Stratigraphic and electron microprobe data for Holocene tephra from Makushin Volcano, Alaska, and for interbedded tephra from other volcanoes located among or near the islands of the eastern Aleutians

Stratigraphic and electron microprobe data for Holocene tephra from Makushin Volcano, Alaska, and for interbedded tephra from other volcanoes located among or near the islands of the eastern Aleutians, Raw Data File 2026-12, summarizes tephrostratigraphy and electron probe microanalytical (EPMA) data from Makushin Volcano and regional tephras in the Unalaska Island area. The data were collected by scientists from the Alaska Volcano Observatory (AVO) and the Cascades Volcano Observatory during fieldwork from 2011 to 2024. Additional EPMA analyses from this time interval are reported in Larsen and others (2020). Makushin Volcano is part of the Makushin Volcanic Field (McConnell and others, 1998) in the north central part of Unalaska Island, Alaska, approximately 1,290 km southwest of Anchorage and 20 km west of the City of Unalaska and the Port of Dutch Harbor. Makushin erupted explosively to produce two large-volume, explosive Holocene deposits with ages of 9,040 (Makushin Valley) and 7,900 (Driftwood) cal. yr B.P. Since then, Makushin Volcano has erupted numerous times, though individual eruptions have been significantly less voluminous than those of the early Holocene events. The most recent eruption in 1995 produced small ash plumes but left no clearly preserved deposits. Eruptions from volcanoes on neighboring islands also deposited significant tephra fall on Unalaska Island. Tephra from the Okmok II caldera-forming eruption about 2050 years ago is 1-2 cm thick and drapes the area near Dutch Harbor and the City of Unalaska. Tephra from two large explosive eruptions of the Akutan volcano also covered the area 1,600 and 8,700 years ago. Tephra from the older Akutan eruption is up to 40 cm thick in the City of Unalaska. An additional, older silicic tephra sample originated from a distant volcano, but its provenance remains undetermined. Data in this report are included in the public Geologic Database of Information on Volcanoes in Alaska (GeoDIVA; Cameron and others, 2022, http://doi.org/10.14509/geodiva). These data and accompanying discussion are released as a DGGS Raw Data File, and all publication components are available from the DGGS website at: http://doi.org/10.14509/32059.

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Organization: State of Alaska