Commentary: A Mountainous Bastion Faces An Ecological Threat

I was researching the 1897 Shillong earthquake, a major seismic event that occurred over a century ago. I started my journey from Thiruvananthapuram in Kerala to Shillong, Meghalaya, to study the field impacts of the great earthquake of 1897, and when I reached Cherrapunji, I had to buy an umbrella. Caught up in that incessant rain in Cherrapunji, I realised I had been chased and overtaken by monsoon clouds.

On the southern side of the Shillong Plateau near Cherrapunji, a huge escarpment exists — the massive vertical cliff at Dauki. Standing on a rocky ledge on a foggy morning, I could see the faint outlines of the plains of Bangladesh through wispy clouds.

The Shillong Plateau, with its elevated position (1.5 to 2 kilometres), acts as a barrier to humid air masses of the Indian Summer Monsoon from the Bay of Bengal forcing the wind to ascend on its southern windward side causing high rain to fall on the southern side, with areas like Cherrapunji experiencing record-breaking rainfall. The plateau’s southern flank is one of the wettest places on Earth. The plateau also creates a rain shadow effect on its lee side, reducing rainfall in the Himalayan range downwind.

This is why I was intrigued when, in March, the residents said they didn’t get enough usable water despite the rains. This is the type of area from which a new geological time interval was first deciphered, called the ‘Meghalayan Age’ — a global rock boundary signifying a near-global drought about 4,200 years ago that destabilised ancient civilisations because of the weakened monsoon.

I wondered — are we approaching a similar climatic impasse that happened several thousand years ago? The region’s geological history tells us why the plateau has evolved into a dynamic entity shaped by the climate and tectonics.

A raised continental basement with an average altitude of more than 1,500 metres in the proximity of the Himalayas is a very curious landform entity. This massive hard rock batholith with a 1.5-km deep basin filled with sediments on its southern side, has an outsize influence on climate.

Once near sea level and shoved itself above the water about 15 million years ago, it started rising actively around four million years ago. The uplift of the plateau region reorganised the Brahmaputra drainage. The plateau’s topographic growth deflected the river, which previously flowed to the south and the west around two million years ago.

The plateau’s presence not only modulates monsoon precipitation but may also regulate the rate of tectonic convergence of the Indian and Asian plates along the eastern Himalayas. The northern side of the plateau, bordered by a fault, was the site of a great earthquake in 1897, which devastated the Brahmaputra valley and the highlands. The seismic potential of the Dauki fault on the southern part of the plateau remains an interesting scientific question with implications for both Bangladesh and India.

Theories of the Plateau’s origin dwell upon the northward movement of the Indian plate beneath Tibet. The plateau is considered as a ‘pop up’ structure between Dauki fault in the south and Brahmaputra fault in the north, due to bending stresses from the plate collision. More recent studies attribute plateau uplift to subduction attempts of the India plate under the plateau region.

In the geological past, interactions between the land and the sea in the southern part had initiated continental and marine deposition, creating mineral resources like coal and limestone. The Meghalaya coal was formed about 50 to 33 million years ago in the lakes. Because the coal was formed in spatially restricted lakes, the coal seams are lensoidal (lenticular): thick in the middle but pinching out laterally, and with a scattered distribution. Therefore, it is not feasible to conduct large-scale commercial mining like in other parts of the country where large coal deposits are formed in aerially huge swamps.

A serious water crisis is also brewing on the plateau, mostly due to unscientific mining activities. Thousands of miners have lost lives while engaged in rat-hole mining after they got trapped due to sudden flooding.

Meghalaya has an estimated 559 million tonnes of coal reserves. Long before the National Green Tribunal banned coal mining in the region, local people used small mine pits close to each other and engaged in what was described as rat-hole mining.

The coal seam occurs at a depth of nearly 150 metres, so a vertical pit must be dug to reach it. The miners who extract the coal must climb 500 feet down into the mine. Then, at that level, they are forced to crawl for about 150 metres horizontally. In these situations, they risk coming upon another abandoned, collapsible mine or an abandoned mine that has since become an underground reservoir. When they encounter the latter, the result is a flash flood.

Many abandoned mines are left unworked and aren’t filled up once all the coal has been extracted. These gaping pits and rat holes provide easy routes for the water to flow through. Consequently, surface runoffs have considerably reduced in volume: the expanding network of underground channels of human creation is now draining the rivers. This, in turn, explains why there is an acute shortage of potable water on the surface.

Meghalaya’s water bodies are impacted by acidic mine drainage from the sulphur-rich coal mines. The coal and other mining activities, already wreaked havoc in the social and cultural lives of the region’s people. Several civil rights activists have voiced their concerns about the worsening environmental conditions in Meghalaya.

The timber logging has destroyed swathes of forests, threatening biodiversity and water resources. In a recent study, it is reported that in East Khasi, the dense forest area declined sharply from 1,480 km² to 828 km² between 2002 and 2013, driven by extensive deforestation, logging, and land conversion.

The advisory committee of the Union Ministry of Environment, Forest and Climate Change has now granted an ‘in-principle’ approval for the diversion of about 35 hectares of reserved and deemed forest area in East and North Garo Hills districts for widening of the National Highway – NH 127B, and about 4,500 trees that belong to dense forest will have to be cut. The wildlife includes barking deer, leopard, wild boar, fox, mongoose, monitor lizard, Malayan giant squirrel, jungle fowls and other animals.

The reported unearthing of significant mineral deposits in various districts of Meghalaya raises alarm bells. Among the key findings are moderate-quality bauxite resources, high-grade limestone, and traces of lithium. It is unclear how such mining activities are likely to impact the state’s natural environment. The people of Meghalaya must come together and raise their concerns in one voice against actions that can have a negative impact on the environment.

(Published under Creative Commons from Mongabay India. Read the original article here)