Ancient lava flows from Eastern Washington
April 29, 2010
From the tri-city herald — Lava flows that helped shape the sprawling Columbia River Plateau occurred faster than geologists previously believed and likely contributed to massive climate changes, said a Washington State University researcher.
Steve Reidel, research professor of geology at WSU Tri-Cities, British researcher Tiffany Barry and others studied so-called Grande Ronde basalt lavas in the plateau region, which covers much of eastern and central Washington, northeastern Oregon and parts of western Idaho.
Their studies indicate the Grande Ronde flows, which include at least 66 percent of the basalt in the Columbia River plateau, occurred over a period of about 420,000 years and between 15.6 million and 16 million years ago.
That’s faster than what geologists previously believed. And at least 110 eruptions occurred during that time frame, according to a paper Reidel co-authored with Barry for the international geological journal Lithos.
The researchers said the frequency and size of the eruptions likely had a widespread impact on the environment. Just one of the lava flows could have covered much of Washington with nearly 10,000 cubic kilometers of lava, which is about 10,000 times the volume of ash produced by the eruption of Mount St. Helens in 1980, according to WSU.
“We realize with the eruptions of these basalts that there was a lot of carbon dioxide, sulfur dioxide and chlorine that went into the air that had big environmental consequences,” Reidel said.
A single flow could have been as hot as 2,000 degrees and could have taken up to 50 years to cool. Reidel said that could have created monsoon rains in the Northwest and emitted plenty of heat and sulfur to alter the climate.
One result could have been the extinction of some plants and animals that lived at the time, although there has been little fossil evidence uncovered from lava flows to date aside from petrified wood.
“People are now starting to look for extinctions in the rock of this period in the Pacific Northwest,” Reidel said
Reidel said the flows likely were slow-moving enough for animals to outrun it and escape to higher ground in the Blue Mountains or Cascades.
“This was a golden age for horses, but there haven’t been any fossils found yet,” he said. “Petrified wood couldn’t run, but horses could.”
The belief that species were extinguished is based on evidence from other lava flows that occurred in the world millions of years ago, Reidel said.
For instance, a large extinction occurred during the end of the Triassic Period about 200 million years ago that coincided with lava flows coming from what is now northeastern South America and eastern North America, according to WSU. And gases from lava flows on India’s Deccan plateau initiated a mass extinction about 65 million years ago.
Reidel, who has been studying local rocks for years, and Barry — of Great Britain’s Open University — began collaborating more than five years ago. They got basalt samples from Hanford and outcroppings between Vantage and Lewiston, Idaho.
Grande Ronde basalt lavas were found stacked on each other with little or no accumulation of sediment, suggesting the succession of lava flows occurred quickly geologically, according to the manuscript to be published in Lithos.
Barry also compared argon isotopes in the oldest and deepest levels of the basalt to younger and shallower levels, and used the decay rate of the element to determine the relative ages of the rock.
Measurements of Grande Ronde basalt show it ranged from about 1,640 feet thick in some areas to almost 2.4 miles thick in others, producing enough basalt to sink the earth’s crust and create the Columbia River Plateau, according to the manuscript.
