Frost weathering of volcanic glass can increase health hazards
Weathering of volcanic glass produces particles that can increase respiratory health hazards and complicate the estimation of volcanic explosivity of volcanoes. These results were recently published in the Bulletin of Volcanology by a team led by Dr Sebastiaan de Vet from the Institute for Biodiversity and Ecosystem Dynamics (IBED).
Fragmental volcanic glass or ‘hyaloclastite’ is formed when volcanoes erupt under glaciers. While basaltic volcanic glass is fairly common, rhyolitic volcanic glass (found on the other side of the 'rock spectrum') is much rarer and these deposits may also be more susceptible to weathering. The research team therefore set-out to experimentally study how these volcanic glass is weathered by environmental processes such as frost weathering and transport and collected glass samples from the Grænagil (‘green gorge’) in the colourful area Landmannalaugar in Southern Iceland.
Daily trips into a -20°C freezer
A battery of tests was used to study the physical alteration of the sampled volcanic glass. Daily trips into a -20°C walk-in-freezer were undertaken by De Vet to freeze and thaw samples over the course of several days to quantify the effects of frost weathering. Other particles were crushed in specialised test benches, or subjected to more than 500 km of transport inside rock tumblers. Detailed particle size analyses of the produced fragment in these experiments showed that especially frost weathering was effective in modifying these volcanic glasses.
Health hazards and complications
Frost weathering does not occur without risks. One notable effect observed by the team was the formation of small dust particles <10 µm, or about a tenth the thickness of an average human hair. These particles are fine enough to be inhaled and may cause problems in the human respiratory track. In addition, studies that rely on particle diameters to estimate the explosive energies of volcanoes may also run into difficulties. Estimating the explosivity of an eruption may not be as straightforward in cold regions if fine-grained materials have been drastically altered by frost weathering.
de Vet, S.J., Mittelmeijer-Hazeleger, M.C., Braakhekke, J.J.M., Cammeraat L.H. Physical weathering and fracturing of a rhyolitic hyaloclastite in Iceland. In: Bulletin of Volcanology (2014), 76(833), doi:10.1007/s00445-014-0833-7