The earthquake of December 25, 2004, was considered a major disaster but dismissed because it was half a world away. Earthquakes occurred in the middle east over the past few months and many people died or were left homeless. Tsunamis occur regularly around the hot rim of the Pacific Ocean. However, the tsunami that resulted from the volcanic explosion on the northwestern end of Sumatra brought out the best of the human race. Many countries came forward with assistance of technology, people, and money. Concerns are many. The World Health Organization (WHO) estimated there were more than half a million people injured and in need of medical care in six nations. Fears grew that diseases like cholera and malaria would break out among the five million displaced.

What is a tsunami?

A tsunami (pronounced tsoo-nah-mee) is a wave train, or series of waves, generated in a body of water by an impulsive disturbance that vertically displaces the water column. Earthquakes, landslides, volcanic eruptions, explosions, and even the impact of cosmic bodies, such as meteorites, can generate tsunamis. Tsunamis can savagely attack coastlines, causing devastating property damage and loss of life.

Word origin

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.

Tsunami explained

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.

Information from www.geophys.washington.edu

November 4, 1952 - off the coast of the Kamchatka Peninsula, Russia.
On November 4, 1952, at 16:52 GMT, an earthquake occurred off the coast of the Kamchatka Peninsula, Russia. A Pacific-wide tsunami was triggered by the earthquake, which had a surface-wave magnitude of 8.2, an epicenter of 52.8° N, 159.5° E, and a focal depth of 30 km. Six cows died and no human lives were lost in Hawaii where damage estimates ranged from $800,000- $1,000,000 (1952 dollars).

1960 - off the coast of Chile
The tsunami traveled across the Pacific Ocean to Japan, which is over 17,000 km away from the tsunami's source off the coast of Chile and 200 lives were lost. The wave crests bent as the tsunami traveled - 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.

March 28, 1964 - Prince William Sound of Alaska
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.

June 3, 1994 - off the southeastern coast of Java
At 1:18 a.m. Java time, June 3, 1994, a large earthquake occurred off the southeastern coast of Java near the east end of the Java Trench in the Indian Ocean. The earthquake, which had a surface-wave magnitude of 7.2 and a moment magnitude of 7.8, generated a devastating tsunami that took the lives of more than 200 East Java coastal residents.

An international tsunami survey team, composed of tsunami scientists and engineers from Indonesia, Italy, Japan, Thailand, and the United States, visited the impacted areas of Bali and Java from June 20 to June 25, 1994. The survey team observed the most severe tsunami damage along the southern coast of East Java. Significant earthquake-induced ground shaking was not experienced by the coastal residents interviewed in Bali and Java, suggesting that this tsunami may have generated by a tsunami earthquake.

November 15, 1994 - near Verde Island, Philippines
On November 15, 1994, at 03:15 (local time), an earthquake occurred near Verde Island, Philippines. The magnitude 7.1 earthquake had an epicenter of 13.5° N, 121.1° E, and a hypocenter of 15 km. The tsunami totally destroyed 1530 houses and killed 41 people.

February 21, 1996 - northern coastal region of Peru
On February 21, 1996, at 12:51 p.m. GMT (7:51 a.m. local time), a large earthquake struck approximately 130 Km off the northern coastal region of Peru (9.6S, 80.2W). The earthquake had a Harvard Mw estimate of 7.5 and USGS Mw estimate of 7.3. The earthquake created a tsunami that reached Peru centering on the city of Chimbote. Effects of the tsunami were observed from Pascasmayo, in the department of La Libertad, to the Port of Callao near Lima. The straight line distance between these two locations is approximately 590 Km. The tsunami was recorded by mid-Pacific tide gages, 60 cm at Easter Island, and 25 cm at Hilo, Hawaii. The aftershock pattern ranged from 120 to 180 Km offshore near the Peru-Chile trench and appeared to parallel the Peruvian coastline.

July 17, 1998 - north central coast of Papua New Guinea
On July 17, 1998 a Mw = 7.0 earthquake struck the north central coast of Papua New Guinea. Following the earthquake a large tsunami also struck the region. Initial reports claimed that the wave was between 7 and 10 meters and that up to 3000 persons were killed or missing. This seemed to be an unusually damaging tsunami given the size of the earthquake.

November 3, 2002 - Alaska along the Denali Fault
Away from populated areas, the Denali Fault experienced a 7.9 earthquake that was notable but not destructive in terms of human or monetary damage. The Alaska pipeline was built across the faultline shown in the USGS photos by Robert Kayen during the study of the quake site from November 5 through November 12.