TY - JOUR
T1 - The architecture, eruptive history, and evolution of the Table Rock Complex, Oregon
T2 - From a Surtseyan to an energetic maar eruption
AU - Brand, Brittany D.
AU - Clarke, Amanda
N1 - Funding Information:
The authors would like to thank Grant Heiken for suggesting this field area and spending several days in the field with B.B. We are especially grateful for the assistance of Mike, Jean, and Josh Bandfield, and Adam Frus in the field during summer 2006. This work greatly benefited from the thorough and insightful reviews of John Smellie and Corina Risso, and guest editor Károly Németh. Funding for this research was provided by an Arizona NASA Space Grant Consortium Student Fellowship, and the National Science Foundation, USA (EAR 0538125).
PY - 2009/3/10
Y1 - 2009/3/10
N2 - The Table Rock Complex (TRC; Pliocene-Pleistocene), first documented and described by Heiken [Heiken, G.H., 1971. Tuff rings; examples from the Fort Rock-Christmas Lake valley basin, south-central Oregon. J. Geophy. Res. 76, 5615-5626.], is a large and well-exposed mafic phreatomagmatic complex in the Fort Rock-Christmas Lake Valley Basin, south-central Oregon. It spans an area of approximately 40 km2, and consists of a large tuff cone in the south (TRC1), and a large tuff ring in the northeast (TRC2). At least seven additional, smaller explosion craters were formed along the flanks of the complex in the time between the two main eruptions. The first period of activity, TRC1, initiated with a Surtseyan-style eruption through a 60-70 m deep lake. The TRC1 deposits are dominated by multiple, 1-2 m thick, fining upward sequences of massive to diffusely-stratified lapilli tuff with intermittent zones of reverse grading, followed by a finely-laminated cap of fine-grained sediment. The massive deposits are interpreted as the result of eruption-fed, subaqueous turbidity current deposits; whereas, the finely laminated cap likely resulted from fallout of suspended fine-grained material through a water column. Other common features are erosive channel scour-and-fill deposits, massive tuff breccias, and abundant soft sediment deformation due to rapid sediment loading. Subaerial TRC1 deposits are exposed only proximal to the edifice, and consist of cross-stratified base-surge deposits. The eruption built a large tuff cone above the lake surface ending with an effusive stage, which produced a lava lake in the crater (365 m above the lake floor). A significant repose period occurred between the TRC1 and TRC2 eruptions, evidenced by up to 50 cm of diatomitic lake sediments at the contact between the two tuff sequences. The TRC2 eruption was the last and most energetic in the complex. General edifice morphology and a high percentage of accidental material suggest eruption through saturated TRC1 deposits and/or playa lake sediments. TRC2 deposits are dominated by three-dimensional dune features with wavelengths 200-500 m perpendicular to the flow, and 20-200 m parallel to the direction of flow depending on distance from source. Large U-shaped channels (10-32 m deep), run-up features over obstacles tens of meters high, and a large (13 m) chute-and-pool feature are also identified. The TRC2 deposits are interpreted as the products of multiple, erosive, highly-inflated pyroclastic surges resulting from collapse of an unusually high eruption column relative to previously documented mafic phreatomagmatic eruptions.
AB - The Table Rock Complex (TRC; Pliocene-Pleistocene), first documented and described by Heiken [Heiken, G.H., 1971. Tuff rings; examples from the Fort Rock-Christmas Lake valley basin, south-central Oregon. J. Geophy. Res. 76, 5615-5626.], is a large and well-exposed mafic phreatomagmatic complex in the Fort Rock-Christmas Lake Valley Basin, south-central Oregon. It spans an area of approximately 40 km2, and consists of a large tuff cone in the south (TRC1), and a large tuff ring in the northeast (TRC2). At least seven additional, smaller explosion craters were formed along the flanks of the complex in the time between the two main eruptions. The first period of activity, TRC1, initiated with a Surtseyan-style eruption through a 60-70 m deep lake. The TRC1 deposits are dominated by multiple, 1-2 m thick, fining upward sequences of massive to diffusely-stratified lapilli tuff with intermittent zones of reverse grading, followed by a finely-laminated cap of fine-grained sediment. The massive deposits are interpreted as the result of eruption-fed, subaqueous turbidity current deposits; whereas, the finely laminated cap likely resulted from fallout of suspended fine-grained material through a water column. Other common features are erosive channel scour-and-fill deposits, massive tuff breccias, and abundant soft sediment deformation due to rapid sediment loading. Subaerial TRC1 deposits are exposed only proximal to the edifice, and consist of cross-stratified base-surge deposits. The eruption built a large tuff cone above the lake surface ending with an effusive stage, which produced a lava lake in the crater (365 m above the lake floor). A significant repose period occurred between the TRC1 and TRC2 eruptions, evidenced by up to 50 cm of diatomitic lake sediments at the contact between the two tuff sequences. The TRC2 eruption was the last and most energetic in the complex. General edifice morphology and a high percentage of accidental material suggest eruption through saturated TRC1 deposits and/or playa lake sediments. TRC2 deposits are dominated by three-dimensional dune features with wavelengths 200-500 m perpendicular to the flow, and 20-200 m parallel to the direction of flow depending on distance from source. Large U-shaped channels (10-32 m deep), run-up features over obstacles tens of meters high, and a large (13 m) chute-and-pool feature are also identified. The TRC2 deposits are interpreted as the products of multiple, erosive, highly-inflated pyroclastic surges resulting from collapse of an unusually high eruption column relative to previously documented mafic phreatomagmatic eruptions.
KW - Surtseyan
KW - Table Rock Complex
KW - base surge
KW - maar
KW - phreatomagmatic
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U2 - 10.1016/j.jvolgeores.2008.10.011
DO - 10.1016/j.jvolgeores.2008.10.011
M3 - Article
AN - SCOPUS:61849182594
SN - 0377-0273
VL - 180
SP - 203
EP - 224
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
IS - 2-4
ER -