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The previously accepted estimates for the areal extent (200,000 km2) and volume (325,000 to 382,000 km3) of the Columbia River Basalt Group (CRBG) have, upon reevaluation, been found to be too large. New area and volume estimates for 38 units that compose most of the CRBG indicate that it once covered an area of approximately 163,700 ± 5,000 km2 and has a volume of approximately 174,300 ± 31,000 km3. Our work further suggests that the volume of individual flows is huge, on average exceeding hundreds of cubic kilometers. The maximum known volume of an individual flow exceeds 2,000 km3, and some flows may have volumes on the order of 3,000 km3. Typically such huge-volume flows (here termed “great flows”) were able to travel hundreds of kilometers from their vents, with some flows known to have advanced more than 750 km. The eruption of great flows generally ceased with the end of Wanapum volcanism. The extent and volume of great flows qualifies them as the largest known terrestrial lava flows.

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