Mystery Volcano Behind Enormous 1831 Eruption Identified

Between the years of 1831 and 1833 the northern hemisphere was a lot cooler than it should have been. Scientists have long known that this significant and sudden cooling was caused by an enormous volcanic eruption in the year 1831, but the precise location of the volcano behind the climate change has long been a mystery.

Now, a new study from a team at the School of Earth and Environmental Sciences in the University of St Andrews and published in PNAS has revealed the identity of the volcano responsible, and also sheds light on why it took so long to find. The culprit is the Zavaritskii volcano on Simushir island in the remote Kurils, an isolated island chain between Japan and the far east of Russia.

We know about the cooling in these years because of trace chemicals trapped in ice cores which correspond to this date, as well as contemporary accounts. The entire period of c1800 to 1850 was characterized by repeated global volcanic events, which contributed to a prolonged cooling of the planet over this period, known as the last phase of the “Little Ice Age.”

These eruptions include the famous Indonesian eruption of Tambora in 1815, the Nicaraguan eruption of Cosegüina in 1835 and two more unknown eruptions in 1808/9 and 1831, the latter of which is the subject of this study. Combined this series of eruptions injected significant amounts of sulfur into the atmosphere which blocked sunlight and cooled the surface of the planet.

The 1831 eruption disrupted the monsoon and led to major famines in India. Contemporary accounts also talk of spectacular colors in the sky across multiple locations in the northern hemisphere, blues, greens and purples caused by the scattering of solar radiation in a dense volcanic aerosol plume.

It had been thought that this 1831 eruption might have been the Babuyan Claro volcano in the Philippines, but there was no firm evidence from historical sources that this volcano erupted at that time. Another candidate was Ferdinandea, a volcano some 50km southwest of Sicily which definitely did erupt in 1831, but it was simply too small an eruption and did not produce nearly enough atmospheric sulfur to match that trapped in the sampled ice cores.

It was an analysis of the glass tephra shards (fragments ejected from the eruption) that allowed the team to home in on the volcano responsible. The composition did not match Ferdinandea at all, and the closest match was to either Japan or the Kuril islands.

Volcanic eruptions in 19th century Japan were well documented, excluding that location as a source. This left the Kurils, and specifically Simushir island where the largest deposits of the tephra were found. Eventually the search was narrowed down to the Zavaritskii volcano on the island.

Is this a slam dunk? Not entirely, but the match is compelling and it seems we now know the origin of another major contributor to the coldest period in the last 500 years.

Original Study: https://www.pnas.org/doi/10.1073/pnas.2416699122.

Header Image: Big Bada Boom! Simushir Island in the Kurils with the Zavaritskii caldera in the center. Source: NASA / Public Domain.