HR: 17:45h
AN: V44B-07    [Abstracts]
TI: Rethinking Volcanic Rifts on the East Snake River Plain
AU: * Helm-Clark, C M
EM: helmcc@inel.gov
AF: Idaho National Laboratory, PO Box 1625 MS 2107, Idaho Falls, ID 83415-2107 United States
AB: There is no agreement on the number and character of volcanic rifts on the East Snake River Plain (ESRP). Previous studies have enumerated rifts on the ESRP from three to over twenty. Criteria for rifts also vary greatly, including everything from mappable vent and fissure trends to buried near-vent facies which divert ground water flow. The research results presented here are criteria that classify ESRP rifts as active or inactive, eruptive or non-eruptive. Active rifts are those with mappable Quaternary or latest Pleistocene features such as surface flows and/or scarps, concentrated deposits of near-vent facies, and are associated with elevated topography almost without exception, though such uplifts are as subdued as the rest of the mostly-flat ESRP. Young vents are strongly correlated with steepest elevation gradients whereas correlations between rifts and heat flow are inconclusive due to the thick basalt-hosted Snake River Aquifer which masks regional heat flow. Using elevation criteria potentially contradicts a previous hypothesis that rifts are on-plain extensions of Basin and Range faults. Inactive rifts are more difficult to define. Lines of vents in kipukas are easiest to identify. Trends in the subsurface such as scoria recovered in drill cores can also be diagnostic though identifying of these features on wireline logs is inconclusive without some integration with core. Using diversions from the regional trend of groundwater flow as a criterion is currently problematic since not all rifts are associated with such trends and not all groundwater flow diversions are associated with recognizable buried rift facies.
DE: 0915 Downhole methods
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8486 Field relationships (1090, 3690)
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005