Japan has begun a massive relief operation in response to three consecutive emergencies: earthquake, tsunami, and the threat of nuclear radiation from damaged reactors. The full extent of the disaster has yet to be assessed, but the prime minister, Naoto Kan, described it as the worst crisis in his country since the second world war.

The magnitude 9 earthquake, which triggered a devastating tsunami that ravaged the northeast coast of Japan, was one of the strongest since records began (more than a century ago) and the worst in Japanese history. The epicentre was 120 km off the coast, causing a 10 m high wave that surged 0.5 km inland in some areas, destroying everything in its …