[jaysay]

When you actually think about it, we've been taking resources from under the earths crust for the last 100 years or so (oil and gas) when these materials are drawn to the surface there must be a huge void left behind, to me its like an egg, remember when we were kids collecting birds eggs (its illegal now) you used to remove the licked through a pin hole just leaving the empty shell which then had to be kept in a box packed with cotton wool as they were saw fragile. It makes you think if this isn't have the same effect there must be some huge hollow spaces bellow the earths surface, somethings going to give sometime