Every now and again, Earth suffers from tremendous explosive volcanic eruptions, much bigger than those witnessed in modern times.  Although the return period for such events is long, perhaps every 10-100,000 years depending on the size, it is statistically more likely that Earth will next experience a large super-eruption (defined here as one producing more than ~ 450 km3 of rhyolitic magma) than a large meteorite impact.  Depending on where the volcano is located, the effects of such an event will be felt worldwide, or at least by a whole hemisphere, and the associated phenomena will spread quickly within a couple of weeks.  These effects include temporary darkness with severe reduction in amounts of solar radiation reaching the surface, unseasonal cooling and warming coupled with strange weather patterns, and, of course, widespread ash fallout.  Major disruptions of services that our society depends upon can be expected for periods of months, to even a few years.

Past explosive super-eruptions, including the latest very large one, the Toba event in Sumatra 74,000 years ago, will be discussed, as well as some of the impacts of such events.  Another type of super-eruption has also affected our world, but at times in the distant past.  These are flood basalt events, vast lava flow-producing eruptions that have occurred in 1-2 million-year-long episodes throughout Earth history.  Such events have occurred every few tens of million-years or so and seem somehow to be related to mass extinctions of life on Earth.  Possible linkages between these two time-series of events will also be discussed.

The environmental effects of the largest historic eruptions, such as Tambora and Laki, can be usefully used as small-scale analogs for the impact of much greater volcanic events.  The Laki (Iceland) eruption, which can be viewed as a small-scale flood basalt analog, took place at a high latitude and impacted the whole northern part of the North Hemisphere for several years.  We must ask: Is our global society ready for the next super-eruption?