U-series dating of Lake Nyos maar basalts, Cameroon (West Africa); implications for potential hazards on the Lake Nyos Dam

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doi: 10.1016/j.jvolgeores.2008.04.009
Authors:Aka, Festus T.; Yokoyama, Tetsuya; Kusakabe, Minoru; Nakamura, Eizo; Tanyileke, Gregory; Ateba, Bekoa; Ngako, Vincent; Nnange, Joseph; Hell, Joseph
Author Affiliations:Primary:
Okayama University at Misasa, Tottori-ken, Japan
Institute of Mining and Geological Research, Cameroon
Volume Title:Journal of Volcanology and Geothermal Research
Source:Journal of Volcanology and Geothermal Research, 176(2), p.212-224. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-0273
Publication Date:2008
Note:In English. 77 refs.; illus., incl. 2 tables, geol. sketch maps
Summary:From previously published 14C and K-Ar data, the age of formation of Lake Nyos maar in Cameroon is still in dispute. Lake Nyos exploded in 1986, releasing CO2 that killed 1750 people and over 3000 cattle. Here we report results of the first measurements of major elements, trace elements and U-series disequilibria in ten basanites/trachy-basalts and two olivine tholeiites from Lake Nyos. It is the first time tholeiites are described in Lake Nyos. But for the tholeiites which are in 238U-230Th equilibrium, all the other samples possess 238U-230Th disequilibrium with 15 to 28% enrichment of 230Th over 238U. The (226Ra/230Th) activity ratios of these samples indicate small (2 to 4%) but significant 226Ra excesses. U-Th systematics and evidence from oxygen isotopes of the basalts and Lake Nyos granitic quartz separates show that the U-series disequilibria in these samples are source-based and not due to crustal contamination or post-eruptive alteration. Enrichment of 230Th is strong prima facie evidence that Lake Nyos is younger than 350 ka. The 230Th-226Ra age of Nyos samples calculated with the (226Ra/230Th) ratio for zero-age Mt. Cameroon samples is 3.7±0.5 ka, although this is a lower limit as the actual age is estimated to be older than 5 ka, based on the measured mean 230Th/238U activity ratio. The general stability of the Lake Nyos pyroclastic dam is a cause for concern, but judging from its 230Th-226Ra formation age, we do not think that in the absence of a big rock fall or landslide into the lake, a big earthquake or volcanic eruption close to the lake, collapse of the dam from erosion alone is as imminent and alarming as has been suggested. Abstract Copyright (2008) Elsevier, B.V. [G.L.B.]
Sections:Age determination; Geochemistry
Subjects:Absolute age; Alkali basalts; Alteration; Basalts; Basanite; Cenozoic; Dams; Dates; Enrichment; Floods; Geologic hazards; Holocene; ICP mass spectra; Igneous rocks; Maars; Major elements; Mass spectra; Olivine tholeiite; Quaternary; Spectra; Th/U; Tholeiite; Trace elements; Trachybasalts; Uranium disequilibrium; Volcanic rocks; X-ray fluorescence spectra; Africa; Cameroon; Lake Nyos; West Africa; Lake Nyos Dam
Coordinates:N062600 N062800 E0101830 E0101730
Abstract Numbers:08M/3905
Record ID:2009024129
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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