CARSON, Eric C. and FOURNELLE, John H., Department of Geology & Geophysics, University of Wisconsin-Madison, 1215 W. Dayton St., Madison, WI 53706, ecarson@geology.wisc.edu and johnf@geology.wisc.edu

The Quaternary history of the Alaska volcanic arc is characterized by numerous explosive eruptions. Holocene volcanic activity has been documented from at least 33 volcanic centers on the Alaska Peninsula and eastern Aleutian Islands. Eight volcanoes within 150 km of Cold Bay--the Emmons-Pavlof complex, Mt. Dutton, Frosty Peak, Round Top, Isanotski volcano, Shishaldin volcano, Fisher Caldera, and the Pogromni-Westdahl complex, as well as possibly Amak volcano--have been active during the Holocene (Miller and Richter, 1994).

The stratigraphy of the area is complex, with ash layers interbedded with glacial deposits, aeolian silts, and peats. Erosion, weathering, and reworking of the ash layers have resulted in a complex, extensive record of tephra deposits in the vicinity of Cold Bay. Several ash horizons in the Cold Bay area have been analyzed be electron microprobe for their major and minor element chemical compositions. An extensive layer of rhyodacitic glass (68 - 70 wt. % SiO₂) overlain by andesitic basalt (52 - 55 wt. % SiO₂) was originally recognized by Funk (1973). This deposit is believed to be a result of the Fisher Caldera eruption, which has been dated here by relation to unerlying peat at 9090 140 ¹⁴C yr BP (Dochat, 1996). A high-Si rhyolite (76 - 78 wt. % SiO₂) with low K₂O (about 1.5 wt. %) and a rhyolite (72 - 74 wt. % SiO₂) with high K₂O (3.6 - 3.8 wt. %) have both been found on the eastern side of Cold Bay. The sources of these ashes are possibly Mt. Dutton or Mt. Emmons, due to their proximity.

Additional samples have been collected in 1995, 1996, and 1997. Age control for them is provided by radiocarbon dating of interbedded peat and human habitations. These samples will be analyzed and correlated to the existing framework to establish a more complete Holocene eruptive chronology at the southwest end of the Alaska Peninsula. The study of these tephras also allow for refinements in the chronology of glacial events in the Cold Bay area, as well as the correlation of local archaeological sites.