On April 10, 1815, Mount Tambora eruption killed at least 92000 people, that is definitely the biggest volcano eruption on modern history. Tambora eruption is the only one that has level 7 on Volcanic Explosivity Index (VEI) in modern history.
The eruption of Mt. Tambora cast a veil of ash around the world, lowering global temperatures by more than 5 degrees Fahrenheit. The result was the "year without a summer" in 1816. A foot of snow fell in Quebec City, Quebec, in June. Crops failed worldwide in what historian John Post called "the last great subsistence crisis of the Western world."
US in June, Snow everywhere
The eruption is also tangentially credited with the invention of the bicycle, as the cost of maintaining horses rose, both because of the cost of oats and the death of many horses.