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114-460: The community had to rebuild after a tsunami in 1964. The tsunami heavily damaged the village and forced many people to move away. The Hesquiaht were affected by the 1990s economic collapse of their traditional fishery and forestry activities. The Ha’wiih system functions in Hesquiaht. Four hereditary chiefs guide the community and inform the work of council. The chiefs sit hierarchically, matching

228-430: A wave shoaling process described below. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas. On April 1, 1946, the 8.6 M w   Aleutian Islands earthquake occurred with a maximum Mercalli intensity of VI ( Strong ). It generated a tsunami which inundated Hilo on the island of Hawaii with a 14-metre high (46 ft) surge. Between 165 and 173 were killed. The area where

342-643: A country. It has an average depth of 3,741 m. All of the Indian Ocean is in the Eastern Hemisphere . Unlike the Atlantic and Pacific, the Indian Ocean is bordered by landmasses and an archipelago on three sides, making it more like an embayed ocean centered on the Indian Peninsula. Its coasts and shelves differ from other oceans, with distinct features, such as a narrower continental shelf . In terms of geology,

456-427: A few minutes at a time. The Tauredunum event was a large tsunami on Lake Geneva in 563 CE, caused by sedimentary deposits destabilised by a landslide. In the 1950s, it was discovered that tsunamis larger than had previously been believed possible can be caused by giant submarine landslides . These large volumes of rapidly displaced water transfer energy at a faster rate than the water can absorb. Their existence

570-407: A global rise in sea level. Sea level also increases in the Indian Ocean, except in the south tropical Indian Ocean where it decreases, a pattern most likely caused by rising levels of greenhouse gases . Among the tropical oceans, the western Indian Ocean hosts one of the largest concentrations of phytoplankton blooms in summer, due to the strong monsoon winds. The monsoonal wind forcing leads to

684-432: A huge wave. As the tsunami approaches the coast and the waters become shallow, wave shoaling compresses the wave and its speed decreases below 80 kilometres per hour (50 mph). Its wavelength diminishes to less than 20 kilometres (12 mi) and its amplitude grows enormously—in accord with Green's law . Since the wave still has the same very long period , the tsunami may take minutes to reach full height. Except for

798-530: A key role in early human migrations and the spread of civilizations. In modern times, it remains crucial for global trade, especially in oil and hydrocarbons. Environmental and geopolitical concerns in the region include the effects of climate change , piracy, and strategic disputes over island territories. The Indian Ocean has been known by its present name since at least 1515, when the Latin form Oceanus Orientalis Indicus ( lit.   ' Indian Eastern Ocean ' )

912-537: A large problem of awareness and preparedness, as exemplified by the eruption and collapse of Anak Krakatoa in 2018 , which killed 426 and injured thousands when no warning was available. It is still regarded that lateral landslides and ocean-entering pyroclastic currents are most likely to generate the largest and most hazardous waves from volcanism; however, field investigation of the Tongan event , as well as developments in numerical modelling methods, currently aim to expand

1026-528: A massive landslide from Monte Toc entered the reservoir behind the Vajont Dam in Italy. The resulting wave surged over the 262-metre (860 ft)-high dam by 250 metres (820 ft) and destroyed several towns. Around 2,000 people died. Scientists named these waves megatsunamis . Some geologists claim that large landslides from volcanic islands, e.g. Cumbre Vieja on La Palma ( Cumbre Vieja tsunami hazard ) in

1140-663: A maximum depth of 7,290 m (23,920 ft). All of the Indian Ocean is in the Eastern Hemisphere and the centre of the Eastern Hemisphere, the 90th meridian east , passes through the Ninety East Ridge . Within these waters are a number of islands. These include those controlled by surrounding countries, and independent island states and territories. Of the non-coastal islands, there are two broad clusters: one around Madagascar, and one south of India. A few other oceanic islands are scattered elsewhere. In contrast to

1254-463: A period of six years, except for debris that gets indefinitely stuck in the centre of the gyre. The garbage patch in the Indian Ocean will, according to a 2012 study, decrease in size after several decades to vanish completely over centuries. Over several millennia, however, the global system of garbage patches will accumulate in the North Pacific. There are two amphidromes of opposite rotation in

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1368-787: A process of aridification began in the southwest Indian Ocean began around 4,000 years ago. Mammalian megafauna once widespread in the MPA was driven to near extinction in the early 20th century. Some species have been successfully recovered since then — the population of white rhinoceros ( Ceratotherium simum simum ) increased from less than 20 individuals in 1895 to more than 17,000 as of 2013. Other species still depend on fenced areas and management programs, including black rhinoceros ( Diceros bicornis minor ), African wild dog ( Lycaon pictus ), cheetah ( Acynonix jubatus ), elephant ( Loxodonta africana ), and lion ( Panthera leo ). This biodiversity hotspot (and namesake ecoregion and "Endemic Bird Area")

1482-570: A reference sea level. A large tsunami may feature multiple waves arriving over a period of hours, with significant time between the wave crests. The first wave to reach the shore may not have the highest run-up. About 80% of tsunamis occur in the Pacific Ocean, but they are possible wherever there are large bodies of water, including lakes. However, tsunami interactions with shorelines and the seafloor topography are extremely complex, which leaves some countries more vulnerable than others. For example,

1596-462: A ridge and a trough. In the case of a propagating wave like a tsunami, either may be the first to arrive. If the first part to arrive at the shore is the ridge, a massive breaking wave or sudden flooding will be the first effect noticed on land. However, if the first part to arrive is a trough, a drawback will occur as the shoreline recedes dramatically, exposing normally submerged areas. The drawback can exceed hundreds of metres, and people unaware of

1710-467: A significant tsunami, such as the 1977 Sumba and 1933 Sanriku events. Tsunamis have a small wave height offshore, and a very long wavelength (often hundreds of kilometres long, whereas normal ocean waves have a wavelength of only 30 or 40 metres), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimetres (12 in) above the normal sea surface. They grow in height when they reach shallower water, in

1824-464: A strong coastal and open ocean upwelling , which introduces nutrients into the upper zones where sufficient light is available for photosynthesis and phytoplankton production. These phytoplankton blooms support the marine ecosystem, as the base of the marine food web, and eventually the larger fish species. The Indian Ocean accounts for the second-largest share of the most economically valuable tuna catch. Its fish are of great and growing importance to

1938-628: A transoceanic tsunami has not occurred within recorded history. Susceptible locations are believed to be the Big Island of Hawaii , Fogo in the Cape Verde Islands , La Reunion in the Indian Ocean , and Cumbre Vieja on the island of La Palma in the Canary Islands ; along with other volcanic ocean islands. This is because large masses of relatively unconsolidated volcanic material occurs on

2052-445: A tsunami can be calculated by obtaining the square root of the depth of the water in metres multiplied by the acceleration due to gravity (approximated to 10 m/s ). For example, if the Pacific Ocean is considered to have a depth of 5000 metres, the velocity of a tsunami would be √ 5000 × 10 = √ 50000 ≈ 224 metres per second (730 ft/s), which equates to a speed of about 806 kilometres per hour (501 mph). This

2166-434: A tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved. Movement on normal (extensional) faults can also cause displacement of the seabed, but only the largest of such events (typically related to flexure in the outer trench swell ) cause enough displacement to give rise to

2280-473: A tsunami, which is that of an extraordinarily high tidal bore . Tsunamis and tides both produce waves of water that move inland, but in the case of a tsunami, the inland movement of water may be much greater, giving the impression of an incredibly high and forceful tide. In recent years, the term "tidal wave" has fallen out of favour, especially in the scientific community, because the causes of tsunamis have nothing to do with those of tides , which are produced by

2394-464: Is a patchwork of small forested areas, often with a unique assemblage of species within each, located within 200 km (120 mi) from the coast and covering a total area of c. 6,200 km (2,400 sq mi). It also encompasses coastal islands, including Zanzibar and Pemba, and Mafia. This area, one of the only two hotspots that are entirely arid, includes the Ethiopian Highlands ,

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2508-467: Is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake . Earthquakes , volcanic eruptions and underwater explosions (including detonations, landslides , glacier calvings , meteorite impacts and other disturbances) above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind , or tides , which are in turn generated by

2622-612: Is also accustomed to tsunamis, with earthquakes of varying magnitudes regularly occurring off the coast of the island. Tsunamis are an often underestimated hazard in the Mediterranean Sea and parts of Europe. Of historical and current (with regard to risk assumptions) importance are the 1755 Lisbon earthquake and tsunami (which was caused by the Azores–Gibraltar Transform Fault ), the 1783 Calabrian earthquakes , each causing several tens of thousands of deaths and

2736-557: Is also used to refer to the phenomenon because the waves most often are generated by seismic activity such as earthquakes. Prior to the rise of the use of the term tsunami in English, scientists generally encouraged the use of the term seismic sea wave rather than tidal wave . However, like tidal wave , seismic sea wave is not a completely accurate term, as forces other than earthquakes—including underwater landslides , volcanic eruptions, underwater explosions, land or ice slumping into

2850-835: Is artificially connected to the Mediterranean Sea without ship lock through the Suez Canal , which is accessible via the Red Sea. The Arabian Sea is connected to the Persian Gulf by the Gulf of Oman and the Strait of Hormuz . In the Persian Gulf, the Gulf of Bahrain separates Qatar from the Arabic Peninsula. Along the west coast of India, the Gulf of Kutch and Gulf of Khambat are located in Gujarat in

2964-700: Is attested, named after India, which projects into it. It was earlier known as the Eastern Ocean , a term that was still in use during the mid-18th century, as opposed to the Western Ocean ( Atlantic ) before the Pacific was surmised. In modern times, the name Afro-Asian Ocean has occasionally been used. The Hindi name for the Ocean is हिंद महासागर ( Hind Mahāsāgar ; lit. transl.  Ocean of India ). Conversely, Chinese explorers (e.g., Zheng He during

3078-736: Is bounded by the Southern Ocean , or Antarctica , depending on the definition in use. The Indian Ocean has large marginal, or regional seas, such as the Andaman Sea , the Arabian Sea , the Bay of Bengal , and the Laccadive Sea . Once called the Eastern Ocean, it is now named after India , which protrudes into it, and has been known by its current name since at least 1515. It is the only ocean named after

3192-491: Is designed to help accurately forecast the passage of tsunamis across oceans as well as how tsunami waves interact with shorelines. The term "tsunami" is a borrowing from the Japanese tsunami 津波 , meaning "harbour wave." For the plural, one can either follow ordinary English practice and add an s , or use an invariable plural as in the Japanese. Some English speakers alter the word's initial / ts / to an / s / by dropping

3306-426: Is ecologically diverse, with important marine life and ecosystems like coral reefs, mangroves, and sea grass beds. It hosts a significant portion of the world's tuna catch and is home to endangered marine species. It faces challenges like overfishing and pollution , including a significant garbage patch . Historically, the Indian Ocean has been a hub of cultural and commercial exchange since ancient times. It played

3420-543: Is elected every four years. Chief and Council meet monthly, and a joint Chief and Council, membership, and the Hereditary Chiefs meeting is held yearly. The Chief and Council are responsible for management of band affairs. The Chief and Council and their portfolios include: The Hesquiaht Chief and Council rely on administrators to conduct the day-to-day management of tribal affairs, program delivery, and coordination with government agencies. The Hesquiaht traditionally use

3534-515: Is not favoured by the scientific community because it might give the false impression of a causal relationship between tides and tsunamis. Tsunamis generally consist of a series of waves, with periods ranging from minutes to hours, arriving in a so-called " wave train ". Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous, and they can affect entire ocean basins. The 2004 Indian Ocean tsunami

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3648-763: Is now Shakespear Regional Park at the tip of the Whangaparāoa Peninsula in the Auckland Region of New Zealand ; the attempt failed. There has been considerable speculation about the possibility of using nuclear weapons to cause tsunamis near an enemy coastline. Nuclear testing in the Pacific Proving Ground by the United States generated poor results. In Operation Crossroads in July 1946, two 20-kilotonne-of-TNT (84 TJ) bombs were detonated, one in

3762-464: Is projected to push the tropical Indian Ocean into a basin-wide near-permanent heatwave state by the end of the 21st century, where marine heatwaves are projected to increase from 20 days per year (during 1970–2000) to 220–250 days per year. South of the Equator (20–5°S), the Indian Ocean is gaining heat from June to October, during the austral winter, while it is losing heat from November to March, during

3876-426: Is the formula used for calculating the velocity of shallow-water waves. Even the deep ocean is shallow in this sense because a tsunami wave is so long (horizontally from crest to crest) by comparison. The reason for the Japanese name "harbour wave" is that sometimes a village's fishermen would sail out, and encounter no unusual waves while out at sea fishing, and come back to land to find their village devastated by

3990-430: The 1883 eruption of Krakatoa , and the 2022 Hunga Tonga–Hunga Ha'apai eruption . Over 20% of all fatalities caused by volcanism during the past 250 years are estimated to have been caused by volcanogenic tsunamis. Debate has persisted over the origins and source mechanisms of these types of tsunamis, such as those generated by Krakatoa in 1883, and they remain lesser understood than their seismic relatives. This poses

4104-666: The 1908 Messina earthquake and tsunami. The tsunami claimed more than 123,000 lives in Sicily and Calabria and is among the deadliest natural disasters in modern Europe. The Storegga Slide in the Norwegian Sea and some examples of tsunamis affecting the British Isles refer to landslide and meteotsunamis , predominantly and less to earthquake-induced waves. As early as 426 BC the Greek historian Thucydides inquired in his book History of

4218-711: The Arabian Peninsula in the Northern Hemisphere and north of the trade winds in the Southern Hemisphere. The Indonesian Throughflow is a unique Equatorial connection to the Pacific. The climate north of the equator is affected by a monsoon climate. Strong north-east winds blow from October until April; from May until October south and west winds prevail. In the Arabian Sea, the violent Monsoon brings rain to

4332-413: The Canary Islands , may be able to generate megatsunamis that can cross oceans, but this is disputed by many others. In general, landslides generate displacements mainly in the shallower parts of the coastline, and there is conjecture about the nature of large landslides that enter the water. This has been shown to subsequently affect water in enclosed bays and lakes, but a landslide large enough to cause

4446-560: The East African Rift valley , the Socotra islands, as well as some small islands in the Red Sea and areas on the southern Arabic Peninsula. Endemic and threatened mammals include the dibatag ( Ammodorcas clarkei ) and Speke's gazelle ( Gazella spekei ); the Somali wild ass ( Equus africanus somaliensis ) and hamadryas baboon ( Papio hamadryas ). It also contains many reptiles. In Somalia,

4560-608: The Malacca , Sunda and Torres Straits . The Gulf of Carpentaria is located on the Australian north coast while the Great Australian Bight constitutes a large part of its southern coast. Several features make the Indian Ocean unique. It constitutes the core of the large-scale Tropical Warm Pool which, when interacting with the atmosphere, affects the climate both regionally and globally. Asia blocks heat export and prevents

4674-773: The Mascarene Basin the CDW becomes a deep western boundary current before it is met by a re-circulated branch of itself, the North Indian Deep Water. This mixed water partly flows north into the Somali Basin whilst most of it flows clockwise in the Mascarene Basin where an oscillating flow is produced by Rossby waves . Water circulation in the Indian Ocean is dominated by the Subtropical Anticyclonic Gyre,

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4788-703: The Ming dynasty ) who traveled to the Indian Ocean during the 15th century called it the Western Oceans. In Ancient Greek geography , the Indian Ocean region known to the Greeks was called the Erythraean Sea . The borders of the Indian Ocean , as delineated by the International Hydrographic Organization in 1953 included the Southern Ocean but not the marginal seas along the northern rim but in 2002

4902-720: The Sea of Zanj is located north of Madagascar. On the northern coast of the Arabian Sea , Gulf of Aden is connected to the Red Sea by the strait of Bab-el-Mandeb . In the Gulf of Aden, the Gulf of Tadjoura is located in Djibouti and the Guardafui Channel separates Socotra island from the Horn of Africa. The northern end of the Red Sea terminates in the Gulf of Aqaba and Gulf of Suez . The Indian Ocean

5016-523: The gravitational pull of the Moon and the Sun , a tsunami is generated by the displacement of water from a large event. Tsunami waves do not resemble normal undersea currents or sea waves because their wavelength is far longer. Rather than appearing as a breaking wave , a tsunami may instead initially resemble a rapidly rising tide . For this reason, it is often referred to as a tidal wave , although this usage

5130-562: The runoff water to the Indian Ocean. Mainly in summer, this runoff flows into the Arabian Sea but also south across the Equator where it mixes with fresher seawater from the Indonesian Throughflow . This mixed freshwater joins the South Equatorial Current in the southern tropical Indian Ocean. Sea surface salinity is highest (more than 36  PSU ) in the Arabian Sea because evaporation exceeds precipitation there. In

5244-423: The "Hinge zone may represent the relict of continental and proto-oceanic crustal boundary formed during the rifting of India from Antarctica ." Australia, Indonesia, and India are the three countries with the longest shorelines and exclusive economic zones . The continental shelf makes up 15% of the Indian Ocean. More than two billion people live in countries bordering the Indian Ocean, compared to 1.7 billion for

5358-427: The "t," since English does not natively permit /ts/ at the beginning of words, though the original Japanese pronunciation is /ts/ . The term has become commonly accepted in English, although its literal Japanese meaning is not necessarily descriptive of the waves, which do not occur only in harbours. Tsunamis are sometimes referred to as tidal waves . This once-popular term derives from the most common appearance of

5472-694: The Arabian Peninsula) and Limpopo rivers. After the breakup of East Gondwana and the formation of the Himalayas, the Ganges-Brahmaputra rivers flow into the world's largest delta known as the Bengal delta or Sunderbans . Marginal seas , gulfs, bays and straits of the Indian Ocean include: Along the east coast of Africa, the Mozambique Channel separates Madagascar from mainland Africa, while

5586-473: The Atlantic and 2.7 billion for the Pacific (some countries border more than one ocean). The Indian Ocean drainage basin covers 21,100,000 km (8,100,000 sq mi), virtually identical to that of the Pacific Ocean and half that of the Atlantic basin, or 30% of its ocean surface (compared to 15% for the Pacific). The Indian Ocean drainage basin is divided into roughly 800 individual basins, half that of

5700-482: The Atlantic and Pacific, the Indian Ocean is enclosed by major landmasses and an archipelago on three sides and does not stretch from pole to pole, and can be likened to an embayed ocean. It is centered on the Indian Peninsula. Although this subcontinent has played a significant role in its history, the Indian Ocean has foremostly been a cosmopolitan stage, interlinking diverse regions by innovations, trade, and religion since early in human history. The active margins of

5814-569: The Comoros. Although both species represent an order of lobe-finned fishes known from the Early Devonian (410 mya ) and though extinct 66 mya, they are morphologically distinct from their Devonian ancestors. Over millions of years, coelacanths evolved to inhabit different environments — lungs adapted for shallow, brackish waters evolved into gills adapted for deep marine waters. Of Earth's 36 biodiversity hotspots nine (or 25%) are located on

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5928-472: The East India Coastal Current to the Arabian Sea from January to April. An Indian Ocean garbage patch was discovered in 2010 covering at least 5 million square kilometres (1.9 million square miles). Riding the southern Indian Ocean Gyre , this vortex of plastic garbage constantly circulates the ocean from Australia to Africa, down the Mozambique Channel , and back to Australia in

6042-785: The Great Lakes, the Aegean Sea, the English Channel, and the Balearic Islands, where they are common enough to have a local name, rissaga . In Sicily they are called marubbio and in Nagasaki Bay, they are called abiki . Some examples of destructive meteotsunamis include 31 March 1979 at Nagasaki and 15 June 2006 at Menorca, the latter causing damage in the tens of millions of euros. Meteotsunamis should not be confused with storm surges , which are local increases in sea level associated with

6156-669: The IHO delimited the Southern Ocean separately, which removed waters south of 60°s from the Indian Ocean but included the northern marginal seas. Meridionally , the Indian Ocean is delimited from the Atlantic Ocean by the 20° east meridian , running south from Cape Agulhas , South Africa, and from the Pacific Ocean by the meridian of 146°49'E, running south from South East Cape on the island of Tasmania in Australia. The northernmost extent of

6270-447: The Indian Ocean (including marginal seas) is approximately 30° north in the Persian Gulf . The Indian Ocean covers 70,560,000 km (27,240,000 sq mi), including the Red Sea and the Persian Gulf but excluding the Southern Ocean, or 19.5% of the world's oceans; its volume is 264,000,000 km (63,000,000 cu mi) or 19.8% of the world's oceans' volume; it has an average depth of 3,741 m (12,274 ft) and

6384-405: The Indian Ocean have an average width (horizontal distance from land to shelf break ) of 19 ± 0.61 km (11.81 ± 0.38 mi) with a maximum width of 175 km (109 mi). The passive margins have an average width of 47.6 ± 0.8 km (29.58 ± 0.50 mi). The average width of the slopes (horizontal distance from shelf break to foot of slope) of

6498-457: The Indian Ocean includes beaches and intertidal zones covering 3,000 km (1,200 sq mi) and 246 larger estuaries . Upwelling areas are small but important. The hypersaline salterns in India covers between 5,000–10,000 km (1,900–3,900 sq mi) and species adapted for this environment, such as Artemia salina and Dunaliella salina , are important to bird life. Coral reefs, sea grass beds, and mangrove forests are

6612-470: The Indian Ocean is the youngest of the major oceans, with active spreading ridges and features like seamounts and ridges formed by hotspots . The climate of the Indian Ocean is characterized by monsoons . It is the warmest ocean, with a significant impact on global climate due to its interaction with the atmosphere. Its waters are affected by the Indian Ocean Walker circulation , resulting in unique oceanic currents and upwelling patterns. The Indian Ocean

6726-424: The Indian Ocean region, or almost half of the world's mangrove habitat, of which 42,500 km (16,400 sq mi) is located in Indonesia, or 50% of mangroves in the Indian Ocean. Mangroves originated in the Indian Ocean region and have adapted to a wide range of its habitats but it is also where it suffers its biggest loss of habitat. In 2016, six new animal species were identified at hydrothermal vents in

6840-666: The Indian Ocean, during the past six decades. The tuna catch rates have also declined 50–90% during the past half-century, mostly due to increased industrial fisheries, with the ocean warming adding further stress to the fish species. Endangered and vulnerable marine mammals and turtles: 80% of the Indian Ocean is open ocean and includes nine large marine ecosystems : the Agulhas Current , Somali Coastal Current , Red Sea , Arabian Sea , Bay of Bengal , Gulf of Thailand , West Central Australian Shelf , Northwest Australian Shelf and Southwest Australian Shelf . Coral reefs cover c. 200,000 km (77,000 sq mi). The coasts of

6954-432: The Indian Ocean, probably caused by Rossby wave propagation. Icebergs drift as far north as 55° south latitude , similar to the Pacific but less than in the Atlantic where icebergs reach up to 45°S. The volume of iceberg loss in the Indian Ocean between 2004 and 2012 was 24  Gt . Since the 1960s, anthropogenic warming of the global ocean combined with contributions of freshwater from retreating land ice causes

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7068-411: The Indian Ocean. While the Indian Ocean warmed at a rate of 1.2°C per century during 1950–2020, climate models predict accelerated warming, at a rate of 1.7 °C–3.8 °C per century during 2020–2100. Though the warming is basin-wide, maximum warming is in the northwestern Indian Ocean including the Arabian Sea, and reduced warming off the Sumatra and Java coasts in the southeast Indian Ocean. Global warming

7182-401: The Indian subcontinent. In the southern hemisphere, the winds are generally milder, but summer storms near Mauritius can be severe. When the monsoon winds change, cyclones sometimes strike the shores of the Arabian Sea and the Bay of Bengal . Some 80% of the total annual rainfall in India occurs during summer and the region is so dependent on this rainfall that many civilisations perished when

7296-407: The M t scale match as closely as possible with the moment magnitude scale. Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering 70,560,000 km (27,240,000 sq mi) or approximately 20% of the water area of Earth's surface . It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it

7410-408: The Monsoon failed in the past. The huge variability in the Indian Summer Monsoon has also occurred pre-historically, with a strong, wet phase 33,500–32,500 BP; a weak, dry phase 26,000–23,500 BC; and a very weak phase 17,000–15,000 BP, corresponding to a series of dramatic global events: Bølling–Allerød warming , Heinrich , and Younger Dryas . The Indian Ocean is the warmest ocean in

7524-422: The Pacific coasts of the United States and Mexico lie adjacent to each other, but the United States has recorded ten tsunamis in the region since 1788, while Mexico has recorded twenty-five since 1732. Similarly, Japan has had more than a hundred tsunamis in recorded history, while the neighbouring island of Taiwan has registered only two, in 1781 and 1867. All waves have a positive and negative peak; that is,

7638-399: The Pacific, of which 50% are located in Asia, 30% in Africa, and 20% in Australasia. The rivers of the Indian Ocean are shorter on average (740 km (460 mi)) than those of the other major oceans. The largest rivers are ( order 5 ) the Zambezi , Ganges - Brahmaputra , Indus , Jubba , and Murray rivers and (order 4) the Shatt al-Arab , Wadi Ad Dawasir (a dried-out river system on

7752-410: The Peloponnesian War about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause. The oldest human record of a tsunami dates back to 479 BC , in the Greek colony of Potidaea , thought to be triggered by an earthquake. The tsunami may have saved the colony from an invasion by the Achaemenid Empire . The cause, in my opinion, of this phenomenon must be sought in

7866-441: The Southeast Arabian Sea salinity drops to less than 34 PSU. It is the lowest (c. 33 PSU) in the Bay of Bengal because of river runoff and precipitation. The Indonesian Throughflow and precipitation results in lower salinity (34 PSU) along the Sumatran west coast. Monsoonal variation results in eastward transportation of saltier water from the Arabian Sea to the Bay of Bengal from June to September and in westerly transport by

7980-411: The Southwest Indian Ridge, from where it continues into the Mozambique Channel and Prince Edward Fracture Zone . North of 20° south latitude the minimum surface temperature is 22 °C (72 °F), exceeding 28 °C (82 °F) to the east. Southward of 40° south latitude , temperatures drop quickly. The Bay of Bengal contributes more than half (2,950 km or 710 cu mi) of

8094-399: The Southwest Indian Ridge: a "Hoff" crab, a "giant peltospirid" snail, a whelk-like snail, a limpet, a scaleworm and a polychaete worm. The West Indian Ocean coelacanth was discovered in the Indian Ocean off South Africa in the 1930s and in the late 1990s another species, the Indonesian coelacanth , was discovered off Sulawesi Island , Indonesia. Most extant coelacanths have been found in

8208-450: The air over and one underwater within the shallow waters of the 50-metre (164 ft) deep lagoon at Bikini Atoll . The bombs detonated about 6 km (3.7 mi; 3.2 nmi) from the nearest island, where the waves were no higher than 3 to 4 m (9.8 to 13.1 ft) when they reached the shoreline. Other underwater tests, mainly Operation Hardtack I /Wahoo in deep water and Operation Hardtack I/Umbrella in shallow water, confirmed

8322-722: The austral summer. In 1999, the Indian Ocean Experiment showed that fossil fuel and biomass burning in South and Southeast Asia caused air pollution (also known as the Asian brown cloud ) that reach as far as the Intertropical Convergence Zone . This pollution has implications on both a local and global scale. Forty percent of the sediment of the Indian Ocean is found in the Indus and Ganges fans. The oceanic basins adjacent to

8436-466: The berries of Vaccinium myrtilloides to make pies and preserves. They use the berries of Vaccinium vitis-idaea ssp as food. Fisheries are an important source of employment. The Nation operated a boat building yard. The Hesquiaht are an isolated community in the Clayoquot region. Sustainable transportation, community infrastructure, sustainable energy production and keeping or re-attracting members to

8550-400: The bordering countries for domestic consumption and export. Fishing fleets from Russia, Japan, South Korea , and Taiwan also exploit the Indian Ocean, mainly for shrimp and tuna. Research indicates that increasing ocean temperatures are taking a toll on the marine ecosystem. A study on the phytoplankton changes in the Indian Ocean indicates a decline of up to 20% in the marine plankton in

8664-686: The centre of the 1,500,000 km (580,000 sq mi) hotspot, the landscape is dominated by Acacia - Commiphora deciduous bushland, but also includes the Yeheb nut ( Cordeauxia edulus ) and species discovered more recently such as the Somali cyclamen ( Cyclamen somalense ), the only cyclamen outside the Mediterranean. Warsangli linnet ( Carduelis johannis ) is an endemic bird found only in northern Somalia. An unstable political situation and mismanagement has resulted in overgrazing which has produced one of

8778-465: The community are issues affecting their future. Hesquiaht are working on developing community resources. This includes eco-tourism, infrastructure and housing, treaty negotiations, and the marketing of the community and territory. Tsunami A tsunami ( /( t ) s uː ˈ n ɑː m i , ( t ) s ʊ ˈ -/ (t)soo- NAH -mee, (t)suu- ; from Japanese : 津波 , lit.   'harbour wave', pronounced [tsɯnami] )

8892-496: The continental shelves are 50.4–52.4 km (31.3–32.6 mi) for active and passive margins respectively, with a maximum width of 205.3–255.2 km (127.6–158.6 mi). In correspondence of the Shelf break , also known as Hinge zone, the Bouguer gravity ranges from 0 to 30 mGals that is unusual for a continental region of around 16 km thick sediments. It has been hypothesized that

9006-541: The continental slopes mostly contain terrigenous sediments. The ocean south of the polar front (roughly 50° south latitude ) is high in biologic productivity and dominated by non-stratified sediment composed mostly of siliceous oozes . Near the three major mid-ocean ridges the ocean floor is relatively young and therefore bare of sediment, except for the Southwest Indian Ridge due to its ultra-slow spreading rate. The ocean's currents are mainly controlled by

9120-413: The danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed. A typical wave period for a damaging tsunami is about twelve minutes. Thus, the sea recedes in the drawback phase, with areas well below sea level exposed after three minutes. For the next six minutes, the wave trough builds into a ridge which may flood the coast, and destruction ensues. During

9234-455: The deep ocean has a much larger wavelength of up to 200 kilometres (120 mi). Such a wave travels at well over 800 kilometres per hour (500 mph), but owing to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 metre (3.3 ft). This makes tsunamis difficult to detect over deep water, where ships are unable to feel their passage. The velocity of

9348-487: The earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska. Examples of tsunamis originating at locations away from convergent boundaries include Storegga about 8,000 years ago, Grand Banks in 1929, and Papua New Guinea in 1998 (Tappin, 2001). The Grand Banks and Papua New Guinea tsunamis came from earthquakes which destabilised sediments, causing them to flow into

9462-408: The earthquake. At the point where its shock has been the most violent the sea is driven back, and suddenly recoiling with redoubled force, causes the inundation. Without an earthquake I do not see how such an accident could happen. The Roman historian Ammianus Marcellinus ( Res Gestae 26.10.15–19) described the typical sequence of a tsunami, including an incipient earthquake, the sudden retreat of

9576-667: The eastern extension of which is blocked by the Southeast Indian Ridge and the 90°E Ridge. Madagascar and the Southwest Indian Ridge separate three cells south of Madagascar and off South Africa. North Atlantic Deep Water reaches into the Indian Ocean south of Africa at a depth of 2,000–3,000 m (6,600–9,800 ft) and flows north along the eastern continental slope of Africa. Deeper than NADW, Antarctic Bottom Water flows from Enderby Basin to Agulhas Basin across deep channels (<4,000 m (13,000 ft)) in

9690-406: The flanks and in some cases detachment planes are believed to be developing. However, there is growing controversy about how dangerous these slopes actually are. Other than by landslides or sector collapse , volcanoes may be able to generate waves by pyroclastic flow submergence, caldera collapse, or underwater explosions. Tsunamis have been triggered by a number of volcanic eruptions, including

9804-516: The four fingers of the hand. The Ha'wiih are: Klukwana (the traditional governance system) includes the continued existence of Tikawiilth, those who manage the nation’s affairs on behalf of the hereditary chiefs. The Tikawiilth traditionally manage the affairs of the hereditary chiefs, which in modern times often coincides with the role of Chief and Council. The current Tikawiilth are Pat Charleson (Head Wolf Chief) - (thumb), Larry Paul, Remi Charleson, Eugene August and Chancellor Amos. Hesquiaht Council

9918-491: The gravitational pull of the moon and sun rather than the displacement of water. Although the meanings of "tidal" include "resembling" or "having the form or character of" tides, use of the term tidal wave is discouraged by geologists and oceanographers. A 1969 episode of the TV crime show Hawaii Five-O entitled "Forty Feet High and It Kills!" used the terms "tsunami" and "tidal wave" interchangeably. The term seismic sea wave

10032-409: The harbour at Halifax , Nova Scotia , Canada . There have been studies of the potential for the use of explosives to induce tsunamis as a tectonic weapon . As early as World War II (1939–1945), consideration of the use of conventional explosives was explored, and New Zealand's military forces initiated Project Seal , which attempted to create small tsunamis with explosives in the area of what

10146-546: The intensity of tsunamis were the Sieberg - Ambraseys scale (1962), used in the Mediterranean Sea and the Imamura-Iida intensity scale (1963), used in the Pacific Ocean. The latter scale was modified by Soloviev (1972), who calculated the tsunami intensity " I " according to the formula: where H a v {\displaystyle {\mathit {H}}_{av}} is the "tsunami height" in metres, averaged along

10260-545: The intensively studied tsunamis in 2004 and 2011, a new 12-point scale was proposed, the Integrated Tsunami Intensity Scale (ITIS-2012), intended to match as closely as possible to the modified ESI2007 and EMS earthquake intensity scales. The first scale that genuinely calculated a magnitude for a tsunami, rather than an intensity at a particular location was the ML scale proposed by Murty & Loomis based on

10374-580: The islands of the Indian Ocean are textbook cases of evolutionary processes; the dung beetles , day geckos , and lemurs are all examples of adaptive radiation . Many bones (250 bones per square metre) of recently extinct vertebrates have been found in the Mare aux Songes swamp in Mauritius, including bones of the Dodo bird ( Raphus cucullatus ) and Cylindraspis giant tortoise. An analysis of these remains suggests

10488-483: The low barometric pressure of passing tropical cyclones, nor should they be confused with setup, the temporary local raising of sea level caused by strong on-shore winds. Storm surges and setup are also dangerous causes of coastal flooding in severe weather but their dynamics are completely unrelated to tsunami waves. They are unable to propagate beyond their sources, as waves do. The accidental Halifax Explosion in 1917 triggered an 18-metre (59 ft) high tsunami in

10602-481: The margins of the Indian Ocean. The origin of this diversity is debated; the break-up of Gondwana can explain vicariance older than 100 mya, but the diversity on the younger, smaller islands must have required a Cenozoic dispersal from the rims of the Indian Ocean to the islands. A "reverse colonisation", from islands to continents, apparently occurred more recently; the chameleons , for example, first diversified on Madagascar and then colonised Africa. Several species on

10716-457: The monsoon. Two large gyres , one in the northern hemisphere flowing clockwise and one south of the equator moving anticlockwise (including the Agulhas Current and Agulhas Return Current ), constitute the dominant flow pattern. During the winter monsoon (November–February), however, circulation is reversed north of 30°S and winds are weakened during winter and the transitional periods between

10830-602: The monsoons. The Indian Ocean contains the largest submarine fans of the world, the Bengal Fan and Indus Fan , and the largest areas of slope terraces and rift valleys . The inflow of deep water into the Indian Ocean is 11  Sv , most of which comes from the Circumpolar Deep Water (CDW). The CDW enters the Indian Ocean through the Crozet and Madagascar basins and crosses the Southwest Indian Ridge at 30°S. In

10944-535: The most productive ecosystems of the Indian Ocean ;— coastal areas produce 20 tones of fish per square kilometre. These areas, however, are also being urbanised with populations often exceeding several thousand people per square kilometre and fishing techniques become more effective and often destructive beyond sustainable levels while the increase in sea surface temperature spreads coral bleaching. Mangroves covers 80,984 km (31,268 sq mi) in

11058-611: The nearest coastline, with the tsunami height defined as the rise of the water level above the normal tidal level at the time of occurrence of the tsunami. This scale, known as the Soloviev-Imamura tsunami intensity scale , is used in the global tsunami catalogues compiled by the NGDC/NOAA and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami. This formula yields: In 2013, following

11172-405: The next six minutes, the wave changes from a ridge to a trough, and the flood waters recede in a second drawback. Victims and debris may be swept into the ocean. The process repeats with succeeding waves. As with earthquakes, several attempts have been made to set up scales of tsunami intensity or magnitude to allow comparison between different events. The first scales used routinely to measure

11286-617: The northern end while the Laccadive Sea separates the Maldives from the southern tip of India. The Bay of Bengal is off the east coast of India. The Gulf of Mannar and the Palk Strait separate Sri Lanka from India, while Adam's Bridge separates the two. The Andaman Sea is located between the Bay of Bengal and the Andaman Islands. In Indonesia, the so-called Indonesian Seaway is composed of

11400-847: The ocean and generate a tsunami. They dissipated before travelling transoceanic distances. The cause of the Storegga sediment failure is unknown. Possibilities include an overloading of the sediments, an earthquake or a release of gas hydrates (methane etc.). The 1960 Valdivia earthquake ( M w 9.5), 1964 Alaska earthquake ( M w 9.2), 2004 Indian Ocean earthquake ( M w 9.2), and 2011 Tōhoku earthquake ( M w 9.0) are recent examples of powerful megathrust earthquakes that generated tsunamis (known as teletsunamis ) that can cross entire oceans. Smaller ( M w 4.2) earthquakes in Japan can trigger tsunamis (called local and regional tsunamis) that can devastate stretches of coastline, but can do so in only

11514-437: The ocean, meteorite impacts, and the weather when the atmospheric pressure changes very rapidly—can generate such waves by displacing water. The use of the term tsunami for waves created by landslides entering bodies of water has become internationally widespread in both scientific and popular literature, although such waves are distinct in origin from large waves generated by earthquakes. This distinction sometimes leads to

11628-478: The possibility of a meteorite causing a tsunami is debated. Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. More specifically,

11742-433: The potential energy. Difficulties in calculating the potential energy of the tsunami mean that this scale is rarely used. Abe introduced the tsunami magnitude scale M t {\displaystyle {\mathit {M}}_{t}} , calculated from, where h is the maximum tsunami-wave amplitude (in m) measured by a tide gauge at a distance R from the epicentre, a , b and D are constants used to make

11856-605: The results. Analysis of the effects of shallow and deep underwater explosions indicate that the energy of the explosions does not easily generate the kind of deep, all-ocean waveforms typical of tsunamis because most of the energy creates steam , causes vertical fountains above the water, and creates compressional waveforms. Tsunamis are hallmarked by permanent large vertical displacements of very large volumes of water which do not occur in explosions. Tsunamis are caused by earthquakes, landslides, volcanic explosions, glacier calvings, and bolides . They cause damage by two mechanisms:

11970-426: The sea and a following gigantic wave, after the 365 AD tsunami devastated Alexandria . The principal generation mechanism of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually caused by earthquakes, but can also be attributed to landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests. However,

12084-400: The smashing force of a wall of water travelling at high speed, and the destructive power of a large volume of water draining off the land and carrying a large amount of debris with it, even with waves that do not appear to be large. While everyday wind waves have a wavelength (from crest to crest) of about 100 metres (330 ft) and a height of roughly 2 metres (6.6 ft), a tsunami in

12198-457: The transoceanic reach of significant seismic tsunamis, and 2) that the force that displaces the water is sustained over some length of time such that meteotsunamis cannot be modelled as having been caused instantaneously. In spite of their lower energies, on shorelines where they can be amplified by resonance, they are sometimes powerful enough to cause localised damage and potential for loss of life. They have been documented in many places, including

12312-447: The understanding of the other source mechanisms. Some meteorological conditions, especially rapid changes in barometric pressure, as seen with the passing of a front, can displace bodies of water enough to cause trains of waves with wavelengths. These are comparable to seismic tsunamis, but usually with lower energies. Essentially, they are dynamically equivalent to seismic tsunamis, the only differences being 1) that meteotsunamis lack

12426-457: The use of other terms for landslide-generated waves, including landslide-triggered tsunami , displacement wave , non-seismic wave , impact wave , and, simply, giant wave . While Japan may have the longest recorded history of tsunamis, the sheer destruction caused by the 2004 Indian Ocean earthquake and tsunami event mark it as the most devastating of its kind in modern times, killing around 230,000 people. The Sumatran region

12540-579: The ventilation of the Indian Ocean thermocline . That continent also drives the Indian Ocean monsoon , the strongest on Earth, which causes large-scale seasonal variations in ocean currents, including the reversal of the Somali Current and Indian Monsoon Current . Because of the Indian Ocean Walker circulation there are no continuous equatorial easterlies. Upwelling occurs near the Horn of Africa and

12654-399: The very largest tsunamis, the approaching wave does not break , but rather appears like a fast-moving tidal bore . Open bays and coastlines adjacent to very deep water may shape the tsunami further into a step-like wave with a steep-breaking front. When the tsunami's wave peak reaches the shore, the resulting temporary rise in sea level is termed run up . Run up is measured in metres above

12768-478: The world. Long-term ocean temperature records show a rapid, continuous warming in the Indian Ocean, at about 1.2 °C (34.2 °F) (compared to 0.7 °C (33.3 °F) for the warm pool region) during 1901–2012. Research indicates that human induced greenhouse warming , and changes in the frequency and magnitude of El Niño (or the Indian Ocean Dipole ), events are a trigger to this strong warming in

12882-636: Was among the deadliest natural disasters in human history, with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean . The Ancient Greek historian Thucydides suggested in his 5th century BC History of the Peloponnesian War that tsunamis were related to submarine earthquakes , but the understanding of tsunamis remained slim until the 20th century, and much remains unknown. Major areas of current research include determining why some large earthquakes do not generate tsunamis while other smaller ones do. This ongoing research

12996-515: Was confirmed in 1958, when a giant landslide in Lituya Bay , Alaska, caused the highest wave ever recorded, which had a height of 524 metres (1,719 ft). The wave did not travel far as it struck land almost immediately. The wave struck three boats—each with two people aboard—anchored in the bay. One boat rode out the wave, but the wave sank the other two, killing both people aboard one of them. Another landslide-tsunami event occurred in 1963 when

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