Almost thousand years ago, a serious upheaval occurred in Earth’s atmosphere: a giant cloud of sulphur rich particles flowed throughout the stratosphere turning skies dark for months or even years, before ultimately falling right down to Earth.
We know this event happened because researchers have drilled & analyzed ice cores samples taken from deep within ice sheets or glaciers, which have trapped sulphur aerosols produced by volcanic eruptions reaching the stratosphere & settling back on the surface.
Ice can preserve evidence of volcanism over incredibly long timescales, but pin-pointing the precise date of an event that shows-up in the layers of an ice core remains tricky business.
In this case, scientists assumed the sulphurous deposit was left by a major eruption unleashed in 1104 by Iceland’s Hekla, a volcano sometimes called the ‘Gateway to Hell’. Since the thin strip of ice ranks among the largest sulphate deposition signals of the last millennium, it sounds plausible.
Only, what if the accepted timeline of an ice core turn-out to be time warped? A couple of years ago, one study concluded that a timescale called the ‘Greenland Ice Core Chronology 2005 (GICC05)’ was off by up to 7 years in the first millennium CE and by up to 4 years early in the next millennium.
Those findings, consistent with research published in April 2020 led by palaeoclimatologist Sébastien Guillet from the University of Geneva in Switzerland mean Hekla couldn’t be the culprit for the giant sulphate signal at all.
“A prominent discovery arising from this revised ice core dating is a major & hitherto unrecognized bipolar volcanic signal with Sulphate deposition starting in late 1108 or early 1109 CE & persisting until early 1113 CE in the Greenland record,” Guillet & his co-authors explain in their paper, noting that evidence for same event also can be seen in a similarly-revised Antarctic ice core chronology.
To investigate, what may need been responsible for leaving these ancient tracks at both the top & the bottom of the world, the team combed historical documentation, trying to find medieval records of strange, dark looking lunar eclipses that would correspond to the stratospheric haze of major eruptive events.
“The spectacular atmospheric optical phenomena related to high-altitude volcanic aerosols have caught the attention of chroniclers since the ancient times,” the team writes.
“In particular, the reported brightness of lunar eclipses often employed both to detect volcanic aerosols in the stratosphere and to quantify stratospheric optical depths following large eruptions.”
According to NASA records supported astronomical retrocalculation, 7 total lunar eclipses were observable in Europe in the first 20 years of the last millennium, between 1100 & 1120 CE.
Among these, a witness to lunar eclipse that occurred in May 1110 wrote about the exceptional darkness of the Moon during the phenomenon.
“On the fifth night within the month of May appeared the Moon shining bright in the evening and afterwards by little & little its light diminished, so that as soon as night came, it had been so completely extinguished withal, that neither light, nor orb, nor anything in the least of it had been seen,” an observer wrote in the Peterborough Chronicle.
Many astronomers have since discussed this mysterious & unusually dark lunar eclipse. Centuries after it occurred, English astronomer Georges Frederick Chambers wrote about it, saying: “It is clear that this eclipse was an instance of a ‘black’ eclipse when the Moon becomes quite invisible rather than shining with the familiar coppery hue”.
Despite the event being well-known in astronomy history, researchers haven’t suggested it’d are caused by the presence of volcanic aerosols in the stratosphere, albeit that is the presumably cause, the new study suggests.
“We note that no other evidence of volcanic dust veil like dimming of the Sun, red twilight glows and/or reddish solar haloes, might be found during our investigations for the years 1108–1110 CE,” the researchers write.
If the timing is correct, then what volcano was liable for the sulphur cloud, given Hekla is now out of the frame?
While it’s impossible to know for sure, the team thinks the most probable explanation is Japan’s Mount Asama, which produced an enormous, months-long eruption in the year 1108, significantly, larger than a subsequent eruption in 1783 that killed over 1400 people.
A diary entry recorded by a statesman describes 1108 event: “There was a fire at the top of the volcano, a thick-layer of ash in the governor’s garden, everywhere the fields & the rice fields are rendered unfit for cultivation. We never saw that in the country. It’s a really strange & rare thing.”
In addition to witness accounts, the researchers also checked out tree ring evidence, which suggests 1109 CE was an exceptionally cold year (about 1 degree Centigrade cooler in the Northern Hemisphere), based significantly thinner tree rings.
Other historical documentation, especially accounts of climatic & societal impacts in the years 1109–1111 CE, corroborate the hypothesis that an 1108 eruption (or a series of eruptions began that year), could have led to disastrous effects on affected communities.
The researchers found an “abundance of testimonies pointed to adverse weather, crop failures & famines in these years”, noting that the “assembled evidence suggests that the subsistence difficulties, which began in 1109, deepened into the famine in several regions of western Europe“.
Of course, those long time ago hardships cannot be taken as proof of any particular eruptive event, but the researchers say all the evidence, taken together, suggests a forgotten cluster of volcanic eruptions in 1108 to 1110 unleashed terrible consequences on humanity. We are only rediscovering them now.
These findings are reported in Scientific Reports.