Interview Professor Hugh Sinclair
Interview Hugh Sinclair
Geologists usually think in terms of time scales dating back thousands or millions of years – even billions of years – but as well as studying how the Earth evolved in the past, Professor Hugh Sinclair of the University of Edinburgh also has his sights set on a very different period: the future.
The science of geology is currently advancing at a much faster rate than the processes it seeks to measure, now including global change as well as human activity, all of which shape the surface of the planet we live on. Twenty-five years ago, for example, we knew a lot less about the growth and denudation of mountains because we had so little knowledge of the rates of erosion, including the long - and short-term effects of climate change. But thanks to the development of new techniques, we can now reconstruct more precisely how mountain ranges are formed and how they are destroyed, factoring in the effects of erosion and also calculating the time scales involved. The ability to bridge short and long time scales of erosion and uplift also means that we can now start to forecast what will happen in the future and possibly avert potential disaster.
When he was writing his PhD Thesis in 1989, Hugh Sinclair, who is now the Professor of Surface Geodynamics at the University of Edinburgh, drew a graphic to illustrate how the Himalayas were formed, showing how the two tectonic plates meet, with one sliding downwards and one pushing upwards to create the peaks we see on the surface. In his drawing, almost as an afterthought, he added some clouds and some rainfall, because geologists have known for a long time that the weather also has a major impact on the mountains, breaking off debris and carving out fissures, as well as creating sedimentary layers (more sediment results from more erosion). At that time, it was easy to date sedimentary rocks but not so easy to date the erosion, so geologists did not know that the rate of erosion directly affected how quickly the new rock pushed up to the surface to replace the rock eroded by the annual monsoons. This helps to explain why the Himalayas continue to rise by a few millimetres a year, despite some of the greatest erosion rates on Earth. In other words, the new rocks fill the void created by the rainfall and the erosion it generates, as if the movement of the tectonic plates and the consequent folding and fracturing of rocks are compensating for the loss of material by sending up new stuff to replace the stuff that has been eroded away. This constant replacement of eroded rock challenges many of the classic concepts of geomorphology, where cycles of topographic growth are thought to be followed by prolonged periods of recovery through erosion.
“Using new digital topographic techniques, we can now see the evidence of potentially dangerous faults, where there appears to be no evidence of earthquakes,” says Sinclair. “Where modern rivers don’t transport the amount of sediment that the long-term erosion rates would imply, we suspect historical records have not yet captured the really big, landscape-defining flood events that a system is capable of. These are examples where new techniques that allow us to measure and understand the long-term trajectory of topographic change are able to demonstrate where we expect erosion processes to play catch-up in ways that could be devastating .”
A key breakthrough has been the ability to date the rocks and debris more precisely than ever before using techniques such as thermochronology, which allows us to establish how quickly the rock reached the surface. Radiometric dating techniques also enable us to date the isotopes preserved inside the rocks in crystals of zircon or apatite, based on what are called the ‘closure temperatures’ of rocks. Because the Earth gets hotter as you go deeper (at about 30°C per kilometre), mineral systems with different closure temperatures can record the cooling of rocks during their journey to the surface of the Earth as the overlying rocks are eroded away. Combined with high-performance numerical modelling, these techniques help us to understand the stratigraphic record and reconstruct the process over thousands and millions of years, and thus project possible changes in future.
“The new technologies allow us to progress from making educated guesses to more precise models of elevation and mountain shape through time,” says Sinclair. “This provides a clearer picture of trajectories and rates of change, showing the probable effects of the onset of great climatic processes such as Asian monsoons, to reconstruct the past and see what the future landscape will look like.”
According to Sinclair, the three technologies that have revolutionised these components of geology over the last few decades are thermochronology, the analysis of cosmogenic nuclides (pioneered in Edinburgh and now also well established in Glasgow and at SUERC – the Scottish Universities Environmental Research Centre – to form the UK’s world-leading centre of such expertise), and advanced computer modelling, which makes sense of the huge amounts of data now being captured on the ground and via satellites. And by investing in these technologies right from the start, universities in Scotland and shared facilities such as SUERC have established themselves as leaders in various specialist areas in geoscience, making a major contribution to our knowledge of climate change as well as global change. “The emphasis on cutting-edge facilities in Scotland has driven some world-class research,” says Sinclair, “and SUERC has also played a critical role in breaking down the traditional boundaries between the different disciplines.”
Sinclair also believes that the establishment of SAGES (the Scottish Alliance for Geoscience, Environment and Society), a multidisciplinary partnership between the Universities of Aberdeen, Abertay, Dundee, Edinburgh, Glasgow, St Andrews, Stirling and the West of Scotland, as well as SUERC and the Scottish Association for Marine Science of the University of the Highlands & Islands, has created “a unique grouping that has grown into a world-leading organisation,” seeking to improve our understanding of how the Earth works and predict how it will respond to “anthropogenic and natural changes, on both local and global scales.”
The use of new technologies is breaking down the traditional boundaries between the different scientific disciplines – for example, with physicists, chemists and biologists collaborating closely with geoscientists – and Sinclair sees this happening within geoscience, within the Scottish geosciences community and within his own School. Not only is technology helping to bridge the gap between rates of erosion and the evolution of the landscape, but it is also bringing different scientific disciplines closer together.
All geologists deal with mind-boggling time scales, but recent breakthroughs in technology have also enabled them to rewrite the text books when it comes to the age of the landscape. For example, by analysing cosmogenic nuclides – rare isotopes created when high-energy cosmic rays interact with the atoms in rocks, as if they are giving the atoms a suntan – scientists in Edinburgh have discovered that the rocks we now see sitting on the surface of a valley in Antarctica have been there for over eight million years, compared to similar features elsewhere which have only been exposed to cosmic rays since the end of the last ice age, about 18,000 years ago.
“In Edinburgh, I think we have built a bridge between traditional geology and physical geography,” says Sinclair. Geography has always been the go-to subject for environmental issues, with geologists looking on much longer time scales and at deeper levels of the Earth. Traditional geologists who study plate tectonics and examine rocks and fossils may see themselves as the 'Indiana Jones' of geoscience, sometimes referring to these new advances in understanding the processes at the Earth’s surface as 'gardening,' says Sinclair. But the breakdown of the old discipline boundaries allows new ones to emerge, and that is what the Edinburgh School of GeoSciences intended from the start.
The new technologies are also helping earth scientists play a critical role in the debate about climate change, and Sinclair also believes that so-called 'esoteric' branches of geology are now coming more into the mainstream, providing insights into climate change and landscape evolution which are “just as relevant and topical” as studies for oil and gas exploration and mining.
For Sinclair, this ability to measure things much more precisely translates into his current work investigating flood plains in the Ganges and in the Midwest of the USA, bringing his knowledge of mountain formation (rates of erosion and tectonic movement) down to the flatlands, to help future planning in regions where there are large river systems – for example, locating areas at higher risk of flooding and places better suited to development. Oil and gas companies are also showing an interest in this relatively new field of research because it gives a much more detailed overview which helps them with longer-term planning – some places are simply more stable than others.
Are geologists becoming more like meteorologists forecasting weather? “Meteorologists can test their theoretical predictions on a daily basis and modify their models accordingly,” says Sinclair, “but geologists will have to wait a long time to see if their forecasts come true.”
Sinclair may not become a weatherman but he did get directly involved in a study to understand what happened in 2010 when monsoon rains devastated fragile communities in the western Himalayas, caused flooding, landslides and debris flows, with the worst effects across the floodplains of Pakistan.
Because there were no records of conditions at the time, Sinclair and his colleagues used the geomorphic record of sedimentation and debris flows to reconstruct what happened during the storm and, by combining this with topographic analysis, reconstructed the whole event – one of the first times such techniques have been used. Hopefully, this will help the authorities take measures to reduce the damage caused by future storms.
These new techniques also enable geologists to ask if big events are part of the natural variability of the system or one-off anomalies – for example, a tsunami, which leaves a highly visible signature in sedimentary layers, may be a random event or part of a more regular sequence. Ultimately, says Sinclair, this means we should not be surprised so much when some events take place – e.g. devastating monsoons or tsunamis. Precise predictions may still be impossible, but at least we have a better idea of what to expect and understand the sensitivities of the planet much better than ever before. We have known about the fundamental processes for centuries through simple observations, but now we have a “higher-resolution image” of change, and can see what happens almost in real-time.
“Geology has a lot to offer in terms of using modern processes to understand the stratigraphic record and help explain the world as it is now and what it will look like in future,” says Sinclair. “The historical record is not good enough. We have to be able to understand the changes which have taken place in ancient times, as well as understand more recent anthropogenic change – the impact of man on the landscape. That is why earth sciences are playing an increasingly prominent role, taking advantage of the latest techniques to measure rates of erosion as well as analyse sedimentary layers and image the landscape.”
Sinclair also believes these advances are leading to a greater integration in geoscience, as the study of surface processes is combined with our knowledge of deep-earth and deep-time geological processes, and also with physical and human geography.
“There are multiple signals and multiple frequencies in geology,” says Sinclair, “and our job is to tune in and interpret the message.”