Sequence and Characteristics of the 2007 Eruptions at Showa Crater of Sakurajima Volcano

2007年5月から6月のおよそ40日間にわたって，桜島昭和火口で噴火活動が発生した。2007年噴火初期には，それまで火道内を埋めていたと考えられる比較的低温の灰放出が観測された。第2活動期は，100℃を超える噴煙が頻繁に観測され，初動の立ち上がりが明瞭な，いわゆる爆発型の空気振動を伴う噴火である。赤熱物質の放出や火映が観察されるなど，2007年噴火の活動最盛期であったといえる。噴火活動が終息する直前2週間は，20縲・0℃の低温噴煙が放出され，この現象に対応する空気振動は約1 Hzに卓越周波数を持つ単調微動型であった。
Showa crater of Sakurajima volcano erupted again in 2007 after 1 year's interval. Activity of this 2007 eruptions was able to be divided into three stages. The first stage was characterized by weak ejection of volcanic materials without significant infrasound signals. This stage lasted only for the first few days. Main explosive eruptions accompanying with impulsive infrasound waves occurred in the second stage (about two weeks). During this stage, incandescent reddish ejecta were frequently observed. Temperatures of the eruption clouds were relatively high (~160°C). Final two weeks was categorized into the third stage of the 2007 eruptions. Peculiar infrasound tremor signals (peak frequency was about 1.0 Hz) were recorded associated with minor ash eruptions.