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How hazardous is the gas accumulation in Lake Kivu? Arguments for a risk assessment in light of the Nyiragongo Volcano eruption of 2002
... Stratification andmixing Damas 1937;Tietze 1978;Newman 1976;Halbwachs et al. 2002;Schmid and Wüest 2012. Fluxes, turbulent and double diffusion Schmid et al. 2004Schmid et al. , 2005Schmid et al. & 2010Pasche et al. 2009Pasche et al. & 2010Wüest et al. 2012;Sommer et al. 2013a & b;Hirslund 2012;Schmid and Wüest, 2012;Schmid et al. 2010;Carpenter et al. 2012a & b;Katsev et al. 2014;Ross et al. 2015a;Toffolon et al. 2015;Sommer et al. 2014Sommer et al. & 2019. Warming and climate Lorke et al. 2004;Borges et al. 2011;MacIntyre, 2013;Katsev et al. 2014;Thiery et al. 2014aThiery et al. , 2014bKranenburg et al. 2020. ...
... Hydrology Bergonzini 1998Bergonzini et al. 2002;Munyaneza et al. 2009;Habiyaremye et al. 2011;Muvundja et al. 2009. Gases and geochemistry Degens and Kulbicki 1973Tietze 1978Tietze , 1980Jannasch 1975;Tietze et al. 1980;Botz et al. 1988;Schmid et al. 2004Schmid et al. & 2005Tassi et al. 2009;Borges et al. 2011;Roland et al. 2016Roland et al. & 2018. Nutrient and organic matter cycling Kilham and Kilham 1990;Muvundja et al. 2009;Pasche et al. 2012;Kneubühler et al. 2007;Al-Mutlaq et al. 2008;Morana et al. 2014Morana et al. , 2015aMorana et al. & 2015bBorges et al., 2014. ...
... Pasche 2012;Pasche et al. 2010;Ross et al. 2015b;Votava et al. 2016. Lake Kivu natural hazards Balagizi et al. 2018;Delvaux et al. 2015;Doevenspeck 2007;Ross et al. 2014Ross et al. , 2015aTassi and Rouwet 2014;Schmid et al. 2004Schmid et al. & 2005 in the northwestern part of the lake such as volcanic cones, tuff rings, and traces of past lava flows (Ross et al., 2014). Lake Kivu is an ancient rift lake, existing since the mid-Pleistocene. ...
Lake Kivu is one of the African Great Lakes lying in the Albertine Rift. It provides livelihoods to 5.7 million people living in the two riparian countries of the Democratic Republic of the Congo and the Republic of Rwanda. Lake Kivu is currently experiencing numerous stressors, including fish habitat destruction, pollution, invasive species, weak governance and law enforcement as well as conflict between riparian countries. One of the biggest challenges on Lake Kivu is the limitation of coordinated and consistent research on the lake. Scientific attention to large lakes is often not seen as a high enough priority by the riparian countries, despite the lake sustaining millions of people’s livelihoods, and contributes to the GDP of both countries. Although we have a fair understanding of the basic geology, physics, chemistry, and biology of the lake, there is a need for stronger long-term monitoring and research frameworks to gain more comprehensive understanding of the changes resulting from human uses and global warming. These would be needed to develop good policies and management decisions for sustainable and long-term health and use of the lake’s resources. This manuscript presents an opinion of experts on what is known about the current lake’s current status and its resources as well as about what should be done. It highlights key threats, issues and gaps that needs to be urgently addressed, and provides specific and strategic ways forward for long-term monitoring and management, essential to achieving a healthy Lake Kivu, able to sustain its dependents.
... This new flank eruption, which generated lava flows, was larger (25 million m 3 over 14 km 2 ) and more destructive than that of 1977 (Wisner, 2017;Wauthier et al., 2012;Smets et al., 2015a). In less than 24 h, Goma was crossed by two lava flows, one of which reached Lake Kivu (Schmid et al., 2002). Komorowski et al. (2002) estimate that 40 people died and that 120 000 people had their homes destroyed. ...
Risk perception is an essential element to consider for effective risk management at the time of eruption , especially in densely populated cities close to volcanoes like Goma in the east of the Democratic Republic of the Congo, which is highly exposed to volcanic hazards from Nyiragongo. The perception of volcanic risk involves the processes of collecting, selecting and interpreting signals about uncertain impacts of volcanic hazards. Using a questionnaire survey, this study describes the spatial differences and factors influencing the individual volcanic risk perception of 2224 adults from eight representative neighbourhoods of Goma before the May 2021 Nyiragongo eruption. A composite risk perception indicator was built from the perceived severity and perceived vulnerability. Statistical analysis of the survey's results shows that the risk perception was high (mean = 3.7 on a five-point Likert scale) and varies less with demographic and contextual factors than with cognitive and psychological factors. Volcanic hazards were perceived to be more threatening the city and its functioning than the individuals themselves. The spatial analysis shows that respondents from the eastern neighbourhoods, affected by the 2002 eruption , demonstrated a significantly higher level of risk perception than participants living in the western neighbourhoods. This study will help to improve volcanic risk awareness raising in Goma.
... We think this may be related to the fact that the other villages are close to Lake Kivu and Kabuno bay and may reflect the fear that regional earthquakes could trigger a limnic eruption or a tsunami (see Ref. [53] for a review of the potential effects of earthquakes on the stability of Lake Kivu). The lake contains high quantities of dissolved gases: ~250 km 3 of CO 2 and ~55 km 3 of CH 4 stored in deeper water layers [78,79], which might be catastrophic for the population living on its shores. Recently [38], highlighted that earthquakes were strongly felt by the inhabitants of Goma and Gisenyi, located on the shores of Lake Kivu (Fig. 1), a few hours after the last Nyiragongo eruption. ...
... Groundwater inflow to the lake is known and has mainly been documented from the north, where active volcanoes dominate the geology (Schmid et al., 2002;Ross et al., 2015). The soil in this area originates from acid metamorphic and volcanic parent materials, and is characterized by the presence of narrow-to-wide fractures varying from shallow to deep, in addition to fissures acting as high-rate water infiltrating sites. ...
Due to their biological and chemical inertness, noble gases in natural waters are widely used to trace natural waters and to determine ambient temperature conditions during the last intensive contact with the atmosphere (equilibration). Noble gas solubilities are strong functions of temperature, with higher temperatures resulting in lower concentrations. Thus far, only common environmental conditions have been considered, and hence investigated temperatures have almost never exceeded 35 °C, but environmental scenarios that generate higher surface-water temperatures (such as volcanism) exist nonetheless. Recently published measurements of noble gas concentrations in Lake Kivu, which sits at the base of the Nyiragongo volcano in East Africa, unexpectedly show that the deep waters are strongly depleted in noble gases with respect to in-situ conditions, and so far no quantitative explanation for this observation has been provided. We make use of recently published noble gas solubility data at higher temperatures to investigate our hypothesis that unusually high equilibration temperatures could have caused the low measured noble gas concentrations by applying various approaches of noble gas thermometry. Noble gas concentration ratios and least squares fitting of individual concentrations indicate that the data agrees best with the assumption that deep water originates from groundwater formed at temperatures of about 65 °C. Thus, no form of degassing is required to explain the observed noble gas depletion: the deep water currently contained in Lake Kivu has most probably never experienced a large scale degassing event. This conclusion is important as limnic eruptions were feared to threaten the lives of the local population.
... Two years earlier in 1984, the very first fatal eruption happened in Lake Monoun (Cameroon, Africa) killed about 40 people (Sigurdsson et al., 1987). These disasters started from the CO 2 leaking into the water through the crack of the rock near the lake floor (Schmid et al., 2004). Then the CO 2 dissolved into the water and after a long period of time, the concentration of CO 2 reached a level close to the saturation condition at a certain depth. ...
Gas-driven limnic eruption can happen in a lake with an aqueous gas solution that becomes supersaturated due to some reason. In this case, the exsolution of massive gases dissolved in the water could occur in a very short time, resulting in a disaster as happened in the Lake Nyos (Cameroon, Africa) in 1986. Using degassing pipe to artificially release the dissolved gases is a good way to minimize the risk of an eruption. In this study, a transient multi-component gas-liquid two-phase flow model of the degassing pipe used in Lake Nyos has been established and verified with the observed eruption data. The drift flux model has been used for modelling of a transient multi-component gas-liquid flow formed due to the spontaneous exsolution of gases dissolved in the water inside the degassing pipe. The governing equations for the mechanistic drift model include continuity equation for each phase, a single momentum equation for a homogeneous mixture of the fluid, constitutive equations for mass transfer rates between the phases, and the drift velocity formulas. The model considered not only CO2 but also CH4 as dissolved gases. The “chain reaction” conjecture predicted to have the degassing-point migrating downward with time during the transient degassing process is verified by using this model. The relationship between the eruption height and the CO2 concentration at the bottom of the degassing pipe has been simulated in detail. This relationship supplies people with a quick and convenient way to estimate the CO2 concentration in the lake, based on which one can evaluate the risk of lake eruption and hence to formulate or adjust the degassing plan. In addition, the effects of diameter and equivalent roughness of the degassing pipe on the eruption height has been investigated. Meanwhile, the eruption height upper-limit in different lake-depth scenarios has also been determined. Finally, the role of CH4 component in the degassing process has been analyzed. Although the influence of CH4 on eruption height can be neglected in Lake Nyos' case, CH4 as a dissolved gas plays an important role at Lake Kivu. The multi-component gas-liquid flow model developed in this study is useful to study the role of CH4 in the degassing process.
... Groundwater inflow to the lake is known and has mainly been documented from the north, where active volcanoes dominate the geology (Schmid et al., 2002;Ross et al., 2015). The soil in this area originates from acid metamorphic and volcanic parent materials, and is characterized by the presence of narrow-to-wide fractures varying from shallow to deep, in addition to fissures acting as high-rate water infiltrating sites. ...
... The same is true of ancient fractures visible only towards the northern shore of the lake, where the various CO exit points called mazukus are located. The concentration of carbon dioxide in these points is too high but varies too little and does not seem to have a direct relationship with the activity of Thus, the northern watershed of Lake Kivu constitutes a large reservoir of carbon dioxide from which gas-rich infiltrated rainwater feeds the deep waters of Lake Kivu through subaqueous springs (Schmid et al., 2004). This lake currently contains 300 cubic kilometers of carbon dioxide and 60 cubic kilometers of methane, which can rise through volcanic vents, which is more than 300 times the volume of gas contained in the waters of Lake Nyos, which caused 1,700 deaths when it erupted (Le lac Kivu menace ses riverains', Courrier international (Afrique Centrale, 2009)). ...
Classical mechanisms of volcanic eruptions mostly involve pressure buildup and magma ascent towards the surface1. Such processes produce geophysical and geochemical signals that may be detected and interpreted as eruption precursors1–3. On 22 May 2021, Mount Nyiragongo (Democratic Republic of the Congo), an open-vent volcano with a persistent lava lake perched within its summit crater, shook up this interpretation by producing an approximately six-hour-long flank eruption without apparent precursors, followed—rather than preceded—by lateral magma motion into the crust. Here we show that this reversed sequence was most likely initiated by a rupture of the edifice, producing deadly lava flows and triggering a voluminous 25-km-long dyke intrusion. The dyke propagated southwards at very shallow depth (less than 500 m) underneath the cities of Goma (Democratic Republic of the Congo) and Gisenyi (Rwanda), as well as Lake Kivu. This volcanic crisis raises new questions about the mechanisms controlling such eruptions and the possibility of facing substantially more hazardous events, such as effusions within densely urbanized areas, phreato-magmatism or a limnic eruption from the gas-rich Lake Kivu. It also more generally highlights the challenges faced with open-vent volcanoes for monitoring, early detection and risk management when a significant volume of magma is stored close to the surface. The 2021 eruption of Mount Nyiragongo, DR Congo demonstrated that magma storage close to the surface in open systems means that eruptions may occur with very short-term precursory activity, raising major challenges for their monitoring.
Risk perception is an essential element to consider for effective risk management at time of eruption. This is especially the case in densely populated cities close to volcanoes like Goma in the East of the Democratic Republic of Congo highly exposed to volcanic hazards from Nyiragongo. The perception of volcanic risk involves the processes of collecting, selecting, and interpreting signals about uncertain impacts of volcanic hazards. Using a questionnaire survey, this study describes the spatial differences and factors influencing the individual volcanic risk perception of 2,224 adults from height representative neighbourhoods of Goma before the May 2021 Nyiragongo eruption. A composite risk perception indicator was built from the perceived severity and perceived vulnerability. Statistical analysis of survey’s results shows that the risk perception varies less with demographic and contextual factors than with cognitive and psychological factors. The spatial analysis shows that respondents from the eastern neighbourhoods, affected by the 2002 eruption, demonstrated a significantly higher level of risk perception than participants living in the western neighbourhood. Therefore, collective memory of past events in the impacted areas does play a role. Evidence from this study will help to develop well-targeted volcanic risk awareness-raising in Goma.
When a sediment laden river flows into a stratified water body, the water mass can either intrude as an overflow, interflow or underflow, depending upon the density contrast. Different modes of sediment driven convection occur in each case. For the case of overflows, convective sedimentation occurs beneath the plume, whereby sediment rich plumes rapidly transport fine materials to depth. If underflow of dense sediment laden waters initially occurs, then after sediment has been deposited, the light interstitial material can subsequently loft and potentially mixes the entire water column. For an interflow, both lofting and sediment driven convection can occur above and below the pycnocline. All of these different regimes can be described in terms of two dimensionless parameters: namely RS = DrS / DrC and RA = DrA /DrC, where DrA is the density contrast between the upper layer and the river inflow (due to just salinity or temperature differences), DrC is the density contrast due to sediment between river and upper‐layer, and DrS is the density contrast between upper and lower layers (due to just salinity or temperature differences). Laboratory experiments were used to describe the vigour of convection in terms of these dimensionless parameters, which then allows behaviour of various inflows to be predicted. In most cases the convective velocities observed were an order of magnitude faster than Stokes settling velocities. These observations are also applied to predict how a turbidity current could lead to lofting and possible overturn of the stratification of Lake Kivu, a large meromictic lake between Rwanda and the Democratic Republic of the Congo.
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