Chilean experts have warned that a ''cork'' of lava could lead to another explosion at the Puyehue volcano, which has caused major flight disruptions from Argentina to Australia.
Seismic activity has declined, with two tremors of a magnitude of about 2.5 recorded every hour on Tuesday, compared with several hundred of a magnitude four or five in the hours preceding the initial June 4 eruption.
But Chile's National Service of Geology and Mining said on Wednesday that the volcano had to be kept on red alert because of the possibility of another explosion.
Geologists said a ''cork'' of lava, which emerged on Tuesday and was blocking even more lava from spewing forth, had the potential to create a huge build-up in pressure. If this continues, ''an explosive event remains possible, because the path the lava is taking is obstructed''.