Prehistoric life
Flood basalt eruptions are a type of large-scale volcanic activity, both in terms of extent and duration, that can occur on land or on the ocean floor. A flood basalt may continue to erupt for tens of thousands - possibly millions - of years and the lava can cover hundreds of thousands of kilometres. Large plateaux and mountains can result from the huge volume of newly surfaced rock. The huge volume of lava is accompanied by a similarly large release of volcanic gases such as sulphur dioxide and carbon dioxide. These can affect climate and cause acid rain, so flood basalts are thought to be a potential cause of mass extinctions.
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Permian extinction explained
Loose ends are tied up at last to explain the Permian mass extinction.
The Permian mass extinction was caused by two things: volcanic eruptions and methane release. This programme was first shown in 2002.
Freeze and burn
Could the Permian flood basalt eruptions have caused mass extinction?
How might Permian flood basalt eruptions have caused mass extinction? The theory of rapid and dramatic temperature change - the initial cooling followed by global warming after a massive CO2 release - is explained. But would it have been enough to wipe out 95% of life on Earth? This programme was first shown in 2002.
Volcanic monster
Evidence of the world's biggest ever eruption lies in the Siberian Traps.
The Siberian Traps are the remnants of huge volcanic eruptions - flood basalt eruptions - that can last for millions of years and may have contributed to the devastating Permian mass extinction. This programme was first shown in 2002.
A flood basalt or trap basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava. Flood basalts have occurred on continental scales (large igneous provinces) in prehistory, creating great plateaus and mountain ranges. Flood basalts have erupted at random intervals throughout geological history and are clear evidence that the Earth undergoes periods of enhanced activity rather than being in a uniform steady state.
One proposed explanation for flood basalts is that they are caused by the combination of continental rifting and its associated decompression melting, in conjunction with a mantle plume also undergoing decompression melting, producing vast quantities of a tholeiitic basaltic magma. These have a very low viscosity, which is why they 'flood' rather than form taller volcanoes. Another explanation is that they result from the release, over a short time period, of melt that has accumulated in the mantle over a long time period.
The Deccan Traps of central India, the Siberian Traps, and the Columbia River Plateau of western North America are three regions covered by prehistoric flood basalts. The two largest flood basalt events in historic time have been at Eldgjá and Lakagigar, both in Iceland. The largest and best-preserved continental flood basalt terrain on Earth is part of the Mackenzie Large Igneous Province in Canada. The maria on the Moon are additional, even more extensive, flood basalts. Flood basalts on the ocean floor produce oceanic plateaus.
The surface covered by one eruption can vary from around 200,000 km² (Karoo) to 1,500,000 km² (Siberian Traps). The thickness can vary from 2000 metres (Deccan Traps) to 12,000 m[citation needed] (Lake Superior). These are smaller than the original volumes due to erosion.
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Cambrian period
Devonian period
Permian period
Triassic period
Jurassic period
Cretaceous period
Palaeocene epoch
Eocene epoch
Miocene epoch
