Titanic disaster.

See also

• Drift ice station
• Ice calving
• Ice drift
• Polar ice cap
• Polar ice packs
• Polynya
• Sea ice
• Shelf ice

External links

• Iceberg Finder Service for east coast of Canada
• Icebergs of The Arctic and Antarctic
•  "Iceberg". Collier's New Encyclopedia. 1921.