June 30 (UPI) -- Scientists have narrowed the date range for a 9th century volcanic eruption in Iceland to within a span of just a few months. It's the oldest volcanic eruption among the northern latitudes to be precisely dated.
The research -- detailed in the journal Geology -- suggests Iceland's Katla volcano erupted sometime between late 822 AD and early 823 AD, prior to the arrival of permanent settlers at the end of the 9th century.
Scientists used a variety of data to inform their dating efforts, including geologic observations, as well as climate and historical records. Analysis of Icelandic tree rings proved most helpful.
Tree rings can offer a detailed record of a region's climatic history, as well was offer insights into the interactions between humans and the surrounding environment.
"In our work, we're trying to reconstruct past natural temperature and precipitation variability from tree rings -- trying to reveal when it was cold and wet or warm and dry for instance," lead researcher Ulf Buntgen, a professor of geography at the University of Cambridge, said in a news release. "We're also interested in detecting and understanding key drivers of the Earth's climate dynamics and their possible linkages with changes in human history."
Today, trees are rare in Iceland. But scientists believe the region was once blanketed in forest. Researchers analyzed the rings in stumps preserved in a prehistoric forest. Until 2003, the Drumbabót forest was buried by sediment, but a spring flood exposed the ancient stumps. Today, Drumbabót is the most well-preserved prehistoric forest in Iceland.
Rings in Drumbabót trees have previously helped scientists pinpoint the date of a massive solar flare, which in 775 BC flooded the atmosphere with radiocarbon -- radiocarbon that was absorbed by Iceland's ancient forests. Researchers were able to count the rings grown since 775 BC to determine when trees perished in the massive Katla eruption.
Researchers cross-referenced and confirmed their tree ring findings with analysis of ash deposits and ice cores. Historical records in Europe and Asia reference a cold spell in the years following the 9th century eruption, which scientists suggest was triggered by a flood of volcanic ash into the atmosphere.
"It was a happy coincidence that we were able to use all these different archives and techniques to date this eruption," said Buntgen. "Data and methods we are using are constantly getting better, and by building more links with the humanities, we can see the real effects volcanoes have on human society."