Lewotobi Volcano Eruption

Syllabus Areas:

GS Paper I Geography

GS Paper III Disaster Management

The volcano on Flores Island erupted twice on 7 July 2025:

  • First, around 11 a.m. local time, it sent an ash plume soaring 18 km (11 miles) into the sky
  • The second eruption occurred in the evening, projecting ash up to 8 km (5 miles) high

Tectonic Setting of Indonesia

Indonesia is one of the most tectonically active regions on Earth because it lies at the convergence of multiple major tectonic plates, notably:

  • Indo-Australian Plate (moving northward)
  • Eurasian Plate (stationary or moving slightly southward)
  • Pacific Plate
  • Philippine Sea Plate

Most of the country’s volcanic and seismic activity is driven by the subduction of the Indo-Australian Plate beneath the Eurasian Plate.

Subduction Zone – Cause of Volcanism

  • At a convergent plate boundary, the denser oceanic crust of the Indo-Australian Plate is forced beneath the lighter continental crust of the Eurasian Plate.
  • As it descends into the mantle (~100–150 km depth), it encounters increasing heat and pressure.
  • The subducted slab contains water and other volatiles (like CO₂, H₂O), which lower the melting point of the overlying mantle.
  • This causes partial melting of the mantle wedge → magma is generated → it rises to the surface → forms a volcano.

Alert & Safety Measures

  • The volcanic alert level remained at its highest status ‘Awas’, in place since June when precursors like volcano inflation and seismic tremors prompted action
  • A 7 km exclusion zone (≈4.3 miles) was enforced. Over 10,000 residents across 10 villages in East Flores and Sikka districts were impacted, with shelters and school closures initiated
  • Authorities distributed 50,000 masks and warned of lahar threats (volcanic mudflows), especially if it rains.

Ash & Pyroclastic Effects

  • Hot pyroclastic flows mixed with gas, rocks, and lava descended up to 5 km (3 miles) down the volcano’s slopes.
  • Surrounding villages and rice fields were covered in thick grey ash, gravel, and possibly hot volcanic material

Impact on Aviation

  • At least 24 flights—primarily to Bali from Australia, Singapore, and South Korea—were cancelled or delayed due to ash hazards.
  • Airlines affected included Virgin Australia, Qantas, Jetstar, and AirAsia.
  • Although Bali’s Ngurah Rai Airport remained operational, flight schedules were disrupted
Lewotobi Volcano Eruption

Satellite Imaging

  • NASA’s Suomi NPP satellite captured a large ash plume drifting west across Flores after the first eruption. It confirmed ongoing activity into the evening.

Why It Matters

  • Mount Lewotobi Laki‑Laki is part of the Laki-Laki and Perempuan twin stratovolcano complex. Laki‑Laki is the more active one
  • The eruption on 7 July continues a period of frequent activity: there were eruptions in March, May, June, and a deadly explosive event in November 2024 (9 killed, many injured)
  • The scale of this eruption is noted as one of Indonesia’s largest since Mount Merapi’s 2010 event

    Prelims Questions:

  1. Which of the following best explains the cause of volcanic activity in the region of Flores Island, Indonesia?
    1. Mantle plume activity beneath oceanic lithosphere
    2. Divergent boundary between the Pacific and Australian plates
    3. Subduction of the Indo-Australian Plate beneath the Eurasian Plate
    4. Transform fault movement along the Ring of Fire

    2. Answer: C

    Explanation:

    Flores Island lies on the Sunda Arc, where the Indo-Australian Plate subducts under the Eurasian Plate, causing volcanic activity. This is a classic convergent plate boundary scenario.

  2. Consider the following statements regarding volcanic hazards:
    1. Pyroclastic flows consist of ash, gases, and solid volcanic material and are typically cooler than lava flows.
    2. Lahars are highly mobile volcanic mudflows that can occur even after the eruption has ended.
    3. Volcanic ash clouds can disrupt aviation but have no effect on agricultural productivity.

    3. Which of the above statements is/are correct?

    1. 1 and 2 only
    2. 2 only
    3. 2 and 3 only
    4. 1, 2 and 3

    Answer: B

    Explanation:

    • Statement 1 is incorrect – Pyroclastic flows are hotter (up to 1000°C) and more dangerous than lava flows.
    • Statement 2 is correct – Lahars can occur even weeks after eruptions, especially if it rains.
    • Statement 3 is incorrect – Volcanic ash reduces sunlight, contaminates water, and damages crops, severely affecting agriculture.
  3. Which of the following correctly describes the characteristics of a Plinian volcanic eruption, such as the one observed during the Mount Lewotobi eruption?
    1. Effusive lava flows with low gas content and wide lava fields
    2. Quiet underwater eruptions forming shield volcanoes
    3. Violent, gas-rich eruptions producing high-altitude ash columns
    4. Moderate explosions with lava fountains and short lava flows

    4. Answer: C

    Explanation:

    Plinian eruptions are highly explosive, ejecting volcanic ash and gas up to the stratosphere (often >10 km), with high viscosity magma and destructive pyroclastic flows.

Mains Question:

  1. How do plate tectonics influence the distribution and intensity of volcanic eruptions?

(10 Marks, 150 words)