Cave roof breakdown

[Juan]

After observing a gentle rain of particles from cave roofs, a 'conversation' was started with Anthropic's AI assistant Claude. The answers range through granular disaggregation, catastophic roof falls, draught testing, and health implications. I found the process interesting from both the AI and caving perspectives!
The developing 'conversation' can be followed here on the Matienzo Caves website.
https://www.matienzocaves.org.uk/science/Breakdown/0107-jc-2025a-RoofBreakdown.htm

 

[Juan]

An observation from Toby Chilton, first published on the Matienzo Caves Facebook page:
When the collapse happened just beyond The Pillars Of Hercules, the Biggo/Hoyuca Rocky Horror connection (myself, Big Nose, Slug and Richard Greenslade) there were VERY fine particles falling through the choke as we went in. As we came back out I was aware of a quietish hissing noise which I saw was caused by grain of sand size particles falling to the right hand side of the route out. Then the collapse started.
I understand that miners take any unexplained small particles falling from the roof (ie they haven't disturbed themselves and are not aware of anything else that has done so) as a sign of imminent collapse and get out immediately.
I'd urge caution!
It would be interesting if movement activated cameras/ sensors could be placed, without wandering around the chamber, sound activated may work.
Having experienced the change from fine particles to boulders/blocks falling and seen how fast this can happen I'd rather stay in the Bar!

 

[davel]

It occurs to me that I’ve seen something similar (though not so obviously falling like rain) in big chambers in the north Wales slate quarries. Other than being vaguely aware of it I’ve not paid much attention to it (other than thinking it’s probably not a place to linger). Trouble is, I can’t remember any specific chambers where I’ve noticed it.

 

[Cantclimbtom]

I've read several accounts of mine collapse when it was almost immediately preceded by someone describing the sound of gentle rain or a hissing sound and sand sized particles dropping

I was once on a chalk mine at what should've been halfway through a solo explore - near the entrance shaft and immediate vicinity of it, I started to hear "rain" and the occasional clunk of small pebbles. I nearly fouled my trousers and jugged up the rope out of there. AFAIK it was a false alarm and some sandy topsoil coming down the shaft, but I didn't take any chances. Cowardly perhaps just wasn't in the mood for bravery on that trip.

 

[Allan]

I've read several accounts of mine collapse when it was almost immediately preceded by someone describing the sound of gentle rain or a hissing sound and sand sized particles dropping

I was once on a chalk mine at what should've been halfway through a solo explore - near the entrance shaft and immediate vicinity of it, I started to hear "rain" and the occasional clunk of small pebbles. I nearly fouled my trousers and jugged up the rope out of there. AFAIK it was a false alarm and some sandy topsoil coming down the shaft, but I didn't take any chances. Cowardly perhaps just wasn't in the mood for bravery on that trip.

I have noticed it in Cae Coch Sulphur mine where the oxidation of the Iron Pyrite crystals causes small flakes of rock to fall on a regular basis.

Also in a gold mine under a glacier in Kyrgzstan, wherever the wooden lining had failed, the warmth of our bodies caused the frozen ground to melt locally if we paused to look at something, again causing a shower of small flakes of rock.

 

[mrodoc]

The one time I experienced this was in Iran (book available). We were in a large sloping chamber with a bouldery floor and at the base I noticed an interesting hole. Squirming through it I looked up to that the whole chamber floor had jammed up against the wall with nothing underneath it. Then a fine drizzle of dust started. I was out like a shot - nothing happened but I don't think I wanted to find out if I continued under the floor!

 

[Peter Ryder]

Many years ago I was surveying in Windegg Mine Caverns, and found a sizeable flat-roofed chamber at the head of a boulder slope. Its floor was all big reckless, and as we scrambled around we heard stones rattling down somewhere beneath us which made us a bit uneasy. We were back a fortnight later, and were puzzled on finding a much taller chamber… then the chilling realisation dawned, the whole floor had fallen/subsided by several metres.

A scary place, really unstable. We thought that it may have been water-filled before the lead miners broke into it a century or so before.

 

[langcliffe]

Many years ago I was surveying in Windegg Mine Caverns, and found a sizeable flat-roofed chamber at the head of a boulder slope. Its floor was all big reckless, and as we scrambled around we heard stones rattling down somewhere beneath us which made us a bit uneasy. We were back a fortnight later, and were puzzled on finding a much taller chamber… then the chilling realisation dawned, the whole floor had fallen/subsided by several metres.

A scary place, really unstable. We thought that it may have been water-filled before the lead miners broke into it a century or so before.

I once dug a blockage in Hebden Horse Level and opened up the continuing passage until it finished in a sump. I returned with Mike Wooding to dive the sump, and found it had disappeared. The roof, no longer being supported by water, had collapsed leaving a considerable amount of air space.

Removing the water had other effects. A few years later I went back in with @Greybeard, and we found a carbon dioxide built-up in the same area. The carbonaceous shales must have oxidised.