Editing Island (section)

== Geology ==

[[File:Hawaii hotspot cross-sectional diagram.jpg|thumb|upright=1.3|alt=A diagram showing the movement of continental plates causing the growth and weathering of an island chain.|[[Cross section (geology)|Cross section]] through Earth at the Hawaii hotspot. [[Magma]] from the [[Earth's mantle|mantle]] rises into the [[lithosphere]], creating a chain of volcanoes as the lithosphere moves over the hotspot.]]

=== Formation in oceans ===
Islands often are found in [[archipelagos]] or island chains, which are collections of islands. These chains are thought to form from [[Hotspot (geology)|volcanic hotspots]], areas of the [[lithosphere]] where the [[Mantle (geology)|mantle]] is hotter than the surrounding area.<ref name=":1">{{Cite journal |last=Wilson |first=J. Tuzo |date=June 1, 1963 |title=A Possible Origin of the Hawaiian Islands |url=http://www.nrcresearchpress.com/doi/10.1139/p63-094 |journal=Canadian Journal of Physics |language=en |volume=41 |issue=6 |pages=863–870 |doi=10.1139/p63-094 |bibcode=1963CaJPh..41..863W |issn=0008-4204}}</ref><ref name=":0" /> These hotspots would give rise to [[volcanoes]] whose [[lava]] would form the rock the islands are made of.<ref name=":1" /> For some islands, the [[Plate tectonics|movement of tectonic plates]] above stationary hotspots would form islands in a linear chain, with the islands further away from the hotspot being progressively older and more [[eroded]], before disappearing under the sea entirely.<ref name=":2">{{Cite journal |last=Jones |first=Anthony T |date=1993 |title=Review of the chronology of marine terraces in the Hawaiian Archipelago |url=https://www.researchgate.net/publication/222594231 |journal=Quaternary Science Reviews |volume=12 |issue=9 |pages=811–823 |doi=10.1016/0277-3791(93)90019-I |bibcode=1993QSRv...12..811J |via=Research Gate}}</ref> An example is the [[Hawaiian Islands]],<ref name=":2" /> with the oldest island being 25 million years old, and the youngest, [[Hawaii (island)|Hawaii]], still being an [[active volcano]].<ref name=":0" /> However, not all island chains are formed this way. Some may be formed all at once by fractures in the tectonic plates themselves, simultaneously creating multiple islands. One supporting piece of evidence is that of the [[Line Islands]], which are all estimated to be 8 million years old, rather than being different ages.<ref name=":0">{{Cite journal |last1=Neall |first1=Vincent E. |last2=Trewick |first2=Steven A. |date=October 27, 2008 |title=The age and origin of the Pacific islands: a geological overview |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |language=en |volume=363 |issue=1508 |pages=3293–3308 |doi=10.1098/rstb.2008.0119 |issn=0962-8436 |pmc=2607379 |pmid=18768382}}</ref>

Other island chains form due to being separated from existing continents. The [[Japanese archipelago]] may have been separated from [[Eurasia]] due to [[seafloor spreading]], a phenomenon where new [[oceanic crust]] is formed, pushing away older crust.<ref name=":0" /> Islands sitting on the [[continental shelf]] may be called continental islands.<ref name=":24" /> Other islands, like those that make up [[New Zealand]], are what remains of continents that shrank and sunk beneath the sea.<ref name=":3">{{Cite journal |last1=Wallis |first1=Graham P. |last2=Trewick |first2=Steven A. |date=2009 |title=New Zealand phylogeography: evolution on a small continent |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2009.04294.x |journal=Molecular Ecology |language=en |volume=18 |issue=17 |pages=3548–3580 |doi=10.1111/j.1365-294X.2009.04294.x |pmid=19674312 |bibcode=2009MolEc..18.3548W |issn=0962-1083}}</ref> It was estimated that [[Zealandia]], the continent-like area of crust that New Zealand sits on, has had 93% of its original surface area submerged.<ref name=":3" />

Some islands are formed when [[coral reefs]] grow on volcanic islands that have submerged beneath the surface.<ref name=":4">{{Cite journal |last1=Nunn |first1=Patrick D. |last2=Kumar |first2=Lalit |last3=Eliot |first3=Ian |last4=McLean |first4=Roger F. |date=March 2, 2016 |title=Classifying Pacific islands |journal=Geoscience Letters |language=en |volume=3 |issue=1 |pages=7 |doi=10.1186/s40562-016-0041-8 |doi-access=free |bibcode=2016GSL.....3....7N |issn=2196-4092}}</ref> When these [[coral islands]] encircle a central [[lagoon]], the island is known as an [[atoll]].<ref>{{Cite web |last=Magazine |first=Smithsonian |title=Why Some Geologists Say Charles Darwin's Theory of Coral Atoll Formation Is Wrong |url=https://www.smithsonianmag.com/science-nature/why-some-geologists-say-charles-darwins-theory-coral-atoll-formation-wrong-180977052/ |access-date=July 13, 2024 |website=Smithsonian Magazine |language=en}}</ref> The formation of reefs and islands related to those reefs is aided by the buildup of sediment in shallow patches of water. In some cases, tectonic movements lifting a reef out of the water by as little as 1 meter can cause sediment to accumulate and an island to form.<ref name=":4" />

[[Barrier islands]] are long, sandy bars that form along shorelines due to the deposition of sediment by [[Wave|waves]]. These islands erode and grow as the wind and waves shift. Barrier islands have the effect of protecting coastal areas from [[Extreme weather|severe weather]] because they absorb some of the energy of large waves before they can reach the shore.<ref>{{Cite web |last=US Department of Commerce |first=National Oceanic and Atmospheric Administration |title=What is a barrier island? |url=https://oceanservice.noaa.gov/facts/barrier-islands.html |access-date=June 28, 2024 |website=oceanservice.noaa.gov |language=EN-US}}</ref>

Antarctic islands, are sometimes permanently connected to another land mass by sea or glacial ice. An example of this is [[Ross Island]] in Antarctica.

=== Formation in freshwater ===
A [[fluvial island]] is an island that forms from the [[erosion]] and [[sedimentation]] of debris in rivers; almost all rivers have some form of fluvial islands.<ref name=":7">{{Cite journal |last=Baubinienė |first=Aldona |date=December 20, 2014 |title=Formation of fluvial islands and its determining factors, case study of the River Neris, the Baltic Sea basin |url=https://d1wqtxts1xzle7.cloudfront.net/48820472/Formation_of_fluvial_islands_and_its_det20160914-14035-1xkcopo-libre.pdf?1473836921=&response-content-disposition=inline%3B+filename%3DFormation_of_fluvial_islands_and_its_det.pdf&Expires=1719430050&Signature=OvtwcmzuH~UdKFPMnT1Xqh9rXXkb41RvtDt8Cdb06gpuroNIfCDzpkcJNWqaU0JZfdYeLcbfVOof4pC52l3i7s5AmzrfbAB8GiI-8lXXj82lbdazKd6Y6p09GRV2i4sizOiiAfl3Y479MVrer-n8CQ6qEquN1tGzfLjWZv0ne6bt1f1JLWpjXWBsgNEb~B3trjUEX3XL-8q9vQ0Msrq504jT77YoDfMCP8P5AbFJrJvNal4u85CUvs88zYY~7iMFiJNiWmw9-M8SzJk1aJMGZTBpiaf2eiRTg8OJa1RYiKs2WWVXaZ1H2NB2vIfFHZXz9a-u54RMWD-C3fJhhGjOfg__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA |journal=Geomorphology |volume= 231|issue=231 |pages=343–352 |doi=10.1016/j.geomorph.2014.12.025 |bibcode=2015Geomo.231..343B |via=Elsevier Science Direct}}</ref> These islands may only be a few meters high, and are usually temporary. Changes in the flow speed, water level, and sediment content of the river may effect the rate of fluvial island formation and depletion.<ref name=":7" /> Permanent river islands also exist, the largest of which (that is completely inland) is [[Bananal Island]] in the [[Tocantins]] of Brazil, which has a maximum width of 55 kilometers.<ref>{{Cite web |title=Bananal Island {{!}} Amazon Rainforest, Wildlife & Conservation {{!}} Britannica |url=https://www.britannica.com/place/Bananal-Island |access-date=June 27, 2024 |website=www.britannica.com |language=en}}</ref>

[[Lakes]] form for a variety of reasons, including [[Glacial lake|glaciers]], plate tectonics, and volcanism.<ref>{{Cite web |title=Lake |url=https://education.nationalgeographic.org/resource/lake |access-date=June 28, 2024 |website=education.nationalgeographic.org |language=en}}</ref> [[Lake island|Lake islands]] can form as part of these processes.<ref>{{Cite web |date=May 18, 2021 |title=Largest And Highest Islands Of The World |url=https://www.worldatlas.com/geography/largest-and-highest-islands-of-the-world.html |access-date=June 28, 2024 |website=WorldAtlas |language=en-US}}</ref>