An iceberg is a piece of fresh water ice more than 15 meters (16 yards) long that has broken off a glacier or an ice shelf and is floating freely in open water. Smaller chunks of floating glacially derived ice are called "growlers" or "bergy bits". Much of an iceberg is below the water's 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. Icebergs vary considerably in size and shape. Icebergs that calve from glaciers in Greenland are often irregularly shaped while Antarctic ice shelves often produce large tabular (table top) icebergs. The largest iceberg in recent history, named B-15, was measured at nearly 300 by 40 kilometres (186 by 25 mi) in 2000. The largest iceberg on record was an Antarctic tabular iceberg measuring 335 by 97 kilometres (208 by 60 mi) sighted 240 kilometres (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.
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 Typically about one-tenth of the volume of an iceberg is above water, which follows from Archimedes's Principle of buoyancy; the density of pure ice is about 920 kg/m3 (57 lb/cu ft), and that of seawater about 1,025 kg/m3 (64 lb/cu ft). The contour of the underwater portion can be difficult to judge by looking at the portion above the surface.
The largest icebergs recorded have been calved, or broken off, from the Ross Ice Shelf of Antarctica. Icebergs may reach a height of more than 100 metres (300 ft) above the sea surface and have mass ranging from about 100,000 tonnes up to more than 10 million tonnes. Icebergs or pieces of floating ice smaller than 5 meters above the sea surface are classified as "bergy bits"; smaller than 1 meter—"growlers". The largest known iceberg in the North Atlantic was 168 metres (551 ft) 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 (5 to −4 °F).
Drift A given iceberg's trajectory through the ocean can be modelled by integrating the equation
m d v → d t = − m f k → × v → + F → a + F → w + F → r + F → s + F → p , {\displaystyle m{\frac {d{\vec {v}}}{dt}}=-mf{\vec {k}}\times {\vec {v}}+{\vec {F}}_{\text{a}}+{\vec {F}}_{\text{w}}+{\vec {F}}_{\text{r}}+{\vec {F}}_{\text{s}}+{\vec {F}}_{\text{p}},}
where m is the iceberg mass, v the drift velocity, and the variables f, k, and F correspond to the Coriolis force, the vertical unit vector, and a given force. The subscripts a, w, r, s, and p correspond to the air drag, water drag, wave radiation force, sea ice drag, and the horizontal pressure gradient force. Icebergs deteriorate through melting and fracturing, which changes the mass m, as well as the surface area, volume, and stability of the iceberg. Iceberg deterioration and drift, therefore, are interconnected. Fracturing must be considered when modelling iceberg drift. Winds and currents may 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.
Mass loss Icebergs lose mass due to melting, and calving. Melting can be due to solar radiation, or heat and salt transport from the ocean. Iceberg calving is generally enhanced by waves impacting the iceberg. Melting tends to be driven by the ocean, rather than solar radiation. Ocean driven melting is often modelled as
M b = K Δ u 0.8 T 0 − T L 0.2 , {\displaystyle M_{b}=K\Delta u^{0.8}{\frac {T_{0}-T}{L^{0.2}}},}
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