Approximately 150,000 cubic meters of mining debris from waste tip No. 7 surged down the mountainside, of which 40,000 cubic metres swept in to the village.
Within seconds a large area of the village was inundated with a thick slurry up to 12 metres deep. A farm and twenty houses on Moy Road disappeared under the surging waste, but the most devastation was wrought on Pantglas Junior School. The landslide smashed into the school and filled the classrooms, which were on the side of the school facing the mountain, with rubble. The children and teachers, who had only arrived a few minutes earlier, were buried alive. Over half the children enrolled at the school died.
Hundreds of people including parents, miners and rescue workers struggled to rescue those trapped beneath the waste. Their efforts were hampered by the continuing flow of water and mud from the tip as well as the lack of space in which to work due to the number of people who had descended on the village to help.
The National Coal Board and its chairman, Alfred Lord Robens, were heavily criticised in the aftermath of the disaster. Lord Robens didn’t go to the scene until the evening of the next day, and claimed that the disaster was caused by ‘natural unknown springs’ despite evidence that the NCB was fully aware that the ground beneath the tips was unstable. The remaining tips were only removed after government intervention.