Monday, July 31, 2017

Then Iceland Struck Back

The Economist of 22 July 2017 reports an intriguing piece of historical detective work that ties together an early medieval famine, a buried volcano, ice cores, and tree-ring isotopes.

Shortly after the death of Charlemagne, western Europe experienced three years (821-24) of terrible weather: hard winters, frozen rivers, failed crops, and famine. The Frankish monk Paschasius Radbertus recorded these “years without summer” but could only attribute them to the wrath of God. Environmental scientists tend to associate “summerless” years not with divine displeasure but with volcanic eruptions, and a large one apparently occurred in this period. Ice core extractions from Greenland show elevated levels of sulfate particles, a marker for volcanism (which ejects sulfur dioxide into the atmosphere), during the third decade of the ninth century.

Identifying the specific volcano responsible for Radbertus’s famine would seem impossible, but in 2003 serendipity provided an important clue. Flooding in southern Iceland uncovered the remains of an old forest in southern Iceland, 20 miles from the Myrdalsjokul glacier. 2,200 feet beneath that glacier lies Katla, a volcano that periodically erupts through its ice cover, producing powerful floods. Such a flood likely killed the now-buried forest: the ancient trees, which had all been knocked down at the same time, pointed away from Katla, indicating that some force from that direction had felled them. 

According to Ulf Buntzen (Cambridge), the trees’ rings give a precise date for their demise: 47 years after 775 CE, when an unknown event (probably heightened solar activity) deposited high levels of Carbon-14 isotope in tree rings worldwide. The flood thus took place in 822, soon after the start of the frigid weather observed by our Frankish monk, and during the period of elevated sulfate levels found in the Greenland ice. This is as close to absolute proof of a volcanic eruption in Iceland as one can get in the absence of on-the-spot observers, who wouldn’t arrive on the island for another half-century.

Iceland has suffered a great deal from outside illnesses and calamities, but one should recall that it is contributed to one or two of its own (crop failures, disrupted air travel, bad music) over the centuries. The world is a small place, and small places can exert an outsized influence on it.

1 comment:

Gorges Smythe said...