Jakarta, ThedailyID — Six Indonesian volcanoes erupted around the same period in early September 2026. The unusual timing has raised questions about whether the eruptions are connected.
The volcanoes include Anak Krakatau, Semeru, Ili Lewotolok, Ibu, Lewotobi Laki-laki and Sinabung.
However, experts say the eruptions do not mean the volcanoes share one volcanic system.
Indranova Suhendro, a lecturer at Gadjah Mada University’s Faculty of Geography, said each volcano has its own activity pattern and cycle.
He said the simultaneous eruptions are more likely the result of different volcanic cycles overlapping.
“In my view, this is more a matter of timing,” Indranova said, according to UGM, Wednesday, September 9, 2026
Some volcanoes naturally erupt more frequently. Semeru and Anak Krakatau are examples.
Other volcanoes can remain dormant for longer periods. They may then become active again when their individual cycles reach a new phase.
Indonesia’s shared subduction zones also do not automatically connect the magma systems beneath different volcanoes.
Each volcano has a local magma system. Therefore, an eruption at one volcano does not automatically trigger another.
The distance between the six volcanoes further weakens the possibility of a direct connection. They are spread across Sumatra, Java, the Sunda Strait, Nusa Tenggara and Maluku.
“The volcanoes currently experiencing eruptions are very far apart from one another, so triggering each other is nearly impossible,” Indranova said.
The volcanoes also show different eruption mechanisms.
At Sinabung, Ibu and Semeru, heat from magma can warm water stored inside the volcano. This process can increase pressure and trigger phreatic eruptions.
These eruptions do not always come with a clear increase in volcanic earthquakes.
Anak Krakatau has a different mechanism. Its eruptions are magmatic and involve magma with high gas content.
Indranova compared the process to a carbonated drink. Rapid decompression can cause gas to form suddenly and produce explosive activity.
External events can also affect some volcanoes under certain conditions.
Indranova pointed to increased volcanic activity at Lewotolok and Lewotobi Laki-laki after the Flores earthquake. However, he stressed that scientists cannot apply this explanation to every volcano.
“Strong increases in volcanic seismic activity at Mount Lewotolok and Mount Lewotobi Laki-laki after the earthquake are a strong indication that they were awakened by seismic activity in Flores,” Indranova said.
The Geological Agency also said simultaneous eruptions are not necessarily unusual in Indonesia.
Indonesia sits along the Pacific Ring of Fire and has many active volcanoes. As a result, several volcanoes can erupt naturally within the same period.
“This does not automatically mean there is one major phenomenon connecting them all,” the Geological Agency said.
Each volcano has different characteristics. Eruptions are also part of normal volcanic activity, although their size and intensity can vary.
Therefore, the simultaneous eruptions should not automatically be interpreted as one large volcanic event. Current evidence instead points to separate volcanic systems becoming active around the same time.
