Years ago I wondered why the Carolingian Empire faded after Charlemagne and then led into the Dark Ages. Then I read a book on nutrition and history. There it explained that in the 100 years after the Emperors death there were over 30 major climate disruptions that led to famine and starvation, some of which last 2 or 3 years. Strange climate caused ergot fungus on rye in northern Europe, and wheat rust in southern Europe played counterpart. Charlemagne died in 814. Mt. Churchill blew in 843, so no doubt was one of the impactors. I will look for others tomorrow.
If you read the article, the “blanket of ash” was vanishingly thin. It is unlikely to have had any significant impact at all in Europe, other than some pretty sunsets. David Key tried to attribute the 6th c “dark ages” onset to a volcano eruption in SE Asia I think it was. That would be even less destructive, unless an even bigger eruption (and much bigger) had taken place, and gone unremarked in, for example, annalists in India and China.