Mica in the upper mantle

Despite several lines of indirect evidence, there has hitherto been little unambiguous evidence of a volatile bearing phase in the upper mantle. Mica has been found as a primary phase in several specimens of peridotite and one specimen of garnet lherzolite from the Lashaine volcano, northern Tanzania.     

Étude pétrographique de l'Oehningien (Tortonien) du Locle (Suisse occidentale)

Sans résumé     

Quantifying impacts of forecast uncertainties on predicted storm surges

In this paper, we propose a framework for quantifying risks, including (1) the effects of forecast errors, (2) the ability to resolve critical grid features that are important to accurate site-specific forecasts, and (3) a framework that can move us toward performance-based/cost-based decisions, within an extremely fast execution time. A key element presently lacking in previous studies is the interrelationship between the effects of combined random errors and bias in numerical weather prediction (NWP) models and bias and random errors in surge models. This approach examines the number of degrees of freedom in present forecasts and develops an equation for the quantification of these types of errors within a unified system, given the number of degrees of freedom in the NWP forecasts. It is shown that the methodology can be used to provide information on the forecasts and along with the combined uncertainty due to all of the individual contributions. A potential important benefit from studies using this approach would be the ability to estimate financial and other trade-offs between higher-cost “rapid” evacuation methods and lower-cost “slower” evacuation methods. Analyses here show that uncertainty inherent in these decisions depends strongly on forecast time and geographic location. Methods based on sets of surge maxima do not capture this uncertainty and would be difficult to use for this purpose. In particular, it is shown that surge model bias can play a dominant role in distorting the forecast probabilities.     

Three-dimensional structure of flow at a confluence of river channels with discordant beds

This paper presents three-dimensional data of the mean and turbulent structure of flow collected at a natural confluence of rivers with discordant beds to (1) describe the three-dimensional flow field of a natural junction of channels; (2) assess the role of changes in bed morphology occurring during transport-effective events on the structure of flow at a confluence; and (3) examine how the three-dimensional structure of flow varies with changes in the ratio of momentum flux between the two confluent streams. Three-dimensional measurements of velocity were reconstructed from the measurements obtained with an array of four, two-component electromagnetic current meters. Six detailed velocity profiles were taken at five cross-sections in a wide range of flow conditions. The mean field of flow is characterised by (1) the acceleration of flow in the downstream portion of the post-confluence channel, but by lower velocities upstream in the mixing layer area; (2) a stagnation zone at the apex of the junction; (3) a zone of flow deviation, and strong fluid upwelling, close to the avalanche face and at the margin of the tributary mouth bar; and (4) reduced velocities over the depositional bar at the downstream junction corner. The position and extent of these zones vary with changes in the ratio of momentum flux. Very high intensity of turbulence (peaks up to 50%) and turbulent kinetic energy were observed in the mixing layer region. Distortion of the mixing layer, characteristic of flow where bed discordance is present between the two tributary channels, was evident from mean and turbulent flow data. This field study suggests that the effects of bed discordance on flow, sediment transport, and the resultant bed morphology must be incorporated into conceptual and numeric models of these sites of complex flow.     

The international at-sea intercomparison of fCO2 systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean

The ‘International Intercomparison Exercise of fCO₂ Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (fCO₂) systems, one discrete fCO₂ system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater fCO₂ measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO₂, temperature measurements) and a common procedure for calculation of final fCO₂ were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO₂ in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete fCO₂ measurements can be made in good agreement (±3 μatm) with underway fCO₂ data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the fCO₂ system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO₂ results. Calculation of fCO₂ from high-quality total dissolved inorganic carbon (C_T) and total alkalinity (A_T) measurements does not yield results comparable in accuracy and precision to fCO₂ measurements.     

Variability of the transgressive stacking pattern under environmental changes control: Example from the Post-Glacial deposits of the Gulf of Lions inner-shelf,Mediterranean, France

At a regional scale, high-resolution seismic dataset analysis provides an accurate image of the stratigraphic organization of the Post-Glacial transgressive deposits of the Gulf of Lions inner-shelf. Architectural and stratigraphic characteristics are different in four main sectors, clearly demonstrating that depositional models have to be adapted from place to place following the interplay of various genetic factors.     

Investigating crater lake warming using ASTER thermal imagery: Case studies at Ruapehu,Poás,Kawah Ijen,and Copahué Volcanoes

A two-channel or split-window algorithm designed to correct for atmospheric conditions was applied to thermal images taken by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) of Lake Yugama on Kusatsu–Shirane volcano in Japan in order to measure the temperature of its crater lake. These temperature calculations were validated using lake water temperatures that were collected on the ground. Overall, the agreement between the temperatures calculated using the split-window method and ground truth is quite good, typically ± 1.5 °C for cloud-free images. Data from fieldwork undertaken in the summer of 2004 at Kusatsu–Shirane allow a comparison of ground-truth data with the radiant temperatures measured using ASTER imagery. Further images were analyzed of Ruapehu, Poás, Kawah Ijen, and Copahué volcanoes to acquire time-series of lake temperatures. A total of 64 images of these 4 volcanoes covering a wide range of geographical locations and climates were analyzed. Results of the split-window algorithm applied to ASTER images are reliable for monitoring thermal changes in active volcanic lakes. These temperature data, when considered in conjunction with traditional volcano monitoring techniques, lead to a better understanding of whether and how thermal changes in crater lakes aid in eruption forecasting.     

Unraveling the roles of asymmetric uplift,normal faulting and groundwater flow to drainage rearrangement in an emerging karstic landscape

Landscape adjustment to tectonic, lithologic and climatic forcing leads to drainage reorganization and migration of divides. The respective contribution of these forcings, especially on carbonate landscapes is not well defined. Here, we have addressed this issue by combining field observations, satellite image interpretation and digital elevation model (DEM) quantitative analysis to assess drainage response to spatially heterogeneous rainfall, asymmetric uplift, and normal faulting on an emerging carbonated platform (Sumba Island, Indonesia). We map geomorphic markers of fluvial dynamics and drainage rearrangement and compute a χ parameter that incorporates the contributions of unevenly distributed precipitation and asymmetric uplift to estimate erosional disequilibrium across drainage divides. We find that asymmetric emergence of Sumba Island created an initial parallel drainage, asymmetric across a divide that propagates landwards. Soon after establishing itself on the emerging slopes this drainage was disturbed by normal faulting, which has become the main force driving drainage rearrangement. Vertical offsets across normal fault scarps first triggered aggradation within valleys over the hanging walls, and then disconnected upstream reaches from downstream reaches, leading to the formation of wind gaps atop the fault scarps and upstream perched sedimentary basins. The defeat of rivers by growing fault scarps was catalysed by the possibility for surface water to be rerouted near the fault scarps into underground water networks inside the underlying carbonates. At the end of the process, the opposite drainage across the main water divide captured the struggling drainage. Capture mechanisms include initial groundwater capture of the perched alluvial aquifers, followed by ground sapping at the head of the opposite drainage and surface stream diversion by avulsion. Finally, normal faulting is the main driving force of drainage rearrangement allowing avulsion and karstic rerouting whereas asymmetric uplift and climate forcings have shown a low efficiency. The role of karstification is more ambiguous, catalysing or inhibiting drainage rearrangement. Copyright © 2018 John Wiley & Sons, Ltd.