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Semeru Volcano | Dr John Seach
Last updated: January 2026
East Java, Indonesia
8.11 S, 112.92 E
summit elevation 3676 m
Stratovolcano
Semeru, Java's highest volcano, is one of Indonesia's most active and dangerous. Persistent dome growth at Jonggring Seloko crater produces near-continuous explosions (every 20-30 minutes on average), ash plumes, incandescent avalanches, and frequent pyroclastic flows down SE valleys. Major dome collapses generate deadly flows and lahars affecting downstream communities.
Warning: The summit and SE flank are extremely hazardous due to sudden explosions, ballistic projectiles, and pyroclastic flows. Exclusion zones (typically 1-8 km from crater, extended SE) are enforced; climbing requires permits and caution.
Geology and Volcanology
Semeru is a basaltic-andesitic stratovolcano in the Tengger-Semeru massif, part of the Sunda Arc subduction zone. Its active Jonggring Seloko crater (SE of Mahameru summit) hosts persistent lava dome extrusion and explosions driven by gas-rich magma ascent. Frequent dome collapses produce block-and-ash flows. Monitored by PVMBG with seismicity, deformation, thermal cameras, and gas measurements to forecast larger events.
Current Activity (January 2026)
Semeru continues its long-term eruption (since 1967) with frequent explosions from Jonggring Seloko crater (alert level 3/Siaga). Ash plumes typically 100-1000 m above crater, occasional incandescent avalanches, and minor pyroclastic flows down SE flanks. Seismic activity elevated with explosion signals. Exclusion zone: 1 km radius from crater, 8 km SE. Communities remain vigilant for lahars during rains. Monitoring by PVMBG ongoing.
Semeru volcano photos by Dr John Seach
Semeru volcano
Dr John Seach at summit of Semeru volcano
Warning: The summit region of Semeru is very dangerous due to explosive activity.
Summit eruption Semeru volcano 2000
Dr John Seach and climbers at 2700 m on the northern approach to Semeru from Ranu Pani village
2026 Eruption
Explosive activity continues with a notable eruption on 12 January 2026 at approximately 10:20 local time. Pyroclastic flows extended up to 5 km from the crater. Multiple eruptions recorded in recent days, with high seismic amplitude. Alert level remains 3 (Siaga). No damage or injuries reported yet.
2025 Eruption
A major explosive eruption occurred on 19 November 2025. Ash plumes rose to 16.5-18 km altitude (54,000-59,000 ft). Pyroclastic flows traveled 13-14 km down the S and SE flanks. Alert level raised to 4 (Awas) temporarily, then lowered to 3 (Siaga). Hundreds of residents and climbers evacuated; ashfall damaged homes, crops, and infrastructure. Three severe burn injuries reported; no fatalities.
2022 Eruption
A large explosive eruption occurred on 4 December 2022. Ash emissions reached 15 km (50,000 ft) altitude. Pyroclastic flows extended up to 13 km S and SE. Hundreds evacuated due to heavy ashfall and subsequent lahars. No fatalities reported.
2021 Eruption
A major dome-collapse eruption occurred on 4 December 2021. Ash column reached 15 km (50,000 ft) altitude. Pyroclastic flows traveled up to 19 km, burying villages and destroying bridges. 48 confirmed fatalities (plus missing), over 11,000 evacuated. One of Semeru's deadliest recent events.
2020 Activity
Ongoing dome growth with explosions. A notable 3 minute 50 second eruption on 18 January 2020 produced ash to 15,000 ft (1,300 ft above crater). Lava and pyroclastic flows down SE flank. Exclusion zone: 1 km radius from crater, 4 km SSE.
2018 Activity
Persistent dome extrusion with frequent incandescent avalanches and small explosions. Possible ash emissions reported in August 2018. Activity typical of Semeru's long-term eruptive phase since 1967.
2011-2012 Activity
Eruptions were observed at the volcano on 9, 14, and 17 June 2011. Activity at Semeru resumed at the end of December 2011. Between 29th December 2011 and 15th January 2012 there were eight explosions at Jonggring Seloko crater, sending ash up to 600 m high. Incandescent fallout was observed 200 m radius from the crater. On 2nd February 2012 a pyroclastic flow reached 2.5 km from the crater. The alert status at Semeru volcano was raised to Level 3 (out of a maximum 4) on 3rd February 2012. A 4 km exclusion zone was placed on the SE slopes of the volcano where pyroclastic flows occur. Climbers were advised to remain at least 1 km from Jonggring Seloko crater.
2009 Eruptions
Increased activity has been reported at Semeru volcano in Indonesia. Between 6th February and 4th March 2009 there were 873 explosion earthquakes registered, with an average of 34 events per day. On 5th March there was one period of tremor recorded. On 6th March one episode of tremor was recorded accompanied by booming sounds which were heard at Semeru observatory. On 6th March at 10:28 hr a booming noise was heard while the summit was covered in cloud. Semeru is at level 2 alert (Waspada) out of a maximum of 4. Explosions occur at an interval of 20-30 minutes, with ash emissions 100-400 m above Jonggring Seloko crater. So far the current eruptions have not been accompanied by pyroclastic flows, but this remains a danger. Areas which may be affected by pyroclastic flows include inhabited areas of Rowo Baung, Supit, Pronojiwo, Urip, and Umbulandi Urang Supit. Rowo Baung and Supit are the nearest villages to the eruptive centre, 9 km from the peak of Gunung Semeru. There is a potential threat to sand mining activities at Supit and Rowo Baung. Recommendations from the Indonesian Centre of Volcanology and Geology are that people avoid the area 4 km SE of the active crater at Semeru due to the threat of pyroclastic flows. People are advised not to climb to the summit peak (Mahameru). Residents should prepare for possible ashfall. Aircraft should beware of explosion hazards, and ash emissions from Semeru.
July 2000 Summit Fatalities
A scientific team was caught in an eruption at the summit of Semeru on 27th July 2000. At approximately 0706 hr an explosion resulted in two deaths and injuries to five other volcanologists near the NE rim of the active summit crater Jonggring Seloko. Members of the group had approached the rim of the active crater which is always dangerous. The two fatalities were from Volcanological Survey of Indonesia. Injuries were sustained by climbers from Semeru Volcano Observatory, Hebrew University in Israel, University of Pittsburgh, the Smithsonian Institution. This was the second fatal field trip after an IAVCEI meeting. The first was in Galeras, Colombia in 1993.
2000 Expedition by Dr John Seach
Dr John Seach made observations during a 3-hour summit stay on 2 May 2000. During the climb from Ranu Pani village in the N, ash deposits were observed to cover vegetation at a distance of 10 km from the volcano. The bottom third of the cone was vegetated, and zones of mass-wasting had sliced away 20-m-wide sections of forest. The top two-thirds of the cone consisted of ash, cinders, and blocks up to 1.5 m in diameter. There were areas of deep erosion and the risk of rockfalls posed a hazard to climbers. The summit area (Mahameru) lay covered by ash and baseball-sized blocks with a density of 50/m2. A 20-m-wide, 60-m-deep, W-sloping valley separated Mahameru from the active Jonggring Seloko crater, but they are joined by a ridge. The highest N rim of the crater was approximately 30 m below the summit peak. A 2-m-diameter block was located 15 m below the summit on the wall of the valley. Between 0725 and 1010, 13 eruptive events were observed. During this interval the N rim of Jonggring could not be approached because of the intermittent rain of blocks falling outside the crater and into the valley 50 m from the crater. Two vents produced short-lived Vulcanian eruptions with variable timing and size. Eruptions commenced with degassing, explosions, or the sound of breaking rock, followed by falling bombs and brown ash emission. The explosions were relatively quiet and not accompanied by groundshaking. Brown ash clouds rose to 600 m above the vent and drifted SE. The plume detached from the summit before the next eruption began. Steam emission occurred between eruptions.
1999 Summit Fatalities
Two climbers died near the crater on 2nd September after being struck by large ejected ballistics. The two men were part of a group of 17 from Germany. The victims, together with the group leader, had separated from the group to check the crater when the accident occurred.
1994 Eruptions
On 3 February lava avalanches and pyroclastic flows from the summit crater descended SE along the Kembar and Kobokan rivers, reaching 7.5 km and 11.5 km from the summit. Six people were killed and 275 people were evacuated from Sumbersari village.
1981 Eruptions
On 14th May heavy rains created mudflows/landslides which killed 252 persons, left 152 injured and 120 missing. The location of the landslide was similar to that of 1909.
1957 Debris Flow
A debris flow occurred at Semeru volcano in 1957 which reached Lumajang city.
1946 Eruptions
In February 1946 ash rain fell in Malang. On 27th May 1946 a report from Aneta, Batavia stated "Semeru volcano lately became active, and ash, stoneblocks and mud were thrown out. A hundred dwelling houses and about 150 hectares of rice fields were destroyed, and lahar-floods were caused." Ash fell in Malang.
1941 Eruption
An eruption occurred at the base of Semeru volcano in 1941.
Further reading
Nishimura, T., Iguchi, M., Kawaguchi, R., Hendrasto, M. and Rosadi, U., 2012. Inflations prior to Vulcanian eruptions and gas bursts detected by tilt observations at Semeru Volcano, Indonesia. Bulletin of Volcanology, 74(4), pp.903-911.
Siswowidjoyo, S., Sudarsono, U. and Wirakusumah, A.D., 1997. The threat of hazards in the Semeru volcano region in East Java, Indonesia. Journal of Asian Earth Sciences, 15(2-3), pp.185-194.
Doyle, E.E., Cronin, S.J., Cole, S.E. and Thouret, J.C., 2010. The coalescence and organization of lahars at Semeru volcano, Indonesia. Bulletin of Volcanology, 72(8), pp.961-970.
Semeru Volcano Eruptions
1967-2026 (ongoing), 1950-1964, 1946-1947, 1946, 1945, 1941-1942, 1913, 1912, 1911, 1910-1911, 1909-1910, 1908, 1907, 1905, 1904, 1903, 1901, 1900, 1899, 1898, 1897, 1896, 1895, 1893-1894, 1893, 1892, 1889-1891, 1888, 1887, 1886, 1884-1885, 1879, 1878, 1877, 1872, 1867, 1865, 1860, 1857, 1856, 1851, 1848, 1845, 1844, 1842, 1838, 1836, 1832, 1830, 1829, 1818