Mount Agung which erupted on Tuesday (21/11/2017) at 17:05 WITA, considered as phreatic eruption type. The height of thick-gray smoke with medium pressure is 700 meters. The phreatic eruption occurs due to high pressure water vapor. Water vapor is formed along sub-soil water heating or rain that infiltrates into the soil inside the crater and then directly contacts with magma. Phreatic eruption is followed by smoke, ashes and materials from inside the crater.
Phreatic eruption is unpredictable. It can suddenly occurs and often with no indication of increasing seismic activity. Several volcanoes in Indonesia erupt phreatic when their status is at Level 2 (Waspada) such as the eruption of Mount Dempo, Mount Dieng, Mount Marapi, Mount Gamalama, Mount Merapi and others. The height of phreatic eruption can reach 3000 meters depending on its water vapor intensity. Therefore phreatic eruption is not unusual when the volcano status is above normal. Usually the impact of the eruption is rain of ashes, sand or gravels around the mountain.
Phreatic eruption is not so harmful compared to magmatic eruptions. Phreatic eruptions could happen without magmatic eruptions. But phreatic eruption can also be an early indicator of a volcanic eruption.
Magmatic eruption is an eruption caused by magma inside the volcano. Magmatic eruption signs are measurable and observable. Indonesia has 127 active volcanoes of which each has different characteristic. Citizens in Bali are advised to obey the recommendations of PVMBG. Science and technology combined with local wisdom can effectively save the surrounding community.
Up to now, the status of Gunung Agung is on “Siaga" (level 3) without status upgrade. PVMBG carefully monitors and analyzes volcanic activity of the mountain. Early tremors is being detected.
The free space recommendation also remains at 6-7.5 km from the summit crater. That area should be clear of any activities. On Tuesday (21/11), as many as 29,245 people are currently staying in 278 evacuation points. This number will rise considering there are more residents moving out from their villages.
People are encouraged to remain calm. Do not panic and provoked by misleading issues. PVMBG will continue to provide up-to-date information. BNPB, TNI, Polri, Basarnas, BPBD, SKPD, volunteers and all related elements is providing evacuation treatments.
Situation in Bali remains safe. The Ngurah Rai International Airport is also safe and having normal activities. Tourism in Bali is also normal apart from the 7.5 Km radius around Mount Agung.
Source: Sutopo Purwo Nugroho, Head of Information Data and Public Relations Center of BNPB
Read this original article from Indonesian National Disaster Management Authority Official Website