A 66-Million-Year-Old Navigational Hazard
The Banni grasslands, a vast expanse of arid ecosystem covering 3,847 square kilometers in India's Kutch district, conceal a powerful secret beneath their surface. This region exhibits a significant magnetic anomaly, a localized variation in the Earth's magnetic field. The cause lies in thick subsurface deposits of sediments with many ferrimagnetic minerals, primarily magnetite. These minerals create a magnetic field strong enough to interfere with compasses and other navigational instruments.
The origin of these magnetic sediments is recorded in deep time. Around 66 million years ago, massive volcanic eruptions formed the Deccan Traps, a large igneous province that once covered a significant portion of India with basaltic lava flows. Basalts are often rich in minerals like magnetite. Over millions of years, weathering and erosion broke down these volcanic rocks. Rivers, including the ancient Indus which once flowed through this region, transported these magnetite-heavy sediments and deposited them in the Banni plains. In the Kutch region, these Deccan Trap basalt layers can be hundreds of meters thick, lying beneath younger Tertiary sediments. This long geological process concentrated the magnetic minerals, creating the anomaly that exists today.