(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

Mount Tambora caldera. Photo by Jialiang Gao /peace-on-earth.org

Skies darkened, temperatures plunged, crops failed, and disease and famine ensued. These and other strange phenomena afflicted people around the world in 1816, known as “The Year without a Summer.” We now know that the great eruption of Mount Tambora, in Indonesia, the previous year had triggered these changes. With Mount Tambora rumbling again this month, are we about to experience another global catastrophe?

Before we answer that, let’s examine the 1815 eruption and its remarkable effects. Mount Tambora became restless in 1812 and in April 1815 produced a series of major explosions that peaked on April 10-11. Large ash plumes rose to great heights, and pyroclastic flows swept down the flanks for several days, wiping out entire villages. When the pyroclastic flows reached the sea, they triggered tsunamis that further devastated the surrounding areas.

The eruption was massive, rated as a 7 on the Volcanic Explosivity Scale of 0-8. By comparison, the volume of magma it erupted was about 40 times greater than that of the 1980 eruption of Mount St. Helens and 10 times greater than that of the 1991 eruption of Pinatubo.

When the eruption was over, a caldera 6 km (3.7 miles) in diameter had formed, and more than 70,000 had died in the surroundings areas, making this the greatest death toll known for a volcanic eruption. The eruption also caused suffering around the world.

The 60 megatons of sulfur ejected into the atmosphere led to major temperature drops and increased rainfall the following year in many places, including New England and Europe. In fact, based on tree-ring studies, 1816 stands as having one of the coldest summers of the past six centuries.

Frosts in New England occurred throughout the summer, resulting in almost total failure of major crops. This triggered a mass exodus of farmers from northern locales, like Vermont, to points south. Crop failures in Europe led to soaring prices and civil unrest, with rioters in England carrying spiked sticks and demanding “Bread or Blood.” The famine has been called “the last great subsistence crisis in the Western World.”

With malnutrition prevailing across the land, typhus and dysentery became rampant in Europe, and the combined effects of famine and disease killed more than 40,000 in Ireland alone. One positive outcome, however, was that the cold and wet summer of 1816 kept Mary Shelley sheltered inside, penning the story of Frankenstein to pass the time. Also, the skies were illuminated with brilliant reddish hues, said to have inspired many paintings of the period.

Aware of the devastation that Tambora had wrought in 1815-1816, one might wonder if its recent activity could be the start of a repeat performance. Indonesia’s Center of Volcanology and Geological Hazard Mitigation (CVGHM) reported this month that seismicity at Tambora has been increasing since April, and steam plumes have been observed above the volcano on numerous occasions. On September 8, the alert level was raised to 3 (on a scale of 1 to 4). Could another massive eruption happen at Tambora in the near future?

The answer: almost certainly not. The 1815 eruption was enormous, and many hundreds, if not thousands, of years would be needed for Tambora’s magma chamber to recharge for another eruption of that scale. In fact, the 1815 eruption was the largest known in the past two thousand years, and eruptions of that scale probably occur on average only about once or twice a millennium – worldwide. That is, in the unlikely event we were to experience another 1815-scale eruption in the near future, it would most likely come from another volcano.

Tambora might continue to let off steam, and it might experience a small to moderate eruption (like the minor one that occurred sometime between 1847 and 1913), but it probably won’t have a cataclysmic eruption any time soon. Its recent activity is a good reminder that calderas, like the one at Tambora, frequently experience unrest. A 1988 review study by USGS geologists Chris Newhall and Dan Dzurisin showed that unrest is, in fact, quite common at calderas, and such activity does not necessarily mean that the big one is coming any time soon.