After the epicentre of the earthquake cracked the earth’s crust 160 kilometres west of Sumatra, the break headed northwest, traveling 1200 kilometres in 500 seconds like a slowly unfastening zip. The crack created a newly formed cliff face on the ocean floor, in some places 12 metres high.

By any measure, the earthquake was large. Its energy equalled all of the world’s quakes over the previous thirty years combined. Had its force been nuclear, it would have powered 23 000 Hiroshima bombs. The massive release of energy caused the earth to wobble on its axis by up to 2.5 centimetres and shortened the day by about 3 microseconds.

But its work was unfinished. As the seabed rose to form the new cliff, it lifted the entire column of water above it – in some places the sea was 4.5 kilometres deep – towards the surface.

The crest created on top of the ocean would have felt gentle enough to anyone who happened to be sailing past, but by the time it roared into Banda Aceh, capital of the Indonesian province of Aceh, at nine minutes past eight that morning, the wall of water beneath it had formed into waves that were up to 30 metres high. When they pounded onto land, they swallowed up 250,000 people. No one outside of that zone of death had a clue what was coming for us.

As the people of Aceh climbed onto debris to survive – or to die– the wave that was destined for Golden Buddha Beach was already galloping towards us, trough-first, from a point approximately 750 kilometres west of our beach where the sea floor had bowed before the new cliff face. But its progress was relatively slow because it was travelling across a shallow continental shelf that juts out from the coast of Thailand.

Because the earthquake rupture was long and thin, the ripple of waves it created were shaped like a set of repeating parentheses. This meant that the wave’s force was focused east and west of the break; its impact to the north and south was muted, which is why Bangladesh and Australia were left virtually unscathed.

The waves that travelled west towards Sri Lanka had risen above the top of the new underwater cliff and were travelling in deeper water. The first wave would arrive on Sri Lanka’s east coast, crest first, forty minutes sooner than their partner ripples, which formed on the other side of the rupture, would take to travel to Golden Buddha Beach, despite the fact that Sri Lanka was about 300 kilometres further away from the earthquake.

Fifteen minutes after the dramatic drop in sea level recorded near Phuket, tsunami waves rushed into underground supermarkets and tore up the cliffs at the island’s famous Patong Beach.

Ten minutes later and 100 kilometres further north, thousands of people perished in Khao Lak as walls of water, strong enough to carry a police patrol boat a kilometre inland, saturated the dense strip of resorts.

Minute by minute, the destruction travelled a path north, up the coast towards us, while we sat, unaware, on a platform built for yoga.

(extract from Out of the Blue – Facing the Tsunami).
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