Long term variation in rainfall erosivity in Uruguay: a preliminary Fournier approach

In order to explore the consequences of precipitation increase on soil erosion in Uruguay, the monthly Fournier Index (FI) and the annual Modified Fournier Index (MFI) were developed as a preliminary approach, covering consecutive decadal periods from 1931 to 2000. Rainfall data were used from 13 stations distributed all over the country. MFI shows a decrease in the 1940s, an increase during the 1950s, then a little decrease during the 1960s and 1970s and an increase in the 1980s, remaining near these last values during the 1990s. FI behavior in July and October in the last two decades shows a decrease in the Northeast region of the country—the region with highest annual precipitation—and a slight increase over the Southeast—the region with the lowest annual precipitation and the only region with a winter rainfall maximum. For the core months of winter and early spring there is a decline in erosivity in the Northeast, but an increase in the Southeast. January shows erosivity decreasing in the South during the last two decades. In April there is a peak in precipitation variability all across the country. FI shows an early increase during the 1940s in the Northwest, and generally very low values during the 1970s, with the return of high values in the 1990s, especially in the Northern corner. Results pose a challenge in order to improve research on the erosion problem, since the main source of freshwater nationwide remains surface river flow, which is prone to higher turbidity problems in areas of high soil erosion.     

The metamorphic evolution of the high pressure mafic granulites of the Bacariza Formation (Cabo Ortegal Complex, Hercynian belt, NW Spain)

The high pressure mafic granulites of the Bacariza Formation outcrop in the two uppermost structural units of the Cabo Ortegal Complex (La Capelada unit and Cedeira unit) were separated by a Variscan thrust. In both cases, they appear as heterogeneous metabasites in normal contact between ultramafic rocks and other more homogeneous and less differentiated metabasic rocks, also affected by catazonal metamorphism. The main difference between the mafic granulites in the two units is the degree of deformation, which is higher in the underlying Cedeira unit. Petrologic and mineralogical data indicate that the high-pressure (HP) granulites (Gt-Cpx±Amp-Pl±Qtz±Scp-Rt±Ilm-Czo) are already retrograde (M2 Stage), post-dating an earlier eclogite facies metamorphism (M1 Stage) characterised by the mineral associations: Gt-Cpx±Amp±Ky±Qtz-Rt and Gt-Cpx±Amp±Qtz±Zo-Rt. The main structure related to the exhumation processes is the development of a general mylonitic foliation that, although initiated in granulite facies conditions, was mainly equilibrated in amphibolite facies (M3 Stage). This foliation was affected by isoclinal folds, which led to the formation of the Variscan thrusts responsible for the present stacking position. Thrust conditions were transitional between amphibolite and greenschist facies (M4 Stage). Thermobarometric data point to different P–T exhumation paths in the two units. Estimated P–T conditions were higher in La Capelada unit during M1 (P≥13 kbar; 860°C) and M2 (15 kbar; 800°C) than in the Cedeira unit (M1: P≥11 kbar, 770°C; M2: 12 kbar; 750°C). Temperatures for the M3 stage were comparable (720°C) in both units but rocks from the Cedeira unit show a much bigger drop in pressure. This resulted in an isothermal decompression type path for the Cedeira unit, while both P and T decreased more steadily in La Capelada rocks. These were always located at deeper level than the Cedeira rocks before the Variscan stacking. The difference in the two paths is related to different exhumation rates; higher in rocks from the Cedeira unit than in those from La Capelada. Exhumation processes coeval with underthrusting, and a different location of the rocks with respect to the main shear zone responsible for the exhumation would account for the distinct paths.     

Stratigraphic record of continental breakup,offshore NW Australia—Discussion

Reeve et al. (2022) address the stratigraphic record of continental breakup by focusing on a set of stratigraphic unconformities from a proximal sector of the NW Australian continental margin, inboard from the Exmouth Plateau. They suggest that such unconformities can potentially document a well-defined three-stage process: end of the syn-rift phase, formation of a wide continent-ocean transition zone (COTZ) and generation of ‘true’ Penrose-type oceanic crust. We counterargue that continental breakup is a protracted event that can only be understood via seismic- and chronostratigraphic correlations of strata, and their composing sequences, across and along rifted margins. Tying proximal stratigraphic unconformities to magnetic anomalies outboard from the study area in Reeve et al. (2022) is open to question. In parallel, we suggest that age resolutions of ca. 1 Ma are not achievable using the micropaleontological data presented in Reeve et al. (2022), with an important reworking of microfossil assemblages potentially occurring during the erosional process forming local and regional unconformities. Our discussion addresses these points in more detail.     

Rescue of the historical sea level record of Marseille (France) from 1885 to 1988 and its extension back to 1849–1851

This paper describes the historical sea level data that we have rescued from a tide gauge, especially devised originally for geodesy. This gauge was installed in Marseille in 1884 with the primary objective of defining the origin of the height system in France. Hourly values for 1885–1988 have been digitized from the original tidal charts. They are supplemented by hourly values from an older tide gauge record (1849–1851) that was rediscovered during a survey in 2009. Both recovered data sets have been critically edited for errors and their reliability assessed. The hourly values are thoroughly analysed for the first time after their original recording. A consistent high-frequency time series is reported, increasing notably the length of one of the few European sea level records in the Mediterranean Sea spanning more than one hundred years. Changes in sea levels are examined, and previous results revisited with the extended time series. The rate of relative sea level change for the period 1849–2012 is estimated to have been \(1.08\pm 0.04\)  mm/year at Marseille, a value that is slightly lower but in close agreement with the longest time series of Brest over the common period ( \(1.26\pm 0.04\)  mm/year). The data from a permanent global positioning system station installed on the roof of the solid tide gauge building suggests a remarkable stability of the ground ( \(-0.04\pm 0.25\)  mm/year) since 1998, confirming the choice made by our predecessor geodesists in the nineteenth century regarding this site selection.     

Experimental study of friction dissipators for seismic protection of building structures

This paper presents the results from unidirectional shaking table tests of two reduced scale steel models of a building frame, with one and two floors, respectively. These frames incorporate friction dissipators at every floor. The inputs are sine-dwells and artificial and registered earthquakes. This study is part of a larger research project aiming to assess the seismic efficiency of friction dissipators by means of an integrated numerical and experimental approach. Inside this framework, the main objectives of these experiments are to: (i) collect a wide range of results to calibrate a numerical model derived within the project, (ii) clarify some of the most controversial issues about friction dissipators (including behavior for inputs containing pulses, capacity to reduce resonance peaks, introduction of high frequencies in the response, and self-generated eccentricities), (iii) better understand their dynamic behavior, (iv) provide insight on the feasibility and reliability of using simple friction dissipators for seismic protection of building structures and (v) characterize the hysteretic behavior of these devices. Most of these objectives are satisfactorily reached and relevant conclusions are stated.     

NH4-bearing micas in poly-metamorphic Alpuj��rride micaschists and gneisses from the central zone of the Betic Cordillera (Spain): tectono-metamorphic and crystal-chemical constraints

The content and distribution of NH₄-bearing micas in micaschists and paragneisses of the Alpujárride complex (Betic Cordillera, Spain) are interpreted on the basis of textures, metamorphic history and crystal-chemical constraints. NH₄ is present in important amounts in early micas, recording their older diagenetic-to-metamorphic history. NH₄ was inherited by micas formed in successive metamorphic events. At similar metamorphic grade, annite is enriched in NH₄ relative to muscovite with a fractionation of 4:1. Maximum NH₄ contents were estimated in golden annite from medium-grade schists and in retrogressive annite-chlorite mixed-layers (~1.0?wt.%). A Ti-NH₄ avoidance gives rise to associated chemical changes, such as the enrichment in Mg and in ^VIAl. These data suggest that NH₄ can be a decisive factor in chemical equilibrium and element partitioning between coexisting phases, thus affecting to the commonly used thermobarometers. Estimation of the P-T conditions from texturally different muscovite-annite pairs reveals the superposition of several stages of mica growth, under different geothermal gradients.     

Analysis of tsunami impact scenarios at an oil refinery

This work analyses the potential consequences of two tsunami scenarios and their impacts on an oil refinery located in Sicily. Two credible tsunamis originating in the Tyrrhenian Sea were selected based on historical data. The potential for damage and hazardous materials releases resulting from the tsunami impacts to a refinery was assessed. The results obtained by the JRC tsunami propagation and inundation code HyFlux2 indicate that in both scenarios there would be eighteen storage tanks (of 43 located within 400 m from the shoreline) at the refinery subject to flooding. Water flow velocities were found to be generally low, <1 m/s, except for a central section of the refinery near the shoreline where the water flow velocities reach 3?C4 m/s. These results indicate that any damage would most likely occur due to buoyancy loads particularly in the western part of the facility where inundation levels are higher and storage tanks are less protected. Potential damage caused by impact of floating debris may be a problem in the central area of the refinery near the shoreline due to high flow velocities (3?C4 m/s) in both tsunami scenarios. Small hazardous materials releases could occur due to breakage of connected pipes and flanges caused by floating off of almost empty storage tanks or other equipment. Salt water intrusion could affect electrical equipment, such as control panels, pumps, and motors that are not raised above the inundation level. We conclude that in the two tsunami scenarios analysed, the risk to nearby residents and neighbouring facilities from potential hazardous materials releases, fires or explosions triggered by the tsunamis is likely to be small. Nonetheless, recommendations are made on prevention measures to reduce the risk of tsunami-triggered accidents and to mitigate their consequences if they do occur. The results of this study are limited by the uncertainty in the input data and most importantly by the accuracy of the elevation data and the model resolution.     

Regional scenarios of sea level rise and impacts on Basque (Bay of Biscay) coastal habitats,throughout the 21st century

Global climate models have predicted a rise on mean sea level of between 0.18 m and 0.59 m by the end of the 21st Century, with high regional variability. The objectives of this study are to estimate sea level changes in the Bay of Biscay during this century, and to assess the impacts of any change on Basque coastal habitats and infrastructures. Hence, ocean temperature projections for three climate scenarios, provided by several atmosphere–ocean coupled general climate models, have been extracted for the Bay of Biscay; these are used to estimate thermosteric sea level variations. The results show that, from 2001 to 2099, sea level within the Bay of Biscay will increase by between 28.5 and 48.7 cm, as a result of regional thermal expansion and global ice-melting, under scenarios A1B and A2 of the Intergovernmental Panel on Climate Change. A high-resolution digital terrain model, extracted from LiDAR, data was used to evaluate the potential impact of the estimated sea level rise to 9 coastal and estuarine habitats: sandy beaches and muds, vegetated dunes, shingle beaches, sea cliffs and supralittoral rock, wetlands and saltmarshes, terrestrial habitats, artificial land, piers, and water surfaces. The projected sea level rise of 48.7 cm was added to the high tide level of the coast studied, to generate a flood risk map of the coastal and estuarine areas. The results indicate that 110.8 ha of the supralittoral area will be affected by the end of the 21st Century; these are concentrated within the estuaries, with terrestrial and artificial habitats being the most affected. Sandy beaches are expected to undergo mean shoreline retreats of between 25% and 40%, of their width. The risk assessment of the areas and habitats that will be affected, as a consequence of the sea level rise, is potentially useful for local management to adopt adaptation measures to global climate change.     

Radiative backwarming in white-light flares

We examine empirical atmospheric structures that are consistent with enhanced white-light continuum emission in solar flares. This continuum can be produced either by hydrogen bound-free emission in an enhanced region in the upper chromosphere, or by H^- emission in an enhanced region around the temperature minimum. In the former case, weak Paschen jumps in the spectrum will be present, with the spectrum being dominated by a strong Balmer continuum, while in the latter case the spectrum exhibits a weaker, flat enhancement over the entire visible spectrum.We find that when proper account is taken of radiative backwarming processes, the two enhanced atmospheric regions above are not independent, in that irradiation by Balmer continuum photons from the upper chromosphere creates sufficient heating around the temperature minimum to account for the temperature enhancements there. Thus the problem of main phase white-light flare production reduces to one of creating temperature enhancements of order 10⁴ K in the upper chromosphere; radiative backwarming then naturally accounts for the enhancements of order 100 K around the temperature minimum.Heating by electron and proton bombardment, and by XUV irradiation from above, are then considered as candidates for creating the necessary enhancements in the upper chromosphere. We find that electron bombardment can be ruled out, whereas bombardment by protons in the few-MeV energy range is a viable candidate, but one without strong observational support. The XUV irradiation hypothesis is examined by incorporating it self-consistently into the PANDORA radiative transfer algorithm used to construct the empirical model atmospheres; we find that the introduction of XUV radiation, with flux and spectrum appropriate to white-light flare events, does indeed produce sufficient radiative heating in the upper chromosphere to balance the radiative losses associated with the required temperature enhancements.In summary, we find that the radiative coupling of (i) the upper chromosphere and temperature minimum regions (through Balmer continuum photons) and (ii) the transition region and upper chromosphere (through XUV photons) can account for white-light emission in solar flares.Presidential Young Investigator.     

The effect of long-lived vortical circulation on the dynamics of dust particles in the mid-plane of a protoplanetary disc

We investigate the response of dust particles in the mid-plane of a protoplanetary disc to the turbulent velocity field of long-lived, large-scale vortical circulation. The dynamical problem is studied through numerical integrations of the equations of motion for individual particles (the sizes of which range from centimetres to metres) subject to the solar gravity and the friction drag of the nebular gas. It is found, neglecting the thickness of the disc, that the particles do not drift inwards to the central star as occurs in a standard symmetrical nebula. Vortices tend to capture a large number of the particles. The effectiveness of this size-selective concentration mechanism depends not only on the value of the drag and the distance from the Sun, but also on the elongation of the vortex and its characteristic lifetime. Typical anticyclonic vortices with exponential decay times of 30 orbital periods and semi-axis ratios of 4 can increase the local surface density by a factor of 4 in a lifetime and accumulate 0.03–0.3 Earth masses. If the elongation is significant (>7), the vortex cannot concentrate any significant amount of solid material. Vortices with an elongation of about 2 are the most effective as regards trapping of dust. We have also found analytical expressions for the capture time as well as capture constraints as a function of the friction parameter, the elongation of the vortex and the impact parameter. By increasing the lifetime and the surface density of the solid particles, this confining mechanism can make the agglomeration of the solid material of the nebula (through collisional aggregation or gravitational instabilities) much more efficient than previously believed. This offers new possibilities for the formation of the planetesimals and the giant planet cores, and may explain the rapid formation of extrasolar giant planets.