Monday, November 10, 2025

Sand mining threatens the future of critical SE Asian ecosystem

University of Southampton

Cambodia riverbanks — image:
Riverbank collapses triggered by lowered riverbed levels on the Mekong River in Cambodia
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Credit: Andy Ball / University of Southampton

Intense sand mining is putting the largest freshwater lake in Southeast Asia at risk of collapse with catastrophic consequences, a new study has found.

The huge Tonlé Sap Lake in Cambodia, a UNESCO Biosphere Reserve, is one of the world’s most ecologically diverse lake ecosystems, home to endangered amphibians, reptiles, mammals and birds, with a diverse array of 885 species. It provides livelihoods for almost two million fishers, and its fish feed millions more.

But its future is in danger as the intensity of the unique ‘reverse flow’ that feeds water into the lake has been declining year-on-year.

Scientists have now conclusively determined the cause of this decline to be sand mining in the Mekong River in Cambodia and Vietnam.

Sand mining is the practice of extracting sand from the riverbed, with the majority used in the construction industry.

Rates of sand mining in the Mekong have rapidly increased, with over 100 million tonnes of sand now being removed every year.

Steve Darby, Professor of Physical Geography at the University of Southampton and co-author of the new research, said: “There has been lots of speculation as to why the intensity of the reverse flow has been declining, with climate change and damming on the Mekong upstream in China and Laos previously being identified as possible causes.

“Our work demonstrates that, while climate change and damming are minor contributory factors, by far the dominant driver has been riverbed incision caused by largely rampant sand mining on the Mekong.”

The reverse flow system

Tonlé Sap Lake is sustained by an unusual reverse flow system. The Tonlé Sap River normally drains the lake, flowing downstream to Phnom Penh, where it joins the Mekong River.

But, during the monsoon season, the Mekong’s flood pulse rises high enough to force the Tonlé Sap River to reverse for several months, filling the lake.

The Tonlé Sap Lake stores so much water during this seasonal flood pulse that it acts as a giant ‘flood capacitor’, regulating flood water levels down across the Mekong Delta – home to 23 million people – before releasing the stored freshwater back downstream to the Delta during the dry season.

The study, published in Nature Sustainability, shows that between 1998 and 2018, riverbed lowering of the Mekong River mainstem, driven by sand mining and upstream sediment trapping, has reduced the reverse flow volumes by between 40 and 50 per cent.

Projections to 2038, with additional riverbed lowering driven by ongoing sand mining, suggest that the reverse flow could decline by up to 69 per cent compared to 1998.

Dr Quan Le, Research Associate in Delta Flood Risk at Loughborough University and lead author of the study, said: “Rapid urban growth has fuelled a global surge in a demand for construction sands, increasing river sand mining rates.

“Our study finds that this intensive sand extraction, combined with sediment being trapped by dams in the Lower Mekong basin, has already weakened the Tonle Sap lake’s flood pulse, causing lasting environmental harm and underlining an urgent need for sustainable sediment management to ensure that these future projections are not realised.”

On average, riverbed levels across much of the Lower Mekong’s course in Cambodia and Vietnam have dropped by two to three metres in the last two decades.

“At this rate, within 10 years the system is at risk of a near total collapse,” said Professor Darby. “The Mekong is the second most biodiverse aquatic ecosystem in the world, after the Amazon, and its health depends on the normal functioning of the Tonlé Sap Lake. A collapse of the lake system would have catastrophic consequences for the biosphere, for millions of people’s livelihoods and food sources, and for flooding in the region.”

Understanding and mitigating the impact

Scientists are continuing to assess the consequences of sand mining in the region.

A project called Hidden Sands, led by Professor Julian Leyland at the University of Southampton, is investigating the impact of sand mining on the environment and on communities in Cambodia. The team has also been working with agencies in Vietnam to provide a more risk-based approach to the governance of sand mining.

Along with the above researchers, Craig Hutton, Professor of Sustainability Science and director of the Sustainability and Resilience Institute, and Paul Kemp, Professor of Ecological Engineering, both at the University of Southampton, are embarking on a new project to fully understand the ecological impact on Tonlé Sap Lake, particularly the impact on fish.

Professor Hutton said: “The lake is estimated to feed about six million people and provide as much as 60 per cent of Cambodia’s protein. The disruption in lake levels from sand extraction along with deforestation, illegal fishing and extreme pesticide and fertilizer use are exacting a heavy toll on fish production. This decline is threatening both food security and livelihoods.”

Professors Hutton and Kemp interviewed fishing communities in a recent visit to the region.

“Struggling fisher folk have seen as much as an 80 per cent mortality in aquaculture fish, declines in wild catch and mounting household debt,” said Professor Hutton. “One interviewee told us, ‘We just want another life for our children now. Anything but fishing’.”

ENDS

Journal

Nature Sustainability

DOI

10.1038/s41893-025-01677-8

Article Title

Sand mining driven reduction in Tonle Sap Lake’s critical flood pulse

Article Publication Date

10-Nov-2025

Sand mining on the Mekong River at Phnom Penh, Cambodia

Credit

Andy Ball / University of Southampton

Pesticide sheen on the surface of Tonlé Sap Lake

Arrow Head fishing traps are deployed in their hundreds across the Tonlé Sap Lake

Credit

Edward Bellomy

Climate’s impact on earthquakes

New research from scientists at Syracuse University and the University of Auckland highlights the connections between climate, tectonics and human evolution

Syracuse University

Aerial view of Lake Turkana — image:
An aerial view of Lake Turkana, the world’s largest permanent desert lake. A recent study reveals that climate-driven fluctuations in lake levels can significantly influence fault activity in the region.
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Credit: Chris Scholz, Syracuse University

Lake Turkana in northern Kenya is often called the cradle of humankind. Home to some of the earliest hominids, its fossil-rich basin has helped scientists piece together the story of human evolution. Now, researchers from Syracuse University and the University of Auckland are revealing that the lake’s geologic history may be just as significant as its anthropological one.

Their findings, published in Scientific Reports, show that climate-driven changes in lake levels have influenced fault activity and magma production in the East African Rift Valley—challenging the long-held belief that continental rifting is governed solely by solid Earth processes.

“Continental break-up (‘rifting’) is generally thought of as a process fundamentally rooted in plate tectonics,” explains Chris Scholz, professor of Earth sciences at Syracuse University and co-author of the study. “Our research shows that rifting is also shaped by surface processes, including regional climate.”

Lead author James Muirhead, senior lecturer at the University of Auckland, emphasizes the study’s implications for understanding human evolution. “This work reveals a complex environmental backdrop to the landscape occupied by early hominids, early modern humans and recent members of our species,” says Muirhead, who conducted much of the research and analysis as a postdoctoral associate in Scholz’s lab at Syracuse.

Climate and the Crust

Lake Turkana's formation is a story of tectonic forces, volcanic eruptions and climate shifts. Around 2.2–2.0 million years ago, volcanic activity blocked the basin's natural outlet, forming Lake Lorenyang, which eventually evolved into Lake Turkana. Over millennia, fluctuating climate patterns caused dramatic changes in lake levels—sometimes rising over 350 feet higher than today. These changes, the researchers found, had a profound effect on the Earth's crust.

"Water levels in Lake Turkana reflect regional 'hydroclimate', and during wetter intervals approximately 9,600-5,300 years ago the lake was hundreds of feet higher than today," Scholz explains. "We found that faults slipped faster and that more magma was produced under the regional volcanoes when the lake was lower."

According to Muirhead, this is because during drier periods with lower lake levels, less water weight presses down on the Earth's surface, reducing pressure in the crust. "These pressure changes lead to increased melting in hot regions deep in the Earth and also make faulting or earthquakes more likely to occur," he says.

Fieldwork in the Rift

Researchers in Syracuse’s Department of Earth and Environmental Sciences (EES) conducted fieldwork in Turkana—an extremely challenging environment. "The conditions on Lake Turkana in the northern part of the Kenya Rift were among the most challenging our team has encountered anywhere in the world," says Scholz. "The lake is the largest in the world in a desert, is in one of the windiest places in Africa and is extremely remote."

The team transported their research vessels overland to Lake Turkana and carried out surveys and sampling with meticulous care, as there are no coast guard or marine rescue operations available on the lake. Despite the logistical hurdles, their efforts paid off: they successfully collected subsurface data across 27 faults below the lake. These high-resolution fault scans, Muirhead notes, provide “arguably the best estimates on fault activity rates over the past 10,000 years of any rift basin in the East African Rift System.”

The data revealed that fault lines moved faster and more magma was produced during drier periods when lake levels were lower. This finding aligns with similar studies in places like Iceland and the western United States, where the loss of glacial ice weighing-down the earth’s surface, has been linked to increased tectonic activity.

"What was surprising was just how much the rate of faulting can change due to just a few hundred meters of lake level change," Muirhead says. "This is likely because rock melting and the generation of magma below the rift further enhances the tectonic response to these lake level changes."

Consequences for Early Humans—and Us

The research offers a vivid glimpse into the environmental pressures faced by early human ancestors. During drier climate phases, they likely endured heightened volcanic and seismic activity, which reshaped landscapes and affected access to vital resources like food and water.

Today, the implications go well beyond anthropology. As climate change continues to alter hydrological systems, the study suggests that tectonic and volcanic activity could also be influenced—though such changes would unfold over geological spans.

“Climate change, whether human-induced or not, will likely impact the probability of future volcanic and tectonic activity in East Africa,” Muirhead explains. “However, these changes occur over geological rather than human timescales, so their effects would be subtle and largely imperceptible within a single lifetime or even across generations.”

In the near term, climate projections for Lake Turkana show a dramatic shift from earlier expectations. Rather than shrinking, models now suggest the lake could rise over the next two decades due to increased rainfall in its river inflows—raising the risk of flooding. These changes in water levels, whether through natural events or human-driven water resource development, could also influence crustal pressure dynamics.

A New Framework for Hazard Assessment

The findings contribute to a growing body of evidence supporting an Earth Systems view of plate tectonics—one that integrates atmospheric and hydrospheric influences, not just those below the surface.

"We are heading towards a more holistic understanding of the processes that drive plate tectonics," Muirhead says, "and also recognizing the role of plate tectonics in controlling long-term climate and its impact on the evolutionary trajectory of life on our planet."

This shift in perspective has real-world implications for hazard assessment and policy. Fault lines in continental rift zones may behave differently depending on the climate state they are experiencing. Muirhead believes that future assessments must account for these variables.

"If I were doing a hazard assessment for a fault line in a continental rift like Turkana," he says, "I would need to consider how its rate of activity, and resulting likelihood of an earthquake, is affected by the current climate state and associated lake water volumes."

Building a Safer Future

By revealing the deep connections between climate and tectonic activity, the team’s research is helping to reshape how scientists—and policymakers—think about Earth's dynamic systems. As climate change continues to unfold, understanding these connections will be critical for building resilient communities and preparing for the geologic challenges of tomorrow.