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Mulwa J, Barongo J, Fairhead D, Mariita N, Patel J. "Heat source in Lake Bogoria basin mapped using integrated geophysical methods." African Journal of Science and Technology (AJST). 2010;11(1):90-98. Abstract

The Lake Bogoria basin, here in referred to as the study area, is located in the greater Baringo-Bogoria basin (BBB), about 100 km to the north of Menengai geothermal prospect on the floor of Kenya Rift Valley (KRV). It is bound by latitudes 0o 00’ and 0o 30’N and longitudes 35o45’E and 36o15’E within the rift graben. The study area is characterised by geothermal surface manifestations which include hot springs, spouting geysers, fumaroles/steam jets and mud pools. The area is overlain by Miocene lavas mainly basalts and phonolites, and Pliocene to recent sediments and pyroclastics such as tuffs, tuffaceous sediments, superficial deposits, volcanic soils, alluvium and lacustrine silts. The terrain is characterized by extensive faulting forming numerous N-S ridges and fault scarps.

Gravity and magnetotelluric (MT) surveys were undertaken in the basin in an attempt to determine the heat source, characterize the geothermal reservoir, and evaluate the geothermal resource potential of the basin.

Gravity survey results indicate Bouguer anomaly having an amplitude of ~40 mGals aligned in a north-South direction and interpreted to be due to a series of dyke injections and hence the heat source in the basin. The interpretation of Bouguer anomaly has been constrained by using previous seismic results. Seismic velocities were converted to densities using the expression derived from Gardner et al. (1974). The MT survey results show that the geothermal prospect in Lake Bogoria basin is overlain by high resistivity (50-1000 -m) thin (100-500 m) layer which forms a cap rock for the geothermal reservoir, which is subsequently underlain by three distinct relatively thick layers within the geothermal prospect. The first of these thick layers is ~3 km thick and has resistivities ranging between 4-30 -m. This layer is interpreted as the geothermal reservoir and the low resistivities are due to circulating hot mineralized geothermal fluids. The underlying layer is ~10 km thick and resistivity values range between 85-2500 -m and is interpreted to be a fractured and hydrothermally altered basement metamorphic rocks. The relatively high degree of fracturing allows deep circulation of water where it gets heated up by the underlying dyke injections, and convective heat transport to the geothermal reservoir. The substratum is characterized by resistivities ranging between 0.5-47 -m and is interpreted as hot dyke injections which are the heat sources for this geothermal prospect.

On the basis of gravity and MT results, the heat source in Lake Bogoria basin is due to cooling dyke injections occurring at depths of ~6 – 12 km in the subsurface. Gravity method however favours depths of ~3 – 6 km for the heat source. The geothermal reservoir is probably two-phase and the temperature ranges between 150-400oC (Karingithi, 2006). Previous microseismic studies by Young et al. (1991), Tongue (1992) and Tongue et al., (1992, 1994) show that Lake Bogoria basin geothermal prospect is characterised by high frequency of low magnitude (< 3) seismic events which are correlated with surface faulting and multiple episodes of dyke injections. The gravity and MT results in this study are therefore fairly consistent with results from previous microseismic studies undertaken in the basin.

Mulwa J, Fairhead D, Barongo J, Mariita N. "Heat source mapping and evaluation of geothermal resource potential in Lake Bogoria basin, Kenya." Society of Exploration Geophysicists. 2009;28:1294-1299. AbstractWebsite

The Lake Bogoria basin, here in referred to as the study area, is located in the greater Baringo-Bogoria basin (BBB), about 250 km to the north of the city of Nairobi and about 100 km to the north of Menengai geothermal prospect on the floor of Kenya Rift Valley (KRV). It is bound by latitudes 0o 00’ and 0o 30’N and longitudes 35o45’E and 36o15’E within the rift graben. The study area is characterised by geothermal surface manifestations which include hot springs, spouting geysers, fumaroles/steam jets and mud pools. The area is overlain by Miocene lavas lavas, mainly basalts and phonolites, and Pliocene to recent sediments and pyroclastics such as tuffs, tuffaceous sediments, superficial deposits, volcanic soils, alluvium and lacustrine silts. The terrain is characterized by extensive faulting forming numerous N-S ridges and fault scarps.

Gravity survey was undertaken in the study area to map the possible heating source and evaluate the geothermal resource potential of the basin. Gravity survey results indicate Bouguer anomaly having an amplitude of ~40 mGals aligned in a north-South direction and interpreted to be due to a series of dyke injections and hence the heat source in the basin. The interpretation of Bouguer anomaly has been constrained by using results from previous seismic surveys undertaken in the Kenya rift valley by Simiyu and Keller (2001), Keller et al., (1994a) and Braile et al., (1994). P-wave velocities have been converted to densities using the equation derived from Gardner et al. (1974).

Microseismic studies in Lake Bogoria basin by Young et al. (1991), Tongue (1992) and Tongue et al., (1992, 1994) show that the basin is characterised by high frequency of low magnitude (< 3) seismic events which are correlated with surface faulting and multiple episodes of dyke injections. The gravity results in this study are therefore fairly consistent with results of previous microseismic studies undertaken in the basin.

On the basis of the gravity results, the heat source in Lake Bogoria basin is due to cooling dyke injections occurring at depths of ~3 – 6 km. Since a heat source, in addition to fluid circulation, is an integral component of a geothermal system, it is evident that a geothermal reservoir exists in Lake Bogoria basin and the fluids can be tapped for generation of geothermal power.

Mulwa JK, Mwega BW, Kiura MK. "Hydrogeochemical analysis and evaluation of water quality in Lake Chala catchment area, Kenya." Global Advanced Research Journal of Physical and Applied Sciences. 2013;2(1):001-007. AbstractHydrogeochemical analysis and evaluation of water quality in Lake Chala catchment area, Kenya

Lake Chala is a transboundary fresh water resource with no surface water inflow or outflow and is located in the southwestern part of Kenya on the Kenya-Tanzania border. The lake catchment area is bound by longitudes 370 41’ E and 370 43’ E and latitudes 30 18’ S and 30 20’ S. The Lake has a surface area of 4.2 km2 and lies within a surface catchment area of about 16.23 km2, which falls within a semiarid region frequently facing severe water scarcity especially during periods of prolonged drought. The major economic activities in this area are agriculture, horticulture and animal husbandry which account for about 75-80% of household income. Due reliance on rain fed agriculture, water scarcity has often had negative impact on the people and there is need to tap the lake water for irrigation purposes. As such, water samples were collected on the Kenya and Tanzania sides from eleven (11) sites in March 2011 and subjected to analysis for chemical characteristics. Ten of the water samples show that the type of water that predominates in the study area is Ca-Mg-HCO3 type, while one water sample from a shallow well is a Ca-Mg-chloride type based on hydro-chemical facies. The suitability of water for irrigation has been evaluated based on sodium percent, residual sodium carbonate, sodium adsorption ratio and salinity hazard and is therefore suitable for irrigation purposes.

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