An overview of the structure, hazards, and methods of investigation of Nyos-type lakes from the geochemical perspective

Limnic eruptions represent a natural hazard in meromictic lakes hosted in volcanoes releasing CO2-rich magmatic gases. Biogeochemical processes also contribute to dissolved gas reservoirs since they can produce significant amounts of gases, such as CH4 and N2. Dissolved gases may have a strong influence of the density gradient and the total dissolved gas pressure along the vertical profile of a volcanic lake. An external triggering event, possibly related to uncommon weather conditions, volcanic-seismic activity, or landslides, or spontaneous formation of gas bubbles related to the progressive attainment of saturation conditions at depth, may cause a lake rollover and the consequent release of dissolved gases. This phenomenon may have dramatic consequences due to i) the release of a toxic CO2-rich cloud able to flow long distances before being diluted in air, or ii) the contamination of the shallow water layer with poisonous deep waters. The experience carried out over the past twelve years at Lake Nyos, where a pumping system discharges CO2- rich deep water to the surface, has shown that controlled degassing of deep water layers is the best solution to mitigate such a hazard. However, the application of this type of intervention in other lakes must be carefully evaluated, since it may cause severe contamination of shallow lake water or create dangerous density instabilities. Monitoring of physical and chemical parameters controlling lake stability and the evolution in time of dissolved gas reservoirs can provide essential information for evaluating the risk associated with possible rollover phenomena. Conceptual models for the description of limnological, biogeochemical and volcanic processes regulating water lake stability have been constructed by interpreting compositional data of lake water and dissolved gas compositions obtained by applying different sampling and analytical techniques. This study provides a critical overview of the existing methodological approaches and discusses how future investigations of Nyos-type lakes, aimed at mitigating the hazard for limnic eruptions, can benefit from i) the development of new technical and theoretical approaches aimed to constrain the physical-chemical mechanisms controlling this natural phenomenon, and ii) information from different scientific disciplines, such as microbiology, fluid dynamics and sedimentology

2016 Jeffrey M. Hoeg Award Lecture: Immune Checkpoints in Atherosclerosis: Toward Immunotherapy for Atheroprotection

Innate and adaptive immune effector mechanisms, in conjunction with hyperlipidemia, are important drivers of atherosclerosis. The interaction between the different immune cells and the secretion of cytokines and chemokines determine the progression of atherosclerosis. The activation or dampening of the immune response is tightly controlled by immune checkpoints. Costimulatory and coinhibitory immune checkpoints represent potential targets for immune modulatory therapies for atherosclerosis. This review will discuss the current knowledge on immune checkpoints in atherosclerosis and the clinical potential of immune checkpoint targeted therapy for atherosclerosis

Geochemical monitoring of volcanic lakes. A generalized box model for active crater lakes

In the past, variations in the chemical contents (SO4 2−, Cl−, cations) of crater lake water have not systematically demonstrated any relationships with eruptive activity. Intensive parameters (i.e., concentrations, temperature, pH, salinity) should be converted into extensive parameters (i.e., fluxes, changes with time of mass and solutes), taking into account all the internal and external chemical–physical factors that affect the crater lake system. This study presents a generalized box model approach that can be useful for geochemical monitoring of active crater lakes, as highly dynamic natural systems. The mass budget of a lake is based on observations of physical variations over a certain period of time: lake volume (level, surface area), lake water temperature, meteorological precipitation, air humidity, wind velocity, input of spring water, and overflow of the lake. This first approach leads to quantification of the input and output fluxes that contribute to the actual crater lake volume. Estimating the input flux of the "volcanic" fluid (Qf - kg/s) –– an unmeasurable subsurface parameter –– and tracing its variations with time is the major focus during crater lake monitoring. Through expanding the mass budget into an isotope and chemical budget of the lake, the box model helps to qualitatively characterize the fluids involved. The (calculated) Cl− content and dD ratio of the rising "volcanic" fluid defines its origin. With reference to continuous monitoring of crater lakes, the present study provides tips that allow better calculation of Qf in the future. At present, this study offers the most comprehensive and up-to-date literature review on active crater lakes

A science & arts sensitization program in Chapultenango, 25 years after the 1982 El Chichόn eruptions (Chiapas, Mexico)

Volcanic risk perception may drastically decrease after eruptions and during periods of volcanic quiescence. Despite the fact that the adults in Chapultenango, a Zoque indigenous community near El Chichόn volcano (Chiapas, Mexico), lived through the 1982 Plinian eruptions, their awareness of present volcanic risk is low. In particular, children, adolescents and young adults (born after 1982) should be informed about the activity of El Chichόn, as they are more likely to be affected by possible future eruptions. This grass roots level sensitization project uses a novel approach to poll risk perception and to transmit knowledge of El Chichόn volcano among 6- to 11-year old children by combining scientific information sessions with arts workshops. Similar scientific sessions, although without the arts workshops, were less efficient for the older age group (Secondary School students). Moreover, the local Proteccion Civil and Gobierno Municipal was invited to participate in a basic monitoring of El Chichόn volcano. A lack in continuity in local political terms presented the major barrier for an effective and self-sufficient following-up of the volcanic surveillance. The entire population of Chapultenango was involved during informal meetings and semi-scientific projections of "their volcano", offering an alternative and more scientific view on El Chichόn's activity, often referenced in a more mystical-religious frame. It is experienced that the volcanologist is recognized as a highly trusted professional, bridging the gap between the official authorities and society

HCl degassing from extremely acidic crater lakes: preliminary results from experimental determinations and implications for geochemical monitoring.

Crater lakes are monitored to detect volcanic unrest starting from the assumption that they behave as condensers for magmatic gases. A further assumption is that acidic gases such as HCl are conservative once dissolved in water. This is not true for extremely acidic crater lakes, whose H + activity is high enough to induce Cl2 hydrolysis and consequently HCl degassing. This study presents the results of experimental determinations at 40–458C demonstrating that HCl degassing from acidic water depends on pH and Cl2 concentration. HCl degassing starts at pH values c. 0.05–0.1 with a rate of 5–10 mg min21 l21, increasing up to c. 70 mg min21 l21 at pH,20.2. This implies that the rate of HCl removal from a crater lake with a volume of 104–105 m3 and a seawater-like Cl2 concentration ranges from 5 to 50 t h21. The estimated HCl/H2O ratio in the separated vapour phase (0.01–0.2) is coherent with HCl/H2O ratios of fumaroles. Our experiments imply that: (i) the presence of very acidic gas species in fumaroles can be associated with a liquid-dominated feeding system, and (ii) dissolved in extremely acidic crater lakes, Cl2 behaves as a non-conservative component.Published97-1064V. Dinamica dei processi pre-eruttiv

Dynamics and mass balance of El Chichón crater lake, Mexico.

The mass balance of El Chichón crater lake is controlled by precipitations, evaporation and seepage through the lake bottom. The main non-meteoric source of water and Cl for the lake is a boiling spring (Soap Pool) discharging saline and neutral water with a variable flow rate from 0 to 30 kg/s inside the El Chichón crater. Variations in lake volume over time were approximately determined from digitized photographic views of the lake using an empirical relationship between depth of the lake and surface area, obtained after four bathymetric surveys. The best correlation between the observed changes in lake volume, Cl content and the measured flow rate of Soap Pool was obtained by a box-model for the Cl mass balance. Based on a trend in the Cl content of the Soap Pool water a model of a “buried” initial crater lake is proposed

Modeling CO2 air dispersion from gas driven lake eruptions (Invited)

The most tragic event of gas driven lake eruption occurred at Lake Nyos (Cameroon) on 21 August 1986, when a dense cloud of CO2 suffocated more than 1700 people and an uncounted number of animals in just one night. The event stimulated a series of researches aimed to understand gas origins, gas release mechanisms and strategies for gas hazard mitigation. Very few studies have been carried out for describing the transport of dense CO2 clouds in the atmosphere. Although from a theoretical point of view, gas dispersion can be fully studied by solving the complete equations system for mass, momentum and energy transport, in actual practice, different simplified models able to describe only specific phases or aspects have to be used. In order to simulate dispersion of a heavy gas and to assess the consequent hazard we used a model based on a shallow layer approach (TWODEE2). This technique which uses depthaveraged variables to describe the flow behavior of dense gas over complex topography represents a good compromise between the complexity of computational fluid dynamic models and the simpler integral models. Recently the model has been applied for simulating CO2 dispersion from natural gas emissions in Central Italy. The results have shown how the dispersion pattern is strongly affected by the intensity of gas release, the topography and the ambient wind speed. Here for the first time we applied TWODEE2 code to simulate the dispersion of the large CO2 clouds released by limnic eruptions. An application concerns the case of the 1986 event at lake Nyos. Some difficulties for the simulations were related to the lack of quantitative information: gas flux estimations are not well constrained, meteorological conditions are only qualitatively known, the digital model of the terrain is of poor quality. Different scenarios were taken into account in order to reproduce the qualitative observations available for such episode. The observations regard mainly the effects of gas on the people living in the surrounding areas. Simulation results are in good agreement with these observations. Another application is focused on a hypothetical gas release from lake Albano (Italy), a volcanic lake that probably degassed on the past as reported in historical chronicles by the Roman historian Titus Livius. At the present time the lake is far from saturation conditions and the occurrence of such an event is impossible. However a recent re-interpretation of literature data clearly show the presence of anomalous CO2 enrichment of the lake waters during the last seismic crisis which affected the area. For these reasons a future limnic eruption can not be ruled out completely. The simulations we present show the potential effect of a gas driven eruption from lake Albano in this densely populated area located 20 km south-east from the centre of Rome

CO2 and H2S Degassing at Fangaia Mud Pool, Solfatara, Campi Flegrei (Italy): Origin and Dynamics of the Pool Basin

The Fangaia mud pool provides a "window" into the hydrothermal system underlying the degassing Solfatara crater, which is the most active volcanic centre inside the restless Campi Flegrei caldera, Southern Italy. The present study aimed at unravelling the degassing dynamics of CO2 and H2S flushing through the pH 1.2 steam-heated Fangaia mud pool, an ideal field laboratory as a proxy of an active crater lake. Our results from MultiGAS measurements above Fangaia's surface show that H2S scrubbing, demonstrated by high CO2/H2S ratios, was most efficient in the portions of the basin affected by diffusive degassing. Convective bubbling degassing instead was the most effective mechanism to release gas in quantitative terms, with lower CO2/H2S ratios, similar to the Solfatara crater fumaroles, the high-T end member of the hydrothermal system. Unsurprisingly, total estimated CO2 and H2S fluxes from the small Fangaia pool (~184 m2 in June 2017) were at least two orders of magnitude lower (CO2 flux < 64 t/d, H2S flux < 0.5 t/d) than the total CO2 flux of the Campi Flegrei caldera (up to 3000 t/d for CO2), too low to affect the gas budget for the caldera, and hence volcano monitoring routines. Given the role of the rising gas as "sediment stirrer", the physical and chemical processes behind gas migration through a mud pool are arguably the creating processes giving origin to Fangaia. Follow-up studies of this so far unique campaign will help to better understand the fast dynamics of this peculiar degassing feature