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61-424: Indian River Bay is unique among Delaware's inland bays in that it is a drowned river valley , whereas Delaware's other bays are estuaries built on sand bars . Boating, fishing, shellfishing, and crabbing are among the most common recreational uses of Indian River Bay. In addition, the bay is bordered by several protected environmental areas, including Delaware Seashore State Park , Holts Landing State Park , and

122-430: 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

183-427: 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

244-432: 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

305-541: 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

366-538: 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

427-577: 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,

488-462: 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

549-467: 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

610-655: 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

671-445: 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

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732-434: 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

793-473: 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

854-463: Is a stub . You can help Misplaced Pages by expanding it . Drowned river valley A ria ( / ˈ r iː ə / ; Galician : ría , feminine noun derived from río , river) is a coastal inlet formed by the partial submergence of an unglaciated river valley . It is a drowned river valley that remains open to the sea. Typically rias have a dendritic , treelike outline although they can be straight and without significant branches. This pattern

915-405: Is a coastline having several parallel rias separated by prominent ridges, extending a distance inland. The sea level change that caused the submergence of a river valley may be either eustatic (where global sea levels rise), or isostatic (where the local land sinks). The result is often a very large estuary at the mouth of a relatively insignificant river (or else sediments would quickly fill

976-467: 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

1037-620: 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

1098-562: 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

1159-496: 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

1220-520: Is inherited from the dendritic drainage pattern of the flooded river valley. The drowning of river valleys along a stretch of coast and formation of rias results in an extremely irregular and indented coastline. Often, there are naturally occurring islands, which are summits of partly submerged, pre-existing hill peaks. (Islands may also be artificial, such as those constructed for the Chesapeake Bay Bridge-Tunnel .) A ria coast

1281-515: 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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1342-791: 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

1403-426: 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

1464-430: 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

1525-688: 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

1586-413: 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

1647-530: 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

1708-427: 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

1769-709: The 21st century, however, the preferred usage of ria by geologists and geomorphologists is to refer solely to drowned unglaciated river valleys. It therefore excludes fjords by definition, since fjords are products of glaciation. The funnel-like shape of rias can amplify the effects of tsunamis , as demonstrated in the seismicity of the Sanriku coast , most recently in the 2011 Tōhoku earthquake and tsunami . 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] )

1830-836: The Assawoman Wildlife Area. Most pollution of the Indian River Bay is due to agricultural and urban runoff . Two solutions have been proposed. The first requires cutting an inlet through Delaware Seashore State Park , which would involve building a bridge and jetty. The other is dredging and widening the Assawoman Canal to improve the flow of tidal water to and from Indian River Bay and the Indian River Inlet. 38°36′N 75°06′W  /  38.6°N 75.1°W  / 38.6; -75.1 This Delaware state location article

1891-818: 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

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1952-540: 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,

2013-597: 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

2074-450: 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

2135-413: 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

2196-455: 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

2257-494: 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

2318-408: 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

2379-406: 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

2440-494: 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

2501-409: 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

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2562-557: 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

2623-562: 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

2684-483: 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

2745-636: 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

2806-405: 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

2867-856: 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

2928-437: 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

2989-482: 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,

3050-433: 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

3111-605: 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:

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3172-609: The ria). The Kingsbridge Estuary in Devon , England, is an extreme example of a ria forming an estuary disproportionate to the size of its river; no significant river flows into it at all, only a number of small streams. The word ria comes from Galician ría which comes from río (river). Rias are present all along the Galician coast in Spain . As originally defined, the term was restricted to drowned river valleys cut parallel to

3233-426: 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,

3294-400: 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

3355-440: The structure of the country rock that was at right angles to the coastline. However the definition of ria was later expanded to other flooded river valleys regardless of the structure of the country rock. For a time European geomorphologists considered rias to include any broad estuarine river mouth, including fjords . These are long narrow inlets with steep sides or cliffs, created in a valley carved by glacial activity . In

3416-457: 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

3477-447: 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

3538-457: 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

3599-399: 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

3660-576: 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

3721-521: 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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