The crack runs for about 36 feet "outby" -- toward the mine's opening -- from the longwall section mining face, the geologist said. When it reaches a crosscut tunnel, the crack itself disappears, but the floor heaving continues for another 10 feet, the geologist said. The crack is about five inches deep and the floor heaving is six to 10 inches high, MSHA's geologist found.
Also, the geologist found that the crack is not "rooted," meaning it doesn't appear connected to the coal seam or a void below the active mining area, officials said.
"It wasn't a massive crack," Stricklin said. "It was what you would typically see in a longwall mine."
MSHA officials have not said the floor crack and similar smaller cracks are not evidence worth examining. Instead, they have disputed Massey's description of their size and the conclusions the company has drawn from the cracks' presence in the mine.
Such cracks and floor heaving is typically caused by the shifting of ground pressures during highly mechanized longwall mining, and can release methane from coal seams and geologic formations below.
Since early June, federal and state investigators have focused on, among other things, incidents in 2003 and 2004 when methane "outbursts" from the mine floor inundated the Upper Big Branch with the explosive gas. No ignitions or injuries were reported in those two incidents.
MSHA documents show Massey had proposed a number of steps, including de-gasification wells, to prevent a recurrence, and federal experts proposed additional measures, but MSHA has been unable to explain which of those steps were eventually implemented, and Massey has not responded to questions about the matter.
"There may be a crack in there that was involved in the explosion," Stricklin said, "but we don't know that yet."
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.