The Columbia River Basalt Group: A massive, rapid volcanic event that reshaped the Northwest.

Nature · Published 3 October 2026 Swipe more like this →

In short: Between 17 and 6 million years ago, a series of colossal volcanic eruptions flooded the Pacific Northwest with enough lava to create a plateau over a mile thick. These flows were so rapid they forced the Columbia River into its current path, leaving behind a vast, layered geological record.

The Columbia River Basalt Group (CRBG) stands as the youngest and best-preserved continental flood basalt province on Earth. During the Miocene epoch, roughly 174,300 cubic kilometers of lava engulfed over 163,000 square kilometers of the Pacific Northwest. While eruptions occurred over an 11-million-year span, the vast majority—over 99 percent—of this molten rock was released in a highly vigorous burst between 17 and 14 million years ago.

The mechanism behind this event is widely attributed to the Yellowstone hotspot. As the North American Plate drifted westward, the hotspot initiated massive basaltic volcanism near Steens Mountain. This upwelling of hot mantle plume material created magma that breached the surface through thousands of fissures. The sheer weight of these accumulating layers caused the Earth's crust to subside, forming the Columbia Basin. The flows were so extensive that they reached the Pacific Ocean, traveling hundreds of kilometers from their origin points.

Geologists have determined that these eruptions were remarkably rapid. Analysis of the 500-kilometer-long Ginkgo flow suggests it was emplaced in less than a week, maintaining a nearly uniform temperature throughout its journey. This speed prevented the lava from cooling prematurely, allowing it to cover vast distances as a laminar sheet. Today, these flows are exposed by the erosion of the Missoula Floods, providing a detailed, layered history of the region's volcanic past, including rare captures of geomagnetic field reversals preserved within the cooling rock.

Beyond the physical landscape, these eruptions had significant atmospheric consequences. Volcanic degassing released massive quantities of sulfur dioxide, hydrochloric acid, and hydrofluoric acid. For instance, the Roza flow alone is estimated to have emitted billions of tonnes of sulfur dioxide, which subsequently interacted with the atmosphere to produce sulfuric acid. This event remains a primary subject of study for understanding the relationship between large igneous provinces and global environmental shifts.

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