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.