The Deccan Traps: Inside India's vast volcanic province

Sprawling across western and central India lies one of Earth's most extraordinary volcanic landscapes, the Deccan Traps. In some Northern European tongues, "trap" refers to a stair, and stacked lava flows have shaped this subcontinent corner for tens of millions of years. Covering more than half a million square kilometres, the formation rivals Australia's ancient Pilbara basalt plains in scale.

The Traps preserve a near-continuous record of colossal eruptions coinciding with one of life's most debated turning points, the end of the Cretaceous period. For researchers in Australia and abroad, these rocks serve as a deep-time archive, helping geologists reconstruct how sudden environmental upheaval reshapes oceans, atmospheres, and ecosystems.

The origin story is tied to plate tectonics on a planetary scale. As the Indian plate drifted northward from Gondwana, it passed over a stationary mantle plume, sometimes called the Réunion hotspot. That plume punched through the crust, unloading layer upon layer of runny basaltic lava into a pile more than two kilometres deep.

Researchers from Sydney and Melbourne universities now collaborate with Indian colleagues to map aquifers trapped between flows and to sample minerals that record ancient carbon and sulphur cycles. The Deccan Traps serve as a natural laboratory where deep past intersects with present-day concerns about water security and climate resilience.

A flood-basalt province forged in fire

The eruptions that built the Traps unfolded over a geologically brief but cataclysmic window, with the most intense pulses concentrated around sixty-six million years ago. Recent radiometric dating suggests a pulsed history, with several massive episodes separated by quieter intervals.

Such findings shape models linking volcanism to the global extinction that wiped out the non-avian dinosaurs. Researchers at geoscience agencies in Canberra have applied similar dating techniques to Australian basalts, helping refine the chronostratigraphic tools Indian teams now rely upon.

Rock types and the stair-step landscape

The dominant lithology is tholeiitic basalt, a fine-grained, dark rock rich in iron and magnesium. Geologists recognise distinct formations such as the Bushe, Poladpur, and Mahabaleshwar units, each named after localities where they are best exposed.

The stepped landscape arises because each flow erodes back as a small cliff while the flow beneath forms a gentler slope, producing a characteristic terrace-and-scarp morphology. Comparable basaltic terrains in Victoria's Newer Volcanics Province, near Hamilton, exhibit similar dyke swarms that Australian geologists use as natural laboratories for understanding magma emplacement.

Columnar basalt and striking landforms

Among the most photogenic features are towering cliffs of columnar basalt, where hexagonal and pentagonal columns stack like organ pipes. Famous exposures near Pune, Mumbai, and Aurangabad draw geology students from across India, including exchange cohorts from the University of Adelaide and the Australian National University.

The region also hosts caves carved by ancient rivers into softer flow tops, laterite-capped mesas, and the gorge cut by the Narmada River. Hill forts such as Raigad and Sinhagad sit atop resistant flow units, and their fortification walls double as convenient exposures for tracing successive lava boundaries.

Soils, water, and weathering chemistry

Once basalt meets the monsoon climate, it weathers into distinctive soil types. The most famous is the black cotton soil, technically a Vertisol, which swells when wet and cracks deeply when dry. This behaviour stems from swelling clay minerals, particularly smectite.

The interlayered flows create complex aquifer systems that millions of people depend upon. Hydrologists from IIT Bombay and partners at the University of Western Australia have mapped how contaminants move through these fractured-rock aquifers, work equally relevant for managing aquifers beneath Perth's suburban fringe.

Fossils and the end-Cretaceous debate

Sedimentary layers sandwiched between lava flows preserve a remarkable fossil record. Lake and river deposits contain pollen, leaves, fish bones, and occasional dinosaur remains that document ecosystems flourishing just before the end-Cretaceous extinction. Intertrappean beds share genera with Late Cretaceous deposits from Australia, hinting at the close biogeographic connections that existed while the southern continents were separating.

Geochemical analyses reveal large releases of carbon dioxide and sulphur dioxide during eruption, compounds capable of driving sharp global warming followed by cooling and acid rain. This fingerprint is central to debates about whether the Traps were the primary driver of the end-Cretaceous extinction, a co-conspirator with the Chicxulub asteroid impact, or a less decisive accomplice. Sediment cores collected by CSIRO research vessels offer independent Australian climate archives for comparison.

Research approaches used in modern studies

Investigators now combine field mapping with high-precision laboratory techniques to extract information from these rocks. Australian collaborators at the University of Queensland have contributed expertise in argon-argon dating, complementing Indian capabilities and strengthening joint research programmes.

Common methods applied to the Traps include:

Distinctive features worth knowing

The province hosts a recognisable suite of features that researchers use as quick reference points. These elements also support practical applications, from construction materials to groundwater exploration.

Notable features include:

For a curious reader in Adelaide or Brisbane, the Deccan Traps may feel impossibly distant, yet their lessons arrive in everyday forms. The same mantle-plume dynamics that built the Indian plateau shaped flood-basalt provinces across the geological record, including remnants hidden beneath the pastoral landscapes of inland Australia. Recognising those connections deepens our sense of a planet whose continents share a restless, deeply volcanic past.

The publication's feedback page archives reader comments on geological topics ranging from mantle plumes to monsoon soils. A flat white in a Melbourne laneway café offers a quiet moment to consider that the basalt beneath your feet and the basalt beneath an Indian farmer's field are distant cousins, products of the same planetary engine still rumbling beneath our continents today.