Scientists uncovered six shards of glass flying 5,000 kilometers south. Buried beneath the 279-meter Antarctic ice sheet for nearly 2,000 years, these rocks preserved traces of a catastrophic explosion. But none of them revealed the real issue: where exactly the explosion occurred. The seventh fragment, formed by the eruption of the same volcano, helped the team determine their origin and pinpoint the exact date of the event.

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New Zealand’s Taupo volcano has been active for about 300,000 years, but the timing of the last major eruption (one of the largest and most energetic eruptions on Earth in the last 5,000 years) is surprisingly difficult to determine.

• Historical records of ancient Rome and China describe recent events 186 AD, testifies to a distant volcanic eruption darkening the sky half a world away: The Sun rose “blood-red and devoid of light” and “the sky burst into flames,” two writers of the time wrote. However, no matter how vivid these explanations are, they do not coincide with geological data.
• Sulfur deposits in ice cores are a common signal of volcanic activity, and ice cores from Antarctica and Greenland shift the time of Taupo’s eruption to about 1,000 years ago. 230 AD, plus or minus a few decades. But sulfur is emitted from volcanoes around the world, so it’s not as accurate as scientists would like.
• Radiocarbon dating of wooden logs buried in hot volcanic flows after the Taupo eruption pinpointed the approximate time of the eruption. 232 (1790 years ago). The fruits and seeds on these preserved trees, as well as the absence of darker trees on the outside, suggest that the volcano erupted in late summer or autumn.

As you can see, the year of the explosion was still in dispute. But a recent discovery leads to new regulations. Scientists examined a 764-meter-long ice core extracted from the Ross Ice Sheet in West Antarctica. It contains 83,000 years of climate information.

Researchers found seven glass fragments 10 to 20 microns long, formed from the granite-like mineral rhyolite, at a depth of 279 meters. Their geochemical composition matched other samples from the Taupo eruption collected in New Zealand.

Scanning electron microscope image of glass shards / Photo: Stephen Piva

One piece in particular stood out: It completely matched volcanic glass from an earlier volcanic eruption called Ōruanui, 25,600 years ago.

While ice core dating still has some margin of error, the researchers say their findings provide an estimate of the age of the buried logs, which were likely destroyed instantly when engulfed by a hot explosion. Taupo volcano.