An earthquake's force has the caprice of a wild, giant child, flattening this and pardoning that, as if according to some mad moral scheme. But the tsunami allows no such cosy anthropomorphism: nothing within its compass is spared. Everything, excepting only the peculiarly rugged, is demolished, dismembered, pulverised, atomised, by nothing more awesome than the power of water.

No one who visited Banda Aceh after the earthquake and tsunami of Boxing Day 2004 will forget that vista of devastation: something like half of the large and prosperous seaside city reduced to stinking matchwood; its population simply abolished. And where the force of the water was spent, at a point one could almost have drawn on the ground, normal life or something like it continued just as before.

Any disaster zone, whether natural or man-made, has psychic ramifications for the survivors, but again the tsunami was unique in my experience in wiping out their self-confidence and self-awareness with a sort of clinical completeness. The surviving masters of the city called press conferences and announced plans for recovery and rehabilitation, but it dawned quite quickly that they were living in a world that bore little relation to the one the tsunami bequeathed them. The havoc was so complete it beggared all efforts to comprehend or confront it. A realistic recovery plan had to wait on the arrival of untraumatised outsiders.

Film of the disaster helped us to understand its mental effects. Like the quake, the first note of terror is the familiar element misbehaving: earth turning to jelly, water turning to steel. Witnesses on that day recalled how something strange, some behaviour of the sea that defied experience, a churning, strange patterns on in the surface, uncanny noises, evolved at stunning speed into the nightmare Hokusai painted, the mighty wave coming deep inshore so fast it could not be outrun. Those who could not haul themselves on to roofs or hillsides were lost, without hope.