China’s incredible ‘Heavenly Pits’ (also known as Tiankeng) are the result of carbonate bedrock dissolved over time by underground water. As these underground rivers created large caves, they eventually collapsed, leaving vertical chasms or giant dolines 500 to 600 meters deep. These areas are like giant greenhouses – they trap heat and moisture so that the climate remains stable and humid. The absence of external winds, coupled with extreme temperature variations from day to night, provides an ideal environment for pristine forests as well as a unique type of biodiversity. According to the scientific community and UNESCO, the deep karst landscape provides a ‘thermal buffer’, allowing many rare species to thrive in isolated primitive ecosystems that act as prehistoric biological refuges.
How China’s deepest sinkhole created its own microclimate
According to the research paper published on ResearchGate, with such great depth and verticality, ‘Heavenly Pits’ like Xiaozhai Tiankeng form a semi-insulated physical barrier that maintains a ‘thermal buffer’ due to the constant temperature difference between the cold summer/warm winter bottom and the outside air. In addition, the vast depressions also retain the humidity created by the underground river systems flowing through them. Their deep, enclosed structure allows them to function like naturally occurring, self-sustaining greenhouses with stable temperatures, regardless of what is happening in the environment outside them.Tiankeng is formed through the ‘collapse-type’ formation of karst, caused by the slow dissolution of carbonate rock (mostly limestone) by powerful underground rivers running through the area over thousands of years, creating vast underground voids. When the roof of one of these spaces loses its structural integrity due to long-term erosion or tectonic uplift, it collapses, resulting in a vertical cave more than 500 meters deep, as reported in the UNESCO World Heritage Centre.
How do craters protect ancient life?
Sinkholes are also known as ‘evolutionary islands’ or biological refugia because they are isolated from other habitats by steep cliffs and significant depth. More than 1,200 species of animals and plants have been found in sinkholes, including more primitive forms such as ginkgo trees and some rare animal species, including the Chinese giant salamander.
Protecting the world’s lost species
According to the Karst Mountain Sinkhole Journal, many of the species present in sinkholes have either become extinct or have changed significantly from the outside world due to the effects of climate change or human activity. These unique ecosystems preserve species that have been destroyed by climate change or have been significantly altered to meet human needs or desires.
How trapped air nourishes vast forests
The air quality within Tiankeng is very different from the air above it. The dense vegetation and the fact that each sinkhole contains a significant source of moisture (usually from internal springs and rivers) create an environment with very high levels of humidity from the constant presence of large amounts of negative oxygen ions and moisture. This stable micro-environment prevents soil erosion and allows the growth of massive trees (some more than 40 meters tall) that are protected from the damaging winds found on the plateau surrounding Tiankeng.
