One of the most significant climate forcing eruptions of the nineteenth century occurred in 1831. It contributed to delaying the end of the Little Ice Age and, hence, the onset of anthropogenic warming, until the 1850s. This thesis concludes that the identity of the volcano responsible is not Babuyan Claro, in the Philippines, as had commonly been assumed, but Ferdinandea, located about 50km off the south-west coast of Sicily, Italy.
Babuyan Claro had been the only eruption in 1831 assigned a Volcanic Explosivity Index (VEI) ≥ 4 in the Smithsonian Institution Global Volcanism Program (GVP) database, associated with ‘definite’ stratospheric injection. Re- examination of historical accounts of this volcano’s activity nevertheless reveals it to be a false event: Babuyan Claro volcano did not erupt in 1831.
Observations of a blue, green or purple sun reported in August 1831 are used to reconstruct a stratospheric sulphate aerosol plume that is instead traced back to the eruption of Ferdinandea, which occurred between 28 June and 16 August 1831.
The Ferdinandea eruption is assigned a VEI of only 3. However, examination of historical accounts of its activity and other analysis suggests that its sulphur yield was enhanced through interaction between magma and sulphur-rich sedimentary deposits, probably Messinian evaporites, and that convective instability in the troposphere contributed to the injection of that sulphur into the stratosphere. This provides a striking example of a modest eruption having a significant climate impact.
These results have consequences for the representation of the 1831 eruption in climate models as well as for the assessment of the hazards posed by the volcanoes. They underline that historical accounts can be valuable sources of scientific data but the primary, rather than secondary, sources must be examined for the data to be as reliable as possible.