AN INTRODUCTION TO THE VISION OF THEME SESSION T17: LARGE ERUPTIONS IN THE ALEUTIANS: NEW INSIGHTS INTO CHRONOLOGY, PHYSICAL VOLCANOLOGY, TEPHROCHRONOLOGY, PETROLOGY, AND IMPACTS

In support of a cohesive synthesis of the significant tephra record in Alaska, this session invited contributions that cover a broad array of geological, volcanological, and archaeological work. Presentations include recent studies of large caldera systems and individual large eruptions in the Aleutian volcanic arc. The goals of this session are to (1) encourage collation of the existing data on the character and distribution of ash deposits to improve their use as tephrostratigraphic markers, (2) continue to document and refine the timing, location and character of large eruptions, (3) improve estimations of local and arc-wide impacts from large-scale eruptions, and (4) bring together the multidisciplinary community focused on large eruptions in the Aleutians.

Descriptive information and analytical data for Alaska’s large tephra-producing eruptions are currently scattered throughout many researchers, scientific disciplines, and in a variety of formats, ranging from modern digital data to unpublished documents. A product that we aim to complete in the coming years is an updated database of large tephra-producing eruptions in Alaska, their field descriptions, best ages, distribution, and glass compositions. Such a product will aid those working on tephra-related stratigraphic issues in Alaska to determine more quickly and confidently which tephra deposits are relevant to their study areas and what geochronologic constraints they may provide.

Deposition of volcanic ash onto a landscape is a short-term process that is essentially instantaneous in geologic time. Thus, if the ages of volcanic-ash layers are known or if the ashes can be correlated to deposits of known age, they are excellent time-stratigraphic markers used in volcanology, archaeology, and paleoclimate research. Volcanic-ash deposits from large tephra-producing eruptions (e.g. caldera-forming eruptions) are most likely to be well-preserved for long distances from their sources and therefore often encountered in field studies. Physical and chemical characterization of ash, and geospatial distribution of ash deposits from these centers provide important chronological references to support research in many disciplines.