Effects Of Sea Water Intrusion On The Chemistry Of Hotsprings:A Comparative Study Between Majimoto Hotsprings In The Kenyan South Coast And Bogoria Hotsprings In The Rift Valley

Abstract

The Majimoto hotsprings are located outside the active volcanic Rift Valley in the Kenyan coast. They lie on south of the Kenyan Coast in the Kwale district. The hotsprings are located approximately 18kms from the Indian Ocean and are important since they manifest geothermal potential in the area. Three hotsprings occur in the vicinity with temperatures ranging from 55- 70ºC and an average flow rate of approximately 90 l/s. The project presents the evaluation of geochemical results of the sampled three hotsprings in Majimoto, three hotsprings from Bogoria and the sea water with the aim of evaluating sea water influence in the Majimoto hotsprings. Majimoto hotsprings give unreliable geothermometry temperature due to the influence of the sea water in its chemistry. Due to this, it is necessary to recalculate the chemistry of the hotspring to find out the actual chemistry of the hotspring without the sea water and find out the actual characteristics of the reservoir that hosts the hotspring. The study was done in Majimoto hotsprings which are located outside the active volcanic Rift Valley in the Kenyan coast and the results compared with the chemistry of Bogoria hotsprings located within the Rift floor which are free from sea water contamination. The Majimoto hotsprings are located approximately 18kms off the Indian Ocean and are important since they manifest geothermal potential in the area. Three hotsprings occur in the vicinity with surface temperatures ranging from 55-70ºC and an average outflow rate of approximately 90 l/s.The project presents the evaluation of geochemical results of the sampled three hotsprings in Majimoto, three hotsprings from Bogoria and the sea water with the aim of evaluating sea water influence in the Majimoto hotsprings. The Majimoto hotsprings are characterized by NaCl-NaHCO3 waters, suggesting that the springs are most likely being controlled underneath by an intrusive hot body. Bogoria hotsprings are characterized by Na-HCO3 type of waters. The major thermal manifestations within this Bogoria are geysers, hotsprings and fumaroles which can be observed along the shores of the lake with surface temperatures ranging from 85-98°C. The results indicate that 3% of sea water is found in the Majimoto hotsprings. The Na-K-Mg ternary denotes that the original Majimoto chemistry hotsprings compares with sea water. Geothermometry temperature calculations display a 5˚C temperature difference between the original and recalculated Majimoto hotspring water. The comparative K/Mg vs. K/Ca plot designates that the Majimoto hot springs waters are either mixed or part of a flow-through type convective system. Sea water is also typical of Na-Cl type of water.Further work involving a numerical model to investigate the occurrence of sea water iv intrusion in Majimoto and hydrogeochemical processes that may accompany sea water intrusion into these hotsprings should be carried out in order to support and validate the presence of sea water in Majimoto hotsprings.