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

  • Landsat 5 was launched from Vandenberg Air Force Base in California on March 1, 1984, and like Landsat 4, carried the Multispectral Scanner (MSS) and the Thematic Mapper (TM) instruments. Landsat 5 delivered Earth imaging data nearly 29 years - and set a Guinness World Record For 'Longest Operating Earth Observation Satellite', before being decommissioned on June 5, 2013.
    The Landsat 5 satellite orbited the the Earth in a sun-synchronous, near-polar orbit, at an altitude of 705 km (438 mi), inclined at 98.2 degrees, and circled the Earth every 99 minutes.  The satellite had a 16-day repeat cycle with an equatorial crossing time: 9:45 a.m. +/- 15 minutes.  Landsat 5 data were acquired on the Worldwide Reference System-2 (WRS-2) path/row system, with swath overlap (or sidelap) varying from 7 percent at the Equator to a maximum of approximately 85 percent at extreme latitudes. 
    Landsat 5 long outlived its…

    read more
    01/03/1984
  • Landsat 4 was launched on July 16, 1982. The Landsat 4 spacecraft was significantly different than that of the previous Landsats, and Landsat 4 did not carry the RBV instrument.
    In addition to the Multispectral Scanner System (MSS) instrument, Landsat 4 (and Landsat 5) carried a sensor with improved spectral and spatial resolution, i.e., the new satellites could see a wider (and more scientifically-tailored) portion of the electromagnetic spectrum and could see the ground in greater detail. This new instrument was known as the Thematic Mapper (TM).
    Landsat 4 was kept in orbit for housekeeping telemetry command and tracking data (which it downlinked via a separate data path, the S-band) until it was decommissioned in 2001.
    While Landsat 4 was built and launched by NASA, NOAA initially oversaw the operations of the satellite. Landsat 4 operations were contracted out to the Earth Observation Satellite Company (…

    read more
    16/07/1982
  • Landsat 3 was launched on March 5, 1978, three years after Landsat 2.
    The Landsat program’s technical and scientific success together with political and economic pressures lead to the decision to commercialize an operational Landsat. To this end, responsibility was slated to shift from NASA (a research and development agency) to the National Oceanic and Atmospheric Administration (NOAA), the agency charged with operating the weather satellites. This was done via Presidential Directive/NSC-54 signed on Nov. 16, 1979 which assigned NOAA “management responsibility for civil operational land remote sensing activites.” (However, operational management was not transfered from NASA to NOAA until 1983).
    Landsat 3 carried the same sensors as its predecessor: the Return Beam Vidicon (RBV) and the Multispectral Scanner (MSS). The RBV instrument on-board Landsat 3 had…

    read more
    05/03/1978
  • Landsat 2 was launched into space onboard a Delta 2910 rocket from Vandenberg Air Force Base, California on January 22, 1975, two and a half years after Landsat 1. Originally named ERTS-B (Earth Resource Technology Satellite B), the spacecraft was renamed Landsat 2 prior to launch. The second Landsat was still considered an experimental project and was operated by NASA.
    Landsat 2 carried the same sensors as its predecessor: the Return Beam Vidicon (RBV) and the Multispectral Scanner System (MSS).
    On February 25, 1982 after seven years of service, Landsat 2 was removed from operations due to yaw control problems; it was offically decommissioned on July 27, 1983.

    Instruments:
    Return Beam Vidicon (RBV)
    Multispectral Scanner (MSS)
     

    read more
    22/01/1975
  • Landsat 1 was launched on July 23, 1972; at that time the satellite was known as the Earth Resources Technology Satellite (ERTS). It was the first Earth-observing satellite to be launched with the express intent to study and monitor our planet’s landmasses. To perform the monitoring, Landsat 1 carried two instruments: a camera system built by the Radio Corporation of America (RCA) called the Return Beam Vidicon (RBV), and the Multispectral Scanner (MSS) built by the Hughes Aircraft Company. The RBV was supposed to be the prime instrument, but the MSS data were found to be superior. In addition, the RBV instrument was the source of an electrical transient that caused the satellite to briefly lose altitude control, according to the Landsat 1 Program Manager, Stan Weiland.
    To help understand the data and to explore the potential applications of this new technology, NASA oversaw 300 private research investigators. Nearly one third of these were international scientists…

    read more
    23/07/1972
  • The Copernicus Coastal Hub offers free and openly accessible geospatial information for download regarding subject that impact coastal regions around the world.
    Publishing institution:
  • In 2015 the United Nations declared that each year 5 November would be observed as World Tsunami Awareness Day – a reminder that when a tsunami strikes, everyone must be ready to get to high ground.

    Like all disasters, tsunamis have an unequal and unique impact on the affected population. Poverty levels, exposure, discrimination and other vulnerabilities all play a key role in determining who is likely to be affected and how. For example, following the Indian Ocean tsunami of 2004 that affected 12 countries, it was found that poor households were more likely to see their “flimsy houses” wash away, while the brick houses of richer households proved sturdier.

    Satellites equipped with specialized sensors can detect and monitor various indicators, such as sea surface temperatures, ocean currents, and underwater seismic activities. By analyzing these data, scientists can identify potential tsunami-triggering events, like underwater earthquakes or volcanic eruptions.…

    read more
    06/11/2023
  •  

     

     

    read more

Term Parents

UN-SPIDER Regional Support Offices with hazard-specific expertise