Matthew Loewen Jordan Lubbers 20260420 raster digital data ScienceBase ScienceBase https://doi.org/10.5066/P1PV2QWT The Alaska Volcano Observatory conducted overflights of Shishaldin Volcano, Alaska, in July–August 2024 to characterize the morphological changes to the summit area following the 2023 and 2019–2020 eruptions. Oblique airphotos were taken during helicopter overflights on July 30 and August 1. The photos were processed with structure-from-motion (SfM) photogrammetric methods to derive a digital elevation model (DEM) and orthoimagery. A combined mosaicked DEM from both surveys and two orthoimages, one for each date, are provided with this data release. Comparison of this DEM with pre-eruptive data from 2018 shows extensive morphological changes associated with these eruptions. The 2023 eruption resulted in development of an east-northeast to west-southwest oriented trough that bisected the summit cone of the volcano. Compared to the pre-eruption DEM, the western trough had up to 113-meters of elevation loss, and the eastern trough up to 84-meters of elevation loss. The northern and southern intact rims of the summit crater have increased elevation with the apparent summit of the volcano increasing to 2877-meters from 2856-meters in the 2018 survey, and shifting to the northeast onto new cone material built up during these two recent eruptions. The Alaska Volcano Observatory conducted two aerial photography surveys of Shishaldin Volcano, Alaska, in July–August 2024 in order to quantify the volcano’s surface morphology following major eruptions in 2019–2020 and 2023. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 20240730 20240801 ground condition Complete None planned -164.00006 -163.92968 54.77406 54.73320 USGS Thesaurus elevation volcanic eruption stratovolcano structure-from-motion digital elevation model orthoimagery USGS Metadata Identifier USGS:69d93b1ab66b0192e7e603d7 None Alaska Unimak Island Shishaldin Volcano None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Matthew W Loewen U.S. Geological Survey, Alaska Volcano Observatory Research Geologist mailing and physical

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Anchorage AK 99508 907-786-7036 mloewen@usgs.gov Processed on Microsoft Windows, Agisoft Metashape Professional 2.1.3 and QGIS v. 3.44. File names: dem_shishladin.tif, 2.2 GB; dem_hillshade_shishaldin.tif, 562 MB; orthophoto_20240730.tif, 801 MB; orthophoto_20240801.tif, 564 MB; elev_change.tif, 3.1 MB; Shishaldin_20240730_optical.zip, 13.9 GB; Shishaldin_20240801_optical.zip, 3.8 GB; model_extents.gpkg, 96 KB. The July 30 orthophoto has a horizontal resolution of 0.31-meters, while the August 1 orthophoto has a horizontal resolution of 0.09-meters. The merged DEM has a 0.18-meter horizontal resolution; this matches the actual resolution of the August 1 model of the summit region and oversamples the July 30 DEM which covered a larger area but at a lower resolution of 0.63-meters. The root mean square error (RMSE) of the DEM based on the fit to the ground control points on the July 30 model compared to the USGS 2018 IfSAR DEM is 6.3-meters (Easting = 1.9-meters, Northing = 4.2-meters, Elevation = 4.3-meters). While higher resolution, the August 1 model is georeferenced to the July 30 model and thus has additional uncertainty. Matching features on the two orthophotos in places have up to a 25-meter offset. The magnitude of the error is similar to the resolution of the reference 2018 IfSAR DEM (USGS, 2018; RMSE 2-meters). However, this is error calculated from the same points used to reference the model and are thus not independent. Unfortunately, significant changes in the ground surface from recent eruptions and steep glaciated ground surfaces precluded identification of robust check points. Absolute coordinates from these models should therefore be viewed with caution. Steam, clouds, and other noise produced minor data gaps and spurious values, especially near the conduit within the summit crater and near the margins of the model space. Results were evaluated relative the USGS 2018 IfSAR DEM. The point cloud used to construct this dataset was checked for accuracy by rotating the point cloud to view from multiple angles. Points obviously offset from the surface were eliminated prior to constructing the elevation model. Limited options were available for ground control due to lack of bare ground surfaces (much of the edifice is covered by continuously shifting glacial ice), and changes from the 2019-2020 and 2023 eruptions at the summit and northern flanks. The August 1 model was offset -4.3-meters from the georeferenced July 30 model, and thus we applied a univform +4.3-meters increase to elevation values August 1 model before merging.With the offset a <2-meter step is still visible along some adjacent surfaces, but is within the model error. Imagery was collected to target the summit and upper flanks of Shishaldin Volcano to document morphology changes following the 2019-2020 and 2023 eruptions. Small areas within the model space were obscured by steam and clouds resulting in spurious data artifacts. DEM and orthophotos have a horizontal error of 4.2-meters estimated from reference points on the USGS 2018 IfSAR DEM. DEM has a vertical error of 4.3-meters estimated from reference points on the USGS 2018 IfSAR DEM. The first survey was conducted on July 30, 2024, between 11:33 and 12:03 AKDT. This survey covered a 1.7–2.8-kilometers radius around the volcano’s summit, however, the summit crater was substantially obscured by steam emissions from the active volcanic summit crater. The second survey was conducted on August 1, 2024, between 11:49 and 11:56 AKDT. This survey focused on a smaller radius of 400–750-meters near the summit of the volcano, but with less visual obstruction of the vent area by steam. Both surveys were conducted with counter-clockwise orbits around the volcano from an AStar 350 B2 helicopter with oblique photos acquired at 3000 to 3200-meters above sea level and >80% image overlap. 20240801 Matthew Loewen U.S. Geological Survey, Alaska Volcano Observatory Research Geologist mailing and physical

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Anchorage AK 99508 907-786-7036 mloewen@usgs.gov Photos were acquired with a Fujifilm XT-5 camera and an XF 23 mm f/2 R WR lens. Both surveys were acquired at constant aperture (f5.6) and focal length (23 mm), with variable ISO and shutter speed to adjust exposure and prevent image blur. Individual images are 7728x5152 pixels, and RAW files were processed in Adobe Lightroom Classic to adjust exposure before exporting to jpeg format for SfM processing. Initial georeferencing of the photos was provided by a handheld GPS unit (Garmin eTrex 30x) running in the cabin of the helicopter. 20240802 Matthew Loewen U.S. Geological Survey, Alaska Volcano Observatory Research Geologist mailing and physical

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Anchorage AK 99508 907-786-7036 mloewen@usgs.gov The digital elevation models and orthophotos were processed using Agisoft Metashape v. 2.1.3. Each survey was processed separately to generate point clouds referenced only from the handheld GPS geotagging. The referencing was then refined using approximate ground-control identified from features in the photographs that match known locations on the pre-eruption 2018 5-meter-resolution DEM (USGS, 2018). The larger-area July 30 model was georeferenced from 11 locations around the flank of the volcano, at bare-rock locations not affected by 2019 or 2023 eruption deposits. The smaller August 1 model was then georeferenced to 12 points identified in both models in QGIS v.3.44. A +4.3-meter vertical offset to the August 1 model was required to match the overall average elevation of both models where they overlapped. With this offset up to a 2-meter step can still be seen at the model boundary—this step however is within the overall model uncertainty. The DEMs were merged together to generate a single DEM to combine the broad extent of the July 30 data with the steam-free, high-resolution model of the August 1 data using the ArcGIS pro v. 3.5.6 mosaic tool and matching the higher resolution August 1 model and oversampling the July 30 model. The extent of the August 1 model was manually chosen to exclude edge regions with higher noise elevation data. 20260319 Matthew W Loewen U.S. Geological Survey, Alaska Volcano Observatory Research Geologist mailing and physical

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Anchorage AK 99508 907-786-7036 mloewen@usgs.gov Raster Grid Cell 24321 24227 1 Universal Transverse Mercator 3 0.9996 -165.0 0.0 500000.0 0.0 row and column 0.18 0.18 meters WGS_1984 WGS 84 6378137.0 298.257223563 North American Vertical Datum of 1988 0.001 meters Explicit elevation coordinate included with horizontal coordinates U.S. Geological Survey - ScienceBase mailing address

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Denver CO 80225 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. Digital Data https://doi.org/10.5066/P1PV2QWT None 20260420 Matthew W Loewen U.S. Geological Survey, Alaska Volcano Observatory Research Geologist mailing and physical

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Anchorage AK 99508 907-786-7036 mloewen@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-012-2002