The principal hazard associated with future explosive eruptions of Alaska volcanoes is the generation of volcanic ash clouds which are explosively blasted high into the atmosphere and then drift away from the volcano with the wind. The fragments in the ash cloud (tephra) vary in size and the heavier particles fall near the source while finer particles travel downwind. This transported tephra will fall out of the cloud and accumulate on surfaces and structures, contaminate water sources, and infiltrate electronics and motors. The weight of significant accumulations may collapse structures and cause other damage. Chronic exposure to ash may be a significant public health hazard. This publication presents the frequency and location of tephra fall throughout Alaska and into the Yukon Territory of Canada, resulting from eruptions of Alaska volcanoes from the Pleistocene to the present. The tephra occurrence map facilitates better visualization of areas in Alaska with past occurrences of ashfall. The map is a useful indicator of regional potential ashfall hazards. All files can be downloaded free of charge from the DGGS website (http://doi.org/10.14509/30059).

Alaska Volcano Observatory (AVO) geologists from the U.S. Geological Survey (USGS) and the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted fieldwork at Mount Veniaminof during field excursions between 2001 and 2016. The primary purpose of the fieldwork was geologic investigation of Veniaminof volcano to elucidate its eruptive history and understand its eruptive behavior. Teams of geologists focused on 1) edifice lava flows, 2) flowage deposits (lahars and pyroclastic flows), and 3) tephra-fall deposits. This Raw Data File comprises 61 whole-rock analyses of pumices from Holocene-age tephra deposits collected from 36 field stations on the flanks of Veniaminof volcano in 2001-2004, 2010, and 2016. All but four samples in this report were collected by geologists Kristi Wallace and Chris Waythomas during 1- to 2-week summer fieldwork campaigns. Thomas Miller and Charles Bacon contributed four pumice samples of a young dacite-composition tephra collected in 2001 and 2002. Mount Veniaminof is an ice-clad, basalt-to-dacite stratovolcano topped by an ice-filled caldera 10 km (about 6 mi) in diameter, located 775 km (482 mi) southwest of Anchorage on the Alaska Peninsula. With a volume of approximately 350 km3 (approximately 84 mi3) Veniaminof is one of the largest and most active volcanoes of the Aleutian Arc. Two Holocene caldera-forming eruptions are recorded in extensive pyroclastic-flow deposits around the volcano. Veniaminof has had at least 15 eruptions in the past 200 years, all from the approximately 300-m-high (about 984-ft-high) intracaldera cone and all largely basaltic-basaltic andesite composition, producing small lava flows and minor tephra deposits mostly confined to the caldera boundaries. The most recent explosive eruption was in 2018. Geochemical characterization of tephra deposits is most commonly executed by using glass-phase chemistry rather than whole-rock (bulk) geochemistry. The bulk composition of a tephra may change over fallout distance by eolian fractionation and therefore cannot be used to correlate tephra deposits over long distances. Whole-rock composition is commonly used to characterize juvenile material from flowage deposits (lahars and pyroclastic flows) and lavas. In order to readily compare (correlate) juvenile material from proximal tephra-fall deposits with other proximal deposits, tephra whole-rock analysis is required. This Raw Data File is focused only on whole-rock geochemical analyses of significant coarse-grained tephra deposits exposed on the flanks of Veniaminof volcano for use in correlating tephra deposits across the large volcanic edifice, and with proximal flowage deposits and edifice lava flows. Results of glass geochemistry of Veniaminof tephra and all other whole-rock analyses of samples collected is part of an ongoing study and not included in this report. Files can also be downloaded from the DGGS website (http://doi.org/10.14509/30578) and is also available in .html and .csv from the AVO Geochemical Database (https://avo.alaska.edu/geochem). Sample descriptions, locations, and sample types are included in the analytical data table. Samples collected during this project, including hand sample material, remaining powder from these whole-rock analyses, and partially crushed sample remains are stored at the Alaska Geologic Materials Center or at the USGS Alaska Tephra Laboratory in Anchorage.

Tephra samples and analyses from the 2018-2023 eruption of Semisopochnoi Volcano, Alaska, Raw Data File 2025-15, includes samples and analyses collected from the 2018-2023 eruption of Semisopochnoi volcano in the western Aleutian Islands, Alaska. Samples were collected during two field visits: May 30 to June 1, 2021, and June 10, 2023. A total of sixteen samples were collected across Semisopochnoi Island at varying distances from the eruption source, the north crater of Mount Young. Samples were collected from the surface on snow, grass, or other substrates that suggested deposition during recent eruptive activity but are, in all cases, aggregates of prior eruption events up to the sample date and may contain minor wind-blown contamination from older surfaces. These data and report are available from the DGGS website: http://doi.org/10.14509/31645 and a subset of the results are archived in the Geologic Database of Information on Volcanoes in Alaska (GeoDIVA; Cameron and others, 2022, doi.org/10.14509/geodiva).

This USGS Data Release presents major-oxide glass geochemical results from tephras erupted form Alaska volcanoes. This data set is in support of volcano hazard studies by the Alaska Volcano Observatory (AVO) where tephra (volcanic ash) deposits are used to assess eruption frequency, magnitude, and character of eruption. These data are part of a larger effort to identify and characterize tephra deposits from Alaskan volcanoes and the data set will continue to grow (versioned) as new data are generated.

This USGS Data Release presents major-oxide glass geochemical results from tephras erupted form Alaska volcanoes. This data set is in support of volcano hazard studies by the Alaska Volcano Observatory (AVO) where tephra (volcanic ash) deposits are used to assess eruption frequency, magnitude, and character of eruption. These data are part of a larger effort to identify and characterize tephra deposits from Alaskan volcanoes and the data set will continue to grow (versioned) as new data are generated.

Tephra samples and analyses from Cook Inlet source volcanoes and Anchor Point, Alaska, Raw Data File 2023-25, proivides samples and analyses collected from source volcanoes of the Cook Inlet region, Alaska, including Hayes Volcano, Mount Spurr, Redoubt Volcano, Iliamna Volcano, Augustine Volcano, Mount Douglas, Fourpeaked Mountain, and Kaguyak Crater. The report also includes tephra and soil samples and analyses from a stratigraphic section examined near Anchor Point, Alaska. These samples were collected over many years during geologic investigations of the eruptive histories for these source volcanoes, and in regional studies of eruption impacts, and are compiled here to support research characterizing the composition and impacts of these volcanoes on the Cook Inlet region. The analytical data tables associated with this report are provided in digital format as comma-separated value (CSV) files. They are available from the DGGS website: http://doi.org/10.14509/31090 and are archived in the Geologic Database of Information on Volcanoes in Alaska (GeoDIVA; Cameron and others, 2022, doi.org/10.14509/geodiva).

The Wrangell region of eastern Alaska represents a zone of extensive volcanism marked by intermittent pyroclastic activity during the late Holocene. The most recent and widely dispersed pyroclastic deposit in this area is the White River tephra, a distinct tephra-fall deposit covering 540 000 km 2 in Alaska, Yukon, and the Northwest Territories. This deposit is the product of two Plinian eruptions from Mount Churchill, preserved in two distinct lobes, created ca. 1887 years B.P. (northern lobe) and 1147 years B.P. (eastern lobe). The tephra consists of distal primary air-fall deposits and proximal, locally resedimented volcaniclastic deposits. Distinctive layers such as the White River tephra provide important chronostratigraphic control and can be used to interpret the cultural and environmental impact of ancient large magnitude eruptions. The resedimentation of White River tephra has resulted in large-scale terraces, which flank the margins of Klutlan Glacier. Preliminary analysis of resedimented deposits demonstrates that the volcanic stratigraphy within individual terraces is complex and unique.

A database of the geologic map of the Katmai Volcanic Cluster as described in the original abstract: This digital publication contains all the geologic map information used to publish U.S. Geological Survey Geologic Investigations Map Series I-2778 (Hildreth and Fierstein, 2003). This is a geologic map of the Katmai volcanic cluster on the Alaska Peninsula (including Mount Katmai, Trident Volcano, Mount Mageik, Mount Martin, Mount Griggs, Snowy Mountain, Alagogshak volcano, and Novarupta volcano), and shows the distribution of ejecta from the great eruption of June, 1912 at Novarupta. Widely scattered erosional remnants of volcanic rocks, unrelated to but in the vicinity of the Katmai cluster, are also mapped. Distribution of glacial deposits, large landslides, debris avalanches, and surficial deposits are a snapshot of an ever-changing landscape.

A database of the geologic map of the Katmai Volcanic Cluster as described in the original abstract: This digital publication contains all the geologic map information used to publish U.S. Geological Survey Geologic Investigations Map Series I-2778 (Hildreth and Fierstein, 2003). This is a geologic map of the Katmai volcanic cluster on the Alaska Peninsula (including Mount Katmai, Trident Volcano, Mount Mageik, Mount Martin, Mount Griggs, Snowy Mountain, Alagogshak volcano, and Novarupta volcano), and shows the distribution of ejecta from the great eruption of June, 1912 at Novarupta. Widely scattered erosional remnants of volcanic rocks, unrelated to but in the vicinity of the Katmai cluster, are also mapped. Distribution of glacial deposits, large landslides, debris avalanches, and surficial deposits are a snapshot of an ever-changing landscape.