Health & safety
comparing them for movement. With enough photos, experts can calculate the average velocity of a particular dam – and predict when it might fail. That sounds excellent in theory. But the problem with traditional InSAR technology is that it functions much better in places where the characteristics of the materials being measured don’t change. This makes intuitive sense: you can’t accurately compare apples to oranges. In other words, InSAR has historically worked well analysing bare rock, immovable brick houses and other solid objects. But rural, vegetated areas, where natural processes change soil and plants and trees, are far harder to get a grip of. Yet these wild places are precisely where tailings dams are most common – something both Fox and Grebby say limits the ability of many InSAR models to track how dams are doing.
Spaced out Earlier this year, researchers at the University of Nottingham made a remarkable claim. The experts suggested that ‘intermittent small baseline subset’ (ISBAS), a new type of InSAR, could have predicted the Brumadinho catastrophe down to the week that it happened. Crucially, Grebby and his team argued they could have spotted the looming collapse 40 days before it struck. “It very much works,” emphasises Fox of the platform, marketed by Geospatial Insight as MotionMonitor (Terra Motion, another UK company, is involved in the project too). “You could have seen that there certainly was cause for concern – and that action therefore should have been initiated.” It goes without saying that this is big news – for mining companies, for miners and for the environment. But how does the MotionMonitor system actually work? Unsurprisingly, the most significant breakthrough involves that thorny question of vegetation. Using what Fox describes as a “secret sauce” of complex data analysis, MotionMonitor allows researchers to accurately measure movement even in satellite images of rural districts. “When applied over tailings dams,” says Grebby, “we can analyse how different parts of the dam are moving.” If the InSAR data reveals that the tailings are indeed shifting, moreover, researchers can then use a well- established technique called the ‘inverse velocity method’ to predict when they might fail. Another pillar of the MotionMonitor platform involves the imagery itself. Beamed down from a satellite called Sentinel-1 – with new snaps taken every six or twelve days – the pictures themselves are free to access. What makes this new system special, however, is how the photos are then exploited. It may not be quite ‘plug in and play’ but Fox says that all the analysis is done remotely, with mining operators not needing to invest in expensive algorithms themselves. Even better, Geospatial Insight is working to ensure that companies can
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easily understand the results. As Fox puts it, “We’re building a platform that enables users to easily interact with that data and derive outputs from it.” As this last comment implies, the benefits here extend to far more than straightforward health and safety considerations. For one thing, there are clear financial advantages to MotionMonitor, and not simply because it’s cheaper than training experts inhouse. As Fox rightly says, environmental, social and corporate governance is now a major consideration at mining companies everywhere, and a Glencore or a RioTinto is more likely to secure favourable investment if it can show their tailings dams are stable. That this new form of InSAR is free from corporate interference is likely to reassure responsible investors too, hardly irrelevant given that Vale was allegedly aware of the dangers at Brumadinho, but failed to address them.
Chasing their own tailings With mining multinationals already expressing interest in MotionMonitor, it seems poised to begin a long and productive life. Not that the path to seamless tailings analysis is totally free of pitfalls. One challenge, emphasises Grebby, is that the new InSAR platform offers data that “complements” the information obtained by traditional monitoring techniques. This isn’t necessarily a problem – but it could become one if mine operators are lax about maintaining sensors. There are more fundamental drawbacks to Grebby’s platform too. If the slope near a tailings dam is too steep, for instance, it could cast shadows that obscure the mine. To be fair, this difficulty can be overcome by drafting in another satellite, one with a different viewing perspective. But Grebby freely admits that other obstacles are tougher to surmount. That includes water on the surface of the tailings beach, which can make getting accurate results hard, as well as sudden collapses that strike too fast to predict.
All this raises an obvious question: why do we tolerate tailings dams at all? Mining operators have leaned on them for years, certainly, but alternatives do exist. Beyond reinforcing fragile upstream dams with concrete, some companies have begun experimenting with so-called waterless mines. Among other things, that involves dehydrating tailings, allowing them to be neatly stacked – rather than haphazardly piled behind a dam. Anglo American announced a move in this direction two years ago, using additives to separate water from copper tailings. Given over 70% of the water used by Anglo American is related to tailings, it’s clear that even an incremental move away from traditional dams could really help the planet, to say nothing of the broader safety implications. In the meantime, though, MotionMonitor is surely a step in the right direction – especially if it prevents another Hpakant on some other rainy morning. ●
23 270 BBC 200
People killed by the Hpakant
disaster in 2020. New York Times
People killed by the Brumadinho disaster in 2019.
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