The Aberfan disaster was the catastrophic collapse of a colliery spoil tip on 21 October 1966 in Wales. The tip had been created on a mountain slope above the village of Aberfan, near Merthyr Tydfil, and overlaid a natural spring. A period of heavy rain led to a build-up of water within the tip leading to 'liquefaction', causing it to suddenly slide downhill as a slurry, killing 116 children and 28 adults as it engulfed Pantglas Junior School and other buildings. The tip was the responsibility of the National Coal Board (NCB), and the subsequent inquiry placed the blame for the disaster on the organisation and nine named employees.