One of the largest salt mines in the world exists under Lake Erie in the US

Salt pillars, left behind for support during mining, line the tunnels in the Cargill salt mine about 550m below the surface of Lake Erie on Whiskey Island.

Below Cleveland, Ohio in the United States, in a subterranean world many surface dwellers don’t know exists, miners extract a crucial winter mineral – salt.

The Whiskey Island salt mine, owned by food giant Cargill, helps supply road salt across the Northeast and Great Lakes, where a colder, snowier-than-usual winter has driven demand.

Many municipalities exhausted supplies that typically last through spring, said Cargill spokesperson Emily Tangeman."Our teams have been working overtime since September to support customers across the snowbelt,” Tangeman said in a statement, noting that early, persistent winter weather boosted demand across the industry.

The mine beneath Lake Erie

, one of the world’s largest, produces three million to four million tons (2.7 million to 3.6 million tonnes) annually, although that can fall short of demand in especially harsh winters.

The salt, formed 440 million years ago, is mucked up and loaded onto a conveyor belt.

Located 1,800ft (549m) underground, it's accessed from Whiskey Island, an industrial area on the shore right beside downtown Cleveland. The mine opened in the 1960s and operates year-round, with salt extracted by drilling and blasting through vast tunnels formed from an ancient inland sea that dried up millions of years ago.

Inside, the mine is a maze of roughly rectangular caverns with chalky white walls and ceilings that extend for miles. It’s dimly lit and often pitch-black beyond the glare of headlamps and floodlights. Heavy machinery and conveyer belts rumble as small ATVs whisk miners around.

The absolute darkness of the mine is broken as supervisor Andrew Adkins uses a headlamp to look over a map of drilling sites at the Cargill Salt Mine.

Maintenance superintendent George Campbell said operations are continuous, with downtime used for upkeep and repairs to keep production steady.

Cargill said it is prioritising shipments to ensure salt reaches the areas of greatest need as winter lingers in some regions. Frequent smaller storms also increase usage, Tangeman said in the statement, requiring repeated salting and creating logistical challenges.

A return to harsher conditions across the Eastern US meant some cities – including Boston; Bangor, Maine; and Ithaca, New York – shivered through their coldest seasons in more than a decade.

Campbell said there’s still decades of salt left to be extracted.

"I think that we have enough reserves to continue to keep people working for a long time,” Campbell said. – AP