Some tiptoe in like the barest summer breeze. Others crash ashore with the full force of a thousand cymbals, leaving no doubt about the tremendous power they carry. Their regularity, one after another after another, can create the most peaceful setting imaginable and eventually will turn even the hardest rock into sand. They are waves.

TO THE ARTIST AND POET, WAVES ARE BEAUTY packaged in moving water. To the hardened sailor, they are things to respect and fear. And to the surfer, waves are the stuff of awe, legend, and experiences approaching rapture. But in fact, waves are just energy moving through the water.

A wave is born when some natural phenomenon imparts energy to water. That energy source can be something dramatic, such as an underwater earthquake, volcano, or landslide, and the resulting waves can tower 100 feet above the sea. Earthquakes and volcanoes are rare, and landslides are only slightly more common; together they produce fewer than one percent of all waves. Instead, it is the wind blowing on the surface of the water that sets most waves in motion, though the wind, too, can generate so-called killer waves.

Such was the case with the great Halloween storm of 1991, which produced the largest waves ever documented150 feet tall, surpassing the old record of 112 feet set in 1933. An enormous low-pressure system parked off the Nova Scotia coast whipped up what ocean engineer William Dally called a once-in-10,000-years storm. The storms gale-force winds generated the giant waves, which are still cresting at over 15 feet when they hit Floridas beaches.

It was a stupendous display unlike anything Ive ever seen, says Dally, an avid surfer and Florida Institute of Technology professor The whole town of Melbourne just sat on the boardwalk and watched like it was the Fourth of July.

How were such enormous waves born? Their genesis began with the wind blowing across the Atlantic. Friction between wind and water ruffled the ocean surface, producing small ripples or capillary waves that move in the direction of the wind. These ripples then were able to catch some of the wind as it blew by and rise higher above the sea surface. As the wind blew harder and harder, the waves grew taller and taller.

On an average day at sea, wind-driven waves are about five to ten feet high, measured from the top or crest, of the wave to the lowest point, or trough, in front of the wave. But this was no average day at sea, for a storm was passing overhead.

During the typical ocean storm, strong winds might force the water to pile up in waves that crest at 70 feet or more. Certainly, these are big waves, although they would begin decaying as soon as they moved away from the storm. But this was no typical storm.

THIS WAS A MONSTER STORM WITH THE THREE TRAITS THAT MAKE FOR RECORD-BREAKING WAVES: It had fairly strong winds that blew for a long time and over a great distance, or fetch.

Strong winds alone produce big waves, but not enormous waves, says Rick Grigg, the 1967 world surfing champion who now is a professor of oceanography at the University of Hawaii in Honolulu. In fact, when wind speed reaches 70 knots, it blows the tops of the waves off, and they cannot grow as fast. And when wind speed hits 100 knots, it totally destroys any big waves, knocking them right over.

On Halloween 1991, winds blowing just under 70 knots whipped the seas into what is called a fully developed stage. Large, slanted waves, some with whitecaps, moved southward from the storm. But this storm had an enormous fetch so the winds continued to push against the waves, piling them ever higher.

Even this storm had its edge, however, and once the waves crossed that edge they coalesced into swells. These are the rounded form of waves that can travel thousands of miles over the course of two weeks or more. Swells are tame compared to the waves of a fully developed sea, but they carry just as much energy as their violent progenitors. Instead of being tall, they are widethe distance between troughs increases as the waves of a fully developed sea turn into swells.

From a ship, swells appear to be traveling hills of water, but the water in a swell travels little, if any, through the open ocean. Instead, it is the energy imparted from the wind that moves through the waterat speeds of 25 miles per hourcausing the water to rise and fall in place as the energy passes. If this is hard to fathom, think of those amber waves of grain: The wheat doesnt actually move through the field even though it appears to do just that.

Left to its own devices, a swell will travel through the ocean, losing some of its energy as friction with each passing mile until it ceases to exist. Occasionally, swells from different storms may cross each others path. If the crests of the two sets of swells intersect, they will combine into one set of gigantic swells called rogue waves. Though short-lived, rogue waves can capsize ocean-going ships.

If the initial wave is large, the swell can travel several thousand miles before it dies. Hawaiis renowned summer surf, for example, starts in the large storms that develop 4,000 miles away off the Antarctic coast. The waves produced when the volcano Krakatoa erupted in the Pacific Ocean reached New York City, though they were only three inches tall when they rolled ashore.

Eventually, though, most swells pass close to land. There, whats known as the swells cone of energythe energy beneath the waters surfacehits the seafloor, which forces the cone toward the surface. As the energy rises so, too, does the top of the swell, and it once again becomes a wave. As the wave moves further ashore, two things happen.

First, the wave slows as its cone of energy drags along the seafloor, and as a result, the wave turns toward shore. This is called refraction, and it is the reason that waves come ashore parallel to the shoreline. It is the same phenomenon that causes light waves to bend as they pass from air into water.

At the same time, the sea bottom continues to push upward on the cone of energy, forcing the wave crest to grow ever higher until it becomes unstable. It is then that the wave breaks: The crest curls over and produces a whitecap or spindrift. It is here, beneath the whitecap on the part of the wave known as the tunnel or pipeline, that the surfer catches and rides a wave.

THIS INTERACTION BETWEEN THE CONE OF ENERGY AND THE SEAFLOOR DETERMINES, TO A LARGE PART, WHETHER WAVES ROLL ASHORE GENTLY or form the big breakers that surfers love to ride. Where the seafloor rises gradually, waves build gradually and eventually spill onto the beach. But if the seafloor rises suddenly, or if there are reefs or shoals not far from the shore, then the waves plunge forward as their energy is thrust upward. Appropriately placed undersea canyons also can focus wave energy much like a lens.

Dally has studied the interactions between seafloor and surfability and, together with some colleagues at Florida Tech, has developed a computer program that can predict what surfing conditions will be like three days in advance. Dally starts by determining a beachs Iribarren number, a constant that relates the slope of the seafloor at a particular beach to the average wave size at that beach. A larger Iribarren number means that the beach is more likely to have plunging breakers, which is what surfers desire.

The wave forecaster runs the data on barometric pressure and wind speeds through a sophisticated numerical model of the Atlantic Ocean, producing a map of wave heights and periods (the time between passing wave crests). Finally, the model runs these waves into shallow water and onto each beach along the U.S. Atlantic coast, predicting the surfability at each beach three days into the future. Beach observers have confirmed the models predictions, and the Florida Tech team plans to make this information available on a 1-900 number. Work now is underway to modify the model to make predictions for Pacific Ocean beaches.

Though some surfers may disagree, Stephan Grilli, an avid sail surfer and assistant professor of ocean engineering at the University of Rhode Island, claims that the beaches in Narrangansett, Rhode Island are the best on the east coast because of the structure of the seafloor just offshore. There are a number of underwater shoals at just the right distance from the beach that interrupt the waves at just the right time as they make their way into the beach, says Grilli. Not incidentally strong storms frequently pass the Rhode Island coast, which is not protected by barrier islands as is most of the rest of the east coast.

Good as the Rhode Island surf is, it is nothing compared to the waves that come ashore on Hawaiian beaches, where the waves can routinely top 20 feet. The difference, says Grigg, lies in Hawaiis location in the middle of the Pacific Ocean, home of the worlds biggest, most powerful storms. In summer, the islands receive waves that originated near Antarctica, while in winter the waves descend southward from the far North Pacific.

In all his 40-some years of surfing, Grigg says that he has seen waves of 30 feet only five times. In 1981 he tried surfing one of them and broke a bone in his back in the process. He still surfs as often as he can, but 30 footers are now just for watching in amazement.

Seeing one takes your breath away, says Grigg.

Joseph Alper is a free-lance writer whose works appear in The Los Angeles Times, The Atlantic Monthly, Science, and Sea Frontiers.


From Sea Frontiers, Vol. 39, 1993. © 1993 by the International Oceanographic Foundation. Reprinted by permission.





Men have always been fascinated, and sometimes awed, by the rhythmic motions of the seas surface. A century of observation and experiment has revealed much about how these waves are generated and propagated


By Willard Bascom



an is by nature a wave-watcher. On a ship he finds himself star­ing vacantly at the constant swell that flexes its muscles just under the sea's surface; on an island he will spend hours leaning against a palm tree absently watching the rhythmic breakers on the beach. He would like to learn the ways of the waves merely by watching them, but he cannot, because they set him dreaming. Try to count a hundred waves sometime and see.

Waves are not always so hypnotic. Sometimes they fill us with terror, for they can be among the most destructive forces in nature, rising up and over­whelming a ship at sea or destroying a town on the shore. Usually we think of waves as being caused by the wind, be­cause these waves are by far the most common. But the most destructive waves are generated by earthquakes and under­sea landslides. Other ocean waves, such as those caused by the gravitational at­traction of the sun and the moon and by changes in barometric pressure, are much more subtle, often being imper­ceptible to the eye. Even such passive elements as the contour of the sea bot­tom, the slope of the beach and the curve of the shoreline play their parts in wave action.; A wave becomes a breaker, for example, because as it advances into in­creasingly shallow water it rises higher and higher until the wave front grows ton steep and topples forward into foam and turbulence. Although the causes of this beautiful spectacle are fairly well understood, we cannot say the same of many other aspects of wave activity. The questions asked by the wave-watcher are nonetheless being answered by intensive studies of the sea and by the examination of waves in large experimental tanks. The new knowledge has made it possible to measure the power and to forecast the

actions of waves for the welfare of those who live and work on the sea and along its shores.

Toss a pebble into a pond and watch the even train of waves go out. Waves at sea do not look at all like this. They are confused and irregular, with rough diamond-shaped hillocks and crooked valleys. They are so hopelessly complex that 2,000 years of observation by sea­farers produced no explanation beyond the obvious one that waves are somehow raised by the wind. The description of the sea surface remained in the province of the poet who found it "troubled, un­settled, restless. Purring with ripples un­der the caress of a breeze, flying into scattered billows before the torment of a storm and flung as raging surf against the land; heaving with tides breathed by a sleeping giant."

The motions of the oceans were too complex for intuitive understanding. The components had to be sorted out and dealt with one at a time. So the first the­oreticians cautiously permitted a perfect train of waves, each exactly alike, to travel endlessly across an infinite ocean. This was an abstraction, but it could at least be dealt with mathematically.

Early observers noticed that passing waves move floating objects back and forth and up and down, but do not trans­port them horizontally for any great dis­tance. From the motion of seaweeds the motion of the water particles could be deduced. But it was not until 1802 that Franz Gerstner of Germany constructed the first wave theory. He showed that water particles in a wave move in circu­lar orbits. That is, water at the crest moves horizontally in the direction the wave is going, while in the trough it moves in the opposite direction. Thus each water particle at the surface traces a circular orbit, the diameter of which is equal to the height of the wave [see illus­tration on next page]. As each wave passes, the water returns almost to its original  position. Gerstner observed that the surface trace of a wave is approxi­mately a trochoid: the curve described by a point on a circle as it rolls along the underside of a line. His work was ampli­fied by Sir George Airy later in the 19th century, by Horace Lamb of England in the present century, and by others.

The first wave experimentalists were Ernst and Wilhelm Weber of Germany, who in 1825 published a book on studies employing a wave tank they had in­vented. Their tank was five feet long, a foot deep and an inch wide, and it had glass sides. To make waves in the tank they sucked up some of the fluid through a tube at one end of it and allowed the fluid to drop back. Since the Weber brothers experimented not only with wa­ter and mercury but also with brandy, their persistence in the face of tempta­tion has been an inspiration to all subse­quent investigators. They discovered that waves are reflected without loss of energy, and they determined the shape of the wave surface by quickly plunging in and withdrawing a chalk-dusted slate. By watching particles suspended in the water they confirmed the theory that wa­ter particles move in a circular orbit, the size of which diminishes with depth. At the bottom, they observed, these orbits tend to be flattened.

As increasingly bolder workers con­tributed ideas in the 20th century, many of the complexities of natural waves found their way into equations. How­ever, these gave only a crude, empirical answer to the question of how wind en­ergy is transferred to waves. The neces­sity for the prediction of waves and surf for amphibious operations in World War TI attracted the attention of Harald U. Sverdrup and Walter Munk of the Scripps Institution of Oceanography. As a result of their wartime studies of the interaction of winds and waves they were the first investigators to give a rea­sonably complete quantitative descrip­tion of how wind gets energy into the waves. With this description wave stud­ies seemed to come of age, and a new era of research was launched.

Let us follow waves as they are gen­erated at sea by the wind, travel for per­haps thousands of miles across the ocean and finally break against the shore. The effectiveness of the wind in making waves is due to three factors: its average velocity, the length of time it blows and the extent of the open water across which it blows (called the fetch).

Waves and the Wind


Waves start up when the frictional drag of a breeze on a calm sea creates ripples. As the wind continues to blow, the steep side of each ripple presents a surface against which the moving air can press directly. Because winds are by na­ture turbulent and gusty, wavelets of all sizes are at first created. The small, steep ones break, forming whitecaps, releasing some of their energy in turbulence and possibly contributing part of it to larger waves that overtake them. Thus as ener­gy is added by the wind the smaller waves continually give way to larger ones which can store the energy better. But more small waves are continually formed, and in the zone where the wind moves faster than the waves there is a wide spectrum of wavelengths. This is the generating area, and in a large storm it may cover thousands of square miles. If storm winds apply more force than a wave can accept, the crest is merely steepened and blown off, forming a breaking wave at sea. This happens when the wave crest becomes a wedge of less than 120 degrees and the height of the wave is about a seventh of its length. Thus a long wave can accept more energy from the wind and rise much higher than a short wave passing under the same wind. When the wind produces waves of many lengths, the shortest ones reach maximum height quickly and then are destroyed, while the longer ones continue to grow.

A simple, regular wave-train can be described by its period (the time it takes two successive crests to pass a point), by its wavelength (the distance between crests) and by its height (the vertical distance between a trough and a suc­ceeding crest). Usually, however, there are several trains of waves with different wavelengths and directions present at the same time, and their intersection creates a random or a short-crested dia­mond pattern. Under these conditions no meaningful dimensions can be assigned to wave period and length. Height, how­ever, is important, at least to ships; sev­eral crests may coincide and add their heights to produce a very large wave. Fortunately crests are much more likely to coincide with troughs and be canceled out. There is no reason to believe that the seventh wave, or some other arbitrar­ily numbered wave, will be higher than the rest; that is a myth of the sea.

Since waves in a sea are so infinitely variable,. statistical methods must be em­ployed to analyze and describe them. A simple way to describe height, for exam­ple, is to speak of significant height-the average height of the highest third of the waves. Another method, devised in 1952 by Willard J. Pierson, Jr., of New York University, employs equations like those that describe random noise in infor­mation theory to predict the behavior of ocean waves. Pierson superposes the regular wave-trains of classical theory in such a way as to obtain a mathematically irregular pattern. The result is most con­veniently described in terms of energy spectra. This scheme assigns a value for the square of the wave height to each



CROSS SECTION OF OCEAN WAVE traveling from left to right shows wavelength as distance between successive crests. The time it takes two crests to pass a point is the wave period. Circles are orbits of water particles in the wave. At the surface their diameter equals the wave height. At a depth of half the wavelength (left), orbital diameter is only 4 per cent of that at surface.


frequency and direction. Then, by de­termining the portion of the spectrum in which most of the energy is concen­trated, the average periods and lengths can be obtained for use in wave fore­casting.

Over a long fetch, and under a strong, steady wind, the longer waves pre­dominate. It is in such areas of sea that the largest wind waves have been re­corded. The height of the waves in a train does not, however, bear any simple relationship to their other two dimen­sions: the period and the wavelength. The mariner's rule of thumb relates wave height to wind velocity and says that the height ordinarily will not be greater than half the wind speed. This means that an 80-mile-per-hour hurricane would pro­duce waves about 40 feet high.

The question ,of just how large indi­vidual waves at sea can actually be is still unsettled, because observations are difficult to make and substantiate from shipboard in the midst of a violent storm. Vaughan Cornish of England spent half a century collecting data on waves, and concluded that storm waves over 45 feet high are rather common. Much higher waves have been fairly well authenticated on at least two oc­casions.

In October, 1921, Captain Wilson of the 12,000-ton S.S. Ascanius reported an extended storm in which the recording barometer went off the low end of the scale. When the ship was in a trough on an even keel, his observation post on the ship was 60 feet above the water level, and he was certain that some of the waves that obscured the horizon were at least 10 feet higher than he was, ac­counting for a total height of 70 feet or more. Commodore Hayes of the S.S. Ma­jestic reported in February, 1923, that his ship had experienced winds of hurri­cane force and waves of 80 feet in height. Cornish examined the ship, close­ly interrogated the officers and concluded that waves 60 to 90 feet high, with an average height of 75 feet, had indeed been witnessed.

A wave reported by Lieutenant Com­mander R. P. Whitemarsh in the Pro­ceedings of the U. S. Naval Institute tops all others. On February 7, 1933, the U.S.S. Ramapo, a Navy tanker 478 feet long, was en route from Manila to San Diego when it encountered "a disturb­ance that was not localized like a typhoon . . . but permitted an unob­structed fetch of thousands of miles." The barometer fell to 29.29 inches and the wind gradually rose from 30 to 60 knots over several days. "We were run­ning directly downwind and with the sea. It would have been disastrous to have steamed on any other course." From among a number of separately de­termined observations, that of the watch officer on the bridge was selected as the most accurate. He declared that he "saw seas astern at a level above the main­mast crow's-nest and at the moment of observation the horizon was hidden from view by the waves approaching the stern." On working out the geometry of the situation from the ship's plan, White­marsh found that this wave must have been at least 112 feet high [see illustra­tion at the bottom of the next two pages]. The period of these waves was clocked at 14.8 seconds and their velocity at 55 knots.

As waves move out from under the winds that raise them, their character changes. The crests become lower and more rounded, the form more symmetri­cal, and they move in trains of similar period and height. They are now called swell, or sometimes ground swell, and in this form they can travel for thousands of miles to distant shores. Happily for mathematicians, swell coincides much more closely with classical theory than do the waves in a rough sea, and this re­news their faith in the basic equations.


                 WAVE ADVANCE

MOVING TRAIN OF WAVES advances at only half the speed of as its individual waves. At top is a wave train in its first position. At bottom the train, and its energy, have moved only half as far as wave 2 has. Meanwhile wave 1 has died, but wave 4 has formed at the rear of the train to replace it. Waves arriving at shore are thus remote descendants of waves originally generated.



DIFFERENT TRAINS OF WAVES, caused by winds of different directions and strengths, make up the surface of a "sea." The various trains, three of which are represented diagrammatically here, have a wide spectrum of wavelengths, heights and directions.  When they meet, the result is apparent confusion, represented at far right by a topographic diagram drawn from actual photographs of the sea surface. The pattern becomes so complex that statistical methods must be used to analyze the waves and predict their height.




Curiously enough, although each wave moves forward with a velocity that corresponds to its length, the energy of the group moves with a velocity only half that of the individual waves. This is because the waves at the front of a group lose energy to those behind, and gradu­ally disappear while new waves form at the rear of the group. Thus the composi­tion of the group continually changes, and the swells at a distance are but re­mote descendants of the waves created in the storm [see illustration on preced­ing page]. One can measure the period at the shore and obtain from this a correct value for the wave velocity; however, the energy of the wave train traveled from the storm at only half that speed.

Waves in a swell in the open ocean are called surface waves, which are de­fined as those moving in water deeper than half the wavelength. Here the bot­tom has little or no effect on the waves because the water-particle orbits dimin­ish so rapidly with depth that at a depth of half the wavelength the orbits are only 4 per cent as large as those at the surface. Surface waves move at a speed in miles per hour roughly equal' to 3.5 times the period in seconds. Thus a wave with a period of 10 seconds will travel about 35 miles per hour. This is the average period of the swell reaching U. S. shores, the period being somewhat longer in the Pacific than the Atlantic. The simple re­lationship between period and wave­length (length=5.12T2) makes it easy to calculate that a 10-second wave will have a deep-water wavelength of about 512 feet. The longest period of swell ever reported is 22.5 seconds, which cor­responds to a wavelength of around 2,600 feet and a speed of 78 miles per hour.

Waves and the Shore


As the waves approach shore they reach water shallower than half their wavelength. Here their velocity is con­trolled by the depth of the water, and they are now called shallow-water waves. Wavelength decreases, height increases and speed is reduced; only the period is unchanged. The shallow bottom greatly modifies the waves. First, it refracts them, that is, it bends the wave fronts to approximate the shape of the underwater contours. Second, when the water be­comes critically shallow, the waves break [see illustration on page 11].

Even the most casual observer soon notices the process of refraction. He sees that the larger waves always come in nearly parallel to the shoreline, even though a little way out at sea they seem to be approaching at an angle. This is the result of wave refraction, and it has considerable geological importance be­cause its effect is to distribute wave energy in such a way as to straighten coastlines. Near a headland the part of the wave front that reaches shallow wa­ter first is slowed down, and the parts of

it in relatively deep water continue to move rapidly. The wave thus bends to converge on the headland from all sides. As it does, the energy is concentrated in less length of crest; consequently the height of the crest is increased. This ac­counts for the old sailors' saying: "The points draw the waves."

Another segment of the same swell will enter an embayment and the wave front will become elongated so that the height of the waves at any point along the shore is correspondingly low. This is why bays make quiet anchorages and exposed promontories are subject to wave battering and erosion-all by the same waves. One can deal quantitatively with this characteristic of waves and can plot the advance of any wave across wa­ters of known depths. Engineers plan­ning shoreline structures such as jetties or piers customarily draw refraction dia­grams to determine in advance the effect of waves of various periods and direc­tion. These diagrams show successive



















positions of the wave front, partitioned by orthogonals into zones representing equal wave energy [see illustration on next page]. The ratio of the distances be­tween such zones out at sea and at the shore is the refraction coefficient, a con­venient means of comparing energy re­lationships.

Refraction studies must take into ac­count surprisingly small underwater ir­regularities. For example, after the Long Beach, Calif., breakwater had withstood wave attack for years, a short segment of it was suddenly wrecked by waves from a moderate storm in 1930. The break­water was repaired, but in 1939 waves breached it again. A refraction study by Paul Horrer of the Scripps Institution of Oceanography revealed that long-period swell from exactly 165 degrees (south ­southeast), which was present on only these two occasions, had been focused at the breach by a small hump on the bot­tom, 250 feet deep and more than seven miles out at sea. The hump had acted as a lens to increase the wave heights to 3.5 times average at the point of damage.

During World War II it was necessary to determine the depth of water off ene­my-held beaches against which am­phibious landings were planned. Our scientists reversed the normal procedure for refraction studies; by analyzing a carefully timed series of aerial photo­graphs for the changes in length (or velocity) and direction of waves ap­proaching a beach, they were able to map the underwater topography.

The final transformation of normal swell by shoal or shallow water into a breaker is an exciting step. The waves have been shortened and steepened in the final approach because the bottom has squeezed the circular orbital motion of the particles into a tilted ellipse; the particle velocity in the crest increases and the waves peak up as they rush land­ward. Finally the front of the crest is un­supported and it collapses into the trough. The wave has broken and the orbits exist no more. The result is surf.

If the water continues to get shallow­er, the broken wave becomes a foam line, a turbulent mass of aerated water. However, if the broken wave passes into deeper water, as it does after breaking on a bar, it can form again with a lesser height that represents the loss of energy in breaking. Then it too will break as it moves into a depth critical to its new height.

The depth of water beneath a break­er, measured down from the still-water level, is at the moment of breaking about 1.3 times the height of the breaker. To estimate the height of a breaker even though it is well offshore, one walks from the top of the beach down until the crest of the breaking wave is seen aligned with the horizon. The vertical distance between the eye and the lowest point to which the water retreats on the face of the beach is then equal to the height of the wave.

The steepness of the bottom influences.


WAVE 112 FEET HIGH, possibly the largest ever measured in the open sea, was en. countered in the Pacific in 1933 by the U.S.S. Ramapo, a Navy tanker. This diagram shows how the great wave was measured. An observer at A on the bridge was looking toward the stern and saw the crow's-nest at B in his line of sight to crest of wave, which had just come in line with horizon. From geometry of situation, wave height was calculated.



the character of the breakers. When a large swell is forced by an abrupt under­water slope to give up its energy rapidly, it forms plunging breakers-violent waves that curl far over, flinging the crest into the trough ahead. Sometimes, the air trapped by the collapsing wave is compressed and explodes with a great roar in a geyser of water [see illustration on opposite page]. However, if the bot­tom slope is long and gentle, as at Waikiki in Hawaii, the crest forms a spilling breaker, a line of foam that tum­bles down the front of the partly broken wave as it continues to move shoreward.

Since waves are a very effective mech­anism for transporting energy against a coast, they are also effective in doing great damage. Captain D. D. Gaillard of the U. S. Army Corps of Engineers de­voted his career to studying the forces of waves on engineering structures and in 1904 reported some remarkable ex­amples of their destructive power. At Cherbourg, France, a breakwater was composed of large rocks and capped with a wall 20 feet high. Storm waves hurled 7,000-pound stones over the wall and moved 65-ton concrete blocks 60 feet. At Tillamook Rock Light off the Oregon coast, where severe storms are commonplace, a heavy steel grating now protects the lighthouse beacon, which is 139 feet above low water. This is neces­sary because rocks hurled up by the waves have broken the beacon several times. On one occasion a rock weighing 135 pounds was thrown well above the

lighthouse-keeper's house, the floor of which is 91 feet above the water, and fell back through the roof to wreck the interior.

At Wick, Scotland, the end of the breakwater was capped by an 800-ton block of concrete that was secured to the foundation by iron rods 3.5 inches in diameter. In a great storm in 1872 the designer of the breakwater watched in amazement from a nearby cliff as both cap and foundation, weighing a total of 1,350 tons, were removed as a unit and deposited in the water that the wall was supposed to protect. He rebuilt the structure and added a larger cap weigh­ing 2,600 tons, which was treated simi­larly by a storm a few years later. There is no record of whether he kept his job and tried again. Gaillard's computations show that the wave forces must have been 6,340 pounds per square foot.



WAVE-REFRACTION DIAGRAM shows how energy of wave front at A is all concentrated by refraction at A' around small headland area. Same energy at B enters a bay but is spread at beach over wide area B'. -Horizontal lines are wave fronts; vertical lines divide energy into equal units for purposes of investigation. Such studies are vital preliminaries to design of shoreline structures.




Even more destructive than wind ­generated waves are those generated by a sudden impulse such as an underwa­ter earthquake, landslide or volcano. A man-made variation of the sudden im­pulse is the explosion of nuclear bombs at the surface of the sea, which in recent years have become large enough to be reckoned with as possible causes of de­structive waves.

The public knows such waves as tidal waves, although they are in no way re­lated to the tides and the implication has long irritated oceanographers. It was proposed that the difficulty could be re­solved by adopting the Japanese word tsunami. Some time later it was discov­ered that Japanese oceanographers are equally irritated by this word; in literal translation tsunami means tidal wave! However, tsunami has become the favored usage for seismic sea waves.

Like the plunger in a wave channel, the rapid motion or subsidence of a part of the sea bottom can set a train of waves in motion. Once started, these waves travel great distances at high velocity with little loss of energy. Although their height in deep water is only a few feet, on entering shallow water they are able to rise to great heights to smash and inun­date shore areas. Their height depends almost entirely on the configuration of the coastline and the nearby underwater contours. Tsunamis have periods of more than 15 minutes and wavelengths of several hundred miles. Since the depth of water is very much less than half the wavelength, they are regarded as longer shallow-water waves, even in the 13,000-foot average depth of the open ocean, and their velocity is limited by the depth to something like 450 miles per hour.

These fast waves of great destructive potential give no warning except that the disturbance that causes them can be detected by a seismograph. The U. S. Cast Guard operates a tsunami warning network in the Pacific that tracks all earthquakes, and when triangulation in­dicates that a quake has occurred at sea, it issues alerts. The network also has de­vices to detect changes in wave period which may indicate that seismic waves are passing [see "Tsunamis," by Joseph Bernstein; SCIENTIFIC AMERICAN, Aug­ust, 1954. Curiously the influence of the system may not be entirely beneficial.

Once when an alert was broadcast at Honolulu, thousands of people there dashed down to the beach to see what luckily turned out to be a very small wave.

Certain coasts near zones of ;wrest in the earth's crust are particularly prone to such destructive waves, especially the shores of the Mediterranean, the Carib­bean and the west coast of Asia. On the world-wide scale, they occur more fre­quently than is generally supposed: nearly once a year.

A well-known seismic sea wave, thor­oughly documented by the Royal So­ciety of London, originated with the eruption of the volcano Krakatoa in the East Indies on August 27, 1883. It is not certain whether the waves were caused by the submarine explosion, the violent movements of the sea bottom, the rush of water into the great cavity, or the dropping back into the water of nearly a cubic mile of rock, but the waves were monumental. Their period close to the disturbance was two hours, and at great distances about one hour. Waves at least 100 feet high swept away the town of Merak, 33 miles from the volcano; on the opposite shore the waves carried the man-of-war Berow 1.8 miles inland and left it 30 feet above the level of the sea. Some 36,380 people died by the waves in a few hours. Tide gauges in South Africa (4,6.90 miles from Krakatoa), Cape horn (7,820 miles) and Panama (11,470 miles) clearly traced the prog­ress of a train of about a dozen waves, and showed that their speed across the Indian Ocean had been between 350 and 450 miles per hour.

A tsunami on April 1, 1946, originat­ing with a landslide in the Aleutian sub­marine trench, produced similar effects,


WAVE-CREATED "GEYSER" results when large breakers smash into a very steep beach. They curl over and collapse, trapping and compressing air. This compressed air then ex­plodes as shown here. with spray from a 12-fool breaker leaping 50 feet into the air.



WAVE BREAKS UP at the beach when swell moves into water shallower than half the wavelength (1). The shallow bottom raises wave height and decreases length (2). At a water depth 1.3 times the wave height, water supply is reduced and the particles of water

in the crest have no room to complete their cycles; the wave form breaks (3). A foam line forms and water particles, instead of just the wave form, move forward (4). The low remaining wave runs up the face of the beach as a gentle wash called the uprush (5).



fortunately on less-populated shores. It struck hard at the Hawaiian Islands, kill­ing several hundred people and damag­ing property worth millions of dollars. At Hilo, Hawaii, the tsunami demon­strated that such waves are virtually in­visible at sea. The captain of a ship standing off the port was astonished up­on looking shoreward to see the harbor and much of the city being demolished by waves he had not noticed passing un­der his ship. The same waves caused considerable damage throughout the is­lands of Oceania, 4,000 miles from epicenter, and on the South American coast, but they were most spectacular at Scotch Cap in Alaska. There a two-story reinforced-concrete lighthouse marked a channel through the Aleutian Islands. The building, the base of which was 32 feet above sea level, and a radio mast 100 feet above the sea were reduced to bare foundations by a wave estimated to be more than 100 feet high.

Uncontrollable geologic disturbances will cause many more seismic sea waves in the future, and since the world's coast­al population is continuously increasing, the greatest wave disaster is yet to come. Within the next century we can expect that somewhere a wave will at least equal the one that swept the shores of the Bay of Bengal in 1876, leaving 200,000 dead.


Tides and Other Waves


The rhythmic rise and fall of the sea level on a coast indicate the passage of a true wave we call a tide. This wave is driven, as almost everyone knows, by the gravitational influence of the sun and the moon. As these bodies change their relative positions the ocean waters are attracted into a bulge that tends to re­main facing the moon as the earth turns under it; a similar bulge travels around the earth on the opposite side. The wave period therefore usually corresponds to half the lunar day.

When the sun and the moon are aligned with the earth, the tides are large (spring tides) ; when the two bod­ies are at right angles with respect to the earth, the tides are small (neap tides). By using astronomical data it is possible to predict the tides with considerable ac­curacy. However, the height and time of the tide at any place not on the open coast are primarily a function of the shape and size of the connection to the ocean.

Still another form of wave is a seiche, a special case of wave reflection. All en­closed bodies of water rock with charac­teristics related to the size of the basin. The motion is comparable to the slosh­ing of water in the bathtub when one gets out quickly. In an attempt to return to stability the water sways back and forth with the natural period of the tub (mine has a period of two seconds). Similarly a tsunami or a barometric pres­sure-change will often set the water in a bay rocking as it passes. In fact, the tsu­nami itself may reflect back and forth across the ocean as a sort of super-seiche.

In addition to seiches, tides, tsunamis and wind waves there are other waves in the sea. Some travel hundreds of feet be­neath the surface along the thermocline, the interface between the cold deep wa­ter and the relatively warm surface lay­er. Of course these waves cannot be seen, but thermometers show that they are there, moving slowly along the boundary between the warm layer and the denser cold water. Their study awaits proper instrumentation. Certain very low waves, with periods of several minutes, issue from storms at sea. These long-period "forerunners" may be caused by the barometric pulsation of the entire storm against the ocean sur­face. Since they travel at hundreds of miles an hour, they could presumably be used as storm warnings or storm-center locators. Other waves, much longer than tides, with periods of days or weeks and heights of less than an inch, have been discovered by statistical methods and are now an object of study.

The great advances both in wave the­ory and in the actual measurement of waves at sea have not reduced the need for extensive laboratory studies. The so­lution of the many complex engineering problems that involve ships, harbors, beaches and shoreline structures re­quires that waves be simulated under ideal test conditions. Such model studies in advance of expensive construction permit much greater confidence in the designs.


Experimental Tanks


The traditional wave channel in which an endless train of identical small waves is created by an oscillating plung­er is still in use, but some of the new wave tanks are much more sophisticated. In some the channel is covered, so that a high velocity draft of air may simulate the wind in making waves. In others, like the large tank at the Stevens Institute of Technology in Hoboken, New Jersey, artificial irregular waves approach the variability of those in the deep ocean. In such tanks proposed ship designs, like those of the America's Cup yacht Colum­bia, are tested at model size to see how they will behave at sea.

The ripple tank, now standard appa­ratus for teaching physics, has its place in shoreline engineering studies for con­veniently modeling diffraction and re­fraction. Even the fast tsunamis and the very slow waves of the ocean can be modeled in the laboratory. The trick is to use layers of two liquids that do not mix, and create waves on the interface be­tween them. The speeds of the waves can be controlled by adjusting the densi­ties of the liquids.

To reduce the uncertainties in ex­trapolation from the model to prototype, some of the new wave tanks are very large. The tank of the Beach Erosion Board in Washington, D.C. (630 feet long and 20 feet deep, with a 500-horse­power generator), can subject quarter­scale models of ocean breakwaters to six-foot breakers. The new maneuvering tank now under construction at the David Taylor Model Basin in Carderock, Md., measures 360 by 240 feet, is 35 feet deep along one side and will have wave generators on two sides that can inde­pendently produce trains of variable waves. Thus man can almost bring the ocean indoors for study.      The future of wave research seems to lie in refinement of the tools for measur­ing, statistically examining and repro­ducing in laboratories the familiar wind waves and swell as well as the more re­cently discovered varieties. It lies in completing the solution of the problem of wave generation. It lies in the search for forms of ocean waves not yet discov­ered-some of which may exist only on rare occasions. Nothing less than the complete understanding of all forms of ocean waves must remain the objective of these studies.

The AuthorWILLARD BASCOM served on the staff of the National Academy of Sci­ences as executive secretary of the Mari­time Research Advisory Committee and (lately) of the AMSOC Committee, which first nurtured the project of drilling a "Mohole" through the earth's subcrustal Mohorovicic discontinuity. Bascom is a native New Yorker who in the years be­fore World War II learned geology dur­ing alternate periods of work as a miner and as a student at the Colorado School of Mines, which he left a few months short of his degree in order to become a mining engineer in Arizona, Idaho, Col­orado and New York. In 1945 he joined the University of California, first as a research engineer to make studies of waves and beaches. Later he moved to the University's Scripps Institution of Oceanography at La Jolla to work on the instrumentation of nuclear-bomb tests at the Pacific Proving Grounds. Bascom joined the National Academy staff in 1954. Since then he has served as execu­tive secretary of the Academy's Com­mittee on Meteorology; traveled to Sweden and the Netherlands as a U. S. delegate to International Geophysical Year conferences; spent nine months in Tahiti installing I. G. Y. wave-measuring instruments and writing on Polynesian history; and advised the producers of the Columbia Broadcasting System Sunday evening television series "Conquest," which popularizes science. Bibliography BREAKERS AND SURF: PRINCIPLES IN FORECASTING. Hydrographic Office Publication No. 234, 1944.

THE OCEANS: THEIR PHYSICS, CHEMIS­TRY AND GENERAL BIOLOGY. H. U. Sverdrup, Martin W. Johnson and Richard H. Fleming. Prentice-Hall, Inc., 1942.

PRACTICAL METHODS FOR OBSERVING AND FORECASTING OCEAN WAVES BY MEANS OF WAVE SPECTRA AND STA­TISTICS. Willard J. Pierson, Jr., Ger­hard Neumann and Richard W. James. Hydrographic Office Publication No. 603, 1958.


Willard Bascom

Biography of Willard Bascom


Willard Bascom has been described as an ocean engineer, diver, and ocean adventurer. He had wide-ranging interests, demonstrated extreme independence, had impatience with orthodox viewpoints. He has been described as a maverick innovator, passionate about art and science. He studied poetry, music, painting (an avid oil painter, with an affinity for seascapes and landscapes), photography, cinematography, and underwater archaeology.

Willard Bascom was born in New York City (Bronxville) in 1916 by a single mother. In his teens worked as a ‘mucker’ on the Delaware Aqueduct tunnel during the Great Depression. He studied mining at the Colorado School of Mines, where a disagreement with the school president prompted him to leave before graduating. He worked as an engineer in mines in Arizona, Idaho, and Colorado.  

Willard Bascom’s career in ocean science began in 1945 when he joined John Isaacs to work as a research engineer, conducting studies of waves and beaches first at Berkeley and later at Scripps Institution of Oceanography (SIO). He lived in Monterey after the war, friends included John Steinbeck (who he had befriended while at UC Berkeley) and Ed Ricketts. He was a member of John Isaacs’ scientific party during the Bikini Atoll atomic bomb test. Willard Bascom joined SIO in 1951, and was chief scientist on two ships of Capricorn Expedition, an eight-month geophysical exploration of the bottom of the equatorial Pacific. This study yielded information about the thickness of the earth’s crust which led to the plate theory of tectonics. He pioneered use of SCUBA for scientific diving on SIO’s Capricorn Expedition.

During the expedition, Willard was diagnosed with bone cancer. As a result, he took unreasonable risks as the ships dredged the seafloor. Subjecting himself to the largest amount of radiation ever given a person, he completely recovered after about four years.

In 1954, Willard joined the staff at the National Science Foundation, where he organized and directed the first phase of Project Mohole (involving SIO and other institutions), the first effort to drill in deep water through the earth’s crust. Drilling was conducted in 1961 at depths of 11,700 ft near Guadalupe I., Mex. (the previous depth record was 400 ft). It collected samples of earth’s ‘second layer’ and measured the temperature increase 600 ft below the bottom of the seafloor. His involvement in this project resulted in book (see below) and Steinbeck wrote an article about it for Life magazine. The project was abandoned in 1966 because the ever-increasing costs failed to gain congressional approval. However, the Mohole Project laid the foundations for the Deep-sea Drilling Project, which incorporated Project Mohole’s ship positioning and design as well as its drilling technology. 

In 1962, Willard Bascom founded Ocean Science and Engineering, Inc., and became its president. He pioneered undersea exploration for diamonds, discovering about 20 million carats of gem diamonds for De Beers diamond company in underwater areas off the coasts of South Africa and Namibia. He also found lost objects and ships on the seafloor. His company developed an arm attached to a ship Alcoa Seaprobe which could retrieve sunken vessels to 1000 ft beneath the sea, developed a manned-underwater dredge to replace beach sand, and developed a ship with on-board mechanical processing of scallops for commercial use. It also salvaged airplane parts and bodies from depths of the ocean from two jet plane crashes off Los Angeles in the early 1970s.

While at Ocean Science and Engineering, Willard Bascom founded Seafinders, Inc.,  in 1972 and discovered an long lost wreck of a Spanish galleon, Nuestra Señora de la Maravillas

Willard Bascom was the director of the Southern California Coastal Water Research Project (SCCWRP) from 1973-1984. During this period he helped establish SCCWRP as an ocean research organization, with a focus on marine pollution problems of southern California. He added photographic and cinematographic technology to SCCWRP’s capabilities and used this for exploring the southern California marine environment and assessing pollution problems. He also initiated special scientific studies to study marine pollution problems and sponsored early regional assessments of the southern California marine environment. He started the SCCWRP Annual Report, an annual/biennial series with articles and papers describing the results of SCCWRP research projects.

In 1980 he received the Explorer’s Club (New York) Medal for his work in deep water archaeology and ocean geophysics. He was also an adjunct professor at SIO.

After leaving SCCWRP in 1985, Willard resumed his undersea search ventures in Greece, finding a wreck off Cape Artemision which yielded three high-quality bronze statues for the Greek National Museum. In 1992 was awarded an honorary doctorate by the University of Genoa on the 500th anniversary of Columbus’ first landing in the America’s. In 1996, he was involved in the successful search and recovery of gold treasure from Brother Jonathan, a Civil-war era side-wheel paddle-wheel steamer that sank off the northern California coast more than 134 years ago 

Willard Bascom was the author of several books and many scientific papers (including many in Scientific American). Some of his books include Waves and beaches, A hole in the bottom of the sea (1961) (describing the Mohole Project he directed), Great sea poetry (included works by Rudyard Kipling and others), Deepsea archaeology, Deepsea salvaging, The crest of the wave (1988), The gold of Brother Jonathan (about his recovery of gold from a Civil-war era sidepaddle steamer which sunk off northern California.


SIO. 2000. In memoriam. SIO Log, 37(38), Sept. 29

Williams, Jack. 2000. Willard Bascom, 83; maverick oceanographer, deep-sea explorer. San Diego Tribune, Sep. 21(?), 2000.

Additional information from SCCWRP staff recollections





We are sad to report the death of Willard N. Bascom, our second director, who led the Southern California Coastal Water Research Project from 1973 to 1984. He died on September 20, 2000 at his home as a result of infections resulting from multiple fractures sustained in a car accident in June 2000.

"Willard Bascom had a momentous impact on my life and career. His passing hasn't sunk in yet. Last year he invited me to La Jolla to help sort out his films for transfer to video tape. My colleagues must see them. I deeply regret not responding to the opportunity. He filmed the Santa Barbara Oil Spill (1969), documented several nuclear tests in the Pacific (including a follow up showing resurgence of coral growth), and produced several award-winning ocean engineering films at Cannes Industrial Film festivals. He was a visual person, trying to instill in us the need to present ideas simply and clearly so that non-scientists could understand and decision-makers decide.  We were still fresh out of graduate school but Ph.D. be damned. You did not work for Willard. You were his student. His goal was to culture you toward new vistas. If you did not recognize this you were left behind. It took me a while.  He was adamant about writing and writing well. I have failed to keep to his insistence to write 700 words a day (or was it 1700?). He wore down red pencils, marking up my disastrous first articles for the SCCWRP annual reports. Many nights and drafts later I barely passed muster.  He challenged me to take several views of a problem. He wanted you to barge into his office early in the morning and insist that he listen to your new idea or take. Regulations and laboratory science were only partial truths. The real truth was in the ocean. I began feeling comfortable with challenging dogma, status quo, blind adherence and conventional wisdom.  Physics, chemistry, biology and engineering were inseparable parts of a whole. He supported and rewarded integration at the highest levels and used his influence to help us find the funding to keep it up.  He expected and rewarded higher achievement. He would give me a rough time in private, then proudly praise me in public. One evening in Washington, he took me to the Explorers Club and graciously introduced this young and bedazzled scientist to a few of the Captains of Discovery, and the memorabilia of all of them. He felt strongly that SCCWRP and its science and support staff was special and unique. He took Bonnie and me to Europe and presented me and colleagues as "pioneers" in applied marine science. When I left SCCWRP, very reluctantly, he told me he expected me to become head of NOAA. Another failure. When I left, at the ripe young age of thirty-something, I felt I was graduating all over again.  He taught not by telling but by doing. He was suspicious that none of us had any idea about the region-wide picture of the health of the of the whole coast. He could not stand not knowing what was going on between the small "puddles" of data around the outfalls, and made us equally uncomfortable with the thought. One day he called Jack Word and me into his office, unrolled a map of the entire Bight, forced us then and there to start mapping the biology of the sea floor, and then supported our first region wide surveys.  He wanted all of us to conceive and consider the practical consequences of alternatives. Criticism to the contrary, he truly was concerned about the health of both the oceans and the land and felt that we had to continuously avoid the trap of small scales and watch out for the "big one" that could bite us while we pondered minutiae. He daily, but indirectly, made us pay attention to the teachings of life-friend and philosopher John Isaacs: beware of thinking small. However he was not above challenging even this giant of the oceans. He reminded us that we had no assurance that we would be employed Monday morning: I think he felt SCCWRP's two-to-three year charter renewal process was an asset to hone our senses and make our expectations practical. He wanted you to be an explorer and gave you the courage to do so. Since the real answers were in the water he made sure we had no lack of time on and in it. He gave us the best of professional field support. But you had to know when and where you were and he would embarrass you if you didn't. He demanded navigational accuracy and quality control. He and Rhoda were delightful and the most gracious of hosts. They constantly introduced us to famous professors, engineers, explorers, scientists, artists and authors. He wanted us in the company of visionaries.  I have not yet missed Willard. I am still trying to meet his expectations. Many of us who intimately shared his life have been sharing his legacy. We must continue to do so."

Alan Mearns
Student, National Oceanic and Atmospheric Administration

10   TSUNAMI   (tsoo-nah-mee)


What does "tsunami" mean?

Tsunami is a Japanese word with the English translation, "harbor wave." Represented by two characters, the top character, "tsu," means harbor, while the bottom character, "nami," means "wave." In the past, tsunamis were sometimes referred to as "tidal waves" by the general public, and as "seismic sea waves" by the scientific community. The term "tidal wave" is a misnomer; although a tsunami's impact upon a coastline is dependent upon the tidal level at the time a tsunami strikes, tsunamis are unrelated to the tides. Tides result from the imbalanced, extraterrestrial, gravitational influences of the moon, sun, and planets. The term "seismic sea wave" is also misleading. "Seismic" implies an earthquake-related generation mechanism, but a tsunami can also be caused by a nonseismic event, such as a landslide or meteorite impact.

How do tsunamis differ from other water waves?

Tsunamis are unlike wind-generated waves, which many of us may have observed on a local lake or at a coastal beach, in that they are characterized as shallow-water waves, with long periods and wave lengths. The wind-generated swell one sees at a California beach, for example, spawned by a storm out in the Pacific and rhythmically rolling in, one wave after another, might have a period of about 10 seconds and a wave length of 150 m. A tsunami, on the other hand, can have a wavelength in excess of 100 km and period on the order of one hour.

As a result of their long wave lengths, tsunamis behave as shallow-water waves. A wave becomes a shallow-water wave when the ratio between the water depth and its wave length gets very small. Shallow-water waves move at a speed that is equal to the square root of the product of the acceleration of gravity (9.8 m/s/s) and the water depth - let's see what this implies: In the Pacific Ocean, where the typical water depth is about 4000 m, a tsunami travels at about 200 m/s, or over 700 km/hr. Because the rate at which a wave loses its energy is inversely related to its wave length, tsunamis not only propagate at high speeds, they can also travel great, transoceanic distances with limited energy losses.

  This animation shows the propagation of the earthquake-generated 1960 Chilean tsunami across the Pacific. Note the vastness of the area across which the tsunami travels - Japan, which is over 17,000 km away from the tsunami's source off the coast of Chile, lost 200 lives to this tsunami. Also note how the wave crests bend as the tsunami travels - this is called refraction. Wave refraction is caused by segments of the wave moving at different speeds as the water depth along the crest varies.

What happens to a tsunami as it approaches land?

As a tsunami leaves the deep water of the open ocean and travels into the shallower water near the coast, it transforms. If you read the "How do tsunamis differ from other water waves?" section, you discovered that a tsunami travels at a speed that is related to the water depth - hence, as the water depth decreases, the tsunami slows. The tsunami's energy flux, which is dependent on both its wave speed and wave height, remains nearly constant. Consequently, as the tsunami's speed diminishes as it travels into shallower water, its height grows. Because of this shoaling effect, a tsunami, imperceptible at sea, may grow to be several meters or more in height near the coast. When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide, a series of breaking waves, or even a bore.

Tsunamis rarely transform into the great, towering breaking waves many of us imagine. In video footage taken in Japan during the 1983 Sea of Japan tsunami, we see the tsunami attack as a very fast-rising flood.  The bystanders on the sea wall who can barely outrun the on-rushing water.

Sometimes a tsunami may break far offshore, out in deeper water than the wind-generated swell typically breaks.

As a tsunami propagates from open water into an abruptly shallower bay or river, it may form into a bore. A bore is a step-like wave with a steep breaking face connecting the undisturbed water in front of the bore with the deeper water behind it.

What happens when a tsunami encounters land?

As a tsunami approaches shore, we've learned in the "What happens to a tsunami as it approaches land?" section that it begins to slow and grow in height. Just like other water waves, tsunamis begin to lose energy as they rush onshore - part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and turbulence. Despite these losses, tsunamis still reach the coast with tremendous amounts of energy. Tsunamis have great erosional potential, stripping beaches of sand that may have taken years to accumulate and undermining trees and other coastal vegetation. Capable of inundating, or flooding, hundreds of meters inland past the typical high-water level, the fast-moving water associated with the inundating tsunami can crush homes and other coastal structures. Tsunamis may reach a maximum vertical height onshore above sea level, often called a runup height, of 10, 20, and even 30 meters.

During the 1993 Hokkaido tsunami, the village of Aonae, located at the southern tip of Okushiri Island, Japan, was devastated by waves that swept across the exposed peninsula.


                            1957 Aleutian Tsunami

On March 9, 1957, at 14:22 GMT, an earthquake occurred south of the Andreanof Islands, in the Aleutian Islands of Alaska. A Pacific-wide tsunami was triggered by the earthquake, which had a surface-wave magnitude of 8.3, an epicenter of 51.5° N, 175.7° W, and a focal depth of 33 km. Even though no lives were lost, the Hawaiian Islands suffered the greatest with damage costs approximately $5 million (1957 dollars).

First photo in a series of three sequential photos show the arrival of a major wave at Laie Point on the Island of Oahu, Hawaii about 3,600 km from the source. The Island of Kauai, Hawaii, was hit twice as hard by this tsunami than by the Aleutian Islands tsunami in 1946. Houses were washed out and destroyed at Wainiha and Kalihiwai. At Haena, the waves reached heights of 16 m. In addition to that bridges were destroyed and sections of highways were flooded. At Hilo, Hawaii, the run-up was reached 3.9 m and damaged buildings. In Hilo Bay, Cocoanut Island was covered by 1 m of water and the bridge connecting it to shore was destroyed.

Second photo in a series of three sequential photos show the arrival of a major wave at Laie Point on the Island of Oahu, Hawaii. Although the northwest side of the Hawaiian Islands received high levels of water, the rest of the islands only received elevated water levels on average of 2 to 3 m. Both the 1946 and 1957 tsunamis occurred in the same general location (the Aleutian Islands). Even though the 1957 earthquake released more energy than the earthquake of 1946. The tsunami generated by this 1957 event caused less damage than the tsunami of 1946. This uncertainty of the potential destructive power of a tsunami forces Pacific Tsunami Warning System to issue warnings even when a tsunami may have little or no effect.

             1964 Prince William Sound Tsunami

On March 28, 1964, at 03:28 GMT, an earthquake occurred in Prince William Sound of Alaska triggering a Pacific-wide tsunami. The earthquake had a surface-wave magnitude of 8.4, an epicenter of 61.1° N, 147.5° W, and a depth of 23 km. The earthquake, local tsunamis due to landslides, and the regional tsunami were responsible for taking the lives of more than 122 people and causing over $106 million in damage.  The Surge wave left a 2 x 12 in. (5.2 x 31 cm) plank in a truck tire at Whittier, Alaska. Whittier incurred $10 million in property damage. One of the waves, probably the same one that caused the major damage in Whittier, reached a height of 31.7 m above low tide. At Whittier the waves destroyed two saw mills; the Union Oil Company tank farm, wharf and buildings; the Alaska Railroad depot; numerous frame dwellings; and the railroad ramp handling towers at the army pier. They also caused great damage to the small boat harbor. The tsunami killed thirteen people at Whittier, then a community of 70 people.  The greatest amount of damage suffered by any location was Alaska. In Alaska the death toll was 106 and there was $84 million in damage. Among Alaskan areas the run-up measurements varied from 24.2 m at Blackstone Bay, 27.4 m at Chenega, 9.1 m at Valdez, and 6.1 m at Kodiak. Outside Alaska it took 5.4 hrs for the first wave to arrive at Hilo, Hawaii, where the run-up was measured at 3.0 m. Another city outside Alaska that received measurable run-up was Crescent City, CA, where a 4.3 m run-up was recorded 4.1 hrs after the tsunami was triggered. Even though the regional tsunami was very destructive the local tsunamis also caused significant damage. The local tsunamis were generated by landslides, which were triggered by the earthquake. At the Valdez Inlet a large landslide was triggered by the earthquake generated a tsunami that had a run-up measured at 67.0 m in the inlet. In areas where local tsunamis were generated by landslides nearby cities were given no warning of the oncoming waves. The inability to properly warn the Alaska region prompted the creation of the Alaska Tsunami Warning Center. The warning center can quickly warn towns of any threat of local tsunamis.

                            1975 Hawaiian Tsunami

 On November 29, 1975, at 14:48 GMT, an earthquake occurred off the coast of the Island of Hawaii. A locally felt tsunami was triggered by the earthquake, which had a surface-wave magnitude of 7.2, an epicenter of 19.3° N, 155.0° W, and a focal depth of 8 km. The greatest lost was at Halape, a beach park at the base of a large cliff, on the Island of Hawaii.

At Halape, of the 32 campers 19 suffered injuries and 2 died. It was the sounds of the falling rocks from the cliff and the trembling that caused the campers to awake and a few moved to a coconut grove that was closer to the ocean. The campers were awaken by a second quake that sent large boulders down the cliff and forced the rest of the campers to flee toward the sea. However, these campers were forced back to cliffs when the campers at the coconut grove fleeing the rising ocean with cries of tsunami. The first wave that alarmed the campers was only 1.5 m. The second wave, however, was 7.9 m carried campers into a ditch near the base of cliff where they remained until the ordeal ended. Two of the campers were not so lucky and died. The coconut grove that a few campers took shelter in received permanent subsidence between 3.0 and 3.5 meters.

The largest recorded run-up was 14.3 m at Keauhou Landing, Hawaii Island. Also on the Island of Hawaii in the small bay of Punaluu the run-up reached 7.6 m. At Punaluu houses were swept off their foundations and properties were damaged. By the time local authorities could sound the coastal sirens the first wave had already arrived. As in the 1964 in Alaska the best warning to the possible danger of a local tsunami is the trembling from the earthquake that triggers it.


In the case of earthquake-generated tsunamis, the water column is disturbed by the uplift or subsidence of the sea floor. Submarine landslides, which often accompany large earthquakes, as well as collapses of volcanic edifices, can also disturb the overlying water column as sediment and rock slump downslope and are redistributed across the sea floor. Similarly, a violent submarine volcanic eruption can create an impulsive force that uplifts the water column and generates a tsunami. Conversely, supermarine landslides and cosmic-body impacts disturb the water from above, as momentum from falling debris is transferred to the water into which the debris falls. Generally speaking, tsunamis generated from these mechanisms, unlike the Pacific-wide tsunamis caused by some earthquakes, dissipate quickly and rarely affect coastlines distant from the source area.   Lituya Bay, Alaska, after a huge, landslide-generated tsunami occurred on July 9, 1958. The earthquake-induced rockslide, shown in upper right-hand corner of this image, generated a 525 m splash-up immediately across the bay, and razed trees along the bay and across LaChausse Spit before leaving the bay and dissipating in the open waters of the Gulf of Alaska.

In June and October 1994 two major undersea earthquakes occurred, the first near Indonesia and the second near Japan. Both generated tsunamis, or seismic sea waves. In both cases reports of water running up onto land to heights of three to five metres were common (1 m is about 3.3 ft). In Indonesia many villages near river inlets were destroyed, and at least 200 people lost their lives. Tsunamis have been a recurring natural hazard throughout history. The Minoan civilization on Crete in the Mediterranean Sea was shaken by the combined effects of a volcanic eruption and a tsunami in the 2nd millennium BC, and Lisbon was devastated by a tsunami in 1755.

The Tsunami Warning System:An international effort to save lives and protect property

Overview of the Tsunami Warning System

The Tsunami Warning System (TWS) in the Pacific, comprised of 26 participating international Member States, has the functions of monitoring seismological and tidal stations throughout the Pacific Basin to evaluate potentially tsunamigenic earthquakes and disseminating tsunami warning information. The Pacific Tsunami Warning Center (PTWC) is the operational center of the Pacific TWS. Located near Honolulu, Hawaii, PTWC provides tsunami warning information to national authorities in the Pacific Basin.

Tsunami Warning Centers

As part of an international cooperative effort to save lives and protect property, the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service operates two tsunami warning centers. The Alaska Tsunami Warning Center (ATWC) in Palmer, Alaska, serves as the regional Tsunami Warning Center for Alaska, British Columbia, Washington, Oregon, and California.

The Pacific Tsunami Warning Center in Ewa Beach, Hawaii, serves as the regional Tsunami Warning Center for Hawaii and as a national/international warning center for tsunamis that pose a Pacific-wide threat. This international warning effort became a formal arrangement in 1965 when PTWC assumed the international warning responsibilities of the Pacific Tsunami Warning System (PTWS). The PTWS is composed of 26 international Member States that are organized as the International Coordination Group for the Tsunami Warning System in the Pacific.

Tsunami Watch and Warning Determination

The objective of the PTWS is to detect, locate, and determine the magnitude of potentially tsunamigenic earthquakes occurring in the Pacific Basin or its immediate margins. Earthquake information is provided by seismic stations operated by PTWC, ATWC, the U.S. Geological Survey's National Earthquake Information Center and international sources. If the location and magnitude of an earthquake meet the known criteria for generation of a tsunami, a tsunami warning is issued to warn of an imminent tsunami hazard. The warning includes predicted tsunami arrival times at selected coastal communities within the geographic area defined by the maximum distance the tsunami could travel in a few hours. A tsunami watch with additional predicted tsunami arrival times is issued for a geographic area defined by the distance the tsunami could travel in a subsequent time period.

If a significant tsunami is detected by sea-level monitoring instrumentation, the tsunami warning is extended to the entire Pacific Basin. Sea-level (or tidal) information is provided by NOAA's National Ocean Service, PTWC, ATWC, university monitoring networks and other participating nations of the PTWS. The International Tsunami Information Center, part of the Intergovernmental Oceanographic Commission, monitors and evaluates the performance and effectiveness of the Pacific Tsunami Warning System. This effort encourages the most effective data collection, data analysis, tsunami impact assessment and warning dissemination to all TWS participants.

Tsunami Warning Dissemination

Tsunami watch, warning, and information bulletins are disseminated to appropriate emergency officials and the general public by a variety of communication methods.

   * Tsunami watch, warning and information bulletins issued by PTWC and ATWC are disseminated to local, state, national and international users as well as the media. These users, in turn, disseminate the tsunami information to the public, generally over commercial radio and  television channels.

   * The NOAA Weather Radio System, based on a large number of VHF transmitter sites, provides direct broadcast of tsunami information to the public.

   * The US Coast Guard also broadcasts urgent marine warnings and related tsunami information to coastal users equipped with medium frequency (MF) and very high frequency (VHF) marine radios.

   * Local authorities and emergency managers are responsible for formulating and executing evacuation plans for areas under a tsunami warning. The public should stay-tuned to the local media for evacuation  orders should a tsunami warning be issued. And, the public should NOT RETURN to low-lying areas until the tsunami threat has passed and the "all clear" is announced by the local authorities.

Marine Science Reading Program 3                       Name____________________________________________pd_____

8. A Wave is Born

___1. According to "A Wave Is Born: How Winds Power and Shape the Surf," the main energy source of waves is:    a. earthquakes.    b. wind.   c. volcanoes.    d. landslides.

___2. As noted in "A Wave Is Born: How Winds Power and Shape the Surf," if the crests of two sets of swells intersect, they will combine into one set of gigantic swells called: 

       a. killer waves.   b. spindrifts.   c. rogue waves.  d. whitecaps.

 ___3. As reported in "A Wave Is Born: How Winds Power and Shape the Surf," most swells do not pass close to land.      a. true       b. false

4. What is the main idea of this article?



......1.  Waves may form from the friction of the wind on the surface but not from air pressure changes

......2.  The size of the waves is dependent upon wind speed, length of time the wind blows, and the distance over which the wind blows

.....3.  While a wave may move past a point, the water making up the wave will show no net movement

.....4.  Water particles in a wave tend to move in circles

......5.  Waves seldom travel more than a few miles

.......6.  Waves "break" because the bottom causes the water particles  to move past the wave

.......7.  Tides are very different from waves

......8.  The much smaller size of the moon makes it have less of an influence on tides than the sun

......9.  At any one time two high tides occur because of the difference in centrifugal force and gravitational attraction

......10.  Earthquakes and similar occurrences can cause waves

.......11.  Waves are ecologically important

.......12.  Waves may keep the upper portion of the intertidal area wet

.......13.  Tides can be predicted from knowledge of the positions and phases of the moon and sun

......14. The height and time of tides is the same from month to month

.......15.  Natural disasters can have an influence on waves

.......16.  Wave action may influence the types of organisms found on a beach

.......17.  Organisms in the intertidal zone would be expected to show special adaptations due to their physical environment

.......18.  As one proceeds up the beach one might expect to see a change in the species composition present

.......19.  The mechanisms controlling tidal action are complex and interrelated

.......20.  While waves may travel thousands of miles, the water particles with it may even travel farther

......21.  All waves are basically similar

......22.  Wave action has little influence on those organisms in the wave zone

......23.  Tidal action places a stress on the organisms which live in the tidal zone due to alternate drying and wetting.



1.What does tsunami mean?

2.  How is a tsunami  (A) the same as   (B) different than regular ocean waves?

3.  What happens to a tsunami as it travels into shallow water?

4.  How would a tsunami appear to an onlooker in (A) the open ocean (B) along the shore?

5.  What is meant by the term run-up?

6.  How does the run-up affect the shoreline?

7.  During the Prince William Sound Tsunami in 1964, what was the largest wave that hit?  (in feet)

8.  How long did it take for this tsunami in 1964 to reach  (A) Hawaii  (B) Crescent City, CA?

9.  What caused the 67m run-up at Valdez Inlet in 1964?

10.  How high was the splash-up at Lituya Bay  on July 9, 1958 and what caused it?

11.  Where are the two tsunami warning centers and what locations do they cover?

12. What is the objective of PTWS?

13.  How are Tsunami warnings disseminated?

14. How would this system still not be able to warn people of a tsunami in time?