The Nilahue and GolGol rivers near the Puyehue-Cordon Caulle volcano are set to burst its banks after large amounts of ash and volcanic rock fell in them, increasing its flow from 30 cubic meters per second to 160 cubic meters per second.
In towns bordering the fiery mount, authorities have warned of imminent flooding after 3,500 residents were evacuated.
While 500 of them were still in shelters, authorities seek legal permission to evacuate a dozen more who refused to leave their property and animals behind.
The weather has forced many planes in South America to remain grounded for a third straight day.
Al Jazeera's Craig Mauro reports from Puyehue.