The gases, sulphuric acid aerosols, and possibly ash from the eruption were carried over Britain by the weather systems at that time.
This 8 month-long eruption from a line of volcanic vents 27 km in length, known as a fissure eruption, also produced the largest lava flow on Earth of the past 1000 years, which covered about 500 square kilometres in southern Iceland.
The Laki eruption was not the first time that such an eruption occurred in Iceland. An even larger one happened around the years AD 935-940. It released more gases, and produced more ash and lava, than Laki, but apart from the evidence from the lava flows and fissure cones themselves, it has been difficult to interpret the degree of effects that this eruption, known as Eldgjá, had on the atmosphere and environment of the northern hemisphere.
Volcano historian and climatologist Richard Stothers of NASA Goddard Institute of Space Studies, New York, published a summary in 1998 of what little can be gleaned from the few written sources dating from those Dark Ages.
Before the AD 930 eruption and up to the time of the Laki eruption, there were also several other smaller eruptions of this type in Iceland, but they released much less ash, sulphur dioxide, and other gases.
When will there be another large eruption in Iceland?
With such few cases of past eruptions to go by, it is difficult to predict when or how big the next occurrence of a similar eruption will be, but one thing is certain, it will happen. Actually, as fair a prediction as any might be that it could be any day now!
It could be next week (unlikely, as there should be some precursor effects such as earthquakes and no anomalous ones are currently being reported), or next year, or five hundred years from now.
Britons may take comfort in not having an active volcano here on our islands, but the one frequently active area that could have a direct effect here on a time scale to which we can relate is Iceland and its many restless volcanoes.
Why is it a potential risk for the UK?
Why should we in the British Isles, suffer with volcanic fumes from Iceland?
The answer is that our islands are generally downwind of Iceland. If you keep an eye on the weather you’ll have noticed how westerly air systems driven by Atlantic Ocean circulation frequently control our weather, and these are often blowing in from across Iceland.
Icelandic volcanoes erupt every 2-3 years on average, and sometimes the volcanic clouds miss the British Isles.
What weather conditions would lead to trouble for Britain?
So, when are conditions right for air masses containing volcanic ash or gas to affect Britain? It is likely when there is an atmospheric high pressure system over the British Isles (and/or the Western European mainland) and the air masses coming from the west are drawn into and down upon our region. This is what happened in the summer of 1783.
The older Eldgjá eruption may have lasted six years, so sometime during that period the wind systems must have been right for spreading the volcanic effluents over every part of Europe!
There are, in fact, two parts to the atmospheric transport of volcanic gases and ash, which are carried in the lower atmosphere (the troposphere), which is what we experience when we get “weather” (clouds, rain, surface winds, etc.).
The second part is that which is carried along in the middle part of the atmosphere (the stratosphere). In the stratosphere (which over Iceland in summer begins at the altitude where jet passenger aircraft fly, 30-33,000 ft or 9-10 km), the air masses (winds) move much more slowly and sometimes in an opposite direction to that in the troposphere.
Thus when Laki erupted, lower-level gases, and the aerosols generated from them, moved eastwards towards Europe bringing the tremendous “dry fogs” that affected the continent for months after the beginning of activity, whereas stratospheric-high injections of sulphur dioxide gas lead to a long-lasting aerosol cloud that moved from East to West around the global atmosphere.
This cloud was resident for 2-3 years after the eruption and led to, or accentuated the record-breaking cold winters of 1783-4 and 1784-5, and the cool summer of 1784.
In fact, large Iceland fissure eruptions must have affected the whole of the northern hemisphere with the noxious gases and sulphuric acid aerosols generated from the sulphur gases ejected into the atmosphere.
New studies by both French and US research groups have shown that the Laki aerosol cloud must have covered the whole of the northern hemisphere down to the latitude of about North Africa. Historical documentation of the atmospheric effects due to these aerosols has been found from Japan to Alaska.
Is there a health risk?
Ironically, the cause of the very hot July-August 1783 temperatures that caused so much discomfort and, perhaps, deaths in Britain and France cannot be specifically linked to the Laki eruption at present
There is a great deal that we still don’t know about the influence of the Laki and Eldgjá aerosol clouds on weather and air quality over the British Isles. The aerosols were mainly sulphuric acid.
We know some of the health effects of ingesting these droplets, such as respiratory illness. But what caused the very hot summer in 1783, and the anomalously high number of deaths in the UK and France, and how much were these influenced by the Laki clouds?
We know that there were devastating effects on agriculture, but how much this was due to the weather, and how much to acid fallout is not well known. If we knew more about these aspects, we could better assess the consequences for our society in the event of a repeat performance from Iceland.
There will be another event like this – and the big question is, will European societies be prepared for the consequences? Right now the answer is that we must wait and see!