Complete Bouguer gravity data of Kīlauea, Island of Hawaiʻi, 2023.

The attached file contains complete Bouguer gravity data collected at Kīlauea volcano from 1/5/2023 - 1/26/2023 using a Scintrex CG-6 gravimeter.

Overview
A Bouguer gravity survey of Kīlauea’s summit was carried out in January 2023 across a grid extending 3 km north, east, and west of the caldera and 6 km to the south (Ruggles and Flinders, 2026). The survey focused on areas with elevated volcanic and seismic activity, including the caldera and its Southwest Rift Zone and East Rift Zone connectors. All work was conducted within permitted areas to avoid cultural and ecological impacts.
The grid consisted of 306 measurement locations, spaced approximately 250–300 m within the caldera and Southwest Rift Zone connector and 500–1000 m elsewhere. Gravity data were collected with a Scintrex CG-6 gravimeter, recording a single 5-minute-long average of the instrument's internal 10 hertz data, with typical errors of 0.03–0.04 mGal. Base station readings were collected daily to monitor and correct for instrument drift.
Each gravity reading was paired with a differential Global Navigation Satellite System (GNSS) measurement. Each GNSS solution includes a formal elevation uncertainty from the network adjustment; across the dataset these uncertainties average 7 cm with a standard deviation of 3 cm. GNSS data were processed relative to the World Geodetic System 1984 (WGS84) and converted to orthometric heights (GEOID12B).

Processing and Correction of Dataset
Initial calibration and corrections for tides, preliminary drift, tilt, and temperature were applied by the instrument. Additional processing included residual drift, latitude, and free-air corrections. A multiday drift adjustment was applied to remove nonlinear drift over the 21-day survey, reducing potential long-wavelength tidal components that were not completely estimated by the instrument software. A polynomial drift model was developed using daily first base readings.
The temporary survey base station was located on the front concrete landing of Hawaiʻi Volcanoes National Park building Quarters 24 and occupied between two to three times daily. Base station data also provided corrections for remaining tidal signals, ocean loading, and daily drift through linear adjustments. Latitude and free-air effects were corrected using standard formulas (Telford and others, 1990). Because of major elevation changes following the 2018 caldera collapse, the free-air gradient was remeasured in 2024 at Uēkahuna, yielding a value slightly smaller than earlier estimates (-0.294 ± 0.002 mGal/m; Ruggles and Flinders, 2026).

Terrain and Bouguer Corrections
A complete Bouguer anomaly was produced by removing the gravitational effects of topography and bathymetry using a prism-based terrain correction (Flinders and others, 2013). Subaerial mass was modeled at an average density of 2.4 g/cm³, based on borehole measurements (Keller and others, 1979). Terrain corrections were computed in two regions: a high-resolution inner zone using a 1-meter digital elevation model (DEM; Mosbrucker and others, 2020) and an outer zone using a 30-meter DEM (USGS, 2023). Bathymetric corrections were computed using the 50-meter Main Hawaiian Islands Multibeam Bathymetry Synthesis (Hawaiʻi Mapping Research Group, 2023) and a submarine mass modeled at 2.7 g/cm³ (Flinders and others, 2013).
Three combinations of inner and outer radii were tested to evaluate sensitivity to DEM resolution. Results showed that lower-resolution elevation data within 2–5 km of a station can alter terrain corrections by several mGal, which is significant given that Bouguer anomalies are commonly of similar magnitude. The scenario using a 5 km inner radius and 150 km outer radius was selected for the final correction because it incorporated the highest-quality data.

References
Flinders, A.F., Ito, G., Garcia, M.O., Sinton, J.M., Kauahikaua, J., and Taylor, B., 2013, Intrusive dike complexes, cumulate cores, and the extrusive growth of Hawaiian volcanoes: Geophysical Research Letters, v. 40, no. 13, p. 3367–3373, https://doi.org/10.1002/grl.50633
Hawaiʻi Mapping Research Group, 2014, Main Hawaiian Islands multibeam bathymetry synthesis: University of Hawaiʻi at Mānoa, School of Ocean and Earth Science and Technology, accessed [date], https://www.soest.hawaii.edu/HMRG/multibeam/index.php
Keller, G.V., Grose, L.T., Murray, J.C., and Skokan, C.K., 1979, Results of an experimental drill hole at the summit of Kīlauea Volcano, Hawaiʻi: Journal of Volcanology and Geothermal Research, v. 5, no. 3–4, p. 345–385, https://doi.org/10.1016/0377-0273(79)90024-6
Mosbrucker, A., Zoeller, M.H., and Ramsey, D.W., 2020, Digital elevation model of Kīlauea Volcano, Hawaiʻi, based on July 2019 airborne lidar surveys: U.S. Geological Survey data release, https://doi.org/10.5066/P9F1ZU8O.
Telford, W.M., Geldart, L.P., and Sheriff, R.E., 1990, Applied geophysics (2d ed.): Cambridge, United Kingdom, Cambridge University Press, 770 p.
Ruggles, C.E., and Flinders, A.F., 2026, Structural controls on magma localization at Kīlauea documented through high-resolution gravity surveys: Bulletin of Volcanology, manuscript submitted.
U.S. Geological Survey, 2018, USGS 1 arc-second digital elevation model (DEM): U.S. Geological Survey 3D Elevation Program (3DEP), accessed 2023, https://viewer.nationalmap.gov/basic/