An underground chemical laboratory
The Baratang limestone caves are a result of millions of years of geological activity. The process began with the accumulation of marine life skeletons and shells on the seabed, which compressed over eons to form sedimentary limestone rock. Tectonic uplift associated with the formation of the Andaman island arc pushed these limestone deposits above sea level.
The caves are an example of karst topography. Rainwater absorbs carbon dioxide from the atmosphere and soil, forming a weak carbonic acid. This acidic water percolates through fractures in the limestone, dissolving the calcium carbonate (CaCO3) and slowly carving out underground passages and chambers.
Inside the cave, the water, now rich with dissolved calcium bicarbonate (Ca(HCO3)2), drips from the ceiling. As a drip is exposed to the air within the cave, the chemical reaction reverses. Carbon dioxide is released from the water, causing the calcium carbonate to precipitate out of the solution and deposit as calcite crystals. Each drop leaves a minuscule mineral deposit behind. Over thousands of years, these deposits create the cave's formations, known as speleothems. Stalactites hang from the ceiling, while the water that drips to the floor builds stalagmites from the ground up. When a stalactite and a stalagmite meet, they form a solid column.
A process measured in human time
The growth of limestone formations is typically slow, often less than 10 cm every thousand years. However, under ideal conditions with a steady supply of mineral-rich water, the growth rate can be faster. Some of the quickest growing stalactites can grow at a rate of 3 mm per year. The formations in the Baratang caves are still active and growing, a dynamic process of deposition that continues to modify the cave's interior.
The trip to the caves is a part of the experience. It begins with a drive from Port Blair that passes through the Jarawa Reserve, a protected forest and the ancestral homeland of the Jarawa people. Travel through this section is restricted to vehicle convoys that run at specific times, and interaction with the tribe is prohibited to protect their community from outside diseases and to preserve their way of life.
From the Nilambur Jetty at Baratang, visitors take a speedboat through a dense network of mangrove creeks. This boat ride, which can take 10-15 minutes, navigates through a natural canopy formed by the mangroves. After docking, a walk of about 1.5 kilometers through a tropical forest leads to the cave entrance. Inside, the air is cool and damp, and guides illuminate the massive, complex calcite structures.