On Thu, 19 Mar 2009 21:02:26 -0400, HK wrote:

I went into a couple of coal mines when I worked for The AP. It was
damned scary being down under all that rock. I did not get the same
feelings of fear in the natural caves tourists like me visit near the
Shenandoah River.

A cave is stable, short term, and the rock usually won't move, short
of an earthquake. In a mine, the support has been removed, and
sometimes replaced with not enough costly timber shoring. Or in the
case of coal, they would leave too small and too widely spaced pillars
of coal that they would rather sell. Then they tease it with constant
blasting or digging. It can take a while for things to reach
equilibrium after a blast, and sometimes you can hear the timbers
groaning. The trifecta of dangerous trades: Farming, fishing, and
mining.

Casady