Geological Note: Hampi

Travelling to Hampi for the first time, one cannot help but remark upon the incredible boulder-strewn landscape. As far as the eye can see, there are massive piles of rocks - like a pebble game played by giants on a checkered board of farmlands and villages. Imagination aside, the geological history of this landscape is just as fascinating.

Geographically, Hampi lie atop the Deccan Traps - the volcanic layers that define the Indian peninsula. The Deccan Traps are among the world's largest volcanic features, consisting of layers of solidified basalt laid down when the Indian Plate was migrating over the Reunion hotspot after breaking off from Gondwanaland, roughly 66 million years ago. The word 'traps' derived from the Swedish word for 'stairs', aptly describes these step-like, layered formations.

To narrow it down further, Hampi is situated on the Dharwar craton - an old, stable chunk of the Earth's crust. The Dharwar craton laid down between 3.6-2.5 billion years ago, is among India's oldest features and lies beneath some parts of Karnataka (the state in which Hampi lies), Goa, and Andhra Pradesh.

However, Hampi's stark, unusual landscape isn't the result of volcanism or upheaval, or of wind erosion but of deep, slow weathering by rainwater, along the cracks and crevices in the granite bedrock. The feature is known as an 'inselberg'. The word 'inselberg' is derived from the German words for 'island mountain’. An inselberg is a residual feature - one that persists in a landscape long after its contemporaries have eroded away.

There are other names for inselbergs, such as nubbins, koppies, tors (geologists consider smaller heaps of rocks to be tors, and larger ones to be inselbergs), and kopjes. These names indicate that inselbergs are a rather prevalent feature across the world, and are seen in other climatic regimes. Yet they are more abundant in tropical regions and occur in outcrops of granite or gneiss (and occasionally in basalt) - Hampi's climate and bedrock fit this bill.

There is still much debate about the formation of inselbergs. Yet most geologists concur that inselbergs were formed as a result of weathering - the breaking down of rocks at site, and some erosion - the transport of weathered material by agents like rainwater, wind, or gravity.

Here’s how inselbergs are formed:

Weathering along joints and cracks: at the first stage, rainwater percolates through the existing joints and cracks in the rock, and leaves behind corestones - unweathered, residual blocks, and grus - weathered, broken-down material. The angular sides of the corestones are smoothened into rounded edges by the weathering action of rainwater.
Erosion of grus: over time, due to gravity, rainwater, or wind, the weathered, gravelly material is carried away, leaving the corestones exposed. This deep weathering process requires long periods of time between 10,000 - 1,00,000 years, and leads to the formation of inselbergs. Such landscapes are also known as 'etched landscapes' - where the rocky surface is corroded, and the weathered material transported off.

Perched or balancing rocks: sometimes, the weathering sculpts the rocks into precarious, gravity-defying piles, with some perched or balancing rocks. Keep an eye out for balancing rocks when you travel through Hampi!

Most inselbergs in the world are remote, fragile ecosystems with uniquely adapted flora and fauna, yet in India, some inselbergs are different. Human settlements dating back from the Iron Age, and pastoral communities have long been changing the ecology of inselbergs. Agrarian communities have been using run-off water from the inselbergs to cultivate fields, and the lees of inselbergs offer some shade to their crops. Grazing animals still roam freely in these landscapes, and their seed-rich droppings have allowed rich biodiversity to flourish. The human imprint is also writ large in the temples and hill forts perched atop rocky outcrops, as well as stone quarries that mine the granite.

These age-old influences mean that inselbergs around Hampi, and elsewhere in India, offer a unique geographical perspective on history, culture, and biogeography, and can present opportunities for inclusive biodiversity conservation by focusing on the role of nature and culture in shaping present-day environments.

In the early 14th Century, Hampi was chosen as a capital by the Vijaynagara Empire - perhaps drawn there because of its history as an ancient pilgrimage site, or its fertile valley irrigated by the Tungabhadra river. The inselbergs formed not just a spectacular backdrop to their civilization, but their monuments were built with rocks from the vicinity. Like the inselbergs, these monuments too, have stood the test of time - and persist in the landscape long after most other signs of the empire have turned to dust.

Words: Devayani Khare

Cover image caption: A traditional basket boat or coracle against the backdrop of Hampi’s boulder-strewn landscape.

Cover image credits: Sandip Dey CC-BY (via Wikimedia Commons)