Over 300 flights cancelled following series of eruptions on Anak Krakatoa.

Over 300 flights have now been cancelled since Anak Krakatoa, a volcanic island located in the Sunda Strait between Sumatra and Java, began erupting on Friday 4 September 2026. The volcano has produced a series of volcanic columns, some of which have reached over 15 000 m above sealevel. This has led to ash falls across the region, with all flights from Soekarno-Hatta International Airport in Jakarta, which is a little over 100 km to the east of the volcano, being cancelled. The Indonesian Ministry of Health is recommending people avoid going outside without dust masks due to the health hazard presented by the ash, which can cause severe breathing problems, and fishing fleets in the area are reportedly avoiding going to sea because of the poor conditions.

Drone footage of an ash column emerging from Anak Krakatoa on Saturday 5 September 2026. Reuters.

Volcanic ash is extremely hazardous to aircraft in a number of ways. At its most obvious it is opaque, both visually and to radar. Then it is abrasive, ash particles physically scour aircraft, damaging components and frosting windows. However the ash is most dangerous when it is sucked into jet engines, here the high temperatures can melt the tiny silica particles, forming volcanic glass which then clogs engine. When this happens the only hope the aircraft has is to dive sharply, in the hope that cold air passing through the engine during the descent will cause the glass to shatter, allowing the engine to be restarted. Obviously this is a procedure that pilots try to avoid having to perform.

Anak Krakatau is a volcanic island located in the Sunda Strait between Sumatra and Java. The volcano (then known simply as Krakatoa) famously exploded in 1883, killing over 36 000 people (possibly over 120 000), largely through a series of tsunamis. This explosion more-or-less completely destroyed the island, but since then a new volcano, Anak Krakatau (meaning the 'son of Krakatoa'), has grown in its place. Anak Krakatau is almost never completely quiet, but goes through periods of greater and lesser activity. An eruption on 22 December 2018 triggered a tsunami which tsunami caused over 430 fatalities, injured 14 000 people, and displaced 33 000 more along the Sunda Strait. The tsunami risk of this area is particularly high as the coast is very popular with both locals and tourists and is home to over 20 million people within a 100 km distance from the volcano.

Anak Krakatau is located to the north of the Sunda Trench, along which the Australian Plate is being subducted beneath the Sunda Plate, on which the island sits. As the Australian Plate is subducted it is partially melted by the friction and the heat of the planet's interior. Some of this melted material then rises through the overlying Sunda Plate, fuelling Krakatau and the volcanoes of Sumatra and Java.

The Subduction zone beneath Sumatra. NASA/Earth Observatory.

See also...

At least 53 dead following Magnitude 7.7 Earthquake off the coast of Flores Island, Indonesia.

The Indonesian Meteorological, Climatological, and Geophysical Agency recorded a Magnitude 7.7 Earthquake at a depth of about 15 km, to the north of the Island of Flores in East Nusa Tenggara Province, Indonesia slightly before 5.00 am on Saturday 15 August 2026, Eastern Indonesian Time (slightly before 10.00 pm on Friday 14 August, GMT). The Earthquake was felt as far away as Bali, and caused a tsunami as high as 1.6 m on some parts of the coast of Flores. The initial event has been followed by more than three hundred aftershocks.

The approximate location of the 15 August 2026 Flores Earthquake. USGS.

At least 53 people have died as a result of this event, the majority of them killed in their sleep as buildings collapsed onto them, making this the most deadly Earthquake to hit Indonesia since 2022. A further 135 people are known to have been injured, with more than 5000 people displaced and over 1900 homes damaged or destroyed. The Earthquake also caused damage to at least 93 educational facilities, 36 health facilities, 38 government offices, and five places of worship. A maritime passenger terminal collapsed in Maumere on the north coast of Flores.

Damaged and collapsed building in the city of Mbay on the north coast of Flores. Ignasius Kunda/EPA.

Flores is one of the Lesser Sunda Islands, which are located on the northern part of the Timor Microplate. This is trapped between the converging Eurasian and Australian Plates, both of which are being subducted beneath it. In the south the Australian Plate is passing under the island of Timor, while in the north the Eurasian Plate is being subducted in the same way. This is not a smooth process; the rocks of the various plates constantly stick together, only to break apart again as the pressure builds up, causing Earthquakes in the process.

The subduction zones beneath the Timor Microplate. Hamson (2004).

Earthquakes along subductive margins are particularly prone to causing tsunamis, since these often occur when the overlying plate has stuck to the underlying plate, being pulled out of shape by its movement. Eventually the pressure builds up too far and the overlying plate snaps back, causing an Earthquake and a tsunami. 

Simplified graphic showing tsunami generation along a convergent margin, and how this can be monitored using ground-based GPS systems to give early warnings of the arrival of tsunamis. NASA/JPL/CalTech.

See also...

Magnitude 6.6 Earthquake beneath Morobe Province, Papua New Guinea.

The United States Geological Survey recorded a Magnitude 6.6 Earthquake at a depth of 99.4 km,approximately 26 km to the southwest of the city of Lae in Morobe Province, Papua New Guinea, slightly after 9.05 pm local time (slightly after 11.05 am GMT) on Tuesday 7 October 2025. The Earthquake was felt as far away as Indonesian Papua and the island of New Britain, but there are no reports of any damage or casualties at this time.

The approximate location of the 7 October 2025 Morobe Province Earthquake. USGS.

The Earthquake happened slightly to the south of the boundary between the South Bismark Plate, which underlies the island of New Britain and parts of the northeastern coast of Papua New Guinea, and the Woodlark Plate, which underlies the Papuan Peninsula and parts of the Solomon Sea. These plates are being pushed together by the northeastward movement of the Australian Plate, to the south, with the South Bismarck Plate being subducted beneath the Woodlark Plate during this process. This is not a smooth process, with the rocks sticking together, then moving sharply as the pressure builds up enough to break them apart, which can also lead to Earthquakes in the region.

Major tectonic boundaries in the Papua New Guinea region along with the plate motion vectors relative to the Pacific Plate. The areas of significant relative motion can be clearly identified from the vectors, with the Australian plate subducting under the Pacific Plate and the Solomon Sea plate subducting under the South Bismarck plate. Shear motion between the North Bismarck plate and South Bismarck plate can also be recognised. Ghasemi et al. (2016).

See also...

Magnitude 6.5 Earthquake beneath Central Papua Province, Indonesia.

The Indonesian Meteorological, Climatological, and Geophysical Agency recorded a Magnitude 6.5 Earthquake at a depth of about 24 km, to the south of the town of Nabire in Central Papua Province, Indonesia slightly before 3.20 am on Friday 19 September 2025, Eastern Indonesian Time (slightly before 6.20 pm on Thursday 18 September, GMT). The event was felt across much of western Central Papua Province and parts of eastern West Papua Province, and is reported to have caused the collapse of the main bridge in Nabire, as well as two houses. Other buildings, including the airport, have recorded minor damage, although no casualties have been reported.

The approximate location of the 18 September 2025 Central Papua Earthquake. USGS.

The tectonic situation underlying the island of Papua is complex, with the island being made up of a number of small tectonic plates being squeezed between the larger Pacific/Caroline and Australian plates. Beneath Central Papua Province the Pacific Plate is being subducted beneath the Australian Plate along the New Guinea Trench, however, this is not a simple tectonic boundary with one plate disappearing beneath another, as a sliver of an older, now almost completely subducted plate caught between the two and being displaced to the west along the Sorong-Yapen Fault. This creates a complex situation in which the various plates stick together until pressure builds up sufficiently to overcome the friction and causes sudden movements we experience as Earthquakes.

(a) Block diagram illustrating kinematic partitioning of oblique convergence (without scale) in northwestern New Guinea. The diagram shows partitioning  as is occurring in the last 4 million years and also notes the timing of major shortening events in the region. Note that shortening in the Lengguru Fold Belt region (including the adjacent Wandamen Peninsula) was replaced by extension after 3 million years ago. Black arrows show GPS vectors. (b) Block diagram showing oblique convergence. Saputra et al. (2023).

See also...

Two deaths following Magnitude 5.8 Earthquake beneath Central Sulawesi, Indonesia.

The United States Geological Survey recorded a Magnitude 5.8 Earthquake at a depth of 12 km, approximately 12 km to the northwest of the town of Poso in Central Sulawesi Province, Indonesia, slightly before 6.40 am local time on Sunday 17 August 2025 (slightly before 10.40 pm on Sunday 16 August, GMT). Twenty nine people are known to have been injured during this event, two of whom subsequently died, one later on the day of the event, and one on Tuesday 19 August. The initial quake was followed by a series of aftershocks.

The approximate location of the 17 August 2025  Central 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).

See also...