Was wondering why the floor C bridge leading to the westerly workings in the back vein is in such a good condition in comparison to those spanning chambers immediately to the east of the back- vein incline. I was under the impression that most of these bridges were brought down or badly damaged during the time the back-vein was flooded.

Was it possibly renewed when Oakeley was working this part of Cwmorthin, after the back vein was dewatered by them in the 1930s?

If so, I should imagine it was mainly used to carry waste trucks, as waste was being tipped in chamber 2 west.
Can anyone throw more light on this?

🔗Cwmorthin-Slate-Mine-User-Album-Image-62682[linkphoto]Cwmorthin-Slate-Mine-User-Album-Image-62682[/linkphoto][/link]

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Are there any documented effects of earthquakes on Cwmorthin/Oakeley and other slate quarries in the area? I am aware that parts of North Wales get the occasional earthquake.
Have also been thinking about the drop fault which is a geological feature of Cwmorthin and the possible effects on the mine of a moderate quake.

Hope I'm not in there at the time :ohmygod:

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I'm not ignoring this - but am just a bit busy at the moment 😞 however I have not come across any references to earthquakes causing any problems between ca 1870 and 1970!

(I'll have think about the western question)

Cheers

Grahami

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there is a crack all the way to the top of the mountain in cwmorthin, its a result of dodgy working practices. not sure about earthquakes as yet 😮

there is a crack all the way to the top of the mountain in cwmorthin, its a result of dodgy working practices. not sure about earthquakes as yet :o

I strongly suspect that this crack is something to do with the significant falls in Cwmorthin/Oakeley in the late 1800's documented in Graham Isherwood's 'Cwmorthin Slate Quarry' and brought about by, as has been said, suspect work practices.
Does this crack effect the overall stability of the mine today?
(Earthquakes in mind again!) :ohmygod:

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there is a crack all the way to the top of the mountain in cwmorthin, its a result of dodgy working practices. not sure about earthquakes as yet :o

Where about in the mine is this crack located? Is it an obvious feature, or just indicated by a heavily collapsed area of workings? Am I right in saying it may therefore be in the upper back-vein?

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There are several cracks which are visible on the surface, most notably running across the dried up bed of Llyn Bach, roughly parallel to the line of the ridge on R'Allt Fawr between Oakeley and Cwmorthin. They can be traced for some little distance to the south west and cross the outcrops roughly at right angles.

There should be either in the Oakeley section here or the Cwmorthin one, a cross section drawn by Thomas Jones the Oakeley consulting surveyor/engineer which shows the presumed line of the major crack and its relation to the drop fault. (And if it isn't, it soon will be!) The cracks are vsisible even on modern aerial photos.
EDIT: Hmm - don't seem to have posted it here. Anyway, here it is:
http://www.aditnow.co.uk/documents/Cwmorthin-Slate-Mine/section-0a.pdf 

Cheers

Grahami

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Is the drop fault in Cwmorthin visible as a surface feature however indistinct ?

When I was a child I lived in Kenya and remember visits to the Great Rift Valley where it passes close to the capital, Nairobi. On loooking back southward from the valley floor, one could see the escarpment of the Great Rift as a series of giant steps, which in retrospect, I believe were a series of drop faults, outlined against the horizon.

This escarpment edge was remote and blue with distance: -
A vision of far away and long ago!

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Is the drop fault in Cwmorthin visible as a surface feature however indistinct ?

According to GrahamI's post above yours it can be seen on aerial photos, so I would have thought it would be visible on the ground (if you know where to look!).

That's a fascinating diagram, thanks for posting. We've been over the watershed a few times lately and had noticed some linear ground features...they run as Graham says, parallel to the ridge and against the lines of strata on the ground as at SH68468.46365. It's a superb spot, well worth the walk esp the views as you come over the bwlch towards Garreg Flaenllym.

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I would tend to concur with the bright being repaired in the 1930s after the Back Vein was dewatered - whether to allow passage of trucks to tip or for access / bypassing the incline.

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Just found this satellite image of Cwm/Oakeley and surroundings.
If you zoom in between Cwmorthin and Oakeley quarries, a series of parallel features which certainly look like cracks can be seen quite distinctly, high up on the mountain. These cut across other geological formations in quite a noticable way and it's both amazing and perhaps a little unnerving to think they were brought about by mining activities below!

Will try and get up there this October.

http://www.flashearth.com/?lat=52.990085&lon=-3.963742&z=15.9&r=0&src=msl 

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53degrees 59' 54.7" N , 3degrees 57' 40.8" W for instance? That's roughly the grid ref I gave.

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Found a reference to the collapse and cracks in ' Cwmorthin Slate Quarry' by Graham Isherwood. Summay below with slightly changed wording: -


In 1884 a major part of Cwmorthin's workings in the back vien collapsed both below ground and on the surface. This had the effect of cracking open the ground over a wide area, the crack reaching the surface at the top of Yr Allt Fawr and draining Llyn Bach.
The collapse closed off more than half the workings and as a result production fell. To restore production, workings were subsequently developed and extended below the level of Llyn Cwmorthin.

Did the lake water mostly find its way down into the mine workings via the cracks which had opened up in it's bed, or did it drain out another way?

I have this vision of all the water disappearing down the cracks!







😢

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i would say it went down into the mine ,i have been in cwm a lot this year when the rain outside was bad over a few days ,and have noticed the water coming through places i not seen before so its all fractured on upper levels ,and getting worse .thats just my opinion but look at thread on m,e on cwm about steps chamber 😠

Presumably this is/was the reservoir?

http://www.flashearth.com/?lat=53.000688&lon=-3.962817&z=15.6&r=0&src=msl 

A lot of the history of the Welsh Slate Company / New Welsh Slate Company is littered with their enthusiasm to leave as little slate in the mountain as was physically possible - and it seemed that they regularly took a little too much out of there.

This is pretty neatly demonstrated by the pretty terrible state of the upper workings, which are mostly inaccessible; and where they are accessible, they're generally smashed.

That said, this won't have been helped by the couple of bouts of unstopping, which will have caused a lot of shaking, farthing bringing things down.

Presumably when the 1884 collapse occurred and the water drained from the lake, some/most of it did end up in the workings - although I'd guess that it wouldn't have come in that quickly as there's a fair bit of ground for it to filter through first.


Turning to the current state of the mine, I don't think there is anything of an usual pattern of falls in there - bits keep dropping off and sometimes they're somewhere well-trodden and you notice them; and sometimes you don't notice them.

It happens pretty much everywhere, but hopefully not when you're under it!

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The drop fault, incidentally, is an interesting, if slightly hard to comprehend aspect.

At the far end of the mine, it's possible to walk out of the Old Vein, then come back into it beyond the drop fault - the drawing that Graham uploaded (linked above) shows this very clearly.

Further into the mountain, there seems to be a very broken band that's been timbered through, but virtually every one of the passages is shattered - whether this is the point at which the drop fault is encountered I don't know, but it seems possible.

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I remember something about areas of Cwm/Oakeley where shale is encountered. If this is the case there will be some areas of the slate veins which never underwent the metamorphic process by which the shale is transformed to slate. Maybe such areas would be more unstable and thus have to be timbered through.
Afraid I can't remember where I saw this reference.

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A few question slightly off topic.......
Were the 3 reservoirs, Llyn bach & the 2 north east of it for public service or to supply Cwmorthin/Oakeley?
I notice from the 1901 O.S map that there is a Level & tramway to the East of Llyn Bach, do we know if this is still open & if so how long is it!

🔗Personal-Album-338-Image-66992[linkphoto]Personal-Album-338-Image-66992[/linkphoto][/link]

.....Lister;~)

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In my post above I mentioned seeing large linear formations between Cwm/Oakeley on the satellite image. Am wondering now if I am looking at the same features as the cracks mentioned by Isherwood as draining the bed of Llyn Bach. I can now clearly see on both the satellite image and the early map above, the former position of the lake, which appears quite small hence its name. The features I focused on earlier lie roughly to the SE of the lake and indeed seem to cross a couple of outcrops or ridges at right angles, as has been described above, but however don't appear to be on the fomer lake bed? To be seen so clearly on the satellite, they must be reasonably large features and probably natural. :confused:

Isherwood mentions the collapse had the effect of cracking the ground over a considerable area, so I should imagine these cracks show up away from the bed of the former lake as well as in it. Would they actually be visible from fairly high up on a satellite image?

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