JAKARTA - Indonesia's national disaster agency has issued warnings over cold lava flows, also known as lahar dingin, around Mount Agung.

Local residents are asked to stay away from rivers whose upstreams are located on the slopes of the volcano, said a spokesman for Indonesia's National Disaster Management Agency (BNPB).

"Lahar floods have already occurred in several places on the slopes," Sutopo Purwo Nugroho said.

"As Bali has entered wet season, watch out for cold lava floods. Do not have activities in the areas near rivers," he told a press briefing on Monday.

Mount Agung is a stratovolcano. According to Oregon State University's Volcano World, stratovolcanoes tend to have cooler, more viscous lava.

The so-called cold lava flows, similar to mud flows, are often a prelude to the blazing orange lava seen in many volcanic eruptions.

Lahars are slurries of rock fragments mixed with water, and have been spotted in fields and rivers near the volcano. They are chiefly caused by pyroclastic flows - fast-moving flows of gas and ash that can reach temperatures of 800 deg C. Lahars can sweep away structures like bridges and houses.

On Monday (Nov27), Indonesian authorities ordered 100,000 residents living near the volcano to evacuate immediately, warning that the first major eruption in 54 years could be "imminent".

Monitoring has shown the northeastern part of Mount Agung's peak had swollen in recent weeks "indicating there is fairly strong pressure toward the surface", said Indonesia's Volcanology and Geological Disaster Mitigation Centre.

An eight to 10 km exclusion zone has been imposed around the summit, the highest peak in Bali.