Tsunamis are giant waves, usually triggered by earthquakes on the sea floor, and are considered one of the deadliest natural disasters of recent decades. They can bring devastating effects to the affected coasts and pose a great danger to people in vulnerable areas. Powerful tsunamis have the power to sweep away land and everything near the coast – even cargo ships or entire buildings. In the past, there have been giant waves that killed many people and left a trail of destruction behind.
Whether in 2004 in the coastal area of the Indian Ocean or in 2011 in Japan, tsunami disasters hit these populations with full force. The 2004 tsunami, the deadliest of its kind, killed more than 220,000 people. Flooding in Japan killed 16,000 people. The 2011 tsunami also triggered the Fukushima nuclear disaster. Fortunately, disaster preparedness in at-risk areas has improved considerably since then.
Giant waves cannot be controlled. It is therefore even more important to learn from past disasters and develop protective measures in the form of early warning systems. Malteser International is also committed to immediate relief measures and the reconstruction of affected areas.
What is a tsunami?
A tsunami consists of a series of waves caused by an external event such as an undersea earthquake. If the ground below the sea level suddenly rises or falls, huge waves are generated above the epicentre and spread in all directions at high speed. While tsunamis have a devastating effect on land, they are hardly noticeable in the open ocean.
This treacherous characteristic of the tsunami coined its name: the word tsunami is Japanese and translates to “harbour wave”. When Japanese fishermen returned to their home port after a calm day at sea and found it completely devastated, they could only explain the disaster by the fact that the giant wave first originated in the port.
In the open ocean, wave peaks usually only reach a maximum height of 80 centimetres and therefore do not pose a threat even to small boats. However, when a tsunami hits low coastal waters, the mass of water becomes higher and higher. The resulting wave brings with it enormous destructive power, and even small waves can reach several kilometres inland. There, the water sweeps away trees, cars and houses. In most cases, it is not just one wave. Instead, several waves often follow one another. Tsunamis are therefore one of the most devastating natural disasters.
What causes a tsunami?
A tsunami occurs when a huge amount of water is suddenly displaced into open water. This is caused by an earthquake, landslide, volcanic eruption or meteorite impact. The most frequent catalysts for tsunamis are underwater earthquakes, known as marine earthquakes. Tectonic plates shift and set large amounts of water in motion, resulting in giant waves. Their height increases as the water becomes shallower. Near the coast, waves are usually several meters high.
But not every underwater earthquake triggers a tsunami – strictly speaking, only 10 to 20 percent of all marine earthquakes cause a giant wave. Only when marine earthquakes reach a magnitude of 7.0 on the Richter scale and the Earth’s tectonic plates shift vertically is there enough force to cause a devastating flood wave.
Less frequently occurring triggers for tsunamis are volcanic eruptions. These can eject huge amounts of rock and ash into the ocean, creating a pressure wave that can trigger a tsunami. An example of this is the eruption of the stratovolcano on Knight Island (Papua New Guinea) in 1888. This natural phenomenon was followed by a tsunami which devastated the neighbouring islands.
Tsunami risk areas: The danger is particularly high in these areas
Tsunamis pose a threat to coastal areas in many parts of the world. In principle, they can occur in all oceans and sea areas. However, regions such as the Pacific Ocean, where tectonic plates adjoin each other, are particularly at risk. On the northern edge of the Pacific plate is the Pacific Ring of Fire. This is one of the most tectonically active regions on Earth. Due to the high incidence of earthquakes, the majority of tsunamis occur here.
However, other regions with significantly less activity on plate margins, such as the Indian Ocean, the Mediterranean Sea or the Atlantic Ocean, are also at risk of tsunamis. Due to their geographical position, coastal countries in these regions are particularly affected. These include Japan, Indonesia and Thailand.
The consequences of tsunamis
Photos of past tsunami disasters paint a picture of total destruction: ports, villages and towns near the coast are swept away. What remains is the debris of uprooted trees, collapsed buildings and destroyed infrastructure. The affected areas are usually covered with mud, sand and garbage. This usually renders fields and other agricultural land completely unusable. Salt and sand from the sea can also clog up water supplies from wells. In addition to the immediate destruction in coastal areas, tsunamis can kill countless people. In addition, many people in the affected areas lose their homes and livelihoods.
Electricity, gas and telephone lines are destroyed. Railways, roads, bridges and ports no longer exist, leaving the entire region cut off from the outside world. This also endangers the supply of food, drinking water and medicines. The long-term economic, social and ecological effects only become apparent in the post-disaster period. Reconstruction after such a devastating tsunami can take years and requires considerable resources and assistance from outside. Still, the devastating tsunami that struck Southeast Asia in 2004 is a rare exception. Only about 10 percent of all giant waves cause such damage or deaths.
The most devastating tsunamis of the last 100 years
The following table shows an overview of the most severe tsunamis since 1923, sorted by the number of fatalities. The data illustrate that even comparatively low waves can cause great damage. The most recent tsunamis to date occurred in 2018 on the Indonesian islands of Java and Sumatra and in 2022 as a result of an eruption of the Hunga Tonga-Hunga Haʻapai underwater volcano. However, both are not among the most devastating giant waves.
| Day of the event | Country | Magnitude of earthquake | Maximum wave height in meters | Number of fatalities |
| 26.12.2004 | Southeast Asia | 9.1 | 50.90 | 227,899 |
| 11.03.2011 | Japan | 9.0 | 38.90 | 15,890 |
| 16.08.1976 | Philippines | 8.1 | 8.50 | 4,376 |
| 27.11.1945 | Pakistan | 8.0 | 15.24 | 4,000 |
| 04.11.1952 | Russia | 9.0 | 18.00 | 4,000 |
| 02.03.1933 | Japan | 8.4 | 29.00 | 3,022 |
| 22.05.1960 | Chile | 9.5 | 25.00 | 2,234 |
| 17.07.1998 | Papua New Guinea | 7.0 | 15.03 | 2,205 |
| 01.09.1923 | Japan | 7.9 | 13.00 | 2,144 |
| 04.08.1946 | Dominican Republic | 7.8 | 5.00 | 1,790 |
Disaster risk reduction, emergency relief and reconstruction: Our tsunami relief efforts
When tsunamis destroy entire coasts, fast and efficient aid is crucial. Malteser International supports affected areas that face numerous challenges after such a natural disaster. Expert teams or emergency medical teams (EMTs), consisting of doctors, paramedics and experts in drinking water and hygiene, can be quickly dispatched in the event of a crisis, such as in October 2018 after a tsunami in Indonesia. We also provided emergency aid and reconstruction support in tsunami-affected communities from 2005 to 2008.
The focus of our tsunami aid was, among other things, on basic medical care, the reconstruction of schools, houses and other infrastructure, and the establishment of income-generating measures. Clean drinking water and hygienic sanitation facilities are essential to prevent the spread of disease after the tsunami. Therefore, we also worked in affected areas to repair damaged water supply systems.
In addition to physical health, the mental health of those affected is also of great importance. Malteser International therefore focuses on psychosocial support in the aftermath of tsunamis, for example in the form of counseling programs. In this way, people receive professional help to cope with their traumas. Our work is generally aimed at helping affected communities on their way to reconstruction.
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