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Special report | Aberfan 50 years on

Aberfan 2 cropped

The Aberfan disaster, 50 years ago, remains deeply etched on the collective memory of the UK populace; indeed, it is one of only a few British peacetime disasters that are familiar even to those born years later.

Fifty years on, there remains tremendous power in the images of the aftermath of the accident, which caught the moments in which hardened miners dug through mounds of mine waste that they had generated with their own hands, in a desperate race to save the children of their community.

Their faces show the grim reality that miners, all too familiar with accidents in which victims are buried, knew well – that the likelihood of survival when engulfed by rock and soil is terrifyingly low, rendered worse by the saturated nature of the filthy coal mine waste that engulfed the school, and by the high vulnerability of children to the effects of burial.

Aberfan 2 cropped

Aberfan 2 cropped

The landslip engulfed Pantglas Junior School: In total 144 people died, of whom 116 were children

The events of that day are well-known, but bear repeating. The flowslide occurred from Tip 7 of the Merthyr Vale colliery on the valley slopes above the village of Aberfan on 21 October 1966.  The progressive failure was first noted when the crew responsible for waste tipping arrived on site at around 7.30am on the morning of the disaster.  

They reported that the tip had deformed by about 3m overnight, and tried to send a message down to the mine office that a landslide was developing. However, this had to be delivered in person as they did not have a telephone, introducing a huge delay.

An hour later, shortly before the collapse, the same crew noted that the slope had deformed by a further 3m or so, and that the movement was now sufficiently rapid to be observed with the naked eye. When the final collapse occurred at around 9.10am, the tipping crew reported that the transition from a visibly creeping mass to a flowslide appeared to be spontaneous and dramatic; they then reported the mass moving as a series of waves down the slope.

Aberfa n graph

Aberfa n graph

The volume of the landslide was estimated to have been about 105,000m3, which is not especially large for a flowslide of this type. The landslide travelled around 500m before entering the village. The official report suggested that the velocity of the landslide front was between 17km/h and 34km/h.

The landslide struck and relentlessly engulfed 16 houses and the Pantglas Junior School, killing 144 people, of whom 116 were children, mostly aged between seven and 10 years old. Five teachers were also killed and a further 29 children and six adults were injured. The last survivor was rescued less than two hours after the accident.

Key moment

Aberfan was a key moment in our understanding of landslides, and of making mining safer. Sitting alongside the 1963 Vajont landslide disaster in Italy, the aftermath of which was also graphically depicted in monochrome photographs, this landslide was hugely significant in terms of the development of science and understanding.

While elements of the aftermath of the landslide were handled in a manner that we might now question – the use of £150,000 of charitable funds to remove spoil tips from above the village even though the money had been donated by the public for the victims, for example – the scientific investigation of the disaster was undertaken rigorously and involved acknowledged authority figures in geotechnical engineering.

Professor Alan Bishop, along with colleagues at Imperial College London, led the scientific investigation. But it also had input from the Meteorological Office, the Institute of Geological Sciences (now the British Geological Survey), the National Coal Board and various other organisations.  

Similar precedents

The investigation demonstrated that the failure in Aberfan’s Tip 7 was just the latest in a long succession of similar events. A significant flowslide had occurred nearby at Abercynon in 1939, an event that was actually larger than Aberfan, and which came close to causing loss of life. Aberfan’s Tip 4 had failed in 1944; and Tip 7 itself had failed in 1963.

Indeed the report of the public inquiry noted: “Tip slides are not new phenomena. Although not frequent, they have happened throughout the world and particularly in South Wales for many years, and they have given rise to quite an extensive body of literature available long before the disaster.” But it added that “there was no general apprehension in the National Coal Board regarding tip stability”.

The public inquiry report, although carefully written, was highly critical of the way in which tip stability had been managed. Thus, Aberfan sent a message through the geotechnical and mining industries about the importance of collecting data on, and learning from, previous events. This message remains current.

Poor understanding

But it is also true to note that the mechanics of flowslides of this type were poorly understood prior to Aberfan. Flowslides in finer-grained materials were reasonably well described, particularly in relation to coastal failures in the Netherlands and quick clay slides in Norway. Bishop wrote a summary of his analyses of Aberfan, and other flowslides, in a 1973 paper in which he highlighted the tendency of soil mechanics at the time to focus on processes up to the point of failure, and to ignore what happens thereafter.

He demonstrated the importance of the brittleness index – the ratio between peak and residual strength, in determining post-failure behaviour. In particular he noted that where the Brittleness Index is large, high strain rates could develop in the post-failure domain. He used multiple examples to highlight and interrogate this behaviour. This observation has proven to be astute.

The Aberfan flowslide also depended on the availability of large volumes of water. In this case the tip had been constructed on top of a spring that created saturated conditions after periods of heavy rainfall. Thus, Aberfan highlighted the importance of understanding site hydrogeology prior to and during tipping.

Unsolved problems

Nonetheless, the investigations immediately after Aberfan did not fully solve the problems of flowslides, and in particular static liquefaction behaviour. Bishop himself noted that aspects of this behaviour remained poorly constrained, and even speculated that air entrainment might play a role, which we now know is not the case in most flowslides of this type. These problems had to wait for several more years to be resolved, but built upon the Aberfan work.

But the investigations of Aberfan were more than sufficient for the public inquiry to make strong recommendations in terms of mine waste management. In particular, they highlighted the need for proper understanding of the hydrology and hydrogeology of tip sites, and of the materials upon which the tip is constructed, as well as proper management of the tips themselves.

The government and the National Coal Board subsequently took up these recommendations, and to a large degree they have also been implemented internationally. Many dangerous spoil heaps were removed or re-engineered, even though in the public inquiry the National Coal Board argued that this might be prohibitively expensive.

Far greater attention was paid to the properties of the location of spoil heaps, in particular in relation to the hydrogeology; to the mechanical properties of the waste itself, in particular in relation to the amount of fine-grained material present; and to the density of the tipped waste.

Screen shot 2016 10 10 at 17.16.24

Screen shot 2016 10 10 at 17.16.24

No large-scale repeat of the Aberfan disaster has occurred in the UK, and given the limited mining that now occurs, and the strict regulatory environment, a similar event does not seem likely.   

Of course the accident at Aberfan also had a profound impact in other areas of understanding of such disasters. Subsequent studies looked at the impact of trauma on communities by: evaluating changes in the birth rate in the village after the disaster; looking at the impact of post-traumatic stress disorder on survivors; and considering the interactions between governments and large-scale disasters. Many of these studies have proven to be as influential in their own fields as was the investigation of the geotechnical aspects of the failure.

However, even after 50 years the lessons of Aberfan have not been learnt universally. In many less developed countries the rate of mining and quarrying related flowslides remains surprisingly high, and these take a terrible toll. The table (see right) lists major fatality-inducing mining, quarrying and waste management flowslides in the last five years; most of these involve sliding in mine waste, and thus are analogous at some level to Aberfan. Some are remarkably similar. The impact has been almost 1,000 deaths, mostly in China and Myanmar.

Acceleration in accident rate

A cumulative plot of human losses over this period shows acceleration in the last three years. This is driven primarily by the sequence of major flowslides in the Hpakant area of Myanmar in the last two years, which have involved the collapse of waste heaps created from jade mining. The high death tolls reflect the dangers of unregulated extraction of jade from the waste piles by artisan, usually poverty-stricken and often blameless miners.

The socio-economic background to these mining operations is complex, but the intensity of jade mining in this area has increased dramatically in recent years as operators try to maximise extraction rates prior to anticipated increased levels of regulation as Myanmar transitions towards a democratic governance system. The consequences for the poor, artisan miners in the Hpakant area are severe.

And of course the failure of tailings dams, and the transition of the waste into highly mobile flowslides, as illustrated by the Bento Rodriguez failure in Brazil in 2015, remains alarmingly common. It is hard to think of any other area of geotechnical engineering that has such a high failure rate with such devastating impacts, and at least superficially it remains deeply surprising that this level of impact is tolerated.

The legacy of Aberfan lives on, and will continue to do so for the foreseeable future. Aberfan highlighted the risks posed by types of materials, changed the ways that mining operations are undertaken in most countries, drove an understanding of the processes of static liquefaction and inspired considerable future research. The challenge now is to ensure that these lessons are applied everywhere.

● Dave Petley is University of East Anglia pro-vice chancellor

 

Readers' comments (2)

  • In my view the above article doesn't go far enough in explaining the causes of the Aberfan disaster. Although it is clear that at the time there was insufficient understanding in the fields of soil mechanics and hydrology in relation to mining waste tips, the tribunal investigating the disaster found that the blame rested with National Coal Board and was shared to varying degrees at national level, divisional level and with several individuals within the NCB. The tribunal also found that there was an absence of tipping policy in the NCB, as they were following in the footsteps of their predecessors and that there was little guidance by Her Majesty's Inspectorate of Mines and Quarries or from legislation, as there was none.

    The NCB nationally and locally had failed to learn lessons from a series of tip failures in the area dating back to 1939 and in particular the latest one at Tymawr in 1965. The NCB engineer responsible for the tips, in the area around Aberfan, was the No 4 Area Mechanical Engineer with no knowledge (as was the same with others who were also responsible for Tip 7) of civil engineering or soil mechanics. Although possibly put in an impossible position by the NCB, as he was not fully qualified to hold that position, failed to heed (as did others referred to) the written warnings from the Borough Engineer for Mertyr Tydfil who was concerned about the safety of the school. In fact the tribunal stated when he did visit the tip complex he treat the situation ".....so cavalierly as to render his visit useless" and allocated blame to him.

    Following the 1965 incident at Tymawr, the Chief Engineer of the South Western Division, a member of the Institutions of: Mechanical, Electrical & Mining Engineers, issued a memorandum, which was an update of a 1939 memorandum "Precautions to Prevent Sliding". The Area Civil Engineer (who had a Masters Degree in Civil Engineering and was Member of the Institution of Civil Engineers), chose to ignore this memorandum as he considered the responsibility for the tip lay with the No 4 Area Mechanical Engineer. He did visit the tip complex in April 1965 in respect of pollution problems and in the tribunal's words took no action, either because he failed to notice the problems of stability, which they considered he should have done as a qualified and experienced civil engineer or because of a strained relationship with the Area Mechanical Engineer and in the opinion of the tribunal "....took the least line of resistance and did nothing".

    So I feel the article gives the impression the disaster took place through a gap at the time in the knowledge of soil mechanics and hydrology, when in fact Professor Bishop's work only described in detail the mechanism of the slip. The cause was I believe due to an inadequate management structure at the NCB, poor leadership and lack of responsibility by individuals who should of had sufficient grasp of the engineering principles available at the time to have constructed Tip 7 safely or at least recognised the seriousness of the problem early enough and taken appropriate action.

    Finally, the Borough Engineer for Merthyr BC had commenced in 1963 to express his written concerns in respect of the safety of Pantglas Junior School, in the event they accepted the assurances of the NCB and therefore the tribunal did not think that they did contribute to the disaster. I wonder if such a conclusion would be reached today? Should the council have closed the school, or at least sought independent expert opinion?

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  • Aberfan

    Fifty years ago I was a student of civil engineering. One morning in October 1966 we students shuffled into our morning lecture on the topic of “soil mechanics”. Our lecturer told us to set aside our course notes for the day. Instead, we were going to talk about Aberfan, the village in South Wales that had, just days before, suffered a catastrophic disaster from the collapse of the mining waste tips that had long been an accepted part of the landscape above the settlement. In the disaster, 144 people lost their lives, 116 of whom were children from the local primary school. The collapsing tip had engulfed the school as well as neighbouring homes just as school had started on the morning of 21st October 1966.

    Our lecture that day turned to the subject of pore water pressures and the use of piezometers to measure and monitor the build up of water pressures in made up ground. It was about how these risks could be assessed, quantified and analysed. By today’s standards it was very basic geotechnics, but in 1966 it was still a relatively new science. New, but beginning to be clearly established within the civil engineering profession but far less so within the mining industry.

    I doubt I was the only student that day who hung on every word and every principle espoused by our lecturer that morning. It inspired me to follow a career in roads engineering and in geotechnical design and risk monitoring that resulted in one of the most dramatic and impressive motorway cuttings in the UK, the 150m deep M40 cutting through the chalk escarpment of the Chilterns on the borders of Oxfordshire and Bucks.

    Civil Engineers in the UK continue to build remarkable, innovative and inspiring structures that push the boundaries of design and materials. Our safety record is second to none. Nevertheless we are all properly humbled by engineering failures and it behooves us all to learn from such tragedies and to improve our understandings of the science of engineering for the benefit of mankind.

    Colin Carritt (Retired Member)

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