Spread across the states of Washington, Oregon and Idaho, the Columbia Plateau was formed by the Grande Ronde lava flows, which produced enough molten basalt to sink the Earth’s crust. The research – by authors Steve Reidel of Washington State University and Tiffany Barry of the UK’s Open University – which appeared in the journal Lithos, suggests that these eruptions happened far more quickly than geologists previously thought.

Using precise equipment, Barry analysed basalt samples from the Grande Ronde flows and compared argon isotopes of the oldest, deepest levels to those of the younger, shallower levels, using the decay rate to work out the relative ages of the rocks. The results suggest that the eruptions occurred between 15.6 million and 16 million years ago over a period of about 420,000 years – the previous estimate was that it took a period of 1.5 million to two million years.

The researchers believe that a single one of the 100 or so flows would have covered the area in 10,000 cubic kilometres of lava – 10,000 times the volume of ash produced by the eruption of Mount St Helens in 1980 – reaching a temperature of almost 1,100°C and taking half a century to cool.

This process would have generated monsoons across the region and emitted enough heat and sulphur to affect the Earth’s climate.

June 2010