Trapps are piles of flood basalts that erupted as part of a volcanic plateau or large igneous province. Most flood basalts erupted subaerially to form thick (500 to more than 3,000 m thick) sequences that cover large areas of continental crust, up to 1.5 million km2 in the case of the largest one, the Siberian Traps.
The term “trapp” derives from the Swedish word for stairs, a reference to the step-like topography of the volcanic sequences. A major portion of the basalts erupted rapidly, often in less than one million years, and some are believed to have contributed directly or indirectly to mass extinctions such as those at the Permian-Triassic and Cretaceous-Tertiary boundaries, through the emission of large volume of toxic, SO2-rich gases or through the combustion of coals and coaly sediments, releasing large volumes of CO2into the atmosphere. Most authors believe that the trapps formed through the melting of large...