How to Determine the Age of Karst Caves: Key Signs of Cave Formation

The age of karst caves ranges from a few thousand years for young Holocene cavities to more than 200 million years for the most ancient examples, and the start of cave formation is judged by the moment a cavity enters its water-gallery stage. Before that point a developing cavity is poorly formed, completely filled with water, and impassable — so it is not yet a cave in the everyday sense.

According to L.I. Maruashvili, the beginning of cave formation should be taken as the period of transition to the natite-sedimentary (water-gallery) stage. At earlier stages the cavity has not yet acquired the open, air-filled galleries that define a true cave, which is why this transition is the meaningful starting marker for measuring a cave's age.

What signs mark the beginning of cave formation?

The clearest sign that cave formation has begun is the shift from a fully water-filled fissure system to a water-gallery stage in which open passages develop. Geologists read this transition through several physical clues:

• The presence of accessible galleries rather than a solidly water-saturated, impassable void.
• The structure of concretionary (chemogenic) formations such as stalactites and flowstone, which only accumulate once air-filled passages exist.
• The morphology of the underground cavities and the degree of fracturing in the host rock.
• The character of the surrounding relief and the position of the cavity relative to surface landforms.

How is the age of caves determined?

The age of caves is determined with several independent methods of cave research, each suited to a different kind of evidence. The main approaches are:

• Paleozoological — dating cave deposits from the animal remains preserved in them.
• Archaeological — using human artefacts and occupation layers to bracket the age of a passage.
• Radiocarbon — measuring carbon isotopes in organic material and carbonate formations.
• Geomorphological — comparing the hypsometric (elevation) level of the caves with the levels of surface landforms.

Most of these methods establish only the upper limit of a cave's age rather than its exact origin, because they date the material found inside a cavity rather than the cavity itself. Even so, direct and indirect data prove that karst caves can persist for a very long time, in some cases for many millions of years.

The age of any given cave depends heavily on the lithologic composition of the rocks in which it forms and on the general physiographic setting. Even in easily soluble sulfate formations such as gypsum and anhydrite, caves can survive for remarkably long spans despite the rock's vulnerability to dissolution.

How old are the gypsum caves of Podolia?

The gypsum caves of Podolia began forming in the Upper Miocene, making them among the most instructive examples of long-lived sulfate cave systems. Working from the geological structure of the territory, the degree of rock fracturing, the character of the relief, the morphology of the underground cavities, and the structure of concretionary formations, I.M. Gunevsky distinguishes seven stages in the formation of the Podolia caves:

1. Upper Sarmatian — beginning of intensive deep erosion.
2. Early Pliocene — intensification of vertical processes.
3. Late Pliocene — horizontal groundwater circulation prevails over vertical processes.
4. Early Pleistocene — cave formation reaches maximum intensity.
5. Middle Pleistocene — underground karst formation begins to subside.
6. Late Pleistocene — accumulation of mineral and chemogenic formations.
7. Holocene — accumulation of clastic sediments.

On the basis of this staged development, the world's largest gypsum caves — Optimistic, Ozernaya, and Kryvchenskaya in Podolia — appear to exceed 10 million years in age. Optimistic Cave is the longest gypsum cave on Earth, which makes the longevity of these sulfate systems all the more striking.

Which are the oldest karst caves?

The oldest known karst caves are far older still: some ancient cavities of the Alai Range in Central Asia, which are of hydrothermal origin, formed in Upper Paleozoic time — more than 200 million years ago, according to Z.S. Sultanov. Limestone caves can therefore reach an age well beyond that of the gypsum systems of Podolia.

Ancient caves of this kind are relatively rare, surviving over such immense timescales only under the most favorable natural conditions. The great majority of karst caves — especially those in heavily watered sulfate rocks — are young, mainly Quaternary or even Holocene in age.

Individual galleries within complex, multistory caves also vary widely in age, because they formed at different times during a cavity's long history. As a result, a single cave system can combine passages separated by hundreds of thousands or even millions of years of development.

How are karst cavities measured quantitatively?

For the quantitative assessment of karst cavities, G.L. Maksimovich (1963) proposed two indicators — density and concentration — that allow caves to be compared across regions:

• Density — the number of caves per 1000 km² of area.
• Concentration — the total combined length of all cavities within that same conditional area.

These two measures together describe how richly cave-bearing a karst region is: density captures how many separate cavities occur, while concentration captures how much passage they add up to. Read alongside dating evidence, they help place a region's caves within both space and geological time.

For more on how cavities are mapped and studied underground, see our wider coverage of Speleology.