Volcanoes that made history - Ars Technica

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The first telegram arrived in Singapore on a Monday, sent from the city of Batavia in the Dutch East Indies (now Jakarta, Indonesia). “Terrific detonations from Krakatau (volcanic island),” it reported. Soon afterward: “Stones falling. Village near Anjer washed away.” The wires continued clattering out news of bridges destroyed, boats smashed, lighthouses “disappeared.” By noon on Tuesday, the scope of the natural disaster was clear: “Where once Mount Krakatau stood the sea now plays.”

Within days, the source of the destruction was known worldwide. On the morning of August 27, 1883, a volcanic eruption had obliterated two islands in the strait between Java and Sumatra, and most of a third. More than 36,000 people perished, the majority in devastating tsunamis that raced outward from the colossal explosion.

Thanks to Victorian-era telecommunications, it was the first time in history that people around the globe could begin to document, in near real time, the immediate and long-term effects of a catastrophic volcanic eruption. What they learned over the next few years laid the foundations for the modern science of volcanology. And it was an especially eye-opening lesson in how the biggest eruptions can influence climate, agriculture, and even the course of human history.

Global effects

In the months after Krakatau, drifting volcanic particles high in the atmosphere circled the globe, causing violently colored sunsets that contemporary artists captured in paintings, likely including the psychedelic background of Edvard Munch’s The Scream.

But the key climate-driving component of the volcano’s emissions was sulfur from the molten rock that fed Krakatau. Once sulfur erupts into the atmosphere, it can form particles called aerosols that reflect sunlight and cool Earth. In the months and years after the eruption, average summer temperatures fell 0.6° Celsius (1.1° Fahrenheit) in the non-tropical regions of the Northern Hemisphere.

Fast-forward more than a century, and researchers now understand that climate changes, especially rapid ones, have transformed societies by affecting agriculture, public health, and living conditions. With what they’ve learned from Krakatau and other eruptions, volcanologists today are identifying past catastrophic blasts that may have contributed to historic events like droughts, famines, epidemics and societal unrest.

“In so many different ways societies were affected … a failure in harvest or flooding or a cold summer or a really cold winter,” says Katrin Kleemann, an environmental historian at the German Maritime Museum in Bremerhaven.

While they can’t prove an eruption caused the demise of a regime, volcanologists have uncovered some intriguing links, including some that could inform our understanding of how today’s society might react to a rapidly changing climate.

536 and all that

The first challenge in making volcano-society connections is to find physical fingerprints of past eruptions. In the year 536, scribes in Europe, the Middle East, and Asia wrote about bizarre weather, including a haze that shrouded the sun for 18 months. Temperatures plummeted, harvests failed, and within a few years, the first documented global plague began.

These early medieval chronicles strongly suggest a major volcanic eruption—but the hard evidence lies deep in polar ice. Scientists can infer that big eruptions happened at certain times in the past by looking for sulfur and ash deposits in ice cores from Greenland and Antarctica. These cores, drilled into ice sheets, preserve an annual record of whatever was circulating in Earth’s atmosphere as it settled onto the surface each year. Researchers can read these frozen layers back in time like turning the pages of a book.

It turns out that polar ice cores do contain large amounts of sulfur dating to 536, a distinct signal of a major eruption. But which volcano went off at the time remains a mystery. There is no known written record from anyone living close to the eruption—Iceland, where it may have occurred, was not yet populated.

Large volcanic eruptions cool Earth’s climate by injecting tiny particles of sulfur high into the atmosphere, where they reflect a portion of incoming sunlight back into space for periods of months or years. The 1257 eruption of the Samalas volcano in Indonesia dwarfed others in recent history as measured by sulfur output, and has been shown to have chilled the climate across the Northern Hemisphere for several years afterward....