Ancient volcanic fissures in the Columbia River flood basalts, exposed by uplifting and erosion, are helping University of Oregon researchers understand how magma that repeatedly erupted 14-16 million years ago transformed the environment into its modern landscape.
In a paper in Nature Scientific Reports, a seven-member team that included UO earth scientists Ilya Bindeman and Leif Karlstrom also found evidence that may explain why greenhouse gases released into the air during the eruptions did not trigger a global extinction event.
The Columbia River flood basalts represent the youngest continental flood basalt province on Earth and one of the best preserved. It covers roughly 210,000 square kilometers, extending from Eastern Oregon and Washington to western Idaho and part of northern Nevada.
The team's insights came from analyses of oxygen and hydrogen isotopes in crustal material, a mix of magma and original rocks. Pivotal to the research, done in Bindeman's Stable Isotope Laboratory, were 27 samples from 22 different dikes, wall-like bodies of magma that cut through the sheeted lava flow landscape during the eruptions.
"We found that when hot basaltic magma intruded into the crust, the heat boiled groundwater and volatilized everything in and near its path, causing chemical and isotopic changes in the rocks and the release of greenhouse gases," said Bindeman, who led the study.
A 10-meter-thick feeder dike into the Wallowa Batholith, formed 16 million years ago from a mix of basaltic magma and granite, likely acted as a magma conduit for seven years. It formed one of the largest surface lava flows and chemically altered about 100 meters of surrounding bedrock. Heating effects may have lasted throughout the region for about 150 years after magma stopped flowing, the researchers concluded.
"The Columbia River basalts that are so dear to us in the Pacific Northwest," Bindeman said. "They are now uplifted and eroded to the level that allows us to sample the contacts of these basalts with the previous rocks. The same process today is happening every hour and every where under midocean ridges and also on continents. By studying these not-so-ancient rocks we have learned what is going on under our feet."
Computer modeling done with the chemical data suggests that the hydrothermal heating of the region's original metasedimentary rocks - a metamorphic rock formed through the deposition and solidification of sediment - and relatively low levels of organic matter would have generated the release of about 18 gigatons of carbon dioxide and methane. One gigaton equals a billion metric tons.
Each of the individual Columbia River basalt eruptions were 10 to 100 times stronger than the largest eruptions of Iceland's Eldgja and Laki volcanic eruptions in the years 934 and 1783, respectively, said study Karlstrom, who, along with Bindeman, is a member of the Oregon Center for Volcanology.
The Laki eruption, which killed thousands of people, released greenhouse gases that generated a year without summer followed by a warm year across Europe and North America, Karlstrom said.
While the Columbia River eruptions released 210,000 cubic kilometers of basaltic magma over 1.5 million years, leading to global climate impacts, they did not cause mass extinctions such as the one triggered by eruptions over a similar timescale that formed the Siberian Traps 250 million years ago.
The difference, Karlstrom said, is in the geology of the regions. The Columbia River eruptions occurred in igneous crust that contained low levels of organic matter that could be released by hydrothermal heating. Eruptions in the Siberian Traps occurred in sedimentary rocks rich in organic content.
Co-authors on the paper included Dylan P. Colón, who holds a doctorate from the UO and is now at the University of Geneva. Others are affiliated with the University of Bern and Moscow State University. The research was funded by the U.S., Russian and Swiss National Science Foundations.
