What were the causes and effects of the Aberfan landslide in 1966?

The Aberfan landslide (also known as the Aberfan disaster) occurred in the village of Aberfan, in Wales on Friday 21 October 1966.

A spoil heap from the Merthyr Vale Colliery which was deposited on the side of Mynydd Merthyr above the village primary school collapsed leading to the formation of a debris flow which ran at very high speed down the hill side destroying a number of houses and ultimately burying the school in over 30 feet (10 metres) of thick mud and rubble. This resulted in the deaths of 116 children and 28 adults.

It was caused by the tipping of spoil onto a site on the hill side where water out flowed in a series of springs. There had been a period of heavy rainfall in the days before the landslide which had caused water to build up within the colliery debris pile. This acted to increase the pore water pressure within the material (this acts to force soil or rock particles apart, causing a decrease in the effective stress of the material essentially making it weaker) and ultimately resulted in a circular slip failure occurring in the slope. This acted to drive up the pore pressure even further causing the fine grained material in the debris pile to effectively liquefy and it was this material that flowed at high speed down the slope carrying larger debris with it that caused the destruction in the village.

The inquiry into the disaster ultimately found that the cause was due to the lack of control over the tipping of debris and a lack of understanding of slope stability issues by the mining engineers running the colliery who concentrated on the safety of the under ground excavations rather than the debris piles produced by mining. Previous instability in the spoil piles had been ignored.

As a result of the disaster and the ensuing enquiry, new legislation was created to remedy the absence of laws and regulations governing the safety and stability of mine and quarry waste tips.

The disaster also had a significant impact on the small community of Aberfan. Local doctors reported an increase in depression and alcohol related health problems after the disaster.

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