Hi! there was a documentry called "One of our mines is missing on one of the cable channels which starts with the explosion in the 1950's which left a crater 60ft deep and 200ft across caused by lightening striking the detination wires the clip is on youtube under the same name and the hill was Vimey ridge which was the austrailians first action of the war and although it cost 5,000 lives they were the first troops to take control of the hill as for the tunnels they were dug by welsh miners and there are still some large mines still unaccounted for some as with the one they found in the programme containing one million pounds of amatol plus many layered detinators
as a mark of gratitude the aussies were given 250 acres of the top of the hill where they built their war memorial complete with mines still underneath sorry to go on but a british historian looking back through military records noticed that the mines had been layed primed etc but for some no records existed of detination that is how they found the one in the programme
i'll end it there but do check out youtube