Tsunami

Definition

A tsunami is a series of travelling waves of extremely long length and period, generated when a large volume of ocean water is rapidly displaced by a sudden displacement of the seabed. These series of waves are generated by a displacement of massive amounts of water through underwater earthquakes, volcanic eruptions or landslides. Tsunami waves travel at very high speed across the ocean but as they begin to reach shallow water they slow down and the wave grows steeper (IRDR Glossary).

The majority of tsunami are generated by shallow large earthquakes in subduction zones. Tsunami is also known as seismic sea waves because it is most often generated by earthquakes (UNESCO).

Facts and figures

The word tsunami is derived from the Japanese word “tsu” and “nami”, meaning “Harbor” and “Wave” respectively.

The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Scientists can predict when a tsunami will arrive at various places by knowing the source characteristics of the earthquake that generated the tsunami and the characteristics of the seafloor along the paths to those places. When the ocean is over 19,685 feet (6,000 m) deep, unnoticed tsunami waves can travel over 500 mph (804.67 kmh). One coastal community may see no damaging tsunami wave activity while in another nearby community destructive waves can be large and violent. Reefs, bays, entrances to rivers, undersea features and the slope of the beach help to modify the tsunami as it approaches the coastline (NOAA).

Dependent on the distance of the tsunami from its source, it may be classified as a:

  • Local/near field tsunami A tsunami from a nearby source for which its destructive effects are confined to coasts less than 1 hour tsunami travel time or typically within about 100 km from its source.
  • Regional tsunami A tsunami that is capable of destruction in a particular geographic region.
  • Destructive tsunami Happens 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 cm high in the deep ocean may grow into a much larger wave 30 m high as it sweeps over the shore.
  • Non-Destructive Tsunami Mostly happens as a result of minor earthquakes and/or other events. It can be due to the source being far away from land or the earthquake being too small to have any effect when approaching the shore. When a small tsunami comes to the shoreline it is often seen as a strong and fast-moving tide (Caribbean Tsunami Information Center).

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    An exploratory study was conducted on the role of coastal ecosystems in protecting communities from the December 2004 Indian Ocean tsunami, focusing on mangrove forests on the Andaman coast of Thailand and how well villages were undertaking environmental conservation. Remote sensing analysis identified predisaster mangrove change and postdisaster structural damage and landscape changes. Field data from five sites (20 villages), gathered via the VIEWSTM data collection system, validated and supplemented this analysis. Key informants at several of these villages were also interviewed. A preliminary comparison of villages that otherwise faced similar tsunami exposure suggests that the presence of healthy mangroves did afford substantial protection. Village performance in mangrove conservation and management efforts, and thus the presence of healthy forests, is influenced by both social capital and the design of external aid delivery programs.

     

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    Tsunami is a series of high waves which is caused by the movement of massive mass of sea water. Tsunami disaster is one of the earth's phenomenon that can not be avoided by human being. Even though, tsunami disaster still can be learned and its impact to humankind and their environment. Remote sensing technology is one of the alternative technologies to extract spatial information on tsunami disaster where it can be utilized to help the planning and reconstruction process in the tsunami impacted region. This study aims to know how far the remote sensing technology can contribute to the tsunami mitigation process. The results obtained from this study are information about destructed buildings, land use change and total coverage of land affected by tsunami in Nangroe Aceh Darussalam (NAD) with Meulaboh City as a case study.

     

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  • At least 160 people are missing from an Indonesian village that was pounded by an enormous wave after a 7.5 magnitude earthquake off the coast of Sumatra caused a local tsunami.

    Source: GLIDEnumber

  • Initial assessments indicate that 800 people have been displaced 76 homes have been destroyed There have been 9 confirmed deaths and a further 5 people in critical condition have been flown to Nuku?alofa

    Source: http://glidenumber.net/glide/public/search/details.jsp?glide=18921.

  • A tsunami following an earthquake in the Pacific Ocean off has caused some deaths in American Samoa , but there is no word of how many died, an official for the U.S. National Park Service said on Tuesday.

    Holly Bundock, spokeswoman for the National Park Service's Pacific West Region in Oakland, California, quoted Mike Reynolds, superintendent of the National Park of American Samoa, as saying there had been some deaths.

    Source:
    http://www.reuters.com/article/usDollarRpt/idUSN2931736820090929.
    http://www.ifrc.org/Docs/News/09/09093001/index.asp.

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    Source: Clide number

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