A 500-YEAR-LONG RECORD OF TEPHRA FALLS FROM REDOUBT VOLCANO AND OTHERVOLCANOS IN UPPER COOK INLET, ALASKA

Volcanic ash layers preserved in glacial-lacustrine sediments at Skila k Lake on the Kenai Peninsula of southcentral Alaska constitute a reco rd of eruptions at Redoubt Volcano and other Alaskan volcanoes which a ffected the upper Cook Inlet area during the last 500 years. High-reso lution magnetic susceptibility profiling delineates similar sequences of tephra layers in several l-m-long lake sediment cores. Electron mic roprobe analyses of glass shards from the tephras indicate correlation of some ash layers with known reference tephras from the source volca noes, while other ash layers record previously unknown prehistoric eru ptions. Skilak Lake cores contain ash from the historic 1912 Katmai er uption, the 1902 Redoubt eruption, and the 1883 Mount St. Augustine er uption as well as prehistoric ash layers erupted from Crater Peak at M t. Spurr ca. 250-350 years ago, from Redoubt Volcano at ca. 300-400 ye ars ago and again at ca. 350-450 years ago, and a 500-year-old ash fro m Mount St. Augustine. Still older tephras from Redoubt Volcano and Cr ater Peak at Mt. Spurr are found lower in the cores. The cores indicat e that volcanoes in the Cook Inlet area have erupted every 10-35 years during the 20th century, and ash falls have occurred at Skilak Lake a t least once every 50-100 years for the last 500 years, with Redoubt, Spurr, and Augustine Volcanoes being the most important sources of tep hra.