As gritting trucks work around the clock during the first cold snap of the year, spare a thought for the miners who dig the salt out of the ground almost a mile down under the North Sea in temperatures which can hit 40C.
And bear in mind that the grime you are smearing across your windscreen was created 260 million years ago when a sea covering a swathe of northern Europe evaporated, leaving millions of tonnes of rock salt deposited under the north-east coast of England.
Boulby Mine, near the tourist village of Staithes, North Yorkshire, is one of only two places in England where the salt used on the country’s roads is mined.
It produces hundreds of thousands of tonnes for National Highways to cover the main routes and for dozens of council contactors to spread across the rest.
When it opened in the 1970s, Boulby was the deepest mine in Europe, and it remains the deepest in the UK.
It is so deep it is home to one of the world’s leading projects trying to find dark matter – the mystery substance that physicists believe makes up most of the universe – as a kilometre of rock blocks out most other “normal” particles.
Boulby’s two shafts are 1,100m deep and lead to hundreds of miles of roadways which descend even further down into the earth.
The mine was opened as a potash mine and the rock salt was produced as the miners pushed through the salt deposits to get to the fertiliser product.
The facility now mines a different fertiliser – polyhaylite – but Boulby still produces hundreds of thousands of tonnes of rock salt, with the exact amount varying hugely dependent on how harsh a winter the country is experiencing.
ICL Boulby chief geologist Thomas Edwards said most gritters in the north of England will probably be filled by salt mined under the North Yorkshire coast.
“I like to tell people that when their cars are a little bit grubby when the roads have been gritted in the winter, that’s 260 million-year-old dirt that’s dirtying your cars,” Mr Edwards told the PA news agency.
“It’s really quite something to think about. And a bit of a positive rather than ‘what’s all this grub on my car’.”
He said people did not realise the salt was mined more than a kilometre underground and “hauled out by people working 24 hours a day, in the dark, beneath the sea”.
Fifty years of digging for potash, rock salt and now polyhylite has left more than 1,100 miles of tunnels under the North Yorkshire coast, between Staithes and Skinningrove and stretching out up to about 15km under the North Sea.
The furthest point takes about an hour to drive to in a Land Rover.
Mr Edwards explained that the deposits were all left when the vast Zechstein Sea dried up multiple times in the Permian geological period and are accessible in this location, but peter out further north and east and are too deep to mine the east and south.
But he said there is no shortage of rock salt available at Boulby.
“We have resources to last us many decades, if not centuries,” he said.
About 600 miles of tunnels remain in use and miner Paul Byrski, 65, from Guisborough, reckons he knows them all, without a map.
Mr Byrski has worked at Boulby for 34 years – rising from shovelling the conveyors belts to a district overseer, and now working part-time as part of the roof inspection team.
He has done just about every job going at the mine and says he knows the labyrinth of tunnels like the back of his hand.
“A lot of the old potash areas are now inaccessible,” he said.
“All remaining roads and the roads we need to inspect, I know them all. Off by heart.”
Mr Byrski said the biggest changes he has seen over the years are the introduction of mechanisation and vast safety improvements.
He said he remembers times when hundreds of thousands of tonnes of potash and rock salt were all moved by hand, and when the miners would ride the conveyor belts around the tunnels.
He said: “This mine has meant 50 years of good employment with good-paying jobs. And it means a lot to the world. Loads of loads of people, if someone left, would apply for the jobs here.”
Darren Clark, severe weather resilience manager at National Highways, said its gritters would be out during the expected “significant snowfall” this weekend spreading some of the 215,000 tonnes of salt that is used on average each winter on motorways and major A roads.
The salt is sourced from the Boulby mine and another in Winsford, Cheshire, while National Highways holds more than 240,000 tonnes stored in three dedicated salt barns, with an additional supply of 90,000 tonnes available if needed.
Mr Clark said: “This ensures we can quickly respond to the type of adverse weather conditions we are expecting over the coming days.
“If you are travelling this weekend, please plan your journeys, check your vehicle, keep your distance, and reduce your speed. Gritters will be out treating our roads around the clock, but it is still important to drive to the conditions and consider packing a snow kit of blankets, food, water and a shovel.”
