Editing Great Barrier Reef (section)

==Geology and geography==
[[File:Part of Great Barrier Reef from Helicopter.jpg|Aerial photography|thumb]]
The Great Barrier Reef is a distinct feature of the [[East Australian Cordillera]] division. It reaches from [[Torres Strait]] (between [[Bramble Cay]], its northernmost island, and the south coast of [[Papua New Guinea]]) in the north to the unnamed passage between [[Lady Elliot Island]] (its southernmost island) and [[Fraser Island]] in the south. Lady Elliot Island is located {{cvt|1915|km|mi}} southeast of Bramble Cay [[as the crow flies]].<ref name=map/> It includes the smaller [[Murray Island, Queensland|Murray Islands]].<ref>{{Cite book |title=Physiographic Diagram of Australia |url=https://books.google.com/books?id=KS0YMQAACAAJ |author=A.K. Lobeck |publisher=The Geological Press, Columbia University |location=New York |date=1951 |quote=to accompany text description and geological sections which were prepared by Joseph Gentili and R.W. Fairbridge of the [[University of Western Australia]] |access-date=19 February 2018 |archive-date=31 December 2023 |archive-url=https://web.archive.org/web/20231231065935/https://books.google.com/books?id=KS0YMQAACAAJ |url-status=live }}</ref>

The [[plate tectonic]] theory indicates Australia has [[continental drift|moved northwards]] at a rate of {{cvt|7|cm|in}} per year, starting during the [[Cainozoic|Cenozoic]].<ref>{{cite journal |author=Davies, P.J., Symonds, P.A., Feary, D.A., Pigram, C.J. |year=1987 |title=Horizontal plate motion: a key allocyclic factor in the evolution of the Great Barrier Reef |journal=Science |volume=238 |issue=4834 |pages=1697–1700 |bibcode=1987Sci...238.1697D |doi=10.1126/science.238.4834.1697 |pmid=17737670 |s2cid=27544990 }}</ref><ref name="HopleySmithers2007"/>{{rp|18}} Eastern Australia experienced a period of [[tectonic uplift]], which moved the [[drainage divide]] in Queensland {{cvt|400|km|mi}} inland. Also during this time, Queensland experienced volcanic eruptions leading to central and shield [[volcano]]es and [[basalt]] flows.<ref name="HopleySmithers2007"/>{{rp|19}} Some of these became [[volcanic island]]s.<ref name="HopleySmithers2007"/>{{rp|26}} After the [[Coral Sea]] [[Oceanic basin|Basin]] formed, coral reefs began to grow in the Basin, but until about 25 million years ago, northern Queensland was still in temperate waters south of the tropics{{snd}}too cool to support coral growth.<ref name="HopleySmithers2007"/>{{rp|27}} The Great Barrier Reef's development history is complex; after Queensland drifted into tropical waters, it was largely influenced by reef growth and decline as sea level changed.<ref name="HopleySmithers2007"/>{{rp|27–28}}

Reefs can increase in diameter by {{convert|1|to|3|cm|in}} per year, and grow vertically anywhere from {{cvt|1|to|25|cm|in}} per year; however, they grow only above a depth of {{convert|150|m|ft}} due to their need for sunlight, and cannot grow above sea level.<ref>{{cite encyclopedia |author=MSN Encarta |year=2006 |title=Great Barrier Reef |url=http://encarta.msn.com/encyclopedia_761575831/Great_Barrier_Reef.html |access-date=11 December 2006 |archive-url=https://web.archive.org/web/20091028020755/http://encarta.msn.com/encyclopedia_761575831/Great_Barrier_Reef.html |archive-date=28 October 2009 |url-status=dead }}</ref> When Queensland edged into tropical waters 24 million years ago, some coral grew,<ref name="HopleySmithers2007"/>{{rp|29}} but a [[sedimentation]] [[regime]] quickly developed with erosion of the [[Great Dividing Range]]; creating [[river delta]]s, [[Pelagic sediments|oozes]] and [[turbidite]]s, unsuitable conditions for coral growth. 10 million years ago, the sea level significantly lowered, which further enabled sedimentation. The reef's substrate may have needed to build up from the sediment until its edge was too far away for suspended sediments to inhibit coral growth. In addition, approximately 400,000 years ago there was a particularly warm [[Interglacial]] period with higher sea levels and a {{convert|4|C-change|0}} water temperature change.<ref name="HopleySmithers2007"/>{{rp|37}}
[[File:Heron Island.jpg|right|thumb|[[Heron Island (Queensland)|Heron Island]], a coral cay in the southern Great Barrier Reef]]

The land that formed the [[wikt:substrate|substrate]] of the current Great Barrier Reef was a [[coastal plain]] formed from the eroded sediments of the [[Great Dividing Range]] with some larger hills (most of which were themselves remnants of older reefs<ref name="AIMSage">{{cite web |last=Tobin |first=Barry |title=How the Great Barrier Reef Was Formed |publisher=Australian Institute of Marine Science |year=2003 |orig-year=revised from 1998 edition |url=http://www.aims.gov.au/docs/projectnet/how-the-gbr-was-formed.html |access-date=22 November 2006 |url-status=dead |archive-url=https://web.archive.org/web/20100917063658/http://aims.gov.au/docs/projectnet/how-the-gbr-was-formed.html |archive-date=17 September 2010  }}</ref> or, in rare cases, volcanoes<ref name="HopleySmithers2007"/>{{rp|26}}).<ref name="HopleySmithers2007"/>{{rp|18}}
The Reef Research Centre, a [[Cooperative Research Centre]], has found coral 'skeleton' [[Deposit (geology)|deposits]] that date back half a million years.<ref name="CRCage">{{cite web |author=CRC Reef Research Centre Ltd |title=What is the Great Barrier Reef? |url=http://www.reef.crc.org.au/discover/coralreefs/coralgbr.html |access-date=28 May 2006 |url-status=dead |archive-url=https://web.archive.org/web/20060822015653/http://www.reef.crc.org.au/discover/coralreefs/coralgbr.html |archive-date=22 August 2006 }}</ref> The [[Great Barrier Reef Marine Park Authority]] (GBRMPA) considers the earliest evidence of complete reef structures to have been 600,000 years ago.<ref name = "GBRMPAage">{{cite web |author=Great Barrier Reef Marine Park Authority |year=2006 |url=http://www.gbrmpa.gov.au/__data/assets/pdf_file/0017/12437/Reef-Facts-01.pdf |archive-url=https://web.archive.org/web/20070620013057/http://www.gbrmpa.gov.au/__data/assets/pdf_file/0017/12437/Reef-Facts-01.pdf |archive-date=20 June 2007 |title=A 'big picture' view of the Great Barrier Reef |work=Reef Facts for Tour Guides |access-date=18 June 2007 }}</ref> According to the GBRMPA, the current, living reef structure is believed to have begun growing on the older platform about 20,000 years ago.<ref name = "GBRMPAage"/> The [[Australian Institute of Marine Science]] agrees, placing the beginning of the growth of the current reef at the time of the [[Last Glacial Maximum]]. At around that time, sea level was {{convert|120|m|ft}} lower than it is today.<ref name="AIMSage"/>
[[File:Arlington-Reef-2018-aerial-view-Luka-Peternel.jpg|thumb|Aerial view of [[Arlington Reef]]]]

From 20,000 years ago until 6,000 years ago, [[Sea level rise|sea level rose]] steadily around the world. As it rose, the corals could then grow higher on the newly submerged maritime margins of the hills of the coastal plain. By around 13,000 years ago the sea level was only {{convert|60|m|ft}} lower than the present day, and corals began to surround the hills of the coastal plain, which were, by then, [[continental islands]]. As the sea level rose further still, most of the continental islands were submerged. The corals could then overgrow the submerged hills, to form the present [[cay]]s and reefs. Sea level here has not risen significantly in the last 6,000 years.<ref name="AIMSage"/> The CRC Reef Research Centre estimates the age of the present, living reef structure at 6,000 to 8,000 years old.<ref name="CRCage"/> The shallow water reefs that can be seen in air-photographs and satellite images cover an area of 20,679&nbsp;km<sup>2</sup>, most (about 80%) of which<ref>{{Cite journal |last1=Harris |first1=Peter T. |last2=Bridge |first2=Thomas C.L. |last3=Beaman |first3=Robin J. |last4=Webster |first4=Jody M. |last5=Nichol |first5=Scott L. |last6=Brooke |first6=Brendan P. |date=1 March 2013 |title=Submerged banks in the Great Barrier Reef, Australia, greatly increase available coral reef habitat |journal=ICES Journal of Marine Science |volume=70 |issue=2 |pages=284–293 |doi=10.1093/icesjms/fss165 |issn=1054-3139 |doi-access=free }}</ref> has grown on top of limestone platforms that are relics of past (Pleistocene) phases of reef growth.<ref name="HopleySmithers2007">{{cite book |last1=Hopley |first1=David |last2=Smithers |first2=Scott G. |last3=Parnell |first3=Kevin |title=The Geomorphology of the Great Barrier Reef: Development, Diversity and Change |url=https://books.google.com/books?id=omr72hD6dvQC |year=2007 |publisher=Cambridge University Press |isbn=978-1-139-46392-8 |access-date=15 October 2016 |archive-date=31 December 2023 |archive-url=https://web.archive.org/web/20231231065925/https://books.google.com/books?id=omr72hD6dvQC |url-status=live }}</ref>

The remains of an ancient barrier reef similar to the Great Barrier Reef can be found in [[The Kimberley]], Western Australia.<ref>{{cite web |author=Western Australia's Department of Environment and Conservation |year=2007 |title=The Devonian 'Great Barrier Reef' |url=http://www.naturebase.net/content/view/668/96/ |access-date=12 March 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070911160512/http://www.naturebase.net/content/view/668/96/ |archive-date=11 September 2007 }}</ref>

The Great Barrier Reef World Heritage Area has been divided into 70 [[bioregion]]s,<ref>{{cite web |author=Great Barrier Reef Marine Park Authority |title=Representative Areas in the Marine Park |url=http://www.gbrmpa.gov.au/corp_site/key_issues/conservation/rep_areas |archive-url=https://web.archive.org/web/20070928020635/http://www.gbrmpa.gov.au/corp_site/key_issues/conservation/rep_areas |archive-date=28 September 2007 |access-date=23 March 2007 }}</ref> of which 30 are reef bioregions.<ref>{{cite web |author=Great Barrier Marine Park Authority |title=Protecting the Bioregions of the Great Barrier Reef |url=http://www.gbrmpa.gov.au/__data/assets/pdf_file/0003/7329/reef.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110602010234/http://www.gbrmpa.gov.au/__data/assets/pdf_file/0003/7329/reef.pdf |archive-date=2 June 2011 }}</ref><ref>{{cite web |author=Great Barrier Reef Marine Park Authority |url=http://www.gbrmpa.gov.au/corp_site/key_issues/conservation/rep_areas/consultation/bio-region_information_sheets_test |title=Bio-region Information Sheets |access-date=23 March 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070831153635/http://www.gbrmpa.gov.au/corp_site/key_issues/conservation/rep_areas/consultation/bio-region_information_sheets_test |archive-date=31 August 2007 }}</ref> In the northern part of the Great Barrier Reef, [[ribbon reef]]s and [[deltaic reef]]s have formed; these structures are not found in the rest of the reef system.<ref name = "CRCage"/> A previously undiscovered reef, 500 metres tall and 1.5&nbsp;km wide at the base, was found in the northern area in 2020.<ref>{{Cite web |last=Woodyatt |first=Amy |date=27 October 2020 |title='Massive' coral reef taller than the Empire State Building discovered in Australia |url=https://www.cnn.com/travel/article/great-barrier-reef-skyscraper-intl-scli-scn/index.html |access-date=27 October 2020 |website=CNN |language=en |archive-date=27 October 2020 |archive-url=https://web.archive.org/web/20201027144209/https://www.cnn.com/travel/article/great-barrier-reef-skyscraper-intl-scli-scn/index.html |url-status=live }}</ref> There are no [[atoll]]s in the system,<ref name="HopleySmithers2007"/>{{rp| 7}} and reefs attached to the mainland are rare.<ref name="HopleySmithers2007"/>{{rp|18}}

[[Fringing reef]]s are distributed widely, but are most common towards the southern part of the Great Barrier Reef, attached to high islands, for example, the [[Whitsunday Islands]]. [[Lagoonal reef]]s are found in the southern Great Barrier Reef, and further north, off the coast of [[Princess Charlotte Bay]]. [[wikt:crescentic|Crescentic]] reefs are the most common shape of reef in the middle of the system, for example the reefs surrounding [[Lizard Island]]. Crescentic reefs are also found in the far north of the Great Barrier Reef Marine Park, and in the Swain Reefs ([[20th parallel south|20]]–[[22nd parallel south|22 degrees south]]). [[Planar reef]]s are found in the northern and southern parts, near [[Cape York Peninsula]], Princess Charlotte Bay, and Cairns. Most of the islands on the reef are found on planar reefs.<ref name="HopleySmithers2007"/>{{rp|158–160}}

[[Wonky hole]]s can have localised impact on the reef, providing upwellings of fresh water, sometimes rich in nutrients contributing to [[eutrophication]].<ref>{{cite web |url=https://www.abc.net.au/catalyst/stories/s1640764.htm |title=Wonky Holes |work=Catalyst transcript |publisher=Australian Broadcasting Corporation |date=18 May 2006 |first=Mark |last=Horstman |access-date=17 April 2019 |archive-url=https://web.archive.org/web/20190419044122/https://www.abc.net.au/catalyst/stories/s1640764.htm |archive-date=19 April 2019 |url-status=live }}</ref><ref>
{{cite journal |url=https://www.newscientist.com/article/dn3049-wonky-holes-blamed-for-coral-death/ |title='Wonky holes' blamed for coral death |journal=New Scientist |date=15 November 2002 |first=Rachel |last=Nowak |access-date=17 April 2019 |archive-url=https://web.archive.org/web/20190417113842/https://www.newscientist.com/article/dn3049-wonky-holes-blamed-for-coral-death/ |archive-date=17 April 2019 |url-status=live}}
</ref>

Navigation through and around the reefs is a major challenge. More than 20 ships were recorded lost in the region between 1791 and 1850, Surveys between 1815 and 1860 by [[Phillip Parker King]] in the Mermaid, [[Francis Price Blackwood]] in HMS ''Fly'', [[Owen Stanley]] in the ''Rattlesnake,'' and [[Henry Mangles Denham]] in the Herald led to considerable navigational improvements, as they outlined the contrasting advantages and perils of the Inner Route (between Australia's east coast and the western edge of the reefs) and the Outer Route, in the open sea.<ref>{{Cite journal |date=18 March 2021 |title=Navigating the Great Barrier Reef: The Inner and Outer Routes, 1815-1860 |journal=[[International Journal of Maritime History]] |doi=10.1177/0843871421991164 |last1=Morgan |first1=Kenneth |volume=33 |pages=37–53 |doi-access=free }}</ref>