The
Belfry
Bulletin
THE JOURNAL OF THE BRISTOL EXPLORATION
Volume 5 No. 44
Feb 1951
Annual General Meeting. A report of the 1950 Annual Genera1 Meeting will appear in the March BB. ********************************************************* Change of Address. Members are asked to note that the Hon. Sec’s address has been changed. Address all letters to Hon. Assist. Sec. if possible; failing this to T.H. Stanbury, c/o D.H. Hasell, 1, Stoke Hill Cottages, Chew Stoke, Nr, Bristol. The Telephone Number 77590 is now longer applicable. This address is only temporary and any further change will be notified in the BB. ********************************************************* The Growth of Stalagmites and Stalactites. by R.M. Wallis. Although stalagmites and stalactites are such a prominent feature in most caves, it is surprising how few cavers have any clear idea of how they are formed. It is the intention of this article to remedy this as far as possible by setting out the processes involved in simple language. No apology is offered for any wounded susceptibilities in the scientifically minded – they should have a good idea of the subject already and this account is not written for them. It must be admitted at the outset that there is a fair amount of doubt about the actual processes involved, but current theories are described here and seem to deal with the matter satisfactorily. All our caves of any importance are situated in Limestone, a rock which is composed almost entirely of Calcium carbonate. In pure water, limestone, like all other rocks, is practically insoluble – it will dissolve to an extent of only one part in 30,000 of water. However, water will dissolve carbon-dioxide, a gas which is exhaled in the breath and is produced in burning and so is found in the atmosphere. It is therefore picked up by water which will then dissolve limestone much more easily, though still in small amounts -- about one part in 7,000. (This is not strictly a true process of solution as a chemical reaction is involved, but it may be regarded as solution without affecting the argument). This increase in the dissolving power of the water is an essential factor in the formation of dripstone. Most people are aware that water dissolves the limestone, and jump to the conclusion that deposits are formed simply by the evaporation of water leaving the limestone behind. A moment’s thought will shew that this can only very rarely be the only mechanism, and in fact is usually of negligible importance. In most caves the air is very humid, as is shown by one's breath forming a mist. The air already holds as much water vapour as it can. This of course means that water vapour cannot evaporate, or at least only very, very slowly so that the water drops which are seen on the end of growing formations grow too big and drop off before they can deposit any of their load of limestone on the end of the stalactite. It may be argued that if the water is saturated with limestone, any evaporation would cause a little addition to be made to the end of the formation and this would be generally true. But is the water saturated? It may be in some cases but unfortunately we have very little evidence on this point.