A national mine safety expert believes the two collapses at the Crandall Canyon Mine — one trapping six miners Aug. 6 and another killing three rescuers Thursday and injuring six others — were caused by "bumps" that resulted from the way operations were being conducted at the Huntington mine.

Mining bumps are pressure-shifting seismic events than can cause the walls, pillars, ceiling and even the floor of a mine to literally explode and disintegrate. They can cause deaths and injuries, and can result in cave-ins. Bumps accounted for 23 mining fatalities in Utah between 1894 and 1978, according to the National Institute for Occupational Safety and Health.

These so-called bumps are not uncommon in mining. But they can be reduced with safe mining practices, said Robert Ferriter, director of the Mine Safety and Health Program at the Colorado School of Mines. And while an investigation ultimately will determine the cause, Ferriter told the Deseret Morning News on Friday he feels certain the bumps were caused by mining activity.

"In my opinion, based on the evidence and the way it's described, I think it definitely was a mining-induced bump," he said of the initial Aug. 6 collapse.

"I think it goes back to the mining plan. How much ground are you going to take out? How much coal are you going to leave to stabilize? What size are the pillars? Again, it's a design-type thing. You want to minimize those bumps as much as possible."

It is common mining practice to leave large pillars of underground rock untouched, in roughly a checkerboard pattern, so that the rock can support the weight of the mountain and prevent cave-ins, Ferriter said. In Utah, those pillars typically are about 80 feet by 80 feet. But leaving a larger pillar, such as 90 feet or as much as 120 feet, can reduce the chances that bumps will occur because "there is less stress," he said.

"Earthquakes happen naturally. Bumps are a coal-mining phenomenon," Ferriter said, adding that bumps are more severe in Utah mining because thick (as much as 300 feet), heavy beds of sandstone often exist above mining operations, placing a great deal of stress on the man-made caves beneath them.

"The other thing that happens there is when you load it up, you are pushing the pillars into the floor, also," he said. "When the stress is overburdening, it pushes it (the pillar) into the floor," which can cause the floor of the mine itself to explode.

Ferriter said it is his understanding that around the time of the Aug. 6 collapse, miners had been extracting coal from the pillars themselves.

"Often, it's when you try and take too much of the pillar" that bumps occur, he said. "I understand they were retreating out of that section and taking some of that pillar out on the way out, maybe shaving it or splitting the pillar to get the coal. The more you take, the greater the load on the rest of the pillar."