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The link between rainfall and groundwater recharge in the Rio del Rey Basin, which is of socio-economic importance to Cameroon, is poorly understood. Accordingly, the stable isotopes in monthly rainfall from January to December 2012 (in Lobe and Mundemba) and 52 surface water and groundwater samples were investigated. High values of δ18O and δD were recorded in the dry period (February to March), and the least values of δ18O and δD were observed in the wet period (September). This indicates that different condensation processes primarily influenced stable isotopes in rainfall as a function of the difference in moisture sources. The relationship between δD and δ18O defined the Lobe meteoric water line as δD = 7.97 δ18O + 12.48 and Mundemba water line as δD = 7.75 δ18O + 10.79. The similarity of their slopes to the global meteoric line suggests that the isotopic composition of investigated rains was not significantly affected by evaporation during precipitation. The ranges in deuterium-excess of precipitation from 5.8 to 16.56‰ suggest the source of vapour is from the Atlantic Ocean. The groundwater isotope values (ranging from −3.81 to −2.52‰ for δ18O) plotted close to and along the GMWL, showing that its isotopic composition is of meteoric origin under rapid recharge conditions. The isotopic similarity between groundwater and June–August rains suggests a significant recharge during this period. [ABSTRACT FROM AUTHOR]

Cameroon was one of the 57 countries that participated in the Global Network of Civil Society Organizations for Disaster Reduction (GNDR) Views from the Frontline (VFL) 2013 project on everyday disasters, community resilience and disaster preparedness. Working with 6 other civil society organizations, Geotechnology, Environmental Assessment and Disaster Risk Reduction administered 400 questionnaires to frontliners in 7 administrative regions of the country on 14 disaster indicators that assessed the underlying causes of disasters and the level of preparedness and resilience of the communities. Scores from the 89% of informants who responded show that Cameroon occupied the 43rd position globally, was 15th out of the 23 African countries, and was 7th out of the 9 West African countries surveyed. Cameroon average scores for all 14 indicators were lower (poorer) than the West African average, suggesting that a lot more effort is needed in managing disaster risks in the country, i.e., reducing vulnerabilities and increasing preparedness and resilience. At the national level, the Center and Adamaoua Regions recorded the lowest scores of the survey. Above-average scores recorded for some indicators in the Southwest, Northwest and Far North Regions are interpreted to be due to disaster prevention activities like monitoring via early warning systems, resilience building and outreach exercises carried out for disasters like landslides, floods, gas explosions from lakes, and volcanic eruptions, in these areas. Cameroon presently has many laws relating to disaster risk management matters, but an analysis of how the laws are applied shows that the expected results have not been attained, mainly because of over-centralization and a reactive, rather than a proactive approach to disaster risk management. Given her current disaster risk profile, Cameroon has to increase research, better manage, and make disaster risks a central tenet in her development project decision-making, if the goal earmarked in her development vision to become a newly industrialized country by 2035 has to be realized. We propose the creation of an autonomous statutory National Disaster Risk Management Agency which will have a local community-driven bottom-top approach to disaster risk management, and disseminate appropriately tailored disaster risk information to promote a proactive community-based resilience and disaster prevention framework. This will fulfill the post-2015 Sendai framework priority of action No. 2 (strengthening disaster risk governance to manage disaster risk) and appropriately prepare Cameroon to face the challenges of the Sustainable Development Goals (SDGs). [ABSTRACT FROM AUTHOR]

Shallow groundwater (>30 mbgl) is an essential source of drinking water to rural communities in the Ndop plain, northwest Cameroon. As a contribution to water management, the effect of seasonal variation on the groundwater chemistry, hydrochemical controls, drinking quality and recharge were investigated during the peaks of the dry (January) and rainy (September) seasons. Field measurements of physical parameters were preceded by sampling 58 groundwater samples during both seasons for major ions and stable isotope analyses. The groundwater, which was barely acidic (mean pH of 6) and less mineralised (TDS < 272 mg/l), showed no significant seasonal variation in temperature, pH and TDS during the two seasons. The order of cation abundance (meq/l) was Na > Ca > Mg > K and Na > Mg > Ca > K in the dry and rainy seasons, respectively, but that of anions ( $$ {\text{HCO}}_{3}^{ - } $$ > $$ {\text{NO}}_{3}^{ - } $$ > Cl > $$ {\text{SO}}_{4}^{2 - } $$ > F) was similar in both seasons. This suggests a negligible effect of seasonal variations on groundwater chemistry. The groundwater, which was CaMgHCO and NaHCO, is chemically evolved rainfall (CaMgSOCl) in the area. Silicate mineral dissolution and cation-exchange were the main controls on groundwater chemistry while there was little anthropogenic influence. The major ions and TDS concentrations classified the water as suitable for human consumption as per WHO guidelines. The narrow cluster of δO and δD of same groundwater from both seasons between the δO and δD values of May-June precipitation along the Ndop Meteoric Water Line indicates meteoric origin, rapid recharge (after precipitation) and timing of recharge between May and June rainfall. Diffuse groundwater recharge mainly occurs at low altitudes (<1,400 m asl) within the plain. Besides major ions and TDS, the similar δO and δD of groundwater from both seasons indicate a consistent groundwater recharge and flow pattern throughout the year and resilience to present day short-term seasonal climatic variations. However, controlled groundwater abstraction is recommended given the increasing demand. [ABSTRACT FROM AUTHOR]

Rainwater characteristics can reveal emissions from various anthropogenic and natural sources into the atmosphere. The physico-chemical characteristics of 44 monthly rainfall events (collected between January and December 2012) from 4 weather stations (Bamenda, Ndop plain, Ndawara and Kumbo) in the Bamenda Highlands (BH) were investigated. The purpose was to determine the sources of chemical species, their seasonal inputs and suitability of the rainwater for drinking. The mean pH of 5 indicated the slightly acidic nature of the rainwater. Average total dissolved solids (TDS) were low (6.7 mg/L), characteristic of unpolluted atmospheric moisture/air. Major ion concentrations (mg/L) were low and in the order K + > Ca 2+ > Mg 2+ > Na + for cations and NO 3 −       ≫       HCO 3 −       >       SO 4 2 −       >       Cl −       >       PO 4 3 −       >       F − for anions. The average rainwater in the area was mixed Ca-Mg-SO 4 -Cl water type. The Cl – /Na + ratio (1.04) was comparable to that of seawater (1.16), an indication that Na + and Cl – originated mainly from marine (Atlantic Ocean) aerosols. High enrichments of Ca 2+ , Mg 2+ and SO 2– 4 to Na + ratios relative to seawater ratios (constituting 44% of the total ions) demonstrated their terrigenous origin, mainly from Saharan and Sahelian arid dusts. The K + /Na + ratio (2.24), which was similar to tropical vegetation ash (2.38), and NO 3 – was essentially from biomass burning. Light (< 100 mm) pre-monsoon and post-monsoon convective rains were enriched in major ions than the heavy (> 100 mm) monsoon rains, indicating a high contribution of major ions during the low convective showers. Despite the acidic nature, the TDS and major ion concentrations classified the rainwater as potable based on the WHO guidelines. [ABSTRACT FROM AUTHOR]

Since the catastrophic releases of CO2 in the 1980s, Lakes Nyos and Monoun in Cameroon experienced CO2 recharge at alarming rates of up to 80 mol/m² per yr. Total gas pressures reached 8.3 and 15.6 bar in Monoun (2003) and Nyos (2001), respectively, resulting in gas saturation levels up to 97%. These natural hazards are distinguished by the potential for mitigation to prevent future disasters. Controlled degassing was initiated at Nyos (2001) and Monoun (2003) amid speculation it could inadvertently destabilize the lakes and trigger another gas burst. Our measurements indicate that water column structure has not been compromised by the degassing and local stability is increasing in the zones of degassing. Furthermore, gas content has been reduced in the lakes ≈12-14%. However, as gas is removed, the pressure at pipe inlets is reduced, and the removal rate will decrease overtime. Based on 12 years of limnological measurements we developed a model of future removal rates and gas inventory, which predicts that in Monoun the current pipe will remove ≈30% of the gas remaining before the natural gas recharge balances the removal rate. In Nyos the single pipe will remove ≈25% of the gas remaining by 2015; this slow removal extends the present risk to local populations. More pipes and continued vigilance are required to reduce the risk of repeat disasters. Our model indicates that 75-99% of the gas remaining would be removed by 2010 with two pipes in Monoun and five pipes in Nyos, substantially reducing the risks. [ABSTRACT FROM AUTHOR]

• Geochemical data have been used to explore the mantle source. • The rocks from WCH volcanoes in whole show an evolution dominated by FC. • The LILE/HFSE, Th/La and La/Nb ratios suggest no crustal contamination. • The incompatible elements ratios confirm the hypothesis of a single source for the WCH rocks. • Enrichment of LREE compared to HREE, Dy/Yb>2, (La/Yb) N >5 and (Tb/Yb) N >1.9 suggests melting in a garnet-bearing mantle. Geochemical and mineralogical analyses data are presented for ignimbritic deposits from the Bambouto volcano. These deposits are characterized by their welded and non-welded massive lapilli tuff and massive lithic breccias facies. The ignimbrites generally display vitroclastic and/or eutaxitic texture characterized by whole or broken minerals, subangular fragments of trachytes, rhyolites, ignimbrites, as well as fiammes, and fragments of glass. The geochemistry of the ignimbrites of Mount Bambouto indicates that they are alkaline and peralkaline with rhyolitic and trachytic composition. The behaviour of the major and trace elements suggest that ignimbrites, as well as felsic and mafic lavas of the Bambouto volcano have an evolution dominated by fractional crystallization (FC). The La/Yb, Ce/Zr and Th/Nb ratios for Mt Bambouto ignimbrites (19.92–52.66; 0–0.48; 0.10–0.12, respectively) and the whole Western Cameroon Highlands (WCH) and Mt Manengouba lavas (15.58–34.29; 0–0.61; 0–0.27, respectively) also reflect the dominant role of FC. This suggests a relatively constant degree of partial melting during the petrogenesis of the lavas and deposits. The high Rb/Sr (0.52–28.98) and the low ratios of LILE/HFSE (Rb/Nb: 0.08–0.95; Rb/Zr: 0.01–0.18; Th/Ta: 1.38–2.1; Ba/Nb: 0.06–8.27) in Mt. Bambouto ignimbrites, compared with the very high value of these ratios in the granitic basement rocks of the area, preclude the petrogenesis of the ignimbrites from the melting of the Pan-African basement. The weak values of Th/La and La/Nb in the studied ignimbrites and other WCH lavas suggest that crustal contamination was insignificant during ascent and storage of the magma in shallow magma chambers prior to their release to the surface. The similarities in Nb/Ta, Zr/Hf and Nb/U ratios in the Mt Bambouto ignimbrites (Nb/Ta: 13.54–20.93; Zr/Hf: 37.39–49.95; Nb/U: 26.04–55.70) and the lavas of the WCH (Nb/Ta: 11.3–19.57; Zr/Hf: 33.16–55.01; Nb/U: 19.83–75.35) corroborated with their similar source origin. The enrichment of light REE relative to heavy REE or their Dy/Yb > 2 (2.03–2.97), (La/Yb) N > 5 (14.29–46.69) and (Tb/Yb) N > 1.9 (1.91–2.9) suggest melting in a garnet-bearing mantle. [ABSTRACT FROM AUTHOR]

Abstract A limnic eruption in 1986 at Lake Nyos in Cameroon was caused by sudden release of magmatic CO 2 dissolved in the lake water. For frequent measurements of CO 2 in the lake water, we developed a simple method of CO 2 monitoring using sound speed (SS) measurement. We measured the depth profile of sound speed at Lake Nyos in 2012, 2013, 2014, and 2015. Furthermore, in the 2014 and 2015 survey, we took movies of the underwater and the bottom of the lake using an underwater camera housed in a pressure-resistant container. The vertical change of transparency of water was checked by the visibility of reflectors set in front of the camera. A pressure sensor monitored the depth simultaneously. In both years, in addition to well-known red surface water, we discovered a cloudy layer near the upper chemocline around 100 m depth. The depth of chemocline is a good indicator of the change of total amount of CO 2 in Lake Nyos. Because the transparency can be detected by a simple optical sensor, we can now apply our low-cost monitoring tool to find the depth of chemocline for Lake Nyos. Highlights • Under-water camera system resistant to water pressure of 200 m was constructed. • Under-water movies of Lake Nyos were taken in 2014 and 2015 survey. • A script to quantify the brightness of the reflector in a movie was made and the transparency of lake water was evaluated. • We found a cloudy layer around the depth of the upper chemocline. [ABSTRACT FROM AUTHOR]

Even though ca 1746 people and over 3000 cattle were killed in 1986 by sudden release of about 800 million m3 of CO 2 from Lake Nyos volcano in northwest Cameroon, the lake's formation history is not known. Here we report results of a lithostratigraphic and petrogenetic study of Nyos volcano that allows us to confirm its phreatomagmatic (maar) origin. Eruptive products are divided into 2 units, the phases of each of which are closely related in time. Unit A comprises 4 phases, the last (A-4) represents the cataclysmic phreatomagmatic formation of Nyos maar and may have been triggered by collapse of the vent system of the previous (A-1 to A-3) phases, and/or reactivation of basement faults. After a repose period, activity shifted NE of the maar to form Unit B products. The B-1 phase of this unit deposited the scoria now covering most of the Lake Nyos area. Unit B-2 constructed the Fon's cone. A small lava flow (Unit B-3) represents the latest phase of volcanic activity of Nyos volcano. Based on area-thickness estimation methods, a total of ca 0.8 km3 of eruptive material was produced from the volcano. Geochemical data suggest that magma of the 2 units probably formed by melting of the same garnet-bearing OIB-like asthenospheric mantle source, and evolved mainly by crustal contamination and fractional crystallization in independent magma batches that erupted without mixing. Our results provide a basis for advice on general hazard mitigation in the Lake Nyos area. • Eruptive products from Nyos (0.8 km3) are divided into 2 units, each of which are from different monogenetic volcanoes. • Magma of 2 units generated by melting of same garnet-bearing OIB-like mantle source and evolved independently without mixing. • The results including lithostratigraphy, geologic map, magma genesis of Nyos provide an important basis for risk management. [ABSTRACT FROM AUTHOR]

The hydrodynamic fragmentation that formed Lake Nyos in northwest Cameroon did not only make it the most unpopular lake in the world from a gas disaster perspective, it also opened a rare and formidable window through which much of the geology of Cameroon can be studied in a single locality. The Cambrian quartz monzonite cliff excavated by the maar-forming explosion and exposed in its northeastern shore is intruded by mafic dykes, two of which we dated. Even though close to one another, the dykes are different in composition. The alkaline dyke yields a slightly older (Carnian) K-Ar fedspar age of 231.1 ± 4.8 Ma, while the sub alkaline dyke yields an age of 224.8 ± 4.7 Ma (Norian). Based on radioisotopic age data available over the last 48 years (347 data) for the Cameroon Line magmatism comprising eruptives and volcano-plutonic complexes, the Nyos dykes are way older than the Cameroon Line, and even pre-date the Lower Cretaceous initiation of west Gondwana fragmentation in Equatorial Atlantic domain. They would therefore not have been directly linked to the formation of the Cameroon Line. Alternatively, they might be associated with the development of intra-continental rift systems in West Central Africa that pre-dated west Gondwana breakup to form the Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Lake Nyos is located at the summit of a stratovolcano in the Oku Volcanic Group (OVG) along the Cameroon Volcanic Line. The sudden release of magmatic CO 2 trapped at the bottom of Lake Nyos in August 1986 caused historical casualties of 1750 people and over 3000 cattle. New geochemical data of volcanic rocks from the Nyos volcano and the first available data for volcanic rocks from other maar-bearing volcanoes (Lakes Elum, Wum and Oku) in the OVG are presented and compared. Lavas from the Nyos, Elum and Wum volcanoes show similarities in major and trace elements and Sr–Nd–Pb isotopes, suggestive of a similar mantle source. However, this source is slightly different from that of the Oku volcano. The samples from Lake Oku have lower alkali, higher TiO 2 and more depletion and enrichment in most incompatible trace elements than those from the Nyos, Elum and Wum volcanoes. These differences and those observed in the Sr–Nd–Pb results are consistent with a heterogeneous source for lavas in the OVG. Trace element compositions suggested the presence of garnet in the source (< 6% garnet) and modelled melting results indicate < 2% partial melting of the source material. Isotope data plot within the focal zone, extending towards enriched mantle 1 (EM1; e.g. Lakes Oku and Nyos samples). This indicates the involvement of at least three mantle components: depleted mid-ocean ridge basalt mantle, high-μ and EM1 components in the magmatism of the lavas studied. The contributions of these components in different proportions, originating from asthenospheric and subcontinental lithospheric mantle sources, can account for the observed variations in geochemical characteristics. The geochemical characteristics of the studied lavas indicate that the magma source need not necessarily have an abnormal CO 2 concentration to pose a potential threat. Degassing of an ordinary magma chamber and the migration of gas to the bottom of the lakes through cracks and faults can lead to the accumulation of CO 2 in lake bottoms. This is controlled by tectonic parameters (fractures and faults) that enhance degassing from the magma chamber to the lake bottom and physical parameters of the lake (e.g. size, depth, temperature and solubility) that control CO 2 stability. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the microbial diversity associated with Lake Nyos, a lake with an unusual chemistry in Cameroon. Water samples were collected during the dry season on March 2013. Bacterial and archaeal communities were profiled using Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) approach of the 16S rRNA gene. The results indicate a stratification of both communities along the water column. Altogether, the physico-chemical data and microbial sequences suggest a close correspondence of the potential microbial functions to the physico-chemical pattern of the lake. We also obtained evidence of a rich microbial diversity likely to include several novel microorganisms of environmental importance in the large unexplored microbial reservoir of Lake Nyos.