Deccan Traps

The Deccan Traps are one of the world’s largest and most significant volcanic provinces, located primarily in the Deccan Plateau region of western and central India. Comprising vast layers of solidified basaltic lava, they represent one of the most extensive volcanic events in Earth’s geological history. The Deccan Traps were formed about 66 million years ago, near the end of the Cretaceous Period, and their eruption is closely linked to major environmental changes and the Cretaceous–Palaeogene (K–Pg) mass extinction event that led to the demise of the dinosaurs.

Etymology and Meaning

The word “Deccan” derives from the Sanskrit “Dakshina,” meaning south, while “Traps” originates from the Swedish word “trappa”, meaning stairs or steps, referring to the step-like landscape formed by successive layers of basaltic lava flows. Together, the term Deccan Traps describes the characteristic terraced terrain resulting from multiple volcanic eruptions that created thick, horizontal sheets of rock.

Geographic Extent and Structure

The Deccan Traps cover an area of approximately 500,000 square kilometres today, though they are believed to have originally spanned over 1.5 million square kilometres before erosion and tectonic shifts reduced their visible extent. The volcanic layers are found across much of Maharashtra, Madhya Pradesh, Gujarat, Karnataka, and parts of Andhra Pradesh.
The basaltic formations are particularly prominent around the Western Ghats, the Satpura Range, and the Narmada Valley. The thickness of the lava deposits varies but can reach up to 2,000 metres in some areas. These layers consist of numerous individual lava flows, each ranging from a few metres to several tens of metres in depth.
The Deccan Traps are composed primarily of tholeiitic basalt, though minor occurrences of andesite, trachyte, and rhyolite have also been identified. These volcanic rocks contain minerals such as plagioclase, pyroxene, and olivine, typical of basaltic compositions.

Formation and Volcanic Activity

The Deccan Traps were formed by a series of massive volcanic eruptions that occurred over a relatively short geological timescale—estimated between 68 and 60 million years ago, with the main phase concentrated around 66 million years ago.
The eruptions were primarily fissure-type basaltic outpourings, where lava erupted through long cracks or fissures in the Earth’s crust rather than through central volcanic cones. This style of volcanism led to the widespread, sheet-like deposition of lava across a vast area.
Geological studies indicate that the volcanic activity occurred in pulses rather than as a continuous event. The largest eruptive phase is believed to have coincided closely with the K–Pg boundary, marking a significant global environmental crisis.

Connection with the Réunion Hotspot

The formation of the Deccan Traps is commonly attributed to the Réunion hotspot, a stationary plume of hot mantle material currently located beneath Réunion Island in the Indian Ocean. Around 66 million years ago, this hotspot was positioned beneath what is now western India.
As the Indian Plate drifted northwards towards the Eurasian Plate, it passed over this hotspot, resulting in extensive melting of the mantle and the extrusion of vast quantities of basaltic magma. The plume’s thermal activity also contributed to crustal uplift and fracturing, facilitating repeated lava eruptions.
This hotspot theory links the Deccan Traps to other volcanic features along the Indian Ocean region, such as the Chagos-Laccadive Ridge and the Mascarene Plateau, which represent the trail of the moving Indian Plate over the stationary plume.

Environmental and Climatic Effects

The Deccan eruptions had profound and far-reaching environmental consequences. The release of enormous quantities of carbon dioxide (CO₂), sulphur dioxide (SO₂), and other volcanic gases into the atmosphere would have caused severe climatic perturbations.
Key impacts included:

• Global Warming and Cooling Cycles: While CO₂ emissions contributed to greenhouse warming, sulphur aerosols reflected sunlight, leading to temporary cooling. These alternating effects caused major climatic instability.
• Ocean Acidification: The influx of carbon dioxide into the oceans altered their chemical balance, affecting marine life and coral reefs.
• Acid Rain: Sulphuric acid formation from volcanic gases led to acid rain, damaging vegetation and soil ecosystems.
• Reduced Photosynthesis: Dust and aerosols likely obscured sunlight for extended periods, disrupting photosynthesis and food chains.

These environmental disruptions would have significantly affected terrestrial and marine ecosystems, contributing to mass extinctions.

The Deccan Traps and the K–Pg Extinction

The Deccan Traps’ eruptions coincide closely with the Cretaceous–Palaeogene extinction event, around 66 million years ago, when approximately 75% of Earth’s species, including the non-avian dinosaurs, perished.
Two primary hypotheses have been proposed to explain this extinction:

1. The Chicxulub impact hypothesis, which attributes the event to an asteroid impact in present-day Yucatán Peninsula, Mexico.
2. The volcanism hypothesis, which argues that prolonged Deccan eruptions released enough gases and particulates to trigger environmental collapse.

Recent research suggests a combined scenario, where the asteroid impact may have intensified the climatic stresses already caused by Deccan volcanism. Radiometric dating indicates that the peak eruptive activity occurred within a few hundred thousand years of the impact, suggesting that both events likely contributed to the mass extinction.

Geological and Scientific Importance

The Deccan Traps provide crucial insights into:

• Flood basalt volcanism, a rare and powerful geological phenomenon.
• Mantle plume dynamics and the interactions between deep-Earth processes and surface geology.
• Mass extinction mechanisms, particularly the relationship between volcanism and biospheric change.
• Plate tectonics, illustrating the movement of the Indian Plate over the Réunion hotspot.

The region is also rich in palaeontological and palaeomagnetic records, offering data on ancient climates, magnetic reversals, and faunal transitions across the K–Pg boundary.

Economic and Environmental Significance

The basaltic rocks of the Deccan Traps have weathered over millions of years to form fertile black cotton soil (regur), which is highly productive for crops such as cotton, sugarcane, and soyabean. The region’s soils retain moisture efficiently, supporting agriculture in semi-arid areas.
The Deccan Plateau also hosts significant mineral resources, including zeolites, bentonite, and bauxite. Furthermore, the traps have geological formations favourable for groundwater storage and carbon sequestration studies.
From an environmental standpoint, the Western Ghats—formed partly along the edge of the Deccan Traps—are a UNESCO World Heritage Site and one of the world’s biodiversity hotspots, supporting unique flora and fauna adapted to volcanic soils.

Modern Research and Conservation

Modern geophysical and geochemical studies, using techniques such as radiometric dating, isotope analysis, and seismic imaging, continue to refine our understanding of the Deccan Traps’ formation and duration. Collaborative international projects have explored how their eruptions influenced global biogeochemical cycles and climate.
At the same time, conservation efforts are underway to protect the unique geological landscapes and fossil-bearing formations found within the traps, recognising their scientific and cultural value.

Legacy and Global Context

The Deccan Traps stand as a monumental record of Earth’s dynamic interior processes and their influence on the biosphere. They represent one of the few continental-scale expressions of flood basalt volcanism, comparable to the Siberian Traps and the Columbia River Basalts.