The magazine “The Economist” took notice of the work of a broad team compiled by prof. Ulf Büntgen (CzechGlobe), which, using isotope analysis in combination with other techniques, have explained the cause of cold years and famine in Europe in the first half of the 9th century, known from the historical chronicles of that time. According to prof. Büntgen, the thing that is behind this temporary climate change is a massive explosion of the Icelandic Katla volcano, about which there has not yet been any records so far.
Thanks to the 2003 flood, 35 km far from the volcano the remnants of the 9th century forest were uncovered, and these proved to be an important material for the reconstruction of historical climate events. Isotope analysis of annular rings revealed double the amount of carbon radioactive isotope 14C in the annular rings of trees of a particular year, and comparison to another described historical event showed that the volcano eruption occurred in 822. It was just this explosion that caused the rupturing and melting of the glacier above the volcano and the subsequent flood “buried” the forest.
The whole article is available here