Great Barrier Reef

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Great Barrier Reef

UNESCO World Heritage Site
Satellite image of part of the Great Barrier Reef adjacent to the Queensland coastal areas of Airlie Beach and Mackay
Location	Off the east coast of the Queensland mainland, Australia
Criteria	Natural: vii, viii, ix, x
Reference	154
Inscription	1981 (5th session)
Area	34,870,000 ha
Website	www.gbrmpa.gov.au
Coordinates	18°17′S 147°42′ECoordinates: 18°17′S 147°42′E
Centre of the Great Barrier Reef  The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,300 kilometres (1,400 mi) over an area of approximately 344,400 square kilometres (133,000 sq mi). The reef is located in the Coral Sea, off the coast of Queensland, Australia. The Great Barrier Reef can be seen from outer space and is the world's biggest single structure made by living organisms. This reef structure is composed of and built by billions of tiny organisms, known as coral polyps. It supports a wide diversity of life and was selected as a World Heritage Site in 1981. CNN labelled it one of the seven natural wonders of the world in 1997. Australian World Heritage places included it in its list in 2007. The Queensland National Trust named it a state icon of Queensland in 2006.

A large part of the reef is protected by the Great Barrier Reef Marine Park, which helps to limit the impact of human use, such as fishing and tourism. Other environmental pressures on the reef and its ecosystem include runoff, climate change accompanied by mass coral bleaching, dumping of dredging sludge and cyclic population outbreaks of the crown-of-thorns starfish. According to a study published in October 2012 by the Proceedings of the National Academy of Sciences, the reef has lost more than half its coral cover since 1985, a finding reaffirmed by a 2020 study which found over half of the reef's coral cover to have been lost between 1995 and 2017, with the effects of a widespread 2020 bleaching event not yet quantified.

The Great Barrier Reef has long been known to and used by the Aboriginal Australian and Torres Strait Islander peoples, and is an important part of local groups' cultures and spirituality. The reef is a very popular destination for tourists, especially in the Whitsunday Islands and Cairns regions. Tourism is an important economic activity for the region, generating over AUD$3 billion per year. In November 2014, Google launched Google Underwater Street View in 3D of the Great Barrier Reef.

A March 2016 report stated that coral bleaching was more widespread than previously thought, seriously affecting the northern parts of the reef as a result of. In October 2016, Outside published an obituary for the reef; the article was criticized for being premature and hindering efforts to bolster the resilience of the reef. In March 2017, the journal Nature published a paper showing that huge sections of an 800-kilometre (500 mi) stretch in the northern part of the reef had died in the course of 2016 due to high water temperatures, an event that the authors put down to the effects of global climate change. The percentage of baby corals being born on the Great Barrier Reef dropped drastically in 2018 and scientists are describing it as the early stage of a "huge natural selection event unfolding". Many of the mature breeding adults died in the bleaching events of 2016–17 leading to low coral birth rates. The types of corals that reproduced also changed, leading to a "long-term reorganisation of the reef ecosystem if the trend continues."

The Great Barrier Reef Marine Park Act 1975 (section 54) demands every five years an Outlook Report on the Reef's health, pressures, and future. The last report was published in 2019.

Geology and geography

Aerial photography

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 1,915 km (1,190 mi) southeast of Bramble Cay as the crow flies. It includes the smaller Murray Islands.

The plate tectonic theory indicates Australia has moved northwards at a rate of 7 cm (2.8 in) per year, starting during the Cenozoic. Eastern Australia experienced a period of tectonic uplift, which moved the drainage divide in Queensland 400 km (250 mi) inland. Also during this time, Queensland experienced volcanic eruptions leading to central and shield volcanoes and basalt flows. Some of these became high islands. After the Coral Sea 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—too cool to support coral growth. 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.

The Great Barrier Reef is clearly visible from aircraft flying over it.

Reefs can increase in diameter by 1 to 3 centimetres (0.39 to 1.18 in) per year, and grow vertically anywhere from 1 to 25 cm (0.39 to 9.84 in) per year; however, they grow only above a depth of 150 metres (490 ft) due to their need for sunlight, and cannot grow above sea level. When Queensland edged into tropical waters 24 million years ago, some coral grew, but a sedimentation regime quickly developed with erosion of the Great Dividing Range; creating river deltas, oozes and turbidites, 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 4 °C (7 °F) water temperature change.

Heron Island, a coral cay in the southern Great Barrier Reef

The land that formed the 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 or, in rare cases, volcanoes). The Reef Research Centre, a Cooperative Research Centre, has found coral 'skeleton' deposits that date back half a million years. The Great Barrier Reef Marine Park Authority (GBRMPA) considers the earliest evidence of complete reef structures to have been 600,000 years ago. According to the GBRMPA, the current, living reef structure is believed to have begun growing on the older platform about 20,000 years ago. 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 120 metres (390 ft) lower than it is today.

Aerial view of Arlington Reef

From 20,000 years ago until 6,000 years ago, 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 60 metres (200 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 cays and reefs. Sea level here has not risen significantly in the last 6,000 years. The CRC Reef Research Centre estimates the age of the present, living reef structure at 6,000 to 8,000 years old. The shallow water reefs that can be seen in air-photographs and satellite images cover an area of 20,679 km², most (about 80%) of which has grown on top of limestone platforms that are relics of past (Pleistocene) phases of reef growth.

The remains of an ancient barrier reef similar to the Great Barrier Reef can be found in The Kimberley, Western Australia.

The Great Barrier Reef World Heritage Area has been divided into 70 bioregions, of which 30 are reef bioregions. In the northern part of the Great Barrier Reef, ribbon reefs and deltaic reefs have formed; these structures are not found in the rest of the reef system. A previously undiscovered reef, 500 meters tall and 1.5 km wide at the base, was found in the northern area in 2020. There are no atolls in the system, and reefs attached to the mainland are rare.

Fringing reefs 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 reefs are found in the southern Great Barrier Reef, and further north, off the coast of Princess Charlotte Bay. 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 (20–22 degrees south). Planar reefs 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.

Wonky holes can have localised impact on the reef, providing upwellings of fresh water, sometimes rich in nutrients contributing to eutrophication.

Ecology

A variety of colourful corals on Flynn Reef near Cairns

 

Moore Reef

The Great Barrier Reef supports an extraordinary diversity of life, including many vulnerable or endangered species, some of which may be endemic to the reef system.

A green sea turtle on the Great Barrier Reef

Thirty species of cetaceans have been recorded in the Great Barrier Reef, including the dwarf minke whale, Indo-Pacific humpback dolphin, and the humpback whale. Large populations of dugongs live there. More than 1,500 fish species live on the reef, including the clownfish, red bass, red-throat emperor, and several species of snapper and coral trout. Forty-nine species mass spawn, while eighty-four other species spawn elsewhere in their range. Seventeen species of sea snake live on the Great Barrier Reef in warm waters up to 50 metres (160 ft) deep and are more common in the southern than in the northern section. None found in the Great Barrier Reef World Heritage Area are endemic, nor are any endangered.

Six species of sea turtles come to the reef to breed: the green sea turtle, leatherback sea turtle, hawksbill turtle, loggerhead sea turtle, flatback turtle, and the olive ridley. The green sea turtles on the Great Barrier Reef have two genetically distinct populations, one in the northern part of the reef and the other in the southern part. Fifteen species of seagrass in beds attract the dugongs and turtles, and provide fish habitat. The most common genera of seagrasses are Halophila and Halodule.

Saltwater crocodiles live in mangrove and salt marshes on the coast near the reef. Nesting has not been reported, and the salt water crocodile population in the GBRWHA is wide-ranging but low density. Around 125 species of shark, stingray, skates or chimaera live on the reef. Close to 5,000 species of mollusc have been recorded on the reef, including the giant clam and various nudibranchs and cone snails. Forty-nine species of pipefish and nine species of seahorse have been recorded. At least seven species of frog inhabit the islands.

215 species of birds (including 22 species of seabirds and 32 species of shorebirds) visit the reef or nest or roost on the islands, including the white-bellied sea eagle and roseate tern. Most nesting sites are on islands in the northern and southern regions of the Great Barrier Reef, with 1.4 to 1.7 million birds using the sites to breed. The islands of the Great Barrier Reef also support 2,195 known plant species; three of these are endemic. The northern islands have 300–350 plant species which tend to be woody, whereas the southern islands have 200 which tend to be herbaceous; the Whitsunday region is the most diverse, supporting 1,141 species. The plants are propagated by birds.

A striped surgeonfish amongst the coral on Flynn Reef

There are at least 330 species of ascidians on the reef system with the diameter of 1–10 cm (0.4–4 in). Between 300–500 species of bryozoans live on the reef. Four hundred coral species, both hard corals and soft corals inhabit the reef. The majority of these spawn gametes, breeding in mass spawning events that are triggered by the rising sea temperatures of spring and summer, the lunar cycle, and the diurnal cycle. Reefs in the inner Great Barrier Reef spawn during the week after the full moon in October, while the outer reefs spawn in November and December. Its common soft corals belong to 36 genera. Five hundred species of marine algae or seaweed live on the reef, including thirteen species of genus Halimeda, which deposit calcareous mounds up to 100 metres (110 yd) wide, creating mini-ecosystems on their surface which have been compared to rainforest cover.

Environmental threats

Sea temperature and bleaching of the Great Barrier Reef

Climate change, pollution, crown-of-thorns starfish and fishing are the primary threats to the health of this reef system. Other threats include shipping accidents, oil spills, and tropical cyclones. Skeletal Eroding Band, a disease of bony corals caused by the protozoan Halofolliculina corallasia, affects 31 coral species. According to a 2012 study by the National Academy of Science, since 1985, the Great Barrier Reef has lost more than half of its corals with two-thirds of the loss occurring from 1998 due to the factors listed before.

Climate change

The Great Barrier Reef Marine Park Authority considers the greatest threat to the Great Barrier Reef to be climate change, causing ocean warming which increases coral bleaching. Mass coral bleaching events due to marine heatwaves occurred in the summers of 1998, 2002, 2006, 2016, 2017 and 2020, and coral bleaching is expected to become an annual occurrence. In 2020, a study found that the Great Barrier Reef has lost more than half of its corals since 1995 due to warmer seas driven by climate change. As global warming continues, corals will not be able to keep up with increasing ocean temperatures. Coral bleaching events lead to increased disease susceptibility, which causes detrimental ecological effects for reef communities.

In July 2017 UNESCO published in a draft decision, expressing serious concern about the impact of coral bleaching on the Great Barrier Reef. The draft decision also warned Australia that it will not meet the targets of the Reef 2050 report without considerable work to improve water quality.

Climate change has implications for other forms of reef life—some fish's preferred temperature range leads them to seek new habitat, thus increasing chick mortality in predatory seabirds. Climate change will also affect the population and sea turtle's available habitat.

Bleaching events in benthic coral communities (deeper than 20 metres or 66 feet) in the Great Barrier reef are not as well documented as those at shallower depths, but recent research has shown that benthic communities are just as negatively impacted in the face of rising ocean temperatures. Five Great Barrier Reef species of large benthic corals were found bleached under elevated temperatures, affirming that benthic corals are vulnerable to thermal stress.

Pollution

Another key threat faced by the Great Barrier Reef is pollution and declining water quality. The rivers of north eastern Australia pollute the Reef during tropical flood events. Over 90% of this pollution comes from farm runoff. 80% of the land adjacent to the Great Barrier Reef is used for farming including intensive cropping of sugar cane, and major beef cattle grazing. Farming practices damage the reef due to overgrazing, increased run-off of agricultural sediments, nutrients and chemicals including fertilisers, herbicides and pesticides representing a major health risk for the coral and biodiversity of the reefs. Sediments containing high levels of copper and other heavy metals sourced from the Ok Tedi Mine in Papua New Guinea are a potential pollution risk for the far northern Great Barrier Reef and Torres Strait regions.

Some 67% of corals died in the reef's worst-hit northern section, the ARC Centre of Excellence for Coral Reef Studies report said.

Loss of coastal wetland

The runoff problem is exacerbated by the loss of coastal wetlands which act as a natural filter for toxins and help deposit sediment. It is thought that the poor water quality is due to increased light and oxygen competition from algae.

Eutrophication

Farming fertiliser runoff release nitrogen, phosphorus, and potassium into the oceanic ecosystem, and these limiting nutrients cause massive algal growth which eventually leads to a reduction in oxygen available for other creatures in a process called eutrophication. This decreases the biodiversity in the affected areas, altering the species composition. A study by Katharina Fabricius and Glen Death of Australian Institute of Marine Science found that hard corals numbers were almost double on reefs that were far from agricultural areas.

Fertilizers also increase the amount of phytoplankton available for the crown-of-thorns starfish larvae to consume. A study showed that a doubling of the chlorophyll in the water leads to a tenfold increase in the crown-of-thorns starfish larvae's survival rate.

Sediment runoff

Sediment runoff from farming carries chemicals into the reef environment also reduces the amount of light available to the corals decreasing their ability to extract energy from their environment.

Pesticides

Pesticides used in farming are made up of heavy metals such as lead, mercury, arsenic and other toxins are released into the wider environment due to erosion of farm soil, which has a detrimental effect on the coral.

Pollution from mining

Mining company Queensland Nickel discharged nitrate-laden water into the Great Barrier Reef in 2009 and 2011 – on the later occasion releasing 516 tonnes (508 long tons; 569 short tons) of waste water. The Great Barrier Reef Marine Park Authority (GBRMPA) stated "We have strongly encouraged the company to investigate options that do not entail releasing the material to the environment and to develop a management plan to eliminate this potential hazard; however, GBRMPA does not have legislative control over how the Yabulu tailings dam is managed".

Crown of thorns

Crown-of-thorns starfish

The crown-of-thorns starfish preys on coral polyps. Large outbreaks of these starfish can devastate reefs. In 2000, an outbreak contributed to a loss of 66% of live coral cover on sampled reefs in a study by the Reef Research Centre (RRC). Outbreaks are believed to occur in natural cycles, worsened by poor water quality and overfishing of the starfish's predators.

Overfishing

The unsustainable overfishing of keystone species, such as the giant Triton, can disrupt food chains vital to reef life. Fishing also impacts the reef through increased water pollution from boats, by-catch of unwanted species (such as dolphins and turtles) and habitat destruction from trawling, anchors and nets. As of the middle of 2004, approximately one-third of the Great Barrier Reef Marine Park is protected from species removal of any kind, including fishing, without written permission.

The Shen Neng 1 aground on the Great Barrier Reef, 5 April 2010

Shipping

Shipping accidents are a pressing concern, as several commercial shipping routes pass through the Great Barrier Reef. Although the route through the Great Barrier Reef is not easy, reef pilots consider it safer than outside the reef in the event of mechanical failure, since a ship can sit safely while being repaired. There have been over 1,600 known shipwrecks in the Great Barrier Reef region. On 3 April 2010, the bulk coal carrier Shen Neng 1 ran aground on Douglas Shoals, spilling up to four tonnes of oil into the water and causing extensive damage to the reef.

Shark culling

The government of Queensland has a "shark control" program (shark culling) that deliberately kills sharks throughout Queensland, including in the Great Barrier Reef. Environmentalists and scientists say that this program harms the marine ecosystem; they also say it is "outdated, cruel and ineffective". The Queensland "shark control" program uses shark nets and drum lines with baited hooks to kill sharks in the Great Barrier Reef – there are 173 lethal drum lines in the Great Barrier Reef. In Queensland, sharks found alive on the baited hooks are shot. Queensland's "shark control" program killed about 50,000 sharks from 1962 to 2018. Also, Queensland's "shark control" program has also killed many other animals (such as dolphins and turtles) — the program killed 84,000 marine animals from 1962 to 2015, including in the Great Barrier Reef. In 2018, Humane Society International filed a lawsuit against the government of Queensland to stop shark culling in the Great Barrier Reef.

Protection and preservation: Reef 2050 plan

In March 2015, the Australian and Queensland's governments formed a plan for the protection and preservation of the reef's universal heritage until 2050. This 35 years plan, titled "Reef 2050 Plan" is a document proposing possible measures for the long-term management of the pollution, climate change and other issues that threaten the life span and value of this global heritage. The plan contains all the elements for measurement and improvements, including; long-term sustainability plan, water quality improvement plan and the investment plan for the protection and preservation of The Reef until 2050.

However, whereas the 2050 plan aims to incorporate protective measures such as improving water quality, reef restoration, killing of predatory starfish, it does not incorporate additional measures to address the root cause the problem namely climate change (which is caused by greenhouse gas emissions). As such, experts doubt on whether it will be enough to save the fragile environment. Another issue is that the time left to the 1.5 °C warming threshold (the temperature limit that coral reefs can still cope with) is very limited.

As part of the Reef 2050 plan, an AUD$443 million grant was given to the Great Barrier Reef Foundation in 2018. The announcement of the grant was subject to backlash as the grant had avoided proper tender and transparency processes.

Human use

The Great Barrier Reef has long been known to and used by the Aboriginal Australian and Torres Strait Islander peoples. Aboriginal Australians have been living in the area for at least 40,000 years, and Torres Strait Islanders since about 10,000 years ago. For these 70 or so clan groups, the reef is also an important cultural feature.

In 1768 Louis de Bougainville found the reef during an exploratory mission, but did not claim the area for the French. On 11 June 1770, HM Bark Endeavour, captained by explorer James Cook, ran aground on the Great Barrier Reef, sustaining considerable damage. Lightening the ship and re-floating it during an incoming tide eventually saved it. One of the most famous wrecks was HMS Pandora, which sank on 29 August 1791, killing 35 men. The Queensland Museum has led archaeological digs to wreck of Pandora since 1983. Because the reef had no atolls, it was largely unstudied in the 19th century. During this time, some of the reef's islands were mined for deposits of guano, and lighthouses were built as beacons throughout the system. as in Raine Island, the earliest example. In 1922, the Great Barrier Reef Committee began carrying out much of the early research on the reef.

Management

Map of The Great Barrier Reef Region, World Heritage Area and Marine Park, 2014

Royal Commissions disallowed oil drilling in the Great Barrier Reef, in 1975 the Government of Australia created the Great Barrier Reef Marine Park and prohibited various activities. The Great Barrier Reef Marine Park does not include the entire Great Barrier Reef Province. The park is managed, in partnership with the Government of Queensland, through the Great Barrier Reef Marine Park Authority to ensure that it is used in a sustainable manner. A combination of zoning, management plans, permits, education and incentives (such as eco-tourism certification) are employed in the effort to conserve the reef.

In 1999, the Australian Parliament passed the Environment Protection and Biodiversity Conservation Act, which improved the operation of national environmental law by providing guidance about regional biodiversity conservation priorities. The marine bioregional planning process came from the implementation of this law. This process conserves marine biodiversity by considering the whole ecosystem a species is in and how different species interact in the marine environment.

There are two steps to this process. The first step is to identify regional conservation priorities in the five (currently) different marine regions. The second step is to identify marine reserves (protected areas or marine parks) to be added to Australia's National Representative System of Marine Protected Areas. Like protected areas on land, marine reserves are created to protect biodiversity for generations to come. Marine reserves are identified based on criteria written in a document created by Australian and New Zealand Environment and Conservation Council called "Guidelines for establishing the national representative system of marine protected areas", also known as just "the Guidelines". These guidelines are nationally recognised and implemented at the local level based on the Australian policy for implementation outlined in the "Goals and Principles for the Establishment of the National Representative System of Marine Protected Areas in Commonwealth Waters". These policies are in place to make sure that a marine reserve is only added to the NRSMPA after careful evaluation of different data.

The priorities for each region are created based on human and environmental threats and the Marine Bioregional Plans are drafted to address these priorities. To assess different region's priorities, three steps are taken, first, a bioregional profile is created, second, a bioregional plan is drafted, and third, the plan is finalised. After the plan is finalised, activity in different bioregions may become limited based on particular threats an activity may pose.

In 2001, the GBRMPA released a report about the declining water quality in the Great Barrier Reef and detailed the importance of this issue. In response to this report, in 2003, the Australian and Queensland governments launched a joint initiative to improve the quality of water entering the Great Barrier Reef. The decline in the quality of water over the past 150 years (due to development) has contributed to coral bleaching, algal blooms, and pesticide pollution. These forms of pollution have made the reef less resilient to climate change.

When the plan was introduced in October 2003, it originally contained 65 actions built on previous legislation. Their immediate goal was to halt and reverse the decline in water quality entering the reef by 2013. By 2020, they hope that the quality of the water entering in the reef improves enough so that it doesn't have a detrimental impact on the health of the Great Barrier Reef. To achieve these goals they decided to reduce pollutants in the water entering the reef and to rehabilitate and conserve areas of the reef that naturally help reduce water pollutants. To achieve the objectives described above, this plan focuses on non-point sources of pollution, which cannot be traced to a single source such as a waste outlet.

The plan specifically targets nutrients, pesticides and sediment that make their way into the reef as a result of agricultural activities. Other non-point sources of pollution that are attributed to urban areas are covered under different legislation. In 2009, the plan was updated. The updated version states that to date, none of the efforts undertaken to improve the quality of water entering the reef has been successful. The new plan attempts to address this issue by "targeting priority outcomes, integrating industry and community initiatives and incorporating new policy and regulatory frameworks (Reef Plan 5)". This updated version has improved the clarity of the previous plan and targets set by that plan, have improved accountability and further improved monitoring and assessment. The 2009 report found that 41 out of the 65 actions met their original goals, however, 18 were not progressing well according to evaluation criteria as well as 6 were rated as having unsatisfactory levels of progress.

Some key achievements made since the plan's initial passing in 2003 were the establishment of the Reef Quality Partnership to set targets, report findings and monitor progress towards targets, improved land condition by landowners was rewarded with extended leases, Water Quality Improvement Plans were created to identify regional targets and identified management changes that needed to be made to reach those targets, Nutrient Management Zones have been created to combat sediment loss in particular areas, education programs have been started to help gather support for sustainable agriculture, changes to land management practices have taken place through the implementation of the Farm Management Systems and codes of practice, the creation of the Queensland Wetland program and other achievements were made to help improve the water quality flowing into the coral reefs.

A taskforce of scientists was also created to assess the impact of different parts of the plan on the quality of water flowing into the coral reefs. They found that many of the goals have yet to be reached but found more evidence that states that improving the water quality of the Great Barrier Reef will improve its resilience to climate change. The Reefocus summit in 2008, which is also detailed in the report, came to similar conclusions. After this, a stakeholder working group was formed that worked between several groups as well as the Australian and Queensland governments to update reef goals and objectives. The updated version of the plan focuses on strategic priority areas and actions to achieve 2013 goals. Also quantitative targets have been made to critically assess whether targets are being met.

Some examples of the water quality goals outlined by this plan are that by 2013, there will be a 50% reduction in nitrogen and phosphorus loads at the end of catchments and that by 2020, there will be a reduction in sediment load by 20%. The plan also outlines a number of steps that must be taken by landholders to help improve grazing, soil, nutrient, and chemical management practices. There are also a number of supporting initiatives to take place outlined in the plan to help create a framework to improve land use practices which will in turn improve water quality.

Through these means the governments of Australia and Queensland hope to improve water quality by 2013. The 2013 outlook report and revised water quality plan will assess what needs to be done in the future to improve water quality and the livelihoods of the wildlife that resides there.

A blue starfish (Linckia laevigata) resting on hard Acropora and Porites corals

In July 2004, a new zoning plan took effect for the entire Marine Park, and has been widely acclaimed as a new global benchmark for marine ecosystem conservation. The rezoning was based on the application of systematic conservation planning techniques, using marxan software. While protection across the Marine Park was improved, the highly protected zones increased from 4.5% to over 33.3%. At the time, it was the largest Marine Protected Area in the world, although in 2006, the new Northwestern Hawaiian Islands National Monument became the largest.

In 2006, a review of the Great Barrier Reef Marine Park Act of 1975 recommended that there should be no further zoning plan changes until 2013, and that every five years, a peer-reviewed outlook report should be published, examining the reef's health, management, and environmental pressures. In each outlook report, several assessments are required. Each assessment has a set of assessment criteria that allows for better presentation of available evidence. Each assessment is judged by these criteria and given a grade. Every outlook report follows the same judging and grading process so that information can be tracked over time. No new research is done to produce the report. Only readily available information goes into the report so little of what is known about the Reef is actually featured in each outlook report.

Abbot Point coal port dredge dumping controversy

In December 2013, Greg Hunt, the Australian environment minister, approved a plan for dredging to create three shipping terminals as part of the construction of a coalport. According to corresponding approval documents, the process will create around 3 million cubic metres of dredged seabed that will be dumped within the Great Barrier Reef marine park area.

On 31 January 2014, the GBRMPA issued a dumping permit that will allow three million cubic metres of sea bed from Abbot Point, north of Bowen, to be transported and unloaded in the waters of the Great Barrier Reef Marine Park. Potential significant harms have been identified in relation to dredge spoil and the process of churning up the sea floor in the area and exposing it to air: firstly, new research shows the finer particles of dredge spoil can cloud the water and block sunlight, thereby starving sea grass and coral up to distances of 80 km away from the point of origin due to the actions of wind and currents. Furthermore, dredge spoil can literally smother reef or sea grass to death, while storms can repeatedly resuspend these particles so that the harm caused is ongoing; secondly, disturbed sea floor can release toxic substances into the surrounding environment.

The dredge spoil from the Abbot Point port project is to be dumped 24 kilometres (15 mi) away, near Bowen in north Queensland, and the approval from the Authority will result in the production of an extra 70 million tonnes of coal annually, worth between A$1.4 billion and $2.8 billion. Authority chairman, Dr Russell Reichelt, stated after the confirmation of the approval:

This approval is in line with the agency's view that port development along the Great Barrier Reef coastline should be limited to existing ports. As a deepwater port that has been in operation for nearly 30 years, Abbot Point is better placed than other ports along the Great Barrier Reef coastline to undertake expansion as the capital and maintenance dredging required will be significantly less than what would be required in other areas. It's important to note the seafloor of the approved disposal area consists of sand, silt and clay and does not contain coral reefs or seagrass beds.

The approval was provided with a corresponding set of 47 new environmental conditions that include the following:

• A long-term water quality monitoring plan extending five years after the disposal activity is completed.
• A heritage management plan to protect the Catalina second world war aircraft wreck in Abbot Bay.
• The establishment of an independent dredging and disposal technical advice panel and a management response group, to include community representatives.

The Australian Federal Government announced on 13 November that there would now be a ban on the dumping of dredge spoil in the Great Barrier Reef Marine Park. The World Heritage Committee asked Environment Minister Greg Hunt to investigate alternative options to dump on land instead. The Queensland government and the Commonwealth have now accepted the alternative option and advice from The World Heritage Committee and will now commence dumping on land. 

Tourism

A scuba diver looking at a giant clam on the Great Barrier Reef

 

Helicopter view of the reef and boats

Due to its vast biodiversity, warm clear waters and accessibility from the tourist boats called "live aboards", the reef is a very popular destination, especially for scuba divers. Tourism on the Great Barrier Reef is concentrated in Cairns and also The Whitsundays due to their accessibility. These areas make up 7%–8% of the park's area. The Whitsundays and Cairns have their own Plans of Management. Many cities along the Queensland coast offer daily boat trips. Several continental and coral cay islands are now resorts, including Green Island and Lady Elliot Island. As of 1996, 27 islands on the Great Barrier Reef supported resorts.

In 1996, most of the tourism in the region was domestically generated and the most popular visiting times were during the Australian winter. At this time, it was estimated that tourists to the Great Barrier Reef contributed A$776 million per annum. As the largest commercial activity in the region, it was estimated in 2003 that tourism generated over A$4 billion annually, and the 2005 estimate increased to A$5.1 billion. A Deloitte report published by the Great Barrier Reef Marine Park Authority in March 2013 states that the Reef's 2,000 kilometres of coastline attracts tourism worth A$6.4 billion annually and employs more than 64,000 people.

Approximately two million people visit the Great Barrier Reef each year. Although most of these visits are managed in partnership with the marine Tourism industry, there is a concern among the general public that tourism is harmful to the Great Barrier Reef.

A variety of boat tours and cruises are offered, from single day trips, to longer voyages. Boat sizes range from dinghies to superyachts. Glass-bottomed boats and underwater observatories are also popular, as are helicopter flights. By far, the most popular tourist activities on the Great Barrier Reef are snorkelling and diving, for which pontoons are often used, and the area is often enclosed by nets. The outer part of the Great Barrier Reef is favoured for such activities, due to water quality.

Management of tourism in the Great Barrier Reef is geared towards making tourism ecologically sustainable. A daily fee is levied that goes towards research of the Great Barrier Reef. This fee ends up being 20% of the GBRMPA's income. Policies on cruise ships, bareboat charters, and anchorages limit the traffic on the Great Barrier Reef.

The problems that surround ecotourism in the Great Barrier Reef revolve around permanent tourism platforms. Platforms are large, ship-like vessels that act as a base for tourists while scuba diving and snorkelling in the Great Barrier Reef. Seabirds will land on the platforms and defecate which will eventually be washed into the sea. The feces carry nitrogen, phosphorus and often DDT and mercury, which cause aspergillosis, yellow-band disease, and black band disease. Areas without tourism platforms have 14 out of 9,468 (1.1%) diseased corals versus areas with tourism platforms that have 172 out of 7,043 (12%) diseased corals. Tourism is a major economic activity for the region. Thus, while non-permanent platforms could be possible in some areas, overall, permanent platforms are likely a necessity. Solutions have been suggested to siphon bird waste into gutters connecting to tanks helping lower runoff that causes coral disease.

The Great Barrier Reef Marine Park Authority has also placed many permanent anchorage points around the general use areas. These act to reduce damage to the reef due to anchoring destroying soft coral, chipping hard coral, and disturbing sediment as it is dragged across the bottom. Tourism operators also must comply with speed limits when travelling to or from tourist destinations, to prevent excessive wake from the boats disturbing the reef ecosystem.

Fishing

The fishing industry in the Great Barrier Reef, controlled by the Queensland Government, is worth A$1 billion annually. It employs approximately 2000 people, and fishing in the Great Barrier Reef is pursued commercially, for recreation, and as a traditional means for feeding one's family.

Dugong hunting

Under the Native Title Act 1993, native title holders retain the right to legally hunt dugongs and green turtles for "personal, domestic or non-commercial communal needs".

Four traditional owners groups agreed to cease the hunting of dugongs in the area in 2011 due to their declining numbers, partially accelerated by seagrass damage from Cyclone Yasi.

Thermal expansion

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Thermal_expansion 

 

Thermodynamics
The classical Carnot heat engine

Expansion joint in a road bridge used to avoid damage from thermal expansion.

Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.

Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below). The relative expansion (also called strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy in particles increases, they start moving faster and faster weakening the intermolecular forces between them, therefore expanding the substance.

Overview

Predicting expansion

If an equation of state is available, it can be used to predict the values of the thermal expansion at all the required temperatures and pressures, along with many other state functions.

Contraction effects (negative thermal expansion)

A number of materials contract on heating within certain temperature ranges; this is usually called negative thermal expansion, rather than "thermal contraction". For example, the coefficient of thermal expansion of water drops to zero as it is cooled to 3.983 °C and then becomes negative below this temperature; this means that water has a maximum density at this temperature, and this leads to bodies of water maintaining this temperature at their lower depths during extended periods of sub-zero weather. Also, fairly pure silicon has a negative coefficient of thermal expansion for temperatures between about 18 and 120 kelvin.

Factors affecting thermal expansion

Unlike gases or liquids, solid materials tend to keep their shape when undergoing thermal expansion.

Thermal expansion generally decreases with increasing bond energy, which also has an effect on the melting point of solids, so, high melting point materials are more likely to have lower thermal expansion. In general, liquids expand slightly more than solids. The thermal expansion of glasses is higher compared to that of crystals. At the glass transition temperature, rearrangements that occur in an amorphous material lead to characteristic discontinuities of coefficient of thermal expansion and specific heat. These discontinuities allow detection of the glass transition temperature where a supercooled liquid transforms to a glass.

Absorption or desorption of water (or other solvents) can change the size of many common materials; many organic materials change size much more due to this effect than due to thermal expansion. Common plastics exposed to water can, in the long term, expand by many percent.

Effect on density

Thermal expansion changes the space between particles of a substance, which changes the volume of the substance while negligibly changing its mass (the negligible amount comes from energy-mass equivalence), thus changing its density, which has an effect on any buoyant forces acting on it. This plays a crucial role in convection of unevenly heated fluid masses, notably making thermal expansion partly responsible for wind and ocean currents.

Coefficient of thermal expansion

The coefficient of thermal expansion describes how the size of an object changes with a change in temperature. Specifically, it measures the fractional change in size per degree change in temperature at a constant pressure, such that lower coefficients describe lower propensity for change in size. Several types of coefficients have been developed: volumetric, area, and linear. The choice of coefficient depends on the particular application and which dimensions are considered important. For solids, one might only be concerned with the change along a length, or over some area.

The volumetric thermal expansion coefficient is the most basic thermal expansion coefficient, and the most relevant for fluids. In general, substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions. Substances that expand at the same rate in every direction are called isotropic. For isotropic materials, the area and volumetric thermal expansion coefficient are, respectively, approximately twice and three times larger than the linear thermal expansion coefficient.

Mathematical definitions of these coefficients are defined below for solids, liquids, and gases.

General thermal expansion coefficient

In the general case of a gas, liquid, or solid, the volumetric coefficient of thermal expansion is given by

${\displaystyle \alpha =\alpha _{\text{V}}={\frac {1}{V}}\,\left({\frac {\partial V}{\partial T}}\right)_{p}}$

The subscript "p" to the derivative indicates that the pressure is held constant during the expansion, and the subscript V stresses that it is the volumetric (not linear) expansion that enters this general definition. In the case of a gas, the fact that the pressure is held constant is important, because the volume of a gas will vary appreciably with pressure as well as temperature. For a gas of low density this can be seen from the ideal gas

Expansion in solids

When calculating thermal expansion it is necessary to consider whether the body is free to expand or is constrained. If the body is free to expand, the expansion or strain resulting from an increase in temperature can be simply calculated by using the applicable coefficient of Thermal Expansion.

If the body is constrained so that it cannot expand, then internal stress will be caused (or changed) by a change in temperature. This stress can be calculated by considering the strain that would occur if the body were free to expand and the stress required to reduce that strain to zero, through the stress/strain relationship characterised by the elastic or Young's modulus. In the special case of solid materials, external ambient pressure does not usually appreciably affect the size of an object and so it is not usually necessary to consider the effect of pressure changes.

Common engineering solids usually have coefficients of thermal expansion that do not vary significantly over the range of temperatures where they are designed to be used, so where extremely high accuracy is not required, practical calculations can be based on a constant, average, value of the coefficient of expansion.

Linear expansion

Change in length of a rod due to thermal expansion.

Linear expansion means change in one dimension (length) as opposed to change in volume (volumetric expansion). To a first approximation, the change in length measurements of an object due to thermal expansion is related to temperature change by a coefficient of linear thermal expansion (CLTE). It is the fractional change in length per degree of temperature change. Assuming negligible effect of pressure, we may write:

${\displaystyle \alpha _{L}={\frac {1}{L}}\,{\frac {dL}{dT}}}$

where ${\displaystyle L}$ is a particular length measurement and ${\displaystyle dL/dT}$ is the rate of change of that linear dimension per unit change in temperature.

The change in the linear dimension can be estimated to be:

${\displaystyle {\frac {\Delta L}{L}}=\alpha _{L}\Delta T}$

This estimation works well as long as the linear-expansion coefficient does not change much over the change in temperature ${\displaystyle \Delta T}$, and the fractional change in length is small ${\displaystyle \Delta L/L\ll 1}$. If either of these conditions does not hold, the exact differential equation (using ${\displaystyle dL/dT}$) must be integrated.

Effects on strain

For solid materials with a significant length, like rods or cables, an estimate of the amount of thermal expansion can be described by the material strain, given by ${\displaystyle \epsilon _{\mathrm {thermal} }}$ and defined as:

${\displaystyle \epsilon _{\mathrm {thermal} }={\frac {(L_{\mathrm {final} }-L_{\mathrm {initial} })}{L_{\mathrm {initial} }}}}$

where ${\displaystyle L_{\mathrm {initial} }}$ is the length before the change of temperature and ${\displaystyle L_{\mathrm {final} }}$ is the length after the change of temperature.

For most solids, thermal expansion is proportional to the change in temperature:

${\displaystyle \epsilon _{\mathrm {thermal} }\propto \Delta T}$

Thus, the change in either the strain or temperature can be estimated by:

${\displaystyle \epsilon _{\mathrm {thermal} }=\alpha _{L}\Delta T}$

where

${\displaystyle \Delta T=(T_{\mathrm {final} }-T_{\mathrm {initial} })}$

is the difference of the temperature between the two recorded strains, measured in degrees Fahrenheit, degrees Rankine, degrees Celsius, or kelvin, and ${\displaystyle \alpha _{L}}$ is the linear coefficient of thermal expansion in "per degree Fahrenheit", "per degree Rankine", “per degree Celsius”, or “per kelvin”, denoted by °F⁻¹, R⁻¹, °C⁻¹, or K⁻¹, respectively. In the field of continuum mechanics, the thermal expansion and its effects are treated as eigenstrain and eigenstress.

Area expansion

The area thermal expansion coefficient relates the change in a material's area dimensions to a change in temperature. It is the fractional change in area per degree of temperature change. Ignoring pressure, we may write:

${\displaystyle \alpha _{A}={\frac {1}{A}}\,{\frac {dA}{dT}}}$

where ${\displaystyle A}$ is some area of interest on the object, and ${\displaystyle dA/dT}$ is the rate of change of that area per unit change in temperature.

The change in the area can be estimated as:

${\displaystyle {\frac {\Delta A}{A}}=\alpha _{A}\Delta T}$

This equation works well as long as the area expansion coefficient does not change much over the change in temperature ${\displaystyle \Delta T}$, and the fractional change in area is small ${\displaystyle \Delta A/A\ll 1}$. If either of these conditions does not hold, the equation must be integrated.

Volume expansion

For a solid, we can ignore the effects of pressure on the material, and the volumetric thermal expansion coefficient can be written:

${\displaystyle \alpha _{V}={\frac {1}{V}}\,{\frac {dV}{dT}}}$

where ${\displaystyle V}$ is the volume of the material, and ${\displaystyle dV/dT}$ is the rate of change of that volume with temperature.

This means that the volume of a material changes by some fixed fractional amount. For example, a steel block with a volume of 1 cubic meter might expand to 1.002 cubic meters when the temperature is raised by 50 K. This is an expansion of 0.2%. If we had a block of steel with a volume of 2 cubic meters, then under the same conditions, it would expand to 2.004 cubic meters, again an expansion of 0.2%. The volumetric expansion coefficient would be 0.2% for 50 K, or 0.004% K⁻¹.

If we already know the expansion coefficient, then we can calculate the change in volume

${\displaystyle {\frac {\Delta V}{V}}=\alpha _{V}\Delta T}$

where ${\displaystyle \Delta V/V}$ is the fractional change in volume (e.g., 0.002) and ${\displaystyle \Delta T}$ is the change in temperature (50 °C).

The above example assumes that the expansion coefficient did not change as the temperature changed and the increase in volume is small compared to the original volume. This is not always true, but for small changes in temperature, it is a good approximation. If the volumetric expansion coefficient does change appreciably with temperature, or the increase in volume is significant, then the above equation will have to be integrated:

${\displaystyle \ln \left({\frac {V+\Delta V}{V}}\right)=\int _{T_{i}}^{T_{f}}\alpha _{V}(T)\,dT}$

${\displaystyle {\frac {\Delta V}{V}}=\exp \left(\int _{T_{i}}^{T_{f}}\alpha _{V}(T)\,dT\right)-1}$

where ${\displaystyle \alpha _{V}(T)}$ is the volumetric expansion coefficient as a function of temperature T, and ${\displaystyle T_{i}}$,${\displaystyle T_{f}}$ are the initial and final temperatures respectively.

Isotropic materials

For isotropic materials the volumetric thermal expansion coefficient is three times the linear coefficient:

${\displaystyle \alpha _{V}=3\alpha _{L}}$

This ratio arises because volume is composed of three mutually orthogonal directions. Thus, in an isotropic material, for small differential changes, one-third of the volumetric expansion is in a single axis. As an example, take a cube of steel that has sides of length L. The original volume will be ${\displaystyle V=L^{3}}$ and the new volume, after a temperature increase, will be

${\displaystyle V+\Delta V=(L+\Delta L)^{3}=L^{3}+3L^{2}\Delta L+3L\Delta L^{2}+\Delta L^{3}\approx L^{3}+3L^{2}\Delta L=V+3V{\Delta L \over L}.}$

We can easily ignore the terms as change in L is a small quantity which on squaring gets much smaller.

So

${\displaystyle {\frac {\Delta V}{V}}=3{\Delta L \over L}=3\alpha _{L}\Delta T.}$

The above approximation holds for small temperature and dimensional changes (that is, when ${\displaystyle \Delta T}$ and ${\displaystyle \Delta L}$ are small); but it does not hold if we are trying to go back and forth between volumetric and linear coefficients using larger values of ${\displaystyle \Delta T}$. In this case, the third term (and sometimes even the fourth term) in the expression above must be taken into account.

Similarly, the area thermal expansion coefficient is two times the linear coefficient:

${\displaystyle \alpha _{A}=2\alpha _{L}}$

This ratio can be found in a way similar to that in the linear example above, noting that the area of a face on the cube is just ${\displaystyle L^{2}}$. Also, the same considerations must be made when dealing with large values of ${\displaystyle \Delta T}$.

Put more simply, if the length of a solid expands from 1 m to 1.01 m then the area expands from 1 m² to 1.0201 m² and the volume expands from 1 m³ to 1.030301 m³.

Anisotropic materials

Materials with anisotropic structures, such as crystals (with less than cubic symmetry, for example martensitic phases) and many composites, will generally have different linear expansion coefficients ${\displaystyle \alpha _{L}}$ in different directions. As a result, the total volumetric expansion is distributed unequally among the three axes. If the crystal symmetry is monoclinic or triclinic, even the angles between these axes are subject to thermal changes. In such cases it is necessary to treat the coefficient of thermal expansion as a tensor with up to six independent elements. A good way to determine the elements of the tensor is to study the expansion by x-ray powder diffraction. The thermal expansion coefficient tensor for the materials possessing cubic symmetry (for e.g. FCC, BCC) is isotropic.

Isobaric expansion in gases

For an ideal gas, the volumetric thermal expansion (i.e., relative change in volume due to temperature change) depends on the type of process in which temperature is changed. Two simple cases are constant pressure (an isobaric process) and constant volume (an isochoric process).

The derivative of the ideal gas law, ${\displaystyle pV=T}$, is

${\displaystyle pdV+Vdp=dT}$

where ${\displaystyle p}$ is the pressure, ${\displaystyle V}$ is the specific volume, and ${\displaystyle T}$ is temperature measured in energy units.

By the definition of an isobaric thermal expansion, we have ${\displaystyle dp=0}$, so that ${\displaystyle pdV=dT}$, and the isobaric thermal expansion coefficient is:

${\displaystyle \alpha _{p}\equiv {\frac {1}{V}}\left({\frac {dV}{dT}}\right)={\frac {1}{V}}\left({\frac {1}{p}}\right)={\frac {1}{pV}}={\frac {1}{T}}}$.

Similarly, if the volume is held constant, that is if ${\displaystyle dV=0}$, we have ${\displaystyle Vdp=dT}$, so that the isochoric thermal expansion coefficient is

${\displaystyle \alpha _{V}\equiv {\frac {1}{p}}\left({\frac {dp}{dT}}\right)={\frac {1}{p}}\left({\frac {1}{V}}\right)={\frac {1}{pV}}={\frac {1}{T}}}$.

Expansion in liquids

Theoretically, the coefficient of linear expansion can be found from the coefficient of volumetric expansion (α_V ≈ 3α_L). For liquids, α_L is calculated through the experimental determination of α_V. Liquids, unlike solids have no definite shape and they take the shape of the container. Consequently, liquids have no definite length and area, so linear and areal expansions of liquids have no significance.

Liquids in general, expand on heating. However water is an exception to this general behaviour: below 4 °C it contracts on heating. For higher temperature it shows the normal positive thermal expansion. The thermal expansion of liquids is usually higher than in solids because of weak intermolecular forces present in liquids.

Thermal expansion of solids usually shows little dependence on temperature, except at low temperatures, whereas liquids expand at different rates at different temperatures.

Apparent and absolute expansion of a liquid

The expansion of liquids is usually measured in a container. When a liquid expands in a vessel, the vessel expands along with the liquid. Hence the observed increase in volume of the liquid level is not actual increase in its volume. The expansion of the liquid relative to the container is called its apparent expansion, while the actual expansion of the liquid is called real expansion or absolute expansion. The ratio of apparent increase in volume of the liquid per unit rise of temperature to the original volume is called its coefficient of apparent expansion.

For small and equal rises in temperature, the increase in volume (real expansion) of a liquid is equal to the sum of the apparent increase in volume (apparent expansion) of the liquid and the increase in volume of the containing vessel. Thus a liquid has two coefficients of expansion.

Measurement of the expansion of a liquid must account for the expansion of the container as well. For example, when a flask with a long narrow stem, containing enough liquid to partially fill the stem itself, is placed in a heat bath, the height of the liquid column in the stem will initially drop, followed immediately by a rise of that height until the whole system of flask, liquid and heat bath has warmed through. The initial drop in the height of the liquid column is not due to an initial contraction of the liquid, but rather to the expansion of the flask as it contacts the heat bath first. Soon after, the liquid in the flask is heated by the flask itself and begins to expand. Since liquids typically have a greater expansion over solids, the expansion of the liquid in the flask eventually exceeds that of the flask, causing the level of liquid in the flask to rise. A direct measurement of the height of the liquid column is a measurement of the apparent expansion of the liquid. The absolute expansion of the liquid is the apparent expansion corrected for the expansion of the containing vessel.

Examples and applications

Thermal expansion of long continuous sections of rail tracks is the driving force for rail buckling. This phenomenon resulted in 190 train derailments during 1998–2002 in the US alone.

The expansion and contraction of the materials must be considered when designing large structures, when using tape or chain to measure distances for land surveys, when designing molds for casting hot material, and in other engineering applications when large changes in dimension due to temperature are expected.

Thermal expansion is also used in mechanical applications to fit parts over one another, e.g. a bushing can be fitted over a shaft by making its inner diameter slightly smaller than the diameter of the shaft, then heating it until it fits over the shaft, and allowing it to cool after it has been pushed over the shaft, thus achieving a 'shrink fit'. Induction shrink fitting is a common industrial method to pre-heat metal components between 150 °C and 300 °C thereby causing them to expand and allow for the insertion or removal of another component.

There exist some alloys with a very small linear expansion coefficient, used in applications that demand very small changes in physical dimension over a range of temperatures. One of these is Invar 36, with expansion approximately equal to 0.6×10⁻⁶ K⁻¹. These alloys are useful in aerospace applications where wide temperature swings may occur.

Pullinger's apparatus is used to determine the linear expansion of a metallic rod in the laboratory. The apparatus consists of a metal cylinder closed at both ends (called a steam jacket). It is provided with an inlet and outlet for the steam. The steam for heating the rod is supplied by a boiler which is connected by a rubber tube to the inlet. The center of the cylinder contains a hole to insert a thermometer. The rod under investigation is enclosed in a steam jacket. One of its ends is free, but the other end is pressed against a fixed screw. The position of the rod is determined by a micrometer screw gauge or spherometer.

To determine the coefficient of linear thermal expansion of a metal, a pipe made of that metal is heated by passing steam through it. One end of the pipe is fixed securely and the other rests on a rotating shaft, the motion of which is indicated by a pointer. A suitable thermometer records the pipe's temperature. This enables calculation of the relative change in length per degree temperature change.

Drinking glass with fracture due to uneven thermal expansion after pouring of hot liquid into the otherwise cool glass

The control of thermal expansion in brittle materials is a key concern for a wide range of reasons. For example, both glass and ceramics are brittle and uneven temperature causes uneven expansion which again causes thermal stress and this might lead to fracture. Ceramics need to be joined or work in concert with a wide range of materials and therefore their expansion must be matched to the application. Because glazes need to be firmly attached to the underlying porcelain (or other body type) their thermal expansion must be tuned to 'fit' the body so that crazing or shivering do not occur. Good example of products whose thermal expansion is the key to their success are CorningWare and the spark plug. The thermal expansion of ceramic bodies can be controlled by firing to create crystalline species that will influence the overall expansion of the material in the desired direction. In addition or instead the formulation of the body can employ materials delivering particles of the desired expansion to the matrix. The thermal expansion of glazes is controlled by their chemical composition and the firing schedule to which they were subjected. In most cases there are complex issues involved in controlling body and glaze expansion, so that adjusting for thermal expansion must be done with an eye to other properties that will be affected, and generally trade-offs are necessary.

Thermal expansion can have a noticeable effect on gasoline stored in above-ground storage tanks, which can cause gasoline pumps to dispense gasoline which may be more compressed than gasoline held in underground storage tanks in winter, or less compressed than gasoline held in underground storage tanks in summer.

Expansion loop on heating pipeline

Heat-induced expansion has to be taken into account in most areas of engineering. A few examples are:

• Metal-framed windows need rubber spacers.
• Rubber tires need to perform well over a range of temperatures, being passively heated or cooled by road surfaces and weather, and actively heated by mechanical flexing and friction.
• Metal hot water heating pipes should not be used in long straight lengths.
• Large structures such as railways and bridges need expansion joints in the structures to avoid sun kink.
• One of the reasons for the poor performance of cold car engines is that parts have inefficiently large spacings until the normal operating temperature is achieved.
• A gridiron pendulum uses an arrangement of different metals to maintain a more temperature stable pendulum length.
• A power line on a hot day is droopy, but on a cold day it is tight. This is because the metals expand under heat.
• Expansion joints absorb the thermal expansion in a piping system.
• Precision engineering nearly always requires the engineer to pay attention to the thermal expansion of the product. For example, when using a scanning electron microscope small changes in temperature such as 1 degree can cause a sample to change its position relative to the focus point.
• Liquid thermometers contain a liquid (usually mercury or alcohol) in a tube, which constrains it to flow in only one direction when its volume expands due to changes in temperature.
• A bi-metal mechanical thermometer uses a bimetallic strip and bends due to the differing thermal expansion of the two metals.

Thermal expansion coefficients for various materials

Volumetric thermal expansion coefficient for a semicrystalline polypropylene.

 

Linear thermal expansion coefficient for some steel grades.

This section summarizes the coefficients for some common materials.

For isotropic materials the coefficients linear thermal expansion α and volumetric thermal expansion α_V are related by α_V = 3α. For liquids usually the coefficient of volumetric expansion is listed and linear expansion is calculated here for comparison.

For common materials like many metals and compounds, the thermal expansion coefficient is inversely proportional to the melting point. In particular, for metals the relation is:

${\displaystyle \alpha \approx {\frac {0.020}{T_{m}}}}$

for halides and oxides

${\displaystyle \alpha \approx {\frac {0.038}{T_{m}}}-7.0\cdot 10^{-6}\,\mathrm {K} ^{-1}}$

In the table below, the range for α is from 10⁻⁷ K⁻¹ for hard solids to 10⁻³ K⁻¹ for organic liquids. The coefficient α varies with the temperature and some materials have a very high variation; see for example the variation vs. temperature of the volumetric coefficient for a semicrystalline polypropylene (PP) at different pressure, and the variation of the linear coefficient vs. temperature for some steel grades (from bottom to top: ferritic stainless steel, martensitic stainless steel, carbon steel, duplex stainless steel, austenitic steel). The highest linear coefficient in a solid has been reported for a Ti-Nb alloy.

(The formula α_V ≈ 3α is usually used for solids.)

Material	Linear coefficient CLTE α at 20 °C (x10−6 K−1)	Volumetric coefficient αV at 20 °C (x10−6 K−1)	Notes
Aluminium	23.1	69
Brass	19	57
Carbon steel	10.8	32.4
CFRP	– 0.8	Anisotropic	Fiber direction
Concrete	12	36
Copper	17	51
Diamond	1	3
Ethanol	250	750
Gasoline	317	950
Glass	8.5	25.5
Glass, borosilicate	3.3	9.9	matched sealing partner for tungsten, molybdenum and kovar.
Glycerine		485
Gold	14	42
Ice	51
Invar	1.2	3.6
Iron	11.8	35.4
Kapton	20	60	DuPont Kapton 200EN
Lead	29	87
Macor	9.3
Nickel	13	39
Oak	54		Perpendicular to the grain
Douglas-fir	27	75	radial
Douglas-fir	45	75	tangential
Douglas-fir	3.5	75	parallel to grain
Platinum	9	27
Polypropylene (PP)	150	450
PVC	52	156
Fused quartz	0.59	1.77
alpha-Quartz	12-16/6-9		Parallel to a-axis/c-axis T = -50 to 150 C
Rubber	disputed	disputed
Sapphire	5.3		Parallel to C axis, or [001]
Silicon Carbide	2.77	8.31
Silicon	2.56	9
Silver	18	54
Glass-ceramic "Sitall"	0±0.15	0±0.45	average for −60 °C to 60 °C
Stainless steel	10.1 ~ 17.3	30.3 ~ 51.9
Steel	11.0 ~ 13.0	33.0 ~ 39.0	Depends on composition
Titanium	8.6	26
Tungsten	4.5	13.5
Water	69	207
Glass-ceramic "Zerodur"	≈0.007-0.1		at 0...50 °C
ALLVAR Alloy 30	−30	anisotropic	at 20 °C