Initial surveys had indicated hard rock throughout the stretches to be tunnelled. But there were unexpected findings, including loose red soil patches amidst the compact basalt formation that comprises almost the entire Western Ghats mountain range, and the discovery of a loose rock mass weighing 200 ton. “These can be attributed to inter-plating between lava and soil mass caused by volcanic eruptions millions of years ago,” said Mundo, who has decades of experience in the field.
The Western Ghats are the mountainous faulted and eroded edge of the Deccan Plateau, formed about 150 million years ago possibly during the breakup of the supercontinent Gondwana. Geophysical evidence suggests that India’s west coast emerged 80-100 million years ago after separating from Madagascar.
This was much before the subcontinental plate was pushed northwards to press into the Eurasian plate owing to continental drift (a process that led to the formation of the Himalayas, a much younger mountain range).