An iceberg is a large piece of freshwater ice that has broken off a glacier or an ice
shelf and is floating freely in open water. It may subsequently become frozen into pack
ice. As it drifts into shallower waters, it may come into contact with the seabed, a process
referred to as seabed gouging by ice.
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 Because the density of pure ice is about 920
kg/m³, and that of seawater about 1025 kg/m³, typically only one-tenth 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
above sea level and weigh 100,000 to 200,000 metric tons. The largest known iceberg in
the North Atlantic was 168 metres above sea level, reported by the USCG icebreaker East
Wind in 1958, making it the height of a 55-story building. These icebergs originate from the
glaciers of western Greenland and may have an interior temperature of −15 to −20 °C.
Icebergs are 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, with
a surface area of 11,000 square kilometres. The largest iceberg on record was an Antarctic
tabular iceberg of over 31,000 square kilometres [335 by 97 kilometres] sighted 150 miles west
of Scott Island, in the South Pacific Ocean, by the USS Glacier on November 12, 1956. This
iceberg was larger than Belgium. When a piece of iceberg ice melts, it makes
a fizzing sound called "Bergie Seltzer". This sound is made when the water-ice interface
reaches compressed air bubbles trapped in the ice. As this happens, each bubble bursts,
making a 'popping' sound. The bubbles contain air trapped in snow layers very early in the
history of the ice, that eventually got buried to a given depth and pressurized as it transformed
into firn then to glacial ice. Recent large icebergs
Iceberg B-15 11,000 km2, 2000 Iceberg A-38, about 6,900 km2, 1998
Iceberg B-15A, 3,100 km2, broke off 2003 Iceberg C-19, 5,500 km2, 2002
Iceberg B-9, 5,390 km2, 1987 Iceberg B-31, 615 km2, 2014
Iceberg D-16, 310 km2, 2006 Ice sheet, 260 km2, broken off of Petermann
Glacier in northern Greenland on Aug 5, 2010, considered to be the 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, 1999, shipping alert issued December 2009.
Shape
In addition to size classification, icebergs can 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, also known as an ice island, 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. 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, 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.
The NIC is the only organization that names and tracks all Antarctic Icebergs. It assigns
each iceberg larger than 10 nautical miles 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
B – longitude 90° W to 180° C – longitude 90° E to 180°
D – longitude 0° to 90° E Iceberg B15 calved from the Ross Ice Shelf
in 2000 and initially had an area of 11,000 square kilometres. It broke apart in November
2002. The largest remaining piece of it, Iceberg B-15A, with an area of 3,000 square kilometres,
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 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 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 1,517 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.
The goal of the IIP was to collect data on meteorology and oceanography 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 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 scientific and commercial purposes. This system was the first
to use synthetic aperture radar, which sends microwave energy to the ocean surface and
records the reflections to track icebergs. The European Space Agency launched ENVISAT
on March 1, 2002. ENVISAT employs advanced synthetic aperture radar technology, which
can detect changes in surface height accurately. The Canadian Space Agency launched RADARSAT-2
in December 2007, which uses SAR and multi-polarization modes and follows the same orbit path as RADARSAT-1.
See also List of recorded icebergs by area
Drift ice station Ice calving
Ice drift Polar ice cap
Polar ice packs Polynya
Seabed gouging by ice Sea ice
Shelf ice References
External links Iceberg Finder Service for east coast of Canada
Icebergs of The Arctic and Antarctic Works related to Iceberg at Wikisource