A comparative account of the flood basalt volcanism of the Columbia Plateau and Eastern Iceland
An introduction to the flood basalt volcanism of the Columbia Plateau and Eastern Iceland is followed by more detailed comparative notes. These stress that the volcanism in the two areas was of the same general type. In both regions sub-aerial fissure eruptions gave rise to very extensive basalt flows, particularly on the Columbia Plateau, where some individual lavas cover more than 10,000 km2. The feeding fissures were localized in swarms, and this led in each case to the development of thick, low, shield-like accumulations of flows over the source areas. Progressive (isostatic?) subsidence of the central parts of the basalt pile accentuated the natural tendency for the succession to be thickest in the neighborhood of the feeding fissure swarms. Related differentiates were erupted from the central parts of the fissure vent areas, while olivine-rich basalt flows were apparently often erupted from the edges of the main swarm.Volcanism in Iceland is clearly directly related to the tensional stresses associated with part of the world ridge-rift system. However, this does not appear to be the case on the Columbia Plateau. Consequently it is suggested that flood basalt volcanism of the type described above is simply related to tensional zones in the crust and not directly to the ridge-rift system.