The head of BPPTKG Hanik Humaida in his official statement said that the tremors were recorded during the observation period from 00.00-06.00 WIB with an amplitude of 3-9 mm and lasted 47-71 seconds.
Visual observations show that the most active volcanic crater in Indonesia has a thin, medium, and white intensity of white and gray smoke up to 20 meters thick above the top of a mountain crater.
On the volcano, the wind blew weakly to the south, the air temperature was 14-20.4 degrees Celsius, air humidity was 59-91 percent, and air pressure was 567-708 mmHg.
Hanik also mentioned that as of June 1, 2019 there have been 72 events of hot clouds with a sliding distance of an average of 1 km and a maximum of 2 km towards Kali Gendol.
Based on the modeling of hot clouds from the potential collapse of the current volume of lava domes of 458,000 cubic meters, the distance of the farthest hot cloud slide is not expected to exceed 3 km from the summit of Mount Merapi towards Gendol River.
Seismicity is currently dominated by earthquake avalanches which are 30 times / day, followed by earthquake multiphase (MP) 4 times / day, low frequency (LF) 3 times / day, and blowing tremor 3 times / day. For shallow volcanic-tectonic earthquakes (VTB) and deep volcanic-tectonic earthquakes (VTA) occur occasionally.
In addition, the emergence of MP seismicity indicates that the supply of magma in Mount Merapi is still ongoing although at a low rate.
"Based on the condition of the volcanic activity, the activity status is still set at the alert level," Hanik said.
In the meantime BPPTKG does not recommend climbing activities except for the purposes of investigation and research related to disaster mitigation.
BPPTKG urged residents not to carry out activities within a three kilometer radius from the summit of Mount Merapi.
However, according to him, tourist objects around Mount Merapi such as the Kaliurang, Kaliadem, Klangon, Deles and other areas outside the 3 km radius from the summit are safe to visit.