At 1700 on 16 September the GMS satellite showed a plume extending WSW from the volcano, at about the cirrus cloud level. By midnight, the plume was less dense, but feeding from the volcano appeared to be continuing. Antara radio reported that an explosion at 0120 on 17 September ejected hot ash, pebbles, and rocks 10-40 cm in diameter. Other explosions occurred at 1014, 1129, 1132, and 1715 the same day. Ejecta sometimes rose to 2 km above the summit. An ash cloud remained over the area for 18 hours. At 1100 on 18 September, a GMS image showed the cloud from a moderate to intense explosion that probably began about 1000 and ended around 1300-1400. No additional activity has been reported (table 1).

Table 1. Cloud-top temperatures for three plumes from Soputan determined by Michael Matson from NOAA 7 polar orbiting satellite images, with altitudes calculated from nearby radiosonde temperature/altitude profiles.

Geological Summary. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano is the only active cone in the Sempu-Soputan volcanic complex, which includes the Soputan caldera, Rindengan, and Manimporok (3.5 km ESE). Kawah Masem maar was formed in the W part of the caldera and contains a crater lake; sulfur has been extracted from fumarolic areas in the maar since 1938. Recent eruptions have originated at both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Information Contacts: M. Matson, D. Haller, and T. Baldwin, NOAA; Antara News Agency, Jakarta.