The commonality of caves depends on whether we count only those that are known or include the vast number that remain hidden. A cave is defined as a natural void in the ground large enough for a human to enter, and these features are found on every continent except Antarctica. While caves are widespread, their distribution is far from uniform, dictated by specific geological conditions. The number of registered caves is small compared to scientific estimates of the total number that likely exist beneath the surface.
Global Estimates and Known Cave Numbers
Official records represent only a fraction of the total number of caves. The worldwide number of officially mapped or registered caves is estimated to be over a quarter million, with new discoveries logged constantly. Speleologists (scientists who study caves) suggest that millions of caves may exist globally, with the vast majority still unexplored.
Registered numbers vary dramatically by country, reflecting geological suitability and the history of exploration. The United States, for example, has documented at least 45,000 caves, a number that grows annually. Countries like Ukraine and Slovenia are also known for significant subterranean networks, with Ukraine recording around 4,000 caves and Slovenia having discovered over 14,000.
These known systems often represent immense scale. The world’s longest known cave system is Mammoth Cave in Kentucky, USA, which has been mapped to over 676 kilometers, with passages still being explored. For vertical scale, Veryovkina Cave in Georgia holds the record as the world’s deepest, plunging to a known depth of 2,212 meters below its entrance.
The Role of Geology in Cave Abundance
The formation of caves depends heavily on specific geological and hydrological conditions, making them abundant only in certain regions. The vast majority of caves are classified as solutional caves, which form within a type of landscape called karst. Karst topography is characterized by underground drainage systems and features like sinkholes, resulting from the dissolution of soluble bedrock.
Solutional networks require rock composed of materials such as limestone, dolomite, or gypsum. Rainwater absorbs carbon dioxide, creating a mild carbonic acid solution. This acidic water seeps into cracks and fissures in the soluble rock, slowly dissolving it over thousands of years and creating interconnected passages.
While solutional caves account for most subterranean voids, other geological processes create different types of caves. In volcanic regions, lava tubes form when the outer surface of a lava flow cools and solidifies while the molten rock beneath flows away, leaving a hollow tunnel. Sea caves are formed by the erosional power of waves against coastal cliffs.
Why Counting Caves Is So Difficult
Determining a definitive number for the world’s caves is practically impossible due to practical and definitional challenges. The most significant difficulty lies in the hidden nature of cave entrances, which are often small, obscured by dense vegetation, or located in remote areas. Cavers regularly discover new systems, underscoring how incomplete current mapping is.
The scientific definition of what qualifies as a “cave” can vary, complicating a global tally. Some caving organizations establish minimum criteria, such as requiring a void to be at least 6 to 7 meters deep or long to be officially registered. This excludes countless smaller rock shelters and shallow voids from official databases.
Many potential cave entrances are sealed by natural processes like landslides or glacial till, making them invisible from the surface. New, significant caves are still being discovered with regularity, often by connecting known, smaller systems into larger, previously unrecognized networks.