Bubbles and Dust: Experimental Results of Dissolution Rates from Metal Salts and Glasses in Volcanic Ash Deposits

Volcanic eruptions are natural hazards due to their explosive nature and widespread atmospheric transportation and deposition of ash particles. After deposition and subsequent leaching in soils or water bodies, volcanic ash can lead to chemically altered water, positively and negatively impacting the health of flora and fauna, including humans. This study determined the control of ash surface area and chemical composition on ash dissolution rates. Fresh, unhydrated ash samples from four volcanoes with diverse environments and morphology, from Pele's spheres to dusty vesicular ash, were analyzed in the laboratory. Column Leachate Tests (CLT) were used to compare leaching rates over a range of basaltic to andesitic ashes as a function of time and surface area, to recreate the effects of ash deposition. Ash morphology was characterized on the SEM before and during leaching in order to calculate geometric surface area. Specific surface area was quantified throughout the leaching experiment by multi-point Brunauer Emmett Teller (BET) analysis. It was found that surface area, measured both geometrically and by BET, generally increases for a short time, gradually decreases, then increases over the rest of the leaching experiment, due to area to mass ratio fluctuations. After the CLT, post-leaching water analyses for elemental compositions were conducted by ICP-MS and IC. Steady state dissolution rates initially decayed rapidly due to the smallest size fraction of ash (dust) which provides high surface area with a great amount of fresh leachable surfaces as well as the rapid dissolution of highly soluble metal salts. Some water concentrations of elements of concern to human and ecosystem health such as F, Cd, Se, As, Cr, were above WHO drinking water standards after the first hour after ash deposition completes, depending on bioaccumulation and chronic exposure, the water may be safe for consumption. This has applications to emergency response and preparedness in volcanic regions.