DISSOLUTION OF COLUMBIA RIVER BASALT AND IMPLICATIONS OF CO₂ SEQUESTRATION

Flood basalt volcanism occurred in the Pacific Northwest between 17.5 and 6 Ma when over 300 basaltic lavas of the Columbia River Basalt Group were erupted from fissures in eastern Washington, eastern Oregon, and western Idaho. These flood-basalts cover over 200,000 km² and have an estimated volume of more than 234,000 km³. Many of the lavas were of extraordinary size with some exceeding 10,000 km³ and traveling many hundreds of kilometers westward from vent systems. The presence of naturally occurring siderite and calcite indicate that the basalt flows have reacted with CO₂ in the past. In order to understand these conditions and the potential for basalt to sequester greenhouse gases, we have under taken dissolution experiments. Steady-state dissolution rates of two samples of the Sentinel Bluffs Member, Grande Ronde Basalt were measured in a well-mixed batch reactor over a range of pH values (3.0 to 7.0) and temperatures (22º, 40º, 70º, and 90ºC). Results show that as the pH increases from 3 to 7, the dissolution rate decreases. When normalized by initial geometric surface area, the basalt samples have similar dissolution rates found in the literature for olivine, augite, anorthite, and basaltic glasses. These results show the potential basalt formations have to convert injected CO₂ into solid carbonate minerals.