Editing Iceberg (section)

==Overview==
Typically about one-tenth of the volume of an iceberg is above water, which follows from [[Buoyancy|Archimedes's Principle of buoyancy]]; the [[density]] of pure ice is about 920&nbsp;[[kilogram per cubic metre|kg/m<sup>3</sup>]] (57&nbsp;lb/cu&nbsp;ft), and that of [[seawater]] about {{convert|1025|kg/m3|lb/ft3|abbr=on|0}}. The contour of the underwater portion can be difficult to judge by looking at the portion above the surface. 
[[File:Research on Iceberg B-15A by Josh Landis, National Science Foundation (Image 4) (NSF).jpg|thumb|upright=1.2|Northern edge of [[Iceberg B-15]]A in the Ross Sea, Antarctica, 29 January 2001]]

{| class="wikitable"
|+ Iceberg size classifications according to the International Ice Patrol<ref name=":0" />
! Size class
! Height (m)
! Length (m)
|-
| Growler
| <1
| <5
|-
| Bergy bit
| 1–5
| 5–15
|-
| Small
| 5–15
| 15–60
|-
| Medium
| 15–45
| 60–122
|-
| Large
| 45–75
| 122–213
|-
| Very large
| >75
| >213
|}

The largest icebergs recorded have been [[Ice calving|calved]], or broken off, from the [[Ross Ice Shelf]] of [[Antarctica]]. Icebergs may reach a height of more than {{convert|100|m|ft|sigfig=1}} above the sea surface and have mass ranging from about 100,000 tonnes up to more than 10&nbsp;million tonnes. Icebergs or pieces of floating ice smaller than 5&nbsp;meters above the sea surface are classified as "bergy bits"; smaller than 1&nbsp;meter—"growlers".<ref>{{Cite web |url=https://www.universalcompendium.com/tables/science/iceb.htm |title=Iceberg Classification Systems}}</ref> The largest known iceberg in the [[Atlantic Ocean#Northern Atlantic|North Atlantic]] was {{convert|168|m|ft}} above sea level, reported by the USCG icebreaker [[USCGC Eastwind (WAGB-279)|''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 {{convert|-15|to|-20|C|F}}.<ref name="cgfoi">{{cite web |url=http://www.canadiangeographic.ca/magazine/MA06/indepth/justthefacts.asp |work=Canadian Geographic |title=Facts on Icebergs |date=2006 |archive-url=https://web.archive.org/web/20060331032737/https://www.canadiangeographic.ca/magazine/MA06/indepth/justthefacts.asp |archive-date=2006-03-31 |url-status=dead}}</ref>

[[File:Grotto in an iceberg.jpg|thumb|upright|[[Grotto]] in an iceberg, photographed during the [[Terra Nova Expedition|British Antarctic Expedition]] of 1911–1913, 5&nbsp;Jan 1911]]

=== Drift ===
A given iceberg's trajectory through the ocean can be modelled by integrating the equation

: <math>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},</math>

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.<ref>{{Cite journal |last1=Carlson |first1=Daniel F. |last2=Boone |first2=Wieter |last3=Meire |first3=Lorenz |last4=Abermann |first4=Jakob |last5=Rysgaard |first5=Søren |date=2017-08-28 |title=Bergy Bit and Melt Water Trajectories in Godthåbsfjord (SW Greenland) Observed by the Expendable Ice Tracker |journal=Frontiers in Marine Science |volume=4 |pages=276 |doi=10.3389/fmars.2017.00276 |issn=2296-7745 |doi-access=free}}</ref><ref name=":2">{{Cite journal |last1=Bigg |first1=Grant R. |last2=Wadley |first2=Martin R. |last3=Stevens |first3=David P. |last4=Johnson |first4=John A. |date=October 1997 |title=Modelling the dynamics and thermodynamics of icebergs |url=https://linkinghub.elsevier.com/retrieve/pii/S0165232X97000128 |journal=Cold Regions Science and Technology |language=en |volume=26 |issue=2 |pages=113–135 |doi=10.1016/S0165-232X(97)00012-8|bibcode=1997CRST...26..113B }}</ref>

Icebergs deteriorate through melting and fracturing, which changes the mass ''m'', as well as the surface area, volume, and stability of the iceberg.<ref name=":2" /><ref>{{Cite journal |last1=Crawford |first1=Anna |last2=Mueller |first2=Derek |last3=Joyal |first3=Gabriel |date=2018-04-08 |title=Surveying Drifting Icebergs and Ice Islands: Deterioration Detection and Mass Estimation with Aerial Photogrammetry and Laser Scanning |journal=Remote Sensing |language=en |volume=10 |issue=4 |pages=575 |doi=10.3390/rs10040575 |bibcode=2018RemS...10..575C |issn=2072-4292 |doi-access=free|hdl=10023/16996 |hdl-access=free }}</ref> Iceberg deterioration and drift, therefore, are interconnected ie. iceberg thermodynamics, and fracturing must be considered when modelling iceberg drift.<ref name=":2" />

Winds and currents may move icebergs close to coastlines, where they can become frozen into [[Drift ice|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 by ice|seabed gouging]].

=== Mass loss ===
Icebergs lose mass due to melting, and [[Ice calving|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

: <math>M_{b} = K \Delta u^{0.8} \frac{T_0-T}{L^{0.2}},</math>

where <math>M_\text{b}</math> is the melt rate in m/day, <math>\Delta u</math> is the relative velocity between the iceberg and the ocean, <math>T_0-T</math> is the temperature difference between the ocean and the iceberg, and <math>L</math> is the length of the iceberg. <math>K</math> is a constant based on properties of the iceberg and the ocean and is approximately <math>0.75^\circ \text{C}^{-1} \text{m}^{0.4} \text{day}^{-1} \text{s}^{0.8}</math> in the polar ocean.<ref name="Cenedese">{{cite journal |last1=Cenedese |first1=Claudia |last2=Straneo |first2=Fiamma |title=Icebergs Melting |journal=Annual Review of Fluid Mechanics |date=19 January 2023 |volume=55 |issue=1 |pages=377–402 |doi=10.1146/annurev-fluid-032522-100734|doi-access=free |bibcode=2023AnRFM..55..377C }}</ref>

The influence of the shape of an iceberg<ref>{{cite journal |last1=Hester |first1=Eric W. |last2=McConnochie |first2=Craig D. |last3=Cenedese |first3=Claudia |last4=Couston |first4=Louis-Alexandre |last5=Vasil |first5=Geoffrey |title=Aspect ratio affects iceberg melting |journal=Physical Review Fluids |date=12 February 2021 |volume=6 |issue=2 |page=023802 |doi=10.1103/PhysRevFluids.6.023802|arxiv=2009.10281 |bibcode=2021PhRvF...6b3802H }}</ref> and of the Coriolis force<ref>{{cite journal |last1=Meroni |first1=Agostino N. |last2=McConnochie |first2=Craig D. |last3=Cenedese |first3=Claudia |last4=Sutherland |first4=Bruce |last5=Snow |first5=Kate |title=Nonlinear influence of the Earth's rotation on iceberg melting |journal=Journal of Fluid Mechanics |date=10 January 2019 |volume=858 |pages=832–851 |doi=10.1017/jfm.2018.798|bibcode=2019JFM...858..832M |s2cid=126234419 }}</ref> on iceberg melting rates has been demonstrated in laboratory experiments.

Wave erosion is more poorly constrained but can be estimated by

: <math> M_\text{e} = cS_s(T_\text{s}+2)[1+\text{cos}(I_\text{c}^3\pi)],</math>

where <math>M_\text{e}</math> is the wave erosion rate in m/day, <math>c = \frac{1}{12} \text{m day}^{-1}</math>, <math>S_\text{S}</math> describes the sea state, <math>T_\text{S}</math> is the sea surface temperature, and <math>I_\text{c}</math> is the [[sea ice]] concentration.<ref name="Cenedese" />

=== Bubbles ===
Air trapped in snow forms bubbles as the snow is compressed to form firn and then glacial ice.<ref name=":3">{{Cite journal |last1=Scholander |first1=P. F. |last2=Nutt |first2=D. C. |date=1960 |title=Bubble Pressure in Greenland Icebergs |journal=Journal of Glaciology |language=en |volume=3 |issue=28 |pages=671–678 |doi=10.3189/S0022143000017950 |issn=0022-1430 |doi-access=free}}</ref> Icebergs can contain up to 10% air bubbles by volume.<ref name=":3" />{{not in source|reason=The article only reports gas pressures in the bubbles up to 20 atm, without volume estimations, but saying that "At high pressures the bubbles are compressed so the difference in density between glacier ice and bubble-free ice becomes only a small fraction of 1 per cent". Since air even at 20 atm is ≳30 times lighter than pure ice, this by no means can be interpreted as "10% air bubbles by volume".|date=August 2022}} These bubbles are released during melting, producing a fizzing sound that some may call "Bergie [[Carbonated water|Seltzer]]". This sound results when the water-ice interface reaches compressed air bubbles trapped in the ice. As each bubble bursts it makes a "popping" sound<ref name="cgfoi" /> and the acoustic properties of these bubbles can be used to study iceberg melt.<ref>{{Cite journal |last1=Glowacki |first1=Oskar |last2=Deane |first2=Grant B. |last3=Moskalik |first3=Mateusz |date=2018-05-16 |title=The Intensity, Directionality, and Statistics of Underwater Noise From Melting Icebergs |journal=Geophysical Research Letters |language=en |volume=45 |issue=9 |pages=4105–4113 |doi=10.1029/2018GL077632 |bibcode=2018GeoRL..45.4105G |s2cid=135352794 |issn=0094-8276|doi-access=free }}</ref>

=== Stability ===
An iceberg may flip, or capsize, as it melts and breaks apart, changing the [[Center of mass|center of gravity]]. Capsizing can occur shortly after calving when the iceberg is young and establishing balance.<ref>{{Cite journal|last1=MacAyeal|first1=Douglas R.|last2=Abbot|first2=Dorian S.|last3=Sergienko|first3=Olga V.|date=2011|title=Iceberg-capsize tsunamigenesis|journal=Annals of Glaciology|language=en|volume=52|issue=58|pages=51–56|doi=10.3189/172756411797252103|bibcode=2011AnGla..52...51M|issn=0260-3055|doi-access=free}}</ref> Icebergs are unpredictable and can capsize anytime and without warning. Large icebergs that break off from a glacier front and flip onto the glacier face can push the entire glacier backwards momentarily, producing 'glacial earthquakes' that generate as much energy as an atomic bomb.<ref>{{cite web |url=https://www.sciencenewsforstudents.org/article/flipping-icebergs |title=Flipping Icebergs  |work=ScienceNews for Students |author=Stephen Ornes |date=April 3, 2012 |access-date=June 9, 2019}}</ref><ref>{{cite web |url=https://www.npr.org/sections/thetwo-way/2015/06/25/417457888/study-reveals-what-happens-during-a-glacial-earthquake |title=Study Reveals What Happens During A 'Glacial Earthquake' |work=NPR |author=Nell Greenfieldboyce  |date=June 25, 2015 |accessdate=March 9, 2021}}</ref>

===Color===
Icebergs are generally white because they are covered in snow, but can be green, blue, yellow, black, striped, or even [[rainbow]]-colored.<ref>{{cite web |url=https://www.scientificamerican.com/article/icebergs-can-be-green-black-striped-even-rainbow-slide-show/ |title=Icebergs Can Be Green, Black, Striped, Even Rainbow  |work=Scientific American |author=Katherine Wright  |date=January 5, 2018 |access-date=June 9, 2019}}</ref> Seawater, algae and lack of air bubbles in the ice can create diverse colors. Sediment can create the dirty black coloration present in some icebergs.<ref name="Image of the Week - Super-cool colours of icebergs">{{cite web |last1=Roach |first1=Lettie |title=Image of the Week - Super-cool colours of icebergs |url=https://blogs.egu.eu/divisions/cr/2018/03/30/image-of-the-week-super-cool-colours-of-icebergs/ |website=EGU Blogs |date=11 January 2019 |publisher=European Geosciences Union |access-date=6 November 2020}}</ref>

===Shape===
[[File:Iceberg Shape.svg|thumb|Different shapes of icebergs]]
[[File:Antarctic Sound-2016-Iceberg 02.jpg|thumb|Tabular iceberg, near [[Brown Bluff]] in the [[Antarctic Sound]] off [[Tabarin Peninsula]]]]

In addition to size classification (Table 1), icebergs can be classified on the basis of their shapes. 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.<ref name="iipssc">{{cite web|url=http://www.uscg.mil/lantarea/iip/docs/AOS_2011.pdf|title=Sizes and Shapes of Icebergs|publisher=International Ice Patrol|access-date=2006-12-20}}</ref>

This type of iceberg, also known as an ''ice island'',<ref>Weeks, W.F. (2010), On Sea Ice, University of Alaska Press, p. 399</ref> 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:<ref>{{cite web|url=http://www.canadiangeographic.ca/magazine/ma06/indepth/nathistory.asp|title=Iceberg Physiology|publisher=Canadian Geographic|date=2006|archive-url=https://web.archive.org/web/20060331032649/https://www.canadiangeographic.ca/magazine/ma06/indepth/nathistory.asp|archive-date=2006-03-31|url-status=dead|author=Holly Gordon}}</ref>

* ''Dome'': An iceberg with a rounded top.
* ''Pinnacle'': An iceberg with one or more [[spire]]s.
* ''Wedge'': An iceberg with a steep edge on one side and a slope on the opposite side.
* ''Dry-dock'': An iceberg that has [[Erosion|eroded]] to form a slot or [[Channel (geography)|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.