The technical term for what it is doing is ‘block cave mining’ and the concept of it is enough to induce a wince. While most underground mining involves digging along a seam of rock and then drilling or blasting the ore out, block caving is somewhat more brutal. Rather than following a seam you dig a tunnel underneath the ore and then plant large quantities of high explosive into the rocks above your head. Having stepped back some distance you blast those rocks and then let gravity do its job, collapsing hundreds of thousands of tonnes of rocks into that tunnel.
