A Brine Evolution Model and Mineralogy of Chemical Sediments in a Volcanic Crater, Lake Kitagata, Uganda

Ma, Lichun; Lowenstein, Tim K.; Russell, James M.

doi:10.1007/s10498-010-9108-x

Cited by 15 publications

(5 citation statements)

References 27 publications

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“…All the 81 lakes are classified as maar lakes (Melack, 1978). An early study by Mungoma (1990) revealed that the lake water chemistry of eight lakes in the Katwe-Kikorongo (Kikorongo, Nyamunyuka, Katwe, Bunyampaka and Kitagata;Lowenstein and Russell, 2011) and Bunyaruguru (Maseshe, Bagusa, Mahega) are highly saline (Conductivity 16.3 to 455 mS cm-1) and alkaline (pH 9-10.5), caused by water-rock interaction and enhanced evaporation of the generally small and shallow maar lakes. Solar heating results in mesothermal stratification of the studied lakes, shown by inverted vertical temperature profiles.…”

Section: Ugandamentioning

confidence: 99%

Volcanic Lakes in Africa: The VOLADA_Africa 2.0 Database, and Implications for Volcanic Hazard

et al. 2021

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Volcanic lakes pose specific hazards inherent to the presence of water: phreatic and phreatomagmatic eruptions, lahars, limnic gas bursts and dispersion of brines in the hydrological network. Here we introduce the updated, interactive and open-access database for African volcanic lakes, country by country. The previous database VOLADA (VOlcanic LAke DAta Base, Rouwet et al., Journal of Volcanology and Geothermal Research, 2014, 272, 78–97) reported 96 volcanic lakes for Africa. This number is now revised and established at 220, converting VOLADA_Africa 2.0 in the most comprehensive resource for African volcanic lakes: 81 in Uganda, 37 in Kenya, 33 in Cameroon, 28 in Madagascar, 19 in Ethiopia, 6 in Tanzania, 2 in Rwanda, 2 in Sudan, 2 in D.R. Congo, 1 in Libya, and 9 on the minor islands around Africa. We present the current state-of-the-art of arguably all the African volcanic lakes that the global experts and regional research teams are aware of, and provide hints for future research directions, with a special focus on the volcanic hazard assessment. All lakes in the updated database are classified for their genetic origin and their physical and chemical characteristics, and level of study. The predominant rift-related volcanism in Africa favors basaltic eruptive products, leading to volcanoes with highly permeable edifices, and hence less-developed hydrothermal systems. Basal aquifers accumulate under large volcanoes and in rift depressions providing a potential scenario for phreatomagmatic volcanism. This hypothesis, based on a morphometric analysis and volcanological research from literature, conveys the predominance of maar lakes in large monogenetic fields in Africa (e.g. Uganda, Cameroon, Ethiopia), and the absence of peak-activity crater lakes, generally found at polygenetic arc-volcanoes. Considering the large number of maar lakes in Africa (172), within similar geotectonic settings and meteoric conditions as in Cameroon, it is somewhat surprising that “only” from Lake Monoun and Lake Nyos fatal CO2 bursts have been recorded. Explaining why other maars did not experience limnic gas bursts is a question that can only be answered by enhancing insights into physical limnology and fluid geochemistry of the so far poorly studied lakes. From a hazard perspective, there is an urgent need to tackle this task as a community.

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Section: Ugandamentioning

confidence: 99%

Volcanic Lakes in Africa: The VOLADA_Africa 2.0 Database, and Implications for Volcanic Hazard

et al. 2021

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“…Modern examples of magadiite precipitation are rare, so the physical state of magadiite soon after precipitation is unclear. However, recent magadiite formation has been documented in a core from Lake Kitagata (Uganda), a small shallow (9 m deep) perennial saline (>170 g/LTDS) alkaline (pH 9.7) crater lake fed mainly by groundwater 80 . There, the magadiite forms in the silica-rich (256 ppm SiO 2 ) water column as a primary mineral that settles upon the substrate and in places forms thin beds.…”

Section: Discussionmentioning

confidence: 99%

Animal bioturbation preserved in Pleistocene magadiite at Lake Magadi, Kenya Rift Valley, and its implications for the depositional environment of bedded magadiite

Buatois

Renaut

Owen

et al. 2020

Sci Rep

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Magadiite, a rare hydrous sodium-silicate mineral [naSi 7 o 13 (oH) 3 ·4(H 2 O)], was discovered about 50 years ago in sediments around Lake Magadi, a hypersaline alkaline lake fed by hot springs in the semiarid southern Kenya Rift Valley. today this harsh lacustrine environment excludes most organisms except microbial extremophiles, a few invertebrates (mostly insects), highly adapted fish (Alcolapia sp.), and birds including flamingos. Burrows discovered in outcrops of the High Magadi Beds (~25-9 ka) that predate the modern saline (trona) pan show that beetles and other invertebrates inhabit this extreme environment when conditions become more favourable. Burrows (cm-scale) preserved in magadiite in the High Magadi Beds are filled with mud, silt and sand from overlying sediments. Their stratigraphic context reveals upward-shallowing cycles from mud to interlaminated mud-magadiite to magadiite in dm-scale units. The burrows were formed when the lake floor became fresher and oxygenated, after a period when magadiite precipitated in shallow saline waters. the burrows, probably produced by beetles, show that trace fossils can provide evidence for short-term (possibly years to decades) changes in the contemporary environment that might not otherwise be recognised or preserved physically or chemically in the sediment record.Saline lakes precipitating evaporites are among the most extreme environments on Earth and include the most important stressors for metazoan life 1-3 . Hypersalinity is commonly accompanied by high pH (hyperalkalinity), anoxia and high turbidity, all of which are major stressors in underfilled evaporitic lakes 4-7 . Although metazoan diversity is typically low in these harsh settings, microbial communities often flourish 8,9 . Soda lakes frequently have very high microbial biomass (mainly photoautotrophs) and productivity 10,11 . Such lakes, with their carbonate-rich waters, are most common in regions with volcanic bedrock or hydrothermal recharge 12,13 . Lake Magadi, a hypersaline (>300 g/kg TDS: Total Dissolved Solids) alkaline (pH: 10-11) soda lake, 0-2 m deep, lies in faulted volcanic terrain in the axial depression of the southern Kenya Rift 14-16 just south of the equator (1°53′S). Modern lake sediments, cores and Quaternary deposits exposed around its margins have provided details of the sedimentary facies, including thick deposits of trona [Na 3 (CO 3 )(HCO 3 )·2H 2 O] that underlie the modern lake floor 14,16,17 . The Pleistocene sediment record includes abundant bedded, nodular and intrusive chert (including dykes) of diverse origins and the rare sodium-silicate mineral, magadiite [NaSi 7 O 13 (OH) 3 ·4(H 2 O)] 18-23 . Lake Magadi, the most saline of the major lakes in the East African Rift, is one of the most chemically stressful lacustrine settings on the planet 24 . In this paper, we describe and interpret unusual trace fossils that are preserved in terminal Pleistocene magadiite. This soft silicate mineral, a precursor of quartzose chert, is an improbable host for invertebrate ichnof...

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“…If these dynamics are applied to calcite precipitation in the playa, and it is assumed that the water-soluble fraction samples the most recent evaporative event, D w-a should correlate with the size of the water-soluble Ca pool (Eugster and Jones, 1979;Sanford and Wood, 1991;Gamazo et al, 2011;Ma et al, 2011). The size of the water-soluble Ca pool is related to the chemical evolution of the brine, i.e.…”

Section: Evaluating Calcite Chemistry As the Control On D W-amentioning

confidence: 99%

The Ca isotopic composition of dust-producing regions: Measurements of surface sediments in the Black Rock Desert, Nevada

Fantle

Tollerud

Eisenhauer

et al. 2012

Geochimica et Cosmochimica Acta

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A Brine Evolution Model and Mineralogy of Chemical Sediments in a Volcanic Crater, Lake Kitagata, Uganda

Cited by 15 publications

References 27 publications

Volcanic Lakes in Africa: The VOLADA_Africa 2.0 Database, and Implications for Volcanic Hazard

Volcanic Lakes in Africa: The VOLADA_Africa 2.0 Database, and Implications for Volcanic Hazard

Animal bioturbation preserved in Pleistocene magadiite at Lake Magadi, Kenya Rift Valley, and its implications for the depositional environment of bedded magadiite

The Ca isotopic composition of dust-producing regions: Measurements of surface sediments in the Black Rock Desert, Nevada

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