Description

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Context

Mount Lewotobi in Indonesia East Nusa Tenggara erupted spewing a 3,500 metre ash column & prompting orange-level aviation alerts, evacuation advisories & safety warnings for residents near active volcano.

Mount Lewotobi

Feature	Details
Location	Flores Island, East Nusa Tenggara province, Indonesia
Coordinates	Approximately 8.5° S, 122.8° E
Type	Stratovolcano (composite volcano)
Composition	Andesitic to basaltic andesite
Part of	Pacific Ring of Fire
Peaks	Two main peaks Lewotobi Lakilaki (1584 m) & Lewotobi Perempuan (1703 m)
Separation	2 km separated by a saddle of 1232 m elevation
Crater Features	Lakilaki 400 m wide open to north; Perempuan 700 m wide
Flank Cone	Iliwokar on east flank of Lewotobi Perempuan
Historical Eruptions	Lakilaki Frequent activity in 19th–20th century; Perempuan Only two historical eruptions
2024 Activity	Major eruption with ash plumes up to 8,000 m; aviation warning issued (Orange Level)
Volcanic Hazards	Ashfall, hot clouds, lava flows, lahars during rainfall
Local Response	6 km exclusion zone; facemask advisory; aviation rerouting below 5,000 m
Nearby Settlement Risk	High due to proximity of human habitation & farming communities

Tectonic Plates Related to Indonesia & Ring of Fire

Eurasian Plate

Feature	Details
Type	Major tectonic plate
Boundaries	Converges with Indian, Arabian & Philippine Sea plates
Interaction with Indo-Australian Plate	Subduction of Indo-Australian Plate beneath Eurasian Plate creates volcanic arcs
Relevance to Indonesia	Forms northern boundary; causes volcanism & earthquakes
Geological Significance	Part of complex Sunda Arc tectonic interaction

Australian Plate

Feature	Details
Type	Major tectonic plate
Boundary Type	Convergent (subducts under Eurasian Plate)
Motion Direction	Northward at ~7 cm/year
Interaction with Indonesia	Responsible for Sunda Trench & volcanic arc in Java-Sumatra chain
Importance	Drives seismicity in southern Indonesian region

Pacific Plate

Feature	Details
Type	Largest tectonic plate
Motion Direction	Westward movement
Plate Boundaries	Interacts with Philippine Sea, North American & Indo-Australian plates
Indonesia Relevance	Less direct than Eurasian/Australian but contributes to broader Pacific seismicity
Key Feature	Dominates Ring of Fire encircling Pacific Basin

Sunda Arc

Feature	Details
Location	Extends from northern Sumatra through Java, Bali, Lombok, Sumbawa, Flores, to Banda Sea
Tectonic Setting	Formed by subduction of Indo-Australian Plate beneath Eurasian Plate
Arc Type	Continental volcanic arc
Length	Over 3,000 km
Key Islands	Sumatra, Java, Bali, Lombok, Sumbawa, Flores, Wetar
Oceanic Feature	Lies above Sunda Trench a major subduction zone
Major Volcanoes	Mount Merapi, Mount Agung, Mount Bromo, Mount Rinjani, Mount Tambora, Mount Lewotobi
Plate Interaction	Indo-Australian Plate (subducting) & Eurasian Plate (overriding)
Volcanic Activity	High includes several of world’s most explosive & active volcanoes
Hazards	Earthquakes, tsunamis, pyroclastic flows, lahars, ashfall, volcanic lightning
Most Famous Eruption	Mount Tambora (1815) largest eruption in recorded history; caused “Year Without a Summer”
Modern Monitoring	Managed by Indonesia PVMBG (Volcanology & Geological Hazard Mitigation Centre)
Geological Importance	Vital for understanding plate tectonics, subduction volcanism & hazard mitigation

Geological & Tectonic Information

Aspect	Details
Subduction Zone	Indo-Australian Plate descends below Eurasian Plate
Trench System	Sunda Trench (a deep oceanic trench parallel to arc)
Magma Generation	Caused by water-rich oceanic crust melting in mantle wedge forming andesitic magma
Seismicity	Frequent earthquakes due to plate movement; includes megathrust & deep-focus quakes
Tsunami Potential	High especially where underwater quakes rupture sea floor (e.g., 2004 Indian Ocean Tsunami)
Banda Arc Connection	The eastern end transitions into complex Banda Arc involving multiple microplates
Economic Impact	Affects agriculture, infrastructure & human settlement due to fertile soils but high risk

Major Volcanoes of Sunda Arc

Volcano	Island	Elevation (m)	Last Major Eruption	Notes
Mount Merapi	Java	2,963	2023	Most active volcano in Indonesia
Mount Tambora	Sumbawa	2,850 (after 1815)	1815	Deadliest eruption in history
Mount Agung	Bali	3,031	2019	Known for 1963 catastrophic eruption
Mount Rinjani	Lombok	3,726	2016	Second highest in Indonesia
Mount Lewotobi	Flores	1,703 / 1,584	2024	Twin volcano, recent aviation alerts issued

For more such articles, please refer to IAS GYAN

Sources:

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PRACTICE QUESTION

Q. Sunda Arc exemplifies dynamic interaction of tectonic plates shaping Southeast Asian geography & hazards. Examine geological significance & implications of volcanic activity along Sunda Arc for regional disaster preparedness.