of these radioactive elements that can be leached from wastes disposed of in salt repositories. To set upper limits, data are needed for solid phases that form readily, have low solubilities, and either are present in wastes (spent fuel, waste glasses, etc.) or can form readily in the geologic environment. Factors that would lower the maximum concentrations in leachates include an increase in the crystallinity of amorphous precipitates, the presence of crystalline solids in the wastes, and the formation of solid solutions of the actinides. 11 refs.
Following the May 2000 Cerro Grande fire at Los Alamos, NM, surface water control structures were constructed near Los Alamos to mitigate the transport of contaminant‐bearing sediment toward the Rio Grande river due to increased runoff caused by the removal of vegetation by the fire. A low‐head weir was constructed in Los Alamos Canyon, 5 km to the east of Los Alamos, to capture contaminant‐bearing sediments and to allow runoff to pass downstream without significant ponding behind the weir. During construction of the weir, channel alluvium was removed and the underlying fractured basalt was exposed. To monitor any downward transport of contaminants into fractured basalt, and potentially downward to the regional groundwater, three boreholes (one vertical, and two angled) were installed for environmental monitoring. An innovative monitoring system was installed using FLUTe (Santa Fe, NM) liners for both vadose zone and perched groundwater zones. The vertical borehole intersects several perched water zones, and groundwater can be sampled from four ports. One angled borehole has an inflatable liner with sensors to measure relative water content. The second angled borehole was abandoned. Tracer tests were initiated in April 2002 and June 2003 with the application of solutions of potassium bromide and potassium iodide, respectively, onto the basin floor above the weir. The hydrogeologic characterization from drilling the boreholes, in conjunction with groundwater elevation and vadose zone moisture monitoring, and results from the tracer tests show that the subsurface hydrogeology is complex, and surface water and perched groundwater systems are in apparent close communication. Infiltration is rapid, and movement from the surface to the deepest perched zone (at a depth of 78 m) occurs within 8 to 14 d. Downward flow occurs predominantly via fracture flow.
Research Article| July 01, 2008 Orogen-parallel extension and exhumation enhanced by denudation in the trans-Himalayan Arun River gorge, Ama Drime Massif, Tibet-Nepal Micah J. Jessup; Micah J. Jessup * 1Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 37996, USA * E-mail: mjessup@utk.edu. Search for other works by this author on: GSW Google Scholar Dennis L. Newell; Dennis L. Newell 2Hydrology, Geochemistry and Geology Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar John M. Cottle; John M. Cottle 3Department of Earth Sciences, University of Oxford, Oxford OX1 3PR, UK Search for other works by this author on: GSW Google Scholar Aaron L. Berger; Aaron L. Berger 4Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA Search for other works by this author on: GSW Google Scholar James A. Spotila James A. Spotila 4Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA Search for other works by this author on: GSW Google Scholar Geology (2008) 36 (7): 587–590. https://doi.org/10.1130/G24722A.1 Article history received: 28 Dec 2007 rev-recd: 04 Mar 2008 accepted: 11 Mar 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Micah J. Jessup, Dennis L. Newell, John M. Cottle, Aaron L. Berger, James A. Spotila; Orogen-parallel extension and exhumation enhanced by denudation in the trans-Himalayan Arun River gorge, Ama Drime Massif, Tibet-Nepal. Geology 2008;; 36 (7): 587–590. doi: https://doi.org/10.1130/G24722A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Focused denudation and mid-crustal flow are coupled in many active tectonic settings, including the Himalaya, where exhumation of mid-crustal rocks accommodated by thrust faults and low-angle detachment systems during crustal shortening is well documented. New structural and (U-Th)/He apatite data from the Mount Everest region demonstrate that the trans-Himalayan Ama Drime Massif has been exhumed at a minimum rate of ~1 mm/yr between 1.5 and 3.0 Ma during orogen-parallel extension. The Ama Drime Massif offsets the South Tibetan detachment system, and therefore the South Tibetan detachment system is no longer capable of accommodating south-directed mid-crustal flow or coupling it with focused denudation. Previous investigations interpreted the NNE-SSW–striking shear zone on the west side of the Ama Drime Massif as the Main Central thrust zone; however, our data show that the Ama Drime Massif is bounded on either side by 100–300-m-thick normal-sense shear zone and detachment systems that are kinematically linked to young brittle faults that offset Quaternary deposits and record active orogen-parallel extension. When combined with existing data, these results suggest that the Ama Drime Massif was exhumed during orogen-parallel extension that was enhanced by, or potentially coupled with, denudation in the trans-Himalayan Arun River gorge. This model provides important insights into the mechanisms that exhumed trans-Himalayan antiformal structures during orogen-parallel extension along the southern margin of the Tibetan Plateau. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
