LES RISQUES LIES AUX MAZUKU DANS LA REGION DE GOMA, REPUBLIQUE DEMOCRATIQUE DU CONGO (RIFT EST-AFRICAIN)

   Dans la région au nord du lac Kivu située dans la partie occidentale du rift africain, des fractures profondes permettent la remontée de gaz, surtout du gaz carbonique, dans des zones localement appelées mazuku; en Kiswahili des endroits où un gaz diabolique tue les gens.  Généralement, les mazuku sont des dépressions et/ou des fronts des coulées de lave où le CO2 s’accumule par gravité, formant des lieux où l’air est très riche en CO2 et donc toxique, voire même létal. Le CO2 est un gaz plus lourd que l’air, asphyxiant, irrite les yeux, le nez et la gorge, et mortel à des concentrations supérieures à 15%. Malheureusement beaucoup de mazuku sont localisés dans le périmètre de la ville de Goma et dans les environnements immédiats. La population de Goma croit que la concentration en CO2 a diminué avec le temps dans les mazuku, pourtant quatre campagnes de mesures effectuées dans les mazuku de la ville de Goma montrent le contraire ; les concentrations en CO2 culminent à 70% dans quelques sites. On trouve les mazuku en pleine ville de Goma, mais ils abondent surtout dans les régions de Kituku, Lac Vert, Bulengo. C’est fort malheureusement de ce côté que sont orientées les nouvelles constructions d’habitations ce qui les expose au risque de CO2. Ici des espaces à fortes concentrations en CO2 sont déjà lotis. Ce gaz volcanique a causé et continue de causer des morts d’humains et d’animaux dans les zones concernées. Nous proposons que les panneaux d’alerte soient replacés dans ces zones à haut risque et les campagnes d’information et de sensibilisation sur les risques liés aux mazuku  sont également fortement recommandées

Synoptic analysis of a decade of daily measurements of SO2 emission in the troposphere from volcanoes of the global ground-based Network for Observation of Volcanic and Atmospheric Change

Volcanic plumes are common and far-reaching manifestations of volcanic activity during and between eruptions. Observations of the rate of emission and composition of volcanic plumes are essential to recognize and, in some cases, predict the state of volcanic activity. Measurements of the size and location of the plumes are important to assess the impact of the emission from sporadic or localized events to persistent or widespread processes of climatic and environmental importance. These observations provide information on volatile budgets on Earth, chemical evolution of magmas, and atmospheric circulation and dynamics. Space-based observations during the last decades have given us a global view of Earth's volcanic emission, particularly of sulfur dioxide (SO2). Although none of the satellite missions were intended to be used for measurement of volcanic gas emission, specially adapted algorithms have produced time-averaged global emission budgets. These have confirmed that tropospheric plumes, produced from persistent degassing of weak sources, dominate the total emission of volcanic SO2. Although space-based observations have provided this global insight into some aspects of Earth's volcanism, it still has important limitations. The magnitude and short-term variability of lower-atmosphere emissions, historically less accessible from space, remain largely uncertain. Operational monitoring of volcanic plumes, at scales relevant for adequate surveillance, has been facilitated through the use of ground-based scanning differential optical absorption spectrometer (ScanDOAS) instruments since the beginning of this century, largely due to the coordinated effort of the Network for Observation of Volcanic and Atmospheric Change (NOVAC). In this study, we present a compilation of results of homogenized post-analysis of measurements of SO2 flux and plume parameters obtained during the period March 2005 to January 2017 of 32 volcanoes in NOVAC. This inventory opens a window into the short-term emission patterns of a diverse set of volcanoes in terms of magma composition, geographical location, magnitude of emission, and style of eruptive activity. We find that passive volcanic degassing is by no means a stationary process in time and that large sub-daily variability is observed in the flux of volcanic gases, which has implications for emission budgets produced using short-term, sporadic observations. The use of a standard evaluation method allows for intercomparison between different volcanoes and between ground- and space-based measurements of the same volcanoes. The emission of several weakly degassing volcanoes, undetected by satellites, is presented for the first time. We also compare our results with those reported in the literature, providing ranges of variability in emission not accessible in the past. The open-access data repository introduced in this article will enable further exploitation of this unique dataset, with a focus on volcanological research, risk assessment, satellite-sensor validation, and improved quantification of the prevalent tropospheric component of global volcanic emission

River geochemistry, chemical weathering and atmospheric CO2 consumption rates in the Virunga Volcanic Province (East Africa)

© 2015. American Geophysical Union. All Rights Reserved. We report a water chemistry data set from 13 rivers of the Virunga Volcanic Province (VVP) (Democratic Republic of Congo), sampled between December 2010 and February 2013. Most parameters showed no pronounced seasonal variation, whereas their spatial variation suggests a strong control by lithology, soil type, slope, and vegetation. High total suspended matter (289-1467 mg L-1) was recorded in rivers in the Lake Kivu catchment, indicating high soil erodibility, partly as a consequence of deforestation and farming activities. Dissolved and particulate organic carbon (DOC and POC) were lower in rivers from lava fields, and higher in nonvolcanic subcatchments. Stable carbon isotope signatures (δ13C) of POC and DOC mean δ13C of -22.5‰ and -23.5‰, respectively, are the first data to be reported for the highland of the Congo River basin and showed a much higher C4 contribution than in lowland areas. Rivers of the VVP were net sources of CH4 to the atmosphere (4-5052 nmol L-1). Most rivers show N2O concentrations close to equilibrium, but some rivers showed high N2O concentrations related to denitrification in groundwaters. δ13C signatures of dissolved inorganic carbon suggested magmatic CO2 inputs to aquifers/soil, which could have contributed to increase basalt weathering rates. This magmatic CO2-mediated basalt weathering strongly contributed to the high major cation concentrations and total alkalinity. Thus, chemical weathering (39.0-2779.9 t km-2 yr-1) and atmospheric CO2 consumption (0.4-37.0 × 106 mol km-2 yr-1) rates were higher than previously reported in the literature for basaltic terrains.status: publishe

River geochemistry, chemical weathering, and atmospheric CO2 consumption rates in the Virunga Volcanic Province (East Africa)

We report a water chemistry data set from 13 rivers of the Virunga Volcanic Province (VVP) (Democratic Republic of Congo), sampled between December 2010 and February 2013. Most parameters showed no pronounced seasonal variation, whereas their spatial variation suggests a strong control by lithology, soil type, slope, and vegetation. High total suspended matter (289–1467 mg L−1) was recorded in rivers in the Lake Kivu catchment, indicating high soil erodibility, partly as a consequence of deforestation and farming activities. Dissolved and particulate organic carbon (DOC and POC) were lower in rivers from lava fields, and higher in nonvolcanic subcatchments. Stable carbon isotope signatures (δ13C) of POC and DOC mean δ13C of −22.5‰ and −23.5‰, respectively, are the first data to be reported for the highland of the Congo River basin and showed a much higher C4 contribution than in lowland areas. Rivers of the VVP were net sources of CH4 to the atmosphere (4–5052 nmol L−1). Most rivers show N2O concentrations close to equilibrium, but some rivers showed high N2O concentrations related to denitrification in groundwaters. δ13C signatures of dissolved inorganic carbon suggested magmatic CO2 inputs to aquifers/soil, which could have contributed to increase basalt weathering rates. This magmatic CO2‐mediated basalt weathering strongly contributed to the high major cation concentrations and total alkalinity. Thus, chemical weathering (39.0–2779.9 t km−2 yr−1) and atmospheric CO2 consumption (0.4–37.0 × 106 mol km−2 yr−1) rates were higher than previously reported in the literature for basaltic terrains.AFRIVA