A depth average SPH model including μ(I) rheology and crushing for rock avalanches

Classical depth-integrated smoothed particle hydrodynamics (SPH) models for avalanches are extended in the present work to include a μ(I)− rheological model enriched with a fragmentation law. With this improvement, the basal friction becomes grain distribution dependent. Rock avalanches, where grain distribution tends to change with time while propagating, are the appropriate type of landslide to apply the new numerical proposal. The μ(I)− rheological models considered in the present work are those of Hatano and Gray, combined with two different fragmentation laws, a hyperbolic and a fractal-based law. As an application, Frank avalanche, which took place in Canada in 1903, is analyzed under the scope of the present approach, focusing in the influence of the rheological and fragmentation laws in the evolution of the avalanche.     

The Cabo Frio upwelling overrides geographical patterns in the population dynamics of the shrimp Artemesia longinaris Spence Bate, 1888 (Decapoda: Penaeidae)

Upwelling areas are among the most productive ecosystems on the planet, influencing the biology of marine organisms. This study investigated the population dynamics of the shrimp Artemesia longinaris in two regions in southeastern Brazil, one inside (Macaé—Rio de Janeiro State) and one outside (Ubatuba—State of São Paulo) the Cabo Frio upwelling area. The aim was to verify the influence of the upwelling phenomenon on the abundance, growth, longevity, size of sexual maturity, and reproductive period of the species. In total, 188,902 individuals were captured at Macaé and 3,461 at Ubatuba. Individuals captured at Macaé showed larger maximum size, higher longevity, and slower growth rate, besides reaching sexual maturity at larger sizes than at Ubatuba. Continuous reproduction was observed in both regions, with juvenile recruitment peaks in spring and summer. Local conditions observed at Macaé were influenced by the Cabo Frio upwelling zone, characterized by productive and cooler waters that are around 20°C during most of the year. The upwelling phenomenon is probably the main factor influencing the population parameters studied here, changing the geographic patterns previously observed for the variation of these parameters in A. longinaris.     

Using low-density discrete Airborne Laser Scanning data to assess the potential carbon dioxide emission in case of a fire event in a Mediterranean pine forest

The aim of study is to map the carbon dioxide (CO₂) emission of the aboveground tree biomass (AGB) in case of a fire event. The suitability of low point density, discrete, multiple-return, Airborne Laser Scanning (ALS) data and the influence of several characteristics of these data and the study area on the results obtained have been evaluated. A sample of 45 circular plots representative of Pinus halepensis Miller stands were used to fit and validate the model of AGB. The ALS point clouds were processed to obtain the independent variables and a multivariate linear regression analysis between field data and ALS-derived variables allowed estimation of AGB. Then, the influence of several characteristics on the residuals of the model was analyzed. Finally, conversion factors were applied to obtain the CO₂ values. The AGB model presented a R² value of 0.84 with a relative root-mean-square error of 27.35%. This model included ALS variables related to vegetation height variability and to canopy density. Terrain slope, aspect, canopy cover, scan angle and the number of laser returns did not influence AGB estimations at plot level.     

Scilla e Cariddi e le correnti di marea nello Stretto di Messina

Riassunto L'A. sottopone ad una dettagliata analisi idrodinamica i fenomeni relativi alle maree ed alle correnti di marea dello Stretto di Messina, appoggiandosi sui dati mareografici dei due mari adiacenti nonchè sulle misure ed osservazioni di F. Vercelli e G. Mazzarelli. I risultati mostrano come il fenomeno delle maree nello Stretto di Messina consista nell'accoppiamento delle maree proprie delle masse d'acque dello Stretto con gli impulsi che le stesse masse ricevono dai due mari Jonio e Tirreno. In tale processo i fenomeni d'attrito (attrito esterno e turbolenza) rivelano un'importanza fondamentale. La sovrapposizione di una corrente generale più forte con la corrente di marea dà luogo nell'imbocco Nord dello Stretto a quelle convergenze di corrente alle quali si connettono i «tagli» e le «scale di mare», nonchè i vortici di Capo Peloro (Cariddi), Scilla e San Raineri. Seguono considerazioni sulla possibilità di alterazioni morfologiche dello Stretto di Messina da epoche preistoriche con abbassamento del fondo o con allargamento delle sponde in guisa da spiegare l'indebolimento dei medesimi fenomeni.

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Zusammenfassung Die Gezeiten und Gezeitenströmungen in der Strasse von Messina, an die sich die bekannten Schilderungen der alten Sagen der Scylla und Charybdis knüpfen, werden hier einer eingehenden hydrodynamischen Analyse unterzogen. Die Grundlagen für diese bilden einerseits die bekannten Grundwerte der vertikalen Gezeit in den angrenzenden Meeren im Norden und Süden der Strasse, andererseits die neueren Messungen der Gezeitenströme im engsten Querschnitt der Strasse durch Prof. Vercelli und die Beobachtungen von Prof. G. Mazzarelli. Die Ergebnisse dieser Analyse zeigen, dass das Phänomen der Gezeiten in der Meeresstrasse nichts anderes ist, als die Mitschwingungsgezeiten der Wassermassen der Strasse mit den Impulsen, die sie vom Jonischen und Thyrrhenischen Meer her empfagen. Dabei spielen die Reibungseinflüsse (äussere Reibung und Turbulenz) im engsten Teil der Strasse für die Intensität und Phase der Ströme eine ausschlaggebende Rolle. Die Superposition einer stärkeren allgemeinen Strömung und des Gezeitenstromes gibt am Nordausgang der Meeresstrasse an der Meeresoberfläche zweimal in jeder Mondperiode jene Stromkonvergenzen, an die die bekannten Sprungwellen (tagli o scale di mare) gebunden sind. Mit ihnen in Zusammenhang stehen such die Wirbel vor Cap Peloro (Charybdis), vor Scilla und vor San Raineri. Dieser Zusammenhang wird in der Arbeit näher erörtert, sowie Betrachtungen darüber angestellt, ob nicht möglicherweise morphologische Aenderungen in der Strasse von Messina seit vorhistorischer Zeit durch Vertiefung und vielleicht auch Verbreiterung der Meeresstrasse eine Schwächung der Phänomens bewirkt haben könnten. So könnte man verstehen, dass «Scylla und Charybdis» das sind die von Homer so eindrucksvoll geschilderten Gefahren für die Schiffahrt allmählich verloren gegangen sind.

     

Impact of data model and point density on aboveground forest biomass estimation from airborne LiDAR

Background

Accurate estimation of aboveground forest biomass (AGB) and its dynamics is of paramount importance in understanding the role of forest in the carbon cycle and the effective implementation of climate change mitigation policies. LiDAR is currently the most accurate technology for AGB estimation. LiDAR metrics can be derived from the 3D point cloud (echo-based) or from the canopy height model (CHM). Different sensors and survey configurations can affect the metrics derived from the LiDAR data. We evaluate the ability of the metrics derived from the echo-based and CHM data models to estimate AGB in three different biomes, as well as the impact of point density on the metrics derived from them.

Results

Our results show that differences among metrics derived at different point densities were significantly different from zero, with a larger impact on CHM-based than echo-based metrics, particularly when the point density was reduced to 1 point m^?2. Both data models-echo-based and CHM-performed similarly well in estimating AGB at the three study sites. For the temperate forest in the Sierra Nevada Mountains, California, USA, R² ranged from 0.79 to 0.8 and RMSE (relRMSE) from 69.69 (35.59%) to 70.71 (36.12%) Mg ha^?1 for the echo-based model and from 0.76 to 0.78 and 73.84 (37.72%) to 128.20 (65.49%) Mg ha^?1 for the CHM-based model. For the moist tropical forest on Barro Colorado Island, Panama, the models gave R² ranging between 0.70 and 0.71 and RMSE between 30.08 (12.36%) and 30.32 (12.46) Mg ha^?1 [between 0.69–0.70 and 30.42 (12.50%) and 61.30 (25.19%) Mg ha^?1] for the echo-based [CHM-based] models. Finally, for the Atlantic forest in the Sierra do Mar, Brazil, R² was between 0.58–0.69 and RMSE between 37.73 (8.67%) and 39.77 (9.14%) Mg ha^?1 for the echo-based model, whereas for the CHM R² was between 0.37–0.45 and RMSE between 45.43 (10.44%) and 67.23 (15.45%) Mg ha^?1.

Conclusions

Metrics derived from the CHM show a higher dependence on point density than metrics derived from the echo-based data model. Despite the median of the differences between metrics derived at different point densities differing significantly from zero, the mean change was close to zero and smaller than the standard deviation except for very low point densities (1 point m^?2). The application of calibrated models to estimate AGB on metrics derived from thinned datasets resulted in less than 5% error when metrics were derived from the echo-based model. For CHM-based metrics, the same level of error was obtained for point densities higher than 5 points m^?2. The fact that reducing point density does not introduce significant errors in AGB estimates is important for biomass monitoring and for an effective implementation of climate change mitigation policies such as REDD + due to its implications for the costs of data acquisition. Both data models showed similar capability to estimate AGB when point density was greater than or equal to 5 point m^?2.

     

The influence of elevation on soil properties and forest litter in the Siliceous Moncayo Massif,SW Europe

Understanding the effects of elevation and related factors (climate, vegetation) on the physical and chemical soil properties can help to predict changes in response to future climate or afforestation forcings. This work aims to contribute to the knowledge of soil evolution and the classification of forest soils in relation to elevation in the montane stage, with special attention to podzolization and humus forms. The northern flank of the Moncayo Massif (Iberian Range, SW Europe) provides a unique opportunity to study a forest soils catena within a consistent quartzitic parent material over a relatively steep elevation gradient. With increasing elevation, pH, base saturation, exchangeable potassium, and fine silt-sized particles decrease significantly, while organic matter, the C/N ratio, soil aggregate stability, water repellency and coarse sand-sized particles increase significantly. The soil profiles shared a set of properties in all horizons: loamy-skeletal particle-size, extreme acidity (pH-H₂O<5.6) and low base saturation (<50%). The most prevalent soil forming processes in the catena include topsoil organic matter accumulation and even podzolization, which increases with elevation. From the upper to lower landscape positions of wooded montane stage of the Moncayo Massif, mull-moder-mor humus and an Umbrisol-Cambisol-Podzol soil unit sequences were found.     

Origin of peraluminous granites and granodiorites, Iberian massif, Spain: an experimental test of granite petrogenesis

The discrimination between potential source materials involved in the genesis of Iberian granites and granodiorites, as well as the role of mantle-crust interactions, are examined using constraints imposed by melting experiments, melting-assimilation experiments and Sr-Nd isotope systematics. The Sr-Nd isotope relationships indicate the existence of different genetic trends in which juvenile mantle materials are involved by different mechanisms: (1) a source trend, traced by a particular evolution of the pre-Hercynian basement and indicating mantle participation at the time of sedimentation; (2) a set of magmatic trends traced by gabbro-tonalite-enclave-granodiorite associations, implying the incorporation of new mantle material at the time of granite generation. These relationships strongly support a pure crustal origin for the peraluminous leucogranites, derived from partial melting of crustal protoliths, and a hybrid origin for the peraluminous granodiorites. These granodiorites are the most abundant granitic rocks of the Central Iberian zone (CIZ) of the Iberian massif, implying that processes of hybridisation by assimilation and/or magma mixing played an important role in granitoid production during the Hercynian orogeny. These hypotheses have been tested by means of melting and assimilation experiments. Melting experiments in the range 800–900 °C and at pressures of 3, 6, 10 and 15 kbar indicate that: (1) several potential source materials such as Bt-Ms gneisses and metagreywackes are suitable for the production of peraluminous leucogranite melts; (2) the melt compositions are always leucogranitic, regardless of pressure; (3) pressure exerts a strong influence on the fertility of the source: experiments at 3 kbar produce more than 20 vol% of melt, compared with less than 5 vol% of melt produced at 10 and 15 kbar and at the same temperature. The melting-assimilation experiments carried out at 1000 °C and 4, 7 and 10 kbar and using a proportion of 50% gabbro and 50% gneiss give high melt proportions (more than 50 vol.%) and noritic residues. These melts have the composition of leucogranodiorites, and overlap with part of the compositional range of peraluminous granodiorites of the Iberian massif. The generation of more mafic granodiorites may be explained by the incorporation of some residual orthopyroxene to the granodiorite magmas. The low solubility of Fe + Mg prevents the generation of granodiorite melts with more than 3 wt% of MgO + FeO at all crustal pressures. The large volumes of peraluminous, hybrid granodiorites, produced by assimilation of crustal rocks by mantle magmas, imply that an important episode of crustal growth took place during the Late-Palaeozoic Hercynian orogeny in the Iberian massif. Received: 30 June 1998 / Accepted: 27 November 1998     

Frontal dynamics boost primary production in the summer stratified Mediterranean sea

Bio-physical glider measurements from a unique process-oriented experiment in the Eastern Alboran Sea (AlborEx) allowed us to observe the distribution of the deep chlorophyll maximum (DCM) across an intense density front, with a resolution (～ 400 m) suitable for investigating sub-mesoscale dynamics. This front, at the interface between Atlantic and Mediterranean waters, had a sharp density gradient (Δρ ～ 1 kg/m³ in ～ 10 km) and showed imprints of (sub-)mesoscale phenomena on tracer distributions. Specifically, the chlorophyll-a concentration within the DCM showed a disrupted pattern along isopycnal surfaces, with patches bearing a relationship to the stratification (buoyancy frequency) at depths between 30 and 60 m. In order to estimate the primary production (PP) rate within the chlorophyll patches observed at the sub-surface, we applied the Morel and Andrè (J Geophys Res 96:685–698 1991) bio-optical model using the photosynthetic active radiation (PAR) from Argo profiles collected simultaneously with glider data. The highest production was located concurrently with domed isopycnals on the fresh side of the front, suggestive that (sub-)mesoscale upwelling is carrying phytoplankton patches from less to more illuminated levels, with a contemporaneous delivering of nutrients. Integrated estimations of PP (1.3 g C m^?2d^?1) along the glider path are two to four times larger than the estimations obtained from satellite-based algorithms, i.e., derived from the 8-day composite fields extracted over the glider trip path. Despite the differences in spatial and temporal sampling between instruments, the differences in PP estimations are mainly due to the inability of the satellite to measure DCM patches responsible for the high production. The deepest (depth > 60 m) chlorophyll patches are almost unproductive and probably transported passively (subducted) from upper productive layers. Finally, the relationship between primary production and oxygen is also investigated. The logarithm of the primary production in the DCM interior (chlorophyll (Chl) > 0.5 mg/m³) shows a linear negative relationship with the apparent oxygen utilization, confirming that high chlorophyll patches are productive. The slope of this relationship is different for Atlantic, mixed interface waters and Mediterranean waters, suggesting the presence of differences in planktonic communities (whether physiological, population, or community level should be object of further investigation) on the different sides of the front. In addition, the ratio of optical backscatter to Chl is high within the intermediate (mixed) waters, which is suggestive of large phytoplankton cells, and lower within the core of the Atlantic and Mediterranean waters. These observations highlight the relevance of fronts in triggering primary production at DCM level and shaping the characteristic patchiness of the pelagic domain. This gains further relevance considering the inadequacy of optical satellite sensors to observe DCM concentrations at such fine scales.     

Numerical modeling of storm surges in the coast of Mozambique: the cases of tropical cyclones Bonita (1996) and Lisette (1997)

The coast of Mozambique is often affected by storms, particularly tropical cyclones during summer or sometimes midlatitude systems in the southern part. Storm surges combined with high freshwater discharge can drive huge coastal floods, affecting both urban and rural areas. To improve the knowledge about the impact of storm surges in the coast of Mozambique, this study presents the first attempt to model this phenomenon through the implementation of the Princeton Ocean Model (POM) in the Southwestern Indian Ocean domain (SWIO; 2–32°S, 28–85°E) using a regular grid with 1/6° of spatial resolution and 36 sigma levels. The simulation was performed for the period 1979–2010, and the most interesting events of surges were related to tropical cyclones Bonita (1996) and Lisette (1997) that occurred in the Mozambique Channel. The results showed that the model represented well the amplitude and phase of principal lunar and solar tidal constituents, as well as it captured the spatial pattern and magnitudes of SST with slight positive bias in summer and negative bias in winter months. In terms of SSH, the model underestimated the presence of mesoscale eddies, mainly in the Mozambique Channel. Our results also showed that the atmospheric sea level pressure had a significant contribution to storm heights during the landfall of the tropical cyclones Bonita (1996) and Lisette (1997) in the coast of Mozambique contributing with about 20 and 16% of the total surge height for each case, respectively, surpassing the contribution of the tide-surge nonlinear interactions by a factor of 2.     

A Method to Estimate the Hydraulic Conductivity of the Ground by TRT Analysis

The knowledge of hydraulic properties of aquifers is important in many engineering applications. Careful design of ground‐coupled heat exchangers requires that the hydraulic characteristics and thermal properties of the aquifer must be well understood. Knowledge of groundwater flow rate and aquifer thermal properties is the basis for proper design of such plants. Different methods have been developed in order to estimate hydraulic conductivity by evaluating the transport of various tracers (chemical, heat etc.); thermal response testing (TRT) is a specific type of heat tracer that allows including the hydraulic properties in an effective thermal conductivity value. Starting from these considerations, an expeditious, graphical method was proposed to estimate the hydraulic conductivity of the aquifer, using TRT data and plausible assumption. Suggested method, which is not yet verified or proven to be reliable, should be encouraging further studies and development in this direction.