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Tsunami

Tsunami

Alternative rock band

For the Record

Selected discography

Sources

Tsunami is an Arlington, Virginia, based band fronted by the razor-sharp smarts of Jenny Toomey and Kristin Thomson, who also boast musical talent in such excess that they moonlight in other bands. Furthermore, Toomey and Thomson run their own label, Simple Machines, dedicated to providing welcoming business turf for fledgling indie bands. That label is also home of the Tsunami catalog, which includes a staggering number of singles in near-collectible sleeve designs. Tsunami come across like a kind of teen gang, wrote Melody Makers Sharon OConnell. Its their autonomy, their spirit and their drive, and the way they celebrate the raw and the very ordinary; the way it is when youre very young and every feeling is new each time you feel it.

Tsunami was formed inside the suburban Washington, DC house that Toomey and Thomson shared with John Pamer in the last months of 1990. Toomey had been in a band called Geek, where she met Andrew Webster, and she talked him into moving to the area so they could form a band with Pamer and Thomson; their goal was to play a New Years Eve 1990 party. Toomey and Thomson were no newcomers to the music scene, having already formed the Simple Machines label with the help of their friend Ian MacKaye, head of the famed DC label Dischord. By February of 1991, they took their fledgling band on the road.

During 1991, Tsunami came into being as a band with some difficult tours and a well-packaged single or two. Touring was a strictly low-budget affair, with the band and gear loaded into a sometimes unreliable Isuzu Trooper, playing college towns across the country. Their worst show ever, Toomey told ViVidzins Juliette Morris, was at a college in Ohionot at a bar, but at some really bad fraternity-type of party and it was Morns Night, which meant that everywhere we looked, we saw mothers with their arms around their staggering, drunk children. A bad sound system, and a sound man who mistakenly thought Toomey was making fun of him and began lousing up everything during their performance completed the farce. Their first single, released in the spring of 1991, was Headringer, followed by that summers Genius of Crack.

Tsunami recorded and toured with pals Velocity Girl, and also recorded split singles with them, such as 1992s SubPop release Left Behind. Another track from 1992 sums up the unique attitude with which Toomey and Thomson hurtle through the male-dominated world of indie rock: Punk Means Cuddle calls for a nicer, less belligerent attitude among their college-radio bands and fans. Toomey used to be active in the riot-grrl movement, but came to some realizations about what Tsunami call the loadhog phenomenon, and even wrote a song about it. Loadhogs are people who martyr themselves for the cause, Toomey told Melody Make fsSaWy Margaret Joy. People who would rather do the work for you than teach you how to do it yourself. In the song, Toomey explained, she was trying to explore the delicate problem of how work is delegated.

In early 1993 a national promoter phoned and asked them if they might be interested in playing on that summers Lollapalooza tour. Originally, they assumed it was a prank call. Their six shows on a side stage shared with other acts such as Sebadoh and Thurston Moore dovetailed nicely with the release of their first full-length record, Deep End. Later that year Tsunami recorded their follow-up, The Hearts Tremolo, in Chicago and it was released in 1994. Like all of their Tsunami issues, the two albums boasted beautifully designed covers; one single, from the previous year, Diner, featured the menu from their favorite low-budget restaurant.

This irreverence infects much of what Tsunami does. They once undertook a microphone relay race from their office to a club, taped it, and played it live during a show. Yet they also donate money to non-profit organizations and are quite serious about the seemingly insurmountable wall between feminist ideology and alternative music. I believe that women will never be accepted in punk rock, and that is why Tsunami walks the line between pop and punk, Toomey told Melody

For the Record

Original members are John Pamer, drums (left band, c. 1996); Kristin Thomson, guitar, vocals (married Brian Dilworth, a musician, c. 1996); Jenny Toomey, guitar, vocals; and Andrew Webster, bass; Luther Trip Gray, joined as a replacement for Pamer, c. 1996.

Toomey was a philosophy major in college and had previously been in the band Geek; Toomey and Thomson founded Simple Machines Records, c. 1990; Gray played drums in Sea Saw.

Band formed, late 1990; released several singles on Homestead, SubPop, C/Z and Simple Machines Records; 1991-92; released first full-length record, Deep End, on Simple Machines, 1993; played Lollapalooza 1993.

Addresses: Record company Simple Machines Records, P.O. Box 10290, Arlington, VA 22210-1290. E-mail [email protected]

Maker. Band members still had their day jobs in 1993: Toomey worked as a bookkeeper for an anti-nuclear organization, while Thomson worked in a food co-opbut continued to run the Simple Machines label. Its office was at their houseso we wake up, put on our clothes, and start work, Thomson told Joy in Melody Maker. We have no free time at all. [L]uckily, there are no pubs near where we live.

The members of Tsunami were busy throughout 1993 and 1994. They had a friend in England, John Loder, who owns a studio, and began traversing back and forth to do recordings. They toured with the bands Rodan and Eggs, and, when asked how England responds to Tsunami, Toomey told ViVidzine that the music press there is quite fickleIts depending on what bands are popular at the moment, you could be everyones darlings or everyone could hate you. Its such a small country, and they start these weird little trends a lot. Sharon OConnell reviewed a live show for Melody Maker and lauded it: They bang and strum, leaving slight spaces before they storm in to mess things up.

Tsunami completed two American tours in 1994 in addition to more dates in England, but time became more unmanageable with Pamer still in college and living elsewhere. During their get-togethers, the band was forced to write and record real fast, so were very goal-oriented, Toomey told Melody Makers Joy. Toomey also explained to ViVidzine that her bandmate has had a hard time on tour, she said of Thomson, because shes a good workaholic and its been hard for her to get in the van, because theres no desk in there.

Though the band has managed to issue a full-length record annually, it is their singles that fuel the Tsunami wave. In 1994 they released Be Like That, as well as a split CD with Rodan and Eggs from their U.K. tour entitled Cowed by the Blah Blah. After releasing World Tour and Other Destinations in 1995containing 22 singles previously released and difficulttofindthe band went on hiatus so Pamer could finish his degree. Toomey and Thomson continued to run the label and work with other bands. Toomey moonlighted in Liquorice, signed to Englands 4AD label. Thomson married and began spending time in Philadelphia with her husband, Brian Dilworth, of the band the Gelcaps and head of the Compulsiv record label. Webster began a career as a documentary filmmaker. Yet after Pamer graduated in 1996, he remained in Massachusetts and made clear his intention to live in New York, not Virginia.

The break seemed to have changed everyone. When we stopped playing, I was exhausted, Toomey told Magnets Cyndi Elliott. It was because we didnt want to play. Ive always thought that a band benefits from not having to be a band all the time. We always held day jobs and did other things. Thats one of the reasons we were able to stay a band for so long. When you are forced to play because you have to pay rent, you lose quality control and a lot of the joy of it. In a decision made with some trepidation, they hired another drummer, Luther Gray. Formerly an intern at Simple Machines, Gray has a jazz background and brought a new rhythmic dimension to their music. It fit in perfectly with their maturation as a band, with Toomey and Thomson writing more melodic and less strident songs, which was evident on their 1997 release A Brilliant Mistake. Many of Tsunamis friends from the Chicago music scene contributed as well, including members of the Coctails and Poi Dog Pondering, and Rob Christiansen from Liquorice, who played bass on half the record.

Despite her work with Liquorice and Tsunami, Toomey admits to being insecure about her songwriting abilities: Very rarely Ill have something I think I should write, she told Magnet. Except e-mails and purchase orders. Both Toomey and Thomson are confident about their business acumen, however. They claim anyone can begin a label, and have even written a booklet on how to do it, but we dont talk about ambition in it, Toomey told Joy in the Melody Maker interview. Referring to the observation that substance abuse sometimes prevents creative types from accomplishing things, Toomey noted that You cant give people energy and enthusiasm. Sometimes other labels or bands call the Simple Machines offices and ask to have their radio-station mailing list, for instance, and Toomey and Thomson must refuse. Notes Toomey: The only reason those stations play us is because of our track record with them. You have to find the addresses of the stations you like and send them nice lettersjust like we had to.

Selected discography

Singles; on Simple Machines unless otherwise noted

Headringer, 1991.

Genius of Crack, Homestead, 1991.

Left Behind (split single with Velocity Girl; on SubPop), 1992.

Punk Means Cuddle, C/Z, 1992.

Beautiful; Arlington VA, 1992.

Seasons Greetings (split single with Velocity Girl), 1992.

Diner, 1993.

Matchbook, 1993.

Be Like That, 1994.

Cowed by the Blah Blah (split CD with Rodan and Eggs), 1994.

She Cracked (split single with Superchunk; on Huggy Bear Records), 1995.

Poodle/Old City, 1997.

LPs; on Simple Machines

Deep End, 1993.

(Contributor) The Machines 1990-1993, 1993.

The Hearts Tremolo, 1994.

World Tour and Other Destinations, 1995.

A Brilliant Mistake, 1997.

Sources

Melody Maker, January 30, 1993, p. 16; February 20, 1993, pp. 36-37; June 3, 1995, p. 37.

ViVidzine, December 1994.

Carol Brennan

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Tsunami

Tsunami

Tsunami, or seismic sea waves, are a series of very long wavelength ocean waves generated by the sudden displacement of large volumes of water . The generation of tsunami waves is similar to the effect of dropping a solid object, such as a stone, into a pool of water. Waves ripple out from where the stone entered, and thus displaced, the water. In a tsunami, the "stone" comes from underneath the ocean or very close to shore, and the waves, usually only three or four, are spaced about 15 minutes apart.

Tsunami can be caused by underwater (submarine) earthquakes, submarine volcanic eruptions , falling (slumping) of large volumes of ocean sediment, coastal landslides, or even by meteor impacts. All of these events cause some sort of landmass to enter the ocean and the ocean adjusts itself to accommodate this new mass. This adjustment creates the tsunami, which can circle around the world. Tsunami is a Japanese word meaning "large waves in harbors." It can be used in the singular or plural sense. Tsunami are sometimes mistakenly called tidal waves, but scientists avoid using that term since they are not at all related to tides .

Tsunami are classified by oceanographers as shallow water surface waves. Surface waves exist only on the surface of liquids. Shallow water waves are defined as surface waves occurring in water depths that are less than one half their wavelength. Wavelength is the distance between two adjacent crests (tops) or troughs (bottoms) of the wave. Wave height is the vertical distance from the top of a crest to the bottom of the adjacent trough. Tsunami have wave heights that are very small as compared to their wavelengths. In fact, no matter how deep the water, a tsunami will always be a shallow water wave because its wavelength (up to 150 mi [240 km]) is so much greater than its wave height (usually no more than 65 ft [20 m]).

Shallow water waves are different from deep water waves because their speed is controlled only by water depth. In the open ocean, tsunami travel quickly (up to 470 mph [760 kph]), but because of their low height (typically less than 3 ft [1 m]) and long wavelength, ships rarely notice them as they pass underneath. However, when a tsunami moves into shore, its speed and wavelength decrease due to the increasing friction caused by the shallow sea floor.

Wave energy must be redistributed, however, so wave height increases, just as the height of small waves increases as they approach the beach and eventually break. The increasing tsunami wave height produces a "wall" of water that, if high enough, can be incredibly destructive. Some tsunami are reportedly up to 200 ft (65 m) tall. The impact of such a tsunami can range miles inland if the land is relatively flat.

Tsunami may occur along any shoreline and are affected by local conditions such as the coastline shape, ocean floor characteristics, and the nature of the waves and tides already in the area . These local conditions can create substantial differences in the size and impact of the tsunami waves, even in areas that are very close geographically.

Tsunami researchers classify tsunami according to their area of effect. They can be local, regional, or ocean-wide. Local tsunami are often caused by submarine volcanoes, submarine sediment slumping, or coastal landslides. These can often be the most dangerous because there is often little warning between the triggering event and the arrival of the tsunami.

Seventy-five percent of tsunami are considered regional events. Japan, Hawaii, and Alaska are commonly hit by regional tsunami. Hawaii, for example, has been hit repeatedly during this century, about every 510 years. One of the worst was the April 1, 1946, tsunami that destroyed the city of Hilo.

Pacific-wide tsunami are the least common as only 3.5% of tsunami are this large, but they can cause tremendous destruction due to the massive size of the waves. In 1940 and 1960, destructive Pacific-wide tsunami occurred. More recently, there was a Pacific-wide tsunami on October 4, 1994, which caused substantial damage in Japan with 11.5 ft (3.5 m) waves. However, waves of only 6 in (15 cm) over the normal height were recorded in British Columbia.

Tsunami are not only a modern phenomenon. The decline of the Minoan civilization is believed to have been triggered by a powerful tsunami that hit the area in 1480 b.c. and destroyed its coastal settlements. Japan has had 65 destructive tsunami between a.d.684 and 1960. Chile was hit in 1562 and Hawaii has a written history of tsunami since 1821. The Indian and Atlantic Oceans also have long tsunami histories. Researchers are concerned that the impact of future tsunami, as well as hurricanes, will be worse because of intensive development of coastal areas in the last 30 years.

The destructive 1946 tsunami at Hilo, Hawaii, caused researchers to think about the problem of tsunami prediction. It became clear that if scientists could predict when the waves are going to hit, steps could be taken to minimize the impact of the great waves.

In 1965, the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific, and Cultural Organization agreed to expand the United States' existing tsunami warning center at Ewa Beach, Hawaii. This marked the formation of the Pacific Tsunami Warning Center (PTWC), which is now operated under the U.S. Weather Service. The objectives of the PTWC are to "detect and locate major earthquakes in the Pacific basin; determine whether or not tsunami have been generated; and to provide timely and effective information and warnings to minimize tsunami effects."

The PTWC is the administrative center for all the associated centers, committees, and commissions of the International Tsunami Warning System (ITWS). Japan, the Russian Federation, and Canada also have tsunami warning systems and centers and they coordinate with the PTWC. In total, 27 countries now belong to the ITWS.

The ITWS is based on a world-wide network of seismic and tidal data and information dissemination stations, and specially trained people. Seismic stations measure movement of the earth's crust and are the foundation of the system. These stations indicate that some disturbance has occurred that may be powerful enough to generate tsunami. To confirm the tsunami following a seismic event, there are specially trained people called tide observers with monitoring equipment that enables them to detect differences in the wave patterns of the ocean. Pressure gauges deployed on the ocean can detect changes of less than 0.4 in (1 cm) in the height of the ocean, which indicates wave height. Also, there are accelerometers set inside moored buoys that measure the rise and fall of the ocean, which will indicate the wave speed. These data are used together to help researchers confirm that a tsunami has been generated. Tsunami can also be detected by satellite monitoring methods such as radar and photographic images.

The ITWS is activated when earthquakes greater than 6.75 on the Richter scale are detected. The PTWC then collects all the data, determines the magnitude of the quake and its epicenter. Then they wait for the reports from the nearest tide stations and their tide observers. If a tsunami wave is reported, warnings are sent to the information dissemination centers.

The information dissemination centers then coordinate the emergency response plan to minimize the impact of the tsunami. In areas where tsunami frequency is high, such as Japan, the Russian Federation, Alaska, and Hawaii, there are also Regional Warning Systems to coordinate the flow of information. These information dissemination centers then decide whether to issue a "Tsunami Watch," which indicates that a tsunami may occur in the area, or a more serious "Tsunami Warning," which indicates that a tsunami will occur. The entire coastline of a region is broken down into smaller sections at predetermined locations known as "breakpoints" to allow the emergency personnel to customize the warnings to account for local changes in the behavior of the tsunami. The public is kept informed through local radio broadcasts. If the waves have not hit within two hours of the estimated time of arrival, or, the waves arrived but were not damaging, the tsunami threat is assumed to be over and all Watches and Warnings are canceled.

One of the more recent changes in the ITWS is that the Regional Centers will be taking on greater responsibility for tsunami detection and warning procedures. This is being done because there have been occasions when the warning from Hawaii came after the tsunami hit the area. This can occur with local and regional tsunami that tend to be smaller in their area of effect. Some seismically active areas need to have the warning system and equipment closer than Hawaii if they are to protect their citizens. For example, the Aleutian Islands near Alaska have two to three moderate earthquakes per week. As of May 1995, centers such as the Alaska Tsunami Warning Center located in Palmer, Alaska, have assumed a larger role in the management of tsunami warnings.

In terms of basic research, one of the biggest areas of investigation is the calculation of return rates. Return rates, or recurrence intervals, are the predicted frequency with which tsunami will occur in a given area and are useful information, especially for highly sensitive buildings such as nuclear power stations, offshore oil drilling platforms, and hospitals. The 1929 tsunami in Newfoundland has been studied extensively by North American researchers as a model for return rates and there has been some dispute. Columbia University researchers predict a reoccurrence in Newfoundland in 1,00035,000 years. However, some geologists argue that it may reoccur as soon as 1001,000 years. These calculations are based on evidence from mild earthquakes and tsunami in the area. They also suggest that the 1929 tsunami left a sedimentary record that is evident in the soil profile, and that such records can be dated and used to calculate return rates. Research is currently ongoing to test this theory.

See also Seismology; Wave motions

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Tsunamis

Tsunamis

A tsunami is a powerful wave, usually created by a large-scale motion of the ocean floor. Although they are almost imperceptible at sea, tsunami waves increase in height as they reach a coastline and are capable of causing great destruction. The term "tsunami" is taken from the Japanese words for "harbor" and "wave."

In the 1990s, eighty-two tsunamis were reported worldwide, taking more than four thousand lives and causing hundreds of millions of dollars in damage. Most tsunamis occur in seismically active regions such as the Pacific Ocean, but tsunamis can occur anywhere in the world where there are large bodies of water.

Mechanics of Tsunami Generation and Propagation

A tsunami can be caused by any disturbance that moves a large amount of water. The vast majority of tsunamis originate during undersea earthquakes when water is moved by the uplift or subsidence of hundreds of square kilometers of the sea floor. Landslides (which often accompany large earthquakes), volcanic eruptions and collapses, and explosions and meteor impacts can also disturb enough water to generate a tsunami.

Propagation.

The wind-generated waves usually seen breaking on the beach arrive every 10 to 15 seconds and have wave crests tens of meters apart. In contrast, tsunamis can have crests that are more than 20 minutes and hundreds of kilometers apart (see figure).

Most tsunamis are classified as long wavesthat is, waves with long wavelengths relative to their water depth. They travel with speeds proportional to the square root of the water depth. In the deep ocean, their speed can be similar to that of a jet plane, as high as 700 kilometers per hour. Closer to shore, in shallow water, they slow down appreciably. At sea, the height of a tsunami wave is not usually distinguishable from the surrounding wind waves without sensitive measuring equipment because the wave often is only 1 to 2 meters high and hundreds of kilometers long.

Tsunamis generated by earthquake movement of the seabed can travel thousands of miles across the ocean without losing their energy. For example, in 1960 a tsunami generated in Chile, South America caused substantial damage nearly 14,500 kilometers (9,000 miles) away in Japan. Hawaii, in the middle of the Pacific Ocean, is particularly susceptible to tsunamis that travel across the ocean.

Unlike earthquake-caused waves, tsunamis generated by mechanisms like landslides and eruptions dissipate quickly and rarely affect coastlines far away from the source. Their local effects, however, can sometimes be just as damaging: in 1883, the tsunami caused by the eruption of the volcano Krakatau killed more than 36,000 people on the nearby islands of Java and Sumatra.

Landfall.

As tsunami waves approach the coastline, a large change takes place in their shape. Since the landward portion of the wave is in shallower water than the seaward portion, it travels relatively slower. This allows rear portions of the wave to "catch up" with the front of the wave, concentrating the wave energy into ever-higher growing crests as it approaches land. The shoaling waves can reach crest heights of tens of meters, either breaking and flowing onto the shore as violent bores or surging onshore as flood waves.

When a tsunami reaches the shore, the impact can destroy buildings and other coastal structures. The flowing water can move boats, vehicles and debris. Further destruction results when these objects collide like battering rams with anything in their path. Gas lines broken during the tsunami often cause fires that increase the tsunami damage. Tsunamis can flood low-lying areas, destroying crops with salt water and leaving behind sand and boulders.

Mitigation and Research

Efforts to protect people from tsunamis center on proper preparation of tsunami-prone areas. Many lives have been saved when residents of coastal communities were aware that earthquake shaking was a signal to evacuate to high ground.

Although certain tsunamis, such as those generated by landslides, arrive without warning, tsunami researchers are focusing on better predicting these locally destructive waves as well as the transoceanic ones. The tools that researchers use include seismic stations, deep-ocean pressure gauges, and physical and numerical models. Field surveys of recent tsunamis and geological investigations of ancient waves also help scientists and hazards planners design structures and plan communities so that casualties and damage can be reduced.

see also Human Health and the Ocean; Landslides; Waves.

Catherine M. Petroff

Bibliography

Folger, T. "Killer Waves, the Struggle to Predict Tsunamis." Discover Magazine May 1994, 6673.

Gonzalez, F. "Tsunami, Predicting Destruction by Monster Waves." Scientific American May 1999, 5665.

McCredie, S. "Tsunamis, the Waves that Kill." Smithsonian Magazine March 1994, 2839.

Internet Resources

Tsunami! University of Washington. <http://www.geophys.washington.edu/tsunami>.

USC Tsunami Research Group. University of Southern California. <http://www.usc.edu/dept/tsunamis>.

Tsunami Research Program. National Oceanic and Atmospheric Association. <http://www.pmel.noaa.gov/tsunami>.

TSUNAMIS ARE NOT TIDAL WAVES

At one time, tsunamis were called tidal waves for the way that the water flowed on and offshore like a quickly rising and falling tide. But because tsunamis are not caused by the gravitational pull of the Moon and Sun, the term tidal wave is no longer used.

SEA OF JAPAN: 1993

A 7.8-magnitude earthquake in the Sea of Japan caused waves 5 to 10 meters high that swept up buildings and vehicles on the island of Okushiri. Although 239 people died from the Okushiri tsunami, many residents saved themselves by fleeing to high ground immediately after the earthquake.

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tsunami

tsunami (tsŏŏnä´mē), series of catastrophic ocean waves generated by submarine movements, which may be caused by earthquakes, volcanic eruptions, landslides beneath the ocean, or an asteroid striking the earth. Tsunamis are also called seismic sea waves or, popularly, tidal waves.

In the open ocean, tsunamis may have wavelengths of up to several hundred miles and travel at speeds up to 500 mi per hr (800 km per hr), yet have wave heights of less than 3 ft (1 m), which pass unnoticed beneath a ship at sea. The period between the crests of a tsunami's waves varies from 5 min to about 1 hr. When tsunamis approach shallow water along a coast, they are slowed, causing their length to shorten and their height to rise sometimes as high as 100 ft (30 m). When they break, they often destroy piers, buildings, and beaches and take human life. The wave height as they crash upon a shore depends almost entirely upon the submarine topography offshore. Waves tend to rise to greater heights along gently sloping shores, along submarine ridges, or in coastal embayments. Tsunamilike waves can also occur on lakes and within inlets and small bays as a result of large landslide into the water or an underwater landslide.

There is little warning of approach; when a train of tsunami waves approaches a coastline, the first indication is often a sharp swell, not unlike an ordinary storm swell, followed by a sudden outrush of water that often exposes offshore areas as the first wave trough reaches the coast. After several minutes, the first huge wave crest strikes, inundating the newly exposed beach and rushing inland to flood the coast. Generally, the third to eighth wave crests are the largest.

Since tsunamis principally occur in the Pacific Ocean following shallow-focus earthquakes over magnitude 6.5 on the Richter scale, one of the best means of prediction is the detection of such earthquakes on the ocean floor with a seismograph network (see seismology). Tsunamis may be detected by wave gauges and pressure monitors, such as those emplaced as part of the U.S. Tsunami Warning System; established in 1949 and originally confined to the Pacific region, the system has been expanded to the Caribbean and the W North Atlantic. An early warning system for the Indian Ocean began operating in 2006. Measurement of sudden sea level changes from satellites are also used to warn of a potential tsunami.

One of the most destructive tsunamis to occur during historical times followed the explosive eruption of the volcano Krakatoa in the East Indies on Aug. 27, 1883, when over 36,000 people were killed as a result of the wave. Waves were up to 100 ft (30 m) high. Its passage was traced as far away as Panama. On Dec. 26, 2004, a 9.1 earthquake off NW Sumatra, Indonesia, caused a tsunami with waves as high as 65 ft (20 m) nearest the epicenter. Some 230,000 people are believed to have died. The waves devastated many areas in the E Indian Ocean basin, particularly the nearby coast of N Sumatra, the Andaman and Nicobar Islands, and the E and S coasts of Sri Lanka. Areas of SE India and SW Thailand were also hard hit. The 9.0 earthquake off NE Honshu, Japan, on Mar. 11, 2011, caused a tsunami that devastated nearby areas on the Honshu coast. The water overtopped 33 ft (10 m) seawalls and in some locations reached places as far as 5 mi (8 km) inland. Most of the nearly 18,500 killed or missing as a result of the earthquake were lost to the tsunami. It is believed that a 0.6-mi-wide (1-km-wide) asteroid that struck the ocean SW of New Zealand about AD 1500 created a tsunami that reached heights of more than 425 ft (130 m).

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tsunami

tsunami (seismic sea wave) Ocean wave caused by a submarine earthquake, subsidence or volcanic eruption. Sometimes erroneously called a tidal wave, tsunamis spread radially from their source in ever-widening circles. Tsunamis travel across oceans at speeds up to 400km/h (250mph) and reach heights of 10m (33ft). On December 26, 2004 a massive Tsunami, resulting from an earthquake near to Sumatra in the Indian Ocean, killed more than 250,000 people, mostly in Indonesia (particularly western Sumatra), Sri Lanka, India and Thailand.

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tsunami

tsunami A seismic sea wave of long period, produced by a submarine earthquake, underwater volcanic explosion, or massive gravity slide of seabed sediment. In the open ocean, such waves are barely noticeable even though they may be travelling at 700 km/h, but on reaching shallow water they build up to heights of more than 30 m and can cause severe damage in coastal areas.

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tsunami

tsunami A seismic sea wave of long period, produced by a submarine earthquake, underwater volcanic explosion, or massive gravity slide of sea-bed sediment. In the open ocean such waves are barely noticeable even though they may be travelling at 700 km/h, but on reaching shallow water they build up to heights of more than 30 m and cause severe damage in coastal areas.

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tsunami

tsunami a long high sea wave caused by an earthquake or other disturbance; the word is Japanese, and comes from tsu ‘harbour’ + nami ‘wave’.

On 26 December, 2004, an undersea earthquake in the Indian Ocean resulted in a tsunami which devastated coastal regions of Indonesia, Thailand, India, and Sri Lanka, causing great loss of life.

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tsunami

tsu·na·mi / (t)soōˈnämē/ • n. (pl. same or -mis ) a long high sea wave caused by an earthquake, submarine landslide, or other disturbance. ORIGIN: late 19th cent.: from Japanese, from tsu ‘harbor’ + nami ‘wave.’

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tsunami

tsunamichamois, clammy, gammy, Grammy, hammy, jammy, mammae, mammee, mammy, Miami, ramie, rammy, Sammy, shammy, whammy •acme, drachmae •Lakshmi •army, balmy, barmy, gourami, macramé, origami, palmy, pastrami, salami, smarmy, swami, tsunami, Yanomami •Clemmie, Emmy, jemmy, lemme, semi •elmy •Amy, cockamamie, flamy, gamy, Jamie, Mamie, samey •beamy, creamy, dreamy, gleamy, Mimi, preemie, seamy, steamy •gimme, shimmy, Timmy •pygmy • filmy •arch-enemy, enemy •synonymy • Jeremy • sashimi •blimey, gorblimey, grimy, limey, slimy, stymie, thymy •commie, mommy, pommie, pommy, tommy •dormy, stormy •foamy, homey, loamy, Naomi, Salome •polychromy

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Tsunami

Tsunami

Resources

The word tsunami is derived from Japanese words that translate as harbor wave, and refers to the series of waves that arise when a lot of ocean water is displaced. This displacement most commonly occurs when there is an undersea earthquake. Other sources of disturbance include underwater volcanic eruptions and even the impact of a meteorite.

The displaced water ripples out from the point of the disturbance as a series of waves. When the disturbance occurs far from shore, the waves have a very long wavelength (the distance from the crest of one wave to the crest of the next wave); wavelengths in excess of 62 mi (100 km) are not uncommon. As well, these waves are not high (around 20 in or 50 cm). A boat at sea will experience only a gentle rocking motion as the wave passes underneath. However, these waves can be moving at about 375-500 miles per hour or 600-800 kilometers per hour (similar to the speed of a jet airliner). As the sea depth decreases nearer to shore, the huge amount of energy contained in the waves drives the conversion of the waves to much larger and very destructive walls of water. Wave heights of up to 200 feet (61 meters) have been reported. The impact of such a tsunami can range miles inland if the land is relatively flat.

A recent example is the tsunami that occurred on December 26, 2004, following a massive undersea earthquake off of the coast of Sumatra. The earthquakewhich was violent enough to affect Earths rotationspawned waves that initially slammed into coastal regions of Indonesia and Malaysia. The waves continued to move thousands of kilometers across the Indian Ocean, into coastlines of Bangladesh, India, Sri Lanka, and the Maldives.

The destruction and loss of life was immense. Estimates are that the loss of life approached 300,000, with at least 170,000 people killed in Indonesia alone. In some regions, the waves completely obliterated the coastline (including villages) and caused great damage even several miles inland.

The destructive power of a tsunami is influenced by local conditions such as the coastline shape, ocean floor characteristics, and the nature of the waves and tides already in the area. In some cases, tsunami waves can travel for thousands of kilometers with little loss of energy. Thus, even coastal regions very far from the site of the undersea disturbance can suffer great damage. The varying local conditions can create substantial differences in the size and impact of the tsunami waves even in areas that are very close geographically. This was evident in the 2004 tsunami, where some coastal regions were wiped off of the map while others nearby were only marginally affected.

Because the waves can be a great distance apart, the waves may impact the shore minutes to hours apart. Indeed, in the 2004 tsunami, survivors flocked to the affected beaches after the first wave, only to be caught in the next wave, which arrived about 30 minutes later.

Tsunamis can occur along any shoreline and are not limited to southern latitudes. For example, a tsunami triggered by another earthquake struck the south coast of the Canadian province of Newfoundland in 1929. Twenty-seven people died. In another example, an earthquake in the Aleutian Islands on April 1, 1946 created a tsunami that killed 164 people in Alaska and Hawaii. Later, an earthquake off the coast of southern Alaska in March 1964 triggered tsunamis that struck the west coast of Canada and the United States. More than 100 people perished in Alaska, with 4 killed in Oregon and 12 in California.

Tsunamis have led scientists to address the challenge of predicting the occurrence of such waves. After the 1964 tsunami, researchers looked into monitoring the location and strength of an undersea earthquake and tracing the path of the resulting waves. People in the waves path could be notified, hopefully minimizing the impact of the great waves.

In 1965, the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific, and Cultural Organization agreed to expand the United States existing tsunami warning center at Ewa Beach, Hawaii. This marked the formation of the Pacific Tsunami Warning Center, which is now operated under the U.S. Weather Service. In the 2004 tsunami, the center was able to issue a warning to impacted areas (all outside its normal operating area), but the warnings came too late to help save those in coastal regions affected within the first few hours of the earthquake.

Resources

BOOKS

Krauss, Erich. Wave of Destruction: The Stories of Four
Families and Historys Deadliest Tsunami.
New York: Rodale Books, 2005.

Stewart, Gail. Overview Series - Catastrophe in Southern
Asia: The Tsunami of 2004.
Lucent Books, 2005.

Tibballs, Geoff. Tsunami: The Most Terrifying Disaster.
London: Carlton Publishing Group, 2005.

Jennifer LeBlanc

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Tsunami

Tsunami

Tsunami devastates Papua New Guinea
The Indian Ocean tsunami of 2004
Dangerous science: How tsunamis happen
Consequences of tsunamis
The technology connection
A matter of survival
For More Information

One early morning over one hundred years ago, a group of fishermen from a small Japanese village sailed out to set their nets. After fishing all day long, they returned late in the evening to find their village and the whole harbor devastated by what appeared to be a huge wave. Since they had felt nothing while out at sea, they concluded it was some sort of freak wave that only happened in harbors. So they called it a tsu (harbor) nami (wave).

A tsunami (pronounced tsoo-NAH-mee) is not a "harbor wave." It is a long-wavelength, low-amplitude wave or series of waves caused by a large displacement of water. Tsunamis usually move very rapidly across the ocean. In deep water, they are almost undetectable. Only when they move into shallow water do they reach terrifying heights and cause massive destruction. These sea waves have killed more people in Japan than in any other place else in the world. While tsunamis are sometimes called "tidal waves," they have nothing to do with the tides (the rise and fall of water caused by the gravitational attraction of the Sun and Moon).

Tsunamis are triggered by sudden disturbances, most often earthquakes (sudden movements of Earth's outermost layer, or crust) that occur on the ocean bottom or along the coasts. Tsunamis are also set in motion when large amounts of material are cast onto the ocean floor by landslides, volcanic eruptions, or meteorites. The energy released by that activity ripples outward from the point of origin in a series of ring-shaped waves.

Tsunamis are nearly undetectable in deep ocean water, where they are typically around 16 inches (41 centimeters) or less in height. Their wavelengths, the distance between wave peaks (called crests), may be hundreds of miles (hundreds of kilometers). The Japanese fishermen who originally invented the term had returned to port to find the area surrounding their harbor devastated, although they had not been aware of any wave in the open water; tsunamis do not reach their towering heights until they approach land. As the depth of water decreases, the energy of the wave forces water upward into swells that are shorter in length but greater in height. It is typical for a tsunami to be 60 to 100 feet (18 to 30 meters) tall by the time it reaches land. The highest tsunami on record, that devastated the Ryukyu Islands south of Japan in 1771 and caused 13,486 deaths, was 280 feet (85 meters) tall.

Large tsunamis are incredibly forceful. When they crash onto land they cause tremendous property damage and loss of life. Tsunamis occur most often in the Pacific Ocean, since the ocean floor in that area is prone to earthquakes and volcanoes. The locations most vulnerable to tsunamis include Japan, Hawaii, Alaska, Russia, the Philippines, Indonesia, Peru, and Ecuador.

Tsunami devastates Papua New Guinea

On July 17, 1998 the most lethal tsunami of the twentieth century struck Papua New Guinea, a poor Pacific Island nation of 4.3 million people about 90 miles (145 kilometers) north of Australia. Papua New Guinea occupies the eastern half of the island of New Guinea; the western half is part of Indonesia. The death toll from the disaster was estimated at over two thousand people. Many of those who perished died instantly from the impact of the wave or from drowning. Others were swept into the jungle and died of their injuries before medical help could reach them. At least six hundred people were critically injured and more than six thousand, most of them small farmers and fishermen, were left homeless. The 1998 tsunami was one of the worst natural disasters in Papua New Guinea's history.

WORDS TO KNOW

crest:
the highest point of a wave.
crust:
the outermost layer of Earth, varying in thickness from 3.5 miles (5 kilometers) to 50 miles (80 kilometers).
epicenter:
the point on Earth's surface directly above the focus of an earthquake, where seismic waves first appear.
focus:
the underground starting place of an earthquake (also called the hypocenter).
magnitude:
the power of an earthquake.
oceanography:
the study and exploration of the ocean.
period:
the time between two successive waves.
plate:
a large section of Earth's crust.
Richter scale:
the scale developed by American seismologist Charles Richter that describes the amount of energy released by an earthquake on a scale from 1 to 10. Each whole number increase in value on the scale indicates a tenfold increase in the energy released. Earthquakes measuring 7 to 7.9 are major and those measuring 8 or above cause widespread destruction.
seismic waves:
vibrations that move outward from the focus of an earthquake, causing the ground to shake.
seismograph:
an instrument used to detect and measure seismic waves.
tidal station:
a floating instrument center in the ocean that records water levels.
trough:
the lowest point of a wave.
tsunami:
a series of giant ocean wave waves caused by a large displacement of water.
tsunami warning:
an alert stating that a tsunami has been detected and is approaching the designated area. People are instructed to move to higher ground immediately.
tsunami watch:
an alert stating that an earthquake has occurred with sufficient magnitude to trigger a tsunami. People are instructed to listen for further news.

Earthquake and landslide cause wave

The tsunami was originally believed to have been set in motion by an earthquake of 7.0 magnitude (power) on the Richter scale, the scale that describes the amount of energy released by an earthquake from 1 to 10. The earthquake was located 12 to 30 miles (19 to 48 kilometers) out to sea. This originally puzzled researchers, because earthquakes that size rarely trigger tsunamis, and especially not large tsunamis. Later studies revealed that the earthquake had caused a landslide on the ocean floor. An investigation of the seafloor about 15 miles (24 kilometers) off the coast found that a huge area of soft earth and rock had collapsed and slid into a trench 2.5 miles (4 kilometers) deep. Scientists determined that it was this huge landslide that had generated the tsunami.

Just minutes after the landslide, a series of three giant waves swept onto shore in the rugged and remote northwestern part of the country. The smallest of the waves was estimated at 10 feet (3 meters) tall, and the largest was 32 to 46 feet (9.8 to 13.7 meters). One measurement, based on the height of a fishing net found in a tree, put the height of the largest wave at 57.5 feet (17.5 meters)—as tall as a seven-story building. The waves crashed onshore at speeds of 22 to 44 miles (35 to 71 kilometers) per hour.

Strip of land hit hard by tsunami

The area hardest hit by the tsunami was a 22-mile-long (35-kilometer-long) narrow stretch of land that stands between the Pacific Ocean and the Sissano lagoon. (The lagoon itself had been created by a giant tsunami in 1907.) The surrounding jungles and mangrove swamps formerly had a population of about ten thousand people. The 1998 tsunami, however, reduced the area to a barren wasteland. Villages were swallowed up, and their inhabitants were swept into the lagoon or out to sea. The waves destroyed wood and palm-frond houses and concrete schools and churches alike. The wall of water was so strong that it bent iron and steel beams around coconut trees.

The majority of those killed by the tsunami were children and elderly people—those least able to outrun the rushing water or climb trees fast enough to save themselves. Among the tsunami's first victims were about two hundred schoolchildren, on holiday from school and picnicking on the beach in the village of Arop. Along the coastline, so many children died that locals began calling the tragedy "the loss of a whole generation of children." So few children survived the catastrophe that no plans were made to rebuild the schools.

"First the houses trembled," read an account of the disaster in Asiaweek. "Then a sound swelled like an approaching jet engine. Excited children ran out onto the shore, expecting a glimpse of a low-flying aircraft in the darkening sky. Instead they met an impenetrable wall of water. There was simply nowhere to run."

People tried desperately to survive the wave by clinging to boats or climbing to treetops. Many survivors experienced the terrifying ordeal of having their children ripped from their arms by the cascading water. One woman managed to save herself and her one-month-old twins by tying herself to a palm tree.

Dr. James Goff of New Zealand's Institute of Geological and Nuclear Sciences described the wave in the Evening Post (of Wellington, New Zealand) as follows: "Imagine a four-story wave traveling at 70 kilometers [43 miles] per hour."

"There was so much devastation it was hard to comprehend what happened," Goff continued. "You couldn't see houses or where they had been, the road and even the graveyard had gone."

Relief efforts get underway

Immediately after the tsunami, rescue workers began searching for survivors in the jungles and the swamps. Within the first few days they found more than 2,527 people alive. One notable discovery was that of a young girl who had been injured and lost, wandering alone for four days.

Dr. John Sairere, a relief coordinator from Papua New Guinea who lost seventy-one members of his family to the tsunami, helped survivors recover from the emotional trauma. "The hardest thing for me was the horrifying loss of so many relatives," stated Sairere in the Wellington, New Zealand, paper the Dominion. "It came and went so fast—in thirty minutes we lost so many. When I got there, there was nothing left, just stumps of coconut trees."

Emergency personnel from around the world, including doctors, nurses, and engineers, arrived on the scene to help treat the injured. Several countries sent food, drinking water, medicine, tents, beds, clothing, tools, medical supplies, and building materials. The United States donated more than $1 million to the rescue effort. Part of that sum was for an earthquake-detection system that would provide advance warning for future tsunamis. New Zealand also donated $1 million in aid. Australia coordinated the international relief operation.

Twelve days after the disaster, search crews gave up hope of finding survivors. The government ordered remaining coastal residents to evacuate a 45-square-mile (120-square-kilometer) area around the lagoon.

The plight of the survivors

In the wake of the tsunami, most of the survivors fled inland. They had lost children, friends, spouses, homes, and livelihoods, and brought with them very few, if any, possessions. They vowed never to return to their former homes, both out of fear that another wave would come and the superstitious belief that the dead would haunt the area.

One of the refugees was Fabian Nakisony, who lost his one-year-old son in the tsunami. "We have nothing," stated Nakisony in the July 22, 1998, New York Times. "We can get timber from the bush, but we have no hammer, no nails, no saw."

Whereas the villagers' previous staple food had been fish, caught in the lagoon, after the tsunami they subsisted on donated rice, flour, and water, plus the few wild fruits and vegetables they could forage. Within days of the disaster, small villages began to materialize on hills in the jungle. Makeshift dwellings were constructed from woven palm leaves and sticks.

Local hospitals, plus an Australian field hospital, filled up with some seven hundred injured people. As the facilities overflowed, patients had to lie on the floor. Many of those hospitalized had broken bones, cuts, bruises, and internal injuries from being flung against trees or debris by the tsunami. A common problem was the development of gangrene (the death or dying of body tissue) in wounds that had come in contact with bacteria-filled coral sand. Doctors were forced to perform hundreds of limb amputations to halt the spread of gangrene. Another malady affecting survivors, particularly children, was aspiration pneumonia, which is contracted by inhaling large amounts of seawater into the lungs.

The Indian Ocean tsunami of 2004

The twenty-first century had hardly begun when an even more devastating tsunami struck in the Indian Ocean on December 26, 2004. It was triggered by an earthquake of magnitude 9.3 on the Richter scale. (Magnitude is the power of an earthquake; a magnitude of 7 produces major damage on land and a magnitude of 8 produces widespread destruction.) At 9.3, this may have been the most powerful earthquake ever recorded. It caused a series of lethal tsunamis that killed approximately 230,000 people (including 168,000 in Indonesia alone), making it the deadliest tsunami in recorded history. The tsunami killed people in coastal areas from Indonesia, Thailand, and the northwestern coast of Malaysia, to thousands of miles away in Bangladesh, India, Sri Lanka, the Maldives, and even as far as Somalia, Kenya, and Tanzania on the eastern coast of Africa.

Because of the frequent tsunamis in the region, Pacific Ocean countries have an extensive cooperative warning system in place. The tsunami warnings alert people that a tsunami has been detected and is approaching the designated area, and issue instructions to move to higher ground immediately. However, in 2004 there was no similar system in place in the Indian Ocean region. The lack of an organized warning system certainly contributed to the great loss of life. There was no organized alert service covering the Indian Ocean in part because there had been no major tsunami events since the eruption of the island volcano Krakatau in 1883. In response to the devastation resulting from the 2004 Indian Ocean tsunami, UNESCO (United Nations Educational, Scientific and Cultural Organization, established as part of the United Nations in 1945) and other world bodies have called for a worldwide tsunami monitoring system.

Dangerous science: How tsunamis happen

A tsunami is a series of extremely long waves, extending from the ocean floor to the sea surface, that are set in motion when a disturbance—usually an earthquake under the sea or in a coastal region, and sometimes a landslide or volcanic eruption—displaces ocean water. The earthquake or other activity causes the seafloor to suddenly rise or fall. If it rises, it lifts the water above it, all the way to the surface, creating a huge pile of water. If the seafloor falls the water above also falls. At the sea surface, water flows into the low spot (directly above the seafloor depression) from all directions. That action results in the formation of a pile of water. In either case, the piled-up water is then pulled downward by gravity. It travels away from the bulge in rings of waves, similar to the pattern set in motion by tossing a pebble in a pond.

In the deep ocean, tsunamis travel at average speeds of 500 to 600 miles (800 to 965 kilometers) per hour—similar to a jet plane. The deeper the water, the faster the waves travel. Tsunamis in the open sea also have enormous wavelengths, which are measures of length from trough (lowest point) to trough, or crest (highest point) to crest. Far from land they may have wavelengths as great as 600 miles (900 kilometers). The period (time between successive waves) averages about one hour. Out at sea the small height of the waves, an average of 16 inches (41 centimeters), makes them virtually undetectable.

The waves lose very little energy as they travel; they sometimes cross the entire ocean (thousands of miles or kilometers) in less than a day. As a wave enters shallow water near shore, its front end is slowed by friction with the ocean bottom to a speed of about 30 to 200 miles (48 to 322 kilometers) per hour. At the same time, the back of the wave keeps moving at the same speed. As the back catches up to the front, the wavelength shrinks (to less than 10,000 feet [3,050 meters] in most

cases) and the period is reduced to 10 to 30 minutes. The energy carried by the waves, which in the open ocean was spread over hundreds of miles, in the shallow water is compressed into a mountain of water that may grow to more than 100 feet (30.5 meters) tall. That water then comes crashing down on the shoreline.

Tsunami in Hilo, Hawaii

On April 1, 1946, Hawaii experienced its worst natural disaster: a tsunami with 50-foot (15-meter) waves that killed 159 people and injured 163 throughout the island chain. It caused more than $25 million in property damage. The city of Hilo suffered the most from the tsunami; ninety-six of the deaths occurred there, and the waterfront business district was destroyed. The force of the water was so great that it bent parking meters down to the pavement. The tsunami washed away beaches, ripped up railroad tracks, and covered the coastal highways under mountains of sand and debris. Houses could be seen bobbing in the water after the wave washed back to sea.

That tsunami had been set in motion by an earthquake measuring 7.2 on the Richter scale, centered just south of Alaska's Unimak Island, some 2,500 miles (4,000 kilometers) away. The tsunami spurred the creation of the Pacific Tsunami Warning Center (PTWC). Established in 1948, the PTWC monitors ocean conditions and issues tsunami alerts for the Pacific region.

The PTWC's abilities were put to the test in 1960, when Hilo was again targeted by a tsunami. That tsunami was set in motion by an earthquake in the Chilean Andes. Waves measuring 25 feet (7.6 meters) high first damaged the coast of Chile and then moved westward across the Pacific. Besides Hawaii, the tsunami affected New Guinea, New Zealand, Okinawa, the Philippines, and Japan.

When the tsunami hit Hawaii, Hilo experienced three waves between 9:00 pm and 1:00 am. The first two—just 4 feet (2.3 meters) and 9 feet (2.7 meters) high, respectively—were held back by a seawall in the harbor. The third wave, standing 20 feet (6.1 meters) tall, surged into downtown Hilo. Despite timely tsunami warnings, many people chose not to evacuate and sixty-one of those who stayed behind lost their lives. The tsunami destroyed some 230 buildings, including the town's power plant, and flooded the streets with tons of sewage, mud, fish, and garbage. The bill for damages totaled more than $20 million. Eight hours later the tsunami hit Japan, where it killed many more people.

Where tsunamis occur

Ninety percent of the world's tsunamis occur in the Pacific Ocean. The Pacific lies above a geologically active section of Earth's crust called the Pacific plate. (Geologically active means that many earthquakes and volcanic eruptions occur along its boundaries.) On the eastern edge of the Pacific plate is the west coast of North America. The plate extends north to Alaska and the Aleutian Islands. On its western edge the plate is bordered by Japan and it extends southward to Indonesia and New Zealand.

At least one tsunami strikes somewhere in the Pacific Ocean each year, and a tsunami with destructive force occurs about once every ten years. Many Pacific nations have long, exposed shorelines, making them especially vulnerable to the effects of tsunamis. The places that are battered by the greatest number of tsunamis include Japan, Hawaii, Alaska, Russia, the Philippines, Indonesia, and western South and Central America. (The west coast of the United States, which experiences tsunamis very rarely, is nonetheless within the zone where tsunamis are likely to occur.) Between the years 1690 and 1990, the three countries with the greatest number of tsunamis were: Japan, with more than 200; Indonesia, with more than 160; and Chile, with more than 150.

Tsunamis occur infrequently in the Atlantic Ocean and the Mediterranean Sea. In 1755, an earthquake centered in Lisbon, Portugal, caused a tsunami that swept onshore and killed thousands in Portugal, Spain, Madeira, France, the British Isles, the Azore Islands, and the West Indies. In 1908 a tsunami struck Sicily, killing some eight thousand people.

Tsunamis in the Atlantic Ocean are caused by undersea landslides more often than earthquakes. A 20-foot-tall (6-meter-tall) tsunami that struck the Virgin Islands and southeastern Puerto Rico in 1867, for instance, was caused by an undersea landslide.

Landslide-induced tsunamis

Some of the largest tsunamis are produced by slides of vast quantities of material into bays and lakes. Often, the event that triggers the sudden falling of earth or rock is an earthquake. In Loen Lake, Norway, for example, a 230-foot (70-meter) tsunami swept ashore on September 13, 1936. That wave was generated by the cascading of about 1.25 million cubic yards (950,000 cubic meters) of rock into the water.

Lituya Bay, on the northeast shore of the Alaskan panhandle, experienced four tsunamis caused by landslides between the late-nineteenth and late-twentieth centuries. The deep-water bay, which has just a small opening to the sea, is surrounded by the steep, tree-covered, and rocky Fairweather Range of the Saint Elias Mountains. Three glaciers drape down the slopes and feed into the bay. The largest tsunami ever recorded in Lituya Bay occurred on July 9, 1958, when an earthquake shook a 400,000-square-mile (1 million-square-kilometer) area and caused 90 million tons (82 million metric tons) of rock to fall into the bay from 0.5 mile (0.8 kilometers) overhead. The cascading rocks triggered a 200-foot (60-meter) high tsunami that crashed onto the bay's opposite shore and surged as high as 1,700 feet (520 meters). The wall of water destroyed all vegetation on the mountain's rocky face, even uprooting some enormous trees and snapping others off at the base.

Volcano-induced tsunamis

Volcanic eruptions are responsible for triggering a small percentage of tsunamis. When a volcano erupts, it emits ash and magma (molten rock) into the air. Part of the volcano wall, or cone, may break off during an eruption. If the volcano is partially or totally submerged, the material it ejects goes into the ocean and displaces water. When that happens, a tsunami forms.

A devastating tsunami was caused by a volcanic explosion on Krakatau, an island in Indonesia's Sunda Strait of the South Java Sea, on August 27, 1883. The volcano spit out 5 cubic miles (20 cubic kilometers) of rock and dirt, after which its peak collapsed, causing two-thirds of the island to sink into the ocean. Millions of gallons of ocean water were displaced and a tsunami was formed. Waves greater than 115 feet (35 meters) high (the height of a twelve-story building) struck the coasts of western Java and southern Sumatra (parts of Indonesia), where they killed more than thirty-six thousand people and destroyed 165 villages. A full-sized ship was carried 2 miles (3.2 kilometers) inland, and the sea was covered for miles with lightweight volcanic pumice stones that floated on the water and built up to a height of 7 feet (2.1 meters) above the surface in some areas. The explosion was heard nearly 3,000 miles (4,800 kilometers) away. The huge amounts of dust and ash emitted by the volcano rose 20 miles (32 kilometers) into the air and drifted four times around the world, causing brilliant red sunsets as far away as London, England, for the next six months or more.

Consequences of tsunamis

The consequences of a tsunami vary widely, depending on the wave's speed and height. The impact of a tsunami is also influenced by the physical characteristics of the ocean floor near the shore and the shore itself, as well as the angle at which the wave strikes the coast. A tsunami's destructive potential is magnified when it squeezes into a funnel-shaped cove. In that case, the vast quantity of water is forced upward into an immense pile of water. Likewise, where the seafloor rises sharply, the tsunami also grows markedly in height. If, on the other hand, a seafloor rises gradually or the coast is protected by barrier islands, some of the tsunami's energy will be absorbed before it strikes the mainland. If a tsunami meets the coast at an angle it will be less forceful than meeting the coast head-on.

Another factor influencing tsunami strength is the tides, since the height of the tsunami wave combines with the tide as it reaches shore. A tsunami at high tide, therefore, will be larger than a tsunami at low tide.

Sanriku, Japan, socked by tsunamis

Japan has been hit by eight highly destructive tsunamis in the last four hundred years. The worst one occurred on June 14, 1896, when a series of waves, the tallest among them greater than 100 feet (30.5 meters), hit Sanriku on the eastern edge of the main island of Honshu some 300 miles (483 kilometers) north of Tokyo. The tsunami killed between twenty-two thousand and twenty-six thousand people and injured approximately nine thousand others. It destroyed 170 miles (274 kilometers) of coastline, including thirteen thousand homes. Twenty thousand of the dead were of the Shinto faith and had gathered for a festival on the beach at Sanriku. About three-quarters of the population of the neighboring town of Kamaish also lost their lives to the wave.

The tsunami was set in motion by an earthquake beneath the ocean floor, 93 miles (150 kilometers) to the east of Sanriku, at 7:00 pm that evening. Just 20 miles (32 kilometers) out to sea, the wave measured only 15 inches (83 centimeters) and passed undetected beneath the boats of fishermen. The waves reached shore fifty minutes after the earthquake. The fishermen returned to the port the next morning to discover the devastation.

Sanriku was hit again in 1933. The tsunami was caused by an earthquake that measured an incredible 8.9 on the Richter scale. Waves 75 feet (23 meters) tall swept onto shore, sinking eight thousand ships and washing away nine thousand houses. The wall of water killed about three thousand people.

If the coast consists of rocky cliffs, a tsunami will have little effect. If the coastline is relatively flat, in contrast, and contains villages or farms, the tsunami may surge far inland and create incredible damage. Some tsunamis crash down on the shore, shattering any structures they encounter. Other tsunamis force their way ahead like a bulldozer, lifting buildings from their foundations and carrying them inland. When the wave rushes back out to sea, it carries with it virtually everything in its path.

The destructive capabilities of a large, powerful tsunami, in terms of loss of life and property, are almost unimaginable. The wall of water may be as tall as a skyscraper and weigh millions of tons. It comes rushing onward at speeds as great as 150 miles (241 kilometers) per hour, obliterating communities in its path. A 20-foot-high (6.1-meter-high) tsunami traveling at 45 miles (72 kilometers) per hour packs a punch of about 8,000 pounds (3,640 kilograms) on an area the size of an average home's front door.

The technology connection

Technology is employed both to lower the death toll and to limit the destruction caused by tsunamis. Tsunami prediction systems, consisting of devices measuring earthquakes and wave patterns, alert coastal-dwellers to potential tsunamis so they can evacuate. Seawalls and tsunami-resistant buildings provide coastal settlements with a measure of protection against tsunamis.

Forecasting tsunamis

Tsunami prediction has yet to be perfected. Even when a tsunami is detected at sea, it is difficult to determine how it will behave when it reaches land. As the twentieth century came to a close, oceanographers were pursuing the completion of an accurate tsunami warning system. (Note: The following information pertains to tsunamis that originate at sea and travel great distances before reaching land. When tsunamis are generated by local phenomena, such as offshore earthquakes, the waves reach shore in mere minutes, often before any warning can be sounded.)

Responsibility for monitoring ocean conditions and issuing tsunami alerts for the Pacific region falls to the Pacific Tsunami Warning Center (PTWC), located in Ewa Beach, Hawaii. The PTWC was established in 1948, two years after a tsunami killed 159 people in Hilo, Hawaii. The warning center relies on a network of seismographs (instruments used to detect and measure the vibrations caused by earthquakes) located around the world, as well as tidal stations (floating instrument centers that record water levels) throughout the ocean and near the shore.

The best indication that a tsunami may be brewing is the detection of an earthquake under or near the Pacific Ocean. When an earthquake occurs with a magnitude of 6.75 or greater, strong enough to create a tsunami, a tsunami watch is communicated throughout the area. (Magnitude is the power of an earthquake; a magnitude of 7 produces major damage on land and a magnitude of 8 produces widespread destruction.) The tsunami watch instructs people to listen for further news, and forecasters then give the estimated time of arrival of the potential tsunami. They are able to make that prediction based on water depth at the earthquake's epicenter, the point on Earth's surface directly above the focus, or starting point, of an earthquake. Tsunami speed is directly related to water depth and the distance to shore.

Scientists next check readings from tidal stations near the epicenter of the earthquake. (Tidal stations are strategically located throughout the ocean and along the shores.) If a wave pattern resembling the characteristic up-and-down motion a tsunami is detected, a tsunami warning is posted. Forecasters then follow the progress of the tsunami by checking tidal stations along the waves' routes.

The problem with the current tsunami warning system is that oceanographers (scientists who study the ocean) have no way of determining what size a tsunami will be when it reaches shore. Vibrations caused by earthquakes, called seismic waves, that are detected at sea could be anything from inconsequential to devastating on shore. Complicating matters, the destructive potential of a tsunami depends not only the size of the wave but the physical features of the shoreline and the direction the wave is traveling.

Demonstrating the unreliable nature of tsunami prediction, about 75 percent of tsunami warnings (and subsequent evacuation of coastal-dwellers) in the latter half of the 1900s proved unnecessary. Experts fear that the more times residents are made to evacuate needlessly, the less likely they will be to take future warnings seriously and more likely they may be to choose to stay home when a real tsunami strikes. In addition, false alarms are expensive; an unnecessary evacuation of Honolulu in 1948, for example, cost more than $30 million.

New forecasting tools promise greater accuracy

The Pacific Marine Environmental Laboratory (PMEL) of the U.S. National Oceanic and Atmospheric Administration is employing advanced technology to improve the accuracy of tsunami predictions. The Deep-Ocean Assessment and Reporting of Tsunamis (DART) system includes six research stations and sophisticated computer models for forecasting tsunamis. DART has deployed around nineteen buoys in addition to the surface stations and several coastal weather stations operated by the National Weather Service. In 2003, the operation of DART was transferred to the National Data Buoy Center, a part of the U.S. National Tsunami Hazard Mitigation Program (NTHMP). The DART system will enable NTHMP to issue tsunami warnings, with great accuracy, within one hour of an earthquake in the Pacific region.

The research stations are strategically placed throughout the Pacific Ocean. Each station uses a bottom pressure recorder, which is an instrument on the ocean floor that measures tsunami wave heights with a precision of 0.04 inch (1 millimeter). The recorder transmits the wave-height information to the tsunami forecasting center. Each time an earthquake is detected somewhere in the Pacific, data from the recorder is plugged into the computer model that predicts how the wave will behave across the ocean and on the coasts.

Coastal construction

Tsunamis typically wash away buildings they encounter. The damage they inflict is due both to the force of the water and the debris it sweeps along. In some beachfront areas, builders are tackling this problem by creating structures that can withstand the force of a tsunami. They use frames of steel and concrete, with windows and walls that easily give way to the rushing water. With that type of construction, the tsunami crashes through the building yet leaves the frame intact. Occupants of tsunami-resistant high-rise hotels can "evacuate" to the upper floors if a tsunami hits with little warning. The high cost of this type of construction, however, is too expensive for many developing Pacific nations.

Japanese tale recounts Shimoda tsunami

On December 24, 1854, an earthquake off the shore of Japan caused a tsunami. The 30-foot (9-meter) wave entirely washed away numerous seaside villages along the Pacific coast of the island of Honshu. In the village of Hiro, near the city of Wakayama, the residents' lives were saved by the quick thinking of the town squire (a local dignitary of a rural district or small town), by the name of Gohei. The story of how Gohei saved Hiro is printed in many Japanese primary school texts. The following account was reproduced in the essay "The Role of Public Education and Awareness in Tsunami Hazard Management" by M. I. El-Sabh, included in Tsunami: Prediction, Disaster Prevention and Warning, Y. Tsuchiya and N. Shuto, eds., 1995. (Netherlands: Kluwer Academic Publishers. Note: All of this was reprinted in Tsunami by Walter C. Dudley and Min Lee, pp. 296-297.)

"It is not normal," Gohei muttered to himself as he came out of his house. The earthquake was not particularly violent. But the long and slow tremor and the rumbling of the earth were not of the kind old Gohei had ever experienced. It was ominous.

Worriedly he looked down from his garden at the village below. Villagers were so absorbed in the preparation for a harvest festival that they seemed not to notice the earthquake.

Turning his eyes now to the sea, Gohei was transfixed at the sight. Waves were moving back to the sea against the wind. At the next moment the expanse of the sand and black base of rocks came into view.

"My God! It must be a tsunami," Gohei thought. If he didn't do something, the lives of four hundred villagers would be swallowed along with the village. He could not lose even a minute.

"That's it!" he cried and ran into the house. Gohei immediately ran out of the house with a big pine torch. There were piles of rice sheaves lying there ready for collection. "It is a shame I have to burn them, but with this I can save the lives of the villagers." Gohei suddenly lighted one of the rice sheaves. A flame rose instantly fanned by the wind. He ran frantically among the sheaves to light them.

Having lit all the sheaves in his rice field, Gohei threw the torch away. As if dazed he stood there and looked at the sea. The sun was already down and it was getting dark. The fire of the rice sheaves rose high in the sky. Someone saw the fire and began to ring the bell of the mountain temple.

"Fire! It is the squire's house!" Young men of the village shouted and ran hurriedly to the hill. Old people, women and children followed the young men. To Gohei, who was looking down the hill, their pace seemed as slow as ants. He felt impatient. Finally about twenty young men ran up to him. They were going to extinguish the fire. "Leave them! There will be a disaster. Have the villagers come here." Gohei shouted in a loud voice. The villagers gathered one by one. He counted the old and young men and women as they came. The people looked at the burning sheaves and Gohei in turn.

At that time he shouted with all his might. "Look over there! It is coming." They looked through the dim light of dusk to where Gohei pointed. At the edge of the sea in the distance they saw a thin dark line. As they watched, it became wider and thicker, rapidly surging forward.

"It is a tsunami!" someone cried. No sooner than they saw the water in front of them as high as a cliff, crashing against the land, they felt the weight as if a mountain was crushing them. They heard a roaring noise as if a hundred thunders roared all at once. The people involuntarily jumped back. They could not see for a while anything but clouds of spray which had advanced to the hill like clouds.

They saw the white fearful sea passing violently over their village. The water moved to and fro over the village two or three times. On the hill there was no voice for a while. The villagers were gazing down in blank dismay at the place where their village had been. It was now gone without a trace, excavated by the waves.

The fire of the rice sheaves began to rise again fanned by the wind. It illuminated the darkened surroundings. The villagers recovered their senses for the first time and realized that they had been saved by this fire. In silence they knelt down before Gohei.

Seawalls made of reinforced concrete also provide protection to communities at risk for tsunamis. These structures block tsunamis, as long as the water remains below the height of the seawall. Some settlements in tsunami-prone areas simply deal with the problem by not allowing construction along the coast where tsunamis are likely to strike.

A matter of survival

Imagine yourself enjoying a day at the seashore when the water suddenly recedes, leaving fish flopping and boats stranded, and uncovering rocks you never knew were there. At the same time, the sea makes a great hissing noise. These are sure signals that a tsunami is coming. The rushing away of water merely means that a trough, rather than a peak, of a wave has hit first. You can expect the first wave to wash ashore in as little as five minutes, although it may take as long as two hours. Don't wait around to see it! Immediately move away from the water to higher ground.

If you live in an area where tsunamis happen, which includes all places with elevations less than 50 feet (15 meters) above sea level along the Pacific coasts, it is important to learn your evacuation route out of town. If a tsunami warning is issued, you may have just minutes, or possibly even seconds, to act. Turn off the water, gas, and electricity in your home and get to higher ground.

Don't feel that it is safe to return after the first wave has passed. Remember that a tsunami is a series of waves and the first one is often the mildest. The second or third, or even the seventh or eighth wave may be the most powerful. Avoid the danger area until you hear the all-clear signal on radio or television broadcasts.

Notable tsunamis in history

  • In 1868, a major earthquake in Chile unleashed a deadly tsunami that struck the northern Chilean city of Arica. Sixty-foot (18-meter) waves inundated the city, sweeping away houses, flooding streets, and destroying ships in the harbor. More than 25,000 people died in the disaster.
  • In May 1960, an earthquake off the coast of south-central Chile sent waves across the ocean to Hawaii and Japan. Within minutes of the earthquake, waves killed up to 2,000 people along the coasts of Chile and Peru. The tsunami reached Hilo, Hawaii, fifteen hours later, killing 61 people. Twenty-two to twenty-three hours after that, the tsunami reached Japan, where it drowned 199 people. Total damages due to the tsunami were in excess of $500 million.
  • In March 1964, the strongest earthquake ever measured in North America (9.2 on the Richter scale) occurred in Prince William Sound near the Alaskan Kenai Peninsula. The quake set in motion a tsunami that was 30 feet (9.1 meters) tall when it struck the coast at Seward. The rush of water knocked the lids off oil storage tanks, creating a fire that rode and spread on top of the waves. Many coastal settlements were wiped out, and the death toll in Alaska from the tsunami was 106. (The quake itself killed an additional nine people.) The tsunami continued down the coast of the United States. It killed four people on the shore in Oregon, then smashed into the shore at Crescent City, California, in a series of four waves. The last of the four, which at 20 feet (6.1 meters) was the tallest, drowned eleven people. The tsunami traveled so far south that its ripples were detected on the coast of Antarctica.
  • In August 1976, a major earthquake off the shore of the Philippines triggered a tsunami that left 5,000 (by some estimates as many as 8,000) dead in the Moro Gulf area of Mindanao island.
  • The Indonesian island of Flores in December 1992 received a tsunami that left nearly 2,500 people dead and hundreds injured. Thousands of people were left homeless. The tsunami was caused by an earthquake 19 miles (30.6 kilometers) away in the Flores Sea.
  • More than 120 (by some estimates as many as 180) people were killed in July 1993 when a 100-foot-tall (30.5-meter-tall) tsunami crashed into the tiny island of Okushiri, in northwestern Japan. The waves were produced by an earthquake that had occurred just five minutes earlier in the Sea of Japan. Damages were estimated at $600 billion.
  • On December 26, 2004, the deadliest and most devastating tsunami in recorded history struck the coastline in Indonesia and around the Indian Ocean, eventually reaching as far away as Bangladesh, India, Sri Lanka, the Maldives, and even further in Somalia, Kenya, and Tanzania on the eastern coast of Africa. Approximately 230,000 people were killed.
  • A 7.7 magnitude earthquake shocked the Indian Ocean seabed again on July 17, 2006, 125 miles (200 km) south of Pangandaran, a beautiful beach popular with surfers. This earthquake triggered tsunamis whose heights varied from from 6 feet (2 meters) at Cilacap to 18 feet (6 meters) at Cimerak Beach, where it swept away and flattened buildings as far as 1300 feet (400 meters) away from the coastline. More than 600 people were reported killed, and around 150 others were missing.

All buildings in the tsunami warning area should be checked for gas leaks or electrical shorts before being reoccupied. When you return home, have your food and water checked for contamination. Toss out contaminated food; if the water source is deemed unsafe, you must boil it before drinking.

[See AlsoClimate; Earthquake; Volcano; Weather: An Introduction ]

For More Information

BOOKS

Stewart, Gail. Overview Series Catastrophe in Southern Asia: The Tsunami of 2004. San Diego, CA: Lucent Books, 2005.

Tibballs, Geoff. Tsunami: The Most Terrifying Disaster. London, UK: Carlton Publishing Group, 2005.

Zebrowski, Ernest, and Ernest Zebrowski Jr. Perils of a Restless Planet: Scientific Perspectives on Natural Disasters. Ann Arbor: University of Michigan Press, 2005.

PERIODICALS

Geist, Eric L., Vasily V. Titov, and Costas E. Synolakis. "Tsunami: Wave of Change." Scientific American. (January 2006): pp. 56-63.

WEB SITES

Geist, Eric L., and Laura Zink Torresan. "Life of a Tsunami." United States Geological Survey. 〈http://walrus.wr.usgs.gov/tsunami/basics.html〉 (accessed March 24, 2007).

Pacific Tsunami Museum. 〈http://www.tsunami.org/〉 (accessed March 23, 2007).

"Tsunamis." Coastal Ocean Institute. 〈http://www.whoi.edu/institutes/coi/viewTopic.do?o=read&id=281〉 (accessed March 24, 2007).

"Wave that Shook the World." NOVA. 〈http://www.pbs.org/wgbh/nova/tsunami/〉 (accessed March 23, 2007).

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Tsunami

Tsunami

Tsunami, or seismic sea waves, are a series of very long wavelength ocean waves generated by the sudden displacement of large volumes of water . The generation of tsunami waves is similar to the effect of dropping a solid object, such as a stone, into a pool of water. Waves ripple out from where the stone entered, and thus displaced, the water. In a tsunami, the "stone" comes from underneath the ocean or very close to shore, and the waves, usually only three or four, are spaced about 15 minutes apart.

Tsunami can be caused by underwater (submarine ) earthquakes, submarine volcano eruptions, falling (slumping) of large volumes of ocean sediment, coastal landslides, or even by meteor impacts. All of these events cause some sort of land mass to enter the ocean and the ocean adjusts itself to accommodate this new mass. This adjustment creates the tsunami, which can circle around the world. Tsunami is a Japanese word meaning "large waves in harbors." It can be used in the singular or plural sense. Tsunami are sometimes mistakenly called tidal waves but scientists avoid using that term since they are not at all related to tides .

Tsunami are classified by oceanographers as shallow water surface waves. Surface waves exist only on the surface of liquids. Shallow water waves are defined as surface waves occurring in water depths that are less than one half their wavelength. Wavelength is the distance between two adjacent crests (tops) or troughs (bottoms) of the wave. Wave height is the vertical distance from the top of a crest to the bottom of the adjacent trough. Tsunami have wave heights that are very small as compared to their wavelengths. In fact, no matter how deep the water, a tsunami will always be a shallow water wave because its wavelength (up to 150 mi [240 km]) is so much greater than its wave height (usually no more than 65 ft [20 m]).

Shallow water waves are different than deep water waves because their speed is controlled only by water depth. In the open ocean, tsunami travel quickly (up to 470 MPH [760 km/h]), but because of their low height (typically less than 3 ft [1 m]) and long wavelength, ships rarely notice them as they pass underneath. However, when a tsunami moves into shore, its speed and wavelength decrease due to the increasing friction caused by the shallow sea floor.

Wave energy must be redistributed, however, so wave height increases, just as the height of small waves increases as they approach the beach and eventually break. The increasing tsunami wave height produces a "wall" of water that, if high enough, can be incredibly destructive. Some tsunami are reportedly up to 200 ft (65 m) tall. The impact of such a tsunami can range miles inland if the land is relatively flat.

Tsunami may occur along any shoreline and are affected by local conditions such as the coastline shape, ocean floor characteristics, and the nature of the waves and tides already in the area. These local conditions can create substantial differences in the size and impact of the tsunami waves even in areas that are very close geographically.


Types of tsunami

Tsunami researchers classify tsunami according to their area of effect. They can be local, regional, or ocean-wide. Local tsunami are often caused by submarine volcanoes, submarine sediment slumping, or coastal landslides. These can often be the most dangerous because there is often little warning between the triggering event and the arrival of the tsunami.

Seventy-five percent of tsunami are considered to be regional events. Japan, Hawaii, and Alaska are commonly hit by regional tsunami. Hawaii, for example has been hit repeatedly during this century, about every five to 10 years. One of the worst was the April 1, 1946, tsunami that destroyed the city of Hilo.

Pacific-wide tsunami are the least common as only 3.5% of tsunami are this large, but they can cause tremendous destruction due to the massive size of the waves. In 1940 and 1960, destructive Pacific-wide tsunami occurred. More recently, there was a Pacific-wide tsunami on October 4, 1994, which caused substantial damage in Japan with 11.5 ft (3.5 m) waves. North America was lucky that time. Waves of only 6 in (15 cm) over the normal height were recorded in British Columbia.


Tsunami in history

Tsunami are not only a modern phenomenon. The decline of the Minoan civilization is believed to have been triggered by a powerful tsunami that hit the area in 1480 b.c. and destroyed its coastal settlements. Japan has had 65 destructive tsunami between a.d. 684 and 1960. Chile was hit in 1562 and Hawaii has a written history of tsunami since 1821. The Indian and Atlantic Oceans also have long tsunami histories. Researchers are concerned that the impact of future tsunami, as well as hurricanes, will be worse because of intensive development of coastal areas in the last 30 years.

The destructive 1946 tsunami at Hilo, Hawaii, caused researchers to think about the problem of tsunami prediction. It became clear that if we could predict when the waves are going to hit, we could take steps to minimize the impact of the great waves.


Predicting tsunami—The International Tsunami Warning System

In 1965, the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific, and Cultural Organization agreed to expand the United States' existing tsunami warning center at Ewa Beach, Hawaii. This marked the formation of the Pacific Tsunami Warning Center (PTWC) which is now operated under the U.S. Weather Service. The objectives of the PTWC are to "detect and locate major earthquakes in the Pacific basin ; determine whether or not tsunami have been generated; and to provide timely and effective information and warnings to minimize tsunami effects."

The PTWC is the administrative center for all the associated centers, committees, and commissions of the International Tsunami Warning System (ITWS). Japan, the Russian Federation, and Canada also have tsunami warning systems and centers and they coordinate with the PTWC. In total, 27 countries now belong to the ITWS.

The ITWS is based on a world-wide network of seismic and tidal data and information dissemination stations, and specially trained people. Seismic stations measure movement of the earth's crust and are the foundation of the system. These stations indicate that some disturbance has occurred that may be powerful enough to generate tsunami. To confirm the tsunami following a seismic event, there are specially trained people, called tide observers, with monitoring equipment that enables them to detect differences in the wave patterns of the ocean. Pressure gauges deployed on the ocean can detect changes of less than 0.4 in (1 cm) in the height of the ocean, which indicates wave height. Also, there are accelerometers set inside moored buoys that measure the rise and fall of the ocean, which will indicate the wave speed. These data are used together to help researchers confirm that a tsunami has been generated. Tsunami can also be detected by satellite monitoring methods such as radar and photographic images.

The warning system in action

The ITWS is activated when earthquakes greater than 6.75 on the Richter scale are detected. The PTWC then collects all the data, determines the magnitude of the quake and its epicenter. Then they wait for the reports from the nearest tide stations and their tide observers. If a tsunami wave is reported, warnings are sent to the information dissemination centers.

The information dissemination centers then coordinate the emergency response plan to minimize the impact of the tsunami. In areas where tsunami frequency is high, such as Japan, the Russian Federation, Alaska, and Hawaii, there are also Regional Warning Systems to coordinate the flow of information. These information dissemination centers then decide whether to issue a "Tsunami Watch," which indicates that a tsunami may occur in the area, or a more serious "Tsunami Warning," which indicates that a tsunami will occur. The entire coastline of a region is broken down into smaller sections at predetermined locations known as "breakpoints" to allow the emergency personnel to customize the warnings to account for local changes in the behavior of the tsunami. The public is kept informed through local radio broadcasts. If the waves have not hit within two hours of the estimated time of arrival, or, the waves arrived but were not damaging, the tsunami threat is assumed to be over and all Watches and Warnings are canceled.


Current and future research

One of the more recent changes in the ITWS is that the Regional Centers will be taking on greater responsibility for tsunami detection and warning procedures. This is being done because there have been occasions when the warning from Hawaii came after the tsunami hit the area. This can occur with local and regional tsunami that tend to be smaller in their area of effect. Some seismically active areas need to have the warning system and equipment closer than Hawaii if they are to protect their citizens. For example, the Aleutian Islands near Alaska have two to three moderate earthquakes per week. As of May 1995, centers such as the Alaska Tsunami Warning Center located in Palmer, Alaska, have assumed a larger role in the management of tsunami warnings.

In terms of basic research, one of the biggest areas of investigation is the calculation of return rates. Return rates, or recurrence intervals, are the predicted frequency with which tsunami will occur in a given area and are useful information, especially for highly sensitive buildings such as nuclear power stations, offshore oil drilling platforms, and hospitals. The 1929 tsunami in Newfoundland has been studied extensively by North American researchers as a model for return rates and there has been some dispute. Columbia University researchers predict a reoccurrence in Newfoundland in 1,000-35,000 years. However, a marine geologist in Halifax believes that it may reoccur as soon as 100-1,000 years. His calculations are based on evidence from mild earthquakes and tsunami in the area. He also suggests that the 1929 tsunami left a sedimentary record that is evident in the soil profile, and that such records can be dated and used to calculate return rates. He is currently working with an American scientist to test this theory.

See also Earthquake.


Resources

periodicals

Whelan, M. "The Night the Sea Smashed Lord's Cove." Canadian Geographic (November/December 1994): 70-73.


Jennifer LeBlanc

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Breakpoints

—Points at which the Regional Tsunami Warning Centers arbitrarily split their coastline to create smaller sections that receive customized information in the event of a tsunami.

Return rates

—The predicted frequency at which a tsunami will hit a certain area.

Seismic activity/event

—An earthquake or disruption of the earth's crust.

Shallow surface wave

—A wave that exists only on the surface of a liquid and has a wavelength that is greater than the water depth.

Slumping

—A sudden falling of unstable sediments, usually used to refer to underwater environments.

Submarine

—Below the surface of the ocean.

Wave height

—The vertical change in height between the top, or "crest," of the wave and the bottom, or "trough," of the wave.

Wavelength

—The distance between two consecutive crests or troughs in a wave.

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