Iceberg





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 (salt) water. Small bits of disintegrating icebergs are called "growlers" or "bergy bits".

Much of an iceberg is below the surface which led to the expression "tip of the iceberg" to illustrate a small part of a larger unseen issue. Icebergs are considered a serious maritime hazard. The 1912 loss of the "unsinkable" RMS Titanic led to the formation of the International Ice Patrol in 1914.

Icebergs calved by glaciers that face the open sea, such as in Greenland, are irregular shaped piles. In Antarctica, ice shelves calve large tabular (table top) icebergs. The biggest iceberg ever recorded was Iceberg B-15A which split off the Ross Ice Shelf in Antarctica in 2000.



Etymology
The word iceberg is a partial loan translation from the Dutch word 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 about one-tenth of the volume of an iceberg is above water (which follows from Archimedes's Principle of buoyancy). The shape of the underwater portion can be difficult to judge by looking at the portion above the surface. Icebergs are often compared in size to the area of Manhattan.

The visible "tips" of icebergs typically range from 1 to 75 m above sea level and weigh 100000 to 200000 MT. The largest known iceberg in the North Atlantic was 168 m above sea level, reported by the USCG icebreaker Eastwind in 1958, making it the height of a 55-story building. These icebergs originate from the glaciers of western Greenland and may have interior temperatures of -15 to -20 C.

Winds and currents tend to move icebergs close to coastlines, where they can become frozen into pack ice (one form of sea ice), or drift into shallow waters, where they can come into contact with the seabed, a phenomenon called seabed gouging.

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, with a surface area of 11000 km2. The largest iceberg on record was an Antarctic tabular iceberg of over 31000 km2 [335 by] sighted 150 mi west of Scott Island, in the South Pacific Ocean, by the USS Glacier on November 12, 1956. This iceberg was larger than Belgium.

A small iceberg less than 2 meters (6.6 feet) across that floats with less than 1 meter (3.3 feet) showing above water is called a growler, and is smaller than a bergy bit, which is usually less than 5 meters (15 feet) in size. Both are generally spawned from disintegrating icebergs.

As a piece of iceberg ice melts, it produces a fizzing sound called the "Bergie Seltzer". This sound results 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 (up to several kilometers) and pressurized as it transformed into firn then to glacial ice.

An iceberg will flip in the water as it melts and breaks apart because gravity continually pulls the heavier side downward. Most flipping occurs when the iceberg is young and establishing balance. Flipping can occur anytime and without warning. Large icebergs that flip can give off as much energy as an atomic bomb and produce earthquakes.

Color
Icebergs are generally white because they are covered in snow, but can be green, blue, yellow, black, striped, or even rainbow-colored. Seawater, algae and lack of air bubbles in the ice can create diverse colors.

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 aspect ratio, the ratio between its width and height, is small, more like that of a block than a flat sheet.

History


Before the early 1910s, although there had been many fatal sinkings of ships by icebergs, there was no system in place to track icebergs to guard ships against collisions. In 1907, SS Kronprinz Wilhelm, a German liner, had rammed an iceberg and suffered a crushed bow, but was still able to complete her voyage. The advent of steel ship construction led designers to declare their ships "unsinkable".

The April 1912 sinking of the Titanic, which killed 1,518 of its 2,223 passengers and crew, discredited this claim. 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 to measure currents, ice-flow, ocean temperature, and salinity levels. They monitored iceberg dangers near the Grand Banks of Newfoundland and provided the "limits of all known ice" in that vicinity to the maritime community. The IIP published their first records in 1921, which allowed for a year-by-year comparison of iceberg movement.

Technological development
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 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 2007, which uses SAR and multi-polarization modes and follows the same orbit path as RADARSAT-1.

Modern 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. The NIC is the only organization that names and tracks all Antarctic Icebergs. It assigns each iceberg larger than 10 nmi 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 11000 km2. It broke apart in November 2002. The largest remaining piece of it, Iceberg B-15A, with an area of 3000 km2, was still the largest iceberg on Earth until it ran aground and split into several pieces October 27, 2005, an event that was observed by seismographs both on the iceberg and across Antarctica. It has been hypothesized that this breakup may also have been abetted by ocean swell generated by an Alaskan storm 6 days earlier and 13500 km away.

Recent large icebergs

 * 1987, Iceberg B-9, 5390 km2
 * 1998, Iceberg A-38, about 6900 km2
 * 1999, Iceberg B-17B 140 km2, shipping alert issued December 2009.
 * 2000, Iceberg B-15 11000 km2
 * 2002, Iceberg C-19, 5500 km2
 * 2002, Iceberg B-22, 5490 km2
 * 2003 broke off, Iceberg B-15A, 3100 km2
 * 2006, Iceberg D-16, 120 sqmi
 * 2014, Iceberg B-31, 615 km2, 2014
 * 2017, Iceberg A-68, (Larsen C) 5800 km2
 * 2018, Iceberg B-46, 225 km2
 * 2019, Iceberg D-28, 1636 km2
 * Ice sheet, 100 sqmi, broken off of Petermann Glacier in northern Greenland on August 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.