What is a Tsunami?
Tsunamis are large, often destructive sea waves, which are usually caused by earthquakes below the ocean, volcanic eruptions, or underwater landslides.
Tsunami waves have a much longer wavelength than normal waves, reaching hundreds of kilometers in length, while the height (amplitude) of the waves remains just above normal, slowly building until it reaches the shallow waters along the coast. Just before the large wave hits the coast, the water drastically recedes in what is called a drawback. The giant wall of water then travels at high speeds toward land, crashing and destroying everything in its path. The tsunami then recedes back to the ocean, pulling with it much of the debris of the structures it has destroyed.
The slow build-up of the waves is one factor that makes tsunamis difficult to predict. Earthquakes, considered the main cause of tsunamis, are also not absolute predictors of a tsunami, because some large earthquakes do not result in a tsunami, and some small earthquakes do. Most tsunamis occur around the Pacific Ocean because of the high level of seismic activity in this Pacific Ring of Fire.
Destructive tsunamis have occurred in all of the world's oceans and seas. In the second half of the 20th Century, Pacific-wide, destructive tsunamis occurred in 1946, 1952, 1957, 1960, 1964, 2004, 2006, 2007, 2008, 2009, 2011 and 2013
Many more tsunamis occurred in inland seas around the periphery of the Pacific Ocean, which were extremely destructive locally and claimed thousands of lives. Such localized tsunamis occurred in 1975, 1983, 1985, 1992, 1993, 1995, 1998, 1999 and 2001.
History of Tsunami
March 11, 2011: Pacific coast of Japan Earthquake and Tsunami
On March 11, 2011, Japan was hit by an earthquake measuring 9 Mw. The most powerful earthquake to have hit the country, the Great East Japan Earthquake caused untold damages to life, property, and infrastructure. While the Japanese island of Honshu is believed to have shifted about eight feet to the east, the entire planet Earth is estimated to have shifted about four inches on its axis as a result of the earthquake. Know More
The 2004 Indian Ocean Earthquake and Tsunami
History has recorded the 9.0 magnitude earthquake on 26 December 2004 which rose from the Indian Ocean, as the most destructive and powerful earthquakes ever.
The earthquake, an undersea megathrust earthquake, occurred at 00:58:53 UTC on 26 December 2004, with the west coast of Sumatra, Indonesia as the epicentre. Also known as the Sumatra–Andaman Islands Earthquake, it is known as the third largest earthquake ever recorded at a magnitude ranging between 9.1–9.3, also the longest between 8.3 and 10 minutes, and the single-worst tsunami in history.
The earthquake, known to be roughly equivalent to 700 milion Hiroshima bombs, accounted for tens of thousands of lives and unsurmountable destruction of land and property. The earthquake triggered the Tsunami within minutes.
A total of 227,898 people were recorded dead, according to the U.S. Geological Survey, with Indonesia as the worst affected area with the death toll mounting to 170,000. Other majorly affected areas were Sri Lanka, India and Thailand. The tsunami and the earthquake affected Southeast Asian countries and beyond, also include the Maldives, Somalia, Myanmar, Malaysia, Seychelles, and also tourists from Australia and Europe were victims of this tragedy.
The 27 March, 1960, Great Alaska Earthquake and Tsunami
This earthquake is also known as the Good Friday earthquake as it happened on the day of Good Friday at 5:36 P.M. AST (03:36 3/27 UTC), and had a moment magnitude of 9.2 and was 8.4 on Richter scale. It was the most powerful earthquake ever recorded in the U.S. and North America. The epicenter of the earthquake was 61.05, -147.48, 20 km north of Prince William Sound, 125 km (78 miles) east of Anchorage and 64 km (40 miles) west of Valdez.
The powerful earthquake caused some parts of Alaska to be liquefied, causing great damage to property and leading to landslides. The earthquake caused areas to be lifted by 15 m (50 feet) in certain areas, while many other areas subsided greatly. In addition to many local tsunamis generated within the Prince William Sound, vertical crustal displacements averaging 1.8 m (6 ft.) over an area of about 300,000 square kilometers (115,000 square miles) extending in the Gulf of Alaska's continental shelf, generated a Pacific-wide tsunamis. Its waves were very destructive in southeastern Alaska, in Vancouver Island (British Columbia), and in the U.S. States of Washington, California and Hawaii. The tsunami killed more than 120 people and caused more than $106 million in damages, making it the costliest ever to strike the Western United States and Canada. Five of Alaska's seven largest communities were devastated by the combination of earthquake and tsunami wave damage. Alaska's fishing industry and most seaport facilities were virtually destroyed. Tsunami waves at Kodiak Island washed away a total of 158 houses and buildings within two blocks of the waterfront. Fishing boats were carried hundreds of meters inland. The 1964 tsunami waves caused also extensive damage in Vancouver Island (British Columbia), and in the states of Washington, California and Hawaii, in the U.S.. The waves affected the entire California coastline, but were particularly high from Crescent City to Monterey ranging from 2.1 - 6.3 meters (7-21 feet). California was hit hardest, where waves reaching as much as 6 meters (20-21 feet) destroyed half of the waterfront business district. At Santa Cruz Harbor, the tsunami waves reached as high as 3.3 meters (11 feet) causing some damage. There was extensive damage in San Francisco Bay, the marinas in Marin County and at the Noyo, Los Angeles and Long Beach harbors. Estimated losses in California were between $1,500,000 and $2,375,000 (1964 dollars), while at Crescent City tsunami damage was estimated at $7,414,000.
The 22 May, 1960, Chilean Earthquake and Tsunami
The largest earthquake ( magnitude 9.5 on moment magnitude scale) of the 20th century occurred on May 22, 1960, off the coast of south central Chile. It generated a Pacific-wide tsunami, which was destructive locally in Chile and throughout the Pacific Ocean. The tsunami killed an estimated 2,300 people in Chile. There was tremendous loss of life and property in the Hawaiian Islands, in Japan and elsewhere in the Pacific. Destructive waves in Hilo, Hawaii, destroyed the waterfront and killed 61 people. Total damage was estimated at more than $500 million (1960 dollars).
The 9 March, 1957, Aleutian Earthquake and Tsunami
On March 9, 1957, an 8.3 magnitude earthquake occurred south of the Andreanof Islands, in the Aleutian Islands of Alaska. It happened in the same general area as that of April 1, 1946, and generated a Pacific-wide tsunami. Although no lives were lost, there was massive destruction of property in the Hawaiian Islands, with damage estimated at approximately $5 million. The waves were particularly high on the north shore of the island of Kauai where they reached a maximum height of 16 meters, flooding the highway and destroying houses and bridges. This was twice the height of the 1946 tsunami. At Hilo, Hawaii, the tsunami run up reached 3.9 m and there was damage to numerous buildings along the waterfront. Within Hilo Bay, Coconut Island was covered by 1 m of water and the bridge connecting it to the shore, as in 1952, was again destroyed.
The 4 November, 1952, Kamchatka Earthquake and Tsunami
A strong earthquake (magnitude 8.2) off the coast of Kamchatka Peninsula generated a great destructive Pacific-wide tsunami. Its waves struck the Kamchatka Peninsula, the Kuril Islands and other areas of Russia's Far East, causing considerable damage and loss of life. The tsunami was widely observed and recorded in Japan, but there was no loss of life or damage there. There was considerable damage in the Hawaiian Islands and some damage in Peru and Chile. The tsunami was recorded or observed throughout the islands of the Pacific. In New Zealand waves reached height of 1m, and in Alaska, in the Aleutian Islands and in California waves of up to 1.4 meters were observed. The largest waves outside the generating area were observed in the Hawaiian Islands. Fortunately, no human lives were lost in Hawaii from this tsunami, but damages were extensive, ranging from $800,000- $1,000,000. In the Hawaiian island chain, the tsunami waves destroyed boats and piers, knocked down telephone lines, and caused extensive beach erosion.
The north shore of the Island of Oahu experienced higher waves of up to 4.5 meters. On the south shore of the island, tsunamis waves were powerful enough to throw a cement barge in the Honolulu Harbor into a freighter. The island of Hawaii experienced drag up to 6.1 meters. In Hilo, a small bridge connecting Coconut Island to the shore was destroyed by one of the tsunami waves lifting it off its foundation, then smashing it down. The effects of the tsunami in the generating area in Kamchatka, varied significantly. From Kamchatka Peninsula to Kronotsky Peninsula, the wave heights ranged from 0 to 5 meters. From Kronotsky Peninsula to Cape Shipursky the heights ranged from 4-13 meters. The highest wave of 13 meters was the third as observed at Olga Bay, where it caused considerable damage. Travel time of the first tsunami wave to Olga Bay was approximately 42 minutes after the earthquake. From Cape Shipursky to Cape Povorotny, the tsunami waves ranged from 1 to 10 meters and caused considerable loss of life and damage. At Avachinskaia Bay the tsunami height was 1.2 meters and its travel time was about 30 minutes. From Cape Povorotny to Cape Lopatkka the waves ranged from 5 to 15 meters. At Khodutka Bay a cutter was thrown 500 meters back from shore. On the West coast of Kamchatka Peninsula, the maximum tsunami run up at Ozernoe was 5 meters. At Alaid Island of the Kuril Island group, run up was 1.5 meters, while at Shumshu Island it ranged from 7-9 meters. At Paramushir Island, the waves ranged from 4-18.4 meters. At Severo - Kurilsk on Paramushir Island, the second wave was the highest reaching maximum run up of 15 meters. It destroyed most of the town and caused considerable loss of life. At Onekotan Island tsunami run up was 9 meters, while at Shiashkoton Island it was 8 meters and at Iturup Island 2.5 meters. Waves of up to 2 meters were observed at the Komandorsk Islands and at Okhotsk. At Sakhalin - Korsakov a 1-meter tsunami wave was observed.
Where And How Frequently Are Tsunamis Generated
Tsunami waves are generated in large water bodies like oceans and seas, as these waves consist of large volumes of water disturbed by natural or artificial impacts. However the frequency and location of a tsunami depends on the source cause as various affecting factors may have varying availabilities depending on the location. Factors like submarine volcanic eruption, landslides, and earthquakes have major impacts on generating a tsunami, so these factors also decide the frequency and location of a tsunami. The Pacific Ocean occupies more than one third of the earth's surface and is bounded by areas called the "ring of fire", which includes mountain chains, underwater trenches, and islands. This area is on the highest earthquake-prone zone, which include the coastal zones of Kamchatka, Japan, the Kuril Islands, and South America. All the regions of world have differing frequencies of tsunami generation with varying intensities of destruction. Destructive tsunamis have occurred in Nicaragua (1992), Indonesia (1992, 1994, 1996), Japan (1993), Philippines (1994), Mexico (1995), Peru (1996, 2001), Papua-New Guinea (1998), Turkey (1999), and Vanuatu (1999) in the last decade. The 2004 Indian Ocean earthquake provoked world's deadliest tsunami which killed about 250000 people.
How Do Volcanic Eruptions Generate Tsunamis
Primarily a tsunami is generated when any natural or artificial force disturbs large volume of water particularly or largely in vertical direction through sea floor. These water waves have very high frequency and very small wavelengths in onshore areas, which causes mass destruction. A submarine or offshore volcanic eruption can produce high magnitude lifts on seafloors, which pushes large water columns upwards to generate tsunami. Submarine volcanoes can be detected by the presence of high rock content and steam above water surface. These submarine volcanoes form high slope pillars over their craters as compared to their on surface counterparts, which is due to the rapid cooling effect of water and buoyancy. The process of tsunami generation in such cases can be understood through the concept of phreatomagmatic eruption. Such an eruption is an explosive interaction between water and magma, which produces fine grained tephra with the emission of magmatic gases and steam. Another considerable fact is the failure of a submarine volcano's slope which results in sudden disturbance of water resulting in tsunami waves.
What Are The Factors Of Destruction From Tsunamis
Tsunami causes destruction primarily due to the ultrahigh impacts on structures and other assets. The basic factors of destruction include, wave impact, erosion , and inundation. The drag applied by tsunami waves on structures can move them or overturn them. The presence of high salt concentration in tsunami waves causes corrosion of metallic bodies, which decreases their life ultimately leading to failure. As tsunami causes large scale structural destruction, the floating debris so formed poses serious threat to other structures, or floating vessels. Besides the primary destruction, secondary destruction may include fire hazards, and water pollution. Fire hazards may be caused by severed electricity transmission lines, while damaged oil tankers may contribute a serious threat to water quality.
Why Aren't Tsunamis Seen At Sea Or From The Air
It is a well known fact that tsunami waves have very low amplitudes and large wavelengths while offshore due to larger volume of surrounding water. A typical offshore tsunami wave can have an amplitude A of 1 metre and a wavelength L of the order of 799.9 kilometres. So the energy associated with these offshore tsunami waves is also very low due to such lower frequencies, or smaller amplitudes. So these waves are difficult to experience and its virtually impossible to see them at sea or from air.
How Do Earthquakes Generate Tsunamis
Tsunamis can be generated by tectonic earthquakes, which occur due to earth's crustal deformation, and abrupt dynamics of tectonic plates. A geological theory of plate tectonics has been developed to explain the large scale dynamics of the Earth's lithosphere, which sometimes results in tectonic earthquakes. It proposes that Earth's lithosphere is broken up into seven major and many minor plates, called tectonic plates. Tectonic plates or lithospheric plates are large, irregularly shaped slabs of solid rock, consisting of oceanic and continental lithosphere. Plate boundaries at the edge of tectonic plates undergo large deformations due to interaction between two plates, which causes earthquakes. Large volumes of water above the deformed area gets disturbed from its stable equlibrium due to the disturbances caused by these earthquakes. The largely disturbed mass of water strives to gain its original stable equilibrium configuration to minimize system's internal energy. This system includes water mass and earth's surface beneath it, which attracts water to its minimum potential energy position through gravity. This process creates gigantic and massively destructive water waves known as tsunami. Tectonic activities and Tectonic motion have been estimated using various space geodetic technologies such as Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Global Positioning System (GPS).
Why Are Locally Generated Tsunamis So Dangerous
Locally generated tsunami may reach a nearby shore in less than ten minutes due to their high speeds. There is not sufficient time for the Pacific Tsunami Warning Center or for local authorities to issue a warning. For people living near the coast, the shaking of the ground is the only warning that a tsunami may be imminent.
Tsunami Impacts Near The Origin And At A Distant Shore
Tsunami waves are basically mechanical waves, and thus move through the phenomenon of compression and rarefaction. Their energy and momentum is defined by mass (volume), wavelength, frequency, and amplitude. Near their origin tsunami waves have very large wavelengths and thus smaller frequencies and amplitudes. This makes them less threatening when offshore and also its difficult to detect and experience tsunami waves offshore. Tsunami waves reach onshore areas in the form of a series of successive crests and troughs, which have a time period of about 10 to 45 minutes. Tsunami waves have lower speeds in shallow water and vice versa, which implies that tsunami waves traveling at greater depths reach onshore regions in lesser time. So the tsunami waves traveling ahead in shallow waters are continually pushed towards the shore by faster tsunami waves generated through the origin. This causes compression of the slower tsunami waves, which decreases their wavelength and increases their amplitude. This increases the height of these tsunami waves from 1 meter in deep sea to 30-35 meters near shore. These gigantic tsunami waves onshore are highly destructive with their great smashing force, and thus pose a serious threat to life and property.