A new model for the emplacement of Columbia River basalts as large, inflated Pahoehoe Lava Flow Fields

Extensive flows of the Columbia River Basalt (CRB) Group in Washington, Oregon, and Idaho are dominantly inflated compound pahoehoe sheet lavas. Early studies recognized that CRB lavas are compound pahoehoe flows, with textures suggesting low flow velocities, but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks. However, small volume (< 1 km³) compound pahoehoe flows on Kilauea, Hawai'i, demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger (10–20 km3) pahoehoe flows in Iceland. The vertical distribution of vesicles and other morphologic features within CRB lava flows indicate that they grew similarly by inflation. Small pahoehoe lobes at the base and top of many CRB pahoehoe lava flows indicate emplacement in a gradual, piecemeal manner rather than as a single flood. We propose that each thick CRB sheet flow was active for months to years and that each group of flows produced by a single eruption (a flow field) was emplaced slowly over many years.

[1]  D. Swanson,et al.  Chemical data for flows and feeder dikes of the Yakima Basalt Subgroup, Columbia River Basalt Group, Washington, Oregon, and Idaho, and their bearing on a petrogenetic model , 1989 .

[2]  T. J. Griffin,et al.  A major lava tube system from Undara Volcano, North Queensland , 1975 .

[3]  Donald A. Swanson,et al.  Revisions in Stratigraphic Nomenclature of the Columbia River Basalt Group , 1979 .

[4]  J. P. Kauahikaua,et al.  Emplacement and inflation of pahoehoe sheet flows: observations and measurements of active lava flows on Kilauea volcano, Hawaii , 1994 .

[5]  T. Thordarson,et al.  The Laki (Skaftár Fires) and Grímsvötn eruptions in 1783–1785 , 1993 .

[6]  T. Thordarson.  Volatile release and atmospheric effects of basaltic fissure eruptions , 1995 .

[7]  R. Stothers.  Flood basalts and extinction events , 1993 .

[8]  H. Schmincke.  Stratigraphy and Petrography of Four Upper Yakima Basalt Flows in South-Central Washington , 1967 .

[9]  G. Walker.  Morphometric study of pillow-size spectrum among pillow lavas , 1992 .

[10]  P. Hooper,et al.  The Columbia River Basalts , 1982, Science.

[11]  Donald A. Swanson,et al.  Revisions to the estimates of the areal extent and volume of the Columbia River Basalt Group , 1989 .

[12]  M. Rampino,et al.  Flood Basalt Volcanism During the Past 250 Million Years , 1988, Science.

[13]  G. Walker,et al.  Structure, and origin by injection of lava under surface crust, of tumuli, “lava rises”, “lava-rise pits”, and “lava-inflation clefts” in Hawaii , 1991 .

[14]  L. Keszthelyi,et al.  Emplacement of the 75-km-long Carrizozo lava flow field, south-central New Mexico , 1993 .

[15]  J. G. Jones.  Pillow Lava and Pahoehoe , 1968, The Journal of Geology.

[16]  D. Swanson,et al.  Linear vent systems and estimated rates of magma production and eruption for the Yakima Basalt on the Columbia Plateau , 1975 .

[17]  T. Gregg,et al.  Quantification of submarine lava-flow morphology through analog experiments , 1995 .

[18]  G. Walker.  Compound and simple lava flows and flood basalts , 1971 .

[19]  S. Reidel,et al.  Eruption and emplacement of flood basalt: An example from the large-volume Teepee Butte Member, Columbia River Basalt Group , 1992 .

[20]  G. Walker.  Pipe vesicles in Hawaiian basaltic lavas: Their origin and potential as paleoslope indicators , 1987 .

[21]  D. Swanson,et al.  Regional correlation of Grande Ronde Basalt flows, Columbia River Basalt Group, Washington, Oregon, and Idaho , 1986 .

[22]  A. C. Waters,et al.  Stratigraphic and lithologic variations in the Columbia River basalt , 1961 .

[23]  D. W. Peterson,et al.  Transition of basaltic lava from pahoehoe to aa, Kilauea Volcano, Hawaii: Field observations and key factors , 1980 .