Rob said:
In Peak Cavern today with Batgirl doing the Rocky Tube - NCC shaft roundtrip to finally get the survey tied up. Just as we dropped down into Galena Rift (at exactly 14:33) there was a tremenous boom! The sound didn't come from along the passages, it was from the rock! We both felt the ground shake. Lasted for about the same time as i would expect a large explosion to take.
Does anyone have any ideas? Was anyone diggin in there somewhere? Do you think it could have been from the quarry?
Leaving aside obvious but smutty allusions to the mile under club, I'd have thought that blasting activity in the Hope Cement Works quarry could cause this - it's not very far away from parts of the Peak system.
Sitting in our living room in Hucklow I used to be able to clearly distinguish the number of 1/4 second delay detonators they were using when they were still working Milldam Mine. The blast face was probably about 500m away at that point and they were using no more than 100kg of explosive per round. I don't know the exact details of blasting at Hope (although I could probably find out if you really wanted to know) but the charge sizes used in modern quarries are usually measured in tonnes and are initiated with sequenced detonators which spread the explosion out over a period of up to several seconds.
In fact _had_ anyone been using bang in the Peak system (where its use by cavers is banned, BTW) then IME you would have heard/felt it as an air blast rather than through the rock.
I bet if you phone Lafarge tomorrow they will tell you if they were blasting today, and if so at what time. Eddie will also be able to tell you what time they generally blast (usually these things are done on a pretty regular schedule), although I think he was out on business this afternoon.
Nick.
