Peter Burgess
New member
Given that in chemical terms, chalk is very much the same as the massive limestones of our classic karst regions, why is it that there are virtually no known solution caves in the chalk karst regions of Britain?
Chalk downland does exhibit a number of typical karst features which might encourage one to look for caves. These include dry valley systems, innumerable clay-filled solution pockets, and, I believe the occasional closed basin. What we don't find are open shafts, resurgence caves, and, apart from a few rare exceptions, natural collapse features.
With the chalk being the most important exploited aquifer in southern England, you would think we would know all there is to know about it.
One possibly important difference between the chalk landscape and the classic upland karst regions is that very few significant water-courses flow off surrounding impervious strata onto the chalk, and where they do it is usually effectively at sea level (the principal rivers of Kent and Sussex).
One exception is the River Mole. The river crosses the chalk with a steep (for the SE) gradient, and lots of it disappears into swallow holes in the river bed and bank. These are choked with flints and dead leaves etc. The water rises again at Leatherhead in the river bed. There have been a few reported collapse features in the area.
There are one or two other sites where smaller streams flow off impervious beds onto the chalk and disappear. There is a well-known one near Potters Bar, and another one in Farnham Park. The one in Hertfordshire was being dug by a caver some 20 or so years ago, and a short length of stream passage was seen, but nothing came of it. There are other similar locations, but not many.
The caves at Beachy Head and St Margaret's Bay are fossil cave passages.
So, one reason for there being no caves might be that unlike limestone areas, the chalk downs tend to be the highest features of the landscape, with no significant water flows crossing it at a point where the vertical range to a potential resurgence might encourage caves to form.
Another reason may be the structural strength of chalk. Could chalk simply not be strong enough to support a permanent cave passage system? The fact that a few caves do exist suggests that this is not a valid reason.
Perhaps it's the way water flows through the chalk. Perhaps water finds its way through innumerable fissures rather than migrating through a few discrete joints and fissures in the rock. By its flow not being concentrated, the solutional effect is dispersed and no large passages result, with a few exceptions. But the evidence from wells sunk into the chalk might suggest this to be a false premise also. When 19th century engineers were digging deep wells to tap the large reserves of water held in the chalk aquifer, they often had disappointing results. Having reached the saturation level, the flow of water into the new well was often insufficient. So the engineers resorted to driving a number of levels from the base of the well, below saturation level, (which indicates how poor the water flow was), until they intersected fissures from which substantial amounts of water then flowed. The well then often filled up to a level well above that of the horizontal tunnels. This suggests that the water flow is contained within discrete fissures.
Much of the rain that falls on the chalk downs finds its way underground. Much of it does not sink at discrete locations, but generally through the soil and into the bedrock. It all comes out somewhere else - the River Wandle, for example. So who can tell me why cave systems, however modest, have by and large not been discovered?
Chalk downland does exhibit a number of typical karst features which might encourage one to look for caves. These include dry valley systems, innumerable clay-filled solution pockets, and, I believe the occasional closed basin. What we don't find are open shafts, resurgence caves, and, apart from a few rare exceptions, natural collapse features.
With the chalk being the most important exploited aquifer in southern England, you would think we would know all there is to know about it.
One possibly important difference between the chalk landscape and the classic upland karst regions is that very few significant water-courses flow off surrounding impervious strata onto the chalk, and where they do it is usually effectively at sea level (the principal rivers of Kent and Sussex).
One exception is the River Mole. The river crosses the chalk with a steep (for the SE) gradient, and lots of it disappears into swallow holes in the river bed and bank. These are choked with flints and dead leaves etc. The water rises again at Leatherhead in the river bed. There have been a few reported collapse features in the area.
There are one or two other sites where smaller streams flow off impervious beds onto the chalk and disappear. There is a well-known one near Potters Bar, and another one in Farnham Park. The one in Hertfordshire was being dug by a caver some 20 or so years ago, and a short length of stream passage was seen, but nothing came of it. There are other similar locations, but not many.
The caves at Beachy Head and St Margaret's Bay are fossil cave passages.
So, one reason for there being no caves might be that unlike limestone areas, the chalk downs tend to be the highest features of the landscape, with no significant water flows crossing it at a point where the vertical range to a potential resurgence might encourage caves to form.
Another reason may be the structural strength of chalk. Could chalk simply not be strong enough to support a permanent cave passage system? The fact that a few caves do exist suggests that this is not a valid reason.
Perhaps it's the way water flows through the chalk. Perhaps water finds its way through innumerable fissures rather than migrating through a few discrete joints and fissures in the rock. By its flow not being concentrated, the solutional effect is dispersed and no large passages result, with a few exceptions. But the evidence from wells sunk into the chalk might suggest this to be a false premise also. When 19th century engineers were digging deep wells to tap the large reserves of water held in the chalk aquifer, they often had disappointing results. Having reached the saturation level, the flow of water into the new well was often insufficient. So the engineers resorted to driving a number of levels from the base of the well, below saturation level, (which indicates how poor the water flow was), until they intersected fissures from which substantial amounts of water then flowed. The well then often filled up to a level well above that of the horizontal tunnels. This suggests that the water flow is contained within discrete fissures.
Much of the rain that falls on the chalk downs finds its way underground. Much of it does not sink at discrete locations, but generally through the soil and into the bedrock. It all comes out somewhere else - the River Wandle, for example. So who can tell me why cave systems, however modest, have by and large not been discovered?