One set of lessons, in two views. Learn what to do when the ground shakes, then check yourself. Teachers get the notes, the answers and the timings.
Student view. Switch to the teacher view for answer keys and lesson notes.
Never forget
Strong or long shaking near the coast is your warning. Do not wait for a siren, a phone alert or a friend.
Head away from the sea and up, on foot. A tsunami is a series of waves, so the first one is not the last.
Waves can keep coming for hours and later ones can be larger. Go back only on the official all-clear.
Based on guidance from the Indian Ocean Tsunami Warning and Mitigation System and the International Tsunami Information Center.
The idea that saves lives
A hazard is natural. A disaster is not. The same wave only becomes a disaster where it meets people who are exposed and unprotected. That part is made by us, and so is the fix.
Exposure is who and what is in harm's way. Vulnerability is who is left unprotected, often because of poverty or exclusion. Change those, and the same hazard takes far fewer lives.
Early warning, safety plans, protection for the most at risk, and buildings that can stand up to the shaking: these are deliberate decisions. Failing to make them is the real cause of disasters.
The same 2004 earthquake would take far fewer lives today, because those decisions have now been made. That is why you are reading this page.
Nature warns you first, with no technology
Feel it
Strong or long shaking near the coast, long enough to knock you off balance.
See it
The sea pulls back and exposes the seabed, or the water behaves strangely.
Hear it
A loud roar or boom from the ocean, like a train or a low flying plane.
Step 1
You are on the coast when the ground shakes. Pick a setting and make your choices. See where each one leads.
How to run this in class
Step 2
27 questions on the signs, the science and who warns you. Every answer explains why, and links to the official source.
Check yourself
Seven topics, in order, from how a tsunami is born to what to do. Each answer explains why.
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How a tsunami is born
What does the seafloor do in an earthquake that causes a tsunami?
Answer: It moves up or down, pushing the water above it.
A tsunami needs the seafloor to move vertically. When a block of ocean floor lifts or drops, it moves the entire column of water above it, and that displacement becomes the wave.
Source: International Tsunami Information CenterEvery earthquake under the ocean causes a tsunami.
Answer: False
Most do not. A tsunami usually needs a large, shallow earthquake that moves the seafloor up or down. Earthquakes that only slide sideways move little water.
Source: International Tsunami Information CenterA tsunami is a tidal wave, caused by the daily tide.
Answer: False
Tsunamis come from earthquakes, landslides or volcanic eruptions that displace a huge volume of water. The tide has nothing to do with them, which is why the name tidal wave is misleading.
Source: International Tsunami Information CenterHow fast it travels
How fast can a tsunami cross the deep, open ocean?
Answer: About as fast as a jet airliner, around 700 to 800 km/h.
In the deep ocean a tsunami moves at jet speed, often 700 to 800 km/h. It slows and grows taller only as it reaches shallow coastal water.
Source: NOAA Tsunami SafetyThe deeper the water, the faster a tsunami travels.
Answer: True
The speed depends only on depth, c = sqrt(g x depth). In the deep ocean it is fast and low, and it slows down only near the coast.
Source: International Tsunami Information CenterA tsunami travels fastest in the shallow water near the coast.
Answer: False
It is the opposite. It races through deep water and slows sharply in the shallows, and that slowdown is exactly what makes it grow tall.
Source: International Tsunami Information CenterWhy it grows at the coast
Why does the wave grow tall as it reaches the coast?
Answer: It slows down, so the water behind piles up and the height rises.
This is shoaling. As the water shallows, the wave slows and the energy that was spread through the whole column is squeezed into a shorter and taller wave.
Source: NOAA Tsunami SafetyWhat is run-up?
Answer: The height the water reaches on land, above sea level.
Run-up is how high the water climbs on land. It depends on the wave and on the shape of the coast, which is why it can be very different even a short distance away.
Source: International Tsunami Information CenterWhich description of a tsunami is correct?
Answer: A series of waves that can keep arriving for hours.
A tsunami is a series of waves. The first is often not the largest, and later waves can be bigger, which is why you wait for the official all-clear.
Source: International Tsunami Information CenterWarnings you can see
The ground shakes hard near the coast, strong enough that standing is difficult, and it lasts more than 20 seconds. What do you do first?
Answer: Move inland and to higher ground immediately, on foot.
Strong, long shaking near the coast is nature telling you a tsunami may be coming. Close to the source there may be no time for an official alert, so you move first and ask questions later.
Source: International Tsunami Information CenterYou are near the beach when the sea suddenly pulls back and exposes the seabed. What does this most likely mean?
Answer: A tsunami may be arriving. Move to higher ground immediately.
The sea drawing back is a classic natural warning sign. The water retreats as the front of the wave arrives, and the wave can reach the shore soon after.
Source: International Tsunami Information CenterThe sea pulls back and the seabed is exposed. A friend starts filming for their feed. What should you do?
Answer: Drop the phone, tell your friend to run, and move inland and uphill now.
The receding sea is the front of the tsunami, not a safe spectacle. People have died walking onto the exposed seabed to film it. No clip, no likes and no live gifts are worth your life, so leave at once and take your friend with you.
Source: International Tsunami Information CenterBesides shaking and the sea pulling back, what is another natural warning?
Answer: A loud roar or boom from the ocean, like a train or a plane.
Many survivors describe a loud roar or boom as the wave approaches. It is another sign you can hear, and it means the water is close.
Source: International Tsunami Information CenterWhat to do
When you evacuate from a tsunami, what is usually the safest way to move?
Answer: On foot, heading inland and uphill.
Evacuating on foot keeps the roads clear and lets you move over ground a car cannot. Near the coast you may have far less time than a traffic jam allows.
Source: Indian Ocean Tsunami Warning and Mitigation System (UNESCO IOC)The first wave of a tsunami is always the largest, so once it passes you are safe.
Answer: False
The first wave is often not the largest, and more waves keep coming for hours. Return only when officials say it is safe.
Source: International Tsunami Information CenterAfter the water from a tsunami has pulled back, it is safe to return to the beach.
Answer: False
Waves keep arriving over a long period and can be larger than the last. Only the official all-clear means it is safe to return.
Source: International Tsunami Information CenterIf you are on a boat in deep, open ocean when a tsunami passes, what should you do?
Answer: Stay in deep water, where the tsunami is a low swell that a boat can ride out.
In deep water a tsunami is a low, fast swell that a boat can ride out. In a harbour the same wave can become a dangerous surge, so deep water is the safer place.
Source: International Tsunami Information CenterPut the local tsunami response in the right order, from first to last.
Answer: 1. Feel strong or long shaking near the coast 2. Move inland and to higher ground on foot 3. Stay there until officials give the all-clear
Act on the natural warning straight away, evacuate on foot, and only return when the official all-clear is given.
Source: International Tsunami Information CenterWho warns you
Which agency issues official earthquake and tsunami information for Indonesia?
Answer: BMKG
BMKG, the Meteorology, Climatology and Geophysics Agency, runs the national tsunami warning system, InaTEWS.
Source: BMKGIndia has one national tsunami warning centre. Where is it?
Answer: Indian Tsunami Early Warning Centre at INCOIS, Hyderabad
INCOIS in Hyderabad operates the Indian Tsunami Early Warning Centre, the single national authority for tsunami bulletins.
Source: INCOISIn the Philippines, which agency is the official source of tsunami warnings?
Answer: PHIVOLCS
PHIVOLCS, the Institute of Volcanology and Seismology, issues tsunami warnings. PAGASA handles weather, and NDRRMC coordinates the response.
Source: PHIVOLCSWhich department operates Bangladesh's tsunami early warning centre?
Answer: Bangladesh Meteorological Department
The Bangladesh Meteorological Department runs the national tsunami early warning centre and publishes tsunami warnings.
Source: Bangladesh Meteorological DepartmentWhich Malaysian service is the national authority for tsunami warnings?
Answer: The Malaysian Meteorological Department (MetMalaysia)
MetMalaysia is the national tsunami warning centre. NADMA coordinates disaster preparedness and response.
Source: MetMalaysiaThe warning system
Which system connects the participating countries so tsunami warnings are shared across the Indian Ocean?
Answer: The Indian Ocean Tsunami Warning and Mitigation System (IOTWMS)
After the 2004 Indian Ocean tsunami, UNESCO coordinated the IOTWMS so member states receive and share tsunami bulletins.
Source: Indian Ocean Tsunami Warning and Mitigation System (UNESCO IOC)Put these steps of a tsunami warning in the right order.
Answer: 1. An underwater earthquake displaces the seafloor 2. Monitoring centres detect the quake and the change in sea level 3. A tsunami bulletin is sent to national warning centres 4. National agencies alert the public
Sensors detect the event, a regional centre issues a bulletin, and national agencies warn their own communities.
Source: Indian Ocean Tsunami Warning and Mitigation System (UNESCO IOC)A natural hazard becomes a disaster when it meets which two things?
Answer: Exposure and vulnerability.
This is the UNDRR framing: a hazard is natural, but it only becomes a disaster when it meets exposure (people and things in harm's way) and vulnerability (people who are unprotected, often because of poverty or exclusion). Disaster risk = hazard + exposure + vulnerability.
Source: UNDRR, No Natural DisastersThere is no such thing as a natural disaster. What does that mean?
Answer: A hazard is natural, but a disaster is made by our decisions, such as warning, protection and where we build.
The hazard is natural, the disaster is not. The same wave is deadly where there is no warning or protection, and far less deadly where there is. Failing to act on those decisions is the real cause of disasters.
Source: UNDRR, No Natural DisastersStep 3
Bad ideas about tsunamis are dangerous. Tap a card to see the fact and where it comes from.
How to run this in class
Read a myth aloud and ask the class to vote true or false before you reveal the fact. The source on the back of each card is where the correction comes from.
Step 4
The official agency that would warn people in each participating country, plus the science and safety sites behind it. Filter by the kind of resource you need.
Sunda Arc and Sunda megathrust, the source of the 2004 Aceh tsunami
Meteorology, climatology and geophysics agency. Issues national earthquake and tsunami information.
The Indonesia Tsunami Early Warning System, BMKG real time monitoring and bulletins.
What causes a tsunami and what to do, explained by BMKG for the public.
National disaster risk map with local hazard profiles, useful for classroom mapping work.
The Andaman Sea and Sunda Arc, with a long east coast exposed to distant waves
Ocean science institute that runs India national tsunami warning service.
Real time tsunami advisories for India, operated by INCOIS in Hyderabad.
National Disaster Management Authority, with preparedness guidance and school safety material.
The Andaman coast, struck hard by the 2004 Indian Ocean tsunami
National weather and seismology service, a key source of earthquake and tsunami information.
Runs the national disaster warning centre and public alert system.
The Bay of Bengal, exposed to distant waves from the Sunda and Makran zones
Operates the national tsunami early warning centre and publishes warnings.
The live tsunami information page from BMD.
National ministry for disaster preparedness, response and relief.
The Philippine Trench and Manila Trench, both capable of local tsunamis
Institute of volcanology and seismology. The official source of tsunami warnings.
National disaster risk reduction council, coordinating preparedness and response.
Hazard maps and risk assessment from the University of the Philippines.
The Makran subduction zone in the Gulf of Oman, a distant but real source
The tsunami unit of the National Center of Meteorology.
Live seismic monitoring from the National Center of Meteorology.
National emergency crisis and disasters management authority.
The Makran subduction zone, shared with Pakistan along the Gulf of Oman
International Institute of Earthquake Engineering and Seismology, the national seismic science centre.
National meteorological service, a source of official hazard information.
Distant waves crossing the Indian Ocean, arriving hours after the source event
National bureau for risk and disaster management, with public awareness material.
National meteorological service and the main source of official warnings.
The Makran subduction zone, the main local tsunami source in the Arabian Sea
National meteorological service, home of the National Tsunami Early Warning Centre.
National Disaster Management Authority, with preparedness and response guidance.
Distant waves from the Andaman and Sunda zones, reaching the west coast
The Malaysian Meteorological Department, the national tsunami warning centre.
What a tsunami is, its warning signs, and what to do, in plain language.
National Disaster Management Agency, coordinating preparedness and response.
Distant waves from across the Indian Ocean, arriving hours after the source
National weather and warning service, the official source of hazard alerts.
Official government portal, where the Department of Risk and Disaster Management publishes.
The regional bodies that connect every participating country.
The Indian Ocean Tsunami Warning and Mitigation System, linking all eleven countries.
UNESCO and NOAA centre with authoritative safety guidance and teaching material.
Issues the ocean wide bulletins that national agencies in the Indian Ocean receive.
UNESCO centre in Jakarta, producing education and outreach material for the region.
Using these in class
Ask each student to open their own country's warning agency and find one fact they did not know. Then compare: why do some countries have minutes and others hours before a wave arrives?
Step 5 · Case study
This is the event that built the system every country on this page now depends on. On 26 December 2004 an earthquake off Sumatra tore open a rupture about 1,300 kilometres long, and the water it displaced crossed the entire ocean. Around 227,000 people died in 14 countries. Here is how it happened, step by step.
Step through the first minutes at the coast. The sea receding is not a safe moment to walk out and film, it is the front of the wave arriving.
A quiet morning
The sea is calm and the tide is normal. Then, deep below, the fault between two plates gives way.
The receding sea is a warning, not content.
When the sea drains away, the wave is already on its way. Every minute spent filming it, chasing a For You page, likes or live gifts, is a minute you should be running inland. No clip is worth your life, and a screen cannot save you.
How to run this in class
Ask the class why a receding sea is dangerous rather than exciting. In the 2004 tsunami, people walked onto the exposed seabed to collect fish, and children followed, minutes before the wave returned. The drawdown is the one warning that arrives without any technology.
Press play and watch the coasts light up in the order the water reached them, from about twenty minutes in Aceh to about sixteen hours in South Africa.
Coasts reached
Elapsed 0 min
Reached 0/ 13
Press Play, or drag the slider, to move through the sixteen hours after the earthquake.
Wavefront: first arrival time modelled on measured ocean depth (GMRT), using the long wave speed c = sqrt(g · depth), seeded along the 2004 rupture. Markers and the reached list use the recorded arrival at each coast, from USGS and field surveys gathered by the International Tsunami Information Center. The model can reach a coast before the damaging waves, so the two times can differ. A coarse model is not an operational forecast, so in a real event follow your national warning agency.
USGS event page International Tsunami Information Center
How to run this in class
Distance was no guarantee of safety: Somalia was hit harder than Bangladesh, because the shape of the ocean floor and the coastline decides where the energy goes.
Step 6
Seven more events, from 1960 to 2022, each one a lesson. Open an event to see what happened and what it changed. The lessons repeat, because the water behaves the same way every time.
Chile, then across the Pacific · Magnitude 9.5
The most powerful earthquake ever recorded struck Chile and sent a tsunami across the entire Pacific, killing people in Hawaii, Japan and the Philippines many hours later.
Lessons learned
Mindanao, Philippines · Magnitude 8.1
A late night earthquake in the Moro Gulf sent waves onto the coasts of Mindanao while people slept. It remains the deadliest tsunami in Philippine history, with thousands killed.
Lessons learned
Papua New Guinea · Magnitude 7.0
A moderate earthquake triggered an underwater landslide that produced a tsunami far larger than the earthquake alone would suggest. The wave struck villages near Aitape with almost no warning.
Lessons learned
north east Japan · Magnitude 9.1
A massive earthquake off Japan drove a tsunami over sea walls that many believed could never be topped. Around 18,000 people died or went missing, in a country with one of the best warning systems in the world.
Lessons learned
Sulawesi, Indonesia · Magnitude 7.5
An earthquake in Palu Bay triggered a fast local tsunami. Sirens did not sound, an earlier warning had been cancelled, and people were still on the beach when the waves arrived within minutes. Thousands died.
Lessons learned
between Java and Sumatra, Indonesia · Volcanic
An eruption of the Anak Krakatau volcano sent part of the mountain sliding into the sea, creating a tsunami with no earthquake to warn of it. The waves hit coastal communities around the Sunda Strait at night.
Lessons learned
Tonga, then across the Pacific and beyond · Volcanic
A huge undersea volcanic eruption near Tonga produced a tsunami that raced across the Pacific and was measured around the world, with surges reaching distant coasts.
Lessons learned
How to run this in class
Give each group one event and ask them to find the pattern: who acted early and lived, who waited and why. Then, in their own words, they write the one rule their event proves. Almost every group will land on the same three rules, which is the point.
Switch to the teacher view for answer keys, facilitator notes and a ready-made lesson plan, all on this same page.
Teacher view
Built for a single class period. Adjust freely. Everything you need is on this page.
Life-safety wording on this page follows guidance from the Indian Ocean Tsunami Warning and Mitigation System, the International Tsunami Information Center, and the national agencies listed in Step 4. Please review it against your own school's drill procedure before teaching.
Check when your session starts in your own timezone.
