Mount Agung

Deep under Indonesia, hot melted rock pushes up.

It comes out of volcanoes like Agung. Each time, lava and ash pile up. Layer by layer, the mountain grew tall.

The Global Volcanism Program places Agung in the Sunda Volcanic Arc, a chain of volcanoes in Indonesia. Below volcanoes like these, melted rock called magma rises toward the surface.

Agung is a stratovolcano, which means it was built up by eruptions, layer upon layer. Some eruptions pour out lava. Others blast out ash and rock fragments. Over time, these layers piled up into the steep, cone-shaped mountain we see today, next to the large bowl of another volcano, the Batur caldera.

GVP places Agung in the Sunda Volcanic Arc and classifies it as a composite stratovolcano, an edifice built of alternating lava flows and explosive deposits. Its eruptive style is mixed: the 1963-64 eruption was both explosive and effusive, with voluminous ashfall, pyroclastic flows (fast avalanches of hot gas and rock) and lahars (volcanic mudflows), while the 2017-2019 activity included explosions, ash plumes, summit lava flows and incandescent ejecta.

Agung rises above the southeast rim of the Batur caldera, a large collapse depression of a neighboring volcano. Only a few eruptions have been recorded in historical time, dating back to the early 19th century, according to GVP; Britannica notes that before 1963 it had been dormant for 120 years.

Many people live on Bali near the volcano.

Villages, farms and forests surround the mountain. When the volcano is quiet, life goes on as usual.

Agung's slopes reach down to the coast on both its northern and southern sides, and many communities lie around the mountain. Volcano reports name nearby places such as Besakih, Rendang and Selat, where ash sometimes fell during the 2019 eruptions.

The photo of the 2017 eruption, taken from the northeast, shows trees, power lines and small buildings at the foot of the volcano. People living near an active volcano depend on the scientists who watch it and warn them when to leave and when it is safe to return.

GVP's weekly reports track ash falling on surrounding communities during the 2017-2019 activity: on 21 April 2019, for example, ashfall was reported in Besakih (7 km southwest), Rendang, Klungkung, Gianyar, Bangli, Tabanan and at the international airport in Denpasar, about 60 km southwest. Monitoring posts at Rendang and Batulompeh observed the volcano throughout.

Monitoring by the seismic network, ground deformation measurements, satellite thermal data and observers lets the authorities raise and lower alert levels and set exclusion zones. NASA's Earth Observatory adds that volcanic steam, lava and ash tend to have local and regional effects, while gas emissions can sometimes have global consequences.

Agung is an active volcano.

Scientists tell people when it is safe to go near it. Always follow their warnings, and never go into a closed area.

Agung is still an active volcano: the Global Volcanism Program lists small ash plumes in 2022. Indonesia's volcano agency, PVMBG, uses alert levels from 1 to 4. When the alert level is high, it closes a zone around the summit, and no one should enter it.

Before visiting, check the current alert level and local rules. Go onto the volcano only when the authorities allow it, and turn back if warnings change. Ash can also affect air travel, so check flights when the volcano is active.

PVMBG's alert scale runs from 1 to 4; during 2018-2019 Alert Level 3 carried a 4 km exclusion zone around the crater, reduced to 2 km at Level 2 in July 2019 (GVP). Ash from the 2019 explosions reached communities up to about 60 km away, including Denpasar's international airport.

Visitors should consult current PVMBG alert information before approaching the volcano, respect exclusion zones absolutely and follow local regulations on climbing. Because conditions on an active stratovolcano can change quickly, plans should include the possibility of sudden closures.