On August 31, 2026, six volcanoes in Indonesia experienced eruptions within a 24-hour period. Sinabung in North Sumatra, Semeru in East Java, Anak Krakatau in the Sunda Strait, Lewotobi Laki-laki and Ili Lewotolok in East Nusa Tenggara, and Ibu in North Maluku all recorded eruptions on the same day.
The coincidence raises an obvious question: did the six volcanoes trigger one another?
According to Indonesia’s Center for Volcanology and Geological Hazard Mitigation (PVMBG), part of the Geological Agency under the Ministry of Energy and Mineral Resources, the answer is no. There is no evidence that the six eruptions were triggered by a single geological process.
Rita Susilawati, head of PVMBG, put it simply: each volcano has its own “kitchen,” referring to separate magma chambers or reservoirs that are not physically connected.
"We found no evidence of a single geological process that triggered all of these eruptions on August 31," Rita said at the Geological Agency on September 2, 2026, as quoted by Antara.
The timing is more likely a coincidence involving several volcanic systems that were already active. And in Indonesia, where 127 active volcanoes are spread across the archipelago, coincidences like this are more likely than they may appear.
Six Eruptions in One Day, but Not One System
Indonesia has more active volcanoes than any other country in the world. The six volcanoes that erupted on August 31, 2026, however, do not belong to a single magma system.
Most of them lie along a volcanic arc formed by the subduction of the Indo-Australian Plate beneath the Eurasian Plate along the Sunda Trench. This arc stretches from Sumatra through Java to the Lesser Sunda Islands and is home to Sinabung, Semeru, Anak Krakatau, Lewotobi Laki-laki, and Ili Lewotolok.
Mount Ibu, however, sits in a different tectonic setting.
Around the Molucca Sea, where Ibu is located, the tectonic system is far more complex. The area is known as the Molucca Sea Collision Zone, where the Molucca Sea Plate is being subducted in opposite directions by the Halmahera Arc to the east and the Sangihe Arc to the west.
This phenomenon is known as divergent double subduction and is the only known example of its kind in the world.
In other words, the six volcanoes that appear on a map as part of the same country and seemed to erupt in unison on the same day can actually sit above very different tectonic systems and magma reservoirs.
There is no single “engine” beneath Indonesia switching them all on at once.
Why Indonesia Sees Simultaneous Eruptions
Indonesia’s 127 active volcanoes are a direct consequence of its position along the Pacific Ring of Fire. This volcanic and seismic belt stretches for roughly 40,000 kilometers around the Pacific Ocean.
According to data compiled by the United States Geological Survey (USGS), around 75 percent of the world’s active volcanoes are located along the Ring of Fire, while roughly 90 percent of recorded earthquakes worldwide also occur within the region.
Indonesia occupies one of the most active sections of this belt.
Yet the term “Ring of Fire” can make it sound as though all the volcanoes within it are connected as one system. The reality is more complicated. Indonesia sits at the intersection of several tectonic plates and volcanic arcs, with each volcano shaped by its own underground conditions and eruptive history.
That is why when several volcanoes erupt within a short period of one another, sharing a date does not by itself indicate a cause-and-effect relationship. With so many active volcanic systems operating at the same time, their eruption calendars will occasionally overlap.
This Has Happened Before
Eruptions that appear to occur simultaneously have happened before.
In 2010, for example, Mount Sinabung erupted for the first time after around 1,200 years without recorded eruptive activity. About two months later, Mount Merapi in Central Java entered one of its deadliest eruptive phases of the past century, from October to November 2010, killing around 380 people.
The two volcanoes are hundreds of kilometers apart and sit on different segments of the Sunda volcanic arc. There is no evidence that their magma systems are connected.
Cases outside Indonesia also show why distance matters.
The USGS has found no definitive evidence that an eruption at one volcano can trigger an eruption at another volcano located far away, particularly across different regions or continents. Some examples of near-simultaneous eruptions instead involve volcanoes that are very close to one another and belong to the same volcanic complex.
In 1912, for instance, the Novarupta eruption in Alaska drew magma from a system beneath Mount Katmai, about 10 kilometers away. At Rabaul Caldera in Papua New Guinea, two volcanic cones also erupted almost simultaneously in 1994, but both were part of the same volcanic complex, reflecting magma moving toward two different points at the surface.
Even Kilauea and Mauna Loa in Hawaii, which are only about 33 kilometers apart, have separate magma reservoirs. According to the USGS, there is no evidence that an eruption at one triggers an eruption at the other.
Earthquakes Can Affect Volcanoes, but Distance Still Matters
Another possibility often raised is earthquakes. If an earthquake can alter pressure within Earth’s crust, could a single large earthquake set off several volcanoes at once?
A 2017 study by T. Nishimura, published in Geophysical Research Letters, offers a more specific picture.
By analyzing global earthquake and volcanic eruption data, the study found that volcanoes within roughly 200 kilometers of the epicenter of an earthquake with a magnitude of 7.5 or greater experienced an approximately 50 percent increase in the likelihood of erupting within five years after the earthquake.
The pattern, however, did not apply to volcanoes located far from the earthquake’s epicenter.
The study also showed that an earthquake does not automatically cause a volcano to erupt. Its influence is more likely to matter when the volcano’s magma system is already close to its eruptive threshold.
In other words, an earthquake can act as a trigger under certain conditions, but it is not a universal switch capable of setting off distant volcanoes.
So, What Actually Happened on August 31?
The six Indonesian volcanoes that erupted within a 24-hour period certainly created a remarkable pattern from the surface. But from a geological perspective, sharing the same date does not mean sharing the same cause.
Each volcano has its own magma reservoir, supply pathways, internal conditions, and eruptive history. There is therefore no need to invoke a single geological force to explain why six volcanoes could erupt on the same day.
With 127 active volcanoes spread from Sumatra to Papua, Indonesia is essentially monitoring dozens of volcanic systems that continue to evolve independently.
At that scale, eruptions converging on a single date are not impossible. They are the point where many different processes happen to overlap in time. And beneath each volcano, as PVMBG puts it, the kitchen is its own.
