Medieval volcanic eruptions caused icebergs in southwestern Black Sea: Study

GENEVA

Volcanic eruptions in Iceland in the year AD 763 resulted in icebergs, among other objects, forming in the region around present-day Istanbul, according to the leading research centers in Switzerland and Austria.

The study, published Monday on the Swiss University of Bern and the Austrian Academy of Sciences (OAW) website also concludes that the winter of AD 763 was so cold that parts of the Black Sea, north of what was then the city of Constantinople, were covered in ice.

According to researchers, new studies contradict previously held assumptions that there had been a volcanic dormant phase during that era.

Scientists analyzed traces of volcanic ash too small for the human eye to see, known as cryptotephra, for the study.

Using ice cores from Greenland, they conducted high-resolution analyses of chemical indicators of volcanic eruptions.

The study concluded that there was a prolonged episode of volcanic sulphur dioxide emissions between AD 751 and 940, mainly due to the volcanic eruptions in Iceland.

Scientists say the series began with the eruptions of the Katla volcano in AD 751-763. Katla, still one of the most active volcanoes in Iceland, lies in the northern Atlantic island country's southern region, beneath the glacier shield of Myrdalsjokull.

According to the study, the eruptions were so strong that they sometimes extended into the stratosphere layer of the atmosphere, at an altitude of 15-50 kilometers (9.3-31 miles), and coincided with the extremely cold winter in Europe. The study shows extreme climate fluctuations also affected early medieval society.

"The historical sources not only describe that it was very cold, but also that the extreme temperatures caused animals to die and crops to freeze. People not only suffered immediate hardship, but were also deeply shaken on various levels," wrote Byzantine researcher Johannes Preiser-Kapeller, who contributed to the study by OAW.