Soaring temperatures in the lake also damaged monitoring equipment used to gauge activity on the mountain.


"People must be ready to be evacuated again"

Umar Rosadi, volcano expert

Volcano scientists on Thursday said the alert status was lowered after the volcano showed "less intense activity" as it no longer had the energy needed for an explosive eruption.


Umar Rosadi, a member of the monitoring team, however warned that "a sudden increase" in volcanic activity was still possible.


"People must be ready to be evacuated again," he said.


Mount Kelud was on maximum alert three weeks ago. Tens of thousands of villagers were moved to government shelters outside the danger zone near the 1,731-metre peak, but any had ignored the warnings and stayed home.


The volcano has a deadly history of killing at least 30 people in its most recent eruption in 1990. About 5,000 people died when it erupted in 1919, spewing boiling water from its crater lake.


Indonesia has the highest number of active volcanoes in the world, sitting on an active seismic belt known as the "Pacific Ring of Fire".