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

  • The United Nations Office for Outer Space Affairs (UNOOSA) and the National Aeronautics and Space Administration of the United States Government (NASA) signed a landmark Memorandum of Understanding (MoU) on 17 December 2020 pledging cooperation in areas of science and technology to support the peaceful uses of outer space.

    The MoU brings together NASA's wealth of open-source spacecraft data, tools, and expertise and UNOOSA's unique position as the only UN entity dedicated to outer space affairs, to expand global opportunities to leverage the benefits of space. The partners will design capacity-building programmes, particularly for institutions in countries that do not yet have or that are developing space capabilities, to help them access space.

    Together, UNOOSA and NASA will develop ways to leverage the Artemis programme as part of UNOOSA's Access to Space 4 All Initiative, which offers opportunities for international researchers and institutions, especially in...

    read more
    11/01/2021
  • The European Commission plans to rapidly expand its environmental monitoring programme Copernicus. For this purpose, the European Space Agency (ESA) recently pledged 2.55 billion Euros towards contracts to advance the production of six new Copernicus satellite missions. The final of the six contracts was signed last Thursday between ESA and Thales Alenia Space for a mission that will provide new and important information to climate research and disaster management.

    The high-priority Copernicus Radar Observation System for Europe in L-band (ROSE-L) mission is planned to launch in 2028 for a period of 7.5 years. The ROSE-L mission will orbit Earth every few days at an altitude of 690km and will carry a L-Band synthetic aperture radar (SAR). With a wavelength of approximately 23cm, an...

    read more
    18/12/2020
  • The Disasters programme unit at the National Aeronautics and Space Administration (NASA) recently joined a newly launched online platform aimed at placing anticipatory action on the humanitarian agenda. NASA’s involvement in the Anticipation Hub and the subsequent incorporation of Earth observation (EO) tools, serves to improve the capabilities of anticipatory action globally and demonstrates the potential of utilizing satellite-driven data for anticipatory action in disaster management.

    Anticipatory action in the humanitarian context describes disaster mitigation activities based on in-depth forecast information and risk analysis. This approach has gained traction amongst the humanitarian community in recent years as it is viewed as a more efficient and affordable alternative to...

    read more
    02/02/2021
  • A new report outlines the impact of Global Human Settlement Layer (GHSL) data on various policy areas. The 2020 edition of the “Atlas of the Human Planet”, recently published and launched virtually by the Joint Research Centre (JRC) of the European Commission as a deliverable to the Group on Earth Observations (GEO) Human Planet Initiative, explores the impact of GHSL data on various policy areas, including disaster risk management.

    GHSL data refers to “global spatial information, evidence-based analytics and knowledge describing the human presence on the planet”. This data relies on spatial information from Landsat 8, Sentinel-1 and Sentinel-2. It is mainly cost-free and...

    read more
    18/02/2021
  • Recent advances in satellite technology in terms of higher spatial resolution, multi-spectral bands and open data access, have enhanced the ability for the monitoring and management of coastal areas. Satellite images are to be one of the most potential alternatives to water depth estimation due to the wide area coverage, repeatability, and low cost.

    Depth retrieval can be achieved using either Analytical or Empirical Bathymetry methods. Empirical methods need additionally in situ measurements and can follow two approaches: Either the one of Lyzenga et al. (1978, 2006), proposing log-linear correlation between multiband and water depth values, and focusing mainly on removing all other reflected parameters attenuating water bottom signals, or the approach of Stumpf et al. (2003), using a ratio of bands and the difference in attenuation of different bands in water.

    The characteristics of the nearshore are dependent on their bathymetry. Variations in the sea floor can...

    read more
  • The use of multi-risk information systems is crucial in confronting the increasing risks posed by natural hazards. In some cases, risk is increasing due to inadequate land-use norms or regulations that allow for the construction of infrastructure in areas exposed to such natural hazards. In other cases, vulnerability increases due to lack of awareness or extreme poverty.  The need to address risks from the point of view of multiple hazards is necessary to contribute to sustainable development and has been incorporated as an essential element of the Sendai Framework for Disaster Risk Reduction 2015-2030.  For this purpose, the RIESGOS 2.0 project was launched in March 2021. Under the coordination of the German Aerospace Center (DLR), the project builds on the accomplishments of its predecessor - RIESGOS - as a multi-risk information system that models and simulates natural hazards to support disaster...

    read more
    17/03/2021
  • According to the latest issue of an annual disaster statistics report, floods were the deadliest type of disasters in 2019, followed by extreme temperature, while storms affected the highest number of people. Published by the Centre for Research on the Epidemiology of Disasters (CRED), “Natural disasters 2019 - Now is the time to not give up” draws on data recorded in the Emergency Events Database (EM-DAT), which saw the addition of 396 disasters that affected a total of 95 million and caused $103 billion in economic losses around the world. 

    Accounting for 40 per cent of disaster events, Asia suffered the highest impact with 45 per cent of deaths and 74 per cent of total affected. India, which saw cyclone Fani cause destruction in 2019, was the country most...

    read more
    20/08/2020
  • The major thrives of this congress will be discuss and develop an integrated Climate Resilience Ecosystem that will address Future Disaster Risk Reduction and Capacity Development of Vulnerable Communities for Sustainable & Inclusive Growth and Subsequently publish a White Paper that will be submitted to the Government of India and the State Government.
     
    The Conference will discuss different topics, including:
    • Application of GIS & Remote Sensing for Integrated Disaster Risk Reduction
    • Costal Vulnerability and Adaption strategies
    • Water Security and Risk Management
    • Management of Solid Waste for Sustainable Development
    • Climate and Carbon Financing
    • Sustainability and Inclusive Growth
    • Extreme weather Events
    • Global Warming and Coastal Risks
    • Multi hazard Early Warning Systems
    • Water Resource Sustainability and Security
    • Application of GIS& RS for Integrated...
    read more
  • On 22 December 2018 a large chunk of the Anak Krakatau volcanic island collapsed into the ocean, causing a tsunami that swept across Indonesia’s Sunda Strait. Because tsunami early warning systems are exclusively equipped to detect tsunamis that are generated by earthquakes, this volcanic collapse-caused tsunami took place without a warning. In the coastal regions of Java and Sumatra, where people were struck off guard, the tsunami killed 400 people and injured many more.

    A recent research study published in Nature Communications and led by the German Research Centre for Geosciences (GFZ) has detected deformations in Anak Krakatau leading up to the tsunami that could serve as an early warning system for future volcanic collapses. Satellite data plays a key role in developing such early warning systems by providing monitoring capabilities. As early as late June 2018, the Moderate Resolution Imaging...

    read more
    13/11/2019

Term Parents

UN-SPIDER Regional Support Offices with hazard-specific expertise