The Segara Anak caldera in Indonesia -- formed by the 1257 A.D. eruption of Samalas and now the home of Rinjani and its cone, Barujari. Image: rvrastered / Flickr. The source of one of the most enigmatic eruptions over the last 10,000 years may have been conclusively identified. An eruption that occurred in 1257 or 1258 A.D. left one of the largest climate signals in the past few thousands years, producing significant sulfate spikes in the ice caps in 1258-59 and evidence from around the world of dramatic weather shifts for years afterwards. These effects looked to be on par with Tambora in 1815, but the source of such a large climate signal has been enigmatic. How do you hide an eruption that was as large as Tambora and happened less than 1000 years ago? I tried to tackle this mystery, looking at some potential sources for this massive climate signal captured in the ice cores. There were suspects, but none of them really matched perfectly. Then, in 2012, Franck Lavigne said at an American Geophysical Union Chapman Meeting of Volcanoes and the Atmosphere that a source had been identified, but didn't reveal which volcano. I did some sleuthing and made the guess that Rinjani was the volcano that was being implicated. Since then, the mystery of the 1257-58 A.D. eruption source remained.
Map showing the location of Samalas in the Rinjani complex on Lombok, along with directions of pyroclastic flows during the 1257 A.D. eruption. Image: Lavigne and others (2013). However, the study by Franck Lavigne and a legion of others (open access PDF) that implicates the Rinjani Volcanic Complex has finally been released in PNAS. Turns out, I was both right and wrong -- the eruption was from the modern Rinjani area, but the evidence points to an ancestral volcano that Lavigne and others calls Samalas (much like Mazama precedes Crater Lake), part of Rinjani volcanic complex on Lombok (see right). The current active cone of the modern Rinjani complex is Barujari cone within the caldera, a small cinder cone within the Segara Anak caldera. Lavigne and others point to an eruption from Samalas, a volcano that would sit where the modern 6.5 by 8 kilometer caldera (see above) is now as the source of the large sulfate spike, weather phenomena in 1257-59 A.D and the caldera itself. So, what evidence points to Samalas being the culprit? Lavigne and others mapped ash deposits on Lombok and neighboring islands, and by looking at the distribution of ash (with knowledge of local wind patterns), they were able to point back to the Rinjani complex as the source of the large ash fall and pyroclastic flow units in the region. By sampling logs and other vegetation in the deposits, a minimum age of the ash and debris could be determined, which all correlate with these materials being older than the 1257-58 A.D. eruption (
* Further work by Clive Oppenheimer on the record of this eruption in the ice cores suggests that the date of the eruption should be 1257 A.D. +/- 1 year. So, I'll start calling it the 1257 A.D. eruption from here on in.
) Most interestingly, historical chronicles in Indonesia suggest a catalysmic eruption that buried the capital city of Lombok's kingdom at the time (Pamatan) before the end of the 13th century, which would time perfectly with a massive eruption of Rinjani. All this evidence is somewhat circumstantial, but Lavigne and others also break out geochemical evidence that suggests that glass shards in ice cores that correlate temporally with the 1257 eruption. Glass shards can be found in ice cores and by comparing those ash chards to material collected near the suspected volcano, you can determine if the ash is a close match compositionally. It is a little like matching fingerprints, but with volcanic ash, it is like matching partial prints from different fingers -- likely you can't say that it MUST be a certain volcano (as much magma from volcanoes that have massive eruptions is broadly similar in composition), but you can assign a likelihood. Volcanologists have spent a lot of time defining criteria for what constitutes a match between ash from ice cores (or any far away location) and source from the source. Right now, if the match is with 1-2 percent in silica and alumina and <5-10 percent for all other major elements (like Fe, Mg, Na, K, Ca), then you can be pretty confident that the distal ash and the one from the source are the same (see below). In this case, it looks like the ash sampled from polar ice cores and the ash sampled from Samalas deposits are well within those ranges, so another piece of evidence implicated this long-lost volcano.
Silica versus sodium + potassium (Na + K) for ash found in ice cores that date to ~1258-59 sulfate spike and ash collected near Samalas in Indonesia. Overall, the two ash match within defined criteria, supporting Samalas as the source of the polar ash and sulfates. Image: Lavigne and others (2013), PNAS. Put that all together, and it appears Samalas is the source of the 1257 eruption -- one that was very sulfur rich and possibly close to the size of the Tambora eruption. Looking at deposits, total volume of magma erupted close to 35-40 km^3, making it roughly a magnitude 7 (correlates to ~VEI 7) -- definitely putting it in the same class as Tambora, Crater Lake, White River, Taupo. Levigne and others estimate that the eruption produced a 20-30 km eruption plume that lasted a little less than a day, and within that day, 4-6 hours worth of an ultraplinian phase with a plume topped 40 km. It moves the eruption into the same class as that massive ultraplinian eruption at Taupo in 186 A.D. Pyroclastic flow deposits from this eruption can be traced for tens of kilometers from the vent and even at 25 km distance, they are as thick as 35 meters. All in all, this was an eruption the likes of which we have not seen since the Katmai eruption in Alaska in 1912 (yes, even dwarfing Pinatubo in 1991). What I find most remarkable that it took so long to identify the source. This is similar to one eruption I've been working on, the White River Tephra in Alaska, where a massive eruption in 803 A.D. that spread ash across much of eastern Alaska and the Yukon (and is claimed to be the largest plinian eruption of the last 10,000 years) is still not conclusively matched to a source vent. The sources of large eruptions, even in the geologically recent past, can be very mysterious, so to find where these monsters are hiding, you need to do exactly what Lavigne and others did for Samalas: careful combinations of historical, geological and atmospheric research. Now, we can examine the magmas erupted by Samalas in 1257 (and earlier) to determine why it made such a profound impact on the global weather and climate systems. The 1257 A.D. eruption has been linked to mass burials in London, the ease which kings conquered the region in Indonesia not long after the eruption, and even potentially a buried capital city. Finding the source of this eruption will allow us to starting testing to see if the hypotheses of these connections stands true with more refined ages. This also emphasizes how feet-on-the-ground geology is needed to identify the sources of more of these missing monsters, because we still have a number of monsters to slay to understand the sources of the eruptions captured in the global climate record.