Indonesia's Mount Semeru, the highest volcano on the island of Java, erupted violently on Wednesday, November 19, 2025, unleashing towering ash clouds and dangerous pyroclastic flows, prompting the evacuation of hundreds of residents and the issuance of the highest-level aviation warnings. The event serves as a critical reminder of the potential for volcanic activity to cause significant disruption to global air travel, a sector of vital importance to the Kenyan economy.

According to Indonesia's Center for Volcanology and Geological Hazard Mitigation (PVMBG), the eruption began a new phase of intense activity, sending a thick column of hot ash up to 2 kilometers (1.2 miles) into the air. Fast-moving avalanches of hot ash, rock, and gas, known as pyroclastic flows, traveled as far as 7 kilometers (4.3 miles) down its slopes. In response, the PVMBG raised the volcano's alert status to Level IV, the highest possible, signaling an ongoing and hazardous eruption.

Local authorities in the Lumajang Regency of East Java have evacuated more than 900 people from villages near the volcano to temporary shelters. No casualties have been reported, though rescue operations were underway for 170 climbers who were stranded near the volcano but have since been confirmed safe. This eruption follows a deadly event in December 2021, which claimed at least 51 lives and buried entire villages in volcanic debris.

Global Aviation on High Alert

The primary international concern stemming from the eruption is the vast ash cloud, which has risen to altitudes of up to 54,000 feet (16.5 kilometers) — well above the cruising altitude for commercial aircraft. Australia's Bureau of Meteorology, which hosts the Darwin Volcanic Ash Advisory Centre (VAAC), issued a red aviation advisory, its most serious warning, indicating a significant threat to aviation safety. Airlines flying routes between Australia and Southeast Asia have been warned to avoid the area.

Volcanic ash is extremely hazardous to jet engines. The fine particles of rock, glass, and sand can melt in the high temperatures of an engine, solidifying on turbine blades and causing power loss or complete engine failure. While there is no direct impact on Kenyan or East African airspace, the event underscores the vulnerability of global supply chains and travel networks. Past volcanic eruptions, such as the 2011 Nabro eruption in Eritrea, have caused flight disruptions across East Africa, affecting carriers like Ethiopian Airlines.

Geological Context and Historical Activity

Mount Semeru, standing at 3,676 meters (12,060 feet), is one of Indonesia's most active volcanoes. The country is situated on the Pacific "Ring of Fire," a highly active seismic zone where tectonic plates meet, resulting in frequent earthquakes and volcanic activity. Indonesia has approximately 130 active volcanoes, more than any other nation. Semeru itself has been in a state of near-constant eruption since 1967, with its deadliest recorded eruption in 1909 claiming 208 lives.

The current eruption's intensity escalated rapidly on Wednesday. The first pyroclastic flows were reported by the Semeru Volcano Observation Post at 2:12 PM local time (10:12 AM EAT). By 5:00 PM local time (1:00 PM EAT), the PVMBG had raised the alert level from II to IV in just one hour.

No Direct Climate Impact Expected for East Africa

While major volcanic eruptions can have a temporary cooling effect on the global climate by releasing sulfur dioxide into the stratosphere, which reflects sunlight, the current scale of the Semeru eruption is not expected to cause such an impact. Scientists note that an eruption must be powerful enough to inject a significant amount of sulfate aerosols into the stratosphere (above 18 km) to have a noticeable global effect. The current ash plume, while high, is not anticipated to alter global weather patterns or have any discernible climatic consequences for Kenya or the wider East African region. The focus remains on the immediate humanitarian response in Indonesia and the significant, ongoing risk to international aviation.