New research led by The Open University suggests that the volcanic birth of America’s Northwest Columbia Plateau happened much more quickly than previously thought and with an intensity that may have changed the earth’s climate and led to the extinction of some plants and animals.
The lead author of the report published in the journal Lithos, Dr Tiffany Barry of The Open University, said: “Take the inconvenience of the recent Iceland eruption and multiply it by many, many orders of magnitude. The research refines the time frame of the Grande Ronde lava flows, which produced enough molten basalt to sink the earth’s crust and create the vast Columbia River Plateau of Washington, Oregon and Idaho.
The research team, a collaboration between The Open University and Washington State University, dated the Grande Ronde flows by examining basalt samples from outcrops in the centre of Washington State with those at the border with Oregon. With some of the most precise equipment in the world, Dr Barry compared argon isotopes in the oldest, deepest levels and younger, shallower levels and used the element’s decay rate to determine the rocks’ relative ages.
Scientists have long known that thick sheets of molten basalt emerged from present-day eastern Washington, Oregon and Idaho, mainly between 17 and 14 million years ago. The new research estimates that about two-thirds of that material emerged in less than half a million years.
The research suggests the Grande Ronde flows took place between 15.6 and 16 million years ago. The youngest and oldest rock samples were only 420,000 years apart at the most. With a margin of error of 180,000 years, the rock may have been created over an even faster time frame of 240,000 years.
Just one of the 100 or so lava flows would have blanketed much of Washington State in 10,000 cubic kilometres of lava—10,000 times the volume of ash produced by the 1980 eruption of Mount St Helens. The flows moved at walking speed, giving enough time for horses and other animals of the region to get out of their path. But a single flow travelled as far as 400 miles, the same distance as from London to Edinburgh, had a temperature of more than 1,000 degrees Celsius and took half a century to cool. In the process, it would have generated monsoons across Northwest America and had a global impact on climate.
Substantial evidence has implicated other lava flows in the extinction of species. Siberian flows coincided with the epic Permian-Triassic “mass dying” that wiped out 96 percent of the earth’s marine species 250 million years ago. A mass extinction at the end of the Triassic Period 200 million years ago coincided with lava coming out of the Central Atlantic Magmatic Province between what is now north-eastern South America and eastern North America. And gases from flows on India’s Deccan Plateau started a mass extinction some 65 million years ago, with the dinosaur-killing coup de grâce coming from a meteoroid that hit Mexico’s Yucatán Peninsula.
The Grande Ronde had so many flows, with some much larger than others, that it is likely they had a far greater impact on the climate of their era than previously thought. Significantly the researchers noted that: “Some flows may have, at times, been simultaneous and, if so, would have had significant implications for potential environmental effects.” Intriguingly, the new dates coincide with changes in sea water chemistry and life forms in the Atlantic, noted last year in the journal Geology by scientists from the British Geological Survey. “Now we know when the eruptions occurred, we hope more work can be done on the planet’s sediments and fossils to find out what changes occurred in this brief bit of time,” said Dr Barry.
The Lithos article is available via The Open University’s Open Research Online repository: click here
Notes to editors
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