"The Aberfan disaster was the catastrophic collapse of a colliery spoil tip in the Welsh village of Aberfan, near Merthyr Tydfil, that killed 116 children and 28 adults on 21 October 1966. The collapse was caused by the build-up of water in the accumulated rock and shale tip, which suddenly slid downhill in the form of slurry.
More than 1.4 million cubic feet of debris covered the village in minutes. The classrooms at Pantglas Junior School were immediately inundated; young children and teachers died from impact or suffocation. Many noted the poignancy of the situation: if the disaster had struck a few minutes earlier, the children would not have been in their classrooms, and if it had struck a few hours later, they would have left for the half-term holiday.
The official inquiry blamed the National Coal Board for extreme negligence, and its chairman, Lord Robens, for making misleading statements. Parliament passed new legislation regarding public safety in relation to mines and quarries.
Local worries about the tip were generally dismissed. In 1964 local councillor Gwyneth Williams warned that if the tip were to move it could threaten the school. In 1965 a petition against the tip from mothers of children at Pantglas school was presented by headmistress Ann Jennings to Merthyr County Borough Council. Ms Jennings and many of the petitioners' children died in the disaster. Aberfan resident Dai Tudor said "I’ve warned and campaigned for years about that tip. Nobody in authority took any notice. This is not just the greatest tragedy in Wales. It is the biggest scandal."
https://en.wikipedia.org/wiki/Aberfan_disaster
