Sinkhole at Magdalen's Close, Ripon, Monday 17 February 2014

Map of the Ripon area showing the distribution of sinkholes with the dates of reported collapses. The large areas are amalgamations of sinkholes mainly filled with peat and clay.

On 17 February 2014, large cracks appeared in a detached house in Ripon, part of the house later collapsed. The cause of the collapse was due to the formation of a sinkhole resulting from the dissolution of thick gypsum deposits beneath the area.

The sinkhole was roughly oval and measured 11  m from north to south measured between the crack in the house and a crack across the garden near the greenhouse; in an east–west direction it measured about 15 m.

The maximum depression was in the garden between the house and the greenhouse and the depression appeared to be around 0.7 m deep in the middle.

Several cracks up to 5 cm also appeared in the house and paths delineating the maximum extent of the sinkhole.

There were also slight movements in neighbouring garden walls and driveways with slight lateral movements towards the hole opening cracks of 2 mm to 1 cm.

The latest sinkhole is not an unusual event for the Ripon area.

Partial house collapse

On the evening of Monday 17 February 2014, Mr and Mrs Cunningham returned home to their house in Magdalen's Close, Ripon, to find they could not open their back door, they heard noises, looked up and saw that the back of the house was collapsing.

They called the emergency services who broke down the front door and rescued their dog before shutting off utilities to make the house safe from gas, electricity and water problems. Residents of neighbouring houses were also evacuated.

The following morning, the horror of the event was evident with the rear third of the house severely damaged and a crack widening from ground to roof wrenching the house apart.

This crack in the house continued to widen to about 40 cm at the top, during the following day, and the press gathered in anticipation of its total collapse. In the garden, the greenhouse subsided and tilted towards the house.

Historical sinkholes around Ripon

Cross-section through the Ripon area from: (Cooper et al. 2013) showing the water flow through the bedrock and the stylised subsidence features.

About 40 m to the east-north-east a previous sinkhole that collapsed in 1979 and 1980 (Cooper, 1986) also showed slight movement and reactivation cracks in the same place as the previous sinkhole margin.

Gypsum is a highly soluble rock which dissolves very quickly. A gypsum block about 3 m3 that fell from the gypsum cliff at Ripon in 1978 dissolved completely in about 18 months (James et al., 1981).

Underground beneath Ripon the gypsum has dissolved to form a cave system, however, in caves gypsum tends to dissolve more slowly than in rivers, partly because of the generally slower water flow and partly because the water gets saturated with dissolved gypsum (Klimchouk et al., 1996).

Gypsum cave system

The most likely form of the Ripon caves are that they will be similar to the gypsum maze caves of the Ukraine (Klimchouk 1992; Klimchouk and Andrejchuk 1996). Like Ripon these have thick gypsum resting on a porous and jointed aquifer (which is dolomite in the case of Ripon) and a groundwater flow pushing water through the system dissolving the gypsum throughout the area.

In Ripon this water flows from the dip slope catchment of the Cadeby Formation dolomite located on the high ground west of Ripon, through the rock to beneath the gypsum, passing through it and dissolving it before and emerging as artesian sulphate-rich springs in the low ground along the River Ure (Cooper et al., 2013). The dissolution and caves are controlled by the joints in the rock and the resultant maze cave can be likened to the reticulate pattern of the bars of a window with hundreds of panes.

The joints in the rock beneath Ripon trend approximately north–south and east–west defining the orientation of the caves. The water flow under Ripon city runs approximately from west to east. At the intersections of the joints the caves become more enlarged and sinkholes are more likely to form at these positions giving the sinkholes a pattern (Cooper 1986, 1998; Klimchouk and Andrejchouk, 2005).

Frequency of sinkole collapse

Ripon periodically gets sinkholes; in the 1980s and 1990s, one was appearing every two to three years (Cooper, 1998). The last recorded hole was on the flood plain of the River Ure, north of Ripon (Sargent and Goulty, 2009), there have not been any reported in the last seven years so the occurrence of one now is not unexpected.

The triggering mechanisms for these sinkholes to collapse can be one, or a combination of mechanisms, the most common being:

  • enlargement of the caves due to subsurface dissolution
  • infiltration of water from the surface washing down fine materials from the covering deposits
  • fluctuations in the groundwater levels rising to wet the covering materials and then falling leaving the cover saturated and without the hydraulic support offered by the water.

References

Cooper, A H.  1986.  Foundered strata and subsidence resulting from the dissolution of Permian gypsum in the Ripon and Bedale areas, North Yorkshire. In: Harwood, G M & Smith, D B. (eds.)  The English Zechstein and related topics, 127–139.

Cooper, A H.  1998.  Subsidence hazards caused by the dissolution of Permian gypsum in England: geology, investigation and remediation. In: Maund, J G & Eddleston, M. (eds.)  Geohazards in Engineering Geology. Engineering Geology Special Publication 15. The Geological Society of London, 265–275.

Cooper, A H, Odling, N E, Murphy, P J, Miller, C, Greenwood, C J, and Brown, D S.  2013.  The role of sulfate-rich springs and groundwater in the formation of sinkholes over gypsum in Eastern England. In: Land, L, Doctor, D H & Stephenson, J B. (eds.)   Sinkholes and the Engineering and Environmental Imapacts of Karst: Proceedings of the Thirteeth Multidisciplinary Conference, May 6–10. National Cave and Karst Research Institute, Carlsbad, New Mexico, 141–150.

James, A N, Cooper, A H, and Holliday, D W.  1981. Solution of the gypsum cliff (Permian Middle Marl) by the River Ure at Ripon Parks, North Yorkshire. Proceedings of the Yorkshire Geological Society, 43, 433–450.

Klimchouk, A. 1992.  Large gypsum caves in the Western Ukraine and their genesis. Cave Science, 19, 3–11.

Klimchouk, A, and Andrejchouk, V.  2005.  Karst breakdown mechanisms from observations in the gypsum caves of the Western Ukraine: implications for subsidence hazard assessment.  Environmental Geology, 48, 336–359.

Klimchouk, A, and Andrejchuk, V.  1996.  Sulphate rocks as an arena for karst development. In: Klimchouk, A., Lowe, D, Cooper, A, and Sauro, U. (eds.)  Gypsum karst of the world. International Journal of Speleology Vol. 25, 9–20.

Klimchouk, A, Cucchi, F, Calaforra, J M, Aksem, S, Finocchiaro, F, and Forti, P.  1996.  The dissolution of gypsum from field observations. In: Klimchouk, A, Lowe, D, Cooper, A & Sauro, U. (eds.)  Gypsum karst of the world. International Journal of Speleology Vol.25, 37–48.

Sargent, C. and Goulty, N R.  2009.  Seismic reflection survey for investigation of gypsum dissolution and subsidence at Hell Kettles, Darlington, UK.  Quarterly Journal of Engineering Geology and Hydrogeology, 42, 31–38, doi: 10.1144/1470–9236/07–071.

Contact

For more information on deneholes, please contact Dr Vanessa Banks, Dr Andy Farrant or Dr Anthony Cooper (BGS Honorary Research Associate)