I’m starting to write this post with my past experiences and my desire to the great treat so called “Tsunami”. Whole world knows what a tsunami is; but very few has got the big picture and the knowledge about it. So through this post, you will get to know everything about the tsunami.
Tsunami
A Tsunami is a series of ocean waves that sends surges of water onto land. The word ‘tsunami’ origins from Japanese language.
( tsu = harbor ) + ( nami = wave ) = a harbor wave
The reason for the Japanese name “harbor wave” is that sometimes a village’s fishermen would sail out, and encounter no unusual waves while out at sea fishing, and come back to land to find their village devastated by a huge wave.
Reason For Tsunami
Several reasons may cause for a tsunami. E.g.: Earthquake, landslide, volcano eruption, meteorology and also nuclear explosions.
Most tsunamis–about 80 percent–happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where tectonic shifts make volcanoes and earthquakes common.
These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly, it displaces the water above it and launches the rolling waves that will become a tsunami.
Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched, as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean.
A meteotsunami or meteorological tsunami is a tsunami-like sea wave of meteorological origin. Meteotsunamis are generated when rapid changes in barometric pressure cause the displacement of a body of water. In contrast to “ordinary” impulse-type tsunami sources, a traveling atmospheric disturbance normally interacts with the ocean over a limited period of time
Tsunamis race across the sea at up to 500 miles (805 kilometres) an hour—about as fast as a jet airplane. At that pace, they can cross the entire expanse of the Pacific Ocean in less than a day. And their long wavelengths mean they lose very little energy along the way.
Tsunami In Deep Ocean
While everyday wind waves have a wavelength (from crest to crest) of about 100 meters (330 ft) and a height of roughly 2 meters (6.6 ft), a tsunami in the deep ocean has a much larger wavelength of up to 200 kilometers (120 mi). Such a wave travels at well over 800 kilometers per hour (500 mph), but owing to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 meter (3.3 ft). This makes tsunamis difficult to detect over deep water, where ships are unable to feel their passage.
But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height. The tops of the waves move faster than their bottoms do, which causes them to rise precipitously.
When Hits The Land
A tsunami’s trough, the low point beneath the wave’s crest, often reaches shore first. When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. (“Drawback” – You might be able to walk to the deep water where you used to swim around. But DON’T) This retreating of sea water is an important warning sign of a tsunami, because the wave’s crest and its enormous volume of water typically hit shore five minutes or so later. Recognizing this occurrence can save lives.
A tsunami is usually composed of a series of waves, called a wave train, so its destructive force may be compounded as successive waves reach shore. People experiencing a tsunami should remember that the danger may not have passed with the first wave and should await official word that it is safe to return to vulnerable locations.
Some tsunamis do not appear on shore as massive breaking waves but instead resemble a quickly surging tide that inundates coastal areas.
Destruction
The effects of a tsunami on a coastline can range from unnoticeable to devastating. The effects of a tsunami depend on the characteristics of the seismic event that generated the tsunami, the distance from its point of origin, its size (magnitude) and, at last, the configuration of the bathymetry (that is the depth of water in oceans) along the coast that the tsunami is approaching. Small tsunamis, non-destructive and undetectable without specialized equipment, happen almost every day as a result of minor earthquake and other events. They are very often too far away from land or they are too small to have any effect when they hit the shore. When a small tsunami comes to the shoreline it is often seen as a strong and fast-moving tide.
Tsunamis have long periods and can overcome obstacles such as gulfs, bays and islands. These tsunamis make landfall usually in the form of suddenly decreasing and then rapidly increasing water levels (not unlike a tidal bore) a combination of several large waves or bore-type waves. Generally tsunamis arrive, not as giant breaking waves, but as a forceful rapid increase in water levels that results in violent flooding.
However, when tsunami waves become extremely large in height, they savagely attack coastlines, causing devastating property damage and loss of life. A small wave only 30 centimeters high in the deep ocean may grow into a monster wave 30m high as it sweeps over the shore. The effects can be further amplified where a bay, harbor, or lagoon funnels the waves as they move inland. Large tsunamis have been known to rise to over 100 feet!
The amount of energy and water contained in a huge tsunami can cause extreme destruction when it strikes land.
The initial wave of a huge tsunami is extremely tall; however, most damage is not sustained by this wave. Most of the damage is caused by the huge mass of water behind the initial wave front, as the height of the sea keeps rising fast and floods powerfully into the coastal area. It is the power behind the waves, the endless rushing water that causes devastation and loss of life. When the giant breaking waves of a tsunami batter the shoreline, they can destroy everything in their path.
Destruction is caused by two mechanisms: the smashing force of a wall of water traveling at high speed, and the destructive power of a large volume of water draining off the land and carrying all with it, even if the wave did not look large.
Objects and buildings are destroyed by the sheer weight of the water, often reduced to skeletal foundations and exposed bedrock. Large objects such as ships and boulders can be carried several miles inland before the tsunami subsides.
Tsunami waves destroy boats, buildings, bridges, cars, trees, telephone lines, power lines – and just about anything else in their way. Once the tsunami waves have knocked down infrastructure on the shore they may continue to travel for several miles inland, sweeping away more trees, buildings, cars and other man made equipment. Small islands hit by a tsunami are left unrecognizable.
The buildings infrastructure in these poorer nations are not well built and cannot withstand the impact of the tsunami. Whole areas and towns are a picture of destruction as the tsunami leaves at trail devastation and misery behind it.
Characteristics
A tsunami waves show much more differences when compares to the ordinary wind-generated waves. A tsunami wave can have a wavelength of up to 120 miles (200 kilometers) which is more than 30-40 meters of normal ocean waves and travels at speeds of around 500 miles per hour (800 kilometers per hour), which is similar to the speed of a jet airliner. Also a tsunami wave does not break like a regular ocean wave; which reasons for Regional and Distant tsunami.
Types
There are 3 types of tsunamis
- Local
- Regional
- Distant.
Local tsunamis can reach up 100km from the source of the tsunami so in this case the travel time for the tsunami is usually less than one hour.
Regional tsunami is a tsunami that can cause damage from 100 km – 1,000km from the source of the tsunami and can take between 1-3 hours to occur before destruction.
Finally the distant tsunami or the tele-tsunami and the ocean-wide tsunami travel in opposite directions theses tsunamis can be as far as 1,000 km away from the source of the tsunami these tsunamis can take over 3 hours to occur to the affected coasts or beaches.
Mega-Tsunami
A mega-tsunami is a very large wave created by a large, sudden displacement of material into a body of water.
Mega-tsunamis have quite different features from other, more usual types of tsunamis. Most tsunamis are caused by underwater tectonic activity (movement of the earth’s plates) and therefore occur along plate boundaries and as a result of earthquake and rise or fall in the sea floor, causing water to be displaced. Ordinary tsunamis have shallow waves out at sea, and the water piles up to a wave height of up to about 10 meters (33 feet) as the sea floor becomes shallow near land. By contrast, mega-tsunamis occur when a very large amount of material suddenly falls into water or anywhere near water (such as via a meteor impact), or are caused by volcanic activity. They can have extremely high initial wave heights of hundreds and possibly thousands of meters, far beyond any ordinary tsunami, as the water is “splashed” upwards and outwards by the impact or displacement. As a result, two heights are sometimes quoted for mega-tsunamis – the height of the wave itself (in water), and the height to which it surges when it reaches land, which depending upon the locale, can be several times larger.
Some highlights of the modern mega-tsunami happened in the history
- The tsunami with the highest run-up was the 1958 Lituya Bay mega-tsunami, which had a record height of 524 m (1,720 ft) at the entrance of Gilbert Inlet.
- On May 18,1980 Spirit Lake of Mount St. Helens collapsed, creating a massive landslide and a mega-tsunami which measured 260 m (850 ft) tall.
- On October 9, 1963, a landslide above Vajont Dam in Italy produced a 250 m (820 ft) surge that over-topped the newly built dam.
Drawback
All waves have a positive and negative peak; that is, a ridge and a trough. In the case of a propagating wave like a tsunami, either may be the first to arrive. If the first part to arrive at the shore is the ridge, a massive breaking wave or sudden flooding will be the first effect noticed on land. However, if the first part to arrive is a trough, a drawback will occur as the shoreline recedes dramatically, exposing normally submerged areas. The drawback can exceed hundreds of meters, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed.
A typical wave period for a damaging tsunami is about twelve minutes. Thus, the sea recedes in the drawback phase, with areas well below sea level exposed after three minutes. For the next six minutes, the wave trough builds into a ridge which may flood the coast, and destruction ensues. During the next six minutes, the wave changes from a ridge to a trough, and the flood waters recede in a second drawback. Victims and debris may be swept into the ocean. The process repeats with succeeding waves.
History
Some of the biggest, most destructive and deadliest tsunamis on record:
8,000 years ago: A volcano caused an avalanche in Sicily 8,000 years ago that crashed into the sea at 200 mph, triggering a devastating tsunami that spread across the entire Mediterranean Sea. There are no historical records of the event – only geological records – but scientists say the tsunami was taller than 10-story building.
Nov. 1, 1755: After a colossal earthquake destroyed Lisbon, Portugal and rocked much of Europe, people took refuge by boat. A tsunami ensued, as did great fires. Altogether, the event killed more than 60,000 people.
Aug. 27, 1883: Eruptions from the Krakatoa volcano fueled a tsunami that drowned 36,000 people in the Indonesian Islands of western Java and southern Sumatra. The strength of the waves pushed coral blocks as large as 600 tons onto the shore.
June 15, 1896: Waves as high as 100 feet (30 meters), spawned by an earthquake, swept the east coast of Japan.Around 27,000 people died.
April 1, 1946: The April Fools tsunami, triggered by an earthquake in Alaska, killed 159 people, mostly in Hawaii.
July 9, 1958: Regarded as the largest recorded in modern times, the tsunami in Lituya Bay, Alaska was caused by a landslide triggered by an 7.8 magnitude earthquake. Waves reached a height of 1,720 feet (524 meters) in the bay, but because the area is relatively isolated and in a unique geologic setting the tsunami did not cause much damage elsewhere. It sank a single boat, killing two fishermen.
May 22, 1960: The largest recorded earthquake, magnitude 8.6 in Chile, created a tsunami that hit the Chilean coast within 15 minutes. The surge, up to 75 feet (25 meters) high, killed an estimated 1,500 people in Chile and Hawaii.
Oct 9, 1963: The Vajont Dam was completed in 1961, 100 km north of Venice, Italy. At 262 meters (860 feet), it was one of the highest dams in the world. On 9 October 1963 a landslide of about 260 million cubic meters of forest, earth, and rock, fell into the reservoir at up to 110 km per hour (68 mph). The resulting displacement of water caused 50 million cubic meters of water to over top the dam in a 250-meter (820-foot) high mega-tsunami wave. The flooding destroyed the villages of Longarone, Pirago, Rivalta, Villanova and Faè, killing 1,450 people. Nearly 2,000 people perished in total.
March 27, 1964: The Alaskan Good Friday earthquake, magnitude between 8.4, spawned a 201-foot (67-meter) tsunami in the Valdez Inlet. It traveled at over 400 mph, killing more than 120 people. Ten of the deaths occurred in Crescent City, in northern California, which saw waves as high as 20 feet (6.3 meters).
Aug. 23, 1976: A tsunami in the southwest Philippines killed 8,000 on the heels of an earthquake.
May 18, 1980: In the course of a major eruption of Mount St. Helens, the upper 460 m (1400 ft) of the mountain failed, causing a major landslide. One lobe of the landslide surged onto the nearby Spirit Lake, creating a mega-tsunami 260 meters (853 feet) high
July 17, 1998: A magnitude 7.1 earthquake generated a tsunami in Papua New Guinea that quickly killed 2,200.
Dec. 26, 2004: The 2004 Indian Ocean earthquake (moment magnitude 9.1–9.3) triggered a series of tsunamis on 26 December 2004, killing approximately 227,898 people (167,540 in Indonesia alone), making it the deadliest tsunami and one of the deadliest natural disasters in recorded history. The earthquake was the third largest earthquake in recorded history. The initial surge was measured at a height of approximately 33 meters (108 ft), making it the largest earthquake-generated tsunami in recorded history. The tsunami killed people from the immediate vicinity of the quake in Indonesia, Thailand, and the north-west coast of Malaysia, to thousands of kilometers away in Bangladesh, India, Sri Lanka, the Maldives, and as far away as Somalia, Kenya, and Tanzania. This trans-Indian Ocean tsunami is an example of a tele-tsunami, which travels vast distances across the open ocean, and an ocean-wide tsunami. It became known as the “Boxing Day Tsunami” because it struck on Boxing Day (26 December).
(Unlike in the Pacific Ocean, there was no organized alert service covering the Indian Ocean. This was in part due to the absence of major tsunami events since 1883 (the Krakatoa eruption). In light of the 2004 Indian Ocean tsunami, UNESCO and other world bodies have called for an international tsunami monitoring system.)
Nov. 15, 2006: a magnitude 8.3 earthquake occurred off the coast near the Kuril Islands. In spite of the quake’s large 8.3 magnitude, a relatively small tsunami was generated. This tsunami was recorded or observed in Japan and at distant locations throughout the Pacific.
April 02, 2007: a magnitude 8.1 earthquake struck about 40 km (25 mi) south of Ghizo Island in the western Solomon Islands at 7:39 a.m., resulting in a tsunami that was up to 12 m (36 feet) high. The wave, which struck the coast of Solomon Islands (mainly Choiseul, Ghizo Island, Ranongga, and Simbo), triggered tsunami warnings and watches extending from Japan to New Zealand to Hawaii and eastern Australia. The tsunami killed 52 people and dozens were injured when waves inundated towns.
Feb. 27,2010: a 8.8 earthquake offshore of Chile caused a tsunami which caused serious damage and loss of life, it also caused minor effects in other Pacific nations.
March 11, 2011: off the Pacific coast of Japan, a 9.0 magnitude earthquake produced a tsunami 33 feet (10 m) high along Japan’s northeastern coast. The wave caused widespread devastation, with an official count of 18,550 people confirmed to be killed/missing. The highest tsunami which was recorded at Miyako, Iwate reached a total height of 40.5 meters (133 ft).In addition the tsunami precipitated multiple hydrogen explosions and nuclear meltdown at the Fukushima Nuclear Power Plant. Tsunami warnings were issued to the entire Pacific Rim.
Dec. 23, 2018: it was confirmed via satellite data and helicopter footage that the southwest sector of the Anak Krakatau (island with a volcano) had collapsed which triggered the tsunami and the main conduit is now erupting from underwater producing Surtseyan style activity ( an eruption is a type of volcanic eruption that takes place in shallow seas or lakes. It is named after the island of Surtsey off the southern coast of Iceland ). The Indonesian National Board for Disaster Management initially reported 20 deaths and 165 injuries. By the following day, the figure had been revised to 43 deaths, 584 injured, and 2 missing. Of the 43 recorded deaths, 33 were killed in Pandeglang, 7 in South Lampung, and 3 in Serang, with most of the injuries recorded (491) also occurring in Pandeglang. The areas of Pandeglang struck by the wave included beaches which are popular tourist destinations. By 29 December, the death toll had risen to 426, while the injured numbered 7,202 and the missing 24.
Deadliest
The deadliest tsunami in recorded history was the 2004 Indian Ocean tsunami, which killed almost 230,000 people in fourteen countries including Indonesia, Sri Lanka, India, Thailand, Somalia, Myanmar, Maldives, Malaysia, Tanzania, Seychelles, Bangladesh, South Africa, Yemen and Kenya.
Interesting Facts
~ Can you swim with a tsunami
No. Even if you are a professional swimmer or how tough you think you are; you cannot swim against the tsunami wave. The wave force is greater than ordinary wave and you will be drowned or flowed. Best thing to do if you caught up in the middle of the water is to grab the nearest floating material.
~ Can you surf
ABSOLUTELY NO. As you know by now tsunami wave is not continuous or breaking. You need continuous waves to surf. Since tsunami wave has got no breaking for a while; you will loose your balance and fall down to the water. But luckily you have a floating equipment with you.
~ Can we predict a tsunami
A tsunami event cannot be fully predicted. To help identify and predict the size of a tsunami, scientists look at the size and type of the underwater earthquake that precedes it. This is often the first information they receive, because seismic waves travel faster than tsunamis.This information is not always helpful, however, because a tsunami can arrive within minutes after the earthquake that triggered it. And not all earthquakes create tsunamis, so false alarms can and do happen.
~ Can we dive
tsunamis are much less dangerous when you’re out at sea – it is thought that a diver at a depth of around 20 meters and 200 meters away from land would barely notice what’s going on above. A tsunami can affect the underwater world in a number of ways: If the diver is caught in violently spinning currents, it will feel like they’re in a washing machine turning over and over. If the water is surging in one direction, then the diver will be pushed in that direction. Of course, with this kind of extreme movement underwater, divers can become vulnerable to various dangers.
~ Can we survive a tsunami in a pool
Being in the water (swimming pool or any other water) is no protection from the huge wave of a tsunami (sometimes more than one). You cannot just hold your breath and wait for the wave to pass over you. It will pick you up like it uproots a palm tree and carry you away.
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