Volcanic ash leachate and rainwater chemistry from increased 2018 activity of Kilauea Volcano, Hawaii

In early May 2018, activity at Kilauea volcano, Hawaii, increased, with heightened ash production from the summit commencing on May 17. Volcanic ash can scavenge volatile components from volcanic plumes, resulting in the deposition of potentially harmful elements during ash fallout. Leaching of these species (e.g., by rainfall or in water catchment systems) can have implications for agriculture, water resources and human health. The U.S. Geological Survey (USGS) is sampling volcanic ash and utilizing ash leachate analyses as part of the assessment of hazards from the ongoing eruption of Kilauea Volcano. We acquired 30 ash samples erupted from the summit of Kilauea Volcano and collected downwind between May 10 and May 28. The samples were collected by either USGS scientists or citizens who live in areas experiencing ashfall. Care was taken to source both proximal (<0.1 km) and distal samples (up to ~45 km from the summit) to evaluate whether the potential hazard changes with distance. The concentrations of leachable elements reported herein are only an indication of hazard. It is important that other sampling be performed to determine impact; for example, soil sampling, surface and drinking waters sampling, forage sampling, etc. To this end, we collected samples from open water supplies (catchments, troughs) near three different ash sampling locations as comparisons for impact considerations, as well as six rain water samples from the Lower East Rift Zone to quantify the potential for volcanic emissions to affect rain water chemistry and, therefore, catchment water quality. Leachate analyses were conducted following procedures described in an internationally ratified protocol for volcanic ash (Stewart and others, 2013) using deionized water and an ash to leachant ratio of 1:100. The full methods are available in Stewart and others (2013). The pH and specific conductance of leachates were measured, and the concentrations of major anions and cations were quantified using ion chromatography (IC) and inductively coupled plasma optical emission spectrometry (ICP-OES), respectively. One in every five samples was run in duplicate as a check for consistency and is indicated by the designation (2) in the sample name. Leachate data are presented as milligrams of the leachable component per kilogram of ash (mg/kg). Water samples were analyzed undiluted by IC and ICP-OES and the data are presented as milligrams per liter (mg/L). The pH values of the analyzed ash leachates are generally acidic (pH ~4-5), which indicates the potential for irritation of the eyes, mucous membranes and skin, as well as the potential to corrode metal roofing or pipes. The specific conductance values are high relative to previously reported values for volcanic ash globally, indicating the potential for disruption to electricity transmission systems (flashover on insulators) if there is a few millimeters thickness of ash that becomes wet (e.g., from light rain). For leachable elements, concentrations are generally high compared to ash from other volcanic eruptions worldwide (see Ayris & Delmelle, 2012); however, samples from basaltic eruptions are poorly represented in the global dataset and so comparisons should be made with caution. The high concentrations of Ca and SO4 measured in ash leachates derive from abundant, soluble calcium sulfate phases (gypsum, anhydrite) in the ash. Elevated concentrations of Zn in many samples may reflect contamination from collection surfaces (e.g., galvanized metal). In the water samples, concentrations of aluminum (Al), manganese (Mn) and zinc (Zn) are elevated relative to the maximum contaminant levels (MCL) defined by the Environmental Protection Agency (EPA). For health and safety reasons, the Hawaii Department of Health does not recommend using catchment water for drinking or preparing food, and comparison to EPA MCLs is used here solely as a convenient benchmark for considering potential impacts. For information on potential impacts and mitigation strategies, or case studies highlighting the impacts of ashfall, please refer to the Hawaii Interagency Vog Information Dashboard and the Volcanic Ashfall Impacts Working Group webpage. We are grateful to the citizens who provided samples, without which these analyses would not have been possible. version 1.1 References cited: Ayris, P.M., and Delmelle, P., 2012, The immediate environmental effects of tephra emission: Bulletin of Volcanology, v. 74, p. 1905-1936. Stewart, C., Horwell, C., Plumlee, G., Cronin, S., Delmelle, P., Baxter, P., Calkins, J., Damby, D., Morman, S., Oppenheimer, C., 2013, Protocol for analysis of volcanic ash samples for assessment of hazards from leachable elements: International Volcanic Health Hazard Network, http://www.ivhhn.org/guidelines.html (accessed May 2018).