Can volcanic eruptions devastate entire continents – with poisonous gas for example?

Summary:  The recent eruption of Eyjafjallajokull in Iceland has prompted increasingly fevered discussion about the danger of a future eruption — perhaps by Eyjafjallajokull’s sister, Katla.  Might an eruption expel volcanic gases that poison much of Europe?  Just like Laki did in 1783-84.   Or not.  The stories have grown as they circulate around the Internet, exaggerated tales breeding fear of the future.  But their basis in fact is almost non-existent.

From “‘The end is nigh’? Social and environmental responses to volcanic gas pollution”, John Grattan, Mark Brayshay and Ruud T.E. Schüttenhelm, in Natural Disasters and Cultural Change, edited by Robin Torrence and John Grattan (2002).  Citations have been removed.

Introduction

This chapter revisits themes that occur several times in this volume: that catastrophic events may be invisible in the archaeological record; major environmental trauma need not have a permanent impact on the cultures affected; and we can only understand the nature of events and cultural response by adopting the widest possible research framework. It is clear from earlier chapters that these concerns operate at the level of specific sites; here we explore these issues on a continental scale.

This chapter presents compelling evidence to suggest that toxic gases emitted in a volcanic eruption may be transported over great distances and deposited in sufficient concentration to have a severe impact on environments and perhaps cultures in areas far removed from any apparent volcanic threat. This research has implications not only for the better understanding of the relationship between volcanic eruptions and the archaeological record, but also for the impact volcanic eruptions may have on contemporary human societies and environments.

Consideration of the interaction of volcanic eruptions and human society has generally focused on the perilous situation of those living within sight of the volcano’s slopes. True, passing reference may be made to the natural fertility of volcanic soils, but most writers will move swiftly on to the dramatic hazards posed to human society by lava flows, lahars, pyroclastic flows, blast and ash falls. … In the light of such obvious perils few authors pause to debate the potential hazard posed by volcanic gases such as sulphur, ammonia and fluorine; yet in Iceland in AD 1783, while no one was directly killed by the vast lava flows of the Laki Fissure eruption, a quarter of the island’s human population perished following the eruption. These deaths were the consequence of the environmental impact of the volcanic gases emitted, the destruction of crops and grazing, the deaths of nearly 75% of the island’s livestock and the subsequent famine and disease .

Where archaeologists and palaeoenvironmentalists have proposed the eruption of a distant volcano as the cause of cultural change or environmental stress, they have frequently invoked volcanically generated climate change as the mechanism. However, volcanically induced climate change has been shown to be on a comparatively minor scale and no eruption of the past 3,000 years has reduced hemispheric temperature by more than 1 °C, which is within normal fluctuation and hardly of itself likely to bring about long-lasting cultural or environmental change.

In historical times, where poor weather has been coincident with volcanic eruptions and demonstrated social and environmental stress, pre-existing social, cultural, economic, environmental and climatic trends have been in evidence and it is the combination of these that is significant, not the remote influence of a distant volcanic eruption. Where these cannot be identified in the archaeological record, volcanogenic climate change is a theoretical tool which must be used with caution. Even the palaeoenvironmental record is fraught with ambiguity: Blackford et al. (1992) presented an initially convincing correlation between the Hekla tephra fall and the pine decline in Scotland, but this was not observed elsewhere in northern Scotland or further afield in Ireland. These considerations lead one to consider whether volcanic eruptions exert an unambiguous influence on distant cultures and environments at all! A detailed analysis of the impact of an Icelandic volcanic eruption upon European environment and society in historical times may answer this question.

The social and environmental impacts of the Laki Fissure eruption upon Britain and the mainland of Europe in 1783 were profound and illustrate a mechanism by which distant volcanic eruptions may influence distant environments and cultures by the eruption of mainly acid gases into the troposphere. The clearest evidence to date of this phenomenon is to be found in documentary records made in Europe between June and August 1783, some of which have been reviewed by other scholars. This was a period that coincided with the early eruptive phases of the Laki Fissure eruption in Iceland.

In many private journals, letters, scientific papers, newspaper articles and even in poetry, frequent references were made to the worrying presence of a ‘dry fog’, its impact on human health, the strange and often damaging environmental phenomena associated with it and the fear of Armageddon which this fog instilled in many parts of the community. Taken together, these documents demonstrate that toxic volatile gases emitted during volcanic eruptions may exert an influence upon distant peoples and environments in prehistoric and historic times. A selection of these documents is presented and discussed below.

In the summer of 1783 many writers recorded the ‘dry fog’ across large areas of Europe from Aberdeen to Naples and even across the Mediterranean to Malta and Tripoli. This dry fog was formed from the gaseous emissions of the Laki Fissure eruption in Iceland, which had been transported through the atmosphere by air circulation patterns and concentrated near the earth’s surface.

Sulphur gas emissions from the Laki Fissure eruption were amongst the greatest of the Holocene and it is thought that 60% of the c. 90-190 million tons of sulphur emitted by this event were discharged into the troposphere.

The meteorological research of Kington (1980, 1988) describes the atmospheric conditions that may have led to the concentration of volcanic gases in the air over Europe. From late June through most of July 1783 a relatively stable high-pressure air cell was situated over Europe, and it was during this period that most of the dry fogs and associated phenomena described below were noted.

The next section gives excerpts of reports from Britain, France, Germany, Holland, Italy, Switzerland, and North Africa.  Effects on flora, fauna, and people.  Social responses to the dry fog.  Composition of the dry fog.

Discussion

The events of 1783 exhibit all the criteria of an environmental forcing mechanism useful to archaeologists; one can observe strange meteorological phenomena, the blighting of crops and other plants, human illness and death, all of which prompted fear of God and some degree of social unease.  All of these were caused by the eruption of a remote volcano of which, in the summer of 1783, no European chronicler was aware.

The construction of a catastrophic model based on the events of 1783 is a clear, attractive and convenient option: a distant volcano erupts, noxious gases arrive from the heavens and kill crops and people, the culture decides the gods are against them, packs their bags and leaves, or are so weakened that their unaffected neighbours take the opportunity to pay off some old scores! Such a model is certainly more sustainable than those that attempt to invoke extreme climatic change generated by volcanic eruptions as the cause of sudden change in the archaeological record.

As shown above, the largest eruptions of the Holocene did not have a massive or long-lived impact on climate, and any climate change caused is unlikely to have lasted long enough to bring about cultural change identifiable in the archaeological record.  Where volcanic eruptions, cultural stress and poor climate do occur together, it is important to establish the context of the events; the climatic and social trends, and the pre-existing social, economic and environmental stresses that may have been in operation.

However, a hypothesis that used the events of 1783 to support the suggestion of catastrophic change induced by volcanogenic air pollution in the archaeological record is not immune from these contextual considerations and should be constructed with extreme caution. This can be illustrated when we consider the events of the year dispassionately.

  1. Despite the descriptions of crop destruction in many parts of Europe, there were no agricultural crises; in fact rather the opposite was the case, as high temperatures and ample rainfall induced a bumper crop in many areas.
  2. While some fragments of society clearly saw the hand of the supernatural in these events, community leaders did not, and took steps to calm the populace; the role of community leaders in archaeological contexts would be equally important.
  3. Illness and mortality induced by the poor air quality was patchy, and any alarm generated appears to have been entirely local. It may also be telling, that, despite the continental scale of the event and the impact that the dry fog had at the time, there is no evidence that this event entered folk memory to be remembered as a time of stress or hazard.

… That an event of this scale was effectively forgotten suggests that we must use such material with caution. It is clearly dangerous to infer from bad news reported, even from a wide number of locations, that conditions were terrible everywhere. This problem is illustrated in a recent paper, which examines very detailed and plausible descriptions of a volcanic eruption in central Germany in the eighteenth century. The ‘eruption’ was set at the Gleichberg, a mountain now recognised to have been a volcano — but during the Tertiary. While this eruption, the explosions, smoking and fleeing people were reported around Europe, there are no records of the event amongst the communities who actually lived within sight and sound of the eruption. The reports of the eruption are clearly a complex and plausible hoax, perpetrated for unknown reasons. However, the eighteenth-century eruption of the Gleichberg was falsifiable because of its setting in recent history; had this event occurred in ancient times and been reported by a Roman historian we would undoubtedly have accepted the account as true!

That the events of 1783 had no obvious effect on settlement or society also indicates that we must use caution when interpreting and extrapolating catastrophes from fragments of ancient text, or folklore. The survival of a fragment of text from Swinden or Brugmans (cited above) for a few thousand years, coupled with some limited knowledge of the French Revolution and the archaeological identification of destruction layers, perhaps from the Napoleonic Wars, could all too easily be linked together into a grand theory of ecological catastrophe, social breakdown and war — yet we know that these are not linked. How securely then can we link the eruption of Hekla in the second millennium BC with the settlement abandonment in northern Scotland, the construction of defensive structures around Europe, the movement of the sea peoples around the Mediterranean world and the destruction of the city of Ugarit in the Levant? Yet this and similar arguments can be found in the archaeological literature.

… It is clear from the material presented in this paper that toxic volatile volcanic gases emitted in volcanic eruptions may be transported great distances and concentrated sufficiently to have a severe impact upon plants and humans. The cultural stress of such an event will depend on several factors, including the magnitude of the environmental forcing event and the sensitivity of the culture to the stress introduced by the volcanic gases. Thus in a robust culture human illness and damage to plants and animals may result in no more than the introduction of temporary stress from which recovery is rapid and assured.

 

Other posts about volcanoes

  1. About our certain doom from the Yellowstone supervolcano, 11 January 2009
  2. Global warming causes earthquakes and volcanic eruptions (yes, this story is real), 17 April 2010
  3. More about shockwaves of the volcanic kind, 21 April 2010
  4. Might the current eruptions in Iceland become worse, affecting Europe – and perhaps our climate?, 19 May 2010
  5. “2nd Iceland volcano issues warning” (Katla speaks to MSNBC’s newshounds), 28 May 2010

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