Sediment transport at the network scale and its link to channel morphology in the braided Vjosa River system

In this article we apply the CASCADE network-scale sediment connectivity model to the Vjosa River in Albania. The Vjosa is one of the last unimpaired braided rivers in Europe and, at the same time, a data scarce environment, which limits our ability to model how this pristine river might respond to future human disturbance. To initialize the model, we use remotely sensed data and modeled hydrology from a regional model. We perform a reach-by-reach optimization of surface grain size distribution (GSD) and bedload transport capacity to ensure equilibrium conditions throughout the network. In order to account for the various sources of uncertainty in the calculation of transport capacity, we performed a global sensitivity analysis. The modeled GSD distributions generated by the sensitivity analysis generally match the six GSDs measured at different locations within the network. The modeled bedload sediment fluxes increase systematically downstream, and annual fluxes at the outlet of the Vjosa are well within an order of magnitude of fluxes derived from previous estimates of the annual suspended sediment load. We then use the modeled sediment fluxes as input to a set of theoretically derived functions that successfully discriminate between multi-thread and single-thread channel patterns. This finding provides additional validation of the model results by showing a clear connection between modeled sediment concentrations and observed river morphology. Finally, we observe that a reduction in sediment flux of about 50% (e.g., due to dams) would likely cause existing braided reaches to shift toward single thread morphology. The proposed method is widely applicable and opens a new avenue for application of network-scale sediment models that aid in the exploration of river stability to changes in water and sediment fluxes.     

Deformation of a young salt giant: regional topography of the Red Sea Miocene evaporites

The deformational behaviour of ‘salt giants’ during and shortly after their deposition is difficult to decipher in ocean margin settings where the original evaporites have been deeply buried and strongly mobilized. Here, we examine seismic reflection data from the Red Sea, where evaporites deposited until the end of the Miocene (~5.3 Ma), are generally covered by only 200–300 m of low‐density sediments and where the presence of an axial spreading centre allows us to observe how they have responded to a varied configuration of underlying basement. The regional morphology of the S‐reflection, representing the evaporite surface, is mapped out from seismic data from 13 cruises. The S‐reflection is locally rugged and commonly angular. It is either underlain by layered reflectivity, suggestive of layered evaporite beds, or by more transparent seismic character, suggestive of massive halite. On average, the depth of the reflection on the flanks of the axial rift systematically declines from 700 to 1100 m below sea level (mbsl) going northwards from 16 to 23°N. In the central Red Sea, the S‐reflection has 100‐ to 200‐m‐deep depressions, extending towards the coasts in places. In the southern Red Sea, the S‐reflection forms a surface at 300–800 mbsl that appears less disrupted. We suggest that the evaporites originally had a flat, horizontal surface at the end of the Miocene and have subsequently been distorted by isostatic effects and axial rifting, which in turn promoted evaporite flowage. Off‐axis evaporite depressions correspond with flows identified with multibeam sonar. Furthermore, across‐rift lows in Bouguer gravity anomalies represent valleys in the underlying basement. The off‐axis evaporite depressions overlie those valleys, as would be expected if halokinetic movements were greatest where the evaporites are locally thick, leading to deflation of the evaporite surface. The thickness of post‐Miocene sediment, also mapped out as part of this procedure, confirms the generally pelagic nature of this interval and increases on average from ~250 to 300 m from the central to the southern Red Sea, mimicking the variation in pelagic productivity observed in the present water column.     

M4–18: the planetary nebula and its WC10 central star

We present a detailed analysis of the planetary nebula M4–18 (G146.7+07.6) and its WC10-type Wolf–Rayet (WR) central star, based on high‐quality optical spectroscopy (WHT/UES, INT/IDS, WIYN/DensPak) and imaging ( HST /WFPC2). From a non-LTE model atmosphere analysis of the stellar spectrum, we derive T _eff=31 kK,     v _∞=160 km s⁻¹ and abundance number ratios of H/He<0.5, C/He=0.60 and O/He=0.10. These parameters are remarkably similar to those of He 2–113 ([WC10]). Assuming an identical stellar mass to that determined by De Marco et al. for He 2–113, we obtain a distance of 6.8 kpc to M4–18 [ E ( B−V )=0.55 mag from nebular and stellar techniques]. This implies that the planetary nebula of M4–18 has a dynamical age of ∼3100 yr, in contrast to ≥270 yr for He 2–113. This is supported by the much higher electron density of the latter. These observations may be reconciled with evolutionary predictions only if [WC]-type stars exhibit a range in stellar masses.
Photoionization modelling of M4–18 is carried out using our stellar WR flux distribution, together with blackbody and Kurucz energy distributions obtained from Zanstra analyses. We conclude that the ionizing energy distribution from the WR model provides the best consistency with the observed nebular properties, although discrepancies remain.     

Mg-metasomatism of oceanic gabbros and its control on Ti-clinohumite formation during eclogitization

In the high-pressure meta-ophiolites of Western Liguria (Italy), serpentinized ultramafites host bodies of eclogite, metarodingite and Ti-clinohumite ± Ti-chondrodite-bearing rocks. The latter contain relics of augite, ilmenite and apatite, which suggest derivation from pristine Fe-Ti-rich gabbros. The composition of relict mantle clinopyroxene in the host serpentinites indicates primary depleted peridotite compositions. Compared with their inferred protoliths, the Ti-clinohumite dikelets and the host serpentinites display significant changes in their major and trace element concentrations, indicating element exchange between the two rock systems. In particular, the Fe-Ti-rich gabbros were depleted in CaO and FeO and were strongly enriched in MgO. Analogous compositional variations are shown by altered gabbros enclosed in serpentinized peridotites from the obducted ophiolite sequences of the Northern Apennine. This evidence suggests that the observed Mg-enrichment recorded by the Ti-clinohumite metagabbros occurred in oceanic environments as the result of diffusive exchange between ultramafites and gabbros in presence of fluids related to serpentinization of the ultramafic country rocks. Alteration of the gabbro and concomitant Mg-uptake mostly caused extensive chloritization of the igneous plagioclase. Survival of igneous ilmenite and augite and their reaction with the hydrothermal chlorite during high-pressure metamorphism produced the observed Ti-clinohumite and Ti-chondrodite assemblages. The data presented thus indicate that crystallization of Ti-clinohumite assemblages was facilitated by a stage of oceanic alteration leading to Mg-enrichment of original Fe-Ti-rich gabbros. We suggest that during alteration, Mg-metasomatism occurred prior to rodingitization and was related to the earlier stages of peridotite serpentinization. Survival of oceanic chemical heterogeneities in the Ti-clinohumite rocks, indicates that element mobility during high-pressure recrystallization of these rocks was on a limited scale. This allowed preservation of their pre-subduction alteration features. Received: 13 July 1998 / Accepted: 3 November 1998     

A watershed on the Rhine: Changing approaches to international environmental cooperation

Since the 1950s, the governments of the riparian countries of the Rhine have attempted to protect the ecosystems of the river basin through international cooperation. Before 1987, their relations were unproductive and antagonistic. International programs for the protection of Rhine were far less effective than domestic policies. From 1987 onwards, international cooperation on the protection of the Rhine has been exemplary, and has led the way in domestic and international water protection policies. Many existing frameworks of international relations are not able to offer an adequate account of this wholesale change. In this article, an attempt is undertaken with the help of grid-group theory. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Italian guidelines for seismic risk classification of constructions: technical principles and validation

The Italian “Guidelines for the seismic risk classification of constructions” approved in February 2017 define the technical principles for exploiting tax deductions with respect to seismic strengthening interventions on existing buildings (Sismabonus). Tax deductions represent a unique opportunity to improve the seismic safety of the existing Italian building stock. The guidelines are very simple and allow practitioners to deal with the sophisticated concepts behind modern seismic design, such as expected annual losses (EAL) and repair costs (expressed as a fraction of the Reconstruction Cost: %RC). The seismic risk classes of buildings and the class upgrade due to strengthening interventions can be assessed using the principles included in the guidelines. The seismic risk class is the minimum between the class defined by the building safety index at the ultimate limit state and the one related to the EAL. The latter class depends on the area under the curve of the expected losses, which is easily obtained by computing the safety index converted in the return period (annual frequency) at different limit states and the relevant %RC. This paper illustrates the technical principles at the base of the guidelines and the procedure used to calibrate the repair costs associated with the different limit states using the actual repair costs monitored in the reconstruction process following recent Italian earthquakes. Finally, simple tools to estimate the cost of the strengthening interventions to improve the seismic capacity at the life-safety limit states are provided.     

DISOLV: A Python Package for the Interpretation of Borehole Dilution Tests

Single borehole dilution tests (SBDTs) are an inexpensive but effective technique for hydrogeological characterization of hard-rock aquifers. We present a freely available, easy-to-use, open-source Python package, DISOLV, for plotting, analyzing, and modeling SBDT data. DISOLV can significantly reduce the time spent interpreting field data by helping to identify flowing fractures intersecting the borehole and estimate the corresponding flow rates. DISOLV is successfully benchmarked against two analytical solutions. We also present an example application to real data collected in a borehole in a crystalline basement aquifer in southern India.     

A robust debris-flow and GLOF risk management strategy for a data-scarce catchment in Santa Teresa,Peru

The town of Santa Teresa (Cusco Region, Peru) has been affected by several large debris-flow events in the recent past, which destroyed parts of the town and resulted in a resettlement of the municipality. Here, we present a risk analysis and a risk management strategy for debris-flows and glacier lake outbursts in the Sacsara catchment. Data scarcity and limited understanding of both physical and social processes impede a full quantitative risk assessment. Therefore, a bottom-up approach is chosen in order to establish an integrated risk management strategy that is robust against uncertainties in the risk analysis. With the Rapid Mass Movement Simulation (RAMMS) model, a reconstruction of a major event from 1998 in the Sacsara catchment is calculated, including a sensitivity analysis for various model parameters. Based on the simulation results, potential future debris-flows scenarios of different magnitudes, including outbursts of two glacier lakes, are modeled for assessing the hazard. For the local communities in the catchment, the hazard assessment is complemented by the analysis of high-resolution satellite imagery and fieldwork. Physical, social, economic, and institutional vulnerability are considered for the vulnerability assessment, and risk is eventually evaluated by crossing the local hazard maps with the vulnerability. Based on this risk analysis, a risk management strategy is developed, consisting of three complementing elements: (i) standardized risk sheets for the communities; (ii) activities with the local population and authorities to increase social and institutional preparedness; and (iii) a simple Early Warning System. By combining scientific, technical, and social aspects, this work is an example of a framework for an integrated risk management strategy in a data scarce, remote mountain catchment in a developing country.     

Cretaceous tectonic evolution of the Neo-Tethys in Central Iran:Evidence from petrology and age of the Nain-Ashin ophiolitic basalts

The Nain and Ashin ophiolites consist of Mesozoic melange units that were emplaced in the Late Cretaceous onto the continental basement of the Central-East Iran microcontinent(CEIM).They largely consist of serpentinized peridotites slices;nonetheless,minor tectonic slices of sheeted dykes and pillow lavas-locally stratigraphically associated with radiolarian cherts-can be found in these ophiolitic melanges.Based on their whole rock geochemistry and mineral chemistry,these rocks can be divided into two geochemical groups.The sheeted dykes and most of the pillow lavas show island arc tholeiitic(IAT)affinity,whereas a few pillow lavas from the Nain ophiolites show calc-alkaline(CA)affinity.Petrogenetic modeling based on trace elements composition indicates that both IAT and CA rocks derived from partial melting of depleted mantle sources that underwent enrichment in subduction-derived components prior to melting.Petrogenetic modeling shows that these components were represented by pure aqueous fluids,or sediment melts,or a combination of both,suggesting that the studied rocks were formed in an arc-forearc tectonic setting.Our new biostratigraphic data indicate this arc-forearc setting was active in the Early Cretaceous.Previous tectonic interpretations suggested that the Nain ophiolites formed,in a Late Cretaceous backarc basin located in the south of the CEIM(the so-called Nain-Baft basin).However,recent studies showed that the CEIM underwent a counter-clockwise rotation in the Cenozoic,which displaced the Nain and Ashin ophiolites in their present day position from an original northeastward location.This evidence combined with our new data and a comparison of the chemical features of volcanic rocks from different ophiolites around the CEIM allow us to suggest that the Nain-Ashin volcanic rocks and dykes were formed in a volcanic arc that developed on the northern margin of the CEIM during the Early Cretaceous in association with the subduction,below the CEIM,of a Neo-Tethys oceanic branch that was existing between the CEIM and the southern margin of Eurasia.As a major conclusion of this paper,a new geodynamic model for the Cretaceous evolution of the CEIM and surrounding Neo-Tethyan oceanic basins is proposed.