Qualla: Dorothea Quarry

Dorothea Quarry: Introduction

Sun, 24 May 2026 00:00:00 GMT

Photo credit Chris Allen, CC BY-SA 2.0. The deepest of Dorothea's six pits goes down 106 metres - taller than the Statue of Liberty, deeper than the average North Sea oil platform stands above the water. For most of the twentieth century the only thing keeping that pit from being a lake was a Cornish beam engine, installed in 1904, that pounded away day and night pulling groundwater out so the quarrymen below could cut slate from vertical veins. When the engine stopped in 1951 the electric pumps took over. When the electric pumps stopped in 1970 the lake was inevitable. In the decade between 1994 and 2004, twenty-one divers drowned in it.

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Image: Chris Allen | CC BY-SA 2.0

Dorothea Quarry: Cloddfa Turner

Sun, 24 May 2026 00:00:00 GMT

Photo credit Geoff Charles, CC BY-SA 4.0. Quarrying at the Dorothea site began in the early 1820s, but the venture became serious around 1829 when an industrialist named William Turner leased the workings and gave them his own name - Cloddfa Turner, Turner's Quarry. By the 1830s it was generating two thousand pounds in a...

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Image: Geoff Charles | CC BY-SA 4.0

Dorothea Quarry: The Quarrymen Buy In

Sun, 24 May 2026 00:00:00 GMT

Photo credit Geoff Charles, CC BY-SA 4.0. Profits faded in the 1840s and the lease was put up for sale in 1848. What happened next was unusual for the slate industry: a group of the quarrymen themselves - John Robinson, William Owen and John Jones - bought Dorothea from the Turner family for three thousand pounds in 1851...

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Image: Geoff Charles | CC BY-SA 4.0

Dorothea Quarry: The Cornish Beam Engine

Sun, 24 May 2026 00:00:00 GMT

Photo credit Julian Thomas, CC BY-SA 2.0. The geology at Nantlle is strange and lucrative: the slate veins run vertically rather than at an angle, which meant the easiest way to follow the seam was to dig straight down. The deeper the pit went the more groundwater filled it. Steam pumping had been part of the operation a...

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Image: Julian Thomas | CC BY-SA 2.0

Dorothea Quarry: Twenty-One Divers

Sun, 24 May 2026 00:00:00 GMT

Photo credit Chris McKenna (Thryduulf), CC BY-SA 4.0. When quarrying ceased in 1970 the pumps were turned off, the groundwater rose, and Dorothea slowly filled. Within a decade it had become one of the deepest inland diving sites in Britain - more than a hundred metres of cold dark water, with hidden ledges and dropped equipment, dr...

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Image: Chris McKenna (Thryduulf) | CC BY-SA 4.0

Dorothea Quarry: Diving Returns, Carefully

Sun, 24 May 2026 00:00:00 GMT

Photo credit David Stowell, CC BY-SA 2.0. In 2021 controlled diving resumed at Dorothea, this time under proper license from the landowner and managed by the North Wales Technical Divers. The new rules are strict: technical qualifications only, trimix-trained divers, no recreational access. The site is too deep and too c...

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Image: David Stowell | CC BY-SA 2.0