European Middle Ages were an extended period of fluctuating but mostly above-average warm temperatures that by the tenth century had melted the ice sheet of the Arctic Ocean and brought about Viking marine exploration of, and temporary settlement on the eastern shores of North America. Medieval warm climate was punctuated by two short, but extremely cold events. The first was the cold event of 535–6, possibly due to a volcanic catastrophe in the tropics that yielded extensive atmospheric dust veil, followed by a major crop failure through Europe, North Africa and the Middle East, and a subsequent terrifying pandemic of the years 541–2, the Plague of Justinian. The second cold event coincided with a prolonged series of major volcanic eruptions on the Southern Hemisphere during 1315–1322. Extensive crop failure during the years 1315–1317 had led, at the same time, to the Great Famine throughout much of Europe.