SUPER-ERUPTIONS: EFFECTS ON CLIMATE AND LIFE OF THE LARGEST EXPLOSIVE ERUPTIONS

Volcanic super-eruptions that produce more than 1,000 km3 of ejected material and more than 1,000 Mt of stratospheric aerosols and sub-micron dust may be capable of creating global cooling and widespread ecological disturbances, including a severe setback or crash of civilization. The Toba eruption (~73,000 yr BP in Indonesia), the largest known explosive eruption of the last few hundred thousand years, is predicted to have caused a 'volcanic winter' with global cooling of 3 to 5 degrees C, and up to ~15 to 20 degrees C in some regions. Botanical studies suggest that reduction of growing-season temperatures by ~10 degrees C can severely damage temperate forests. Cold-sensitive tropical vegetation might suffer complete above-ground destruction. These results suggest a global ecological crisis, with reductions in standing crops of plants and animals in many regions. Evidence for these abrupt environmental changes may be detectable in high-resolution climate records.

Human genetic studies indicate that prior to ~70,000 yr ago the human population suffered a severe bottleneck (3,000 or less individuals), followed by rapid population increases, technological innovations, and migration out of Africa. The predicted environmental effects of Toba lend support to a possible connection between the super-eruption and the population bottleneck, and suggest that similar bottlenecks in other organisms might be expected at about the same time.

Super-eruptions of similar magnitude are estimated to occur on average about every 100,000 years or so, which may be considerably more frequent than impacts by small asteroids and comets that could cause the same level of climatic disturbance. Super-volcanism might provide an ultimate limit on the longevity of technological civilizations. If the lifetime of civilizations were limited to less than 100,000 years by volcanism, then the number of communicative civilizations in the Galaxy might be less than 1 per 10 million stars.