NEW : ` Peter Cervelli , a research geophysicist with the observatory , told CNN that `` every indication is that we 're heading toward an eruption . '' ` Volcanic tremor '' increasing in `` amplitude , '' observatory says . Comment: Volcano last erupted in December 1989 . Eruption could spawn huge mudflows , disrupt flights with ash .
NEW : `` Volcanic tremor '' increasing in `` amplitude , '' observatory says . Comment: Volcano last erupted in December 1989 . Eruption could spawn huge mudflows , disrupt flights with ash .