A landscape sculpted underground
The surreal boulder-strewn fields of Hampi were were not created by volcanoes, earthquakes, or ancient giants. Their story begins 2.5 billion years ago, deep within one of the Earth's oldest and most stable crustal blocks, the Dharwar Craton. Magma cooled slowly miles beneath the surface to form a massive, solid body of granite known as the Closepet Granite. This rock, a 400-kilometer-long batholith, was a uniform mountain of granite, initially without a single boulder in sight.
The sculpting process started in darkness. Tectonic stresses caused the subterranean monolith to develop a network of deep vertical and horizontal cracks, or joints, splitting the mass into huge, rectangular blocks. For millions of years, acidic groundwater seeped down through the soil and into these fractures. This water began a slow chemical attack on the granite. The feldspar minerals in the rock broke down into a soft clay called kaolinite, while the more resistant quartz crystals remained as sand. This process, a form of chemical weathering called hydrolysis, occurred entirely underground. The chemical attack was most aggressive at the corners and edges of the rectangular blocks, which had more surface area. This differential weathering rate rounded the blocks from the outside in, a process known as spheroidal weathering. This created a subsurface world of hard, rounded "corestones"—the future boulders—entombed in a soft, crumbly matrix of weathered granite called saprolite, or grus.