50 Fun Facts About Tsunami

The word 'tsunami' is Japanese. What does it literally mean?

Fishermen would sail out, notice nothing unusual at sea, and return to find their harbour village destroyed.

What fundamentally causes a tsunami?

Earthquakes are the usual trigger, but landslides, eruptions, glacier calving and even meteorites can do it.

Why do scientists dislike the term 'tidal wave' for a tsunami?

The name stuck because an arriving tsunami often looks like an extraordinarily high tidal bore rather than a breaking wave.

Which ancient Greek historian first argued that tsunamis were caused by undersea earthquakes?

He made the case in his History of the Peloponnesian War around 426 BC; real understanding did not arrive until the 20th century.

The oldest human record of a tsunami, from 479 BC, comes from which Greek colony?

The wave may have saved the colony from an invasion by the Achaemenid Persians.

Which Roman historian described the classic tsunami sequence after the 365 AD wave devastated Alexandria?

He recorded the earthquake, the sudden retreat of the sea and the gigantic wave that followed.

Which country has the longest recorded history of tsunamis?

Tsunami science and response measures began there after a disaster in 1896.

Roughly what proportion of tsunamis occur in the Pacific Ocean?

They can happen wherever there is a large body of water, including lakes.

Roughly how fast does a tsunami travel across the deep ocean?

Speed depends on water depth: over a 5,000-metre-deep Pacific it works out at about 806 km/h, roughly jet-airliner speed.

Roughly how tall is a tsunami in the deep ocean?

With a wavelength of up to 200 km, ships cannot feel one pass; it only rears up as it reaches shallow water.

What is a tsunami's deep-ocean wavelength, compared with about 100 metres for wind waves?

That enormous length is why even the deep ocean counts as 'shallow water' in the wave physics.

What is the process called that makes a tsunami grow taller and slower as it enters shallow water?

Speed drops below 80 km/h and the amplitude grows enormously, following Green's law.

What is the temporary rise in sea level called when a tsunami's peak reaches the shore?

It is measured in metres above a reference sea level, and the first wave is not always the highest.

What is 'drawback'?

It happens when the trough arrives first, exposing the seabed; curious people who go out to collect stranded fish are in mortal danger.

What is a typical wave period for a damaging tsunami?

The sea recedes for about three minutes, floods in over the next six, then drains back out for six more, and repeats.

Where did a 1958 landslide cause the highest wave ever recorded, at 524 metres?

The wave sank two of three boats anchored in the bay but struck land almost at once and did not travel far.

What triggered the record 1958 megatsunami in an Alaskan inlet?

About 30 million cubic metres of rock crashed into the narrow inlet; the impact was heard 80 km away.

In 1963 a landslide from Monte Toc sent a wave over which Italian dam, killing around 2,000 people?

The wave overtopped the 262-metre dam by 250 metres; scientists coined the term megatsunami for such events.

Which La Palma volcano is at the centre of a disputed claim that a landslide could cause an Atlantic megatsunami?

No landslide big enough to cause a transoceanic tsunami has occurred in recorded history, and many geologists doubt the danger.

A tsunami around 1600 BC from which volcano is often blamed for the decline of Minoan civilisation?

The 1883 Krakatoa and 2022 Hunga Tonga eruptions also raised deadly waves; over 20% of volcanic deaths in 250 years came from tsunamis.

The 2018 collapse of which volcano killed 426 people with a tsunami that arrived without warning?

Volcanic tsunamis are less understood than seismic ones, which makes warning much harder.

What is a meteotsunami caused by?

They lack transoceanic reach but can be amplified by resonance; the Balearic Islands call them 'rissaga'.

What is a tsunami called when it cannot be linked to any known earthquake?

Before international communications, a wave in Japan might have come from a quake in the Americas nobody had heard about.

The accidental 1917 explosion in which Canadian harbour triggered an 18-metre tsunami?

It remains one of the few clear examples of a human-made tsunami.

Which country's military tried to create tsunamis with explosives in World War II's failed "Project Seal"?

The tests were run at the tip of the Whangaparaoa Peninsula near Auckland.

Why do underwater nuclear explosions make poor tsunami weapons, as the 1946 Bikini Atoll tests showed?

Waves from the 20-kilotonne bombs were only 3 to 4 metres high by the time they reached shore.

On what date did the great Indian Ocean tsunami strike?

British and Commonwealth media dubbed it the Boxing Day tsunami.

Roughly how many people were killed by the 2004 Indian Ocean tsunami?

Deaths came in 14 countries, worst of all in Aceh, Sri Lanka, Tamil Nadu and Khao Lak.

Off which Indonesian province was the epicentre of the 2004 earthquake?

The Sumatra-Andaman quake ruptured 1,200 to 1,300 km of fault, the longest rupture ever observed.

How long did the faulting of the 2004 earthquake last, the longest ever observed?

It made the whole planet vibrate by as much as 10 mm and triggered quakes as far away as Alaska.

Where had ten-year-old Tilly Smith learned the tsunami warning signs she recognised on a Thai beach in 2004?

She credited her geography teacher, Andrew Kearney; her parents warned others minutes before the wave hit Maikhao beach.

Why was no drawback seen on the African coast in 2004?

The initial wave dropped on the eastern side and rose on the western side, so west-facing coasts got the crest first.

Which animals in Sri Lanka were reported moving inland before the 2004 wave, possibly having heard it coming?

The idea that animals sense tsunamis is controversial; meanwhile some humans walked out to investigate the exposed seabed and drowned.

On what date did the Tohoku earthquake and tsunami hit Japan?

Japanese often refer to it simply by its numerical date, 3.11.

Waves from the 2011 Japanese tsunami may have reached what height at Miyako in Iwate Prefecture?

Around Sendai the water travelled at 700 km/h and reached up to 10 km inland; residents had eight to ten minutes' warning.

Which nuclear disaster was triggered by the 2011 tsunami flooding emergency generators?

The waves overtopped the plant's sea wall; the 2011 tsunami also toppled more than half of Iwate's 25 km of barrier walls.

The 2011 disaster, the costliest natural disaster in history, caused economic damage of over how much?

Official figures in 2021 put the dead at 19,759, with 2,553 still missing.

The 1946 Aleutian Islands earthquake sent a 14-metre surge into which Hawaiian town?

Between 165 and 173 people died; on Molokai, villagers who saw the sea recede fled uphill and all survived.

Where is the Pacific Tsunami Warning System based?

Not every big Pacific earthquake makes a tsunami, so computers weigh the risk of each one.

One of the most successful tsunami detection systems uses what, attached to buoys?

They constantly monitor the weight of the water column above and relay readings in real time.

Japan has built tsunami walls up to what height to protect coastal towns?

Some places also have floodgates up to 15.5 metres, but tsunamis often simply overtop the barriers.

The 1993 Okushiri tsunami in Hokkaido produced waves as tall as what?

The 30-metre waves washed straight over the wall surrounding the port town of Aonae within minutes of the earthquake.

The 1908 tsunami that killed over 123,000 in Sicily and Calabria followed an earthquake at which city?

It is among the deadliest natural disasters in modern Europe, where tsunamis are an underestimated hazard.

On which feast day in 1755 did an earthquake and tsunami devastate Lisbon?

Survivors who fled to the docks watched the sea recede before the wave rushed up the Tagus about 40 minutes after the quake.

The Tauredunum event of 563 CE was a large tsunami on which lake?

A landslide destabilised sedimentary deposits, proving lakes are not immune.

The Storegga Slide, which sent a tsunami towards Britain about 8,000 years ago, happened in which sea?

The cause of the sediment failure is unknown; overloading, an earthquake or escaping gas hydrates are all candidates.

Tsunamis that cross entire oceans after megathrust earthquakes are known by what name?

The 1960 Valdivia, 1964 Alaska, 2004 Indian Ocean and 2011 Tohoku quakes all produced them.

What magnitude was the 1960 Valdivia earthquake, the most powerful ever recorded?

The 1964 Alaska and 2004 Indian Ocean quakes both measured 9.2, and the 2011 Tohoku quake 9.0.

The Sieberg-Ambraseys tsunami intensity scale of 1962 was used in which sea?

The Imamura-Iida scale of 1963 served the Pacific and was later modified by Soloviev in 1972.

How many points are on the Integrated Tsunami Intensity Scale proposed in 2013?

ITIS-2012 was designed to line up with the ESI2007 and EMS earthquake intensity scales after the 2004 and 2011 disasters.