Columbia Plateau Province

| Subprovince index map | Columbia River Basalts | Snake River Plain |

Lava. The Columbia Plateau province is enveloped by one of the worlds largest accumulations of lava. Over 500,000 kilometers² of the Earth's surface is covered by it. The topography here is dominated by geologically young lava flows that inundated the countryside with amazing speed, all within the last 17 million years.

Columbia River basalts

Over 170,000 cubic kilometers of basaltic lava, known as the Columbia River basalts, covers the western part of the province. These tremendous flows erupted between 17-6 million years ago. Most of the lava flooded out in the first 1.5 million years—an extraordinarily short time for such an outpouring of molten rock.

Walls of basaltic lava line the Columbia River Gorge. View from the top of Beacon Rock, Washington. Photo by L. Topinka, Cascades Volcano Observatory, USGS.

It is difficult to conceive of the enormity of these eruptions. Basaltic lava erupts at no less than about 1100ºC. Basalt is a very fluid lava; it is likely that tongues of lava advanced at an average of 5 kilometers/hour—faster than most animals can run. Whatever topography was present prior to the Columbia River Basalt eruptions was buried and smoothed over by flow upon flow of lava.
Over 300 high-volume individual lava flows have been identified, along with countless smaller flows. Numerous linear vents, some over 150 kilometers long, show where lava erupted near the eastern edge of the Columbia River Basalts, but older vents were probably buried by younger flows.