Dendrochronologists shed new light on Thera volcanic eruption date
Several thousand years ago, around 1500 B.C., one of the largest volcanic events in recorded history shook the world. The Minoan eruption of Thera, also known as the Late Bronze Age eruption, caused widespread devastation and triggered a number of earthquakes and tsunamis. The scale of the eruption was such that its tephra (material produced by volcanic events) can still be found throughout the Eastern Mediterranean. The tephra created by this eruption is sufficiently unique that experts are able to identify the sedimentary layers that it forms across a wide geographical range. This is known as a ‘marker horizon’, and many other world events are considered and arranged relative to the time of the Minoan eruption. The exact date of the event is therefore of great significance and is strongly debated by archaeologists.
Charlotte Pearson, an assistant professor of dendrochronology and anthropology from the University of Arizona, recently discovered an unusual ring in a cross-section of a tree found in an ancient tomb in Gordion, Turkey that may provide new evidence of the date of the Late Bronze Age eruption, right down to the year.
Dendrochronology is the study of tree rings, the layers of growth that trees create each year. On a basic level, the number of rings found in the cross section of a tree trunk tells us how old a tree is, but they can provide a huge amount more information. The way that the rings are created changes depending on a range of climatic conditions, which can provide information on things like temperature, soil conditions and rainfall. In this case, the researchers have suggested that the unusual tree ring may represent a possible date for the Minoan eruption of Thera.
The researchers used a technique known as carbon dating to analyse the radioactive carbon isotope carbon-14 within the tree ring. During their growth, trees capture carbon-14 and sequester it within their growth rings. Carbon-14 levels in the atmosphere vary year on year and can be measured very precisely, making it possible to accurately pinpoint the age of a certain tree ring against other sources of carbon-14 with the same date.
In this case, the researchers identified that the carbon-14 in the unusual tree ring matched that that has been previously found in other calendar-dated tree ring sequences. This provided them with a window of time in which the unusual ring should fit. They then compared the ring in the Gordion tree with those found in bristlecone pines from western North America. These trees are known to have existed at the same time as the Gordion tree, and their rings have been previously calendar dated.
Volcanic eruptions cause bristlecone pines to freeze during their growing season, which produces a ‘frost ring’. This scarring enabled the researchers to confirm that the unusual growth ring may have corresponded to a volcanic eruption. The final stage in the analysis involved scanning the wood for chemical anomalies during the time period that the Minoan eruption is known to have happened, which highlighted a slight fluctuation in the levels of calcium present in the unusual tree ring.
Based on these findings, the researchers have suggested that the Minoan eruption of Thera may have happened in the year 1560 B.C. They make it clear that there are a number of other possible factors that might have led to the creation of the unusual tree ring identified by Charlotte Pearson, including wildfire or an entirely different volcanic event, but given that it coincides with the known date range for the Minoan eruption of Thera and exactly matches the evidence of a huge volcanic event found in the North American bristlecone pines, these findings may represent a major step in the right direction.
For more information, visit the press release issued by the University of Arizona.
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