“GODSTONE – Falling-in of the Roadway – Breakage of the Water Main.“
The news headline above doesn’t come from any of the reports on the sinkhole that recently appeared in the High Street at Godstone, Surrey. This unsensational heading comes from a news story that broke over 145 years ago in November 1879. Peter Burgess of the Wealden Cave and Mine Society describes his involvement in this evolving story and provides historical background on the Godstone sand mines.
My interest in the new Godstone sinkhole stems from many years of personal research into subterranean places in Surrey. I feel I should also state that the saying “we stand on the shoulders of giants” applies here – my giant was the late Paul Sowan. Paul and I had very similar interests and he was my first point of reference if I needed to discuss some new idea I had concerning the history or geology of the local mines.
Once the news broke about the dramatic road collapse in Godstone early on 18th February 2025, requests for help and advice started to come through via online points of contact with Wealden Cave and Mine Society and South East Cave Rescue Organisation. Initially these were from local authority officers seeking help to understand what might exist under the village. During that Tuesday, those free to do so went over to Godstone in the evening not only to be physically present to assist if required, but also to check the condition of one particular small sand cave which we monitor. This is some distance away from the sinkhole, does not underlie any public highway or dwellings, and appears to be unaffected.
Overnight into Wednesday, press organisations started to contact us. These were primarily seeking interviews and historical information to pad out the human stories they were putting together as the drama unfolded. As a result, I have been interviewed twice in the village, by BBC Surrey for radio broadcast and by BBC News for their national TV news programme. We were also able to direct the news teams to historic photos and maps to help illustrate their narratives.
The story continued to unfold on Thursday, however, we had to prioritise assistance requests from the relevant authorities over responding to press enquiries. There is something of a parallel with how cave rescue incidents are managed; recovering a casualty takes a much higher priority than talking to reporters! From our perspective, the BBC teams liaised very well on the previous day and the resulting reports were non-sensational and factual.
On Thursday our real involvement started with meeting the team from Surrey County Council tasked with investigation and recovery work. Our knowledge of the history of sand-mining and what little is on record of the sand-mines in Godstone proved useful, and it was very encouraging to be included as a caver able to make useful contributions.
So, what is known about the Godstone sand-workings?
Geology
The village sits on the outcrop of the Folkestone Formation, part of what is known as the Lower Greensand Group. This stratum, of Early Cretaceous age, varies throughout in its thickness but is mainly a fine and reasonably uniform sand. For a few centuries it has been exploited for its particularly fine beds of silver-sand, which in places are almost white due to the low level of impurities, the most common of which are iron oxides. This near purity meant that it was a good source of raw material for the glass-making trade, and later, in the 19th century, for use across the UK as horticultural sand for which “Reigate sand” had a very good reputation. This same bed of sand has been worked extensively in Surrey, particularly around the towns of Dorking, Reigate and the village of Godstone. It continues to be worked from open pits west of the village.The sand is loosely consolidiated. It is very easy to excavate, but also quite easy to dig stable tunnels through it, provided the tunnel dimensions are not excessive. If the moisture content changes too much, however, the ground destabilises very quickly. If too dry, it can crumble, and if too wet it can turn to a slurry. Think of a sandcastle on a beach. If the sandcastle dries out, it quickly turns to dust, and if too wet, it slumps. The geological term that best describes the Folkestone Formation is a “locked sand.”
Mining
Even though the sand beds outcrop widely in the area, early extraction appears to have been mainly by underground mining rather than from surface pits. This could simply be down to the fact that early extraction was on a very small scale, from “caves” behind premises in the local towns, as a matter of convenience for those digging and selling the sand. Reigate and Dorking have a number of surviving “caves” of this nature. The sand-workings were out of sight and could be pursued under neighbouring properties, even if this was technically a form of trespass. Adjacent caves might break into each other accidentally, which certainly happened in Reigate. When mining became more organised, a simple “pillar and stall” grid of galleries was the normal method employed. This seems to have been the principal method employed in Godstone. At the time, earlier in the 19th century, the area being worked lay beyond the northern edge of the village, and working underground may simply have happened so that the overlying farmland could be preserved.
Open Pits
Evidence from contemporary maps shows that in the latter part of the 19th century a number of open pits developed close to Godstone. Where an 1869 map shows an “entrance to subterranean sand pit”, a later 1895 map shows a significant opencast sandpit had been established immediately adjacent. This is likely to be due to the mine-workings having been exhausted, and, by untopping the area undermined, considerably more sand became available at the cost of losing some farmland. This pattern was repeated elsewhere with open pits becoming the norm and mine-workings closing down. Underground working in Reigate appears to have continued for a few years into the twentieth century with larger open pits connected to the rail network becoming the only source of silver-sand by the 1920s.
The above maps are reproduced with the permission of the National Library of Scotland
Other Mines
Importantly, other mine-workings exist in the Godstone area. These are all well to the north of the village and were developed in the Upper Greensand Formation to extract a completely different material. The Godstone firestone quarries, as they were known, started in the 17th century and extraction ceased around the year 1900. The quarries supplied large slabs of “firestone”, which in earlier times was a local building stone, but later was supplied to the glass industry for lining furnaces. The quarries are away from habitation and generally lie below open countryside. These workings are of no concern with regard to the sinkhole event in the village itself. Access to and study of these workings is managed by the Wealden Cave and Mine Society with permission of the owners.
Abandonment
Although the open sand pits removed most traces of underground workings, around the periphery of the pits some tunnels remained intact. This was especially the case on the eastern edge of the pit, close to the main road to Croydon. Over time, the pits were reclaimed, entrances to the tunnels buried, and the exact locations of any remaining mine passages were quickly forgotten. Light industry took over some of the area adjacent to the road. As the village expanded, and local industry moved on, some of the former sandpit areas became prime redevelopment property. Most recently, new properties built on this plot are supported on piles driven down to solid ground and when considering the recent news reports it seems the new subsidence has not adversely affected the integrity of the buildings themselves.
The 1879 “Sinkhole”
In 1867, the Caterham Spring Water Company established a mains water supply to Redhill and to the villages along the route of the main pipe from Caterham. The main feed ran along the route of what is now the A22 and A25 main roads. This route includes the High Street in Godstone village. In November 1879, when staff from the water company were connecting up some new properties in the village to their supply, a horse and van were observed vanishing suddenly into a large hole that had appeared in the road. The subsidence revealed that the relatively new water main had ruptured, and the hole was quickly filling up with water. The driver had made good his escape from the hole; however, the horse was slowly disappearing as the water level rose in the hole. The nearby water company staff realised the urgency of the situation and managed to shut off the water flow at a nearby control valve just in time, with only the horse’s head remaining above the water. The horse was then recovered from the hole, largely unharmed if somewhat wet and probably very frightened.
The Surrey Mirror reported this alarming event on 22nd November, and the account reveals some interesting information, of great relevance to the recent collapse of the road stating: “It appears that the sand had been excavated and removed for some distance under the highway, although some years have elapsed since any work was last carried out at this spot.”
Taking this information, along with the reported breakage of the then recently laid water main from Caterham, it seems possible that the road was undermined by sand-extraction, probably from the area west of the road where an old entrance appeared on the 1869 map, and that the sand mine had stopped working before 1879. One factor that would not have been an issue in 1879 was heavy traffic. Today the likelihood is that heavy vehicles have slowly affecting the ground under the road and the service pipes laid through it. As a particular spot in a mine can only collapse once, the new sinkhole is most likely to be in a slightly different location to the one 145 years ago. Current ground investigations may well reveal more useful information.
The similarities between the incidents in 1879 and 2025 are striking. We have never before had so much information at our fingertips. It is important to learn as much as we can from the resources available to us in order to reduce the chances of such things happening again.
What might have caused this “Sinkhole”?
Dr Andy Farrant of the British Geological Survey says:
“The sinkhole has developed in the weak, often unconsolidated sands of the Folkestone Formation, and not as some early news reports suggested in the Chalk. So, the Godstone collapse is not a true sinkhole caused by dissolution of soluble rocks. What is not clear at this stage is the actual cause. The most likely scenario is that the sinkhole (sensu lato) is due to a burst water main flushing out weak unconsolidated sands from beneath the road over a period of time, creating a cavity which then collapsed when it got big enough. A leaking pipe can wash away a significant amount of sediment over time, leaving a void. However, what is less clear is the role of any unrecorded sand mines in the vicinity. It is possible that a leaking pipe has saturated the ground and weakened the surrounding rock. This may have led to the failure of one or more mine galleries in the immediate area (assuming the sand mines exist and extended under the road), causing a collapse and allowing water to flush further sediment from around the pipe. Sediment flushing along the line of the pipe trench may explain the linear nature of the collapse, but it is possible some of the sinkholes to the side of the road may be collapsed old mine galleries. It seems less likely that the collapse of an old mine caused the pipe to break, given that the pipe is still largely intact, with only a small breach.
An analogous example is the sandstone ‘caves’ in Nottingham, developed in the Permo-Triassic Chester Formation, part of the Sherwood Sandstone Group. The sandstone loses about half of its strength when saturated. The Nottingham ‘caves’ are normally dry as they lie beneath buildings. Nearly all recorded roof failures have occurred where and when the rock has become saturated by water from rainfall or pipe leakages (See Waltham, A C, 1993. Crown hole development in the sandstone caves of Nottingham. Quarterly Journal of Engineering Geology and Hydrogeology, 26, 243 – 251).
By their very nature, collapse features caused by burst pipes or collapsed infrastructure (culverts, drains, pipes) are mostly likely to occur in built up areas or beneath roads, and could happen in other areas with similar geology and aging infrastructure. Many recent sinkholes have been caused by collapses of old sewers or culverts, such as the sinkhole near Merthyr Tydfil last December. There have been other recent instances of sinkholes due to flushing out of sands and weak sandstones, for example the sinkhole that closed Storrington High Street last October. This was also on the Folkestone Formation.
Further investigations may reveal the true cause of the ‘sinkhole’, but without local cavers and mine enthusiasts, exploring, recording and surveying these old mines, including members of the Chelsea Spelaeological Society in the 1960’s, this information might have been lost. Thanks to Jenny Potts at the British Caving Library for digging out some of the references.”
Correspondent: Peter Burgess
Notes:
The 19th century news story was reported in the Surrey Mirror, dated 22nd November 1879. The full article may be read on the British Newspaper Archive website. A subscription is needed for the use of this service.
Similar sand caves in Reigate may be visited on selected open days. Booking is recommended. Open days are once a month from May to September. See this page for details.
