Science & Technology

Hill heavy!

What happens when a rare geological site is squeezed for space

By Shreeshan Venkatesh
Published: Tuesday 01 September 2015

While its sister geological site, Devil's Peak, is a cordoned off national park area, Gilbert Hill is surrounded by a vast expanse of settlements, slums and high-rise structures  (Photographs: Shubinoy Kapoor)

It is one of the rarest residential addresses of the world. To reside beside the Gilbert Hill in Mumbai’s Andheri means being a witness to a geological rarity. The hill is one of the world’s only two basalt monoliths, which were squeezed out of the Earth some 65 million years ago in molten form. The other one is Devil’s Peak in Wyoming in the US.

But off late, the lucky residents are not feeling so possessive about its superlative. Residents in the neighbourhood of Gilbert Hill have been living in a state of constant unease as chunks of rocks tumble down at eerie regularity from the rockface of the hill. “Every year, rocks fall from the top, especially during the monsoon,” says Mohammed Qasim, a local resident. In June this year, two persons were critically injured as chunks of the hill struck them. The geological superlative is surrounded by increasing residential settlements. Over the last few years, the area surrounding the hill has witnessed repeated instances of people getting killed, injured, and property being damaged due to the unpredictable rockfalls.

On the other hand, conservationists and geologists are worried that Gilbert Hill may be wiped out in the future, both due to constant human encroachments as well as from lack of conservation. The 61-metre tall monolith is made up of tightly-packed hexagonal columns of basalt that stretch from the bottom to the top. The formations are rich from the perspective of geological information about the Earth’s evolution.

While Devil’s Peak is a cordoned-off national park area and a tourist attraction, Gilbert Hill is surrounded by a vast expanse of shanty settlements, slums and high-rise structures that have consumed the rock from all sides.

Cracking edifice

The Geological Survey of India has designated Gilbert Hill as a geological monument. In fact way back in 1952, the hill was declared a National Park. But these classifications have not been effective in protecting the hill. Earlier, the area was a vast ridge. But over the years, construction activities have reduced the size of the hill. “What remains today is merely 10 per cent of the entire ridge formation,” says Sinkhalya Kuchalkar, a trustee of the Gaondevi temple that stands atop the hill. “I think the only reason this stretch is still standing is because of the temple,” he adds.

Architect P K Das, who is conducting tests on the hill to ascertain the extent of damage, says, “The problem of rocks detaching from the structure is human-made. Unregulated and unhindered quarrying of the hill and heavy commercial and residential construction in the area have caused the deterioration.” He says water from construction projects and seepage from nearby slums have weakened the structure.

In 2007, the Bombay High Court appointed a two-member expert team to evaluate the structural integrity of Gilbert Hill. After an exhaustive study by geologists and environmentalists, Gilbert Hill was declared as a Grade II Heritage Structure by the Municipal Corporation of Greater Mumbai (MCGM).

“The rock formation is deteriorating for many reasons, but the main reasons are to do with the natural weathering processes of the hill. Water is a double-edged sword; it is both essential and can be extremely detrimental. Any rock formation has joints and fissures. When water seeps through these joints, it exerts pressure on the rocks and causes a cleaving action which loosens them,” explains one geotechnical expert appointed to inspect the site, on condition of anonymity.

The expert team recommended a safe perimeter around the hill for construction using heavy equipment depending on the soil conditions and structural integrity. It also specifically mentioned that there must be no cutting of the banks or slopes of the hill as this will tantamount to removing crucial columns in a framed structure. If the cutting persists, there will be landslides and repeated rockfalls.

“Though most buildings in the area have sprung up according to regulations, this does not mean they have not contributed to the weakening of the structure,” says Kshitija Nadgouda, a professor of civil engineering at the Sardar Patel College of Engineering in Andheri who was briefly involved in the structural evaluation of the hill in 2007.

Despite the recommendations of the High Court-appointed expert panel and the heritage structure classification accorded to the hill, rapid construction in the area has pushed up real estate prices to Rs 17,000 per sq ft. Builders have routinely cut into the mud slopes to create space for residential projects and have created a situation that is dangerous to residents in the area and also detrimental to the hill.

The real worry is the ambiguity regarding protected areas around Grade II Heritage Structures, says Ameet Satam, a member of Maharashtra’s legislative assembly, who has been actively involved in drawing up plans to preserve the hill. “Only a buffer distance of five metres around the structure is required to be maintained. Even so, we see builders cut into the slope of the hill because nowhere has it been mentioned where this five-metre distance is to be measured from. Builders have been taking advantage of this ambiguity in the code and gambling with the lives and property of the residents,” explains Satam.

Retention move

In February this year, a Rs 2-crore grant enabled the construction of a wall around a part of the hill. “The retaining wall is to stop further encroachments and to protect slum dwellings that have cropped up on a mud bank next to the hill,” says Satam. He has engaged international consulting group, Fugro, to evaluate the condition of the hill, including the fractures. “We are awaiting the report so that we can upgrade the hill to a Grade I Heritage Structure. This will stop further construction and encroachment.”

“We have planned a netting around the steep faces of the hill to stop rocks from tumbling onto the settlements. Structural solutions will be also implemented,” he says. We must protect this structure, both for the security of the population as well as to preserve a critical part of our natural history,” adds Satam.

Experts believe that even if nets are put to stop the geological monument from crumbling, the beauty of Gilbert Hill will be affected. “Whatever is done to protect the structure, the aesthetic aspects stand compromised,” says Nadgouda.

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