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Mega-disasters: the 2004 Indian Ocean and 2011 Japan tsunami

Edexcel IAL Geography · WGE01 Global Challenges

Mega-disasters are rare, high-magnitude events that affect more than one country or have unusually large impacts, so they need a regional or global scale of response.

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What makes a mega-disaster?

Very high magnitude (often megathrust earthquakes, large tsunami or regional droughts).
Large areas and often several countries affected.
Huge death tolls or economic losses, with knock-on effects on regional and global economies.
A response that is beyond any one government: international aid, military logistics, insurance and new warning systems.

2004 Indian Ocean tsunami

26 December 2004, magnitude 9.1 earthquake off north-west Sumatra on the India-Burma plate interface (USGS).
More than 200,000 casualties; in Aceh and North Sumatra provinces of Indonesia at least 108,100 people were killed and 127,700 were missing, presumed dead.
The tsunami reached northern Sumatra in about 30 minutes, Thailand in 1.5 to 2 hours and Sri Lanka in 2 to 3 hours, and reached East Africa. Run-up exceeded 30 m in western Sumatra.
There was no ocean-wide warning system. An Indian Ocean system became partially operational in 2005, and by 2011 Australia, India and Indonesia were regional tsunami service providers (UNESCO IOC).

2011 Japan (Tohoku) earthquake and tsunami

11 March 2011, Mw 9.1 on the Japan Trench, the largest recorded in Japan (NOAA NCEI).
15,901 deaths and 2,519 missing, presumed dead (National Police Agency, as of March 2026).
Tsunami up to almost 40 m in Iwate Prefecture, affecting about 2,000 km of coast, arriving within 30 minutes.
Estimated losses about US$220 billion in Japan alone; the tsunami disabled cooling at three Fukushima Daiichi reactors, causing a major nuclear accident, and disrupted global supply chains.
A developed country with warnings and sea walls still suffered huge losses: the waves overtopped defences.

Skill (4): tsunami travel time maps

Travel time maps use isochrones: lines joining places the wave reaches at the same time.

Tsunami speed = square root of (g x depth), with g = 9.8 m/s2 (NOAA). At 4,600 m depth this is about 765 km/h, so a tsunami can cross an ocean in less than a day; near the shore it slows to about 30 to 50 km/h and grows taller.

Use the maps to work out how much warning time different coasts had.

Worked example

Calculate the speed of a tsunami in water 4,000 m deep, in km/h.

v = square root of (9.8 x 4,000) m/s
= 198 m/s
x 3.6 to convert to km/h

Answer: About 713 km/h.

Key idea: Mega-disasters: rare, huge, multi-country, need international response. 2004: Mw 9.1, over 200,000 casualties, no warning system. 2011: Mw 9.1, about 15,900 dead and 2,500 missing, US$220 billion losses, Fukushima.

Check yourself

Using v = square root of (g x depth) with g = 9.8 m/s2, find the tsunami speed in km/h in water 4,600 m deep. Give your answer to 3 significant figures.
Show answer
764 km/h. square root of (9.8 x 4,600) = 212.3 m/s; x 3.6 = 764 km/h (NOAA quotes almost 765 km/h).
Practice question: a coast is 1,600 km from the earthquake across ocean averaging 4,000 m deep. Using v = square root of (9.8 x 4,000) m/s, how many hours does the tsunami take to arrive? Give your answer to 1 decimal place.
Show answer
2.2 hours. Speed = 713 km/h; time = 1,600 / 713 = 2.2 hours.
For the 2011 Japan disaster, the National Police Agency reported 15,901 deaths and 2,519 missing. Find the total dead and missing.
Show answer
18420. 15,901 + 2,519 = 18,420.
In Aceh and North Sumatra, at least 108,100 people were killed and 127,700 were missing, presumed dead (USGS). Find the total.
Show answer
235800. 108,100 + 127,700 = 235,800.
On a tsunami travel time map, an isochrone joins places that
- have the same wave height
- the wave reaches at the same time
- have the same ocean depth
- had the same number of deaths
Show answer
the wave reaches at the same time. Iso = equal, chrone = time.
Which factor did most to raise the 2004 death toll in countries far from Sumatra, such as Sri Lanka?
- The waves arrived within 30 minutes everywhere
- The earthquake was much stronger in Sri Lanka
- Sri Lanka is on a plate boundary
- There was no Indian Ocean tsunami warning system, so people were not evacuated
Show answer
There was no Indian Ocean tsunami warning system, so people were not evacuated. Sri Lanka had 2 to 3 hours, but no warning reached most coasts.
Both earthquakes were Mw 9.1. Explain why the 2011 Japan disaster killed far fewer people than the 2004 Indian Ocean disaster.
Show answer
Japan had a tsunami warning system, evacuation drills and building codes, and higher capacity to cope, while in 2004 there was no warning and coastal communities were poorer and more vulnerable.. Japan had warnings, preparation and high capacity; 2004 coasts had no warning system and higher vulnerability.

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Last updated 8 November 2026. Spotted a mistake? Tell us.