Semeru volcano erupts in Indonesia, spewing powerful pyroclastic flows

Mount Semeru — Java’s highest volcano at 3,676 meters — erupted on the afternoon of November 19, 2025, with pyroclastic flows rushing at high speed more than 8.5 kilometers down its slopes, as seen in videos widely shared on social media platforms such as X.

Mount Semero is one of fifteen active volcanoes in Java, one of the most populated islands in Indonesia. In 2010, an explosion of Mount Merapi triggered a series of deadly pyroclastic flows that killed 350 people and forced more than 10,000 residents to flee.

Pyroclastic flows are avalanches of superheated ash, gases and fragments of volcanic rock, with temperatures that can reach up to 1,000 degrees Celsius. They can travel up the slopes of a volcano at speeds in excess of 99 mph (160 km/h), destroying everything in their path. These flows are deadly even at distances of six to nine miles (10 to 15 km) from the volcano.

There are currently no reports of casualties from the Semeru eruption, but The authorities ordered the evacuation of neighboring villages preventively.

Indonesia frequently experiences earthquakes and volcanic eruptions because the archipelago sits atop the intersection of various tectonic plates, including the Pacific Plate, the Eurasian Plate, the Australian Plate, and the Philippine Sea Plate.

The Philippine plate, composed mostly of heavy oceanic crust, is subducting beneath the Eurasian continental plate. When the Philippine plate reaches a depth greater than 100 kilometers, the water it contains lowers the melting point of the surrounding rocks, which creates magma. This magma is hotter and less dense than the surrounding rocks and therefore begins to migrate towards the surface, where it eventually creates explosive volcanism characteristic of subduction zones.