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you have any memories of Llanberis, did you or one of
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the depot when it was open. Whatever stories you have to tell
about the
depot
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The Glyn Rhonwy Isaf slate quarry variously known as Waterside Quarry and Chwarel Isaf, started working the slate deposits on the shores of Llyn Padarn near Llanberis from 1823. The quarry developed into a series of open pits linked together by tunnels, with a dressing mill along the lakeside. The quarry closed in 1930 and the quarry equipment was removed but following the outbreak of the Second World War in 1939 the air ministry acquired the site for prospective use as an ammunition store. A limestone quarry at Harpur Hill in Derbyshire had been successfully been converted as a ammunition depot for the Royal Air Force during the previous year, by building a re enforced concrete structure within the quarry before placing a protective back filling over the structure, The same technique was used at Glyn Rhonwy Isaf.
Similar Sites
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Ridge Quarry
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The pits at Glyn Rhonwy Isaf were much deeper than Harpur Hill so the planned depot used an adapted design which provided a series of interlinked gallery's over two floors within the quarries lower pit, designed to store 18,000 tons of bombs . The lower floor of the depot used a concrete box structure with the flat roof of the gallery forming the floor of the upper gallery which was capped with arched ceilings like the depot at Harper Hill. Once completed the depot was completely covered by a 40' layer of broken slate waste recovered from the waste tips in the surrounding area. Access to the depot was maintained using the narrow gauge railway tunnel from the mill site which had been converted for unloading ammunition, along with a standard gauge railway tunnel leading from an internal loading/unloading bay within the depot to a link with the Llanberis branch line. Inside the depot three electrical lifts were used for moving bombs between the upper and lower gallery's.
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During the the construction of the deport the treasury pushed for cost cutting measures which had disastrous consequences for the depot. On the 25th of January two thirds of the underground structure collapsed under the weight of the back fill. Completely burying the 14,000 tons of bombs which were stored within the depot along with a 27 wagon train which was in the process of unloading. The official inquiry in to the collapse concluded that the design of the depot was at fault and was the principle cause of the collapse, cracks which had appeared during the final stages of the depots construction had been attributed to minor defects rather than the beginning of a major fault, ignoring them proved to be a fatal mistake.
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In the following years the bombs buried within the depot were recovered and moved off site. Once the collapsed area had been cleared of debris the RAF School of explosives moved on to the site. Part of the training course involved the destruction of explosives and the open pit created when the collapsed area was cleared became an open air demolition area and storage space for the incendiaries and pyrotechnics the school brought to the site, but Llanberis never stored bombs in the underground galleries following the collapse. The School of explosives continued to use the site following the war and became involved in the disposal of surplus ammunition, using quarry pits at the rear of the site used for burning and dumping explosives. By 1955 the last functional ammunition was removed from Llanberis and the depot was officially closed early in 1956.
The ammunition disposed of at Llanberis included examples of every type of ammunition on the RAF's wartime stock list, and despite the Schools of Explosives efforts not all of the ammunition had been completely destroyed successfully, The quarry pits at the rear of the site were known to contain large quantities of explosive materials, some left exposed on difficult to access ledges with much more under the surface of the lakes which had formed in the bottom of the quarry pits.
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In 1969 the decision was made to clear the site of the remaining explosives and the Royal Air Force returned to Llanberis in the form of the No 71 Maintenance Unit Explosive Ordinance Disposal Flight from RAF Bicester. As the unit slowly cleared the quarry pits surrounding the disused depot the team uncovered Incendiary bombs, High Explosive bomb detonators along with a large amount of bomb fuses. Many of the pits were difficult to access so the 38 Engineer Regiment, Royal Engineers was called in to lay roads to many of the more difficult pits. It took 71 MU until 1975 to clear the last of the explosives from the area. and the depot was finally abandoned.
The site has remained unused until the present day, and is awaiting redevelopment, Recent proposals for the construction of a snow dome and bicycle resort have been shelved and the site remains unused and almost forgotten alongside the Lake Padarn road.
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I visited the remains of the Llanberis bomb stores in the summer of 2009 along with a fellow photographer, once we had entered the site from the old RAF road gates we followed one of the roads laid by the royal engineers in the early 1970's along the right hand side of the collapsed storage galleries. Between the pit and the road a thick wood had grown in the slate back fill which had covered the depot. Approaching the the depot and its 80' deep pit from this side seamed foolhardy as warning signs pointed out the danger hidden by the undergrowth. As we reached the end of the pit we reached a modern road laid in preparation of the sites redevelopment. This modern unused road in perfect condition was a surreal site in the quite valley. We followed this road towards along the back of the pit with the surviving gallery beneath our feet until we reached its left hand side, here the undergrowth thinned and we got our first glimpse of the bomb depot.
We made our way through the trees until reaching a point where the slate back fill dropped down a slope to the floor of the collapsed arms depot. Once reaching the floor of the depot we first headed along the narrow gauge railway tunnel following the deep impressions left by rotted railway sleeper is the tunnel floor until we reached the stacked up slate dead's which blocked the tunnel off. The tunnel originally ran between Glyn Rhonwy Isaf quarry and its mill buildings where a modern industrial unit now houses as company manufacturing climbing equipment. We next headed over to the standard gauge railway its loading bay still leaves a deep gash in the floor of the depot. The tunnel was flooded to a depth of 3' s after taking a few pictures along it we headed back out and followed the loading platform towards the remaining galleries at the opposite end of the pit.
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When the collapsed parts of the depot were cleared in 1943 the open faces of the remaining galleries were sealed off with a brick wall leaving only two entrances, one at the loading bay between gallery B and C and another doorway was left in to gallery D which we used. Once inside we found ourselves in one of the 9 adjacent ground floor galleries which ran the length of the depot. The gallery was a long oblong white painted corridor with pillars running its length. There were four square doorways on either side of the gallery which connected to the adjacent gallery, continuing along the entire width of the depot. Each gallery was divided into storage bays by black painted numbers high on the walls .Gallery D was typical of the full length galleries on the lower level from C-G, beyond gallery C a similar long gallery housed the unloading bay with its standard gauge railway line which was unlettered. On the other side of the loading bay lay the smaller gallery's B and A which both featured a raised platform at their end overlooking the storage areas.
After looking around the left hand galleries we made our way into Gallery C where the remains of the two surviving electric lifts remain. both are still in remarkably good condition with their safety cages still painted in dull wartime gray with their counter weights resting at the back of the lift pit. A surviving cast iron motor cover gives their makers name as Etchell's Congdon and Muir of Manchester. The lift cars were left resting on the second floor so to head up to the upper layer today we had to take the only stairway at the rear of gallery C, but before we used these we popped back into galley D to follow one of the quarries original tunnels whose stone cut walls lead to one of the pits at the rear of the site. Since the site had been cleared of explosives the pit had flooded once again but its fern lined sides made a picturesque sight from the tunnels end. Once back in the main depot we headed up to the upper level whose galleries differed from the lower level one only in the shape these were capped with an arched rather than a flat ceiling, Also the cross connecting door ways were completed with an arched lintel rather than the straight one used below. The only relics left in the upper level were the two lift cars whose wooden plank floors still felt reassuringly solid under foot. The brick wall ceiling off the open front of the gallery had been built just over a foot from the lift's opening rendering useless but following the collapse the gallerys were not used for the storage of ammunition again. After a quick tour of the upper galleries J-S we headed back out of the depot and climbed back up the slate slope leaving the silent galleries behind.