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Lecture Dec 15 – Assessing the impact of super-eruptions

Science at Cal Lecture Series

Assessing the potential impact of super‐eruptions on society and the environment

with Prof. Stephen Self

Saturday December 15, 2018 at 11:00 AM
100 Genetics and Plant Biology, UC Berkeley

Rare, but extremely large, explosive super-eruptions Magnitude 8 and above have occurred throughout geologic time. How frequent they have been, and will be, has been estimated in the range of one per 100,000 years. With the latest at 74 ka ago, human society should perhaps not be over concerned about such events. However, the most recent attempt to estimate a mean return period for Magnitude 8 events is one every 17,000 years, which puts a different slant on the future likelihood of a super-eruption occurring. A Magnitude 7 event seems to occur on average one or twice per thousand years, and a recurrence of even these presents a significant challenge for future societies.

Super-eruptions of silicic magma lead to the catastrophic formation of huge calderas, devastation of substantial regions by pyroclastic density currents or flows and their deposits, and ashfall deposits  that can cover continent-size areas. Widely dispersed fine ash means that the effects of future super-eruptions may be felt globally or at least by a whole hemisphere. The most widespread and long lasting effects are likely to derive from the volcanic gases released. These will remain for several years, promoting changes in atmospheric circulation and causing surface temperatures to fall in many regions, leading to short-term temporary reductions in light levels and severe and unseasonable weather (“volcanic winter”). However, the radiative impacts of the aerosols are not expected to be severe enough to cause major climatic changes, and, indeed, some super-eruptions may not release huge amounts of sulfur gases.

If a future super-eruption was predicted, what would, or could, society do? Major disruptions to global societal infrastructure can be expected for periods of months to years, and the cost to global financial markets will be high and sustained. Preparation for such low probability but high consequence events is difficult to imagine, yet some modest early measures can be considered. Volcanologists should refine geologic histories and ensure at least baseline monitoring of candidate volcanoes, and they should consider how they will judge the likelihood that an impending eruption will be of super eruption scale.

volcanic eruption - Stromboli, Italy


Prof. Stephen Self

Professor Stephen Self:  Steve has studied volcanic rocks in many parts of the world, concentrating on large (flood) lava effusions, explosive eruptions, and the impact of volcanism on the atmosphere.  His current research interests include mechanisms and products of flood basalt and explosive super-eruptions plus several other projects (see  He has published and lectured widely on the impact of large-scale volcanic eruptions on the environment and society, relevant to both our present and future world, and past Earth history.

Steve lives in Alameda, California, and retired in 2017 from his position as Senior Geologist/Volcanologist with the US-Nuclear Regulatory Commission.  Previously, he was Chair of Volcanology at The Open University (2001-2008) in England, UK, and a past leader of the UK Volcanic and Magmatic Studies Group.  Before 2001 he was Professor of Geology at the University of Hawai’i-Mānoa.  Steve is currently an Adjunct Professor with the Earth and Planetary Science Department at University of California – Berkeley. 

He is a Life Member of the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI, an association of IUGG) and stepped down as Vice-President of IAVCEI in 2016.  Steve is a Fellow of the American Geophysical Union, the Geological Society of America, and the Geological Society (London).

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