Evaluating societal resilience to Iceland’s largest volcanic eruptions

In a recent study published by GeoSciences PhD candidate Conner Morison, the intricate societal impacts of Iceland’s greatest volcanic events are explored in further depth to produce a rich historical narrative connecting Icelandic societies, separated in time by several centuries, together in a novel way.

Looking at the impacts of the two most voluminous flood-lava eruptions in Iceland – the Eldgjá (c. 939 AD) and Laki (1783-1784 AD) – Morison and his co-authors meticulously combed through existing research of the events to paint a clearer picture of the role that societal structures and environmental conditions played in societal impacts during the times of these eruptions.

Morison’s paper suggests that the 10th-century Icelandic society may have been better positioned to cope with volcanic hazards due to the relative societal and environmental advantages of the Early Medieval period.

The Eldgjá eruption, despite discharging a greater volume of magma than the Laki eruption, may not have ultimately led to the same level of societal devastation due to several factors. The Eldgjá eruption occurred during a period of increasing Christian influence among a predominantly pagan population. This shift may have fostered stronger local allegiances and networks, which in turn served to aid societal resilience.

During this time, Iceland had an abundance of natural resources, such as woodlands and greater soil coverage. Coupled with its smaller population, these factors could have minimised the extent of the Eldgjá eruption's impacts on society. Additionally, the Medieval Climate Anomaly (c. 950 – 1250 CE) provided a relatively warm and stable climate, which supported the subsistence systems that were familiar to Iceland’s Norse settlers.

Fast-forward to the Laki eruption that took place during the Little Ice Age (c. 1400 – 1800 CE), a period characterised by a colder and stormier climate in the North Atlantic.

In contrast to Eldgjá, the Laki eruption had potentially severe societal consequences. This included the "haze famine", which led to the death of one-fifth of Iceland's population and intensified the eruption's impacts. With a less forgiving environment, the larger population of 18th-century Iceland had greater dependency on the island’s depleted natural resources. 

Additionally, the societal structure, limited local governance and reliance on aid from overseas likely hindered effective recovery efforts in response to the volcanic hazards.

Reconstructing the impacts of these eruptions was challenging due to the limited availability of historical records. This was particularly the case for the 10th-century Eldgjá eruption, whose impacts have been traced in far fewer written historical accounts compared to the Laki eruption in the 18th century.

Discussing the difficulties of reckoning with the imbalance of evidence, Morison said:

“The scarcity of analogous, historically documented, flood-lava eruptions resulted in a reliance on just a few events, whose circumstances differed significantly, to understand their impacts. 

In the case of the Eldgjá eruption, the main challenge was that written record-keeping wasn’t established in Iceland by the 10th century, and contemporary textual evidence from which to infer the impacts of the eruption is very limited. In contrast, there are abundant contemporary sources to work with concerning the Laki eruption and its aftermath.”

Beyond looking at the historical accounts surrounding each eruption, Morison’s ongoing research involves fieldwork and on-site visits to the Fire Districts, where both eruptions wrought enduring changes to the landscape. This research includes identifying and analysing the physical and chemical characteristics of tephra (volcanic ash), preserved as layers within Icelandic soils. Such data can contain clues that allow the local environmental conditions at the time of eruptions to be reconstructed, and are an important tool in reconstructing impacts of historic eruptions in Iceland.

However, even tephra layers cannot solely be relied upon to accurately record eruption characteristics, as local preservation of volcanic fallout deposits can be poor.

“No proxy is a silver bullet – all come with inherent uncertainties that must be reckoned with before they can be interpreted reliably. For instance, ice-cores drilled into ice sheets in Greenland can preserve the fallout from Icelandic volcanoes, but these deposits cannot be read simply as a record of the eruption intensity, magnitude or duration due to the ways that volcanic ash and gases are dispersed through the atmosphere.”

In the recent publication, Morison and his co-authors found that tighter community bonds and resource sharing, possibly facilitated by the emerging Christian networks at the time, may have enabled a more effective societal response to the Eldgjá eruption.

“Since we know from contemporary sources that there were profound demographic changes in the aftermath of Laki, it has been assumed that Eldgjá must have wrought at least as devastating impacts. Our interpretation is that the Icelandic society of the tenth-century may have been better positioned to cope with such volcanic hazards.”

Hence, the societal fabric of Icelandic society in the lead up to the Laki eruption during the 18th century was determined to be less resilient than the Eldgjá eruption that occurred several centuries earlier.

Morison’s paper emphasises the importance of weighing multiple factors – societal structures, climate, and natural resources – when assessing the impacts of volcanic eruptions and for better understanding how societal structure dynamics can set the tone for responding to these natural disasters.

The difference in the availability of historical records highlights the difficulty associated with drawing parallels between the two events and underlines the importance of a multidisciplinary approach in understanding volcanic impacts.

“Evidence should, when strung together, form a guide rope through time from which a story can be told. By building a story from the evidence, and not the converse, we have summarised several decades’ worth of research in related sub-disciplines to provide a fresh viewpoint that takes account of uncertainty in existing knowledge. This has shored up our interpretation of the disparate impacts of these enormous but rare flood-lava eruptions.”