On 16 July 2021, measurements were made of the volcanic gases emitted from Iliamna Volcano, Mount Douglas, Mount Martin, and Mount Mageik (Alaska, USA) from aboard a fixed-wing aircraft. Two zenith-facing differential optical absorption spectrometers were used to measure incident scattered solar ultraviolet radiation while traversing beneath the gas plumes on multiple occasions. These data were used to derive volcanic SO2 column densities and emission rates. In addition to the remote sensing payload, two in situ instruments were used to make measurements of trace gas concentrations while on flight paths through the volcanic plumes: a USGS multi-GAS (multiple Gas Analyzer System; Werner et al., 2017) analyzer for H2O-CO2-SO2-H2S, and an Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) instrument manufactured by Los Gatos Research, Inc., for H2O-HCl-HF. The CO2, SO2, and H2S sensors were calibrated five times in-flight at ambient pressures from 804-686 hPa (~1800-3000 m altitude) using standard gases stored in 25-liter capacity tedlar bags (CO2 = 448 ppm, SO2 = 2.1 ppm, H2S, = 2.0 ppm; all gases certified at ±2% accuracy). The H2O/CO2 analyzer’s baseline response was checked using small soda lime and anhydrite cartridges to remove H2O and CO2 from ambient air, and the sulfur sensors’ baselines were derived from their responses while sampling clean ambient air. In situ gas compositions were recorded at 1-second time resolution, while radiance spectra were acquired with variable integration times depending on illumination conditions and ranging from 1 to 3 seconds. Each spectrum and gas measurement was stamped with the GPS time and location. Each spectrum was saved in a separate ASCII file which includes 1024 radiances measured in the 265 - 403 nm spectral region and metadata associated with each acquisition. The in situ measurements are saved in a spreadsheet in the *.csv format.

This release presents data collected during airborne volcanic gas monitoring flights at Iliamna Volcano, Alaska, that were completed between 2004-2017. Instrumented fixed-wing aircraft were used to collect in situ trace gas measurements of volcanic carbon dioxide (CO2), sulfur dioxide (SO2), and hydrogen sulfide (H2S). The sensor payload also included an upward-looking correlation spectrometer (COSPEC) and/or differential optical absorption spectroscopy (DOAS) system. The remote sensing instruments were used to derive volcanic SO2 emission rates by measuring incident scattered solar ultraviolet radiation while traversing beneath the plume. Gas compositions and COSPEC output (volts) were recorded at 1 Hz and DOAS radiance spectra were collected at approximately 1 Hz depending on the ambient light conditions. All data were stamped with the GPS time and location. Trace gas and COSPEC measurements collected on 16 flights from 2004-2017 are included in a compressed file (GasData_2004_2017_v2.zip) that contains spreadsheets saved in the *.csv format and named using the local date on which the flight occurred in YYYYMMDD format (YYYY = year, MM = month, DD = day). The known values of COSPEC calibration cells used to scale raw measurements and information about gas standards used during in-flight CO2, SO2, and H2S sensor verifications are given in an auxiliary file (GasStandards.csv). DOAS data were collected during 3 flights from 2015-2017; each DOAS spectrum was saved in a separate ASCII file which includes 2048 radiances measured in the 285 - 430 nm spectral region and metadata associated with each acquisition. Additional information concerning the instruments and methods used to collect data from 2004-2007 is available in Doukas and McGee (2007), and in Kelly et al. (2013) and Werner et al. (2013) for data collected after 2007. See the associated publication for analysis and discussion of these data: Werner, C., Power, J., Kelly, P., Prejean, S., & Kern, C., 2021, Characterizing unrest: A retrospective look at 20 years of gas emissions and seismicity at Iliamna Volcano, Alaska. Journal of Volcanology and Geothermal Research, 107448. https://doi.org/https://doi.org/10.1016/j.jvolgeores.2021.107448 References Doukas, M. P., & McGee, K. A., 2007, A compilation of gas emission-rate data from volcanoes of Cook Inlet (Spurr, Crater Peak, Redoubt, Iliamna, and Augustine) and Alaska Peninsula (Douglas, Fourpeaked, Griggs, Mageik, Martin, Peulik, Ukinrek Maars, and Veniaminof), Alaska, from 1995-2006. https://pubs.usgs.gov/of/2007/1400/of2007-1400.pdf Kelly, P. J., Kern, C., Roberts, T. J., Lopez, T., Werner, C., & Aiuppa, A., 2013, Rapid chemical evolution of tropospheric volcanic emissions from Redoubt Volcano, Alaska, based on observations of ozone and halogen-containing gases. Journal of Volcanology and Geothermal Research, 259, 317–333. https://doi.org/10.1016/J.JVOLGEORES.2012.04.023 Werner, C., Kelly, P. J., Doukas, M., Lopez, T., Pfeffer, M., McGimsey, R., & Neal, C., 2013, Degassing of CO2, SO2, and H2S associated with the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research, 259. https://doi.org/10.1016/j.jvolgeores.2012.04.012

On 25 July 2016, helicopter-based measurements were made of the volcanic gases emitted from Mount Cleveland, Alaska, USA. An upward-looking differential optical absorption spectroscopy (DOAS) system was used to measure incident scattered solar ultraviolet radiation while traversing beneath the plume on multiple occasions. These data were used to derive volcanic SO2 emission rates. Additionally, a Multicomponent Gas Analyzer System (Multi-GAS) was used to make measurements of trace gas concentrations while on a dedicated measurement flight passing through the volcanic plume. Radiance spectra and gas compositions were both recorded at 1 second time resolution. Each spectrum and gas measurement was stamped with the GPS time and location. Each spectrum was saved in a separate ASCII file which includes 2048 radiances measured in the 285 - 430 nm spectral region and metadata associated with each acquisition. The Multi-GAS measurements are saved in a spreadsheet in the *.csv format. In addition to the helicopter-based measurements, ultraviolet imagery of the volcanic plume emitting from Mount Cleveland was collected on 24 July between 18:00 and 19:30 UTC using a ground-based SO2 camera instrument located 3.4 km east of the volcano's summit. This imagery was used to quantify the absorption of light by SO2 in the volcano's plume, resulting in a time series of SO2 emission rates. For more information see the associated interpretive publication: Werner C., Rasmussen D.J., Plank T., Kelly P.J., Kern C., Lopez T., Gliss J., Power J., Roman D.C., Izbekov P., Lyons J. (2020). Linking subsurface to surface using gas emission and melt inclusion data at Mount Cleveland volcano, Alaska. Geochemistry, Geophysics, Geosystems. https://doi.org/10.1029/2019GC008882

On 25 July 2016, helicopter-based measurements were made of the volcanic gases emitted from Mount Cleveland, Alaska, USA. An upward-looking differential optical absorption spectroscopy (DOAS) system was used to measure incident scattered solar ultraviolet radiation while traversing beneath the plume on multiple occasions. These data were used to derive volcanic SO2 emission rates. Additionally, a Multicomponent Gas Analyzer System (Multi-GAS) was used to make measurements of trace gas concentrations while on a dedicated measurement flight passing through the volcanic plume. Radiance spectra and gas compositions were both recorded at 1 second time resolution. Each spectrum and gas measurement was stamped with the GPS time and location. Each spectrum was saved in a separate ASCII file which includes 2048 radiances measured in the 285 - 430 nm spectral region and metadata associated with each acquisition. The Multi-GAS measurements are saved in a spreadsheet in the *.csv format. In addition to the helicopter-based measurements, ultraviolet imagery of the volcanic plume emitting from Mount Cleveland was collected on 24 July between 18:00 and 19:30 UTC using a ground-based SO2 camera instrument located 3.4 km east of the volcano's summit. This imagery was used to quantify the absorption of light by SO2 in the volcano's plume, resulting in a time series of SO2 emission rates. For more information see the associated interpretive publication: Werner C., Rasmussen D.J., Plank T., Kelly P.J., Kern C., Lopez T., Gliss J., Power J., Roman D.C., Izbekov P., Lyons J. (2020). Linking subsurface to surface using gas emission and melt inclusion data at Mount Cleveland volcano, Alaska. Geochemistry, Geophysics, Geosystems. https://doi.org/10.1029/2019GC008882

On 14-15 August 2015, helicopter-based measurements were made of the volcanic gases emitted from Mount Cleveland, AK. An upward-looking differential optical absorption spectroscopy (DOAS) system was used to measure incident scattered solar ultraviolet radiation while traversing beneath the plume on multiple occasions 14-15 August. This data was used to derive SO2 emission rates. Additionally, a Multi-Component Gas Analyzer System (Multi-GAS) was used to make measurements of trace gas concentrations while on a dedicated measurement flight passing through the gas plume on 15 August (19:15 - 19:56 UTC). Radiance spectra and gas compositions were both recorded at 1 second time resolution. Each spectrum and gas measurement was stamped with the GPS time and location. Each spectrum was saved in a separate ASCII file which includes 2048 radiances measured in the 285 - 430 nm spectral region and metadata associated with each acquisition. The Multi-GAS measurements are saved in a spreadsheet in the *.csv format.

Results from discrete multi-GAS surveys are compiled herein. Gas composition data were obtained using portable multi-GAS instruments that record H2O, CO2, SO2, and H2S gas mixing ratios, GPS coordinates, and pressure and temperature data at 1Hz. Initial surveys were completed in 2017 at East Lake hot springs and Paulina hot springs. In response to reports of anomalous degassing in the summer of 2020 more extensive multi-GAS surveys were completed around Newberry caldera. In 2020 the instruments' CO2, SO2, and H2S sensor responses were verified in the field with portable gas standards; in 2017 the instrument was lab-calibrated only. The collection and processing of multi-GAS data have been discussed in Gunawan et al. (2017) and Lewicki et al. (2017). Definitions of monitored features and any abbreviations are provided in the "Definitions" file found on the parent directory of this release. References Gunawan, H., Caudron, C., Pallister, J., Primulyana, S., Christenson, B., Mccausland, W., Van Hinsberg, V., Lewicki, J., Rouwet, D., Kelly, P., Kern, C., Werner, C., Johnson, J.B., Utami, S.B., Syahbana, D.K., Saing, U., Suparjan, Purwanto, B.H., Sealing, C., Cruz, M.M., Maryanto, S., Bani, P., Laurin, A., Schmid, A., Bradley, K., Agung Nandaka, I.G.M., Hendrasto, M., 2017. New insights into Kawah Ijen’s volcanic system from the wet volcano workshop experiment, Geological Society Special Publication. https://doi.org/10.1144/SP437.7 Lewicki, J.L., Kelly, P.J., Bergfeld, D., Vaughan, R.G., Lowenstern, J.B., 2017. Monitoring gas and heat emissions at Norris Geyser Basin, Yellowstone National Park, USA based on a combined eddy covariance and Multi-GAS approach. J. Volcanol. Geotherm. Res. https://doi.org/10.1016/j.jvolgeores.2017.10.001

Results from discrete multi-GAS surveys are compiled herein. Gas composition data were obtained using portable multi-GAS instruments that record H2O, CO2, SO2, and H2S gas mixing ratios, GPS coordinates, and pressure and temperature data at 1Hz. Initial surveys were completed in 2017 at East Lake hot springs and Paulina hot springs. In response to reports of anomalous degassing in the summer of 2020 more extensive multi-GAS surveys were completed around Newberry caldera. In 2020 the instruments' CO2, SO2, and H2S sensor responses were verified in the field with portable gas standards; in 2017 the instrument was lab-calibrated only. The collection and processing of multi-GAS data have been discussed in Gunawan et al. (2017) and Lewicki et al. (2017). Definitions of monitored features and any abbreviations are provided in the "Definitions" file found on the parent directory of this release. References Gunawan, H., Caudron, C., Pallister, J., Primulyana, S., Christenson, B., Mccausland, W., Van Hinsberg, V., Lewicki, J., Rouwet, D., Kelly, P., Kern, C., Werner, C., Johnson, J.B., Utami, S.B., Syahbana, D.K., Saing, U., Suparjan, Purwanto, B.H., Sealing, C., Cruz, M.M., Maryanto, S., Bani, P., Laurin, A., Schmid, A., Bradley, K., Agung Nandaka, I.G.M., Hendrasto, M., 2017. New insights into Kawah Ijen’s volcanic system from the wet volcano workshop experiment, Geological Society Special Publication. https://doi.org/10.1144/SP437.7 Lewicki, J.L., Kelly, P.J., Bergfeld, D., Vaughan, R.G., Lowenstern, J.B., 2017. Monitoring gas and heat emissions at Norris Geyser Basin, Yellowstone National Park, USA based on a combined eddy covariance and Multi-GAS approach. J. Volcanol. Geotherm. Res. https://doi.org/10.1016/j.jvolgeores.2017.10.001

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.

Airborne electromagnetic (AEM) and magnetic survey data were collected during June 2012 along 556 line-kilometers over Iliamna Volcano, Alaska. These data were collected in support of alteration and volcano flank instability mapping as part of the U.S. Geological Survey (USGS) Volcano Hazards Program. Data were acquired by SkyTEM Survey ApS SkyTEM304 system with the Soloy Helicopters Eurocopter Astar 350 B3 and Bell 407 dual-moment, time-domain helicopter-borne electromagnetic system together with a Geometrics G822A cesium vapor magnetometer with Kroum KMAG4 counter. The survey was flown at a nominal flight height of 30 meters (m) above terrain along block-style lines with a nominal spacing of 250 m. The survey was designed to cover the summit and flanks of Iliamna volcano and includes transit lines east of the volcano which provide additional information on nearby structures and glacial thickness and resistivity. There are data gaps near Iliamna’s summit due to poor flight visibility. Minimally processed binary AEM data received from the contractor were imported into the Aarhus Workbench software (Aarhus Geosoftware, Aarhus, Denmark) and processed. Filters were applied to inclinometer and spatial positioning data to smooth raw data and remove sensor drop outs. Altimeter data were filtered, smoothed, and manually edited to correct false altitudes associated with trees and other obstacles, resulting in processed altitude representative of the distance between the AEM sensor airframe and bare earth. Ground surface elevations were imported from Alaska's 5 m IFSAR Division of Geological and Geophysical Survey elevation dataset (DGGS, 2020, https://elevation.alaska.gov/). Electromagnetic data were averaged using a filter width of 4 seconds applied to both high moment and low moment data. Low-signal data were removed from the averaged data through a combination of filters and manual culling.