The Deccan Traps: A Lava Flow the Size of France

How big are the Deccan Traps, and where did the name come from?

The Deccan Traps are a massive volcanic flood-basalt province, formed entirely by repeated lava flows over time:

• They cover roughly 500,000 sq km today, an area comparable to France. Erosion has shrunk them from an original extent of about 1.5 million sq km.
• The basalt layers reach up to 2 km thick in places. They spread across Maharashtra, Madhya Pradesh, Gujarat, Karnataka, and parts of Andhra Pradesh.
• “Trap” comes from the Swedish word “trappa,” meaning stairs, describing the stepped, terraced landscape these repeated lava flows create.
• This stepped terracing is genuinely visible in satellite imagery, giving the landscape a distinctive layered look.

When exactly did the eruption begin?

• Eruption began around 66 million years ago, right at the exact boundary between the Cretaceous and Paleogene periods.
• This K-Pg boundary marks the mass extinction that wiped out the non-avian dinosaurs entirely.

How long did the eruption last, and how much lava came out?

• The main eruptive pulse lasted roughly one million years, a brief window in geological terms, spanning the K-Pg boundary.
• Total erupted magma volume exceeded a million cubic kilometres, among the largest flood-basalt events in Earth’s history.
• Many geologists link the eruption to India’s tectonic plate passing directly over the Réunion hotspot, a fixed plume of rising mantle material still active today, now under the island of Réunion.

Why did lava spread into flat plateau, not tall volcanic peaks?

• These flood basalts erupted from long, linear fissures rather than a single central volcanic cone.
• This basaltic lava was extremely fluid, letting it spread across huge distances quickly rather than piling up into a tall cone.
• That fluidity is exactly why the Deccan region ended up as broad, layered plateau terrain, not a chain of tall volcanic peaks.
• Weathering of this same basalt over millions of years produced the fertile Black (Regur) Soil found across the Deccan Plateau today, well suited to growing cotton.

What is the case for Deccan volcanism causing the extinction?

• Scientists still debate whether the Chicxulub asteroid impact or Deccan volcanism caused the mass extinction. Both events occurred at almost exactly the same time, roughly 66 million years ago.
• Different dating methods have produced conflicting eruption sequences. Some studies place the main eruptions after Chicxulub; others find major pulses beginning well before it.
• Massive volcanic gas releases from eruptions like this can disrupt global climate for thousands of years afterward, offering a plausible extinction mechanism on their own.
• Roughly two-thirds of the original 1.5-million-sq-km lava field has eroded away entirely, over the 66 million years since it formed.

What other landscape features trace back to this same eruption?

• Much of the Western Ghats escarpment formed along the western edge of these same lava flows, giving that range part of its steep profile.
• Cooling lava sometimes cracked into hexagonal basalt columns, similar in structure to Northern Ireland’s Giant’s Causeway, visible at several Deccan sites today.

Where can you actually see Deccan basalt inside a modern city?

Mumbai’s own black basalt bedrock is a direct legacy of the Deccan Traps eruptions, a tangible link between a modern megacity and a 66-million-year-old mass extinction event. (Source: NDTV, September 3, 2026)

• Basalt is exposed at sites including Borivali in Sanjay Gandhi National Park, and the Elephanta Caves are themselves carved directly from Deccan basalt.
• A 2015 study led by UC Berkeley’s Mark Richards proposed that Chicxulub’s seismic energy may have reached through Earth’s upper mantle and helped trigger Deccan eruptions, though Deccan volcanism was already under way before the impact.
• This is a live, dated illustration of the Deccan-versus-Chicxulub debate, now grounded in the literal rock beneath one of India’s largest cities.