The science behind the bump
Springhill mine would’ve been at the centre of a giant nutcracker in 1958
AMHERST NEWS
While it’s known historically as the Springhill Bump, the 1958 disaster that took the lives of 75 miners has another scientific term.
“Miners used the nickname ‘a bump’ for what was a rock burst,” Nova Scotia Energy and Mines senior geologist John Calder explains. “A rock burst occurs at the coal phase, particularly when you’re involved in long-wall mining, when you have a face-cutting machine that’s running back and forth.”
On the surface, people reported feeling a thump and knew almost immediately what was happening.
“At the surface, people would have felt something like a bump. That wouldn’t explain what the miners felt deep underground. It was much more violent,” said Calder, who wrote his PhD thesis on the Springhill coalfield.
“I always felt the word bump was a bit euphemistic and didn’t really capture the horror of what it was like being underground at the time with the violent release of the coal and the upheaval.
Photos of the mine released by the Royal Commission were amazing. Everything was twisted and mangled. It was unbelievable to look at, and I can’t imagine what the rescuers - the draegermen - saw.”
Nutcracker effect
Coal mining techniques were constantly changing at the time, and while it was the scene of two major mine disasters, Springhill’s mines were considered cutting edge when it came to using new methods of extracting coal from the ground.
For generations, Calder said, mining was done in a room and pillar style with ‘rooms’ where coal was removed using pick and shovel and ‘pillars’ of coal left to hold up the roof rock.
“The thing is, when you’re removing that coal seam, you have all that weight and pressure of the rocks above you all the way to the surface bearing down on the workspace, but you’re also putting pressure right on the face of the coal you’re working on,” Calder said.
“It acts like a lever, almost like a nutcracker, with the coal face being the nut and the handles are the roof and the floor of the open space.”
Unique geography
Unfortunately, the nature of the area’s geology was the reason for the bump. Calder paints a very different picture of Springhill 300 million years ago: a tropical wetland located near the equator.
“Off to the north, there were meandering river systems that wound their way down through the Cumberland Basin, heading northeast toward an unknown sea,” he said. “Those rivers would eventually find their way, moving laterally and over the peatlands, which became coal. Those river systems left behind sandstone bodies about 20 metres thick and about a kilometre in width.”
These massive sandstone deposits sat on top of the coal and normally did not give way easily. The pressure would build up, and instead of dissipating gradually as mining operations continued, it would hold fast until it released in a violent rock burst.
The bump all came down to digging coal at great depths and leaving large empty spaces deep underground. Bumps, he added, would not happen in shallower mines.
“I’ve never been underground where there was a violent rock burst because, by the time I come around in the 1970s, access to the mines in Springhill were all shallow,” he said. “You had to be at a depth, or vertical cover, of about 2,000 feet in order to get enough pressure building up to cause this problem.”
‘A sense of dread’
While it was considered the most sophisticated mining technique of the time, the long-wall mining done in Springhill created a significant problem, Calder said. The royal commission report that followed the 1958 disaster quoted miners as being concerned about three advancing long walls being brought into line with one another at the same time.
“There was a lot of finger-pointing at the time that the alignment of faces was the cause. I’m a professional geologist, not a mining engineer, but from what I’ve read and what I know of the geology, it makes sense. You put the three in line, then you have one very large line that you are exerting pressure on, and the fact there was one colossal rock burst makes sense to me,” Calder said.
Calder said the miners knew their environment very well and he would not be surprised if they knew something was to happen. It has been reported there was a smaller bump earlier the night of the big bump – at least an hour before.
“It’s like an earthquake, you have pre-tremors leading up to the major earthquake as the stresses are starting to give way and you get the warning signs of smaller rock bursts. I have no doubt they sensed what was coming. I imagine there was a sense of dread.”
The bump pretty much ended deep coal mining in the Cumberland Basin. The Springhill mines were among the deepest in the world and the lessons learned from the bump were most likely applied to other coal mines.