Siberian Traps: The Volcanic Eruptions Behind the Great Dying

The Siberian Traps are an enormous body of volcanic rock in central and northern Siberia, formed by flood basalt eruptions and underground intrusions about 252 to 251 million years ago. They are one of the largest volcanic provinces in Earth’s history. Because their main phase coincided almost exactly with the end-Permian mass extinction, the worst biological crisis known, the Siberian Traps are widely regarded as the trigger of the event often called the Great Dying.

What the Siberian Traps are

Flood basalts are not the cone-shaped volcanoes most people picture. Instead, runny basaltic lava pours out of long fissures in the ground, spreading in sheets that can each cover thousands of square kilometres. Repeated over hundreds of thousands of years, these sheets stack into thick piles of rock. Geologists call such regions large igneous provinces.

The name “traps” comes from the Swedish word trappa, meaning stair. When thick lava piles are eroded, harder and softer layers wear away at different rates and leave stepped hillsides and flat-topped mountains. The Putorana Plateau, east of the city of Norilsk, shows this landscape especially well, with canyons cut through basalt layers that are more than 3 kilometres thick in places.

The exposed lavas and related rocks cover roughly 2 million square kilometres today. Much more lies hidden beneath younger sediments of the West Siberian Basin or has been worn away. Estimates of the original extent therefore vary widely, commonly from about 5 to 7 million square kilometres, and estimates of total magma volume range from about 1 to 4 million cubic kilometres.

How the eruptions happened

Not all of the magma reached the surface. A large share was injected sideways into the sedimentary layers of the Tunguska Basin, where it cooled as flat sheets called sills. These sills matter as much as the lavas, because of the rocks they cut through.

The Tunguska Basin contained thick deposits of coal, oil-bearing shale, limestone and dolomite, and rock salt. When hot magma came into contact with these sediments, it baked them and released large volumes of carbon dioxide, methane and halogen compounds containing chlorine and bromine. Gas pressure blasted out vertical structures called breccia pipes, hundreds of which have been mapped in the region. Work by Henrik Svensen and colleagues, published in 2009, argued that this gas venting was a key link between the volcanism and the environmental crisis.

What caused such a huge outpouring of magma is less certain. Many geologists favour a mantle plume, a column of unusually hot rock rising from deep inside the Earth. Others have proposed alternatives involving processes in the upper mantle or at the edges of thick continental crust. The debate is unresolved, but it does not affect the dating of the eruptions or their environmental effects.

How they were dated

Linking the Siberian Traps to the extinction depended on precise dating. In 1991 Paul Renne and Asish Basu used argon-argon dating to show that the lavas were erupted rapidly and close to the Permian–Triassic boundary. Later studies refined the picture using uranium-lead dating of tiny crystals of zircon and perovskite, minerals that lock in uranium when they form.

In 2015 Seth Burgess and Samuel Bowring published a high-precision timeline. Their results suggested that a large volume of lava had already erupted before the extinction began, that magmatism continued through the extinction, and that it went on for around half a million years afterwards. A 2017 study by Burgess, James Muirhead and Bowring argued that the start of widespread sill intrusion, rather than the earliest lavas, coincided with the onset of the extinction about 251.9 million years ago.

That timing fits the gas-release model. Lava erupting at the surface releases gases already dissolved in magma, but sills baking coal and carbonate sediments could release far greater amounts of carbon very quickly.

Effects on the planet

The carbon released by the Siberian Traps drove rapid global warming. Oxygen isotope studies of fossil conodonts, tiny tooth-like structures of extinct eel-like animals, suggest that tropical sea-surface temperatures rose by roughly 8 to 10 °C, reaching levels lethal to many marine organisms.

Warmer oceans hold less oxygen, and large areas of the seas became oxygen-poor or anoxic. Carbon dioxide dissolving in seawater made the oceans more acidic, harming animals that build shells and skeletons from calcium carbonate. On land, halogen gases may have damaged the ozone layer, and some researchers link deformed fossil pollen and spores from this time to increased ultraviolet radiation, though this remains debated.

Sediments around the world from the extinction interval also record a sharp shift in carbon isotopes and spikes in mercury. Mercury is released by volcanic activity and by heating coal, so these spikes are used as a chemical fingerprint of the Siberian Traps far from Siberia. The full story of the extinction itself is told in the article on the Permian–Triassic extinction.

Comparison with other flood basalts

The Siberian Traps are one of several large igneous provinces linked with mass extinctions. About 201 million years ago, the Central Atlantic Magmatic Province erupted as the supercontinent split apart and coincided with the Triassic–Jurassic extinction. About 66 million years ago, India’s Deccan Traps were erupting when the Chicxulub asteroid impact ended the age of dinosaurs.

Not every flood basalt caused a mass extinction. Scientists think the Siberian case was unusually severe because so much magma intruded into carbon-rich and salt-rich sediments, and because it happened on Pangaea, a single supercontinent with a climate and ocean circulation that may already have been vulnerable.

Legacy and economic importance

The Siberian Traps are also one of the world’s great ore regions. Intrusions linked to the province near Norilsk and Talnakh host very large deposits of nickel, copper and platinum-group metals, which have been mined since the twentieth century and make Norilsk one of the most important metal-producing areas on Earth.

The Putorana Plateau was inscribed as a UNESCO World Heritage Site in 2010 for its untouched Arctic and subarctic landscapes, lakes and wildlife. For geologists, the region remains a key natural laboratory for understanding how volcanism can change climate on a global scale.

Timeline

• c. 252.2 million years ago: Major flood basalt eruptions are under way in Siberia, according to uranium-lead dating.
• c. 251.9 million years ago: Widespread intrusion of sills into the Tunguska Basin begins, coinciding with the onset of the end-Permian mass extinction.
• c. 251.9 million years ago: The Permian Period ends and the Triassic begins; the main extinction pulse lasts tens of thousands of years.
• c. 251.5–251.3 million years ago: Siberian magmatism wanes after continuing for several hundred thousand years beyond the extinction.
• 1991: Paul Renne and Asish Basu publish argon-argon dates linking the traps to the Permian–Triassic boundary.
• 2010: The Putorana Plateau is added to the UNESCO World Heritage List.
• 2015: Seth Burgess and Samuel Bowring publish a high-precision uranium-lead timeline of the eruptions.

Why it matters

The Siberian Traps show that volcanic activity on a continental scale can alter the atmosphere, oceans and climate enough to destroy most life on Earth. Because the extinction was driven largely by a rapid release of carbon, the episode is often studied as a deep-time comparison for how the Earth system responds to large carbon emissions, even though the scale and causes differ greatly from today.