On Friday night, thin volcanic ash began pouring out in the area around the observation post, head of Mount Slamet Observation Post, Sudrajat, said here on Saturday.
However, there was no red-hot lava spewing from the volcano, which intersects the five districts of Banyumas, Purbalingga, Pemalang, Tegal and Brebes.
That lava was seen from Monday night (June 30) to Tuesday (July 1).
"Unfortunately, on the last two nights the peak has been covered with mist, so we couldnt make any observations," Sudrajat said.
The activity on Mount Slamet increased again on June 29 and has shown no signs of cooling, according to the observations made so far,
The authorities have imposed alert level II (Waspada) on the volcano, and there was no activity to increase the alert levels, Sudrajat said.
The increasing volcanic activity may have been caused by gases from the previous volcanic activity, that was blocked by stones, forcing the mount to release its trapped energy, Sudrajat said.
"I hope that is the case," he said.
Based on observations conducted from the post located in Gambuhan Village, Pulosari sub-district, Pemalang District on Friday (July 4), Mount Slamet began emitting thin white smoke measuring between 50 and 150 meters in the sky.
There was one internal tremor recorded, one harmonic tremor, 22 volcanic tremors and 306 tremors triggered by the blast.
On March 10 at 22:00 local time, Volcanology and Geology Disaster Mitigation Center (PVMBG) raised the status of Mount Slamet from normal (level I) to alert level II (Waspada) due to increasing volcanic activity.
On April 30, at 10:00 local time, the PVMBG raised Mount Slamets status to alert level III (Siaga) due to increasing tremors and eruptions.
Then on May 12, at 16:00 local time PVMBG reduced the status from alert level III (Siaga) to alert level II (Waspada).
(Reporting by Sumarwoto/Uu.A059/INE/KR-BSR/A014)