Rhosydd Slate Mine

Altitude 450m

Entrance grid refs

Adit : SH 665462

Twll : SH 666453

No. of levels : 14

No. of inclines : 3

Personal experience? : Yes

Stop Apache Web Server! - collapse in Rhosydd

Local area

Rhosydd is in the Moelwyns just to the west of Blaenau Ffestiniog, famous for its slate quarries / mines. The area in which Rhosydd is situated also contains a number of other mines of, namely Wrysgan, Croesor, Pant Mawr, and numerous other scratchings, only noticeable by walking the hills. Most of these mines are all in the same veins of slate, known in Blaenau as the Old Vein and Back Vein. There are also other veins such as the narrow vein, but these were not as effective for producing slate.

It is easy to see the evidence of large scale mining activities, by the vast slate tips on the hillsides. The mining companies obviously had no regard for the scenery whatsoever.

About Rhosydd

Rhosydd is a typical slate mine of its era, neither massive like Oakley / Cwmorthin or Llechwedd, which are both tourist attractions, nor too small to be of interest.

There are two main entrances to Rhosydd. The first entrance is via the 9 adit, which is a horizontal drainage / transport tunnel that goes straight into the hillside from behind some decaying buildings for 2200 feet on a gradient of 1 in 86. At this distance, after travelling through the back vein and narrow vein, it meets the Old vein at right angles. At this point, the mine proper starts, with one of the inclines just to the right. This incline still has a truck on it at the bottom, with the steel winch cable under tension!. All levels below level 9 are flooded, which only leaves about half of the mine accessible.

The dip of the slate is about 22 degrees to the horizontal in this area, and thus the mine is generally a series of large rectangular chambers moving up the vein, with regular perpendicular transport tunnels at roof level (using bridges to cross the chambers) connecting the workings to the inclines.

The second entrance is via an opencast mine in the top of the mountain (locally referred to as a Twll). There are two twlls, the east one is the result of a massive collapse in Rhosydd which occurred at about the turn of the century, and the other twll, the west twll is a quarry. The twll has *very* steep sheer sides, but it is possible to climb down into the hole (about 50 feet), and then walk down into the mine. The twll is basically a chamber that reaches the open air. At the bottom of this chamber on the right is the top of the aforementioned incline, although rumour now has it that there's been a collapse at the bottom of the incline, and the through route is now blocked. Well, it is possible with abseiling gear as you can abseil into a chamber from the incline and pass the blockage that way.

If you go right at the bottom of the chamber you cross through the bottom of a number of chambers and then reach another incline. This incline is nearly complete, the winding gear at the top is intact, if not a little rusty, and the counterbalance truck still has all of the cast iron weights (4 tons) in it. A tunnel from the bottom of this incline takes you through into Croesor where your way is blocked by a 20 ft drop into a lake you cannot see the other side of. It is of course crossable by boat, but that's small beer to some of the other little problems that lie in wait!.


Initally the slate from Rhosydd was taken over the mountain by pack horse down past Llyn Stwlan to the Ffesiniog railway, although this proved to be troublesome. By 1864, Rhosydd had built a tramway which went down the other side of the bwlch (pass) and connected with the Croesor tramway. This then lead directly down the valley to Porthmadog. The tramway has a truly impressive incline to lower it from the head of the valley to the valley floor. The incline drops for 700 feet vertically, or 1250 feet horizontally, in one swoop, with a top slope of 46 degrees. There is also a track up to the mine from Cwmorthin, which was used during the closing years of the mines operation, and has recently been made up - presumably for re-opening the mine.

So then ...

There are some nice chambers leading off the 9 adit, which are suitable for camping in!. Also there are some nice flooded chambers that can be canoed across, although it's to no avail as you eventually reach a dead end.

All in all, Rhosydd is a nice little mine to stroll around if you're in the area and happen to have a torch handy, although it lacks much in the way of machinery or artifacts.

Note: There is talk of re-opening Rhosydd, and as a result, signs have appeared warning you to keep out. You have been warned!

Click here for some pictures from inside Rhosydd.

Rhosydd Collapse

Sometime around August 1998, Rhosydd underwent a significant collapse, with the 5/9 incline becoming completely blocked, and the chamber right at the end of the 9 adit being destroyed. A stroll around the surface reveals that three large new craters have appeared.

However, a through trip is still possible in through the adit, up the incline as far as the collapse, then divert right and go through tipped in chambers and up to emerge at the bottom of the West Twll.

Why did the mine collapse?. Well there is a large dyke (intrusion) running through the slate at this point, which might have had something to do with it. Also pillar robbing in the chamber that was at the end of the 9 adit.

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Last modified on: 25th August 2017 by email the webmaster

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