At 9.15am on October 21, 1966, the children of Pantglas primary school were in their classrooms awaiting the day’s first lesson after morning assembly.
From nowhere there came a thunderous rumbling noise which grew louder and louder. Teachers in the classrooms that backed on to the colliery slag urged their pupils to dive under desks for cover but it was too late.
At the top of the mound, too far off for the children to hear, a miner saw the 40,000 cubic metres of debris start to move and cried in vain for people to flee.
As it gained momentum, a 50ft-wide avalanche raced down the hillside at 30 miles an hour, like a volcano erupting.
A build-up of water following weeks of heavy rain had made the heap of coal waste dangerously unstable and it collapsed, smashing into Aberfan.
