TESTING THE USE OF VEGETATION INDICES AS INDICATORS OF PRE-ERUPTIVE VOLCANIC UNREST AT KILAUEA VOLCANO, HAWAII

Satellite remote sensing has become an integral part of pre-eruptive and long-term volcano monitoring due to its low cost, spatial and temporal coverage, and time-series analysis capabilities. Pre-eruptive unrest at volcanoes can include increased fluxes of heat and volcanic gases, which can be manifested either directly (e.g., the appearance of thermal anomalies or fumaroles) or indirectly (e.g., through impacts on vegetation health and extent). We are evaluating the use of novel, high spatial and temporal resolution data from the Planet Labs cubesat constellation to monitor changes in vegetation related to volcanic unrest. We present results from a study of key locations, including known geothermal areas, within the East Rift Zone (ERZ) of Kilauea volcano, Hawaii, prior to and during the May-August 2018 eruption on the Lower ERZ (LERZ). This proof of concept study investigates possible correlations between the Normalized Difference Vegetation Index (NDVI) stress signature and the formation or growth of geothermal features as well as eruptive events throughout the ERZ. There are a number of factors that can influence the NDVI signature, including changes in soil gas (CO2, H2S) emission rates and ground temperature. Both of these factors can be correlated to subsurface magma movement and migration in the ERZ. Using the PlanetScope OrthoTile dataset (at 3.125 m resolution, with daily revisit time at nadir) from Planet Labs, the NDVI is calculated across the study areas within the ERZ. Using ArcGIS and ERDAS Imagine, pixels are classified according to spectral values in order to delineate different zones of vegetation coverage within the region of interest. The Puhimau geothermal feature shows a clear decrease in NDVI in the lead up to the 2018 eruption. Significant changes in the distribution and general health of vegetation in the region directly surrounding the geothermal vents in the year preceding the eruption show a clear correlation between NDVI and increased volcanic unrest