Whew! I'm doing a lot of articles, without much ad money. Must find a way to stop myself!
A most interesting article. The wonderful Germans thought it would be fun to dump barrels of nuclear waste into a salt mine. Must have been hit by a bout of 'Homeritis'. Now, I remember when everybody was looking into salt for nuclear waste, and the big US bomb-disposal site is in salt.
Salt, but its very nature, is totally unstable. Salt domes are being continuously extruded by rock stresses. Since salt is so weak, it is always at its strength limit, but it has the property to creep slowly. Thus, when you make an excavation, the creep process is immediately activated. (...much like the Niagara tunnel!)
They used to think this was a wonderful thing, since the salt 'closes' any cracks, and is essentially impermeable to water. But, on a longer scale, you are excavating into 'molasses in January'. So, the poor Germans are worried about the whole thing collapsing and closing in, which is what they wanted in the first place. This is a lesson about choosing totally unstable rock, such as for the deep Bruce thingie. It is not a good idea!