The Tierra Blanca Joven eruption of Ilopango

The Tierra Blanca Joven (“young white earth”) eruption was the largest in El Salvador in the last 10,000 years. According to Victoria Smith and colleagues (2020), a co-ignimbrite column some 45 km high dispersed 37–82 km³ of magma (dense-rock equivalent) — 50–95 km³ in all, counting the pyroclastic density currents, which ran up to 50 km from the vent — and ash more than half a metre deep covered some 10,000 km², while a layer at least 0.5 cm thick fell over nearly 2 million km² of Central America. The eruption left the 8 × 11 km caldera now filled by Lake Ilopango.

Much of El Salvador was then inhabited by the Maya. Within about 80 km of the volcano, Smith and colleagues conclude, the land was uninhabitable for years to decades after the eruption; at Chalchuapa, 75 km away, the ash is about 20 cm thick. Farther off, in the Maya lowlands more than 450 km away, where only millimetres of ash fell, the effects appear to have been limited: the number of monuments and the population there were growing at the time. The eruption put about 14 million tonnes of sulphur into the stratosphere, more than Pinatubo in 1991, and probably caused a measurable cooling, stronger in the Southern Hemisphere.

The date was long disputed. Radiocarbon had placed the eruption somewhere between about 410 and 535 — the estimate still given in the Russian article (the English article on the lake cites both this range and 431 ± 2) — and in 2019 Robert Dull and colleagues argued for 539/540, which would have made Ilopango the source of a great sulphate spike of that year in the ice cores. In 2020 Smith and colleagues identified Ilopango ash in a precisely dated Greenland ice core and fixed the eruption at 431 ± 2, that is between 429 and 433, consistent with a radiocarbon sequence of tree rings (425–440) and with the archaeology of Chalchuapa; the English Wikipedia follows this date.