“We didn’t know they had guns,” Santosh Yadav says. “If we knew they had so many guns – that they were planning to commit a massacre – we would never have argued with them.”

Months later Yadav still replays the morning of 19 May in his mind. The decision he made with his uncle and cousins to go to the riverbank. To confront the men mining sand near his village. Not to run when the miners went to their vehicles and returned with guns.

“We were telling them to stop taking the sand,” he says, standing by the same river on the outskirts of Jatpura, his village in the east Indian state of Jharkhand. “They said, who are you to stop us? If we want to lift sand, we will. Then they lifted their guns and fired.”

His cousin, Niranjan Yadav, died first, he says. Then his uncle, Uday, who threw himself on his son’s body. The miners then turned their guns on Vimlesh, the second son. Postmortem reports show all three were shot at close range in the chest. “They also fired at me,” Yadav says. “To save myself, I jumped back and hid behind one of the trucks, and then in a hole behind a nearby bush.”

He stayed in the hole, he says, “shivering in fear” for minutes until other villagers arrived at the river. “It is by sheer luck that I managed to escape death that day.”

The cremation ground of Jatpura village. Photograph: Shaikh Azizur Rahman

The three Yadav men shot in May were victims of an unlikely environmental crisis. Virtually every facet of modern construction depends on sand. Heated, it becomes glass. Mixed with gravel, asphalt. Bound with cement, concrete. With Asia in the midst of history’s largest ever building spree, awareness is growing of the extent to which the world’s supplies are dwindling.

China used more cement between 2011 and 2013 than the US used in the entire 20th century. In India, by some estimates, the amount of sand used for construction has tripled since 2000. Demand is expected to keep soaring: the country plans to build at least 60m new houses by 2024. “Demand for sand now outstrips that of any other raw material,” says Sumaira Abdulali, the convener of the Awaaz Foundation, an activist group that campaigns against illegal sand extraction.

As supplies of sand close to major cities such as Delhi and Mumbai have become exhausted, developers are turning to more remote regions to source it, bringing them into conflict with smaller, usually vulnerable, communities. Groundwater shortages, flooding, and depletion of fish and other animal life often follow in the wake of unsustainable mining, which activists claim can also weaken bridges and barrages along the path of heavily mined rivers, leading some to collapse. No reliable data exists for the amount of sand currently being mined in India, Abdulali says. “But it’s quite clear when you visit the countryside in India, there is hardly a creek, river or beach where you don’t see the effect of sand mining.”

Also unknown is the toll of the hundreds of conflicts erupting in small communities across the country between those who hold mining leases and local residents. “But we know the violence is extremely widespread,” Abdulali says.

Jatpura is a long way from the burgeoning cities of urban India. Ranchi, the Jharkhand state capital, has just over one million residents – tiny by Indian standards – and is six hours away by car, along patchy highways that degrade and narrow as Jatpura nears.

The sand miners arrived at the beginning of the year, using excavators and industrial vacuums that could slurp vast quantities of sand from the riverbed. Watching over them were men the villagers called “lathait” – Hindi for someone skilled at wielding a club.

Niranjan Yadav led the opposition to the project. The mining was veering close to a patch on the banks of the river where Hindu villagers traditionally burned their dead. Local people worried they would wake up one morning to find the sacred earth heaped in the back of a truck.

The dredging also made the river treacherous. Holes began to appear beneath the surface, sometimes 20ft deep. Villagers said that in April, weeks before the Yadavs confronted the miners, a 12-year-old boy had been playing in the water when he slipped into a crevice and drowned.

The widows Bindu Devi (left) and Rekha Devi of Niranjan Yadav and Vimlesh Yadav. Photograph: Shaikh Azizur Rahman

Resentment grew with each chunk of riverbed that was carted away. “People who are in distant areas, rich people – like a mafia – are becoming richer,” says another Jatpura resident, Sudama Ram. “We feel very helpless. But we have our brothers with us in the village. The whole village is with us. We are fighting.”

His remarks were met with approving murmurs among the other Jatpura residents. It was true the village was fighting, but Ram had exaggerated its helplessness. The pressure of runaway resource extraction had not just turned the people of Jatpura into victims. Some believe it made them into killers, too.

Satinder Singh was a manager from a nearby village who oversaw the sand mining in Jatpura and other sites. After the Yadav men were shot and the alleged gunmen fled, he remained close to the river “to keep watch”, according to Neha Arora, the deputy commissioner for Garwha. Officers found him beaten to death, and the house he had been renting in Jatpura razed. Police believe that he was attacked by a mob, “but it’s difficult to pinpoint who was involved,” Arora says. “Nobody is talking.”

The bodies are gone, but the rest of the scene that confronted police when they arrived at the riverbank that morning is unchanged. The shovel of one of the excavators is still half-buried in the sand, as if its owner fled in a hurry. Several other vehicles are strewn about the site, warped and gutted by fire.

Conflict has frequently accompanied mining operations in the Garwha district. “It happens anywhere there is excavation of resources,” Arora says.

The mining licence for Jatpura was held by Dharambeer Singh, a small contractor from a nearby district. His lease permitted him to mine sand close to the cremation ground, but not to use heavy machinery. Arora says that he had been advised, like all contractors, to be “sensitive to the issues of the villages”, to clearly demarcate the mine’s boundaries, and to try to employ the villagers as labourers in order to cushion their discontent.

“But I would not say that sensitivity is what they keep in mind,” she says. The amount of money at stake and the nature of the business models discourage it. “The [contractors] are target-driven, profit-driven,” Arora says.

The shooting in Jatpura triggered protests in Garwha town and was raised in the Jharkhand state assembly. The state has since amended its mining policies. Lifting sand is now permitted only from large rivers, which officials say can be mined more sustainably. The river by Jatpura, classified as medium-sized, is out of bounds.

Arora says she is unsure why the use of heavy machinery, among other legal breaches, continued in Jatpura for months without officials being alerted. “We did not know what tension was brewing there,” she says.

In other cases, she says, village chiefs – or “mukhias” – have struck deals with the miners to overlook their operations in exchange for a cut of the profits. It is a lesser-known consequence of the vast demand for sand: as well as environmental degradation, soaring sand prices encourage corruption and spark conflicts within villages.

The fires that gutted the trucks and excavators on the morning of the killings in May were not the last to be set on the riverbank that day. After midnight, more than 500 men gathered at the cremation ground, metres from where the Yadav men were shot. They watched silently as the three bodies were placed on a wooden pyre.

It burned until dawn, until the men’s ashes caught in the wind and settled with the sand in the riverbank.

Burnt sand-carrying trucks lying by the ghat where sand mining took place near Jatpura village. Photograph: Shaikh Azizur Rahman

Additional reporting by Shaikh Azizur Rahman