As one of the deadliest typhoons in decades ripped through Vietnam, a harrowing video emerged on social media.
The dashcam footage captured the moment a steel and concrete bridge collapsed, taking a truck and motorcyclist with it.
Those who plunged to their death on the Phong Chau Bridge near the northern city of Hanoi were among the hundreds killed by Typhoon Yagi.
And while the storm dealt the final blow to the bridge, it may not be the only thing responsible for the tragedy.
For within the Red River Delta is a highly prized — but often overlooked — commodity.
And the insatiable demand for this substance is putting communities and their livelihoods in danger.
The colossal industry you've probably never heard of
Sand and aggregates like gravel are some of the most important resources on earth.
They are used to manufacture a dizzying array of products, from cement and construction materials, to glass and fibre optics.
An estimated 50 billion tonnes are consumed every year, which is about 18 kilograms for every single person on the planet, every single day.
That makes it the most extracted resource on earth, according to Newcastle University sand mining researcher Chris Hackney.
"It's used in pretty much everything," he said.
"Without sand and its different forms and aggregates, modern developed economies and societies just wouldn't exist as they are."
Demand has skyrocketed in Vietnam in recent decades as the country needs construction materials to fuel its rapid urbanisation.
And while more and more sand is extracted from the Mekong Delta in the south and the Red River in the north, large hydro-electric schemes are blocking the natural flow of sediment that would normally help replenish the resource.
"We're using more than the river can supply," Dr Hackney said.
"As a result of that, the river's morphology, the way it shapes and the way it behaves, starts to change."
Did sand mining cause the bridge's collapse?
The threat to critical infrastructure posed by sand mining can be seen just 12 kilometres away at the Trung Ha Bridge over the adjoining Da River.
Photos published by Tuoi Tre News show the riverbed on which the bridge was built has all but disappeared, exposing the foundations and making the bridge vulnerable to extreme weather.
Vietnamese authorities have blamed the erosion on sand mining and banned heavy vehicles from crossing until further notice.
The government, which did not respond to the ABC's request for comment, is reported to also be investigating the cause of the Phong Chau collapse.
A preliminary report blamed Typhoon Yagi, with the Department of Transportation telling VN Express that the piers had been reinforced in 2018 and treated for erosion in 2019.
Dr Hackney said while it was difficult to determine a single cause of a collapse, he believed sand mining may have been a contributing factor.
"A large flood event, a major storm, brought a lot of water and presumably washed out a lot of material," he said.
"But the gradual lowering of riverbeds has probably primed that system a bit to respond in that way to those big storms."
Doomed bridges and collapsing communities
Elsewhere in the world, riverbed mining and severe storms have proved lethal.
The collapse of the Hintze Ribeiro Bridge in Portugal in 2001, which killed 59 people, was blamed on decades of dredging and a chain of floods.
The previous year, 22 people were injured when the Kaoping Bridge collapsed in Taiwan, largely due to dodgy foundations and nearby gravel extraction.
Mining has also been blamed for numerous incidents across India, including a 2016 collapse in Mahad, although this was rejected by the state government.
And in China, illegal and legal mining has been so pervasive along the Yangtze River, that it has disrupted shipping routes, made droughts more likely and floods harder to control.
Back in Vietnam, severe erosion accelerated by sand mining threatens the homes of half a million people in the Mekong Delta, according to the World Wildlife Fund report.
Dr Hackney said as riverbeds became deeper due to extraction, salt water from the ocean was flowing further inland.
"Which starts to affect the availability of drinking water, the availability of fresh water for agriculture and aquaculture, which are big livelihoods, particularly in the Red River Delta," he said.
"So farmers are having to change their crops, different rice varieties that are more salt water tolerant."
Will the industry continue unabated?
The world's insatiable demand for sand is unlikely to cease. However, in recent years some jurisdictions are taking the environmental impact more seriously and trying to crack down on illegal operations.
PhD student Hannah Runeckles has spent years studying the environmental impact of human activities in the Red River and said the size and complexity of river systems made them difficult to monitor.
"When you've got such a vast area, trying to track mining vessels, it's really difficult, especially trying to see where they're going, where sand is being moved around," she said.
"So we're trying to use high resolution satellite imagery, focusing on the last six years or so, to try and identify where we see sand mining hotspots."
Ms Runeckles said some communities were wary of the industry as they had not seen "any kind of profitability or positive impacts".
"They perceived the sand miners as outsides, coming and taking sand from their areas, from their livelihoods, to be sold elsewhere," she said.
She hoped her research would help policymakers better manage human activities to protect those who live by the river, and their livelihoods.
"We need sand as a society. It's the backbone of the modern world," she said.
"So to say that all kind of sand extraction or hydro-electric power or flood control should stop is not recommend, it's not plausible.
"So we really need to think about where sand mining activities happen."
