Over the history of Iceland, the country has been the site of a number of very large
and destructive volcanic eruptions. However, none of these eruptions were as deadly as the eruption
from Laki in 1783. The eruption had widespread consequences, and is blamed in part for causing
the French revolution. This video covers the large eruption from this fissure system,
and states the general hazard which it poses in the future, as it could erupt again.
The site of the deadly eruption of Laki can be found in the south central portion of Iceland.
Before I begin, I want to note that Laki is not a distinct volcano. Rather, it is a
fissure system of the much larger Grímsvötn volcano which is centered to the northeast.
In early 1783, residents of Iceland noted a number of moderate earthquakes. Over time,
the earthquakes became more and more frequent, until the ground was almost constantly rumbling.
These earthquakes were the result of vast volumes of magma slowly moving towards the surface. Then,
on June 8th, 1783, a 25 kilometer long nearly straight line fissure opened up which trended in a
southwestern direction. As lava began reaching the surface, it encountered pockets of groundwater in
the region. When this occurred, large explosions would take place and blast out craters in the
ground. As an example, one of these energetic explosions formed a 320 meter wide crater in what
is termed a phreatomagmatic eruption (1050 ft). As this highly explosive phase of the eruption ended,
lava erupting from this fissure coalesced into several dozen points. From these points,
lava continued to erupt in a mildly explosive manner which resembled typical volcanic activity
on the island of Stromboli. Every 20 or so minutes, each of these vents produced a series
of mild explosions which ejected lava and ash which largely fell close to the erupting point.
Over time, this explosive activity formed dozens of eruptive features known as cinder cones,
some of which climbed to more than 40 meters higher than the surrounding landscape.
Eventually, eruptions slowly became absent of explosive activity. From these vents and the
related fissures emerged a vast river of lava. Initially, the lava slowly traveled downhill.
However, once low points were filled with cooled lava, the flows traveled in every direction.
As the weeks progressed, more and more lava continued to pour out. Soon,
lava had traveled 5 kilometers from a vent, then 10 kilometers, then 20 kilometers, and
even more. Weeks turned into months, and the eruption was still ongoing.
Large swaths of land continued to get burned and covered by basaltic lava. Then, on February 7th,
1784, the outpouring of lava had stopped. 15 cubic kilometers of lava had erupted in what was the
largest flow of lava on the planet of the last 800 years. In total, 600 square kilometers was covered
with lava, and some of these flows traveled more than 50 kilometers from an erupting vent.
On the volcanic explosivity index, this eruption was rated as a 4. However, as the name implies,
this scale takes into account how explosive an eruption is. This eruption was not very explosive,
but was still quite deadly. During the eruption, what ash was emitted went high into the atmosphere
and fell across Iceland. This ash and a related low fog which spread across the region contained
high amounts of the element fluorine, which fell into drinking water and crops. People and animals
who drank or ate from effected areas soon came down with severe cases of fluorine poisoning,
which causes bones to easily break. Several thousand people on Iceland, and more than half
the population of the animals on the island died due to the 8 million tons of hydrogen fluoride
released by the eruption. In the ensuing famine, one fifth of the population of iceland died.
However, the effects of this eruption were not localized to only Iceland.
120 million tons of sulfur dioxide was released by the eruption into the northern hemisphere,
which caused temperatures worldwide to decrease by 2 degrees Celsius. In the United States, one of
the coldest winters on record occurred. In France, extreme weather continued for more than a decade.
This caused crops to widely fail, which increased the level of poverty and anger in the region.
As a result, this eruption is officially listed as a factor in causing the French revolution.
Although this fissure system has not erupted since, it will almost certainly erupt again.
However, due to globalization and easy movement of people around the planet, the next eruption
of this scale should not be as deadly. I hope that you enjoyed this video. If
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