The Deccan Traps and the K/T Extinction

The volcanism that formed the Deccan Traps was clearly a major event, which would have had significant environmental impacts. These would have included all the effects mentioned in the article: acid rain from SO₂ emissions, enhanced greenhouse warming from the release of CO₂, and global cooling from the formation of aerosols – clearly, a complex series of effects.

Nevertheless, the eruption of the Deccan Traps at the end of the Cretaceous was not the only, or the largest, superplume volcanic event to occur during the Cretaceous. Evolving Life and the Earth (ELE) describes the Cretaceous as a greenhouse world created by intraplate volcanic outgassing from the Pacific superplume during mid-Cretaceous time. This event is known to have created the giant submarine plateaux of the Pacific, such as the Ontong-Java Plateau (see Fig. 4.21, ELE). This superplume volcanism in the Pacific created volcanoes that reached sea level (ELE, p. 159), and the effects of the outgassing of CO₂ and SO₂ to the atmosphere would have been similar to that of the Deccan Traps, though on a larger scale and spread over a greater period of time. The question arises, "If greenhouse warming induced by superplume volcanism has been responsible for mass extinctions, why did the Cretaceous mass extinction not occur in response to the Pacific superplume event, instead of waiting until the Deccan Traps event?"

One could also argue (as in Activity 4.1, The Dynamic Earth) that the degree of global warming induced by the Deccan Traps volcanism would not have been very great (about 0.75° C). Its effect on atmospheric CO₂ levels and GMST would have been muted because the superplume volcanism earlier in the Cretaceous meant that the atmosphere already had a larger concentration of CO₂, and GMST was higher, than it would otherwise have been when the Deccan Traps event occurred.