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).

UN-SPIDER Regional Support Offices with hazard-specific expertise

Related content on the Knowledge Portal

  • Tsunamis are an ever-present threat to lives, infrastructure, and property along the coasts of the world's oceans. Recent tsunamis deeply impacted the shores of Indonesia, calling for early warning systems as well as risk and vulnerability assessment as basis for mitigation strategies, evacuation planning and rehabilitation organization. Research on tsunamis focuses on tsunamis generation, wave propagation, inundation and interactions with structures. This study is focusing on the latter, using the capabilities of high resolution satellite data to assess tsunami vulnerability in urban areas. Based on an object-oriented land-cover classification the physical urban morphology is structured using parameter like built-up density, function, building sizes or location. The distribution of a total population following the structural characteristics of an urban morphology is determined by assuming a dependency between numerical and spatial units. Using the derived physical and…

    read more
  •  

    In the aftermath of the Indian ocean tsunami, the media indicated that the clearing of coastal mangrove ecosystems for tourism and aquaculture may have have exacerbated infrastructure damage and human loss. This paper documents the use of moderate- and high resolution remote sensing imagery to furnish a multi-disciplinary international project team with data to begin scientifically investigating this assertion for the coast of Thailand. High resolution imagery in turn focused on selected study sites within the provinces of Ranong and Phang Nga. Of the multiple analyses that were conducted, this paper first documents the use of an historical sequence of Landsat 5 imagery spanning the past two decades to map changes in mangrove extents as an indicator for pre-tsunami environmental degradation. It goes on to describe the assessment of damage to coastal communities using high-resolution Quickbird and IKONOS imagery collected before and soon after the event. Following a…

    read more
  •  Remote sensing has emerged as a powerful tool for mitigation planning and post-crisis assessment in various natural hazards. The development of advanced remote sensing technologies has improved mapping capabilities and expanded areas of application. The most significant improvement is the commercialization of very high spatial resolution satellite data. Here, remote sensing data and methods were used to support the development of tsunami inundation maps for the City of Rhodes, Greece, as well as to help ground truthing modeling results. Information about the topography was derived using both satellite and aerial images. ASTER (Advanced Spaceborn Thermal Emission and Reflection Radiometer) stereo images were used to provide a Digital Elevation Model (DEM) for the whole island, whereas aerial imagery was used to derive a high resolution DEM for the Northern part where the city of Rhodes is located. These DEMs were used to orthorectify multispectral ASTER and Ikonos images,…

    read more
  •  

    Based on LANDSAT ETM and Digital Elevation Model (DEM) data derived by the Shuttle Radar Topography Mission (SRTM, 2000) of the coastal areas of Northern Venezuela were investigated in order to detect traces of earlier tsunami events. Digital image processing methods used to enhance LANDSAT ETM imageries and to produce morphometric maps (such as hillshade, slope, minimum and maximum curvature maps) based on the SRTM DEM data contribute to the detection of morphologic traces that might be related to catastrophic tsunami events. These maps combined with various geodata such as seismotectonic data in a GIS environment allow the delineation of coastal regions with potential tsunami risk. The LANDSAT ETM imageries merged with digitally processed and enhanced SRTM data clearly indicate areas that might be prone by flooding in case of catastrophic tsunami events.

     

    read more
  •  

    Based on LANDSAT ETM and Digital Elevation Model (DEM) data derived bu the Shuttle Radar Topography Mission (SRTM) of the coastal areas of Greece were investigated in order to detect traces of earlier tsunami events. Digital image processing methods used to produce hillshade, slope, minimum and maximum curvature maps based on the SRTM DEM data contribute to the detection of morphologic traces that might be related to catastrophic tsunami events. These maps combined with LANDSAT ETM and seismotectonic data in a GIS environment allow the delineation of coastal regions with potential tsunami risk. The evaluations of Landsat ETM imageries merged with digitally processed and enhanced SRTM data clearly show areas that must have been flooded in earlier times. In some cases morphologic traces of waves as curvilinear scarps open to the sea-side are clearly visible.

     

    read more
  •  

    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.

     

    read more
  •  

    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.

     

    read more
  • 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.

    read more

Term Parents

UN-SPIDER Regional Support Offices with hazard-specific expertise