CHARACTERIZATION OF HOLOCENE TEPHRA DEPOSITS AT KOROVIN VOLCANO, ATKA ISLAND, CENTRAL ALEUTIANS, USA

The study of tephra deposits in the Aleutian Islands has previously been concentrated in the eastern end of the arc and on the Alaska Peninsula. Some researchers (e.g. Kiriyanov and Miller (1997), Waythomas (1994), Romick et al (1992)) have studied tephra deposits on Adak (176° 45’ W), Great Sitkin (176° 08’ W), and Kanaga Islands (177° 10’ W), but there are still large gaps in the understanding of the spatial and temporal distribution of Central Aleutian tephras.

During the field season of 2002 twenty tephra samples and fourteen soil samples were collected proximal to Korovin Volcano. Korovin is located on the northeast tip of Atka Island at 174° 09’W, significantly east of other Holocene active volcanoes in the Central Aleutians. This study provides a multi parameter data set that includes: field characteristics, mineralogy, radiocarbon ages and glass shard geochemisty. These data are used to characterize both proximal Korovin deposits and distal deposits of unknown origins collected from two stratigraphic sections. The onset of Holocene volcanism on Atka Island is observed in the second stratigraphic section and is constrained by ¹⁴C dates from soil samples.

A single chemical characterization, such as glass geochemistry, is rarely unique enough to discriminate proximal deposits from one another. In order to provide a more complete characterization of the proximal deposits titanomagnetite and bulk tephra chemical data have been collected. A combination of physical and chemical characteristics of each deposit provides a powerful tool for the future correlation of Central Aleutian tephra deposits. Correlated tephra deposits will lead to a subsequent understanding of the spatial and temporal distribution of Holocene eruptions in the Aleutians.