All About the Aravalli Hills: India’s Oldest Mountain Range

December 23, 2025

New Delhi / Northern India: Protests have erupted across northern India following the Supreme Court’s recent redefinition of the Aravalli Hills, one of the world’s oldest geological formations. Spanning Rajasthan, Haryana, Gujarat, and Delhi, the Aravallis play a crucial ecological and geological role in the region.

Under the court’s new definition, accepted following federal government recommendations, an Aravalli hill is now classified as any landform rising at least 100 metres (328 ft) above the surrounding terrain. Furthermore, two or more such hills within 500 metres of each other, along with the land connecting them, are considered an Aravalli range.

• What is Aravalli Hills?

The Aravalli Range is one of the world’s oldest mountain ranges and India’s oldest fold mountain range, estimated to be approximately 1.5 to 2 billion years old. Stretching for approximately 800 kilometers, it begins in Delhi, passes through Haryana and Rajasthan, and ends in Gujarat. Its highest peak is Mount Abu’s Guru Shikhar (1,722 meters). Although the range has eroded significantly over time, its environmental significance remains significant. The Aravalli Range plays a vital role in preventing the expansion of the Thar Desert, recharging groundwater, moderating temperatures, and reducing dust and air pollution in Delhi-NCR. The region is also a major source of biodiversity, wildlife corridors, and forest resources, helping prevent soil erosion and flooding. However, rapid urbanisation, mining, illegal construction and encroachment are posing a serious threat to the existence of the Aravallis, with experts fearing that its degradation could further aggravate water crisis, heat intensity, pollution and desertification.

• facts about the Aravalli Hills

• Age: Approximately 1.5 billion years old
  • The Aravalli Hills are one of the oldest mountain ranges in the world. They were formed around 5 billion years ago, long before the Himalayas. This makes them geologically significant, as they provide insight into Earth’s early formation and evolution.
• States: Rajasthan, Haryana, Gujarat, Delhi
  • The Aravalli range stretches acrossfour states in northwestern India:
    • Rajasthan – largest portion of the range
    • Haryana – southeastern extensions
    • Gujarat – southwestern extensions
    • Delhi – northern tip of the range
  • This shows that the hills influence a large geographical area, affecting climate, water, and ecology across multiple states.
• Ecological Role
  • Desertification Prevention: Acts as a natural barrier preventing the Thar Desert from spreading into fertile regions.
  • Groundwater Recharge: Rainwater flows down the slopes and percolates into underground aquifers, replenishing water sources for villages and cities nearby.
  • Biodiversity Conservation: Home to a variety of plants, animals, and endangered species, providing critical wildlife habitats and maintaining ecological balance.
• Length: Approximately 800 km
  • The Aravalli range stretches about 800 kilometres, making it a major physical feature of northwestern India. Its long stretch ensures ecological connectivity and continuity of habitats.

In short: The Aravalli Hills are ancient, ecologically vital, and geographically extensive, but they face serious threats from human activity that can harm water resources, wildlife, and local livelihoods.

• Benefits of the Aravalli Hills

1. Prevent desertification: The Aravallis prevent the spread of the Thar Desert and retain moisture in the soil.
2. Groundwater recharge: Rainwater in the hillslopes and valleys reaches underground water reserves.
3. Biodiversity and wildlife habitat: The Aravallis are home to numerous flora and fauna, including endangered species.
4. Climate control: Dense vegetation moderates temperatures, improves air quality, and absorbs carbon dioxide.
5. Support for local livelihoods: Rural communities depend on agriculture, forestry, and medicinal plants.
6. Natural flood protection: By controlling the flow of rainwater, the Aravallis reduce the risk of flooding in surrounding areas.
7. Cultural and historical significance: The Aravallis are home to ancient forts, temples, and historical sites.
8. Tourism and recreation: The natural beauty increases tourism and local employment opportunities.

• Why are the Aravallis important for Delhi-NCR?

The Aravalli Hills are crucial for the ecological health of Delhi-NCR, acting as a natural protective barrier for the region. They help block dust and air pollution, especially from the Thar Desert, and play a key role in recharging groundwater by allowing rainwater to percolate slowly into underground aquifers. The presence of forests and rocky terrain in the Aravallis also helps moderate temperatures, reducing the intensity of heatwaves and extreme heat conditions. Additionally, the hills regulate the flow of rainwater, thereby lowering the risk of urban flooding during heavy monsoons. Owing to these vital functions, environmentalists often refer to the Aravallis as Delhi’s “Green Wall.”

The connection between the Aravallis and groundwater is particularly significant. The porous rock formations and forest cover enable rainwater to seep deep into the soil, naturally replenishing aquifers that supply water to Delhi, Gurugram, Faridabad, and Alwar. Beyond recharge, the Aravalli hills also act as natural filters, preventing contaminants from easily entering groundwater sources and thereby protecting water quality across the region.

• Why This Has Sparked Protests?

Environmentalists argue that this height-based definition risks leaving numerous lower, scrub-covered but ecologically vital hills unprotected. These smaller hills are critical for:

• Preventing desertification
• Recharging groundwater
• Supporting local livelihoods and agriculture

Local residents, farmers, environmental activists, lawyers, and some political parties have organized peaceful demonstrations in cities like Gurugram and Udaipur over the weekend

Government’s Response

The federal government has sought to downplay concerns, stating that the new definition is intended to strengthen regulation and bring uniformity in mining and development control. Key points from the government:

• The definition includes slopes, connecting landforms, and intervening areas, protecting hill clusters.
• Mining in the Aravallis remains banned in core “inviolate” areas, including protected forests, eco-sensitive zones, and wetlands.
• Only about 2% of the 147,000 sq km Aravalli range could potentially be mined, and only after detailed studies and official approvals.
• Existing mining leases can continue if they follow sustainable mining norms, while certain strategic and atomic minerals are exempt under law.

Environment Minister Bhupender Yadav stated that the policy does not allow unrestricted mining, and areas below 100 metres will not automatically be opened for exploitation.

• Analysis and Implications

The redefinition of the Aravalli hills highlights the tension between development and ecological conservation in India. While the government claims the new framework will standardize regulation, environmentalists argue that height alone is not a sufficient criterion to preserve ecosystems.

The Aravallis are critical for preventing desertification, maintaining groundwater levels, and supporting biodiversity in northwestern India. Excluding smaller hills from protection could lead to fragmented ecosystems, threatening wildlife corridors and natural water recharge areas.

The protests are likely to continue as activists explore legal avenues to challenge the Supreme Court’s new definition. Observers note that this debate reflects a broader national challenge: balancing economic development, mining, and urban expansion with the need to preserve ecologically sensitive areas.