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In Brief February 2011

Dr Joe McCall

Kenya hot rocks

Geoscientist 21.1 February 2011

Kenya’s Geothermal Development Company is drilling six geothermal wells at Menengai, a huge caldera volcano, just north of Nakuru (Gregory Rift Valley) writes Joe McCall. Due for completion by June 2011, by December Kenya hopes to be looking for developers.

Kenya already has three such installations at Olkoria (Lake Naivasha). Exploration started in 1956 – though production only began in 1981. The field covers 70km2 and boasts 110 wells (50 production, six re-injection). Thirteen further prospects have been identified, of which three (all near caldera volcanoes Longonot, Suswa and Menengai) have been surveyed. The total potential is estimated at >2000 MWe.

Menengai, a trachyte central volcano of shield form is underlain by a high-level magma chamber and encloses a vast caldera first erupted at 0.18 Ma, about 30 km3 in volume and 12km across. The last lavas erupted only 8300 years ago. Active fumaroles produce mainly CO2 with some steam, while there is a danger of asphyxiation from mofettes within the caldera.

During the 1957 groundwater survey of Nakuru, drilling three kilometres north of the caldera produced low pressure steam at 60m. I was dubious about the viability of geothermal resources because of the dominance of CO2 over steam emissions; but several techniques developed since (hot rock, steam and hot groundwater, re-injection), have been successful elsewhere (e.g., in the Paris Basin).

The Menengai venture stands every chance of success in this energy-poor country. The Menengai site lies close to the town of Nakuru, immediately at the foot of the southern outer slope of the slumbering volcano.