Throughout the long history of Iceland, if a truly large volcanic eruption occurred,
it usually originated from the same volcano.
The volcano I am referring to is called Katla, which is the most dangerous volcano in the
country.
In the last 1,000 years, Katla has erupted 21 times.
At least 4 of these eruptions had a volcanic explosivity index of 5, indicating an eruption
an order of magnitude larger than the 2010 eruption of Eyjafjallajökull, which disrupted
air travel all across Europe.
As such, Katla is overdue for its next major eruption.
This video will discuss this volcano, and mention what its future hazards are.
The Katla stratovolcano is located in the south central portion of Iceland.
Specifically, it is 24 kilometers east of its neighboring volcano, Eyjafjallajökull.
The Katla stratovolcano is quite a large volcanic complex, indicating that it must have been
active for hundreds of thousands of years.
However, we aren't exactly sure how old this volcano is.
In all likelihood, it is approximately the same age as its neighboring volcano to the
west, indicating that Katla began forming around 800,000 years ago.
The area where Katla initially erupted represented a zone of weakness in the crust, which in
this case was a northeast trending fissure.
The lava which erupted from Katla, much like the rest of Iceland, had a low silica content
and erupted as a black volcanic rock called basalt.
Over many hundreds of thousands of years, Katla was built by numerous highly explosive
subplinian and plinian style eruptions, which are distinguished by their very tall and sustained
eruptive columns.
These dispersed ash in a wide area surrounding the volcano, leading to prominent layers of
ash in this section of Iceland.
Eventually, this volcano became tall enough that its top became covered by glaciers.
By 20,000 years ago, Katla was more than 1800 meters tall.
Then, 12,000 years ago, a unique highly explosive eruption occurred.
For some reason, a low silica basalt magma chamber mixed with a high silica rhyolite
magma chamber underneath the volcano.
This caused a highly energetic reaction, which triggered the largest known eruption from
Katla.
Eventually, ash and lava explosively erupted through the thick ice sheet, and created a
40 kilometer high ash plume.
Pyroclastic flows were subsequently generated, which raced across the icy terrain.
Then, due to the large volume of lava erupted, a large section of the volcano collapsed downwards,
forming a large caldera.
Today, it is not known whether this collapse created all or only part of the massive 10
by 14 kilometer wide caldera buried beneath Katla's glaciers.
Regardless, this eruption created a large part of this caldera, which forever changed
its topography.
In total, this eruption had a volcanic explosivity index of 6, and distributed a layer of ash
to the United Kingdom, Germany, Italy, and western Russia.
Since then, Katla has been marked by high volume explosive eruptions which occur about
once every 20 to 50 years.
However, one prominent eruption in 934 AD broke this trend.
To the northeast of Katla, a 75 kilometer long fissure opened.
From these fissures emerged a vast volume of lava, which began covering the surrounding
landscape.
By the time the eruption had ended, 800 square kilometers had been covered with a total of
20 cubic kilometers of lava.
Since Iceland was settled, Katla has erupted at least 25 times.
All of these eruptions rated on the volcanic explosivity index as a 3, 4, or 5, indicating
truly large eruptions.
Essentially, when Katla erupts, it does so in a large eruption when compared to other
volcanoes on the planet.
The largest of these eruptions in the last 1,000 years occurred in 1755, which caused
the only known fatalities associated with this volcano.
The last major eruption occurred in 1918, which originated on the southeast of the volcanic
complex.
Although this eruption was relatively small, it melted a large volume of ice, thus creating
a large glacial flood termed a Jökulhlaup.
This flood raced down to the southeast of the volcano, covering a vast area with floodwaters
of more than 80 meters thick.
Since 1918, no eruptions have breached the surface of the glacier.
However, two small subglacial eruptions were recorded in 1955 and then again in 1999.
Since then, no additional eruptions of any kind have occurred.
Typically, when the Eyjafjallajökull volcano erupts to the west, Katla has an eruption
soon after.
However, for the first time in several hundred years, when the adjacent volcano erupted in
2010, Katla did not.
When Katla does erupt again, it will disrupt air travel all across Europe.
Areas within 50 kilometers will receive a heavy coating of ash, which could cause structures
to collapse.
However, the most severe hazard will be glacial floods, which could effect three floodplains
surrounding the volcanic complex.
I hope that you enjoyed this video!
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