Tsunami relief efforts

PJ_Quek SG

Chat anything regarding Tsunami relief efforts in Thailand. Mr. Green

PJ_Quek SG

Tsunami - definition

A tsunami (pronounced soo-nah-mee or tsoo-nah-mee [ IPA /suˈnɑːmi/ or /tsuˈnɑːmi/]) is a natural phenomenon consisting of a series of waves generated when water in a lake or the sea is rapidly displaced on a massive scale. Earthquakes, landslides, volcanic eruptions and large meteorite impacts all have the potential to generate a tsunami. The effects of a tsunami can range from unnoticeable to devastating.

The term tsunami comes from the Japanese language meaning harbour ("tsu", &#27941 Wink and wave ("nami", 波 or &#28010 Wink . Although in Japanese tsunami is used for both the singular and plural, in English tsunamis is well-established as the plural. The term was created by fishermen who returned to port to find the area surrounding the harbour devastated, although they had not been aware of any wave in the open water. A tsunami is not a sub-surface event in the deep ocean; it simply has a much smaller amplitude (wave heights) offshore, and a very long wavelength (often hundreds of kilometres long), which is why they generally pass unnoticed at sea, forming only a passing "hump" in the ocean.

Tsunamis have been historically referred to as tidal waves because as they approach land they take on the characteristics of a violent onrushing tide rather than the sort of cresting waves that are formed by wind action upon the ocean (with which people are more familiar). However, since they are not actually related to tides the term is considered misleading and its usage is discouraged by oceanographers.

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Causes of tsunami

A tsunami can be generated by any disturbance that rapidly displaces a large mass of water, such as an earthquake, volcanic eruption, landslide or meteorite impact. However, the most common cause is an undersea earthquake. An earthquake which is too small to create a tsunami by itself may trigger an undersea landslide quite capable of generating a tsunami.

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Such large vertical movements of the earth's crust can occur at plate boundaries. Subduction earthquakes are particularly effective in generating tsunamis, and occur where denser oceanic plates slip under continental plates in a process known as subduction.

Sub-marine landslides; which are sometimes triggered by large earthquakes; as well as collapses of volcanic edifices, may also disturb the overlying water column as sediment and rocks slide downslope and are redistributed across the sea floor. Similarly, a violent submarine volcanic eruption can uplift the water column and generate a tsunami.

Waves are formed as the displaced water mass moves under the influence of gravity to regain its equilibrium and radiates across the ocean like ripples on a pond.

In the 1950s it was discovered that larger tsunamis than previously believed possible could be caused by landslides, explosive volcanic action and impact events that rapidly displace large volumes of water, as energy from falling debris or expansion is transferred to the water into which the debris falls. Generally speaking, tsunamis generated from these mechanisms, unlike the ocean-wide tsunamis caused by some earthquakes, dissipate quickly and rarely affect coastlines distant from the source area due to the small area of sea affected. However they can give rise to much larger shock waves (solitons) locally, such as the Lituya Bay megatsunami which produced a water wave estimated at 50 150 m and reached 524 m up local mountains.

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Precautions

Tsunamis cannot be prevented or precisely predicted, but there are some warning signs of an impending tsunami, and there are many systems being developed and in use to reduce the damage from tsunamis.

In instances where the leading edge of the tsunami wave is its trough, the sea will recede from the coast half of the wave's period before the wave's arrival. If the slope is shallow, this recession can exceed many hundreds of metres. People unaware of the danger may remain at the shore due to curiosity, or for collecting fish from the exposed sea bed.

Regions with a high risk of tsunamis may use tsunami warning systems to detect tsunamis and warn the general population before the wave reaches land. In some communities on the west coast of the United States, which is prone to Pacific Ocean tsunamis, warning signs advise people where to run in the event of an incoming tsunami. Computer models can roughly predict tsunami arrival and impact based on information about the event that triggered it and the shape of the seafloor (bathymetry) and coastal land (topography).

One of early warnings comes from nearby animals. Many animals sense danger and flee to higher ground before the water arrives. The Lisbon quake is the first documented case of such a phenomenon in Europe. The phenomenon was also noted in Sri Lanka in the 2004 Indian Ocean earthquake ([2]). Some scientists speculate that animals may have an ability to sense subsonic Rayleigh waves from an earthquake minutes or hours before a tsunami strikes shore (Kenneally, [3]).

While it is not possible to prevent a tsunami, in some particularly tsunami-prone countries some measures have been taken to reduce the damage caused on shore. Japan has implemented an extensive programme of building tsunami walls of up to 4.5m (13.5 ft) high in front of populated coastal areas. Other localities have built floodgates and channels to redirect the water from incoming tsunamis. However, their effectiveness has been questioned, as tsunamis are often higher than the barriers. For instance, the tsunami which hit the island of Hokkaido on July 12, 1993 created waves as much as 30m (100 ft) tall - as high as a 10-story building. The port town of Aonae was completely surrounded by a tsunami wall, but the waves washed right over the wall and destroyed all the wood-framed structures in the area. The wall may have succeeded in slowing down and moderating the height of the tsunami but it did not prevent major destruction and loss of life.

The effects of a tsunami can be mitigated by natural factors such as tree cover on the shoreline. Some locations in the path of the 2004 Indian Ocean tsunami escaped almost unscathed as a result of the tsunami's energy being sapped by a belt of trees such as coconut palms and mangroves. In one striking example, the village of Naluvedapathy in India's Tamil Nadu region suffered minimal damage and few deaths as the wave broke up on a forest of 80,244 trees planted along the shoreline in 2002 in a bid to enter the Guinness Book of Records. [4] Environmentalists have suggested tree planting along stretches of sea coast which are prone to tsunami risks. While it would take some years for the trees to grow to a useful size, such plantations could offer a much cheaper and longer-lasting means of tsunami mitigation than the costly and environmentally destructive method of erecting artificial barriers.

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Past tsunamis

6100 B.C. and before
In the North Atlantic Ocean, the Storegga Slides were a major series of sudden underwater land movements over the course of tens of thousands of years, which caused tsunamis and megatsunamis across a wide area.

In 2002 it was suggested that the Bristol Channel floods of 1607 in England and Wales, UK, may have been caused by a tsunami.

1650 B.C. - Santorini
At some time between 1650 BC and 1600 BC (still debated), the volcanic Greek island Santorini erupted, causing a 100 m to 150 m high tsunami that devastated the north coast of Crete, 70 km (45 miles) away, and would certainly have wiped out the Minoan civilization along Crete's northern shore. Santorini is regarded as the most likely source for Plato's literary parable of Atlantis.

1700 - Vancouver Island, Canada
January 26 - The Cascadia Earthquake, one of the largest earthquakes on record, ruptures the Cascadia Subduction Zone offshore from Vancouver Island to northern California, creating a tsunami logged in Japan and oral traditions of the American First Nations.

1755 - Lisbon, Portugal
Tens of thousands of Portuguese who survived the great 1755 Lisbon earthquake were killed by a tsunami which followed a half hour later. Many townspeople fled to the waterfront, believing the area safe from fires and from falling debris from aftershocks. Before the great wall of water hit the harbour, waters retreated, revealing lost cargo and forgotten shipwrecks.

The earthquake, tsunami, and subsequent fires killed more than a third of Lisbon's pre-quake population of 275,000. Historical records of explorations by Vasco da Gama and other early navigators were lost, and countless buildings were destroyed (including most examples of Portugal's Manueline architecture). Europeans of the 18th century struggled to understand the disaster within religious and rational belief systems. Philosophers of the Enlightenment, notably Voltaire, wrote about the event. The philosophical concept of the sublime, as described by philosopher Immanuel Kant in the Observations on the Feeling of the Beautiful and Sublime, took inspiration in part from attempts to comprehend the enormity of the Lisbon quake and tsunami.

1883 - Krakatoa explosive eruption
The island volcano of Krakatoa in Indonesia exploded with devastating fury in 1883, blowing its underground magma chamber partly empty so that much overlying land and seabed collapsed into it. A series of large tsunami waves was generated from the explosion, some reaching a height of over 40 metres above sea level. Tsunami waves were observed throughout the Indian Ocean, the Pacific Ocean, the American West Coast, South America, and even as far away as the English Channel. On the facing coasts of Java and Sumatra the sea flood went many miles inland and caused such vast loss of life that one area was never resettled but went back to the jungle and is now the Ujung Kulon nature reserve.

1929 - Newfoundland tsunami
On November 18, 1929, an earthquake of magnitude 7.2 occurred beneath the Laurentian Slope on the Grand Banks. The quake was felt throughout the Atlantic Provinces of Canada and as far west as Ottawa, Ontario and as far south as Claymont, Delaware. The resulting tsunami measured over 7 metres in height and took about 2½ hours to reach the Burin Peninsula on the south coast of Newfoundland, where 28 people lost their lives in various communities.

1946 - Pacific tsunami
The Aleutian Island earthquake tsunami that killed 165 people on Hawaii and Alaska resulted in the creation of a tsunami warning system, established in 1949 for Pacific Ocean area countries.

1960 - Chilean tsunami
The Great Chilean Earthquake, at magnitude 9.5 the strongest earthquake ever recorded, off the coast of South Central Chile, generated one of the most destructive tsunamis of the 20th century. It spread across the entire Pacific Ocean, with waves measuring up to 25 metres high. When the tsunami hit Onagawa, Japan, almost 22 hours after the quake, the wave height was 3 m above high tide. The number of people killed by the earthquake and subsequent tsunami is estimated to be between 490 and 2,290.

1963 - Vajont Dam disaster
The reservoir behind the Vajont Dam in northern Italy was struck by an enormous landslide. A tsunami was triggered which swept over the top of the dam (without bursting it) and into the valley below. Over 3,000 people were killed.

1964 - Good Friday tsunami
After the magnitude 9.2 Good Friday Earthquake, tsunamis struck Alaska, British Columbia, California and coastal Pacific Northwest towns, killing 122 people. The tsunamis were up to 6 m tall, and killed 11 people as far away as Crescent City, California.

1979 - Tumaco tsunami
A magnitude 7.9 earthquake occurred on December 12, 1979 at 7:59:4.3 (UTC) along the Pacific coast of Colombia and Ecuador. The earthquake and the resulting tsunami caused the destruction of at least six fishing villages and the death of hundreds of people in the Colombian province of Nariño. The earthquake was felt in Bogotá, Cali, Popayán, Buenaventura and several other cities and towns in Colombia and in Guayaquil, Esmeraldas, Quito and other parts of Ecuador. When the Tumaco Tsunami hit the coast, it caused great destruction in the city of Tumaco, as well as in the small towns of El Charco, San Juan, Mosquera and Salahonda on the Pacific Coast of Colombia. The total number of victims of this tragedy was 259 dead, 798 wounded and 95 missing presumed dead.

1993 Okushiri Tsunami
A devastating tsunami occurred off the coast of Hokkaido in Japan as a result of an earthquake on July 12, 1993. As a result, 202 people on the small island of Okushiri lost their lives, and hundreds more were missing or injured.

2004 - Indian Ocean tsunami
Animation of the 2004 Indonesian Tsunami from NOAA/PMEL Tsunami Research ProgramThe 2004 Indian Ocean earthquake, that had a magnitude between 9.1 and 9.3, triggered a series of lethal tsunamis on December 26, 2004 that killed over 310,000 people (more than 220,000 in Indonesia alone), making it the deadliest tsunami in recorded history. The tsunami killed people over an area ranging from the immediate vicinity of the quake in Indonesia, Thailand and the north-western coast of Malaysia to thousands of kilometres away in Bangladesh, India, Sri Lanka, the Maldives, and even as far as Somalia, Kenya and Tanzania in eastern Africa. The disaster prompted a huge worldwide effort to help victims of the tragedy, with hundreds of millions of dollars being raised for disaster relief.

Unlike in the Pacific Ocean, there is no organised alert service covering the Indian Ocean. This is in part due to the absence of major tsunami events between 1883 (the Krakatoa eruption, which killed 36,000 people) and 2004. In light of the 2004 Indian Ocean tsunami, UNESCO and other world bodies have called for a global tsunami monitoring system.

The lack of an established infrastructure within this Indian Ocean region means that any development and reconstruction is subject to internal (political) influences.