Yep. They can be mild or wild. Redstone was especially bad because of the steep angle of the coal seam and rock strata. Of course, Mother Nature abhors a vacuum, and when you remove the coal she tries very hard to close up those empty spaces. This is true not only for coal mining but hard-rock mining.
When I first hired out at Redstone I worked on the Utility Crew, and one of our main jobs was ventilation. This required us to go back into the old workings which often had had 8-foot headroom just a few years back, and now had squeezed down so far you had to crawl through openings a foot or two high! Really freaky.
The veteran miners told us of two men killed a few years before I got there .... they had an especially severe bounce (or bump) and when they dug the guys out, they were still in running positions, buried completely in broken-up coal. I can remember having to dig myself out of the cage on my Joy Loader a number of times when I happened to be next to the wall ("Rib" in hardrock parlance.) You can see why I didn't stay there too long. The folks who work underground in coal deserve a lot of respect.
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