Reid 9628155 Since 1979, the resurgent dome of Long Valley caldera, California has risen more than 50 cm apparently due to the injection of 0.2 km3 of magma at depth. Floodplain geomorphology suggests that the Owens River, that circumvents the dome, oscillates between two parallel meander belts depending on whether the dome is inflated or deflated, and that the current uplift is part of a long term inflation that may total 15-35 meters. The central goal of the renewal proposal is to understand the inflation history of Long Valley and the nearby Inyo Crater eruptions over the past several millenia. The hope is that patterns between eruptions and Owens River avulsions in the past will clarify the potential for future eruptive activity. Efforts with NSF-RUI 91-17474 funding to determine a chronology for these oscillations have revealed three major findings: (1) In dating plant remains in abandoned channel system, with live aquatic plant "ages" as high as 13.3 kyr. Cation geochemistry and 13C in plants and waters suggest predominantly magmatic sources for the "dead" CO2 feeding these plants. Tree kills at Mammoth Mountain also manifest this CO2 release (Farrar et al, 1995) (2) Inyo Crater pumice fills an abandoned channel of the Owens River and contains charcoal apparently derived from trees charred during the pumice eruptions. This suggests a connection between Owens River avulsions and eruptions in the Inyo Craters. The chemical and petrographic stratigraphy of these pumices and the proposed AMS dates on their charcoals will allow the timing of past eruptions and avulsions to be determined, and estimates to be made of where the caldera stands today in terms of potential for similar activity in the future. (3) The topography of deformed shorelines of Pleistocene Long Valley Lake has been measured. The shorelines have recorded caldera floor deformation over longer time periods than the river channels; the data suggest that relatively little net uplift of the dome has occurred over the life of the lake. The proposed research seeks to complete the work that has been begun and includes: (1) synoptic14C, pH, alkalinity, dissolved ion determinations and discharge measurements with finer resolution at sites of major springs to quantify the "dead" CO2 emanations entering the streams, (2a) AMS 14C age determinations on charcoal in the pumice to time earlier river avulsions and associated pumice eruptions, (2b) XRF analyses of a large suite of pumicies to fingerprint them as to their site of origin, and (3) completion of the topographic surveying of the lake shores and dating of tufa cements in them by U-series dating to better understand the longer history of the dome. The results of this study offer valuable information about the recent tectonic history of Long Valley caldera, and perhaps give an indication of the caldera's potential behavior in the near future. They are thus of central concern to residents of Mammoth Lakes, CA. The study offers undergraduate students an excellent opportunity to investigate in the field and in the laboratory an important example of silicic volcanism.
