Continuous thermal monitoring of the 2008 eruptions at Showa crater of Sakurajima volcano, Japan

An infrared thermal monitoring system installed 3.5 km from the Showa crater of Sakurajima volcano, Japan, enabled the capture of continuous thermal waveform data at 1 Hz during two recent episodes of eruptive activity. The eruptions were characterized by a Sudden increase in Volcanic cloud temperature in the first 2-5 s, followed by gradual cooling over a few minutes. The maximum cloud temperature varied widely between individual events with a range of more than 180 C. A positive relation between the maximum temperature and the exit velocity of the cloud has also been established. At higher temperatures and faster exit velocities of the volcanic cloud, the eruptions tend to be accompanied by pyroclastic density currents. However, no strong correlation was observed in a 6-month period of 2008 between temporal changes in surface manifestation of eruptive activity and the change of cloud temperatures. Identification of factors that control such observed apparent temperatures of volcanic cloud would lead to a better understanding of the thermodynamics of the eruption itself.