Minute shards of volcanic glass recovered from the 1645 ¿ 4 BC layer in the Greenland GRIP ice core have recently been claimed to originate from the Minoan eruption of Santorini <Hammer et al., 2003>. This is a significant claim because a precise age for the Minoan eruption provides an important time constraint on the evolution of civilizations in the Eastern Mediterranean. There are however significant differences between the concentrations of SiO2, TiO2, MgO, Ba, Sr, Nb and LREE between the ice core glass and the Minoan eruption, such that they cannot be correlatives. New chemical analyses of tephra from the Late Holocene eruption of the Aniakchak Volcano in Alaska, however, show a remarkable similarity to the ice core glass for all elements, and this eruption is proposed as the most likely source of the glass in the GRIP ice core. This provides a precise date of 1645 BC for the eruption of Aniakchak and is the first firm identification of Alaskan tephra in the Greenland ice cores. The age of the Minoan eruption of Santorini, however, remains unresolved.