New research suggests the volcanic birth of the Northwest's Columbia Plateau happened much more quickly than previously thought and with an intensity that may have changed the earth's climate and caused some plants and animals to go extinct.
"What you're looking at are lava flows that repeat fairly quickly," said Steve Reidel, research professor of geology at Washington State University Tri-Cities. "Not decades or centuries, but months or years."
Reidel is a co-author of a paper in the recent issue of the journal Lithos refining the time frame of the Grande Ronde lava flows, which produced enough molten basalt to sink the earth's crust and created the vast Columbia River Plateau of Washington, Oregon and Idaho.
Just one of the 100 or so lava flows would have blanketed much of Washington State in 10,000 cubic kilometers of lava -- 10,000 times the volume of ash produced by the 1980 eruption of Mount St. Helens.
The flows moved at walking speed, enough time for the horses and other animals of the region to get out of their path. But a single flow could reach as far as Portland, be more than 2,000 degrees Fahrebheit and take half a century to cool. In the process, it would have generated monsoons across the Northwest and emitted enough heat and sulfur to alter the earth's climate, said Reidel.
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 northeastern South America and eastern North America. 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.
To date the Grande Ronde flows, lead author Tiffany Barry of Britain's Open University obtained basalt samples from Hanford, Wash., and outcrops between Vantage, Wash., and Lewiston, Idaho. With some of the most precise equipment in the world, she 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.
Barry, Reidel, WSU Professor Emeritus Peter Hooper and other colleagues estimated the Grande Ronde flows took place between 15.6 and 16 million years ago, give or take 150,000 to 200,000 years. 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.
With less accurate equipment, Reidel and others previously estimated the flows occurred over a period of 1.5 to 2 million years. And because the Grande Ronde had so many flows, with some much larger than others, they likely had a far greater impact on the climate of their era than previously thought.
Some flows, wrote the researchers, "may have, at times, been simultaneous and, if confirmed, would have significant implications for potential environmental effects."
"It's an interesting piece of work and definitely a contribution," said John Wolff, a WSU professor in the School of Earth and Environmental Sciences, who was not involved in the paper. Both Wolff and the paper's authors note that the argon dating conflicts with dates established by looking at how changes in the earth's magnetic field affected the rock.
If the argon dating holds up, Wolff said, it will coincide with changes in the life forms and chemistry in the Atlantic Ocean. Just last summer, British researchers writing in the journal "Geology" described evidence of such changes off the west coast of Africa and singled out the Grande Ronde basalt flows as a possible cause.
- T.L. Barry, S. Self, S.P. Kelley, S. Reidel, P. Hooper, M. Widdowson. New 40Ar/39Ar dating of the Grande Ronde lavas, Columbia River Basalts, USA: Implications for duration of flood basalt eruption episodes. Lithos, 2010; DOI: 10.1016/j.lithos.2010.03.014
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