Croesor Slate Mine Exploration ? 2016


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This location is 480m above sea level so it is an altitude dive 

Divers ? Roman Mihalovic, Arturs Abols

Video reference:  YouTube  ? 1. Croesor mine diving 18/09/16
                                                    2. Diving in Croesor Slate Mine 18/09/2016
                                                    3. Mine Diving In North Wales 28/10/2016
                                                    4. Croesor mine exploration

Our initial plan to start the exploration of this mine was to connect to the existing line reaching to 110m at the deep level /Level C -27m/ laid in May 2016 by MV and DG and to get as far as the first bridge at this level / 250m from DB/ and possibly connect it with shallow level. After a few consecutive dives we got to a place, what we believed to be about 20m short from our goal/ and confirmed later/. Our last tie off was a few metres before a brick building similar to those located next to the incline shaft at both B and C level. These dives /3 in total/ lasted from 50 to 60min.

To continue with the exploration we decided to do it from shallow level to avoid decompression obligation. This would allow us to do longer dives and possibly to attack the deep level progressively from shallow level as we believed and later confirmed that the levels are accessible through the chambers. Part of our plan was to create emergency escape routes by connecting air surfaces from both C and B levels to A Level. There were two candidates/locations/ to start with and later confirmed both, but now we are more than sure that most of the chambers through both levels, except the fallen zone at the beginning of the mine, are connectable with surface.

Our exploration of this level started at the end of an existing line, about 100m from the incline shaft that had been laid some years ago. Although it was not that very line we connected to as this had been replaced recently by a thin  line after somebody accidently cut the original one. During one of our dives we managed to replace it again by a thicker and knotted line. This line finished at the exit from the tunnel in to the Chamber 5 / further C5/. I will be referring to chambers by numbers as I marked them on the map below. To fast forward, during the next four dives we laid 300m of main line getting  to C14, 3 chambers away /cca 50m/ from the end of the main, connected air surface in C6 and C7 and from the main line in C7 also connected to the bridge at 27m in this chamber and connected to our last tie off in the tunnel at C level. We laid in total about 450m of line. Also made a line connection from the 15m bridge to the dive base which is tied off to a steel ring on the wall, 6m deep right next to the shot line so additional 35m of line. The ?T? junction leading from the main line at the bottom of the chamber to the 15m bridge has been removed.
27/12/2016 -  the D level depth has been confirmed to be 45m by J Herbowicz and J Dyminski

The Mine / description
C level /27m/? turning right from on the end of the DB chamber and passing the brick building the passage turns slightly left going through the base of the C1 and entering the tunnel on the left hand side. There are  a series of openings on the right hand side of the tunnel where the first two are the bases of the C2 and C3 and are quite wide, but the next two chamber/ C4,C5/ are connected by a short tunnel to the base of the chambers. There are some remains of wooden chests at the bottom of C2 and C3 from the time when the chambers were used as an explosive ? propellant storage. A pipeline is on the left had side wall and it goes down the whole length of the tunnel. We used it for tie offs. The tunnel then turns slightly left and then with a long bend returns back to the E,NE direction. There are one more tunnel on the right hand side / on the map marked as a tunnel with dead end /,but by the size it looks more like a chamber. There is a wooden bench like artefact near the entrance. From this point the tunnel continues and passing by a small brick building exiting in to the C7 which is the first chamber connecting all levels. There is a wooden bridge crossing the chamber but it is different to those at level B as the bottom of the chamber is at the same level as the exiting tunnel. This is more of a platform with an opening allowing the carts to be hauled through from D level. We did not explore the C level any further.
B level /15m/ - This level is different and more interesting in terms of diversity, features. It was a common practice in this mine to back-fill the chambers with slate waste instead of tipping them outside. It looks like every chamber has been filled in from A level. It has apparently been done a way that in order to protect the lover levels and the bridges at B level they built a kind of retaining walls from loosely stacked slate creating a almost vertical walls that at the top are slightly sloping away leaving a gap that exits to the surface. In some of the chambers these walls offer a quite impressive sight.

C1B ? this chamber contains the brick building and a concrete platform in front of it partially blocking the bottom part of the chamber

C2B ,C3B,C5B ? It is not clear but it looks like in these chambers the retaining walls did not survive, because the whole chambers are full of slate waste and also big blocks that could not have been part of the refill. This indicates some collapses in these chambers. It is apparent that the bridges have been knocked off their places by these blocks and the rails have been snapped off as well. This can?t be seen in any other part of the mine. It might be a result of the roof collapse in C1E, although I do not know when this collapse happened because there are historical pictures of these chambers from 1978 when the mine was still dry and the place looks exactly the same/ see pictures bellow/. There is also in C5 a staircase leading from C5B to C5C.
Interesting is that the chamber C4B, which is between these chambers is intact and this is the only place with the bridge still in place / only the main beams remaining/. There are also some straw formations in C2B that not been found in the other parts of the mine.

C6  ? This is a small side chamber on the right hand side at the beginning of the 70m long tunnel connecting C5 and C7. This chamber has been refilled with the retaining wall leaving a narrow passage at the bottom containing a cart that most likely been pushed down from the top. There are steps alongside the right hand side wall leading to the surface exiting in a small pond. After this point the passages get progressively shallower up to 10m.                   

C7 ? this is the first chamber connecting all levels. We made a connection to surface in this chamber as well.
The rest of the B level to the point we explored it is quite uniform and it is a series of chamber crossings with short tunnel connections except the tunnel between C9B and C10B, and between C11B and C13B. In the latest there are some rails coming from the C14B direction taking a turn and going in to the C13B. There are no bridges apart from some sketchy remains where the bases of the bridges used to be, and some bits hanging from the ceilings. In one of the chambers there is a timber covered with white layer hanging from a ceiling on a rusty rod and seeing it for the first time was a quite eerie experience. Other than that the chambers can only be described as big black voids and swimming trough the black water with no visual reference is another interesting experience. The exit from tunnel in to C14B is partially blocked by collapse.
One more thing I would like to mention ? swimming through some parts of the B level is accompanied with very loud thundering sound and vibration of the water can be felt. We have already experienced it in Hodge Close and its most likely  the sound of the bubbles braking the surface and echoing back from the chambers. This is most intensive around C6B where the surface is nearest.



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C5B History


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