Sulfur in the Tephra of the ca. 1500 BP Opala Eruption, Kamchatka

Abstract

Sulfur-containing ejecta of Plinian-type eruptions can be transported to great distances in gas pores of ash particles. The mean concentration of sulfur in the rhyolite tephra of the ca. 1500 BP Opala eruption is 310 ppm. The maximum concentration can reach 800 ppm. We have found a relationship between sulfur concentration in bulk samples and grain-size composition: sulfur is mostly found in the 0.25‒0.50 mm fraction consisting of elongate ash particles with elongate gas pores 1.0‒10.0 µm long. The most likely cause why sulfur concentration depends on the structure of ash particles consists in the fact that sulfur compounds of the water-soluble complex are preserved inside gas pores; sulfur-containing compounds that have been sorbed on the surface of ash particles were removed by precipitation during the time the tephra resided in continental settings. When ash particles that contain sulfur compounds on the inner surface of gas pores come into bottom sediments during Plinian-type eruptions like that on Opala Volcano ca. 1500 BP, that can affect the geochemistry of lithogeny and rearrange the mineral phases that are sensitive to the presence of oxide-sensitive agents in the sedimentary sequence during diagenesis.