Introduction

Right-hand image: The beginning of the Mount Pinatubo eruption, June 12, 1991, photographed from Clarke Air Base, Philippines. The huge eruption column of ash and gas is rising to heights in excess of 20 km into the atmosphere [USAF Photograph]. This is the largest volcanic eruption for which we have photographs and full documentation, yet its size was minuscule compared to super-eruptions.

There are certain natural events which, as a consequence of their enormous size and catastrophic energy release, can have major adverse global effects, may seriously threaten the stability of the world economy and order, and could well threaten the lives of billions of people.

Impacts of asteroids and comets (“Near Earth Objects” or NEOs), and eruptions from super-volcanoes are the two prime examples of such potentially disastrous natural events. NEOs have received much recent publicity through Hollywood movies and these have helped prompt an investigation instigated by the UK Minister of Science, resulting in a report on potentially hazardous NEOs that was finally presented to the UK Government in September 2000. By contrast, volcanic hazards on a global scale have not (until recently) received much attention outside specialist scientific circles.

Such catastrophic eruptions are rare, and so their probability of occurrence in terms of a human life span is small. When viewed over longer periods of time however, such eruptions are surprisingly common, and on the time scales of civilisations (hundreds to thousands of years) become quite likely. It is inevitable that huge eruptions with potentially catastrophic consequences for humanity will happen again on Earth.

In this report we consider the nature and size-range of super-eruptions, estimate how often they occur, identify parts of the world where dormant super-volcanoes are located, and assess the environmental impact of these eruptions with particular emphasis on climate. We stress that not all “super-volcanoes” have the potential to produce super-eruptions.

The largest volcanic edifices such as Mauna Loa and Mauna Kea on the island of Hawaii, the highest and widest volcanoes on Earth (some 200 km across and over 12 km tall), will never produce a super-eruption. Part of the problem that geologists face is that the source vents of super-eruptions are often hard to locate and many volcanoes that have the potential for producing future super-eruptions still go unrecognized.

Right: Mount Pinatubo’s setting in southeastern Luzon island is shown on this SPOT satellite image captured in 1996 – Pinatubo’s lake-filled summit caldera is the dark circular spot, seen through a ring of white clouds in the top left hand corner of the picture. The area devastated by pyroclastic and mudflows is the grey region around the volcano. Pinatubo is located close to an area of still-active but slumbering super-volcanoes. In the satellite image, SW of Pinatubo, across Manila Bay (centre), lie two large lakes (dark) – both were sites of little known super-eruptions that occurred within the past 1-2 million years. Taal, a 30-km-diameter southern lake with an island in the centre, has had frequent historic eruptions and is an active super-volcano that has the capability to produce another one. About 2 million people live within 20 km of Lake Taal. Manila, with a population in excess of 10 million, is the dark grey area on east shore of Manila Bay. Next to Manila lies Laguna de Bay, the central part of which is the source of extensive volcanic deposits, suggesting that Laguna de Bay might also a super-volcano.

Humans and their civilisation are very vulnerable indeed to unexpected natural events with global impact. The dramatic success of the human species has placed enormous stress on the Earth’s ecology, with consequences familiar to all – like global warming and falling biodiversity. Key factors seem to be population explosion (mostly over the last two centuries) and unprecedented advances in science and technology that have allowed humans to utilise Earth resources on a huge scale.

In the last 200 years the use of hydrocarbons has released enormous quantities of carbon dioxide into the atmosphere, changing its composition at a rate as fast as at any known time in Earth history. Some artificial chemicals have harmful effects on the ozone layer, which protects life from damaging ultraviolet light from the Sun.

The economic, political and social institutions of humanity have also advanced dramatically, even though the proportion of the world's population who benefit greatly from these advances remains relatively small. As stock market crashes and terrorist outrages show, even the economic institutions that help deliver great wealth and well being to many people, can be vulnerable. Such institutions are sustained as much by perceptions of progress and advance as by the underlying natural and human resources that in reality underpin wealth creation.

The United Kingdom is located away from the Earth’s major destructive plate boundaries, and consequently does not suffer directly from the effects of large-scale explosive volcanism. However, two of the UK's Overseas Territories (Montserrat and Tristan de Cunha) are active volcanoes. Moreover, the UK lies downwind from volcanoes that have caused major eruptions in Iceland, so the UK should have a direct interest in the primary effects of volcanic activity. As a member of the European Community, the UK would be vulnerable economically to the effects of super-eruptions in Italy or Greece.

Lefthand image: the Laki fissure, Iceland.

“There seems to be a region higher in the air over all countries, where it is always winter, where frost exists continually, since, in the midst of summer on the surface of the earth, ice falls of ten from above in the form of hail... During several of the summer months of the year 1783, when the effect of the sun’s rays to heat the earth in these northern regions should have been greatest, there existed a constant fog overall all Europe and great part of North America. This fog was of a permanent nature; it was dry, and the rays of the sun seemed to have little effect towards dissipating it, as they easily do a moist fog, arising from water..."The cause of this universal fog is not yet ascertained,…: or whether it was the vast quantity of smoke, long continuing to issue during the summer from Hecla in Iceland, or that other volcano…..”

Extracts from Meterological Imaginations and Conjectures, by Benjamin Franklin, LL.D., Fellow R. Soc., and Acad. Reg. Sci. Paris Soc. etc., Communicated by Dr. Percival Read December 22, 1784, to the Manchester and Liverpool Philosophical Society. Franklin was in Paris, France, in the summer of 1783 as U.S. Ambassador to France.

One impact of the Laki gas and aerosols over the U.K. during 1783 was to increase deaths, possibly due to respiratory disorders. Maps of the time showing the distribution of English parishes experiencing “Crisis Mortality” record much-above-average numbers of deaths per month during the Laki fissure eruption.

The continuing eruption of the Soufrière Hills volcano on Montserrat encouraged a partnership between the geoscience community and Government to address the problems caused. However, the UK is an integral part of the global community, with influence beyond its size due to its recent history and position as one of the world’s wealthiest countries. As we will demonstrate, a huge eruption elsewhere in Europe, or in New Zealand, Indonesia, or Alaska could have serious consequences for the UK. Another large-volume lava eruption in Iceland, with its accompanying major atmospheric pollution (as happened in 1783-84) would create major environmental problems for the whole of the Northern Hemisphere, as well as serious disruption to commercial air traffic across the Atlantic for several years.

Denser parts of the eruption column collapse back to the ground around the volcano, forming rapid and deadly pyroclastic flows. Such flows can travel up to 100 kilometres in super-eruptions, as revealed by the deposits, at speeds up to 100 metres per second (360 km per hr or 250 m.p.h.) or faster. This photograph shows small pyroclastic flows overrunning farmland and dwellings on the island of Montserrat in July 1997. (Photo courtesy of Eliza Calder.)

Link to next section, Super-volcanoes and super-eruptions