Tsunamis: Disasters Explained

Tsunamis can destroy lives, homes, crops and roads in the blink of an eye. Learn more about what they are, what causes them and what devastation they can leave behind.

A tsunami is a series of giant, fast-moving waves caused by volcanic eruptions, earthquakes or landslides.

They are rare, usually happening around twice a year, but they can have devastating effects. Entire communities can be destroyed by these powerful waves – lives, homes, crops, roads, bridges and airports can all be completely swept away.

Find out more about tsunamis, what causes them and what the effects are for families whose lives have been turned upside down by this type of disaster.

What is a Tsunami?

Boats and other debris washed up on the beach, Indonesia

A tsunami is a series of giant waves caused by earthquakes or undersea volcanic eruptions.

It sends a surge of water onto land, often reaching heights of over 100 feet. Although tsunami waves do not reach great heights out in the depths of the ocean, as they enter shallower water they begin to grow in energy and height.

Tsunami waves can tear across the sea at speeds of 500 miles an hour. The speed is determined by the depth of the ocean – travelling as fast as a jet plane over deep waters and slowing down when reaching shallow waters.

In 2004, ShelterBox responded to the Indian Ocean Tsunami, also known as the Boxing Day Tsunami. It is considered to be the most devastating tsunami on record. Over 12,000 families in Indonesia and Sri Lanka received ShelterBoxes following the deadly disaster. The boxes included tents and essential aid items to help families recover. This occasion was the first time that ShelterBox deployed people to the affected countries to oversee the distribution of the aid.

What causes a tsunami?


The most common cause of a tsunami is an earthquake on the seafloor. When slabs of rock move past each other suddenly, it causes the overlying water to move, sending out a series of rolling waves that grow into a tsunami.


Underwater landslides can also cause tsunamis. The movement of rock sliding downhill draws the water down from all sides, colliding in the middle. This launches a great wave radiating out.

Volcanic eruptions

Volcanoes can create a tsunami when an explosive eruption causes the tectonic plates to move, generating huge waves. A tsunamic can also be created when large amounts of lava flow into the ocean.

Asteroid or meteor crashes in the ocean have also been known to cause tsunamis, but these are rare.

What are the effects of a tsunami?

Tsunamis can have a devastating effect on people’s lives.

They can completely wash away homes, causing families to lose everything they own and leaving them exposed to the wind and extreme temperatures.

Their destructive force is so powerful that huge ships can be carried up to a kilometer inland. Families must deal with huge piles of debris that need clearing before they can start rebuilding their homes and lives.

Tsunamis also cause a huge loss of life, as they can be hard to detect. Tsunami waves don’t grow in size until they reach shallower waters, which means they can strike with very little warning.

Learn more about how we responded to the devastating earthquakes and tsunami in Indonesia in 2018.

After a tsunami, floodwaters and damage to infrastructure can lead to contaminated water and food supplies. This increases the risk of dangerous diseases like malaria and cholera. If families are staying in shared shelters and living at close quarters, this can make spreading diseases easier.

As with any disaster, people can suffer from traumatic injuries after a tsunami. What makes a tsunami different is the suddenness with which it strikes. People may even experience mental health issues such as post-traumatic stress disorder.

2011 Tsunami in Japan

Children on top of ShelterBox
Roads cleared, but rubble everywhere else
Aid worker gazing across the waterlogged landscape
Setting up a Tent

In 2011 ShelterBox supported families affected by the Japan earthquake and tsunami with emergency shelter.

The disaster created shortages of food, water, shelter and medicine. Over 1,600 families received essential aid following the tsunami.

We provided families with ShelterBoxes containing tents and other essential items to help with the recovery process.

But the response did not come without challenges. One of the main challenges was managing the threat of nuclear disaster caused by the tsunami.

Our teams needed to make sure that they stayed safe, and that they were not being exposed to dangerous levels of radiation.

To avoid the potential risk of exposure to radiation, teams were provided with personal Dosimeters, which are devices that measure absorbed doses of radiation, and protective suits should unsafe levels be reached. This enabled them to operate safely outside of the restricted zone.

On the ground, we worked with Japanese Rotary members and the local Prefecture governments to help distribute ShelterBoxes.



A tsunami warning system is used to detect tsunamis in advance.

It uses a network of seismic monitoring stations and sea-level gauges to help scientists detect whether a tsunami has been triggered by an earthquake.

Tsunami wave simulations can then predict the wave height and arrival time at the coast.

But because tsunamis can appear so suddenly, the warnings are not always delivered to the communities at risk in time. Before the 2011 Japan tsunami, tsunami warnings were broadcast just minutes before it’s arrival. The warnings also underestimated its size, meaning that many people failed to evacuate.

Education, drills, evacuations signs and clear protocols are key in preventing the loss of life.


People helping each other take ShelterBoxes off a truck

ShelterBox provides emergency shelter and essential tools for families affected by tsunamis and other disasters.

Shelter and essential items like blankets, cooking sets and mosquito nets can allow families to create a safe space to begin to recover.

Families often don’t have access to clean water in the aftermath of disasters like tsunamis so water filters and carriers can allow them to produce clean water.

Power lines can also be damaged for long periods of time, so solar lights are a practical solution, enabling families to pick up their normal routines.

We’ve supported families affected by tsunamis all over the world. In 2004, we supported families in the aftermath of the Indian Ocean Tsunami, and in 2011 we helped families on the road to recovery after the Japan earthquake and tsunami.

More recently, in 2018 we responded to the earthquake and tsunami that shook Indonesia.

Recovery in Indonesia

In 2018, the island of Sulawesi in Indonesia was hit by a 7.5 magnitude earthquake and a devastating tsunami, flattening everything in its path.

Some people’s homes survived the earthquake, only to be swept away moments later by the deadly tsunami that followed.

One of those people was Fatnizar. Read her incredible story of recovery and learn how her new shelter enabled her to reopen her business.

Explore More Disasters


Floods are among the most common and devastating disasters. Read more about why they happen and their effects.


Find out everything you need to know about hurricanes and typhoons.


Learn what volcanoes are, how they erupt, and the effects of a volcano eruption.