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WORLDWATCH TOTAL VOLUMES OF SUBSTANCE RELEASED Canada 1985, 2004, 2014 >34 million m3 USA 1962, 1980, 1994, 2008 >26 million m3 Mexico 1937 > 2 million m3 Guyana 1995 > 4 million m3 Brazil 2007, 2015, 2019 >74 million m3 Spain 1998 > 5 million m3 Hungary 2010 > 1 million m3 USSR 1981 > 3 million m3 Philippines 1982, 1992, 2012 >120 million m3 South Africa 1994 > 0.6 million m3 DAMS Fit to Burst The recent dam collapse in Brazil could just be the beginning of a series of disasters due to inadequate dam technology and monitoring An upstream dam uses far less wall material and occupies less land than a downstream dam, but can be less stable particularly if seismic activity is a feature of the region.’ So wrote mining engineer Chandra Durve and then head of technology at Cornwall technical college, Dr Edward Ferrett, in October 1985 in an article for Geographical about tailings dams – the structures used to contain the waste product of mining operations. The dams, they noted, require constant monitoring using small instruments that measure water pressure: ‘It is this type of continuous monitoring that could provide early warnings of potential failures.’ As recent events in Brazil and around the world indicate, it seems these warnings, already well understood in the 1980s, have not been heeded by some large mining companies. The most recent upstream tailings dam collapse took place on 25 January in the state of Minas Gerais in Brazil when the 280-foot-high structure owned by Vale SA, which towered over the small town of Brumadinho, collapsed, sending 11.7 million cubic metres of toxic mud downstream. The surge crashed into the Vale administration rooms where workers were eating lunch, overwhelmed trains and vehicles and submerged nearby homes. At the time of writing, an estimated 300 people have been killed and the waste is still on the move, contaminating rivers and water supplies in the area. The disaster follows a similar event in 2015, when another tailings dam in Minas Gerais owned by Samarco – a joint venture between Vale and BHP Billiton – collapsed, killing 19 people. Shortly before that, the Mount Polley tailings dam in Canada failed, sending eight million cubic metres of gold and copper waste into a pair of glacial lakes. According to the non-profit organisation World Mine Tailings Failures 6 • Geographical
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Gentrification Modelling the rise of US hipsters Sucker punch The case against octopus farming Hopping off Hares today could be gone tomorrow A ‘river of mud’ following the 2015 Mariana tailings dam failure in Brazil (WMTF), 42 tailings dam failures occurred between 2008 and 2017, resulting in 435 deaths. Speaking more than 30 years after the publication of his original article, Chandra Durve laments the fact that the lessons of the past have consistently been ignored. ‘These dams have been failing for many years,’ he says. ‘There isn’t a lack of knowledge, though unfortunately there aren’t too many experts around in this field and people who profess to be experts unfortunately may not have a full understanding of the intricacies of tailings.’ Upstream tailings dams have the potential to be less secure than other types of dam, largely due to the way water is passed through the dam wall. Unlike a water dam that usually features an impervious wall of concrete or similar material, the wall of a tailings dam is constructed from the coarse portion of the tailings themselves – the waste pulp that results from the mining process in which ore (containing copper, iron, gold and the like) is crushed and ground with huge volumes of water. The finer particles of the tailings are allowed to gravitate away from the wall. Water is allowed to seep through the tailings and the wall in order to consolidate the mud – the idea being that this will compact the tailings and reduce their volume. ‘The key to the stability of these structures lies in the proper control of the seepage and in particular the “phreatic surface”, which is the upper limit of water flowing through the dam,’ explains Durve. ‘The phreatic surface must be intersected well before it reaches the outer part of the tailings dam wall. If it hits the outer part then the tailings dam will collapse. Equally, if it intersects the wall in an uncontrolled way, the whole wall could slide, not only releasing liquefied tailings but adding to the liquefaction of other material.’ Liquefaction is the process in which solid mud is reduced to liquid and though Durve says it is too early to definitively state why the Brumadinho dam collapsed, most experts agree that the dam failure was one of liquefaction. This process can also occur due to seismic activity or a heavy deluge of rainfall. April 2019 • 7

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WORLDWATCH

TOTAL VOLUMES OF SUBSTANCE RELEASED

Canada

1985, 2004, 2014 >34 million m3

USA

1962, 1980, 1994, 2008 >26 million m3

Mexico 1937 > 2 million m3

Guyana

1995 > 4 million m3

Brazil

2007, 2015, 2019

>74 million m3

Spain

1998 > 5 million m3

Hungary 2010 > 1 million m3

USSR 1981 > 3 million m3

Philippines

1982, 1992, 2012 >120 million m3

South Africa 1994 > 0.6 million m3

DAMS

Fit to Burst

The recent dam collapse in Brazil could just be the beginning of a series of disasters due to inadequate dam technology and monitoring

An upstream dam uses far less wall material and occupies less land than a downstream dam, but can be less stable particularly if seismic activity is a feature of the region.’

So wrote mining engineer Chandra Durve and then head of technology at Cornwall technical college, Dr Edward Ferrett, in October 1985 in an article for Geographical about tailings dams – the structures used to contain the waste product of mining operations. The dams, they noted, require constant monitoring using small instruments that measure water pressure: ‘It is this type of continuous monitoring that could provide early warnings of potential failures.’ As recent events in Brazil and around the world indicate, it seems these warnings, already well understood in the 1980s, have not been heeded by some large mining companies.

The most recent upstream tailings dam collapse took place on 25 January in the state of Minas Gerais in Brazil when the 280-foot-high structure owned by Vale SA, which towered over the small town of Brumadinho, collapsed, sending 11.7 million cubic metres of toxic mud downstream. The surge crashed into the Vale administration rooms where workers were eating lunch, overwhelmed trains and vehicles and submerged nearby homes. At the time of writing, an estimated 300 people have been killed and the waste is still on the move, contaminating rivers and water supplies in the area. The disaster follows a similar event in 2015, when another tailings dam in Minas Gerais owned by Samarco – a joint venture between Vale and BHP Billiton – collapsed, killing 19 people. Shortly before that, the Mount Polley tailings dam in Canada failed, sending eight million cubic metres of gold and copper waste into a pair of glacial lakes. According to the non-profit organisation World Mine Tailings Failures

6 • Geographical

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