Bill McGuire* looks back on the legacy of Tambora, the volcano whose eruption created the ‘year without a summer’
When all is quiet on the volcano front, volcanologists get twitchy. As ash stops falling and lava floods become trickles, they start casting around for something else to fixate upon. Looking back often furnishes a sought-after focal point, the anniversary of a bygone blast catching the eye and offering an opportunity for retrospection, reinterpretation or consideration of lessons learned, which might provide a message for contemporary volcanology. In this respect, 2015 does not disappoint - marking as it does the bicentennial of the great Tambora eruption.
Given that, at any given moment, at least one of Indonesia's 78 historically-active volcanoes – the largest number of any country - can be expected to be in eruption or at least restless, falling ash or flowing lava is rarely big news. The April 1815 blast, however, was altogether different. Pumping out five times more ash and debris than the infamous Krakatoa explosion nearly 70 years later, it was simply too big to ignore.
The greatest known volcanic eruption in modern times, and one of the largest since the Ice Age, the event is an important benchmark that helps bracket the potential impacts of large volcanic eruptions on the global environment and society. Reaching out from its host island of Sumbawa, the eruption brought about dramatic changes to weather patterns across the planet, culminating in the so-called 'Year without a Summer' in Europe, parts of the United States and Canada - which in turn spawned crop failures, famine and disease.
Reluctant volcano
Unlike some other Indonesian volcanoes, Tambora's eruption catalogue prior to the 19th Century blast was particularly sparse, with evidence for just a single eruption in the preceding five millennia or so. It seemed that this volcano kept its head down and its violent tendencies under control - so much so that the local populace probably regarded it as long extinct, assuming they considered it a volcano at all. This couldn't last, and as with many other volcanic outbursts in the historical record, Tambora's extended quiescence was always likely to end with a very large bang rather than a whimper.
As rising magma needs to break rock and make space for itself, leading respectively to distinctive earthquake swarms and swelling of the ground surface, no volcano erupts without warning. The duration of the period of restlessness that characterises the build-up to eruption is elastic, although typically on the order of a couple of weeks to a few months. In the case of Tambora, however, the first rumblings, accompanied by small ash explosions, became apparent a good three years in advance of the climactic phase of the eruption.
Had today's sensitive seismic and geodetic monitoring kit been available in 18th Century Indonesia, it seems likely that it would have detected magma on the move even in advance of this - suggesting, perhaps, that eruptions on this prodigious scale might, as a matter of course, be characterised by periods of precursory restlessness measured in years rather than weeks or months.
Whether thought of as ‘a volcano’ or not, Tambora – prior to its obliteration – seems to have been a pretty impressive mountain, dominating the northern end of Sumbawa's Sanggar Peninsula. The volcano's pre-eruption summit may have touched 4300m, making Tambora – at the time – the highest peak in the East Indies. To the west, the volcano would have looked out towards the island of Lombok, and beyond that, Java, while to the east lay the islands of Flores and Sumba.
For today's volcanologists, it was providential that a sequence of fortunate circumstances contributed towards a detailed account of the eruption being left to posterity. In 1811, control of the island of Java was wrested from the Dutch by British forces, following the defeat of defending Dutch and French troops. Even while fighting continued, a certain Thomas Stamford (later Sir Stamford) Bingley Raffles was decreed Lieutenant Governor of the island, at the tender age of 30. Perhaps best known today for the eponymous and iconic hotel in Singapore, the city he founded, (and maybe less so for establishing – with Sir Humphry Davy – London Zoo) Raffles also earned a place in the hearts and minds of volcanologists by means of his accessible descriptions of the Tambora eruption and its impact.
When not busy subjugating uppity local princes, Raffles zealously embraced his temporary home, demonstrating a great interest in Java's archaeology, culture and natural history, and an enthusiasm for committing his thoughts and observations to paper. Thus it is, that we have his History of Java (1817) and his biography – written in 1830 by second wife Sophia - to turn to, in order to cast light on the nature and anatomy of an eruption that occurred eight generations ago. Other invaluable sources of information about the eruption and its aftermath can be found in the Asiatic journal, first published in 1816, and their content is addressed in Clive Oppenheimer's excellent review paper on the eruption and its environmental and social consequences.
Impossible to ignore
Following a steady ramping up of activity after 1812, things really began to get interesting during the first week of April 1815, when Raffles reports that, on the fifth of the month, loud booms were heard across Java, the closest point of which was around 300 km from the volcano. Mistaken for cannon fire, the stupendous explosions elicited the deployment of a detachment of troops from Yogyakarta on Java's south coast, under the false impression that a neighbouring garrison was under attack. Light ash-fall soon shed light on the true origin of the detonations, although the culprit was thought initially to be one of the many ‘active’ Javan volcanoes.
This initial major explosion blasted ash to a height of 33km but, with a duration of just two hours, was short lived. A lull of several days then ensued before an even more colossal detonation, on the tenth, reverberated around the East Indies. This second explosion blasted out a column of ash estimated to have reached the staggering altitude of 43 km. Gravitational collapse of the ash column fed pyroclastic flows that resulted in the eruption's first casualties as the nearby village of Sanggar was obliterated.
Although short-lived, the eruption heralded the onset of a devastatingly violent episode of climactic activity that lasted three to four days, with the destruction of much of the upper part of the volcano and the production of voluminous ignimbrite flows (pumice-dominated pyroclastic flows) that swept the flanks and surrounding area, wiping out the village of Tambora. Taken together, the pyroclastic flows and the great ash clouds that arose from them – known as 'phoenix clouds' - dumped around 50 km3 (dense-rock equivalent) of solidified magma onto Sumbawa and into the surrounding Flores Sea. Up to five centimetres of ash fell as far afield as Borneo and Sulawesi and accumulated to depths in excess of 20 cm in eastern Java. The detonations during the climactic phase were felt over an even wider area, shaking buildings in eastern Java and heard as far away as Trumon in Sumatra, 2600km from the volcano.
On the island itself the density of falling ash in the atmosphere brought darkness so absolute that it was impossible even to see a raised hand held in front of the face. Temperatures plunged as total blackness reigned for two days, followed by another few days during which the sun was barely visible through a heavily ash-charged atmosphere. In Bima, on the east coast of the peninsula, the accumulation of ash was so great that most roofs collapsed. Damage in the town was compounded by the arrival of tsunamis spawned by colossal ignimbrite flows surging into the sea. The gas-rich portions of the flows scooted across the surface of the water in the manner of hovercraft, reaching as far as the neighbouring island of Moyo, immediately to the west. Maximum tsunami run-up heights are estimated to have been 4m and are reported to have scoured much of the coastline of the peninsula of buildings and hurled fishing boats inland.
The surface of the sea enclosing the peninsula was clogged with enormous pumice rafts, some an astonishing five kilometres long, which persisted for up to three years. These proved a particular hindrance for shipping, especially in the narrow strait between Moyo and the Sanggar Peninsula, but were even encountered far out in the Indian Ocean. Hardly surprisingly, the eruption dramatically modified the topography of Tambora, and once the ash had settled the volcano was seen to have been impressively decapitated. In place of a 4300m peak, there now sat a much smaller mountain 2850m high, topped by a six-kilometre caldera one kilometre deep.
Legacy; near and far
For the inhabitants of Sumbawa, neighbouring Lombok and probably other nearby islands, the eruption was a catastrophe. Estimates vary, but it seems that around 12,000 lives were lost during the eruption, due to ash-fall and pyroclastic flows, while a further 60,000 or so succumbed to disease and famine during the following several months. Taken together, this represents close to one in three of all deaths due to volcanic activity since the second half of the 18th Century.
Much as the 'in-theatre' accounts of the Tambora blast excite and enlighten today's volcanologists, the so-called far-field effects attract much broader interest; in particular, the manner in which the consequences of the eruption impinged upon the culture, social fabric and economy of the time. Along with vast quantities of ash, the eruption also pumped out an estimated 60 million tonnes of sulphur; a value a good six times higher than the output of the 1991 Pinatubo (Philippines) eruption, the second largest of the 20th Century.
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Unlike ash, which settles out relatively rapidly in a matter of days to weeks, the residence time of sulphur gases is much greater and - for major eruptions – can be about a couple of years. Combined with atmospheric water, the erupted sulphur gases loaded the stratosphere with around 200 million tonnes of sulphate aerosol. This was rapidly dispersed across the globe by high altitude atmospheric winds, and within months was playing havoc with the optics of the stratosphere. Stories abound of brilliantly flamboyant sunrises and the colourful invigoration of normally crepuscular sunsets. These have been held up as inspiration for the kaleidoscopic skies of some of J W M Turner's post-1814 works (See Turner's Chichester Canal, above).
Veils of volcanic sulphate in the stratosphere are known to cause cooling of the troposphere and surface, so it should come as no surprise to us that 1816 is known as 'the Year Without a Summer'. The year is more widely remembered for Napoleon's defeat at Waterloo, and it has been speculated that the heavy rains that hindered progress of the French troops, allowing his enemies to consolidate positions, may have been the first signs of the climate chaos that Tambora was to inflict upon much of the northern hemisphere. True or not, later weather anomalies provide a far more convincing link to events in Indonesia.
Across the NE United States, sulphate aerosols revealed themselves as 'dry fog' that persisted through spring and summer 1816, bringing unusually severe weather that more than halved the length of the growing season in places. Snow fell in New York State during early June and unprecedented summer frosts wiped out most crops across the region. Bitter weather also affected much of Europe, where summer temperatures were as much as to 2°C down on the decadal average. Additionally, the summer was peculiarly wet and seemingly followed by an especially stormy winter. Unsurprisingly, analysis of climate records indicates that 1816 was the second coldest northern hemisphere summer of the past six centuries, with 1817 and 1818 holding fifth and 22nd places in the rankings.
Societal impact
It has become somewhat de rigeur in recent years for historians and archaeologists to big-up the societal impacts of natural catastrophes, speculating upon causal links for which evidence is often far from robust. In the case of Tambora, however, there can be little doubt that its impact on western culture and society was significant.
Notwithstanding Turner’s possible inspiration, the anomalous weather of 1816 is also charged with supplying the brooding backdrop that - during a 'wet and ungenial' summer at the Villa Diodati on Lake Geneva – prompted Mary Shelley to pen Frankenstein and Lord Byron his desolate poem, Darkness. Beyond this, however, the effects of 'volcano weather' on the average European citizen were deleterious rather than recondite. Harvests failed from Ireland to Poland, resulting in the worst famine for more than a century and leading – according to economic historian John Post - to the 'last great subsistence crisis in the western world'.
Grain prices doubled, prompting insurrection and bread riots in a Europe already stagnating economically following the end of a quarter-century of conflict. In their malnourished and weakened state, people succumbed quickly to disease, and typhus was soon rampant. According to a contemporary account by William Harty, a combination of famine and disease took an estimated 44,300 lives in Ireland alone.
Lessons
Two hundred years on, the Tambora blast bears many lessons. For volcanologists it reinforces the idea that future eruptions with the greatest potential for disruption are likely to occur at volcanoes that have not erupted for millennia. Indeed, half of the 20 biggest eruptions since 1800 occurred at volcanoes that had not erupted in historic time. While not always true, the maxim – 'the longer the wait; the bigger the bang' – is borne out often enough to ensure that it is worth keeping an eye on seemingly innocuous long-dormant volcanoes. One such is the Alban Hills Volcanic Complex, 30km east of Rome. After lying dormant for more than 30,000 years, recent unrest and evidence for a growing magma body beneath the area have fostered concern over the possibility of future eruption.
The societal impact of the 1815 eruption, particularly for agricultural production, reinforce calls for national risk registers to include low-frequency, high-impact geophysical events that have the potential to seriously affect society and economy at the global scale. It also flags the importance of identifying, characterising and cataloguing all manner of natural risks capable of impinging detrimentally upon the planet as a whole (or a significant part thereof), so enabling international agencies and national governments to build a more accurate picture of the future natural risk landscape. Such a move should have the effect of minimising geophysical surprises, such as the 2010 Eyjafjallajökull eruption that played havoc with flights across the UK and Europe.
The establishment of an International Science Panel for Natural Hazard Assessment to take on such a task, a key recommendation of the 2005 report to the UK Government by the Natural Hazard Working Group established by Tony Blair following the 2004 Indian Ocean tsunami, has clearly fallen on deaf ears. The mayhem caused by the Icelandic ash cloud, together with the 1.1 billion Euros it cost the airline industry, already seems to have been forgotten.
With perhaps a one in 10 chance, in the next 50 years, of a Tambora-sized eruption taking centre stage, we might cope far better if - next time – we really did expect the unexpected.
* Bill McGuire is Professor Emeritus in Geophysical & Climate Hazards at UCL. His current book is Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis and Volcanoes.
Further reading
- D'Arcy Wood, G. 2014 Tambora: the eruption that changed the world. Princeton University Press. 312pp.
- Natural Hazard Working Group 2005 The role of science in physical natural hazard assessment. Report to the UK Government. Department of Trade and Industry.
- Oppenheimer, C. 2003 Climatic, environmental and human consequences of the largest known historic eruption: Tambora volcano (Indonesia) 1815. Progress in Physical Geography 27 (2), 230-259.
- Post, J. D. 1977 The last great subsistence crisis in the western world. Johns Hopkins University Press, Baltimore. 240pp.
- Stothers, R. 1984 The great Tambora eruption in 1815 and its aftermath. Science 224, 1191-1198.