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100-508: Waiākea-Uka marks the most mauka portion of human settlement in the Hilo district. Waiākea-Uka has many expensive houses, including a Swiss-style chateau. The area is home to many traditional agricultural Hawaiian-style homes. As the area is mauka of Hilo Bay, there is no threat of tsunami ; earthquakes are always a possibility anywhere on the island, and the area is currently termed lava zone 3. The most recent lava flows were in 1935, 1942 and 1984, with

200-434: A stochastic process , in combination with the physics governing their generation, growth, propagation, and decay – as well as governing the interdependence between flow quantities such as the water surface movements, flow velocities , and water pressure . The key statistics of wind waves (both seas and swells) in evolving sea states can be predicted with wind wave models . Although waves are usually considered in

300-430: 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

400-399: A deep-water wave may also be approximated by: where g is the acceleration due to gravity, 9.8 meters (32 feet) per second squared. Because g and π (3.14) are constants, the equation can be reduced to: when C is measured in meters per second and L in meters. In both formulas the wave speed is proportional to the square root of the wavelength. The speed of shallow-water waves is described by

500-456: A different equation that may be written as: where C is speed (in meters per second), g is the acceleration due to gravity, and d is the depth of the water (in meters). The period of a wave remains unchanged regardless of the depth of water through which it is moving. As deep-water waves enter the shallows and feel the bottom, however, their speed is reduced, and their crests "bunch up", so their wavelength shortens. Sea state can be described by

600-405: A dissipation of energy due to the breaking of wave tops and formation of "whitecaps". Waves in a given area typically have a range of heights. For weather reporting and for scientific analysis of wind wave statistics, their characteristic height over a period of time is usually expressed as significant wave height . This figure represents an average height of the highest one-third of the waves in

700-427: 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

800-429: A given time period (usually chosen somewhere in the range from 20 minutes to twelve hours), or in a specific wave or storm system. The significant wave height is also the value a "trained observer" (e.g. from a ship's crew) would estimate from visual observation of a sea state. Given the variability of wave height, the largest individual waves are likely to be somewhat less than twice the reported significant wave height for

900-432: 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

1000-537: 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

1100-528: 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

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1200-414: A particular day or storm. Wave formation on an initially flat water surface by wind is started by a random distribution of normal pressure of turbulent wind flow over the water. This pressure fluctuation produces normal and tangential stresses in the surface water, which generates waves. It is usually assumed for the purpose of theoretical analysis that: The second mechanism involves wind shear forces on

1300-570: 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,

1400-462: 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

1500-467: 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

1600-513: A spectacular view of the Hilo region, including Hilo bay, as well as Mauna Kea. Waiākea Stream flows from the slopes of Mauna Loa at 19°37′57″N 155°10′41″W  /  19.63250°N 155.17806°W  / 19.63250; -155.17806  ( Waiākea Stream Source ) into Waiākea Pond at an elevation of only 10 feet (3.0 m) at 19°42′53″N 155°4′35″W  /  19.71472°N 155.07639°W  / 19.71472; -155.07639  ( Waiākea Pond ) . As Waiakea-Uka

1700-501: A state forest reserve (Upper Waiākea Forest Reserve). Waiākea-Uka is served by four schools located in the Waiākea area: Waiakeawaena Elementary School, Waiakea Elementary School, Waiakea Intermediate School, and Waiakea High School . The Waiākea-Uka region is home to a million-dollar park and indoor gym. The area also highlights a variety of traditional stone/rock wall and palm grove cutting techniques; many homes have kept these walls up and

1800-473: A sudden wind flow blows steadily across the sea surface, the physical wave generation process follows the sequence: Three different types of wind waves develop over time: Ripples appear on smooth water when the wind blows, but will die quickly if the wind stops. The restoring force that allows them to propagate is surface tension . Sea waves are larger-scale, often irregular motions that form under sustained winds. These waves tend to last much longer, even after

1900-628: 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

2000-445: 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

2100-434: 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

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2200-473: 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

2300-468: A variety of linearly-cut coconut palm groves can be seen as home line designations. The Hele-On bus number 6 runs from Hilo town to Waiākea-Uka, and the bus number 7 runs from Waiākea-Uka to Hilo town. The topography of the entire area is quite varied; The main roads (Hoaka Road, 'Aina'ola Drive, Kawailani Street) are laid over the same active rift zones that created the region over the past 100 years. Further earthquake activity and land settling has created

2400-404: A wind wave system is called a wind sea . Wind waves will travel in a great circle route after being generated – curving slightly left in the southern hemisphere and slightly right in the northern hemisphere. After moving out of the area of fetch and no longer being affected by the local wind, wind waves are called swells and can travel thousands of kilometers. A noteworthy example of this

2500-467: 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

2600-596: 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

2700-557: 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

2800-406: Is called shoaling . Wave refraction is the process that occurs when waves interact with the sea bed to slow the velocity of propagation as a function of wavelength and period. As the waves slow down in shoaling water, the crests tend to realign at a decreasing angle to the depth contours. Varying depths along a wave crest cause the crest to travel at different phase speeds , with those parts of

2900-490: Is concentrated as they converge, with a resulting increase in wave height. Because these effects are related to a spatial variation in the phase speed, and because the phase speed also changes with the ambient current—due to the Doppler shift —the same effects of refraction and altering wave height also occur due to current variations. In the case of meeting an adverse current the wave steepens , i.e. its wave height increases while

3000-491: 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

3100-438: Is inevitable. Individual waves in deep water break when the wave steepness—the ratio of the wave height H to the wavelength λ —exceeds about 0.17, so for H  > 0.17  λ . In shallow water, with the water depth small compared to the wavelength, the individual waves break when their wave height H is larger than 0.8 times the water depth h , that is H  > 0.8  h . Waves can also break if

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3200-406: Is logarithmic to the water surface, the curvature has a negative sign at this point. This relation shows the wind flow transferring its kinetic energy to the water surface at their interface. Assumptions: Generally, these wave formation mechanisms occur together on the water surface and eventually produce fully developed waves. For example, if we assume a flat sea surface (Beaufort state 0), and

3300-497: Is measured in metres. This expression tells us that waves of different wavelengths travel at different speeds. The fastest waves in a storm are the ones with the longest wavelength. As a result, after a storm, the first waves to arrive on the coast are the long-wavelength swells. For intermediate and shallow water, the Boussinesq equations are applicable, combining frequency dispersion and nonlinear effects. And in very shallow water,

3400-515: 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

3500-762: 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

3600-585: Is on the lower flanks of Mauna Loa, the area is known in for its rainfall; in August 2013, the Waiakea-Uka NWS rain gauge showed 83.96 inches of accumulated rain, while the Hilo International Airport rain gauge only registered 57.97 inches for the same length of time; though these two rain gauges are about 6 miles apart, this represents a difference of 25.99 inches, or about the average yearly rainfall of

3700-402: Is sometimes alleged that out of a set of waves, the seventh wave in a set is always the largest; while this isn't the case, the waves in the middle of a given set tend to be larger than those before and after them. Individual " rogue waves " (also called "freak waves", "monster waves", "killer waves", and "king waves") much higher than the other waves in the sea state can occur. In the case of

3800-426: 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

3900-627: Is the wave elevation, ϵ j {\displaystyle \epsilon _{j}} is uniformly distributed between 0 and 2 π {\displaystyle 2\pi } , and Θ j {\displaystyle \Theta _{j}} is randomly drawn from the directional distribution function f ( Θ ) : {\displaystyle {\sqrt {f(\Theta )}}:} As waves travel from deep to shallow water, their shape changes (wave height increases, speed decreases, and length decreases as wave orbits become asymmetrical). This process

4000-510: Is waves generated south of Tasmania during heavy winds that will travel across the Pacific to southern California, producing desirable surfing conditions. Wind waves in the ocean are also called ocean surface waves and are mainly gravity waves , where gravity is the main equilibrium force. Wind waves have a certain amount of randomness : subsequent waves differ in height, duration, and shape with limited predictability. They can be described as

4100-430: 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

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4200-666: 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

4300-544: The 1984 coming quite close to the upper reaches of the area. Driving northwest on the Saddle Road , about 15 miles outside of the Hilo extension, one can see the vast lava fields of the 1881, 1935 and 1942 lava flows. This same lava flow stopped one half mile east of the upper Kaumana area Recently, there has been much growth in the agriculture of the area. Some cattle, goat and dairy farms are located in Waiākea-Uka, as well as

4400-413: 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

4500-656: The Draupner wave , its 25 m (82 ft) height was 2.2 times the significant wave height . Such waves are distinct from tides , caused by the Moon and Sun 's gravitational pull , tsunamis that are caused by underwater earthquakes or landslides , and waves generated by underwater explosions or the fall of meteorites —all having far longer wavelengths than wind waves. The largest ever recorded wind waves are not rogue waves, but standard waves in extreme sea states. For example, 29.1 m (95 ft) high waves were recorded on

4600-500: The RRS Discovery in a sea with 18.5 m (61 ft) significant wave height, so the highest wave was only 1.6 times the significant wave height. The biggest recorded by a buoy (as of 2011) was 32.3 m (106 ft) high during the 2007 typhoon Krosa near Taiwan. Ocean waves can be classified based on: the disturbing force that creates them; the extent to which the disturbing force continues to influence them after formation;

4700-477: 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

4800-430: The sea wave spectrum or just wave spectrum S ( ω , Θ ) {\displaystyle S(\omega ,\Theta )} . It is composed of a wave height spectrum (WHS) S ( ω ) {\displaystyle S(\omega )} and a wave direction spectrum (WDS) f ( Θ ) {\displaystyle f(\Theta )} . Many interesting properties about

4900-427: 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

5000-785: 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

5100-676: The M t scale match as closely as possible with the moment magnitude scale. Wind wave In fluid dynamics , a wind wave , or wind-generated water wave , is a surface wave that occurs on the free surface of bodies of water as a result of the wind blowing over the water's surface. The contact distance in the direction of the wind is known as the fetch . Waves in the oceans can travel thousands of kilometers before reaching land. Wind waves on Earth range in size from small ripples to waves over 30 m (100 ft) high, being limited by wind speed, duration, fetch, and water depth. When directly generated and affected by local wind,

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5200-422: 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,

5300-577: 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

5400-450: 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

5500-471: The crest falling forward and down as it extends over the air ahead of the wave. Three main types of breaking waves are identified by surfers or surf lifesavers . Their varying characteristics make them more or less suitable for surfing and present different dangers. When the shoreline is near vertical, waves do not break but are reflected. Most of the energy is retained in the wave as it returns to seaward. Interference patterns are caused by superposition of

5600-413: 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

5700-455: 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

5800-487: 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

5900-408: 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

6000-464: The equilibrium of the water surface and transfer energy from the air to the water, forming waves. The initial formation of waves by the wind is described in the theory of Phillips from 1957, and the subsequent growth of the small waves has been modeled by Miles , also in 1957. In linear plane waves of one wavelength in deep water, parcels near the surface move not plainly up and down but in circular orbits: forward above and backward below (compared to

6100-475: The extent to which the restoring force weakens or flattens them; and their wavelength or period. Seismic sea waves have a period of about 20 minutes, and speeds of 760 km/h (470 mph). Wind waves (deep-water waves) have a period up to about 20 seconds. The speed of all ocean waves is controlled by gravity, wavelength, and water depth. Most characteristics of ocean waves depend on the relationship between their wavelength and water depth. Wavelength determines

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6200-424: The faster the wave energy will move through the water. The relationship between the wavelength, period and velocity of any wave is: where C is speed (celerity), L is the wavelength, and T is the period (in seconds). Thus the speed of the wave derives from the functional dependence L ( T ) {\displaystyle L(T)} of the wavelength on the period (the dispersion relation ). The speed of

6300-406: 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

6400-418: The formation of the flow structures in wind waves: All of these factors work together to determine the size of the water waves and the structure of the flow within them. The main dimensions associated with wave propagation are: A fully developed sea has the maximum wave size theoretically possible for a wind of specific strength, duration, and fetch. Further exposure to that specific wind could only cause

6500-491: 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

6600-409: 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

6700-460: The hyperbolic tangent approaches 1 {\displaystyle 1} , the speed c {\displaystyle c} approximates In SI units, with c deep {\displaystyle c_{\text{deep}}} in m/s, c deep ≈ 1.25 λ {\displaystyle c_{\text{deep}}\approx 1.25{\sqrt {\lambda }}} , when λ {\displaystyle \lambda }

6800-434: The incident and reflected waves, and the superposition may cause localized instability when peaks cross, and these peaks may break due to instability. (see also clapotic waves ) Wind waves are mechanical waves that propagate along the interface between water and air ; the restoring force is provided by gravity, and so they are often referred to as surface gravity waves . As the wind blows, pressure and friction perturb

6900-546: 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

7000-545: 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

7100-483: 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

7200-611: 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

7300-405: 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

7400-847: 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

7500-437: 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

7600-411: The other hand, the orbits of water molecules in waves moving through shallow water are flattened by the proximity of the sea bottom surface. Waves in water shallower than 1/20 their original wavelength are known as shallow-water waves. Transitional waves travel through water deeper than 1/20 their original wavelength but shallower than half their original wavelength. In general, the longer the wavelength,

7700-478: 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,

7800-433: 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

7900-605: 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:

8000-426: 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,

8100-508: The sea state can be found from the wave spectra. WHS describes the spectral density of wave height variance ("power") versus wave frequency , with dimension { S ( ω ) } = { length 2 ⋅ time } {\displaystyle \{S(\omega )\}=\{{\text{length}}^{2}\cdot {\text{time}}\}} . The relationship between the spectrum S ( ω j ) {\displaystyle S(\omega _{j})} and

8200-483: The size of the orbits of water molecules within a wave, but water depth determines the shape of the orbits. The paths of water molecules in a wind wave are circular only when the wave is traveling in deep water. A wave cannot "feel" the bottom when it moves through water deeper than half its wavelength because too little wave energy is contained in the water movement below that depth. Waves moving through water deeper than half their wavelength are known as deep-water waves. On

8300-400: 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

8400-410: The state of Kansas. As a result, Papaya, Guava, Citrus and Plumeria are grown by many residents. In recent years, plums and peaches can be seen around many of the area's fields. 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] )

8500-471: The surface. The phase speed (also called the celerity) of a surface gravity wave is—for pure periodic wave motion of small- amplitude waves—well approximated by where In deep water, where d ≥ 1 2 λ {\displaystyle d\geq {\frac {1}{2}}\lambda } , so 2 π d λ ≥ π {\displaystyle {\frac {2\pi d}{\lambda }}\geq \pi } and

8600-457: 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

8700-447: 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

8800-457: 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

8900-399: 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

9000-406: The water seas of Earth, the hydrocarbon seas of Titan may also have wind-driven waves. Waves in bodies of water may also be generated by other causes, both at the surface and underwater (such as watercraft , animals , waterfalls , landslides , earthquakes , bubbles , and impact events ). The great majority of large breakers seen at a beach result from distant winds. Five factors influence

9100-414: The water surface. John W. Miles suggested a surface wave generation mechanism that is initiated by turbulent wind shear flows based on the inviscid Orr–Sommerfeld equation in 1957. He found the energy transfer from the wind to the water surface is proportional to the curvature of the velocity profile of the wind at the point where the mean wind speed is equal to the wave speed. Since the wind speed profile

9200-456: The wave amplitude A j {\displaystyle A_{j}} for a wave component j {\displaystyle j} is: Some WHS models are listed below. As for WDS, an example model of f ( Θ ) {\displaystyle f(\Theta )} might be: Thus the sea state is fully determined and can be recreated by the following function where ζ {\displaystyle \zeta }

9300-423: The wave amplitude (height), the particle paths do not form closed orbits; rather, after the passage of each crest, particles are displaced slightly from their previous positions, a phenomenon known as Stokes drift . As the depth below the free surface increases, the radius of the circular motion decreases. At a depth equal to half the wavelength λ, the orbital movement has decayed to less than 5% of its value at

9400-409: The wave in deeper water moving faster than those in shallow water . This process continues while the depth decreases, and reverses if it increases again, but the wave leaving the shoal area may have changed direction considerably. Rays —lines normal to wave crests between which a fixed amount of energy flux is contained—converge on local shallows and shoals. Therefore, the wave energy between rays

9500-464: The wave propagation direction). As a result, the surface of the water forms not an exact sine wave , but more a trochoid with the sharper curves upwards—as modeled in trochoidal wave theory. Wind waves are thus a combination of transversal and longitudinal waves. When waves propagate in shallow water , (where the depth is less than half the wavelength) the particle trajectories are compressed into ellipses . In reality, for finite values of

9600-400: The wavelength decreases, similar to the shoaling when the water depth decreases. Some waves undergo a phenomenon called "breaking". A breaking wave is one whose base can no longer support its top, causing it to collapse. A wave breaks when it runs into shallow water , or when two wave systems oppose and combine forces. When the slope, or steepness ratio, of a wave, is too great, breaking

9700-404: The wind grows strong enough to blow the crest off the base of the wave. In shallow water, the base of the wave is decelerated by drag on the seabed. As a result, the upper parts will propagate at a higher velocity than the base and the leading face of the crest will become steeper and the trailing face flatter. This may be exaggerated to the extent that the leading face forms a barrel profile, with

9800-482: The wind has died, and the restoring force that allows them to propagate is gravity. As waves propagate away from their area of origin, they naturally separate into groups of common direction and wavelength. The sets of waves formed in this manner are known as swells. The Pacific Ocean is 19,800 km (12,300 mi) from Indonesia to the coast of Colombia and, based on an average wavelength of 76.5 m (251 ft), would have ~258,824 swells over that width. It

9900-576: 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

10000-515: 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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