By James Anderson and Lisa Johnston

While investigating forest and bush fires in Indonesia the GFW team stumbled across a surprisingly dense cluster of NASA fire alerts on the Global Forest Watch map in East Java, Indonesia.

Turns out these fires weren’t for clearing forest and scrub land for agriculture. In fact, they weren’t human-caused at all. The fire alerts are clustered around the crater of the Raung Volcano, which reportedly began erupting on Sunday, June 28th, sending clouds of ash thousands of meters into the air.

NASA’s Active Fires data uses the MODIS satellites to detect thermal anomalies. The alerts on the volcano may have been triggered by the intense heat from the crater, the presence of lava flow, or burning vegetation on the slopes ignited by lava or ash.

This isn’t the first time NASA fire alerts have detected volcano eruptions- earlier this year Chile’s Calbuco’s volcano triggered several alerts.