Publications des scientifiques de l'IRD

Delalande-Le Mouellic M., Gherardi F., Williamson David, Kajula S., Kraml M., Noret A., Abdallah I., Mwandapile E., Massault M., Majule A., Bergonzini L. (2015). Hydrogeochemical features of Lake Ngozi (SW Tanzania). Journal of African Earth Sciences, 103, p. 153-167. ISSN 1464-343X.

Titre du document
Hydrogeochemical features of Lake Ngozi (SW Tanzania)
Année de publication
2015
Type de document
Article référencé dans le Web of Science WOS:000350185700014
Auteurs
Delalande-Le Mouellic M., Gherardi F., Williamson David, Kajula S., Kraml M., Noret A., Abdallah I., Mwandapile E., Massault M., Majule A., Bergonzini L.
Source
Journal of African Earth Sciences, 2015, 103, p. 153-167 ISSN 1464-343X
Located on the triple rift junction hosting the Karonga-Usungu depression in Tanzania, Lake Ngozi is the second largest crater lake of the East African Rift. The lake has a number of peculiar features: it has a near constant water level, no permanent surface inlets and outlets, it is vertically well-mixed, with homogeneous distribution of temperature and chemical composition, and it is characterised by near neutral to slightly acid Na-CI waters of comparatively high salinity and high P-CO2. Based on the different chemical signature of surface and ground waters (low-CI type) from lake waters, mass balance methods have been applied to investigate lake dynamics. Water enters the lake mainly by precipitation and groundwater inflow, and leaves by groundwater outflow and evaporation. A large groundwater outflow of 2.4 m yr(-1) has been estimated. The high salinity, Na-CI signature of Lake Ngozi waters, together with He-3/He-4 ratios measured on dissolved gases (between 7 and 8.3 Ra) and high-P-CO2 values estimated all along the water vertical column indicate the inflow of deep-seated fluids, likely magmatic in origin, into the lake. The existence of a hydrothermal system possibly at 250 degrees C in the root of the volcanic edifice is also hypothesised on the basis of solute geothermometry. Despite the current lack of vertical stratification, the lake is suspected to act as condenser for CO2 and other gases of deep magmatic origin, and should be then further monitored for the risk of limnic eruptions as well as for environmental and climatic concerns.
Plan de classement
Hydrologie [062]
Description Géographique
AFRIQUE DE L'EST ; TANZANIE ; NGOZI LAC
Localisation
Fonds IRD [F B010063979]
Identifiant IRD
fdi:010063979
Contact