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Speleothem growth

In caves vs man-made structures

Published: 4 December 2021 (GMT+10)

Joshua from the US wrote into CMI in response to Gavin Cox’s article Defying deep-time dogma: Stunning stalactites in a pub cellar, questioning whether stalactites forming under man-made structures are comparable in terms of their chemistry and growth rate to natural cave formations.

Gavin CoxSalterforth-Pub
Photo 1: The Salterforth Pub by the Leeds and Liverpool Canal.

I have read counter points from many critics of young speleothems claiming that speleothems forming under man-made structures, such as bridges or cellars, involve a different chemistry than those formed in caves. They claim that the mineral being deposited is from the concrete or mortar. However, I noticed you described the stones in the cellar or mortar of “old bridges” to be limestone or lime mortar. Are the speleothems that form under man-made structures due to a different chemistry? And do those forming in or under limestone structures stand against this claim? Thank you!

Hi Joshua,

Thanks for writing into CMI with your question, it gives me opportunity to add more information to my article in terms of some chemistry details.

Firstly, the Anchor Inn, Salterforth pub cellar is made from limestone blocks, presumably set with lime mortar; there was no concrete used in its construction. The Leeds and Liverpool Canal was constructed nearby in 1795 which would have raised the water-table causing the cellar to become damp (see photo 1). It was most likely then, that the stalactites began to form, so as of the date of this writing (November 2021) the longest stalactites are now (a maximum theoretical) 226 years old. Many of the stalactites have grown from the ceiling to the floor level, which I estimated to be approximately 12 feet (3.5 meters) in height (see photo 2). So, using the historical information available, this gives an average approximate growth rate of 12x12/226 = 0.637 inches/ year (1.55cm/ year).

Gavin Cox266-year-old-limestone-block-cellar
Photo 2: 266 year-old limestone block cellar with stalactites and stalagmites.

You are correct that there are counter-claims proffered regarding the speedy formation of speleothems (derived from the Greek words spēlaion ‘cave’ + théma ‘deposit’). This refers to drip-stone formations like stalactites (growing down), stalagmites (growing up) and various linear formations that look like curtains, or ribbons. Dripstones formed in artificial environments are referred to as calthemites (see below). The sceptic’s argument is that: ‘just because stalactites can form quickly under man-made structures like concrete bridges, does not mean they form quickly in natural structures like caves’. The reason being that the chemistry is different, and even the dripstone formations themselves are made of different compounds. 

This feedback article will look at these claims and sort the wheat from the chaff in terms of the details. Biblical creationists do need to be careful about how they use evidence, and as we shall see, stalactites growing under modern concrete bridges are not directly analogous to how speleothems grow in natural caverns.

Firstly, concrete is not the same material as limestone—the source material for most natural cave speleothems. Secondly, it is the rate of deposition which is important. This is dependent upon drip rate and the dissolved minerals in the water—hence, the deposition rate can change drastically through time. Thirdly, ventilation of carbon dioxide is also an important factor. Better ventilation increases the growth rate of speleothems. This applies just as much to dripstones forming under man-made structures as it does to natural formations.

Counter arguments

A good starting point for arguments critical to biblical creationists about speleothem growth rates can be found on the sceptics’ website TalkOrigins,1 where the following claim is stated:

Creationists sometimes point to some very rapid accumulations which superficially resemble the calcium carbonate formations in caves.

For example, on the mortared brickwork of old forts and places of that sort, formations which look to the naked eye like stalactites and stalagmites sometimes form in less than one hundred years. However, those formations are composed of gypsum, which is a salt of calcium sulfate. Unlike calcium carbonate, gypsum is moderately soluble in water, which means that transport and recrystallization can take place much more rapidly (White, 1976, p.304). There is a whole class of cave deposits called evaporite minerals which consist of those minerals which dissolve readily in water. As might be expected, these formations are ephemeral when compared to the carbonates which form all the really large and impressive cave formations. The chemistry of all this is not particularly complex and is very well understood. (Loftin, 1988, p.23)

As per the TalkOrigins claim, there may well be some formations (calthemites) on buildings that are made from gypsum (calcium sulfate dihydrate, CaSO4.2H2O), and certainly, gypsum formations do grow in caves also. However, many of the calthemites growing under buildings (often forming far more quickly than “less than one hundred years”) are indeed made from calcite (CaCO3), the same material that natural speleothems are made from. For instance, a paper published in Cave and Karst Science (C&KS) is titled “Calcite straw stalactites growing from concrete structures”. It states in the abstract:

“In this paper, the term ‘calthemite’ is used to encompass the various concrete-, mortar- or lime-derived secondary deposits consisting primarily of calcium carbonate (CaCO3) that grow from man-made alkaline structures outside the cave environment.”2

So, the TalkOrigins claim that dripstones growing on man-made structures are made from gypsum is likely not the general rule. The C&KS paper discusses the chemistry and growth rates of calcite dripstones growing under a concrete carpark, and draws some conclusions. The published data are of concern to structural engineers, as calthemite growth necessarily involves the degradation of concrete.1 So, in terms of the origins debate, the paper has no axe to grind, so will prove a useful foil to this argument.

Vance Nelson in his excellent book Catastrophic Caves looks at this whole counter-claim regarding speleothem growth rates and chemistry in natural vs. man-made environments, and the implications for the biblical age of the Earth (he also cites the C&KS paper and other literature in his discussion). He states the following:

“I have spent over fifteen years researching speleothems. Much of this time, I have been involved in researching calcite formations on concrete structures. In fact, when I began this research, it was still being claimed by some within the old-Earth secular geology community that these structures were not even calcite.”3

Nelson collected and analysed many samples forming within man-made structures from all over the world including Canada, USA, UK, France, and Korea. He subjected many samples to X-ray diffractometry,4 demonstrating that these formations are indeed made of calcite, compositionally identical to those formed in natural caverns.2 Nelson’s research therefore rebuts the claim made by TalkOrigins that dripstones growing under man-made structures are not made from calcite. As to the Salterforth pub formations, as far as I could tell visually, they were also made from calcium carbonate.

Chemistry of formation

The next argument is in regard to the chemistry involved in the formation of dripstones in natural vs. man-made environments (rather than their actual composition). Again, we can look at the TalkOrigins site to see how the counter-argument is spun before considering the evidence:

Here’s some more information. This point is particularly important since creationists love to point out such examples.

Many people have found that stalactites forming on concrete or mortar outdoors may grow several centimeters each year. Stalactite growth in these environments, however, bears little relation to that in caves, because it does not proceed by the same chemical reaction. Although cement and mortar are made from limestone, the same rock in which the caves form, the carbon dioxide has been driven off by heating. When water is added to these materials, one product is calcium hydroxide, which is about 100 times as soluble in water as calcite is. A calcium hydroxide solution absorbs carbon dioxide rapidly from the atmosphere to reconstitute calcium carbonate, and produce stalactites. This is why stalactites formed by solution from cement and mortar grow much faster than those in caves. To illustrate, in 1925, a concrete bridge was constructed inside Postojna Cave, Yugoslavia, and adjacent to it an artificial tunnel was opened. By 1956, tubular stalactites 45 centimeters long were growing from the bridge, while stalactites of the same age in the tunnel were less than 1 centimeter long. (Moore and Sullivan, 1978, p.47).1

Firstly, yes we (biblical creationists) do love to point out such examples because they are excellent teaching aids that defy deep-time dogma—when handled correctly. Secondly, the point made by TalkOrigins here actually contradicts their first point that these dripstones growing in man-made environments are indeed calcium carbonate (the same compound as cave speleothems).

The C&KS paper measured growth-rates of calcium carbonate stalactites up to 2mm/day in a concrete car-park, (photo 3).

G.K. Smithstalactite
Photo 3: A stalactite was observed to grow 104 mm in 237 days.

C&KS states: “Straws growing from concrete can grow hundreds of times faster than straw speleothems [in natural caverns]”.2 It is interesting to note that the TalkOrigins example provides a measurable case of stalactite growth from concrete 45 times faster than stalactite growth from natural rock inside a tunnel. However, this is far in excess of the claimed very slow natural growth rates of speleothems typically espoused by secular cave guides and literature, which are in the order of 10 cm/thousand years.5

However, an important point is this: measured growth rates are made in the present, and don’t represent the whole story from the initial formation of the speleothem, or throughout the formation’s history. The a priori assumption being made by TalkOrigins (in order to bash creationists) is that present-day measurements can and should be extrapolated backwards in time so as to calculate an age of the speleothem. This becomes especially significant for the origins debate when naturally formed speleothems are claimed to have formed over tens to hundreds of thousands of years (or more)—far in excess of the biblically derived age of the earth.

The Salterforth pub calthemites (stalactites and stalagmites) likely derived their source material from the lime mortar in between the limestone blocks. Here the lime would have originally been baked which would have driven off carbon dioxide. So during the formation of the stalactites, which may have initially been quite fast, carbon dioxide would have been absorbed into the growing tips of the stalactites from the atmosphere available inside the cellar.

The particular type of lime mortar (likely) used (referred to as non-hydraulic6) was chiefly made of (< 95%) calcium hydroxide, Ca(OH)2. This was made by heating pure calcium carbonate in a lime kiln to between 954° and 1,066°C. This process of heating drove off carbon dioxide to produce quicklime (calcium oxide). The quicklime would then have been ‘slaked’ (i.e. re-hydrated) by mixing with water to form lime putty, (or less water if a dry lime powder is required). The hydrated lime (calcium hydroxide) will naturally revert to calcium carbonate (the same compound natural speleothems are made from) by reacting with carbon dioxide in the atmosphere.7

When it comes to the growth rates of calthemites forming under buildings, C&KS states the following:

“The growth rate of calthemite straws can vary considerably due to a wide range of chemical and physical conditions. The most influential factors are the continuity of leachate solution [calcium-rich solution seeping from concrete, or mortar] and drip rate.”2

The paper concludes:

“Given the number of variables that can effect calcium carbonate deposition, it is impossible to predict the exact age of calthemite straws by measuring their length or the solution drip rate at a particular time” (emphases added).2

In other words, it is futile and illogical to insist on uniform rates (uniformitarianism) to calculate ages of dripstone deposits. The C&KS study recognizes two factors that vary over the course of the life of the formation: 1) chemistry, and 2) drip rate. Neither of these factors are constants, so acknowledging their variability means such age calculations for calthemites, or speleothems (without knowing their entire history) are futile to make (however, the historic records were available for the Anchor Inn stalactites article, so that an average growth rate could be calculated). This holds true for natural formations as well, as we shall see. Hence, the vast ages for natural speleothems, typically trotted out by secular cave guides should be dismissed as fallacious guesswork.

The chemistry is not complex for the formation of calthemites in man-made buildings. The C&KS paper provides the reaction sequence:

Ca2+(aq) + CO32−(aq) → CaCO3(s)

The significant chemical difference between natural dripstone formations vs. those formed within man-made buildings is that:

“Deposition of calcium carbonate occurs when atmospheric CO2 diffuses into the drip solution, as opposed to normal cave speleothem chemistry where CO2 is degassed from solution.”2

The central driving factor of the chemistry is the pH factor (referring to the “potential of hydrogen” or “power of hydrogen”, the standard scale used to specify the acidity or basicity/alkalinity of an aqueous solution). The C&KS paper recognizes that:

“Deposition of CaCO3 straws derived from concrete is usually associated with hyperalkaline solution (pH > 9) as opposed to the near neutral pH to mildly alkaline solutions (pH 7.5–8.5) that commonly deposit [cave] speleothems.”2

Vance Nelson also corroborated similar high pH values (pH > 13) for speleothems growing in concrete environments in three Canadian and two American locations. He stated:

This seems to indicate a calcium hydroxide solution, rather than a calcium bicarbonate solution (pH between 6.6 and 9.5). If the chemistry was the same as that in caverns, the pH should be between 6.6 and 9.5, indicating a calcium bicarbonate solution.3

Nelson’s data corroborate the C&KS conclusion that the calthemites growing from concrete absorbed carbon dioxide from the air, rather than losing it (degassing) as in the case of cave speleothems. Nelson therefore recognizes that in modern concrete buildings the chemistry is different from that of cave systems for the formation of speleothems. Therefore, drawing comparisons with modern concrete stalactites to that of cave formations should only be done in a qualified sense.

It’s about time

However, this is where the chemistry gets interesting: Over time, the chemistry does change to be analogous to natural cave chemistry. Leachate leaking from cracks in concrete will be hyperalkaline and absorb CO2 from the atmosphere. The equation is written:

OH(aq) + CO2(g) ↔ HCO3(aq) ↔ CO32−(aq) + H+(aq)

(Where aq = aqueous, g = gas, s = solid.) This results in carbonate ions reacting with calcium ions to precipitate calcium carbonate:

Ca2+(aq) + CO32−(aq) ↔ CaCO3(s)

However, this chemical reaction changes over time as the pH decreases. C&KS states:

If the pH falls below approximately pH 9 carbonic acid (H2CO3) will start to appear … and the chemical reaction will change to a similar process to that which occurs in limestone caves (emphasis added).2

How long this takes to occur is not clear, and the C&KS paper suggests a wide range of “tens” or “hundreds of years”. My article dealt with stalactite growth from limestone blocks in a cellar which is 226 years old, so it would be safe to assume the carbon dioxide had been used up in the seepage pathways in between the blocks during that time.

However, as the C&KS paper recognizes, if new cracks are opened, exposing unaltered concrete (or lime mortar), the chemistry will temporarily revert to a dominant carbon dioxide-absorbing chemistry:

Ca(OH)2(aq) + CO2(g) ↔ CaCO3(s) + H2O(l)

Presumably this would mean the rate of speleothem formation would speed up again.

Natural growth speleothems

Mike Oard has recently written three comprehensive technical articles for CMI’s Journal of Creation on the growth of natural cave speleothems. These are the state-of-the-art when it comes to understanding how fast natural speleothems can grow. I recommend you read them in conjunction with my article.

In “Rapid growth of caves and speleothems: part 1—the excavation of the cave” Oard shows how caves (even huge ones) were excavated quickly by sulphuric acid in solution. The evidence for this is found within the caves, and is a fact increasingly being acknowledged by cave specialists. Oard proposes the sulphuric acid was caused by biological decay processes within the freshly laid sediments of the Flood. It was during the uplift of the Recessional Stage of the Flood that produced erosional conditions that enabled cave openings to be carved out quickly.8

In part 2—growth rate variables, Oard discusses growth rate variables, identifying five major factors including chemical, temperature, ventilation, drip rate, and stalagmite water film thickness. All these factors mean it is impossible to calculate ages of speleothems with (simplistic) uniformitarian assumptions, and demonstrate that initial growth rates can be very fast.9

In part 3—Flood and Ice Age variables, Oard shows that these five variables, plus variables from the Flood, would maximize speleothem growth in the Ice Age, especially in its early stages.10


Stalactites and dripstones growing under artificial concrete structures, or from lime mortar, grow by a different chemical pathway compared to their natural cave counterparts. However, the stalactite/ stalagmite will be made from calcium carbonate, the same compound that cave speleothems are made from. Concrete is obviously a completely different source material compared to limestone. Therefore, it is true that making comparisons between natural vs artificial dripstone formations needs to be done carefully and in a qualified way. However, the over-arching assumptions of uniformitarianism (uniformity of rates) must be unashamedly rejected because rates of deposition of dripstones (both within natural caves and man-made structures) are highly variable involving a number of complex factors. Comparisons between concrete/ lime calthemites vs. cave speleothems highlight the fact that growth rate is dependent both on drip rate and the amount of mineral dissolved, amongst other factors. When these factors are kept in mind, stalactites forming under concrete bridges, or derived from lime mortar are still good object lessons to demonstrate speedy growth rates—thus emphasising the over-extended timescales (often exceeding the biblical age of the planet) conventionally attributed to natural speleothems—should be rejected.

References and notes

  1. Matson, D.E., How good are those Young-Earth arguments? talkorigins.org/faqs/hovind/howgood-yea2.html; accessed 18 Nov 2021. Return to text.
  2. Smith, G.K., Calcite straw stalactites growing from concrete structures, Cave and Karst Science 43(1):4–10,

    Transactions of the British Cave Research Association, 2016.

    Return to text.
  3. Nelson, V. Catastrophic Caves, Untold Secrets of Planet Earth, China, p. 20, 2020; digitalresources.creation.com/product_samples/pdf/10-2-662.pdf. Return to text.
  4. A measuring instrument for analysing the structure of a material from the scattering pattern produced when a beam of X-ray radiation interacts with it. Return to text.
  5. Villazon, L., How long does it take stalagmites and stalactites to form? sciencefocus.com, 9 Nov 2019. Return to text.
  6. Hydraulic lime sets by hydrolysis (the chemical breakdown of a compound due to reaction with water) whereas non-hydraulic lime sets by carbonation (dissolving of carbon dioxide into the slurry). Hydraulic lime is designed to set underwater—because hydrolysis is a reaction caused by water. Non-hydraulic lime requires air to carbonate and thus set. Return to text.
  7. Penelis, G.G., Structural restoration of masonry monuments arches, domes and walls, CRC Press, London, p. 11, 2020. Return to text.
  8. Oard, M.J., Rapid growth of caves and speleothems: part 1—the excavation of the cave, J. Creation 34(1):70–78, 2020; creation.com/speleothems-1. Return to text.
  9. Oard, M.J., Rapid growth of caves and speleothems: part 2—growth rate variables, J. Creation 34(2):90–97, 2020; creation.com/speleothems-2. Return to text.
  10. Oard, M.J., Rapid growth of caves and speleothems: part 3—Flood and Ice Age variables, J. Creation 34(2):98–104, 2020; creation.com/speleothems-3. Return to text.

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