Variations in benthic fauna underneath an effluent mixing zone at a marine oil terminal in Port Valdez, Alaska

The distributions of hydrocarbons and infauna in sediments below a permitted mixing zone for the disposal of treated ballast waters in Port Valdez, Alaska were examined annually, 1999–2001. The associations of biological measures and the abundance of selected benthic organisms to total aromatic hydrocarbons (TARO) ranged up to large-sized effects, as compared against minimum-effect criteria (|r|0.63). The apparent sensitivity of three polychaete worms to low levels of hydrocarbons makes them particularly useful as indicators of future changes in spatial distributions of hydrocarbons associated with discharged effluent. In 2001, sediment TARO concentrations decreased and the correlation values of TARO to biotic variables were generally less than in 1999 and 2000. Evidence supports a conclusion of a strong but spatially limited association of some fauna with accumulations of petroleum hydrocarbons in these sediments.     

Mafic pyroclastic flows at Santa Maria (Gaua) Volcano, Vanuatu: the caldera formation problem in mainly mafic island arc volcanoes

At Santa Maria Volcano (New Hebrides island arc), extensive ash and scoria flow deposits overlie the mainly effusive, pre-caldera cone. Hydromagmatic features characterize these deposits, the composition of juvenile clasts ranges from basalt to acid andesite/dacite (SiO₂= 51–63.6%) with a dominant basaltic composition. The stratigraphic position of this pyroclastic series and its spatial distribution around a 8.5 km × 6 km wide caldera provide evidence of a relationship between this series and the caldera formation. In addition, these pyroclastic deposits are co-genetic to parasitic cones and lava flows developed along faults concentric to the caldera. Both series result from a compositionally layered magma reservoir, the subordinate differentiated magmas being the result of fractional crystallization from the basalts. A model of caldera formation which implies a large hydromagmatic eruption at the central vent and minor magma withdrawal by flank eruptions is proposed. This model emphasizes the importance of mafic hydroclastic eruptions in the caldera forming event and contradicts a model implying only quiet subsidence, a process often proposed for the formation of calderas in island are volcanoes of mainly mafic composition.     

Major and trace element chemistry of Boulder 1 at Station 2, Apollo 17

Twenty-seven samples of matrix and clast materials from Boulder 1 at Station 2, Apollo 17 have been analyzed for major and trace elements as part of the study of this boulder by Consortium Indomitabile. Both unusual and common types of material have been characterized. Gray and black competent breccia (GCBx and BCBx) and anorthositic breccia (AnBx) have compositions which are common at the Apollo 17 site and were common at the site of boulder formation. Light friable breccias (LFBx) have compositions which are not found at the Apollo 17 site other than in the boulder. Pigeonite basalt is a new type of lunar rock and has characteristics that would be expected of a highland volcanic rock. It is associated with LFBx material, and like LFBx material it is exotic to the Apollo 17 site. Coarse norite is an old primitive rock which is no longer (if ever) found as millimeter fragments at the Apollo 17 site. It was, however, present as millimeter fragments associated with GCBx and BCBx materials at the site and time of boulder formation. Therefore the boulder-forming process combined materials from at least two different localities or vertical strata; at least one of these (LFBx) has not been previously sampled and analyzed.     

Morphology and sedimentology of a complex debris flow in a clay‐shale basin

Coupling morphological, sedimentological, and rheological studies to numerical simulations is of primary interest in defining debris‐flow hazard on alluvial fans. In particular, numerical runout models must be carefully calibrated by morphological observations. This is particularly true in clay‐shale basins where hillslopes can provide a large quantity of poorly sorted solid materials to the torrent, and thus change both the mechanics of the debris flow and its runout distance. In this context, a study has been completed on the Faucon stream (southeastern French Alps), with the objectives of (1) defining morphological and sedimentological characteristics of torrential watersheds located in clay‐shales, and (2) evaluating through a case study the scouring potential of debris flows affecting a clay‐shale basin. Morphological surveys, grain‐size distributions and petrographic analyses of the debris‐flow deposits demonstrate the granular character of the flow during the first hectometre, and its muddy character from there to its terminus on the debris fan. These observations and laboratory tests suggest that the contributing areas along the channel have supplied the bulk of the flow material. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydrodynamic convergence of hydropressured and geopressured zones, Central Texas, Gulf of Mexico Basin, USA

Freshwater moving downdip in the Carrizo–Wilcox aquifer, Central Texas, USA, and saltwater and hydrocarbons moving updip from a geopressured zone come together in a groundwater convergence zone, marked by (1) a hydraulic-gradient reversal, (2) “updip” oil fields, and (3) the downdip limit of potable water beyond which there is a marked increase in salinity. Data combined from groundwater-supply and petroleum-extraction industries document the interface between the hydropressured and geopressured zones. The hydraulic-head gradient updip of the convergence zone is 0.001 to 0.002, directed toward the coast; farther downdip it is ?0.02 to ?0.04, directed inland. Salinity increases from <400 mg/L near the outcrop, to ～3,000 mg/L at the downdip limit of potable water, to >100,000 mg/L in the geopressured zone. Upward-directed flow paths probably predominate in the convergence zone. The convergence zone in the study area lies within only 30–50 km of the outcrop because updip extensional faulting offsets permeable aquifer units against low-permeability strata and restricts the downdip flux of recharged water. The major elements of the convergence zone may have been in place since the Miocene development of circulation in the updip coastal aquifer following incision of river valleys and lowering of base level.     

Caractérisation de la structure interne et de l'état hydrique de glissements argilo-marneux par tomographie géophysique : l'exemple du glissement-coulée de Super-Sauze (Alpes du Sud,France)

Geophysical methods such as seismic surveying and electrical resistivity imaging appear to be well-adapted to investigate and understand landslide mechanisms. They allow direct and non-intrusive measurement of acoustic velocity and electrical resistivity, two fundamental parameters used to define the physical properties of the reworked moving materials. Both methods were applied at the Super-Sauze site in the French South Alps, where a typical example of an intra-material earthflow-mudslide can be observed. Measurements were taken simultaneously along two orthogonal profiles: one 325 m in length is perpendicular to the axis of the earthflow; the other 235 m in length is located along the axis of the earthflow. The results show a correlation between the seismic and electrical resistivity data, confirming that the simultaneous use of both methods gives complementary information about landslide mechanisms. The seismic data provide information on fracture density variations, whereas the electrical resistivity data provide information on water content variations. To cite this article: G. Grandjean et al., C. R. Geoscience 338 (2006).     

A Graph Clustering Approach to Localization for Adaptive Covariance Tuning in Data Assimilation Based on State-Observation Mapping

Mathematical Geosciences - An original graph clustering approach for the efficient localization of error covariances is proposed within an ensemble-variational data assimilation framework. Here,...     

Sources of groundwater pumpage in a layered aquifer system in the Upper Gulf Coastal Plain, USA

Understanding groundwater-pumpage sources is essential for assessing impacts on water resources and sustainability. The objective of this study was to quantify pumping impacts and sources in dipping, unconfined/confined aquifers in the Gulf Coast (USA) using the Texas Carrizo-Wilcox aquifer. Potentiometric-surface and streamflow data and groundwater modeling were used to evaluate sources and impacts of pumpage. Estimated groundwater storage is much greater in the confined aquifer (2,200?km³) than in the unconfined aquifer (170?km³); however, feasibility of abstraction depends on pumpage impacts on the flow system. Simulated pre-development recharge (0.96?km³/yr) discharged through evapotranspiration (ET, ～37%), baseflow to streams (～57%), and to the confined aquifer (～6%). Transient simulations (1980–1999) show that pumpage changed three out of ten streams from gaining to losing in the semiarid south and reversed regional vertical flow gradients in ～40% of the entire aquifer area. Simulations of predictive pumpage to 2050 indicate continued storage depletion (41% from storage, 32% from local discharge, and 25% from regional discharge capture). It takes ～100?yrs to recover 40% of storage after pumpage ceases in the south. This study underscores the importance of considering capture mechanism and long-term system response in developing water-management strategies.     

Contribution of interstitial OH groups to the incorporation of water in forsterite

Water incorporation in forsterite samples synthesized under low to medium silica-activity conditions mostly occurs via a substitutional mechanism in which a Si vacancy is compensated by four protons. Corresponding IR absorption spectra display a cluster of narrow and weakly anharmonic OH-stretching bands at wavenumbers above 3,500 cm^?1. However, this diagnostic spectrum is often superimposed to one broader absorption band, rarely two, displaying pronounced temperature-dependent properties and tentatively assigned to H atoms in interstitial position (Ingrin et al. in Phys Chem Miner 40:499–510, 2013). Here, we investigate the structural and vibrational properties of selected interstitial H-bearing defects in forsterite using a first-principles modeling approach. We show that the broad bands discussed by Ingrin et al. (Phys Chem Miner 40:499–510, 2013) are most likely related to interstitial OH groups in the vacant octahedral sites alternating with the M2 sites along the c axis of the forsterite structure. The corresponding OH defects lead to the formation of fivefold coordinated Si species. Their peculiar thermal properties stem from the vibrational phase relaxation due to the anharmonic coupling of the high-energy local OH-stretching mode with a low-energy vibrational mode. This “exchange mode” corresponds to the hindered longitudinal translation of the OH group. These results suggest that at high pressure, hydrogen incorporation in forsterite is dominated by coexisting interstitial OH groups and (4H)_Si defects.     

Landslide kinematics inferred from in situ measurements: the Cliets rock-slide (Savoie,French Alps)

This paper presents an analysis of two large rock toppling/sliding events which occurred in January 2014 and February 2019 at the Cliets unstable slope (Savoie, French Alps). To understand the mechanism involved and its control by external forcings, a multi-technique analysis approach is used combining geological observations, meteorological data analysis, topographic measurements and simple physical modeling. The pre-failure stage of the events is more particularly analyzed. No direct relationships are found between triggering factors and surface motion though a kinematics analysis highlights the transition toppling-sliding. It showed that, at first order, this transition occurred 4 years before the first failure of 2014, while it happened 2 months before the second failure of 2019. From this date, the environment is considered like a block sliding on an inclined plane. By applying a frictional model (Helmstetter et al. in Journal of Geophysical Research: Solid Earth 109(B2), 2004), we illustrated that the two events belong to an unstable velocity-weakening sliding regime. The time to failure (Voight in Science 243(4888):200–203, 1989) is forecasted with the model, and the results are consistent with the observations. They confirm that the gravitational factor is predominant over the triggering factors for the two events.