From the Daily Mail:
Topping the list was the eruption at Samalas, Indonesia in 1257, followed by the Kuwae event of 1452, and Tambora, also in Indonesia, in 1815.
Although the study plots earlier events, the researchers don't know exactly what these explosions were.
Based on the timeline, however, it's possible to estimate what these events may have been.
For example, the fourth most powerful eruption took place in around 674 AD, which could have been the Pago event in Bismarck or the eastern Alaskan eruption in Mount Churchill believed to have take place around 700 AD.
Fifth and sixth place occurred between 531 to 566 AD and could be the Rabaul Caldera explosions in Papua New Guinea that is thought to have took place around 535 onwards.
The seventh most powerful explosion happened shortly after Samalas, and may have been Quilatoa in the Andes in 1280.
Based on the 450 AD date of the eighth place event suggests it was Ilopango in Central America, ninth appears to have been the Grímsvötn and Laki eruptions in Iceland around 1785.
While tenth place happened shortly before Samalas and could have been an earlier eruption of Mount Rinjani, Indonesia.