δ18O and δD variations in some volcanic lakes on the Cameroon Volcanic Line (West-Africa): generating isotopic baseline data for volcano monitoring and surveillance in Cameroon

Tongwa, Festus Aka; Mouliom, Alfred G.; Rouwet, Dmitri; Fantong, Wilson Y.; Tchamabé, Boris Chako; Ohba, Takayoshi; Yoshida, Yutaka; Sighomnou, D.; Sigha, Nkamdjou; Kusakabe, Minoru

doi:10.4081/jlimnol.2014.966

Cited by 7 publications

(14 citation statements)

References 62 publications

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“…The CVL is a 1600 km long chain of volcanoes crossing the Cameroon territory and stretching from the Atlantic Ocean. It hosts more than 40 crater lakes (Kling, 1987;Ngwa et al, 2010;Issa et al, 2014) most of which are maars (Belinga and Njilah, 2001). So far, detailed and systematic volcanostratigraphic descriptions have been done on only two of these maars.…”

Section: Geological Settingmentioning

confidence: 99%

Towards the reconstruction of the shallow plumbing system of the Barombi Mbo Maar (Cameroon) Implications for diatreme growth processes of a polygenetic maar volcano

Tchamabé

Ohba

Keresztúri

et al. 2015

Journal of Volcanology and Geothermal Research

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a b s t r a c tUnderstanding the mechanisms involved in the formation of maars and their diatreme growth processes has been a subject of contention. While there is no direct evidence of the presence of diatremes beneath most of the young maars, their existence is inferred based on the amount and type of country rocks excavated at different depths and deposited as pyroclastic ejecta around their craters. Properly tracing fragmented country rocks in ejecta to interpret their depths of origin and thus the depths of phreatomagmatic explosions require good and detailed information on the substrate geology that is generally lacking at many maars. As an alternative, this paper explores the role of juvenile components in deposits of a maar for understanding the cratering and growth of diatremes during maar-forming eruptions. Based on field investigations, pyroclast distribution, componentry and grain morphology examinations this study reports on the eruptive mechanisms that led to the formation of the Barombi Mbo Maar (BMM), a polygenetic maar volcano in Cameroon. The BMM consists of three diatremes that formed during distinct eruptive events and coalesced to produce an "amalgamated maar-diatreme". Two end-member types of eruption styles from the "dry" magmatic to the "wet" phreatomagmatic explosions governed the formation of the maar. In total, a minimum of~0.0658 km 3 of magma (Dense Rock Equivalent corrected) was ejected based on calculation by applying interpolation techniques on digital elevation models obtained from SRTM30m data corrected by rock textural data collected from the field. The distribution of juvenile clasts throughout the stratigraphic sequence suggests a complex subsurface eruptive process, which originated probably within the uppermost part of the diatreme. From the distribution and morphology of juvenile clasts in the deposits, it is inferred that cratering and country rock excavation during the growth of each of the small diatremes developed mainly from shallow level explosions, sometimes with lateral and vertical variations in the position of the explosion loci. A prospective juvenile-based conceptual model is proposed for the formation of the BMM. The model suggests that, during maar-forming eruptions, explosions taking place at a deeper position might entrain extensive amount of lithics from the mostly lithic-dominated upper crater infill to deposit juvenile-poor (b10 vol.%) tephra beds. Layers with a juvenile content of 10-60 vol.%, for example, might result from deep to shallow-seated explosions, with a common entrainment of lithics from the crater infill region, and with much of the remobilized tephra being transported to the ejecta ring sequence. In contrast, explosions occurring at shallower positions will produce mainly juvenile-rich beds (juvenile N 90 vol.%).

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Section: Geological Settingmentioning

confidence: 99%

Towards the reconstruction of the shallow plumbing system of the Barombi Mbo Maar (Cameroon) Implications for diatreme growth processes of a polygenetic maar volcano

Tchamabé

Ohba

Keresztúri

et al. 2015

Journal of Volcanology and Geothermal Research

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“…Kozono et al [54] confirmed the previous authors, arguing that the 1986 limnic eruptions might have been triggered when the CO2 concentration at some depth of the lake reached saturation. From the numerical model developed, they observed that the CO2 concentration increases with depth, and for some layers, a roughly constant CO2 concentration is observed [74] the results were updated by Kusakabe [15]. This allowed them to investigate the effects of changes in CO2 concentration at the bottom of the lake on the dynamics of the pipe flow and the degree of degassing.…”

Section: The Future Of Lake Nyos and Cameroon Lakesmentioning

confidence: 99%

“…The future lies in prevention. There are at least 39 lakes of volcanic origin distributed along the Cameroon Volcanic Line (CVL) [19,20,74], among which, some remain potential sites of limnic eruptions. Understanding the origin and the geochemistry of CVL magmas is essential.…”

Section: The Future Of Lake Nyos and Cameroon Lakesmentioning

confidence: 99%

Lake Nyos, a Multirisk and Vulnerability Appraisal

Tchindjang

2018

Geosciences

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Situated at the northern flank of the Oku Massif, Lake Nyos crater epitomizes landscape features originating from volcanic explosions during the Quaternary. The Cameroon Volcanic Line (CVL), to which it belongs, constitutes the most active volcanic region in Cameroon. In 1986, an outgas explosion occurred from beneath the lake and killed 1746 people in several neighbouring villages. The event influenced a radial area of 25 to 40 km wide, particularly in eastern and western direction. This was mainly due to: (1) the rugged nature of the landscape (fault fields), which enabled the heavier gas to follow valleys framed by faults corridors without affecting elevated areas; and (2) the seasonal dominating western wind direction, which channeled the gas along tectonic corridors and valleys. This paper assesses the geological risk and vulnerability in the Lake Nyos before and after several proposal to mitigate future outgas events. Remotely sensed data, together with GIS tools (topographic maps, aerial photographs), helped to determine and assess lineaments and associated risks. A critical grid combining severity and frequency analysis was used to assess the vulnerability of the local population. There is evidence that along the main fault directions (SW-NE), anthropogenic activities are most intensive and they may play an aggravating role for disasters. This requires the local population's consciousness-raising. The results also show that population around Lake Nyos still remains vulnerable to volcanic hazards and floods. However, the area has been safe since the last degassing and jet grouting through multiple procedures and actions proposed in the National Contingency Plan, and equally by the relief organization plan (DROP or ORSEC plan) for the Menchum Division. Another issue is that the local population is concerned with the idea of returning to the affected areas in order to stay close to their ancestors or the deceased. Therefore, even after jet grouting and degassing, the problem of risk minimization for local residents remains.

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“…The project went well in terms of scientific achievement. Many scientific papers were published, e.g., Issa et al (2013Issa et al ( , 2014aIssa et al ( , 2014b, Asaah et al (2014Asaah et al ( , 2015, Chako , Fouépé et al (2013), Fantong et al (2013Fantong et al ( , 2015, Tiodjio et al (2014Tiodjio et al ( , 2015Tiodjio et al ( , 2016, Kamtchueng et al (2014Kamtchueng et al ( , 2015aKamtchueng et al ( , 2015b, , Ohba et al (2016), Kozono et al (2016), and Saiki et al (2016).…”

Section: Satreps-nymo: a Project To Reduce The Risk Of Another Limnicmentioning

confidence: 99%

“…There are at least 39 lakes of volcanic origin that are distributed along the CVL (Kling, 1988;Issa et al, 2014a). Lake Nyos in the Northwest Region of Cameroon (06∞26¢ N and 10∞17¢ E) is a meromictic volcanic crater lake with a N-S length of ~2.0 km, E-W length of ~1.2 km, surface area of 1.58 km 2 , and a maximum depth of 209.5 m. It lies in the Oku volcanic field along the CVL, and was formed by a basaltic phreato-magmatic eruption (Lockwood and Rubin, 1989).…”

Section: -2 Cameroon Lakesmentioning

confidence: 99%

δ18O and δD variations in some volcanic lakes on the Cameroon Volcanic Line (West-Africa): generating isotopic baseline data for volcano monitoring and surveillance in Cameroon

Abstract: Based on geo-anthropological and geochemical studies, catastrophes similar to the unprecedented gas explosions in the mid-1980s from the Cameroonian killer lakes

Cited by 7 publications

References 62 publications

Towards the reconstruction of the shallow plumbing system of the Barombi Mbo Maar (Cameroon) Implications for diatreme growth processes of a polygenetic maar volcano

Towards the reconstruction of the shallow plumbing system of the Barombi Mbo Maar (Cameroon) Implications for diatreme growth processes of a polygenetic maar volcano

Lake Nyos, a Multirisk and Vulnerability Appraisal

Lakes Nyos and Monoun Gas Disasters (Cameroon)—Limnic Eruptions Caused by Excessive Accumulation of Magmatic CO<sub>2</sub> in Crater Lakes

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