Mount Rinjani (on the Island of Lombok). Credit: Massew64, CC BY-SA 3.0

I recently drove by Mount Merapi, in Java. It is an impressive sight, rising up almost 3 km, especially when seen from the top of nearby Borobudur, the world’s largest Buddhist temple. Merapi is Indonesia’s most active volcano, which is saying a lot, because there are about 130 currently active volcanoes in Indonesia. Merapi has erupted fairly continuously since 1548. I had also sailed past Mt. Tambora (on the island of Sumbawa), Krakatau (in the Sunda Strait), and Mt. Rinjani (on the Island of Lombok). Java and some of these other Indonesian islands are only there because of the volcanoes. These islands are, essentially, volcanic arcs on steroids. So much volcanism for millions of years has created giant islands with active volcanoes; in the case of Java, spaced about 80 km apart. When you see them, however, it is hard not to put yourself back into the times when they erupted explosively, when these eruptions altered not only the surrounding landscapes but much of humanity, often tens of thousands of kilometers away.

Satellite image of Mount Rinjani. Credit: NASA

Most people are well aware of the global impact of the great eruption of Mt. Tambora in 1815. The eruption significantly altered jet stream patterns and the following year, the “year without a summer,” was significantly cooler in Western Europe and the Eastern U.S. The summer snows in New England prompted an accelerated westward expansion of Americans looking for greener and warmer pastures. Most people are not aware, however, that the eruption of Krakatau in 1883 also had a strong impact on U.S. history. In fact, it was even arguably the cause of the emergence of bandits such as Butch Cassidy and Sundance Kid. The Western U.S. was a fairly prosperous and lawful place up until 1883. However, starting in 1884, climates became significantly colder. Crop failures led to widespread unemployment. The Great White Winter of 1886-1867 saw the death of ¾ of the regional livestock. Robert Leroy Parker, AKA Butch Cassidy, first robbed a bank in 1889. The first robbery of Harry Longabaugh, a.k.a The Sundance Kid, was in 1887.

It was the giant eruption of Mt. Rinjani in the year 1258, however, that may have had the largest global impact of any volcano in recent history. It erupted ~250 metric tons of sulfur aerosols into the atmosphere, more than double the amount of the 1815 Tambora eruption. From this date onward, historical records show a large number of famines and plagues. In Northern Latitudes, the 300-year Medieval Climate Optimum came to an end. This has long been correlated with the onset of the Wolf Minimum, a decrease in solar output. However, the Wolf Minimum began about 1280. The famines and plagues preceded it. Some climate scientists now see the massive eruption of Mt. Rinjani as a possible trigger to the onset of the great famines of the 13th century.

We have been very fortunate as of late. We haven’t had a great volcanic eruption in two centuries. Since the eruption of Tambora in 1815, the world’s population has risen from just over 1 billion people to almost 7.5 billion. However, the year 1258 is really not that long ago. Volcanic eruptions like this do happen, and more frequently than we are comfortable admitting. I enjoyed my recent visits to this gallery of spectacular Indonesian volcanoes. But it made me very, very nervous.

—Michael E. Wysession, Editor, Geophysical Research Letters; email:


Wysession, M. E. (2016), Volcanic java and climate change, Eos, 97, Published on 12 September 2016.

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