The Deccan Traps is a large igneous province of west-central India (17–24°N, 73–74°E). It is one of the largest volcanic features on Earth, taking the form of a large shield volcano. It consists of numerous layers of solidified flood basalt that together are more than about thick, cover an area of about , and have a volume of about . Originally, the Deccan Traps may have covered about , with a correspondingly larger original volume. This volume overlies the Archean age Indian Shield, which is likely the lithology the province passed through during eruption. The province is commonly divided into four subprovinces: the main Deccan, the Malwa Plateau, the Mandla Lobe, and the Saurashtran Plateau.
The term trap has been used in geology since 1785–1795 for such rock formations. It is derived from the Swedish word for stairs (trapp) and refers to the step-like hills forming the landscape of the region. The name Deccan has Sanskrit origins meaning "southern".
Gondwana and opening of western Indian Ocean and Geology of India
The Deccan Traps began forming 66.25 million years ago, at the end of the Cretaceous period, although it is possible that some of the oldest material may underlie younger material. The bulk of the volcanic eruption occurred at the Western Ghats between 66 and 65 million years ago when lava began to extrude through fissures in the crust known as fissure eruptions. Determining the exact age for Deccan rock is difficult due to a number of limitations, one being that the transition between eruption events may be separated by only a few thousand years and the resolution of dating methods used is not able to pinpoint these events. In this way, determining the rate of magma emplacement is also difficult to constrain. This series of eruptions may have lasted for less than 30,000 years.
The original area covered by the lava flows is estimated to have been as large as , approximately half the size of modern India. The Deccan Traps region was reduced to its current size by erosion and plate tectonics; the present area of directly observable lava flows is around .