Volcanic eruptions as we know them today have a place in our lore as terrifyingly powerful acts of nature. Gods have been made of them and cultural touchstones built around them. They remain a disaster that we can do nothing to prevent and can only try to avoid. That said, the volcanoes of human recorded history have literally nothing on the volcanoes of earth's past. They are tiny pimples in comparison to the planet-changing, climate-destroying, extinction-event-triggering behemoths we have evidence of in the geologic record. Geologists categorize these monsters as Mega Colossal and the public calls them supervolcanoes. This list captures some of the largest, most powerful explosive eruptions on the planet, not necessarily the largest or the most volume of ejecta. The Deccan traps are not on this list, for example, because they were not explosive in nature despite the fact they erupted for longer and covered more landmass than some of the explosive events.
These eruptions are all classified as VEI 8, the most cataclysmic you can get. Explosive volcanic eruptions are classified using the Volcanic Explosivity Index, or VEI. It is a logarithmic scale, which means that an increase of one in VEI number is equivalent to a tenfold increase in volume of erupted material. The VEI scale does not distinguish between different types of volcanic ejecta ( ash, lava, ignimbrite), only power. On this scale, VEI 8 eruptions are so cataclysmic that they often form deep circular calderas rather than cones because the downward withdrawal of magma causes the overlying rock mass to collapse into the empty magma chamber beneath it. To give a sense of the VEI scale, St. Helens was a 5. This is a list of the largest, most earth-shaking events in the planet's history - best as we can tell. Let's all hope that there are no new VEI 8s to add to this list any time soon.
The boundaries in the imagery with each entry are as approximate as can be determined from the geologic record.