バジャワ地域のスコリヤ丘群のFe-Ti酸化物の岩石学的検討により,地下の安山岩質のマグマ溜まりにより高温な玄武岩質マグマが供給されたことが明らかとなった。同地域には,最近の70万年の間に3つの長寿命のマグマ溜まりが存在した。マグマ混合は各マグマの定置の初期段階で生じ,それ以後混合が進み通常の結晶分化作用が支配した。 マグマ混合後の安定したマグマはほぼ平衡状態にあり,噴火前の温度は797-997℃(平均900℃)である。チタン磁鉄鉱―チタン鉄鉱による推定温度が,結晶粒界,中心部,周辺部のいずれも865-928℃と集中していることから,0.14Maの噴火の起源マグマでは,混含による不均一は解消されていたと推定される。マグマ溜まりの冷却速度は,0.14Maから現在までは2.7℃/1000年と計算される。

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The system is mainly composed of the underground heat exchangers using 75 building's piles, four 15HP heat pumps, a 140m³ heat storage tank, piping systems, air-conditioning and heating equipments. Each pile is drilled up to 50m deep by the earth drill technique and equipped with a double U-tube which carries the liquid for the geothermal system. The designed quantity of heat exchanged between the underground heat exchangers and these external formations is 114kW. The heat pumps are driven in the night when electricity cost is low, and the water in the storage tank is heated to 50°C in winter and is cooled to 5°C in summer, which are store in the heat storage tank. In the daytime, the former is used for heating the 970m² floor of the gymnasium and the latter for cooling the control room and the special school room. The operating performance of the heat source equipments meets the evaluation standards : in the heating the inlet temperature of the underground heat exchanger t_in> 0°C, the outlet temperature of the underground heat exchanger t_out>atmospheric temperature t_air, the system power q≥132kW, the storage temperature t_s≥50°C and in the cooling t_out>t_air, q≥120kW, t_s≤5°C. Heat pump heating and cooling coefficients of performance are respectively 3.04 and 4.5. The total quantity of heat given by the heating floor face of the gymnasium is 54kW by estimate from the floor temperature of 21.5°C and the room temperature of 15°C. Additionally the energy consumption of the geothermal system is 68 % that of the kerosene boiler and the carbon dioxide emission of the former is 56% that of the latter.

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