Tsunami

Tsunami is the Japanese term meaning wave (‘nami’) in a harbour (‘tsu’). It is a series of travelling waves of extremely long length and period, usually generated by disturbances associated with earthquakes occurring below or near the ocean floor (IOC, 2019).

A tsunami can also be generated by other underwater disturbances such as landslides, volcanic eruption and meteorites. A tsunami consists of a series of 10 or more waves with crests arriving every 10 to 60 minutes. Tsunami waves can be very long (as much as 100 km) and tens or even hundreds of metres high. They can cross entire oceans without great loss of energy. 

Destructive tsunamis can generated by large, shallow earthquakes with an epicentre or fault line near, or on the ocean floor. Usually, it takes an earthquake with a Richter magnitude exceeding 7.5 to produce a destructive tsunami. Receding water is one of the first visual signs of a tsunami. Experts believe that a receding ocean may give people as much as five-minutes warning to evacuate the area (IOC, UNESCO).

The Pacific is by far the most active tsunami zone, according to the US National Oceanic and Atmospheric Administration (NOAA), but tsunamis have been generated in the Caribbean and Mediterranean seas, and the Indian and Atlantic oceans.

On Sunday morning 26 December 2004 at 00:58:53 UTC, a massive earthquake measuring 9.1 on the Richter scale struck off the west coast of Sumatra, Indonesia. The earthquake generated a series of towering waves which could travel at 80 km/h in shallow water, with the largest impact felt in Indonesia and Sri Lanka. Within 15 minutes of the earthquake, waves began striking the coasts of northern Sumatra and the Nicobar islands.Waves of up to 30 metres were recorded as the tsunami swept through Aceh, the hardest hit region of Indonesia. Around two hours after the earthquake struck, waves reached Sri Lanka, India and Thailand. An hour later they reached the Maldives, and, more than seven hours after the initial quake, the tsunami was observed in Mauritius and along the east coast of Africa.

The tsunami waves caused widespread death and injuries, displaced thousands, destroyed towns, homes, livelihoods, infrastructure, and wrecked coastal areas. Due to the scale of destruction estimates for total lives lost vary, according to the United Nations approximately 227,000 people were killed in fourteen countries. Data published by the Tsunami Evaluation Coalition indicated at least 275,000 people were killed. Across the region there are still people believed to have been swept away who have never been accounted for. Measured in lives lost, this makes it one of the 10 worst earthquakes in recorded history, as well as the single worst tsunami in history (Australian Institute for Disaster Resilience).

Risk management for tsunamis includes guidelines on tsunami risk assessment/management. Examples include IOC (2015) and UNDRR (2017). The Intergovernmental Oceanographic Commission is coordinating the implementation of a global tsunami warning system, building upon its experiences in the Pacific to establish regional warning systems for the Indian Ocean (IOTWMS); Caribbean Sea (ICG-CARIBE-EWS); and the North-eastern Aland, the Mediterranean and connected seas (ICG-NEAMTWS). The regional systems coordinate international tsunami warning and mitigation activities, including the issuance of timely and understandable tsunami bulletins to IOC Member States.

Risk factors

  • Living by the sea in earthquake-prone zones.
  • Poor quality buildings.
  • Destruction of the environment and natural barriers.
  • Lack of coastal land-use planning.
  • The development of tourist settlements in tsunami-prone zones.

Vulnerable areas

  • Tsunamis can be generated in oceans and seas around the world.
  • But the Pacific Ocean has a much more frequent occurrence of large, destructive tsunamis because of the many large earthquakes along its edges.

Risk reduction measures

  • Early warning systems.
  • Understand what a tsunami is, how it develops, and its impact on the coast.
  • Hazard map, including clearly designated shelters and safe areas.
  • Reinforce building structures: move homes and buildings away from the shoreline.
  • Protect essential infrastructure such as schools and hospitals, roads, harbours, power plants, banking, and build structures at higher levels if possible.
  • Install seawalls and revetments, structures that can be built along the shoreline to help protect the shore from storm waves.
  • Ensure that natural barriers - dunes, mangroves and coral reefs - are protected.
  • Integrate indigenous knowledge into tsunami protection plans.
  • Educate locals and tourists on tsunami risks and integrate tsunami education in the school curricula.
  • Place tsunami evacuation signs along roadways clearly indicating the route to higher ground.

Tsunami early warning systems

To alert far-away coasts, internationally coordinated tsunami early warning systems, such as the Pacific Tsunami Warning and Mitigation System (PTWS), have been established to quickly provide tsunami threat information to countries.

Latest Tsunami additions in the Knowledge Base

HSS Summit on WTAD 2022 final performance
At the High School Students Summit on World Tsunami Awareness Day 2022 in Niigata, Japan, students from around the world gathered – both virtually and in person – to discuss, learn, and reaffirm their commitment to disaster risk reduction.
United Nations Office for Disaster Risk Reduction - Kobe Office
United Nations Office for Disaster Risk Reduction - Regional Office for Asia and Pacific
Tsunami News 2021
In this edition of Tsunami News, we explore examples of how governments and organizations around the world are increasing their levels of cooperation.
About 40% of public housing provided for those affected by the devastating March 2011 Great East Japan Earthquake in Iwate, Miyagi and Fukushima prefectures, are at risk of flooding from the highest envisioned level of tsunami.
Mainichi Newspapers Co., Ltd., the - Mainichi Daily news, the
CREWS
In response to the unprecedented volcano and tsunami, Kingdom of Tonga develops Tonga Mobile Applications Community MHEW and Response System (MACRES) through the CREWS Accelerated Support Window.
Mangroves and their roots
Dataset measuring full-scale tsunami wave attenuation in mangrove forest wins 2022 DesignSafe Dataset Award.
Natural Hazards Engineering Research Infrastructure
Cover
This systematic review provides a comprehensive overview of tsunami evacuation models. The review covers scientific studies from the last decade (2012–2021) and is explicitly focused on models using an agent-based approach.
The Pacific Coast Tsunami Hazard Zone warning sign warns the public of potential dangers following an earthquake.
Research over the past decade in Alaska’s Aleutian Islands has offered surprising insights into the pulses of great earthquakes that generate dangerous, often long-distance tsunamis.
Earth Observatory of Singapore - Nanyang Technological University
“If you understand the risk, then you can understand how to cope with it,” Esline says. “But if you do not understand, it is going to be hard - slowly you see the impact, but you don’t know how to deal with it”.

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