Evacuations ordered after increase in activity from Mount Ibu on Halmahera Island, Indonesia.

Authorities in North Maluku Province, Indonesia, have ordered the evacuation of six villages close to Mount Ibu, a 1325 m stratovolcano on the northwest coast of Halmahera Island, following a series of eruptions in the first two weeks of 2025. Mount Ibu began its current eruptive cycle in June 2024, but January has seen a significant rise in activity, with more than a thousand eruptions have been recorded on the volcano this year, with the largest producing ash columns reaching as high as 4 km over the summit of the volcano. However, to date only one village, with a population of 517 people, has been evacuated, with about 2500 people in the remaining five villages reluctant to leave without first harvesting crops.

An eruption on Mount Ibu, Halmahera Island, on Wednesday 15 January 2024. Azzam/AFP.

The Halmahera Island chain is a volcanic arc formed where the Halmahera Plate, a northeaster extension of the Molucca Sea Plate is being subducted beneath Philippine Plate from the east and the Eurasian Plate from the west, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

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Exclusion area around Mount Ibu, Halmahera Island, extended following new eruption.

The Indonesian Center for Volcanology and Geological Hazard Mitigation has extended the exclusion zone around  Mount Ibu, a 1325 m stratovolcano on the northwest coast of Halmahera Island, following a new eruption on 18 May 2024. A two kilometre exclusion zone had already been put in place after the volcano began erupting on 28 April, but this has been increased to seven kilometres following the most recent eruption, which produced an ash column which rose to 4 km above the volcano's summit, resulting in seven villages needing to be evacuated. 

An ash column and lava fountain above Mount Ibu on the Indonesian island of Halmahera on 18 May 2024. Several lightning discharges can be seen within the ash column; ash columns can build up considerable charge variations leading to frequent electrical discharges. Indonesian Center for Volcanology and Geological Hazard Mitigation/Reuters.

The Halmahera Island chain is a volcanic arc formed where the Halmahera Plate, a northeaster extension of the Molucca Sea Plate is being subducted beneath Philippine Plate from the east and the Eurasian Plate from the west, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

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Eruption on Mount Ibu, Halmahera Island, Indonesia.

The Regional Disaster Mitigation Agency for West Halmahera District has reported an eruption on Mount Ibu, a 1325 m stratovolcano on the northwest coast of Halmahera Island, Indonesia, on Sunday 28 April  2024 (a stratovolcano is a cone-shaped volcano made up of layers of ash and lava, although Mount Ibu has a truncated shape, having lost its upper part in an explosion at some point in the past). The eruption started at 0.37 am local time, and lasted approximately three minutes and 26 seconds, producing a column of dark ash which rose 3.5 km above the summit of the volcano and drifted to the west. The Regional Disaster Mitigation Agency has asked people not to go within 2 km of the volcano for the time being, and has issued dust masks to residents of 16 villages in the area. Sam Ratulangi International Airport, about 100 km from the volcano in the city of Manado, is closed to flights temporarily.

An ash column over Mount Ibu at 0.44 am local time on Sunday 28 April 2024. Abdul Fatah/Antara News Agency.

The Halmahera Island chain is a volcanic arc formed where the Halmahera Plate, a northeaster extension of the Molucca Sea Plate is being subducted beneath Philippine Plate from the east and the Eurasian Plate from the west, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

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Magnitude 6.2 Earthquake beneath West Sulawesi, Indonesia.

The United States Geological Survey recorded a Magnitude 6.2 Earthquake at a depth of 18.4 km, approximately 36 km to the south of the city of Mamuju in West Sulawesi Province, Indonesia, slightly before 2.30 am local time on Friday 15 January 2021 (slightly before 6.30 pm on Thursday 14 January, GMT). There are no reports of any damage or injuries relating to this event at this time, but people have reported feeling it locally.

 

The approximate location of the 15 January 2021 West Sulawesi Province Earthquake. USGS.

The tectonic situation beneath Sulawesi is complex, as it is caught in the collisional zone between the Eurasian, Pacific and Australian Plates. The north of the island is located on a breakaway section of the Eurasian Plate, called the Sangihe Plate. To the east lies the remnant Molucca Sea Plate, which is being subducted beneath both the Sangihe Plate and the more easterly Halmahera Plate, leading to Earthquakes and volcanism on Sulawesi and the islands of the Sangihe Arc in the west and the islands of the Halmahera Arc in the east.

 

The subduction zones beneath Sulawesi and the surrounding islands. Hall & Spakman (2015).

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Eruptions on Mount Lokon Sulawesi.

Mount Lokon, a 1578 m stratovolcano (cone-shaped volcano) on the northeastern tip of Sulawesi, Inodnesia, began erupting at about 3.00 pm local time on Saturday 13 September 2014, for the first time since September 2013. The volcano reportedly produced a column of ash reaching 600 m above the summit, as well as raining ash down on several local towns, where people have reported respiratory problems. Local authorities have set up a 2.5 km exclusion zone around the volcano as a precaution.

Eruption on Mount Lokon. RRI.

Lokon is a double volcano located near the eastern tip of the northern arm of Sulawesi, Indonesia. It has two cone-shaped peaks, Lokon to the southwest and Empung 2.2 km to the northeast, with a saddle of volcanic rock separating the two. Of these Lokon is the larger, though it has not erupted in recorded history, whereas the slightly smaller Empung last erupted in the late eighteenth century. Situated on the saddle between the two summits is Tompaluan, a double crater that remains active to the current day.

The Lokon-Empung volcanic complex is located at the southern end of the Sangihe Volcanic arc, where an extension Molucca Sea Plate is being subducted beneath an extension of the Eurasian Plate, sometimes called the Sangihe Plate. As this happens part of the subducting plate is melted by the heat of the Earth's interior, and rises up through the overlying plate as liquid magma, forming volcanoes at the surface. 320(ish) km to the east the Molucca Plate is also being subducted beneath an extension of the Philippine Plate, sometimes called the Halmahera Plate, producing a second chain of volcanoes in the Halmahera Islands. At some point in the future the Molucca Plate will vanish and the two volcanic arcs will meet.

The location of Mount Lokon, Sulawesi. Google Maps.

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 Explosive eruption on Mount Lokon.

Mount Lokon, a volcano close to the tip of Sulawesi's northern arm, erupted suddenly at about 6.30 am local time on Monday 9 September 2013 (about 10.30 pm on Sunday 8 September, GMT)...

 Eruption on Mount Karangetang.

On 9 April 2013 the Darwin Volcanic Ash Advisory Centre in Australia reported a 4.3 km ash plume rising from Mount Karangetang, a volcano on Siau Island, one of the Sangihe Islands roughly 130 km north of Sulawesi and 260 km south of Mindanao in the Philippines. The plume drifted about 45 km to the northwest of...

 Eruption on Mount Lokon, Sulawesi.

Mount Lokon on northern Sulawesi erupted explosively slightly before 8.00 am local time on Wednesday 20 March 2013 (slightly before midnight on 19 March, GMT), throwing a column of ask 2 km into the sky, according to Badan Nasional Penangulanggan Bencana (Indonesia's Disaster Mitigation Agency). The eruption...

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Magnitude 6.2 Earthquake off the north coast of Morotai Island.

The Indonesian Baden Meteorologi, Klimatologie, dan Geophysica (Meteorological, Climatological and Geophysical Agency) recorded a Magnitude 6.2 Earthquake at a depth of 11 km off the north coast of Morotai Island in the Halmahera Islands, slightly after 10.30 pm local time (slightly after 1.30 pm GMT) on Tuesday 19 November 2013. There are no reports of any damage or casualties, but this was a large quake and is likely to have been felt across the island.

The approximate location of the 19 November 2013 Morotai Island Earthquake. Google Maps.

The Halmahera Islands arc a volcanic arc; formed where one tectonic plate is being subducted beneath another, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. However the Halmahera Islands are unusual in that they lie on a double subduction zone. The underlying plate, a northeaster extension of the Molucca Sea Plate, is being overridden form the Philippine Plate from the east and the Eurasian Plate from the west. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

Sea also Magnitude 5.7 Earthquake of the north coast of Sulawesi, Explosive eruption on Mount Lokon, Eruption on Gamalama, Earthquake hits Sulawesi and Volcanic activity in the Halmahera Islands.

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Magnitude 5.7 Earthquake of the north coast of Sulawesi.

The United States Geological Survey recorded a Magnitude 5.7 Earthquake at a depth of 46.2 km, approximately 50 km off the north coast of Sulawesi, slightly after 5.40 am local time on Tuesday 10 September 2013 (slightly after 9.40 pm on Monday 9 September, GMT) This is a reasonably large quake, with the potential to be dangerous. However is occurred some way offshore, and at some depth, and there are no reports of any damage or injuries.

The approximate location of the 10 September 2013 North Sulawesi Earthquake. Google Maps.

The tectonic situation beneath Sulawesi is complex, as it is caught in the collisional zone between the Eurasian, Pacific and Australian Plates. The north of the island is located on a breakaway section of the Eurasian Plate, called the Sangihe Plate. To the east lies the remnant Molucca Sea Plate, which is being subducted beneath both the Sangihe Plate and the more easterly Halmahera Plate, leading to Earthquakes and volcanism on Sulawesi and the islands of the Sangihe Ard in the west and the islands of the Halmahera Arc in the east.

See also Explosive eruption on Mount Lokon, Eruption on Mount Lokon, Sulawesi, Earthquake hits Sulawesi, Eruptions from the Tompaluan Crater, Lokon-Empung, Sulawesi and Mount Soputan, Sulawesi, erupts.

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Explosive eruption on Mount Lokon.

Mount Lokon, a volcano close to the tip of Sulawesi's northern arm, erupted suddenly at about 6.30 am local time on Monday 9 September 2013 (about 10.30 pm on Sunday 8 September, GMT) producing a 1500 m high ash column in an explosive eruption that could be heard 10 km away, according to the Pusat Vulkanologi Dan Mitigasi Becani Geologi (Indonesian Centre for Volcanology and Geological Hazard Mitigation). This is the tenth such eruption since July this year, and a 2.5 km exclusion zone is currently being maintained around the volcano.

An eruption on Mount Lokon in July 2011. Reuters.

Lokon is a double volcano located near the eastern tip of the northern arm of Sulawesi, Indonesia. It has two cone-shaped peaks, Lokon to the southwest and Empung 2.2 km to the northeast, with a saddle of volcanic rock separating the two. Of these Lokon is the larger, though it has not erupted in recorded history, whereas the slightly smaller Empung last erupted in the late eighteenth century. Situated on the saddle between the two summits is Tompaluan, a double crater that remains active to the current day.

The Lokon-Empung volcanic complex is located at the southern end of the Sangihe Volcanic arc, where an extension Molucca Sea Plate is being subducted beneath an extension of the Eurasian Plate, sometimes called the Sangihe Plate. As this happens part of the subducting plate is melted by the heat of the Earth's interior, and rises up through the overlying plate as liquid magma, forming volcanoes at the surface. 320(ish) km to the east the Molucca Plate is also being subducted beneath an extension of the Philippine Plate, sometimes called the Halmahera Plate, producing a second chain of volcanoes in the Halmahera Islands. At some point in the future the Molucca Plate will vanish and the two volcanic arcs will meet.

The approximate location of Mount Lokon. Google Maps.

See also Eruption on Mount Karangetang, Eruption on Mount Lokon, Sulawesi, Eruption on Gamalama, Earthquake hits Sulawesi and Eruptions from the Tompaluan Crater, Lokon-Empung, Sulawesi. 

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Eruption on Gamalama.

Gamalama is a largely submerged volcano to the west of Halmahera in Indonesia. It's tip forms the island of Ternate, home to 145 000 people, and formerly the home of the Sultanate of Ternate, which at its height ruled much of what is now eastern Indonesia and the southern part of the Philippines. The island covers 76 km², and the summit of the volcano rises 1715 m above the sea. Gamalama is an active volcano, typically erupting several times a decade, it's last eruptive episode, in December 2011-January 2012, killed at least three people and produced a number of destructive lahars (mudflows triggered by volcanic activity) which destroyed several villages.

A lahar sweeps through a village on Ternate. Pusat Penanggulangan Krisis Kesehatan.

For the first two weeks of September 2012 the summit of Gamalama was obscured by cloud and fog, although what appeared to be a small plume could frequently be seen over the volcano. Then on the evening of 15 September an explosive eruption lead to ashfalls in the capitol (also Ternate). The next day rumbling was audible from the volcano, before a second eruption at about 2.15 pm, which produces a plume roughly 1 km high which drifted to the south and southeast, producing further ashfalls. The alert status on the island remains high, with people recommended to avoid going within 2.5 km of the summit.

Aerial photograph of a plume over Gamalama taken on Sunday 16 September 2012. Jakarta Post.

Halamahera and Ternate lie on the eastern edge of the Molluca Sea, which is underlain by the Molluca Sea Plate, a remnant plate being subducted from both sides. In the west the Molluca Sea Plate is being subducted beneath the Sangihe Plate, which underlies the northern part of Sulawesi, to the east it is being subducted beneath the Philippine Sea Plate, which underlies Halamahera and its surrounding islands. As it is subducted the Molluca Sea Plate is heated by friction with the overlying Sangihe and Philippine Sea Plates, and by the heat of the Earth's interior. Some of the melted material rises through the overlying plates, fueling the volcanoes of Halamahera and Sulawesi.

Map showing the location of Ternate at the eastern edge of the Molucca Sea. Google Maps.

Diagram showing the Molucca Sea Plate beneath the Molucca Sea. Hall & Wilson (2000).

See also Earthquake hits Sulawesi, Eruptions from the Tompaluan Crater, Lokon-Empung, Sulawesi, Volcanic activity in the Halmahera Islands and Volcanoes on Sciency Thoughts YouTube.

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