Anisland orisle is a piece of land, distinct from a continent, completely surrounded by water. There are continental islands, which were formed by being split from acontinent byplate tectonics, and oceanic islands, which have never been part of a continent. Oceanic islands can be formed fromvolcanic activity, grow intoatolls fromcoral reefs, and form fromsediment along shorelines, creatingbarrier islands.River islands can also form from sediment and debris in rivers.Artificial islands are those made by humans, including small rocky outcroppings built out of lagoons and large-scaleland reclamation projects used for development.
Islands are host to diverseplant andanimal life. Oceanic islands have thesea as a natural barrier to the introduction of new species, causing the species that do reach the island to evolve in isolation. Continental islands share animal and plant life with the continent they split from. Depending on how long ago the continental island formed, the life on that island may have diverged greatly from the mainland due tonatural selection.
Humans have lived on and traveled between islands for thousands of years at a minimum. Some islands became host to humans due to aland bridge or a continental island splitting from the mainland, or by boat travel. In the far north or south some islands are joined by seasonal or glacial ice. Today, up to 10% of the world's population lives on islands. Islands are popular targets fortourism due to their perceived natural beauty, isolation, and unique cultures.
An island is an area of land surrounded by water on all sides that is distinct from a continent.[1] There is no standard of size that distinguishes islands andcontinents. Continents have an accepted geological definition – they are the largestlandmass of a particulartectonic plate.[2] Islands can occur in any body of water, includinglakes,rivers,seas.[3]Low-tide elevations, areas of land that are not above the surface during ahigh tide, are generally not considered islands.[4] Islands that have been bridged or otherwise joined to a mainland with land reclamation are sometimes considered "de-islanded", but not in every case.[5]
Etymology
The wordisland derives fromMiddle Englishiland, fromOld Englishigland (fromig orieg, similarly meaning 'island' when used independently, and-land carrying its contemporary meaning.Old Englishieg is actually acognate ofSwedishö andGermanAue, and more distantly related to Latinaqua (water).[6]
The spelling of the word was modified in the 15th century because of afalse etymology caused by an association with theOld French loanwordisle, which itself comes from theLatin wordinsula.[1][7] On that mistaken basis, the word acquired its silents, for which there is "neither phonetic nor etymological justification."[8]
Geology
Cross section through Earth at the Hawaii hotspot.Magma from themantle rises into thelithosphere, creating a chain of volcanoes as the lithosphere moves over the hotspot.
Formation in oceans
Islands often are found inarchipelagos or island chains, which are collections of islands. These chains are thought to form fromvolcanic hotspots, areas of thelithosphere where themantle is hotter than the surrounding area.[9][10] These hotspots would give rise tovolcanoes whoselava would form the rock the islands are made of.[9] For some islands, themovement 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 moreeroded, before disappearing under the sea entirely.[11] An example is theHawaiian Islands,[11] with the oldest island being 25 million years old, and the youngest,Hawaii, still being anactive volcano.[10] 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 theLine Islands, which are all estimated to be 8 million years old, rather than being different ages.[10]
Other island chains form due to being separated from existing continents. TheJapanese archipelago may have been separated fromEurasia due toseafloor spreading, a phenomenon where newoceanic crust is formed, pushing away older crust.[10] Islands sitting on thecontinental shelf may be called continental islands.[3] Other islands, like those that make upNew Zealand, are what remains of continents that shrank and sunk beneath the sea.[12] It was estimated thatZealandia, the continent-like area of crust that New Zealand sits on, has had 93% of its original surface area submerged.[12]
Some islands are formed whencoral reefs grow on volcanic islands that have submerged beneath the surface.[13] When thesecoral islands encircle a centrallagoon, the island is known as anatoll.[14] 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.[13]
Barrier islands are long, sandy bars that form along shorelines due to the deposition of sediment bywaves. These islands erode and grow as the wind and waves shift. Barrier islands have the effect of protecting coastal areas fromsevere weather because they absorb some of the energy of large waves before they can reach the shore.[15]
Antarctic islands, are sometimes permanently connected to another land mass by sea or glacial ice. An example of this isRoss Island in Antarctica.
Formation in freshwater
Afluvial island is an island that forms from theerosion andsedimentation of debris in rivers; almost all rivers have some form of fluvial islands.[16] 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 affect the rate of fluvial island formation and depletion.[16] Permanent river islands also exist, the largest of which (that is completely inland) isBananal Island in theTocantins of Brazil, which has a maximum width of 55 kilometers.[17]
Lakes form for a variety of reasons, includingglaciers, plate tectonics, and volcanism.[18]Lake islands can form as part of these processes.[19]
In biology, endemism is defined as the phenomenon where species or genus is only found in a certain geographical area. Islands isolate land organisms from others with water, and isolate aquatic organisms living on them with land.[21] Island ecosystems have the highest rates of endemism globally. This means that islands contribute heavily to globalbiodiversity.[22] Areas with high lives of biodiversity are a priority target ofconservation efforts, to prevent the extinction of these species.[23] Despite high levels of endemism, the totalspecies richness, the total number of unique species in a region, is lower on islands than on mainlands.[24] The level of species richness on islands is proportional to the area of that island, a phenomenon known as thespecies-area relationship. This is because larger areas have more resources and thus can support more organisms. Populations with a highercarrying capacity also have moregenetic diversity, which promotesspeciation.[21]
Dispersal
TheSeychelles fruit bat has a major role in distributing the seeds of trees between islands, a form of oceanic dispersal.[25]
Oceanic islands, ones that have never been connected to shore, are only populated by life that can cross the sea. This means that any animals present on the island had to have flown there, in the case ofbirds orbats, were carried by such animals, or were carried in a sea current in what is known as a "rafting event". This phenomenon is known asoceanic dispersal.[26]Tropical cyclones have the capacity to transport species over great distances.[27] Animals like tortoises can live for weeks without food or water, and are able to survive floating on debris in the sea.[28] One case study showed that in 1995, fifteeniguanas survived a 300 km journey toAnguilla in theCaribbean, an island which no iguana had lived on previously. They survived floating on a mass of uprooted trees from a storm.[29] Plant species are thought to be able to travel great distances of ocean. New Zealand and Australia share 200 native plant species, despite being separated by 1500 km.[26]
Continental islands, islands that were at one point connected to a continent, are expected to share a common history of plant and animal life up until the point that the island broke away from the continent.[26] For example, the presence offreshwater fish on an island surrounded by ocean would indicate that it once was attached to a continent, since these fish cannot traverse the ocean on their own.[21] Over the course of time, evolution and extinction changes the nature of animal life on a continental island, but only once it splits from the mainland. An example is that of thesouthern beech, a tree that is present in Australia, New Zealand, parts of South American, and New Guinea, places that today are geographically distant. A possible explanation for this phenomenon is that these landmasses were once all part of the continentGondwana and separated by tectonic drift. However, there are competing theories that suggest this species may have reached faraway places by way of oceanic dispersal.[26]
Species that colonize island archipelagos exhibit a specific property known asadaptive radiation. In this process, a species that arrives on a group of islands rapidly becomes more diverse over time, splitting off into new species or subspecies. A species that reaches an island ecosystem may face little competition for resources, or may find that the resources that they found in their previous habitat are not available. These factors together result in individual evolutionary branches with different means of survival.[30]
The classical example of this isDarwin's finches, a group of up to fifteentanager species that are endemic to the Galápagos Islands.[31] These birds evolved differentbeaks in order to eat different kinds of food available on the islands. Thelarge ground finch has a large bill used to crack seeds and eat fruit. TheGenovesa cactus finch preferscacti as a food source, and has a beak adapted for removing pulp and flowers from cacti. Thegreen warbler-finch (in the habit of truewarbler species) consumes spiders and insects that live on plants.[30] Other examples of this phenomenon exist worldwide, including in Hawaii and Madagascar, and are not limited to island ecosystems.[30]
The island rule
The extinctDodo is an example of island gigantism.
Species endemic to islands show a common evolutionary trajectory.Foster's rule (also known as the island rule), states that small mammals such asrodents evolve to become larger, known asisland gigantism. One such example is thegiant tortoise of theSeychelles, though it is unknown if it grew in size before or after reaching the island. Larger animals such as thehippopotamus tend to become smaller, such as in the case of thepygmy hippopotamus. This is known asinsular dwarfism.[32] In the case of smaller animals, it has been hypothesized that animals on islands may have fewerpredators and competitors, resulting in selection pressure towards larger animals. Larger animals may exhaust food resources quickly due to their size, causingmalnutrition in their young, resulting in a selection pressure for smaller animals that require less food. Having fewer predators would mean these animals did not need not be large to survive.[32]
Darwin, the Galápagos, and natural selection
Charles Darwin formulated the theory ofnatural selection through the study of island ecology.[21] The species he observed on theGalápagos Islands, including tanager birds, contributed to his understanding of how evolution works.[33] He first traveled to the islands as anaturalist onHMS Beagle in 1835, as part of a five-yearcircumnavigation of Earth. He wrote that "the different islands to a considerable extent are inhabited by a different set of beings".[34] Through the study of the finches and other animals he realized that organisms survive by changing to adapt to their habitat.[34] It would be over twenty years before he published his theories inOn the Origin of Species.[35]
The first evidence of humans colonizing islands probably occurred in thePaleolithic era, 100,000 to 200,000 years ago. Reaching theIndonesian islands ofFlores andTimor would have required crossing distances of water of at least 29 km (18 mi).[37] Some islands, such asHonshu, were probably connected to the mainland with aland bridge that allowed humans to colonize it before it became an island.[37]
The first people tocolonize distant oceanic islands were thePolynesians.[38] Many of the previous island settlements required traveling distances of less than 100 km (62 mi), whereas Polynesians may have traveled 2,000–3,200 km (1,200–2,000 mi) to settle islands such asTahiti.[37] They would send navigators to sail the ocean without the aid ofnavigational instruments to discover new islands for settlement.[38][39] Between 1100 and 800 BC, Polynesians sailed East fromNew Guinea and theSolomon Islands and reached the islands that make up the modern-dayFiji andSamoa.[40] The furthest extent of this migration would beEaster Island in the East, andNew Zealand in the South, with New Zealand's first settlements between 1250 and 1300.[41]
Historians have sought to understand why some remote islands have always been uninhabited, while others, especially in thePacific Ocean, have long been populated by humans.[37] Generally, larger islands are more likely to be able to sustain humans and thus are more likely to have been settled. Small islands that cannot sustain populations on their own can still be habitable if they are within a "commuting" distance to an island that has enough resources to be sustainable.[37] The presence of an island is marked byseabirds, differences in cloud and weather patterns, as well as changes in the direction of waves.[39][38] It is also possible for human populations to have gone extinct on islands, evidenced by explorers finding islands that show evidence of habitation but no life.[37]
Not all islands were or are inhabited by maritime cultures.[37][42] In the past, some societies were found to have lost their seafaring ability over time, such as the case of theCanary Islands, which were occupied by anindigenous people since the island's first discovery in the first century until being conquered by theSpanish Empire in 1496.[42] It has been hypothesized that since the inhabitants had little incentive fortrade and had little to any contact with the mainland, they had no need for boats.[42]
The motivation for island exploration has been the subject of research and debate. Some early historians previously argued that early island colonization was unintentional, perhaps by a raft being swept out to sea.[43] Others compare the motivations of Polynesian and similar explorers with those ofChristopher Columbus, the explorer who sailed westward over theAtlantic Ocean in search of an alternate route to theEast Indies.[37] These historians theorize that successful explorers were rewarded with recognition and wealth, leading others to attempt possibly dangerous expeditions to discover more islands, usually with poor results.[37]
Lifestyle
About 10% of the world's population lives on islands.[44] The study of the culture of islands is known asisland studies. The interest in the study of islands is due to their unique cultures and natural environments that differ from mainland cultures.[44] This is for a few reasons: First, the obvious political and geographic isolation from mainland cultures.[44] Second, unique restraints on resources and ecology creating marine-focused cultures with a focus onfishing and sailing.[44] Third, a lasting historical and political significance of islands.[44]
A breadfruit tree inMalaysia, used in Polynesia for making an edible breadfruit paste.Cultivated taro plants, astaple food for many island cultures.
Diet
The Polynesian diet got most of its protein from fishing.[45] Polynesians were known to fish close to shore, as well as in deep water. It was reported thatRapa Nui people were known to fish as far as 500 km (310 mi) from shore at coral reefs.[46]Spear,line, andnet fishing were all used,[47] to catchtuna as well assharks andstingrays.[46] Island cultures also cultivate native and non-native crops.[42] Polynesians grew the nativeyam,taro,breadfruit,banana,coconut and other fruits and vegetables.[48] Different island climates made different resources more important, such as the Hawaiian islands being home toirrigated fields of taro,[47] whereas in some islands, like Tahiti, breadfruit was more widely cultivated andfermented in order to preserve it.[49] There is archeological evidence that Canary Islanders would chew the roots offerns for sustenance, a practice that wore heavily on theirmolars.[42] These islanders would also growbarley and raised livestock such asgoats.[42]
Many island nations have little land and a restricted set of natural resources. However, these nations control some of the largestfisheries in the world, deposits ofcopper,gold, andnickel, as well asoil deposits. The natural beauty of island nations also makes them a magnet fortourism. Islands also have geopolitical value fornaval bases,weapons testing, and general territorial control. One such example isFrench Polynesia, a territory that receives substantial military expenditure and aid from France.[50] Three others,Palau,Federated States of Micronesia, and theMarshall Islands, are island nations of the Pacific region that maintain a defense, aid, and immigration agreement with the United States called aCompact of Free Association.[51]
Colonization
Residents ofBikini Atoll leaving due to nuclear testing.
Since the first discoveries of Polynesian,Micronesian, and other islands by Westerners, these nations have been the subject of colonization.[52] Islands were the target ofChristian missionaries. These missionaries faced resistance, but found success when some local chiefs used European support to centralize power. Beginning in the 16th century, European states placed most ofOceania in undercolonial administration.[53]Pohnpei was colonized by Spain as early as 1526. It changed hands from Germany to Japan to the United States before joining theFederated States of Micronesia in 1982, maintaining a "free association" status with the U.S.[54]Guam was a Spanish territory until 1898, and now is anunincorporated territory of the U.S.[55]
Thedecolonization era saw many island states achieve independence or some form ofself-governance.[56] Nuclear weapons testing on theMarshall Islands left many atolls destroyed or uninhabitable, causing theforced displacement of people from their home islands as well as increases in cancer rates due toradiation.[52] Colonization has resulted in a decline of observance of traditional cultural practices in places such as Hawaii, where Native Hawaiians are now a minority. Cultural attitudes related to communal ownership of land as well as a lack of individualistic decision-making may make some island cultures less compatible with the globalcapitalist economy, causing these nations to experience less economic growth.[56]
Tourists are attracted to tropical beaches in large numbers, such as this one inMalapascua, thePhilippines.
Tourism
Islands have long been a popular target fortourism, thanks to their unique climates, cultures, and natural beauty. However, islands may suffer from poor transportation connectivity fromairplanes and boats and strains on infrastructure from tourist activity.[57] Islands in colder climates often rely on seasonal tourists seeking to enjoy nature or local cultures, and may only be one aspect of an island's economy. In contrast, tourism on tropical islands can often make up the majority of the local economy andbuilt environment. These islands sometimes also require consistentforeign aid on top of tourism in order to ensure economic growth. This reliance can result insocial inequality andenvironmental degradation. During tourism downturns, these economies struggle to make up the lost inflow of cash with other industries.[57]
Threats to islands
San Juan, Puerto Rico after Hurricane Maria. Climate change is expected to cause more frequent inland flooding on islands.
Climate change threatens human development on islands due tosea level rise, more dangeroustropical cyclones,coral bleaching, and an increase ininvasive species.[58] For example, in 2017Hurricane Maria caused a loss of almost all the infrastructure in Dominica. Sea level rise and other climate changes can reduce freshwater reserves, resulting indroughts.[58] These risks are expected to decrease the habitability of islands, especially small ones. Beyond risks to human life, plant and animal life are threatened. It has been estimated that almost 50 percent of land species threatened byextinction live on islands.[58] In 2017, a detailed review of 1,288 islands found that they were home to 1,189 highly-threatened vertebrate species, which was 41 percent of the global figure.[59] Coral bleaching is expected to occur with more frequency, threatening marine ecosystems, some of which island economies are dependent on.[58]
Some islands that are low-lying may cease to exist given high enough amounts of sea level rise.Tuvalu received media attention for a press conference publicizing the ongoing submerging of the island country.[60] Tuvalu signed a cooperation agreement with Australia agreeing to annually allow 280 of its citizens to becomepermanent residents of Australia. The Marshall Islands, a country of 1,156 islands, have also been identified as a country that may be existentially threatened by rising seas.[60]
Increasing intensity of tropical storms also increases the distances and frequency with which invasive species may be transported to islands. Floodwaters from these storms may also wash plants further inland than they would travel on their own, introducing them to new habitats.[27]Agriculture and trade also have introduced non-native life to islands. These processes result in an introduction ofinvasive species to ecosystems that are especially small and fragile. One example is theapple snail, initially introduced to the U.S. byaquarium owners. It has since been transported by hurricanes across theGulf Coast and neighboring islands.[27] These species compete for resources with native animals, and some may grow so densely that they displace other forms of existing life.[27]
For hundreds of years, islands have been created throughland reclamation.[61] One of the first recorded instances of this when people of theSolomon Islands created eighty such islands by piling coral and rock in theLau Lagoon.[61] One traditional way of constructing islands is with the use of arevetment. Sandbags or stones are dropped with a barge into the sea to bring the land level slightly out of the water. The island area is then filled with sand or gravel, followed by a construction of this revetment to hold it together.[62] Islands have also been constructed with a permanentcaisson, a steel or concrete structure built in a closed loop and then filled with sand.[62]
Some modern islands have been constructed by pouring millions of tons of sand into the sea, such as withPearl Island in Qatar or thePalm Islands in Dubai.[61] These islands are usually created forreal estate development, and are sold for private ownership or construction of housing.[61]Offshore oil platforms have also been described as a type of island. Some atolls have been covered in concrete to create artificial islands for military purposes, such as those created by China in theSouth China Sea.[61][63] These atolls were previously low-tide elevations, landmasses that are only above water duringlow tide. TheUnited Nations Convention on the Law of the Sea indicates that these islands may not have the same legal status as a naturally occurring island, and as such may not confer the same legal rights.[63]
^Baldacchino, Godfrey (2007).Bridging islands: the impact of fixed links. Charlottetown, Prince Edward Island: Acorn Press.ISBN978-1-894838-24-5.OCLC70884504.
^Fairbairn, Te'o I.J. (1991).The Pacific Islands: Politics, Economics, and International Relations. University of Hawaii Press. pp. 1–11.ISBN0-86638-140-6.
^abBrown, Keith G.; Cave, Jenny (January 1, 2010). G. Brown, Keith; Cave, Jenny (eds.). "Island tourism: marketing culture and heritage – editorial introduction to the special issue".International Journal of Culture, Tourism and Hospitality Research.4 (2):87–95.doi:10.1108/17506181011045163.ISSN1750-6182.
^abcdIntergovernmental Panel on Climate Change (IPCC), ed. (2023),"Small Islands",Climate Change 2022 – Impacts, Adaptation and Vulnerability: Working Group II Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge: Cambridge University Press, pp. 2043–2122,doi:10.1017/9781009325844.017,ISBN978-1-009-32583-7, retrievedJuly 9, 2024
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