Volcanic mountains

Bad astronomy | Volcanic eruption in 1257 AD finally pinned on the Simalas volcano


A titanic volcanic eruption in AD 1257 spat out colossal amounts of ash, sulfur and glassy pumice, and affected the climate over the course of the whole planet. It was one of the biggest, if not the biggest, eruptions of the past 7,000 years, and there’s literally evidence of it from pole to pole.

Corn… What the volcano erupted?

Oddly, until recently, no one knew exactly which volcano on Earth had exploded. Geologists scratched their heads until just a few years ago, when multiple pieces of evidence pointed to the real smoking gun: the Samalas volcano on the island of Lombok in Indonesia.

The strongest evidence of such a catastrophic eruption has come from ice cores, both from the Arctic and Antarctic. Each year, a new layer of ice settles in these areas, trapping gases and particles in the atmosphere. They can be dated with extreme precision, making them essential for determining the age of global climate events.

Volcanic sulphate deposits culminate in ice deposits dated 1257/1258 AD, indicating a much larger eruption than that of Krakatau (in 1883) and Tambura (1815), eight times and twice as powerful, respectively .

New work on the eruption looked at evidence for radiocarbon dating, tree rings, the geochemistry of volcanic deposits, and even an ancient historical document called the Babad Lombok, written in Old Javanese on palm leaves, which documents the explosion.

The Babad Lombok talks about an eruption of a volcano called Samalas, which is now part of a volcanic complex that includes Mount Rinjani (which rises over 3,700 meters above sea level) and a huge partially filled caldera of water, forming a crater lake called Segara Anak. This complex is still active, with eruptions still in progress. A developing cone, called Gunung Barujari, has been developing for some time, most notably via eruptive events in the mid-1990s.

The Babad Lombok place the eruption of the mid to late thirteenth century, which corresponds to the ice cores. In 1258, the northern hemisphere experienced an unusually cold summer for the season, with heavy rains and flooding that resulted in widespread crop failures in Europe. This too is consistent with a huge rash; dark particles can rise into the stratosphere and block a fraction of the sunlight, causing temperatures to drop.

Compellingly, tephra – pieces of rock and ash blown off by volcanic eruptions – dated to this time have been found in the northern and southern hemispheres, implying that the volcano itself was near the equator.

Assuming the Babad Lombok described this eruption, geologists looked to the Samalas caldera and its surroundings for evidence. The trunks and branches of burnt trees have been dated to AD 1257.

Fieldwork in the Samalas caldera and surrounding islands shows deposits of tephra throughout the region. The shards of glass in the deposits also match the chemistry of those found in the ice cores dated to the event. By mapping the tephra deposits in the region, scientists found they totaled up to 7.5 cubic kilometers – up to 7 billion tons of fallout.

But the total volume of the eruption was much, much larger: Models of the volcano before the eruption indicate that it reached a height of about 4,200 meters above sea level (about 13,800 feet – roughly the size of the largest mountains in Colorado Rocky Mountain National Park). During the eruption, the peak collapsed. By examining all components of the event, scientists find that at least 40 cubic kilometers material was blown out, and the ash plume would have risen 43 kilometers into the sky, possibly up to 50 kilometers. It would have been visible for hundreds of kilometers.

Looking at the event in total, he would have scored about 7.0 on the Volcanic Explosive Index, a logarithmic scale where, for example, the 1980 Mount St. Helens eruption gives a rating of 5 and the last supereruption of the Yellowstone caldera 600,000 years ago was an 8 The Samalas eruption was therefore among the largest in the past 12,000 years.

The eruption was apocalyptic and must have been terrifying for the locals (the capital of the kingdom of Lombok, a city called Pamatan, was wiped out and remains unknown; if ever it was found it could look like Pompeii). There were explosions of steam as the hot magma reacted to seawater (called phreatic eruptions), followed by a magmatic explosion that threw pumice stone and rocks over great distances (several hundred kilometers). After that, there were pyroclastic flows; hot ash and gas that can travel hundreds of kilometers per hour and be hot. The deposits on the island of Lombok reached depths of 35 meters, the height of an eight-story building.

Notice that all evidence of this until a few years ago was indirect and scattered. This work ties it all together, including the new effects of climate change in the northern hemisphere.

Speaking of which, and given the recent publication of the IPCC’s Sixth Assessment Report on Climate Change, you might hear some people say that volcanic eruptions make up a large part of the carbon dioxide released into the atmosphere; I myself saw a tweet making this claim. This is not only wrong, but absolutely wrong; human activities emit more than a hundred times the carbon dioxide of all the volcanoes in the world. An eruption by something like Samalas would actually cool us down from the dark particles covering the atmosphere, but only a little, only for a little while, and at a very high cost.

Huge events like the eruption of Samalas can change the course of human history, but on a global scale, they can be difficult to pin down. Human activity, on the other hand, also has the ability to change the planet, and this can be found all over. I was horrified to read about the power of this ancient eruption, but I was sobered to remind myself that we ourselves are doing much worse, and we are continually doing it.

Unlike the planet, we have a choice.