Cation-exchange properties of pumice. Taking a sip from a volcanic cocktail

The search for the telltale signs of volcanic eruptions in easily dateable (biological) material like tree rings or speleothems has been going on for a very long time. Even though the reactions of tree rings to cataclysmic events are fairly well understood, there has not been a satisfactory method to distinguish volcanic from other climatically active events. Recent findings of differing Ba-contents in soil and the unexpected mobility of Ba during volcanic eruptions strongly suggest that tephra changes the concentrations of trace elements in the surrounding topsoil. To better understand the mechanics of this enrichment, leaching experiments with volcanic ashes have been performed that show that pumice acts as a cation-exchanger. Neutron activation analysis (NAA) with its reasonably simple sample preparation and the possibility to distinguish volcanic ashes from contamination of solvents by using activated ashes offers a hands on approach to the problem above. Several samples of known composition of volcanic ashes have been activated and leached with different solvents and solutions, aiming to both recreate a realistic situation comparable to natural leaching due to rain fall and obtain quantifiable results. (author)