The 1458 rhyolite glass in Antarctic ice: what kind of volcano made it
Six rhyolite shards from the Vostok core and seven from the South Pole core (two measured with the precise microprobe). Average glass: about 74 to 76 percent silica, 1.6 to 2.0 iron oxide, 1.2 to 1.4 calcium oxide, 4.7 to 4.9 sodium oxide, 2.6 to 2.9 potassium oxide.
Our comparison, 24 October 2026, using the 2025 study's reference set plus Taupo and Antarctic glass from Piva et al. 2023 (script: scripts/glass_compare_1458.py). Similarity scores, where 1.0 is identical and about 0.95 is usually needed to call it the same volcano: - Reclus, the published candidate: 0.91 against the microprobe shards, 0.87 and 0.85 against the others. - Taupo-type New Zealand rhyolite (Barker 2015 reference glass): 0.90, 0.88, 0.92. - A composite of southern South American tephras: 0.90, 0.88, 0.94. - Kermadec arc (Raoul Island), Antarctic volcanoes (Mt Melbourne, Mt Berlin), Auckland, Taranaki: far lower.
What it means: nothing reaches 0.95, so no volcano is identified. Reclus is not chemically special; Taupo-type and other southern Andean glass fit as well. Potassium rules out two regions: Kermadec and Tonga arc volcanoes make low-potassium rock (Raoul about 0.6 percent) and Antarctic volcanoes make trachyte, while the 1458 glass has about 2.9 percent, typical of volcanoes on continental crust. That leaves the southern Andes or New Zealand's Taupo zone. New Zealand's detailed ash record has no rhyolite eruption after Kaharoa in 1314, which points to the Patagonian and Austral Andes, where icefield volcanoes like Lautaro, Viedma, Aguilera and Monte Burney can erupt unseen.
Caveats: very few shards, sodium readings depend on the instrument, and a six-oxide similarity score is a coarse test. Specialists would use trace elements.
Second comparison, same day, against the whole southern Andes tephra database (BOOM, 39 eruptions with enough rhyolite analyses; script: scripts/boom_compare_1458.py). Best average scores: Chaitén 0.90, Sollipulli 0.89, Quetrupillán 0.88, Grupo Antillanca 0.88, Reclus 0.88, Lautaro 0.86, Monte Burney 0.85; Hudson and Aguilera 0.79. No eruption reaches 0.95, and none of the database eruptions dated to roughly 1350 to 1550 fits: most produced no rhyolite at all, and the two that did (Puyehue-Cordón Caulle's Mil Hojas, and an unidentified lake-core ash dated about 470 radiocarbon years) carry about twice the iron of the 1458 glass and score 0.79 to 0.86.
So the 1458 rhyolite does not match any known, studied eruption anywhere we can check: not the Andes, not New Zealand, not the Kermadecs, not Antarctica. That strengthens the 2025 study's word 'undocumented'. Its fingerprint is sodium-rich (about 4.8 percent), medium potassium (about 2.7) and low iron (about 1.6), with the microprobe's small beam making a sodium loss unlikely to explain the high sodium.