Thermal Baking, Induration and Physical Volcanic Features in Deccan Volcanic Units and Their Suitability for Excavation, Sculpturing as well as Restoration of Geoheritage Sites in Western India

Abstract

Deccan volcanic units cover vast region in west-central India and host some of the monumental geoheritage sites. These basalt units are not suitable either for excavation or sculpturing, because of inherent cooling cracks. Weathering of iron minerals also reduces their utilization for work of art. From the beginning of first century, ancient artisans have identified thermally baked zones in the vicinity of lava tubes, channels and effusive centres. Newly formed rocks within these zones are indurated, hardened and excellent for excavation, sculpturing and polishing. The degree of induration is also skilfully utilized, black basalt has acquired vibrant shades of red by amalgamating iron minerals. Depending on religious believes, Hindus excavated enormous Kailash temple from the top of the hill with intricate sculpturing of idols and statues, while Buddhists excavated large meditation halls (Vihars) with columns and arches. We identified hidden effusive centre in the vicinity of Ellora cave complex. Physical volcanic feature such as portal portion of lava tube is utilized for locating large Saptashrungi temple. Silica rich agglomerate basalt, with large fragments is used for coarse carving of tall Buddha statue, corresponding with the sixth-century Bamiyan caves in Afghanistan, while exceedingly fine-grained agglomerate is preferred for intricate carving of Shiva idol in Elephanta caves. Damage by invaders and erosion are usually repaired by cement and concrete, losing aesthetic sense. We recommend matching rocks for restoration and use of red ochre, blue and green (azurite and malachite) from copper and brown from bark extract for cave paintings.