Why in news?
The volcano erupted recently on November 19, 2025, with a powerful eruption that sent ash clouds up to 13 kilometers high and pyroclastic flows that traveled down its southern slopes for up to 7 kilometers. 

About Semeru volcano

• Semeru is the highest mountain on the Indonesian island of Java and one of Indonesia's most active volcanoes, located in East Java province.
• It stands at 3,676 meters (12,060 feet) above sea level and is part of the Tengger Volcanic Complex.
• Semeru is a stratovolcano also known as Mahameru, meaning "The Great Mountain" in Sanskrit.
• It has a long history of frequent eruptions, with at least 61 eruptive periods recorded since 1818, many involving lava flows and pyroclastic density currents.

Causes of Semeru eruption

• The 2025 eruption of Mount Semeru was caused by the collapse of the lava dome at its summit, which was destabilized by monsoon rains.
• This dome collapse triggered a series of pyroclastic flows (fast-moving avalanches of hot gas, ash, and volcanic rock) that traveled down the mountain's slopes.
• The buildup of volcanic material in the summit area over the past few years reached an unstable threshold, and the heavy rains likely acted as a trigger for the collapse, causing the eruption to occur. 

Historically, Semeru eruptions have been significant and destructive; for example, the 2021 eruption caused fatalities and displacement, highlighting the volcano's potential hazards. Its continuous activity since 1967 makes it one of the most persistently erupting volcanoes globally.

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