Volcanic History

Who doesn’t love a good volcano? Well most people who are around when one erupts probably don’t, but for the rest of us they are endlessly fascinating. One eruption in particular has been fascinating geologists, volcanologists, and climatologists for decades now. Ice cores from Antarctica and Greenland have shown that an immense eruption took place around 1257 A.D. and medieval European records confirm that something extraordinary took place, as winters that year and the year after were so mild they were nearly nonexistent, with flowers and trees blooming as early as January. The allure of this apparent volcanic event is that no one has been able to actually identify where the eruption took place. Somewhere in history, we actually managed to lose a volcano. Until now, that is.

This past week a study was published in the Proceedings of the National Academy of Sciences  that makes one hell of a convincing case for where this lost eruption may have taken place: Mount Samalas in Indonesia. Now this is not the first candidate to be touted as the possible source of the 1257 eruption, previous suggestions including Okataina in New Zealand and El Chichón in Mexico, but it is the first to make such a strong case, one addressing the magnitude of the event, the geochemistry of the site, and the timing of the eruption.

Image
The caldera at Mount Samalas (Source: http://www.hngn.com)

Beyond the earth sciences, the group also made use of Indonesian history, citing the Babad Lombok, a chronicle written in Old Javanese that tells of Samalas’ eruption before the Selaparang period (thus before the end of the thirteenth century). The record describes how the eruption formed a massive crater, called a caldera, and destroyed the Kingdom’s capital, Pamatan. So based on this account, Mount Samalas’ eruption both fits the timeline of the 1257 event and may have been large enough to explain both the ice cores in the Antarctic and the climate shifts in Europe.

The group found that, based on the size of the caldera formed and the density and area of the deposits the eruption left, Samalas’ volcanic plume would have reached about 43 kilometers (or 26.7 miles) at its greatest height. The eruption was about a 7.0 in magnitude, which is actually a conservative estimate, as there were a number of factors the group couldn’t take into account due to lack of data. For those keeping track, that’s a stronger eruption than Vesuvius in 79 A.D. (classified as a 5) and Krakatoa in 1883 A.D. (which was a 6). The group calculated that Samalas’ eruption would have been roughly eight times as large as that of Krakatoa and two times larger than Tambora (another seven). It seems pretty clear that Samalas had the power to take credit for the 1257 disturbances, but what about the chemistry?

Image
The top image is the modern day caldera. It’s tough to make out, but the bottom image shows a reconstruction of the pre-explosion mountain with a black grid overlay.

Well the group compared the composition of the volcanic fragments (called tephra) that were embedded in the ground around the site to those found in the ice cores. The two samples were found to be incredibly similar in their levels of specific volcanic glass, which suggests that the fragments embedded in the ice cores came from the same clouds of volcanic ash and glass that emerged from Samalas. Other volcanoes thought to be the source of the 1257 eruption, such as Quilotoa in Ecuador, had tephra of a very different composition compared to the ice core samples.

So it would seem that the mystery of the missing 1257 eruption has been solved. Mount Samalas fits the bill perfectly to have been responsible for an event that has perplexed researchers for decades, packing the necessary punch, being made of the right stuff, and showing up just on time. But this find does raise another question: what ever happened to Pamatan, the capital city that was destroyed 756 years ago? As the paper itself suggests, it may still sit somewhere beneath the ash and rock, a “Pompeii of the Far East,” waiting to be unearthed, to be rediscovered and to show us who lived there, how they lived, and how they died.

Original article:

http://www.pnas.org/content/110/42/16742.full

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