The towering glacier covered Grimsvotn volcano in Iceland is truly an impressive sight to
behold.
Compared to every other volcano within the country, it has by far been the most active
in the last 1,000 years, with 77 confirmed eruptions.
Yet, despite the fact that no one lives within 40 kilometers or 25 miles of this volcano,
it produced one of the planet's deadliest eruptions.
This deadly eruption from 1783 to 1785 did not harm the majority its victims through
pyroclastic flows or glacial outburst floods but rather through long term fluorine poisoning
and toxic gasses.
The massive fissure eruption of the so-called Laki system produced more than 100 vents along
a 25 kilometer long fissure.
Ejecting molten rock at an incredibly high rate, it would go on to produce 14.7 cubic
kilometers of lava which covered 565 square kilometers of land.
Almost all of these vents ejected significant amounts of fluorine rich ash, which went on
to poison the water supply in Iceland and sections of what is now the United Kingdom.
Due to the ashfall and gasses, widespread crop failures and famine occurred, which resulted
in more than 8,000 fatalities.
Luckily, this eruption was an unusual fluke as such large volume fissure eruptions from
Grimsvotn are quite rare.
The vast majority of this volcano's recent eruptions are far smaller, although, Grimsvotn
did produce one of the largest explosive eruptions in Iceland during the last 15,000 years.
The 1,719 meter or 5,640 foot tall Grimsvotn volcano is located in central southeast Iceland,
where it is 55 kilometers north-northeast of the city of Kalfafell.
Grimsvotn is one of 6 volcanoes located within Iceland's largest ice cap, Vatnajökull, which
is slightly larger than the combined area of Hawaii's smaller 7 of its 8 main islands.
The reason why this area is so volcanically active relates to two reasons.
First, the underlying Iceland hotspot which supplies molten rock to the region's volcanoes
is centered just northwest of Grimsvotn.
Second, Grimsvotn is part of the eastern volcanic zone which is a weak point in the crust which
is spreading apart to the east and west.
This spreading allows for magma to intrude into the crust through a path of least resistance,
eventually erupting onto the surface.
Although the exact age of Grimsvotn is unclear, it is safe to assume based on looking at the
age of similar volcanoes that it has been erupting for at least 75,000 years.
Regardless of how long eruptive activity has been occurring for, it might come as a surprise
that this volcano was not always covered by a thick ice sheet.
In fact, the current ice sheet overlying Grimsvotn has only existed for around 4,500 years.
Grimsvotn likely began as a southwest to northeast trending fissure system until a series of
dominant vents developed.
These more dominant cones grew out of material produced during numerous explosive basalt
composition eruptions.
At the present, Grimsvotn has one of the largest calderas in the country with one part of its
complex measuring 12 kilometer wide.
This complex is made up of 3 overlapping calderas which all formed in presumably VEI 6 eruptions
which were at least 50 times larger than the 2010 eruption of Eyjafjallajökull.
One such large eruption occurred in 8230 BCE which ejected 15 cubic kilometers of tephra.
The caldera formed when a large section of the volcano's underlying magma chamber was
drained.
The ground above the magma chamber then collapsed downwards, producing a massive caldera.
While the vast majority of Grimsvotn's eruptions have averaged approximately as a 2 on the
volcanic explosivity index, the volcano produced an unusually large eruption in 2011, rating
as a 4 and ejecting 0.8 cubic kilometers of volcanic rock.
Due to long term trends, it is quite likely that Grimsvotn will erupt again in the next
24 months although this is not a certainty.
One warning sign which could occur before an eruption is known as a jökulhlaup.
Jökulhlaups are large glacial floods and are either generated by the interaction of
lava with an ice sheet or an increase in temperature of the volcano's numerous fumaroles.
Thanks for watching!
If you would like to request a specific topic, please leave a comment below.
Additionally, I would like to thank my new patron Raymond Desjarlais for supporting this
channel!