Source of the great A.D. 1257 mystery eruption unveiled, Samalas volcano, Rinjani Volcanic Complex, Indonesia

Abstract

Polar ice core records attest to a colossal volcanic eruption that took place ca. A.D. 1257 or 1258, most probably in the tropics. Estimates based on sulfate deposition in these records suggest that it yielded the largest volcanic sulfur release to the stratosphere of the past 7,000 y. Tree rings, medieval chronicles, and computational models corroborate the expected worldwide atmospheric and climatic effects of this eruption. However, until now there has been no convincing candidate for the mid-13th century "mystery eruption." Drawing upon compelling evidence from stratigraphic and geomorphic data, physical volcanology, radiocarbon dating, tephra geochemistry, and chronicles, we argue the source of this long-sought eruption is the Samalas volcano, adjacent to Mount Rinjani on Lombok Island, Indonesia. At least 40 km(3) (dense-rock equivalent) of tephra were deposited and the eruption column reached an altitude of up to 43 km. Three principal pumice fallout deposits mantle the region and thick pyroclastic flow deposits are found at the coast, 25 km from source. With an estimated magnitude of 7, this event ranks among the largest Holocene explosive eruptions. Radiocarbon dates on charcoal are consistent with a mid-13th century eruption. In addition, glass geochemistry of the associated pumice deposits matches that of shards found in both Arctic and Antarctic ice cores, providing compelling evidence to link the prominent A.D. 1258/1259 ice core sulfate spike to Samalas. We further constrain the timing of the mystery eruption based on tephra dispersal and historical records, suggesting it occurred between May and October A.D. 1257.

Keywords: archaeology; caldera; climate; ultraplinian; volcanism.

Fig. 1.

Distribution of PDCs from the Samalas eruption and location of charcoal samples used for radiocarbon dating.

Fig. 2.

Samalas caldera and Segara Anak. (A) Photograph of the present caldera viewed from the east (photo: Zulz, “Gunung Baru” June 26, 2006 via Flickr, Creative Commons License). (B) Present (shaded tones surface) and preexplosion reconstructed topography (black grid). We assume that a caldera was absent before the mid-13th century eruption, because no other large Plinian eruption has been identified.

Fig. 3.

Isopach maps for Samalas plinian and phreatoplinian fall deposits. (A) Samalas F1 compared with the F4 Plinian fall unit of Tambora A.D. 1815 (20, 21). (B) Samalas F2 Phreatoplinian fall unit. (C) Samalas F3 Plinian fall unit. Isopachs were mapped for the F1, F2, and F3, from 44, 22, and 18 thickness measurements in the field, respectively. Interpolation of the data using a multiquadratic radial model was the first step in constructing the final isopach maps. Although much less widespread than the F1 unit, the distributions of the F2 and F3 units are both broader than the main Plinian fall unit of Tambora 1815.

Fig. 4.

Radiocarbon and calibrated ages of the charcoal samples from the Samalas pyroclastic density current deposits using OxCal 4.2.2 and IntCal 09 (32, 33). Although some ages are older, none is younger than A.D. 1257 (at 95% confidence level). Based on this model, the Samalas eruption cannot be correlated with ice-core sulfate anomalies at A.D. 1275 and A.D. 1284 (2), which are clearly too young for our A.D. 1257 age model. This interpretation is consistent with written sources as discussed in the text.

Fig. 5.

Geochemistry of matrix glass [total alkalis vs. silica (TAS) diagram] sampled in pyroclastic fall deposits of the Samalas eruption, compared with the reported composition (13) of glass shards found in polar ice cores for the mid-13th century mystery eruption (mean ± 1σ).