Anhydrite-bearing pumices from Mount Pinatubo: further evidence for the existence of sulphur-rich silicic magmas

Abstract

THE eruption of EI Chichón in 1982 showed that relatively small but sulphur-rich eruptions from calc-alkaline volcanoes can produce long-lived stratospheric clouds of sulphate aerosols^1,2, which affect the global climate^3,4. Here we report the presence of primary anhydrite (CaSO₄) phenocrysts in dacitic pumice clasts from the 14–15 June eruption of Mount Pinatubo, which clearly shows that the Mount Pinatubo magma is also rich in sulphur. The post-eruptive sulphur content of the Pinatubo pumices ranges from 0.37 to 0.48 wt% SO₃. The considerable amount of sulphate aerosol injected into the stratosphere by the Mount Pinatubo eruptions⁵ should lead to a measurable cooling of the Earth's surface over the next few years, and could also trigger heterogeneous chemical reactions leading to stratospheric ozone depletion⁶. This new eruption of a sulphur-rich silicic magma thus shows that the EI Chichón eruption is not unique, and that climate-modifying eruptions of this type may be more common than previously believed.