Mount Semeru, Eruption 4th December 2021

Update 9/12/2021

Sadly the death toll from Mount Semeru now stands at c.40 as of noon today (local time). Over 100 have been injured.

The lava dome collapsed from 1st to 6th December 2021 generating both lava and pyroclastic flows. The largest dome collapse occurred around 14:47 on 4th December 2021 to be followed by pyroclastic flows from 15:10, causing the fatalities. Rescue efforts have been hampered by later eruptive activity.

Sources: and

Original Post, 5/12/2021

Fig 1: Image from 1985 eruption of Semeru, cropped from a photo by Tom Casadevall, 1985 (U.S. Geological Survey).  Source:  GVP

Sadly, 13 people have been killed, 7 missing and c. 100 injured, at the time of writing, following the collapse of the lava dome on Mount Semeru on 4 December 2021. Ash rose to a height of 50,000 feet, covering 11 villages.  Flows of hot gas and lava travelled 800m at least twice on Saturday, reaching a nearby river.  Two bridges were destroyed, including one connecting Lumajang to Malang. 900 people have been evacuated.  10 trapped in mines were rescued. Heavy rain and a thunderstorm had led to destabilisation of the lava dome. The volcano had been on alert level II (Waspada).

Mount Semeru is 3,657m high a stratovolcano with pyroclastic cones and fissure vents. Lake-filled maars follow a N-S trend cutting through the summit. She is located in the Lumajang district, East Java.  Java lies above the subduction zone where the Indo-Australian Plate subducts under Sunda Plate .  Her lavas are Andesite / Basaltic Andesite and Basalt / Picro-Basalt.  Over 1m people live within 30km of the volcano.

GVP records 65 Holocene eruptions since 1818, which range from VEI 1 to VEI 3.

Our thoughts are with those affected.

Armchair Volcanologist

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Source& Further Reading

The Smithsonian Institution’s Global Volcanism Program (GVP):

Indonesia: Mount Semeru volcano eruption kills 13 as thousands flee | The IndependentMount Semeru volcano eruption death toll at 13 as ash covers vehicles up to their roofs – World News – Mirror Online