Potential Flank-Collapse of Soufrière Volcano, Guadeloupe, Lesser Antilles? Numerical Simulation and Hazards

The past history of recurrent flank collapses of la Soufrière volcano of Guadeloupe, its structure, its well-developed hydrothermal system and the current activity constitute factors that could promote a future flank collapse, particularly in the case of a significant increase of activity, with or without shallow magmatic input. To address the hazards associated with such a collapse, we model the emplacement of the debris avalanche generated by a flank-collapse event in 1,250 BC (3,100 years B.P.). We use a finite-difference grain-flow model solving mass and momentum conservation equations that are depth-averaged over the slide thickness, and a Coulomb-type friction law with a variable basal (minimum) friction angle. Using the parameter values determined from this simulation, we then simulate the debris avalanche which could be generated by a potential collapse of the present lava dome. We then discuss the region which could be affected by such a future collapse, and additional associated hazards of concern.     

The oceanic substratum of Northern Luzon: Evidence from xenoliths within Monglo adakite (the Philippines)

Abstract   A 8.65 Ma adakitic intrusive sheet exposed near Monglo village in the Baguio District of Northern Luzon contains a suite of ultramafic and mafic xenoliths including in order of abundance: spinel dunites showing typical mantle-related textures, mineral and bulk rock compositions, and serpentinites derived from them; amphibole-rich gabbros displaying incompatible element patterns similar to those of flat or moderately enriched back-arc basin basalt magmas; and amphibolites derived from metabasalts and/or metagabbros of identical affinity. A single quartz diorite xenolith carrying a similar subduction-related geochemical signature has also been sampled. One amphibolite xenolith provided a whole-rock K–Ar age of 115.6 Ma (Barremian). We attribute the origin of this suite to the sampling by ascending adakitic magmas of a Lower Cretaceous ophiolitic complex located at a depth within the 30–35 km thick Luzon crust. It could represent an equivalent of the Isabela-Aurora and Pugo-Lepanto ophiolitic massifs exposed in Northern Luzon.     

Volcanic red-bed copper mineralisation related to submarine basalt alteration,Mont Alexandre,Quebec Appalachians,Canada

Two types of native copper occur in Upper Silurian basaltic rocks in the Mont Alexandre area, Quebec Appalachians: (1) type 1 forms micrometric inclusions in plagioclase and is possibly magmatic in origin, whereas (2) type 2 occurs as coarse-grained patches rimmed by cuprite in altered porphyritic basalt. Type 1 has higher contents of sulphur (2,000–20,263 ppm) and arsenic (146–6,017 ppm), and a broader range of silver abundances (<65–2,186 ppm Ag) than type 2 (149–1,288 ppm S, <90–146 As, <65–928 ppm Ag). No mineral inclusions of sulphide or arsenide in native copper were observed at the electron-microprobe scale. Primary igneous fabrics are preserved, but the basaltic flows are pervasively oxidised and plagioclase is albitised. Chlorite replaces plagioclase and forms interstitial aggregates in the groundmass and has Fe/(Fe+Mg) ratios ranging from 0.29 to 0.36 with calculated temperatures between 155°C and 182°C. Copper sulphides in vacuoles and veinlets are associated with malachite, fibro-radiating albite and yarrowite (Cu₉S₈ with up to 0.3 wt% Ag). Bulk-rock concentrations of thallium and lithium range from 70 to 310 ppb and 10 to 22 ppm, respectively, and thallium is positively correlated with Fe₂O₃. Such concentrations of thallium and lithium are typical of spilitisation during heated seawater–basalt interaction. Spilitisation is consistent with the regional geological setting of deepwater-facies sedimentation, but is different from current models for volcanic red-bed copper, which indicate subaerial oxidation of volcanic flows. The volcanic red-bed copper model should be re-examined to account for native copper mineralisation in basalts altered by warm seawater.     

Abiotic formation of hydrocarbons under hydrothermal conditions: Constraints from chemical and isotope data

To understand reaction pathways and isotope systematics during mineral-catalyzed abiotic synthesis of hydrocarbons under hydrothermal conditions, experiments involving magnetite and CO₂ and H₂-bearing aqueous fluids were conducted at 400 °C and 500 bars. A robust technique for sample storage and transfer from experimental apparatus to stable isotope mass spectrometer provides a methodology for integration of both carbon and hydrogen isotope characterization of reactants and products generated during abiogenic synthesis experiments. Experiments were performed with and without pretreatment of magnetite to remove background carbon associated with the mineral catalyst. Prior to experiments, the abundance and carbon isotope composition of all carbon-bearing components were determined. Time-series samples of the fluid from all experiments indicated significant concentrations of dissolved CO and C₁-C₃ hydrocarbons and relatively large changes in dissolved CO₂ and H₂ concentrations, consistent with formation of additional hydrocarbon components beyond C₃. The existence of relatively high dissolved alkanes in the experiment involving non-pretreated magnetite in particular, suggests a complex catalytic process, likely involving reinforcing effects of mineral-derived carbon with newly synthesized hydrocarbons at the magnetite surface. Similar reactions may be important mechanisms for carbon reduction in chemically complex natural hydrothermal systems. In spite of evidence supporting abiotic hydrocarbon formation in all experiments, an “isotopic reversal” trend was not observed for ¹³C values of dissolved alkanes with increasing carbon number. This may relate to the specific mechanism of carbon reduction and hydrocarbon chain growth under hydrothermal conditions at elevated temperatures and pressures. Over time, significant ¹³C depletion in CH₄ suggests either depolymerization reactions occurring in addition to synthesis, or reactions between the C₁-C₃ hydrocarbons and carbon species absorbed on mineral surfaces and in solution.     

A continuum-based model on axial pile-head dynamic impedance in inhomogeneous soil

Acta Geotechnica - This paper presents a closed-form solution on the steady dynamic response of circular piles embedded in inhomogeneous soil. The soil is modeled as a viscoelastic continuum, and...     

Active hydrothermal fluids circulation triggering small-scale collapse events: the case of the 2001–2002 fissure in the Lakki Plain (Nisyros Island,Aegean Sea,Greece)

Rip currents are fast moving, offshore flows that have the ability to move even the strongest swimmers into deeper waters. Miami Beach, Florida is one of the most visited beaches in the USA and a sought after destination for citizens and international tourists alike. It is also known to be a rip current “hot spot.” These factors greatly increase the risk of drowning; however, no previous research has focused on beachgoer perception of rip-related risks in South Florida. Over a 12-month period, 203 public surveys were collected to determine the rip current knowledge of beachgoers at Miami Beach based on factors such as swimming ability and frequency of beach visits. The responses were analyzed by constructing a normalized component factor to determine the respondent’s comprehensive knowledge of rips, and multiple regression models were used to assess the net influences of sociodemographic and behavioral characteristics on the responses. A significant proportion of the survey respondents showed insufficient knowledge, indicating they are at risk of drowning in a rip current. Frequent beachgoer’s exposure to the beach environment, maturation, and nativity is identified as the main contributors to knowledge net of other sociodemographic compositions. The most at-risk groups were determined to be young adults, foreign tourists, poor swimmers, and those who infrequently visited the beach. Miami Beach needs to initiate a rip current safety campaign to target these at-risk beachgoers, where interventions beyond familial and educational institutions should be introduced.     

Mineralogy and geochemistry of pozzolans from the Tombel Plain,Bamileke Plateau,and Noun Plain monogenetic volcanoes in the central part of the Cameroon Volcanic Line

Acta Geochimica - Pozzolans from the Tombel Plain, Bamileke Plateau, and Noun Plain, 3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line (the Tombel Plain, Bamileke...     

Correction to: Using Causal Inference in Field Development Optimization: Application to Unconventional Plays

Mathematical Geosciences - Unfortunately, in the original version of the article the first and second name of the fourth author were wrong.     

Farewell to Harry M. Parker (1946–2019)

Mathematical Geosciences -