Aerial IR surveys were carried out in September 2010 over geothermal areas at Usu, Noboribetsu and Hokkaido-Komagatake volcanoes, Japan. The heat discharge rate from steaming grounds that formed during the 2000 eruption of Usu volcano is estimated to be 5.6 MW, which is half the rate measured in September 2006. Integration of the heat discharge rate from April 2000 to September 2010 yields an accumulated discharge of approximately 2.4 × 1016 J. This amount of heat corresponds to several percent of the total intruded magma heat estimated from analyses of ground deformation associated with the 2000 eruption. Areas of steaming ground associated with the 2000 eruption showed rapid growth compared with those of the 1977 eruption but discharged less heat. We suspect that differences in the hydrological environments of the two eruptions, led to contrasting patterns of propagation of the hydrothermal systems around the intruded magmas. The heat discharge rate from the summit areas of Usu volcano, Showa-shinzan and Noboribetsu volcano in 2010 are estimated to be 40, 6.2 and 22 MW, respectively, similar to the rates measured in September 2006. No high-temperature grounds were detected at the vents and fissure formed during the 1942 eruption of Hokkaido-Komagatake volcano. We observed no geothermal activities at vents associated with the 1929, 1996, 1998 and 2000 eruptions, due to the absorption effect of atmospheric cloud.
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