Gilbert Hill: Mumbai’s Forgotten 66 Million Years Old Heritage

Concrete buildings aren’t the only thing that rises vertically in the metropolis of Mumbai, India’s most populous city. In a suburb, north of the city, there is a huge column of basalt rising 200 feet towards the sky. Surrounded on three sides by tall apartment complexes of nearly the same height, this monolith called Gilbert Hill is practically invisible to anyone but the nearest neighbors.

Gilbert Hill is Mumbai’s oldest skyscraper. It formed around 66 million years ago at a time when India was still a floating island south of the equator, but rapidly gaining on the Eurasian plate in the north. In just 15 million years—a short span in geological timescale—the Indian plate would collide violently with the Eurasian plate resulting in the formation of the massive and breathtaking Himalayan range.

66 million years ago, the region that at present times corresponds to the states of Maharashtra, Gujarat and Madhya Pradesh in west-central India was volcanically active. A series of giant volcanic eruptions flooded this entire region and beyond with lava, which solidified to form an enormous plateau of basalt 2 kilometers thick. This plateau known as the Deccan Traps originally covered 1.5 million square kilometers, approximately half the size of modern India. Erosion and plate tectonics reduced the traps to its current size of half a million square kilometers, which is still massive. The timing of this volcanic eruption coincides with the Cretaceous–Tertiary mass extinction of species, including the disappearance of the dinosaurs, which have led some scientists to believe that the volcanic eruptions that led to the formation of the Deccan Traps and the release of volcanic gases may have had a hand on the extinction event. Although the scientific community leans towards the meteorite-impact theory of extinction, there are still others who believe that both the volcanism and the impact event may have caused the extinction.

Gilbert Hill is a very visible remnant of that volatile era. Geologists believe that the monolith was formed when lava was squeezed out of crack in the plateau. As the magma cooled, it formed vertical columns instead of horizontal layers. These rectangular and hexagonal structures are known as columnar basalt or laccolith. There are only a handful of places on earth where you can see such geological structures. The Devil’s Tower and Devils Postpile in the United States, and the Giant's Causeway in Northern Ireland are some examples of columnar basalt.

Gilbert Hill was declared a National Park in 1952, and a Grade II heritage structure in 2007. However, the current condition of this highly encroached-upon natural wonder shows that neither its legal status as a National Park nor its inclusion in the heritage list has made any difference. There are two temples on the top of the hill, accessible by stairs. The vegetation that once surrounded the hill has given way to buildings and dingy slums. The people who live around this geological monument are barely concerned about the hill because of their own struggle for survival. The only people who visit the site are scholars, historians and devotees of the shrines.

Awareness about this natural wonder is low among Indians. Geography lessons in schools do not teach about the existence of this rock. There are no tour guides in the city that bring tourists to the site. We still don’t know how Gilbert Hill got its name. Some say it was named after an American geologist Grove Karl Gilbert who coined the term laccolith. Others say that the hill was named after the then British officer in charge of Andheri Taluka block.

For years, concerned citizens have been asking the Maharashtra Tourism Development Corporation to build a protective wall around the site, and develop it as a tourist attraction. But these demands have not been met. Although the shrines on top of Gilbert Hill are themselves an encroachment on the site, they have now become the unlikely guardian of the hill. Some years ago, a local builder suggested that the hill be demolished to make room for more buildings. This suggestion was appropriately crushed by the temple trustees. The shrines are the only things that’s protecting this geological wonder from complete destruction.