Tsunami Warning System: Preparing for the unpredictable (2023)

How UNESCO’s work on tsunami early warning system reduces the risk of catastrophic coastal hazards that can cause death and destruction.

Tsunami Warning System: Preparing for the unpredictable (1)

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Last update:11 May 2023

UNESCO is the UN Agency in charge of ocean science. With its Intergovernmental Oceanographic Commission joined by 150 Member States, and its expertise in the culture and education fields, UNESCO coordinates actions by governments, scientists, the private sector, civil society and other UN organizations. Together, we created the tsunami warning system. We map the ocean depths, identify species, work to ensure that ocean literacy is included in school curricula and protect ocean sites, which are home to critical biodiversity and incomparable beauty. In this story, we tell you more about UNESCO’s work on the tsunami early warning system, how it works and how it saves lives.

Tsunamis are rare events. But when nature’s fury is unleashed, their deadly effects are devastating. The initial impact may make the front page of news media, but the aftermath on communities, livelihoods and the environment will linger for many years after the natural disaster strikes.

In the last century, 58 of them have claimed more than 260,000 lives, surpassing any other natural hazard.More are expected in the future as the sea-level rises due to climate change.

Therefore, preparing for the unpredictable can mean the difference between surviving and not.

11 March, 14:00 UTC: the Earth shakes

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An earthquake occurs in the Atlantic, 100 kilometres east of the Lesser Antilles – the long, delicate arc of small Caribbean islands fanning out between the Caribbean Sea and the open ocean. The volcanic archipelago, home to 3.2 million people, is perched on one of the tectonic plates that sit on the Earth’s crust.

Just as the plate slips along the Caribbean fault line, a massive burst of energy akin to a nuclear warhead explosion sets off a giant shockwave 25 kilometres beneath the planet’s surface.

Strong earthquakes are highly destructive in their own right. But they can also trigger other cataclysmic natural hazards.

As the seabed suddenly rises, it displaces colossal volumes of water, producing powerful waves that spread outward in all directions, just like the ripples from a stone thrown into a pond.

The smaller, ocean-facing Antilles are on the frontline of the looming wave. The larger islands – Cuba, Haiti, Jamaica and Puerto Rico – as well as the communities in the Gulf of Mexico and coastal Venezuela, are also under threat. Nearly 160 million people are in imminent danger.

Tsunami Waves : digitally-scanned photos from the ITIC collection


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Japan Sea 1983


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Japan Sea 1983


11 March, 14:02 UTC: the earthquake is detected, tsunami sensors activate

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The monitoring station in Martinique picks up the tremor and estimates it at 8.5 on the Richter scale. The large magnitude is cause for concern.Major earthquakes that occur beneath the sea lead to deadly tsunamis. Still, visual detection in the vast open ocean remains challenging because the powerful tsunami waves are low in height while they travel across deep water.

That is why shore-based tide gauges and deep-ocean buoys continuously monitor the oceans to detect any threatening changes. These silent sentinels can spy and track any minuscule change in the temperature of the seafloor and its pressure.

An ocean buoy anchored in the depths of Barbuda – a flat coral island hugged by white-and-pink sand beaches and crystal-clear waters – senses the force of the hidden submarine wave and alerts the monitoring centre on the sister island of Antigua.

11 March, 14:05 UTC: the Tsunami Warning System raises the alarm

Antigua feeds the data on the force of the approaching wave into the Tsunami Warning System, which alerts all observatories in the region. Authorities in all neighbouring countries are immediately alerted: the rapid transmission of information to dedicated centres is vital to lessen the damage caused by tsunamis.

Disaster prediction and prevention

Preventing large-scale disasters calls for a high degree of international and multilateral cooperation. After the 1960 Chilean tsunami, which left a trail of death and damage as far away as Japan, UNESCO’s Intergovernmental Oceanographic Commission (IOC-UNESCO) stepped in to set up the Pacific Ocean Tsunami Warning System, the first of its kind.

The 9.5 magnitude earthquake in Chile, the largest recorded in the 20th century, set off a tsunami that battered the South American coastline for over 4,000 kilometres with waves up to 25 metres high.

Fifteen hours later, the tsunami, which by then had travelled 10,000 kilometres, struck Hawaii, then Japan and the Philippines. The final death toll was over 2,000.

The scale of the disaster highlighted the need for a warning alert system in the Pacific, where most of the world’s deadliest tsunamis occur.Over the years, the alert system has evolved beyond issuing warnings. UNESCO’s role now includes prevention, preparing communities to respond to tsunami threats and fostering the latest tracking and detection technologies.

Other exposed regions, the Indian Ocean, the Caribbean, the Northeast Atlantic and the Mediterranean, have also adopted Early Tsunami Warning Systems based on the Pacific model.

11 March, 14:15 UTC: public alerts go out

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The tidal wave is already in sight of the Lesser Antilles. There is little time left before it hits the coast. Tsunami waves in the deep ocean can travel thousands of kilometres, up to 800 kilometres per hour, the speed of a jet aircraft.

In Martinique, the local government alerts the municipalities and the media, which immediately publish alerts. Police sirens and loudspeakers give evacuation orders. Guided by their teachers, schoolchildren rush out of their classrooms, heading for higher ground. Office workers and tourists seek safety on the rooftops of high-rise buildings.

Empowering communities to react

An early warning system can be effective only when the population is well aware of the tsunami phenomenon and knows what to do in case of an emergency.

This is vital when tsunamis are generated close to the coast and there may not be time for official evacuation orders.

As part of IOC-UNESCO coordination plans, communities are empowered to play an active role through self-evacuation if a strong earthquake is felt or a strong roaring sound – similar to a train or a jet aircraft – is heard. Highly visible and labelled evacuation routes help show the best access to nearby higher grounds or the higher floors of tsunami-proof buildings.

11 March, 14:16 UTC: the sea level drops

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As the tsunami approaches the coast, the sea is drawn back due to the vacuum effect caused by the wave. The water along the shoreline of Anguilla, the most northerly of the Leeward Islands in the Lesser Antilles, is dragged back dramatically, exposing the shallow coral reef and stranding many marine creatures.

The expanding shoreline is nature’s warning that a tsunami is approaching. It is a sign that there are only seconds or, at best few minutes, before the full impact of the first wave.

When the sea disappears

Survivors of the 2004 Indian Ocean tsunami said the water had receded for up to 2.5 kilometres along the coastlines of Indonesia and Thailand. Bystanders, many of them children, lingered on the exposed beach to observe the phenomenon and collect stranded fish.

The lack of tsunami awareness, combined with the absence of a coordinated alert system, contributed to the high death toll. There were an estimated 227,000 fatalities in 14 countries, with India, Indonesia, Sri Lanka and Thailand being the hardest-hit.

Still, some coastal communities in Indonesia were able to evacuate despite the lack of alarms, thanks to local traditions and folklore developed during previous tsunami disasters.

The tragedy highlighted the importance of understanding the early signals of an approaching tsunami.

For example, the "disappearing sea" may not happen at all. Sometimes the sea suddenly swells without any warning signs, surprising people and giving them little time to flee.

Tsunamis can be detected using the human senses

Learn more

Tsunami Evacuation Signs


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When the swell approaches the shore, the leading edge of the wave begins to slow down in shallow waters. As the tsunami loses its speed nearing the coast, the first wave suddenly swells as much as 20 metres in height. The massive wall of water rushes towards the coastline, demolishing everything in its way. The force of the wave is powerful enough to overturn boats, crumble palm trees and sweep away beach shacks.

Why is it called tsunami?

The flatter the coast, the stronger is the impact from the waves. This is the reason why the effects of the tsunamis are more devastating in ports, beaches and in the mouths of the rivers. It also explains the origin of the word. In Japanese, tsunami means bay or harbour wave.

11 March, 14:40 UTC: the second wave hits

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Tsunamis always surge in multiple waves. The first wave may not be the largest, and often it is the second or later waves that are the biggest.

The second wave, towering at 30 metres, hits after as little as five minutes. The coastal areas are completely devastated and under water.

We heard a second wave, and another. There were no houses anymore.

Markus KailhuluTsunami survivor

A tsunami survivor

In 1950, Markus Kailhulu was a 12-year-old living in the village of Hutumuri in Indonesia, when a tsunami hit the Moluccas. The villagers had evacuated to higher ground and witnessed the destruction brought by the waves.

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In line with the World Tsunami Awareness Day 2020, UNESCO's Intergovernmental Oceanographic Commission (IOC) introduces its project on documenting the survivors and eyewitnesses story of 1950 Ambon Tsunami. Marcus Kailuhu is a living witness of the 1950 Tsunami in Ambon. He was 12 years old when the tsunami happened in Hative Kecil Village (Ambon island), Moluccas - Indonesia.


We went to see and it looked like a flood from up there. We heard a second wave, and another. There were no houses anymore, all gone,’ he says. ‘The waves swept it all. It hit the edge of the mountain, it went back while taking the houses. The church was the only building left.

Markus KailhuluTsunami survivor

11 March, 15:00 UTC: other waves hit

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The first two waves were massive walls of water. The others now resemble a surging tide that inundates coastal areas, carrying debris from the destruction caused by previous waves.

Entire neighbourhoods have been washed away. Up on the hills, people stare at the devastation below with fear and incomprehension.

World Tsunami Awareness Day

People experiencing a tsunami should be aware that the danger may not have passed and should await official confirmation that it is safe to return. Raising awareness and education among the coastal communities is essential to prepare citizens on how to respond to the risk of tsunamis and cope with their aftermath. The UN-supported World Tsunami Awareness Day is the brainchild of Japan, which due to its repeated experience with tsunamis, has built up over the years major expertise in early warnings and public awareness to reduce future impacts. The event, held every year on 5 November, calls on countries, international bodies and civil society toraise tsunami awareness and share innovative approaches to reduce the death toll and devastation. Posters, flyers, e-learning courses and guidelines as well as games teach children, who are among the most vulnerable groups, how to identify and cope with a tsunami.

World Tsunami Awareness Day

"The game is fun and worth a try." Tsunami Ready board game, World Tsunami Awareness Day 2021, Indian Ocean.

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In line with the World Tsunami Awareness Day 2021, UNESCO's Intergovernmental Oceanographic Commission (IOC) introduces a series of videos on tsunami awareness and preparedness.


Playing the Tsunami Ready game

The Indian Ocean Tsunami Information Centre has developed a Tsunami Ready board game for children living in the coastal communities. "Playing the game, I’m able to learn a lot, such as what are the mitigation efforts that we can do at community, family as well as individual levels," says Sasa Tsairoo, a young game player who took part in the World Tsunami Awareness Day in 2021. "The game is fun and worth a try."

11 March, 19:43: rescue and recovery begins

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Local authorities issue an "all clear" that it’s safe to return to the coastal areas. People rush out into the streets, stunned. In the midst of flooding and devastation, search and rescue teams are busy across the archipelago in a desperate attempt to find survivors. Essential utilities like water, telecommunications, gas lines and electricity are inoperable. The coastline is devastated with flooding, damaged buildings, debris, fires and hazardous spills. Many are missing. Many more have lost their homes and may have to stay in shelters or public buildings until the reconstruction begins.

Reality or fiction?

This report is, in fact, the fictional scenario of a tsunami in the Caribbean, based on a drill exercise.

Caribe Wave is an annual tsunami preparedness exercise set up by the United Nations and overseen by IOC-UNESCO. The date and time of the simulation are not a random choice: it is the anniversary of the Japan earthquake and tsunami that killed nearly 16,000 people on 11 March 2011.

Under IOC-UNESCO’s oversight, the drills allow different countries and territories, emergency management agencies and communities at risk to test, validate and update their tsunami response plans.

The exercise, which in 2019 involved up to 800,000 people to simulate a catastrophic scenario, focuses on the coordination among countries, improving response procedures and training the local population to become prepared.

It also plays a crucial role in fostering resilient communities. Tsunamis are a real threat in the Caribbean. At least 75 have hit the region over the past 500 years.Some countries facing the Gulf of Mexico are also exposed to the double threat of tsunamis along their Pacific coastlines.

Thanks to Caribe Wave, over 50 coastal communities are now considered Tsunami Ready. This means that these communities now have the tools to face not just tsunamis, but also other coastal hazards.

Tsunami Ready recognition

As of 2021, six countries have piloted UNESCO’s Tsunami Ready Programme, while seven more are in progress.The programme aims to build resilient communities through awareness and preparedness strategies that will protect life, livelihoods and property from future tsunamis.

One of the achievements in becoming Tsunami Ready for us in Saint Kitts and Nevis was the ability to enhance our disaster preparedness. That was very vital and critical in also encompassing coastal hazards

Abdias SamuelNational Disaster Coordinator at the National Emergency Management Agency, Saint Kitts and Nevis

"The ability to enhance our disaster preparedness" – World Tsunami Awareness Day 2021, Saint Kitts and Nevis

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In line with the World Tsunami Awareness Day 2021, UNESCO's Intergovernmental Oceanographic Commission (IOC) introduces a series of videos on tsunami awareness and preparedness.


Preparing for future tsunamis

Millions of people live in coastal areas across the world where the rising sea level is increasing the risk of tsunamis.

In 2021, the United Nations set the goal of making all at-risk communities Tsunami Ready by 2030. IOC-UNESCO Tsunami Ready recognition has shown how different countries and communities can work together to reduce the risk of catastrophic coastal hazards that can cause death and destruction, hitting the livelihoods of vulnerable populations.

By improving warnings, enhancing preparedness and practicing response drills, these communities can prepare and become resilient, together.

"The Tsunami Ready programme reduces the risk for our communities." World Tsunami Awareness Day 2021

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Millions of people live in coastal areas where sea level rise is increasing tsunami risk. For this year's World Tsunami Awareness Day, we highlight how the Tsunami Ready programme reduces risk for our communities.



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