Changes in major element hydrochemistry of the Pecos River in the American Southwest since 1935

The Pecos River, situated in eastern New Mexico and western Texas, receives water from a drainage area of 91 000 km². There are primarily two major water inputs, namely snowmelt from winter storms in the headwater region of the southern Rocky Mountains and runoff from warm-season monsoonal rainfall in the lower valley. The Pecos River suffers from high levels of total dissolved solids (TDS >5000 mg L⁻¹) under normal flow conditions. This not only poses serious problems for agricultural irrigation and safe drinking water supply, but also results in a permanent loss of biodiversity. This study examines changes in stream flow and water chemistry of the Pecos River over the last 70 a to better understand the long-term variability in stream salinity and the role of agricultural practices in salt transfer. A TDS record from the lower Pecos River near Langtry (Texas) back to 1935 was extracted to show a distinct pattern of decadal variability similar to the Pacific Decadal Oscillation (PDO), in which stream salinity is overall above average when the PDO is in positive (warm) phase and below average when the PDO is in negative (cold) phase. This is due to: (1) the dissolved salts contributed to the river are largely from dissolution of NaCl and CaSO₄-bearing minerals (e.g., halite and gypsum) in the upper basin, (2) the amount of the dissolved salts that reach the lower basin is mainly determined by the stream flow yield in the upper basin and (3) the stream flow yield from the upper basin is positively correlated with the PDO index. This further attests that large-scale climatic oscillation is the major source of long-term changes in stream flow and salinity of the Pecos River. On the other hand, there is also a strong indication that the rate of salt export has been affected by reservoir operations and water diversions for agricultural practices.     

Jurassic plume-origin ophiolites in Japan: accreted fragments of oceanic plateaus

The Mikabu and Sorachi–Yezo belts comprise Jurassic ophiolitic complexes in Japan, where abundant basaltic to picritic rocks occur as lavas and hyaloclastite blocks. In the studied northern Hamamatsu and Dodaira areas of the Mikabu belt, these rocks are divided into two geochemical types, namely depleted (D-) and enriched (E-) types. In addition, highly enriched (HE-) type has been reported from other areas in literature. The D-type picrites contain highly magnesian relic olivine phenocrysts up to Fo_93.5, and their Fo–NiO trend indicates fractional crystallization from a high-MgO primary magma. The MgO content is calculated as high as 25 wt%, indicating mantle melting at unusually high potential temperature (T _p) up to 1,650 °C. The E-type rocks represent the enrichment in Fe and LREE and the depletion in Mg, Al and HREE relative to the D-type rocks. These chemical characteristics are in good accordance with those of melts from garnet pyroxenite melting. Volcanics in the Sorachi–Yezo belts can be divided into the same types as the Mikabu belt, and the D-type picrites with magnesian olivines also show lines of evidence for production from high T _p mantle. Evidence for the high T _p mantle and geochemical similarities with high-Mg picrites and komatiites from oceanic and continental large igneous provinces (LIPs) indicate that the Mikabu and Sorachi–Yezo belts are accreted oceanic LIPs that were formed from hot large mantle plumes in the Late Jurassic Pacific Ocean. The E- and D-type rocks were formed as magmas generated by garnet pyroxenite melting at an early stage of LIP magmatism and by depleted peridotite melting at the later stage, respectively. The Mikabu belt characteristically bears abundant ultramafic cumulates, which could have been formed by crystal accumulation from a primary magma generated from Fe-rich peridotite mantle source, and the HE-type magma were produced by low degrees partial melting of garnet pyroxenite source. They should have been formed later and in lower temperatures than the E- and D-type rocks. The Mikabu and Sorachi Plateaus were formed in a low-latitude region of the Late Jurassic Pacific Ocean possibly near a subduction zone, partially experienced high P/T metamorphism during subduction, and then uplifted in association with (or without, in case of Mikabu) the supra-subduction zone ophiolite. The Mikabu and Sorachi Plateaus may be the Late Jurassic oceanic LIPs that could have been formed in brotherhood with the Shatsky Rise.     

Overview of Holocene Tsunami Deposits along the Nankai,Suruga, and Sagami Troughs,Southwest Japan

Tsunami deposits provide a basis for reconstructing Holocene histories of great earthquakes and tsunamis on the Pacific Coast of southwest Japan. The deposits have been found in the past 15 years at lakes, lagoons, outcrops, and archaeological excavations. The inferred tsunami histories span 3000 years for the Nankai and Suruga Troughs and nearly 10,000 years for the Sagami Trough. The inferred histories contain recurrence intervals of variable length. The shortest of these —100–200 years for the Nankai Trough, 150–300 years for the Sagami Trough — resemble those known from written history of the past 1000–1500 years. Longer intervals inferred from the tsunami deposits probably reflect variability in rupture mode, incompleteness of geologic records, and insufficient research. The region's tsunami history could be clarified by improving the geologic distinction between tsunami and storm, dating the inferred tsunamis more accurately and precisely, and using the deposits to help quantify the source areas and sizes of the parent earthquakes.     

Limit states and failure mechanisms of viscous dampers and the implications for large earthquakes

Fluid viscous dampers are used to control story drifts and member forces in structures during earthquake events. These elements provide satisfactory performance at the design‐level or maximum considered earthquake. However, buildings using fluid viscous dampers have not been subjected to very large earthquakes with intensities greater than the design and maximum considered events. Furthermore, an extensive database of viscous damper performance during large seismic events does not exist. To address these issues, a comprehensive analytical and experimental investigation was conducted to determine the performance of damped structures subjected to large earthquakes. A critical component of this research was the development and verification of a detailed viscous damper mathematical model that incorporates limit states. The development of this model and the laboratory and simulation results conclude good correlation with the new model and the damper limit states and provide superior results compared with the typical damper model when considering near collapse evaluation of structures. Copyright © 2010 John Wiley & Sons, Ltd.     

A geological interpretation of the lunar surface

This interpretation of lunar surface features is based on the differentiation of siliceous and basaltic substances similar to those of the earth. Our hypothesis is that lunar maria are composed of basaltic matter similar to that of terrestrial ocean basins, and that the lunar continents (bright regions) are composed of siliceous blocks.     

Melting of Mg2GeO4 under pressure

Melting point of germanate forsterite, Mg₂GeO₄, was raised by compression at the rate of 30°C/GPa. The triple point, at which three phases of olivine- and spinel-type solids and liquid coexisted, was fixed at 1950°C and 3.5GPa. Wen these results are combined with the thermodynamical data of forsterite, Mg₂SiO₄, it is estimated that the triple point of forsterite lies in a region ranging from 2700° to 3000°C in temperature and from 20 to 30GPa in pressure.     

Outflow channel sources, reactivation, and chaos formation, Xanthe Terra, Mars

The undulating, warped, and densely fractured surfaces of highland regions east of Valles Marineris (located north of the eastern Aureum Chaos, east of the Hydraotes Chaos, and south of the Hydaspis Chaos) resulted from extensional surface warping related to ground subsidence, caused when pressurized water confined in subterranean caverns was released to the surface. Water emanations formed crater lakes and resulted in channeling episodes involved in the excavation of Ares, Tiu, and Simud Valles of the eastern part of the circum-Chryse outflow channel system. Progressive surface subsidence and associated reduction of the subsurface cavernous volume, and/or episodes of magmatic-driven activity, led to increases of the hydrostatic pressure, resulting in reactivation of both catastrophic and non-catastrophic outflow activity. Ancient cratered highland and basin materials that underwent large-scale subsidence grade into densely fractured terrains. Collapse of rock materials in these regions resulted in the formation of chaotic terrains, which occur in and near the headwaters of the eastern circum-Chryse outflow channels. The deepest chaotic terrain in the Hydaspis Chaos region resulted from the collapse of pre-existing outflow channel floors. The release of volatiles and related collapse may have included water emanations not necessarily linked to catastrophic outflow. Basal warming related to dike intrusions, thermokarst activity involving wet sediments and/or dissected ice-enriched country rock, permafrost exposed to the atmosphere by extensional tectonism and channel incision, and/or the injection of water into porous floor material, may have enhanced outflow channel floor instability and subsequent collapse. In addition to the possible genetic linkage to outflow channel development dating back to at least the Late Noachian, clear disruption of impact craters with pristine ejecta blankets and rims, as well as preservation of fine tectonic fabrics, suggest that plateau subsidence and chaos formation may have continued well into the Amazonian Period. The geologic and paleohydrologic histories presented here have important implications, as new mechanisms for outflow channel formation and other fluvial activity are described, and new reactivation mechanisms are proposed for the origin of chaotic terrain as contributors to flooding. Detailed geomorphic analysis indicates that subterranean caverns may have been exposed during chaos formation, and thus chaotic terrains mark prime locations for future geologic, hydrologic, and possible astrobiologic exploration.     

Putative ice flows on Europa: Geometric patterns and relation to topography collectively constrain material properties and effusion rates

Europa's surface exhibits numerous small dome-like and lobate features, some of which have been attributed to fluid emplacement of ice or slush on the surface. We perform numerical simulations of non-Newtonian flows to assess the physical conditions required for these features to result from viscous flows. Our simulations indicate that the morphology of an ice flow on Europa will be, at least partially, influenced by pre-existing topography unless the thickness of the flow exceeds that of the underlying topography by at least an order of magnitude. Three classes of features can be identified on Europa. First, some (possibly most) putative flow-like features exhibit no influence from the pre-existing topography such as ridges, although their thicknesses are generally on the same order as those of ridges. Therefore, flow processes probably cannot explain the formation of these features. Second, some observed features show modest influence from the underlying topography. These might be explained by ice flows with wide ranges of parameters (ice temperatures >230 K, effusion rates >10⁷ m³ year⁻¹, and a wide range of grain sizes), although surface uplift (e.g., by diapirism) and in situ disaggregation provide an equally compelling explanation. Third, several observed features are completely confined by pre-existing topographic structures on at least one side; these are the best known candidates for flow features on Europa. If these features resulted from solid-ice flows, then temperatures >260 K and grain sizes <2 μm are required. Such small grain sizes seem unlikely; low-viscosity flows such as ice slurries or brines provide a better explanation for these features. Our results provide theoretical support for the view that many of Europa's lobate features have not resulted from solid-ice flows.     

Mean slope-angle frequency distribution and size frequency distribution of landslide masses in Higashikubiki area, Japan

Landslide mass size frequency distributions and mean slope-angle frequency distributions were calculated for slump, slide, and creep type landslides in the Higashikubiki area. Mean slope-angle frequency distributions closely approximated Weibull distributions. Size frequency distributions show power-law dependencies. Both can be explained by modeling landslides as linked uniform blocks in tensile force. Power coefficients for size frequency distributions were 2.01–2.32 (approximation to power functions) or 2.10–2.24 (approximation to Pareto distributions).