The methodology of quantification of volcanic explosions from broad-band seismic signals and its application to the 2004–2005 explosions at Volcán de Colima, Mexico

A methodology is proposed for the quantification of volcanic explosions based on three parameters derived from broad-band seismic signals: the counter force of the eruption F , the power of the explosion P and the duration of the upward movement of the gas slug in the conduit to the free surface of magma, D . This methodology was applied to the 2004–2005 sequence of explosions at Volcán de Colima, Mexico. The broad-band records of more than 100 explosive events were obtained at a distance of 4 km from the crater. We determined the counter force of the eruption by modelling the low-frequency impulse of the seismic records of 66 volcanic explosions and estimated the power of 116 explosions from the spectra of the high-frequency impulse. The power of Colima explosions spans five orders of magnitude; the counter force spans four orders of magnitude. We show that the power of a volcanic explosion is proportional to the counter force of the eruption. These parameters may be used for the elaboration of a scale of volcanic explosions.     

Optimisation procedure for choosing Cam clay parameters

This paper analyzes the application of a grid-search approach for the estimation of modified Cam clay parameters from triaxial tests. By means of the systematic sampling of the error, in addition to locating the area presenting the smallest error, its “roughness”, is also characterized. This is a valuable information to evaluate the quality of the identification that has been carried out. The methodology proposed here does not aspire to be “the solution” to the problem of parameter identification. The aim is simply to provide a tool which may aid users with criteria.     

Surrogate-based parameter inference in debris flow model

This work tackles the problem of calibrating the unknown parameters of a debris flow model with the drawback that the information regarding the experimental data treatment and processing is not available. In particular, we focus on the evolution over time of the flow thickness of the debris with dam-break initial conditions. The proposed methodology consists of establishing an approximation of the numerical model using a polynomial chaos expansion that is used in place of the original model, saving computational burden. The values of the parameters are then inferred through a Bayesian approach with a particular focus on inference discrepancies that some of the important features predicted by the model exhibit. We build the model approximation using a preconditioned non-intrusive method and show that a suitable prior parameter distribution is critical to the construction of an accurate surrogate model. The results of the Bayesian inference suggest that utilizing directly the available experimental data could lead to incorrect conclusions, including the over-determination of parameters. To avoid such drawbacks, we propose to base the inference on few significant features extracted from the original data. Our experiments confirm the validity of this approach, and show that it does not lead to significant loss of information. It is further computationally more efficient than the direct approach, and can avoid the construction of an elaborate error model.     

Impacts of future climate and land cover changes on landslide susceptibility: regional scale modelling in the Val d’Aran region (Pyrenees,Spain)

It is widely accepted that future environmental changes will affect rainfall-induced shallow slides in high-mountain areas. In this study, the Val d’Aran region located in the Central Pyrenees was selected to analyze and quantify the impacts of land use and land cover (LULC) and climate changes on regional landslides susceptibility. We analyzed 26 climate models of the EURO-CORDEX database focussing on the future rainfall conditions. The IDRISI TerrSet software suite was used to create the future LULC maps. These two inputs were analyzed individually and in a combined way defining 20 different scenarios. All these scenarios were incorporated in a physically based stability model to compute landslides susceptibility maps. The results showed that both environmental conditions will considerably change in the future. The daily rainfall will increase between 14 and 26% assuming a return period of 100 years. This intensification of precipitation will produce an overall decrease of the stability condition in the study area. Regarding the LULC prediction, the forest area will significantly increase, while in particular grassland, but also shrubs decrease. As a consequence, the overall stability condition improves, because the root strength is higher in forest than in grassland and shrubs. When we analyzed the combined impacts, the results showed that the positive effect of LULC changes is larger than the negative influence of rainfall changes. Hence, when combining the two aspects in the future scenarios, the stability condition in the study area will improve.

     

Environmental assessment of two artificial reef systems off southern Portugal (Faro and Olhão): A question of location

This study investigates environmental assessment of artificial reef systems deployed at different areas in terms of nutrient cycling and seabed organic enrichment. Two identical artificial reef systems: Olhão Artificial Reef—OAR (37°00′55″N and 007°44′54″W) and Faro Artificial Reef—FAR (36°58′65″N and 008°00′91″W) were deployed in southern Portuguese coast, adjacent to a highly productive coastal lagoon (Ria Formosa) in 1990 and monitorized over two years (1992–1993). Water samples were collected within OAR and FAR systems, inside the lagoon (L) and in a non-reef area (NRA) to evaluate nutrient dynamics. Settled particles and sediment cores were also sampled within OAR and FAR to determine aluminium, calcium, silicon and chlorophyll a and organic and inorganic carbon, nitrogen and phosphorous. Results obtained showed that: (i) water column nutrients evidenced seasonal and spatial variability. The maximum nutrients concentration was recorded inside the lagoon and in OAR, mainly during warmer periods. Ammonium, nitrate and silicate in OAR were statistically higher (p<0.01, n=18) than in FAR and NRA; (ii) particulate organic carbon and nitrogen in FAR settled particles were significantly higher (p<0.005) than those collected at OAR; and (iii) organic carbon and nitrogen, calcium, aluminium and chlorophyll a in OAR upper sediment were higher than at FAR. The overall results suggest that OAR is a productive system, emphasizing its contribution to the trophic chain pull out, while FAR presented oceanic oligotrophic water.     

Bioturbation and erosion rates along the soil-hillslope conveyor belt,part 2: Quantification using an analytical solution of the diffusion–advection equation

Particles on soil-mantled hillslopes are subject to downslope transport by erosion processes and vertical mixing by bioturbation. Both are key processes for understanding landscape evolution and soil formation, and affect the functioning of the critical zone. We show here how the depth–age information, derived from feldspar-based single grain post-infrared infrared stimulated luminescence (pIRIR), can be used to simultaneously quantify erosion and bioturbation processes along a hillslope. In this study, we propose, for the first time, an analytical solution for the diffusion–advection equation to calculate the diffusivity constant and erosion–deposition rates. We have fitted this model to age–depth data derived from 15 soil samples from four soil profiles along a catena located under natural grassland in the Santa Clotilde Critical Zone Observatory, in the south of Spain. A global sensitivity analysis was used to assess the relative importance of each model parameter in the output. Finally, the posterior probability density functions were calculated to evaluate the uncertainty in the model parameter estimates. The results show that the diffusivity constant at the surface varies from 11.4 to 81.9 mm² a^-1 for the hilltop and hill-base profile, respectively, and between 7.4 and 64.8 mm² a^-1 at 50 cm depth. The uncertainty in the estimation of the erosion–deposition rates was found to be too high to make a reliable estimate, probably because erosion–deposition processes are much slower than bioturbation processes in this environment. This is confirmed by a global sensitivity analysis that shows how the most important parameters controlling the age–depth structure in this environment are the diffusivity constant and regolith depth. Finally, we have found a good agreement between the soil reworking rates proposed by earlier studies, considering only particle age and depth, and the estimated diffusivity constants. The soil reworking rates are effective rates, corrected for the proportion of particles actually participating in the process. © 2019 John Wiley & Sons, Ltd.     

Preliminary characterization of some Argentinean Artemia populations from La Pampa and Buenos Aires provinces

Artemia populations were sampled in four hypersaline ecosystems in continental evaporitic basins from the Argentinean provinces of La Pampa and Buenos Aires. Biometrics of cysts and nauplii were performed. The morphometrics of adult females under standard culture conditions, studied by multivariate discriminant analysis, provided evidence that these populations belonged to the speciesA. persimilis; this was further supported by cross-breeding tests established between one of these populations (Salinas Grandes de Hidalgo, province of La Pampa) and a population ofA. franciscana from San Francisco Bay (California, USA), which showed reproductive isolation and barriers to gene flow between both populations.     

Assessment of the oil source-rock potential of the Pedregoso Formation (Early Miocene) in the Falcón Basin of northwestern Venezuela

The early Miocene Pedregoso Formation is one of the numerous formations rich in organic matter within the stratigraphic record of the Urumaco Trough, in the central area of the Falcón Basin. Due to its lithological characteristics and stratigraphic position, this formation is of great interest regarding the basin's petroliferous systems. The evaluation of various inorganic and organic geochemical parameters indicates that the organic matter is primarily of marine origin, deposited in a marine carbonate environment typical of reefal systems, under oxic-to-dysoxic conditions. The low variability in the TOC concentrations and in the distributions of the biomarkers extracted from the samples suggests that the paleoenvironmental conditions and the organic-matter supply remained approximately constant throughout the sedimentation of this unit. The Pedregoso type-II organic matter (marine origin) and initial organic richness value (∼1.8%) suggest that this unit has probably generated hydrocarbons within the Urumaco Trough. However, present-day thermal maturity parameters reveal that the Pedregoso organic matter is overmature (dry gas window), indicating that this unit is only capable to generate gas. In addition, the geothermal gradient, maturity parameters, and the maximum paleotemperature estimated in this study suggest that the Pedregoso Formation reached a maximum burial depth the ∼6.5 km, consistent with the value obtained from data of stratigraphic thickness in the Urumaco Trough. This implies that the thermal anomaly that affected the basin during the Late Eocene–Early Miocene did not reach the central part of the basin, and therefore, the organic matter maturation in this unit is due to the sedimentary burial.     

Primary production in the Strait of Gibraltar: Carbon fixation rates in relation to hydrodynamic and phytoplankton dynamics

Primary production was studied at nine sites distributed within the Strait of Gibraltar (Southern Spain) and North-Western (NW) Alboran Sea by analyzing photosynthesis-irradiance (P–I) relationships and integrated primary production rates in relation to the different types of Deep Chlorophyll Maxima (DCM) detected in the area. The characteristics of the DCM were examined by several methods, including flow cytometry, quantification of transparent expolymer particles and fluorimetric measurements that were applied in order to assess the photo-physiological state of the phytoplankton assemblages with respect to their species composition and water column structure (hydrology). The photosynthetic parameters (derived from P–I relationships) and integrated primary production (range 6–644 mg m⁻² d⁻¹) responded greatly to the diverse DCM identified and thereby the spatial variability of the primary production observed in the region was found to depend upon the occurrence of the different types of phytoplankton accumulations, which were themselves indicative of the previous history of the water column. The net contribution of the primary production to the air–sea CO₂ exchange process was also evaluated in the area. Results indicated that this region behaved as a net sink for the atmospheric CO₂, with the intensity of the flux being strongly modulated by the wind intensity.