The rocks that grow
The Sangkulirang-Mangkalihat Peninsula in Borneo is a landscape of towering limestone cliffs and deep caves, covering an area of 1.8 million hectares. This is not ordinary limestone. The karst here is a biokarst, meaning the rock itself is actively built by living organisms. In the humid, tropical environment, complex microbial communities, thick biofilms of cyanobacteria, algae, and other bacteria—thrive on the rock surfaces. Microbes facilitate the precipitation of calcium carbonate from the water that seeps through the jungle, adding microscopic new layers to the cave walls and formations. This process of biogenesis means the caves are, in a sense, alive and still growing.
This microbial activity is a fundamental part of what makes the region's geology unique. The Mangkalihat caves are formed by the dissolution of rock by water, which is typical for karst landscapes, the Mangkalihat caves are also shaped by this additive, biological process. The thick mats of microorganisms create their own micro-environment, trapping nutrients and influencing the flow of water, which in turn affects the structure of the caves over geological time. The result is a vast and complex system of hundreds of caves with varied passage shapes, from angular corridors following fault lines to rounded, water-carved tunnels.