Prior to May 2008, it was thought that the last eruption of Chaitén Volcano occurred more than 5,000 years
ago, a rather long quiescent period for a volcano in such an active arc segment. However, increasingly more Holocene
eruptions are being identified. This article presents both geological and historical evidence for late Holocene eruptive
activity in the 17th century (AD 1625-1658), which included an explosive rhyolitic eruption that produced pumice ash
fallout east of the volcano and caused channel aggradation in the Chaitén River. The extents of tephra fall and channel
aggradation were similar to those of May 2008. Fine ash, pumice and obsidian fragments in the pre-2008 deposits are
unequivocally derived from Chaitén Volcano. This finding has important implications for hazards assessment in the area
and suggests the eruptive frequency and magnitude should be more thoroughly studied.