Phreatic explosion at Dieng volcano, Indonesia

A phreatic explosion occurred at Sileri crater of Dieng Volcanic Complex, Java, Indonesia at 11:25 UTC (18:25 LT) on April 29, 2021. The last notable eruption of this volcano took place on July 2, 2017, injuring 10 people.

An examination of the crater at 01:03 UTC (08:03 LT) today, showed traces of the distribution of mud material to the south and east, with a distance of 200 – 400 m (650 – 1 300 feet) from the edge of the crater. A thin white gas gust was observed rising up to 50 m (165 feet) from the surface of the crater.

The results of measurement of gas concentration show the value of SO₂ gas at 2.8 ppm, H₂S 1.8 ppm, and CO₂ 0% vol.

The temperature measurement at the eruption point showed a value of 65 – 89 °C (149 – 192 °F), while at the reference point daily monitoring showed 51.2 °C (125 °F).

The gas concentration and temperature values ​​are still at the average value of normal conditions before the eruption.

The results of visual and instrumental monitoring to date have not detected any signs of increased activity leading to further eruptions.

The level of activity of Dieng is at Level I (Normal) with a recommendation that the community is not active within a radius of 500 m (1 650 feet) from the Sileri crater, and not to move around the Timbang crater to avoid the threat of high concentrations of volcanic gases that endanger lives.

"For the time being, the Banjarnegara-Batang road is closed. Because there are a lot of rocky materials that can endanger motorists. There are rocks as big as an adult's fist, right now, it's a danger to motorists," Batur Police Chief AKP Agung Setyawan told AFP. 

There was no relocation of residents due to the eruption, Agung added.

"The distance of the Sileri crater to the nearest residential areas is about 1 and 1.5 km (0.62 – 0.93 miles). From the experience of the eruptions in 2017 and 2018 [volcanic material] does not reach residential areas, so we urge residents to remain calm."

A sudden phreatic eruption took place at the Sileri crater at about 05:00 UTC (12:00 local time) on Sunday, July 2, 2017. There were 17 people near the crater when the eruption took place. 10 of them suffered minor to moderate injuries.

The eruption spewed ash up to 50 meters (164 feet) from the top of the crater, emitting cold lava.

The 10 injured persons were within 15 m (50 feet) from the crater when the eruption occurred. They have been rushed to Batur Public Health Center for medical treatment, Sutopo Purwo Nugroho, a spokesman for the national disaster management agency, said.

A rescue helicopter sent to assist the evacuation of residents crashed three minutes before arriving at the scene. All eight people on board were killed.

Read more: Rescue helicopter crashes after eruption at Mount Dieng, Indonesia

Geological summary

The Dieng plateau in the highlands of central Java is renowned both for the variety of its volcanic scenery and as a sacred area housing Java's oldest Hindu temples, dating back to the 9^th century CE. The Dieng volcanic complex consists of two or more stratovolcanoes and more than 20 small craters and cones of Pleistocene-to-Holocene age over a 6 x 14 km (3.8 x 8.7 miles) area.

Prahu stratovolcano was truncated by a large Pleistocene caldera, which was subsequently filled by a series of dissected to youthful cones, lava domes, and craters, many containing lakes.

Lava flows cover much of the plateau, but have not occurred in historical time, when activity has been restricted to minor phreatic eruptions. Toxic volcanic gas emission has caused fatalities and is a hazard at several craters. The abundant thermal features that dot the plateau and high heat flow make Dieng a major geothermal prospect. (GVP)

Featured image credit: PVMBG