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HUNTINGTON - The damage to the Crandall Canyon mine and the trapping of six workers appears to have been caused by the floor rising and the walls falling in and not a ceiling collapse, a federal regulator and other sources say.
Instead of raining rubble from above, debris seems to have crashed in from the mine walls, said Richard Stickler, the director of the U.S. Mine Safety and Health Administration.
"The roof line has not collapsed and even in the area where we're doing the cleanup work, we do not see any collapse . . . of the roof itself," Stickler said Saturday.
Also, pressure appears to have pushed up the floor, breaking it into chunks of rock and coal, according to two sources with knowledge of the damage.
"It was a heave," said a source who is a family member of one of the trapped miners and has been briefed on the condition of the mine by those who have assisted in the rescue effort.
"Heave" is a coal miner's term for what happens when the floor rises.
Another source, who has been a coal miner for decades and has assisted in the rescue effort said: "I've never seen anything like this."
The veteran miner said the floor rose about 2 feet.
The sources spoke on the conditions their names not be published because they fear they or their family members will lose their jobs at the coal mines owned in part by Robert Murray, whose holdings include the Crandall Canyon mine.
The descriptions do not necessarily shed light on whether the Monday accident was caused by an earthquake or by the removal of pillars in the mine. Jerry Tien, an associate professor of mining engineering at the University of Missouri-Rolla, said floor heaves have occurred both as a result of earthquakes and downward forces on pillars.
Murray has insisted an earthquake early Monday caused the accident.
Seismology experts have said their data indicates the collapse itself appears to be the cause of the event which registered as a 3.9 magnitude earthquake.
The ownership of the Crandall Canyon mine told the state of Utah last year it would be "pulling pillars." The action refers to the removal of coal deposits which previously were left in place to provide structural support for the mine. The coal industry often refers to the method as "retreat mining."
Both sources who spoke on the condition of anonymity believe the downward push on the pillars suggests retreat mining was to blame for the accident. Critics of the practice have said it is dangerous because of how it eliminates a mine's ceiling support.
Murray in a press conference last week said implications retreat mining had anything to do with the accident were false. "And the damage in the mine was totally unrelated to any retreat mining," he said.
A representative of Murray's company did not respond to requests for comment Saturday.
The veteran miner said the effect on the pillars and floor are similar to what happens when pressure is applied to the top of a cardboard box. The sides of the box are forced down while the bottom rises.
Tien said if removing the pillars did cause the floor to rise, that would not necessarily indicate the mistake lies with removing the pillars. There could have been an error in determining the strength of the floor, he said.
"We're dealing with a lot of unknowns when we go underground. We try to know as much about the floor as possible but we can never know everything."
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* MIKE GORRELL contributed to this report.