Since July 30th of 2022, much attention in Iceland has been placed on the Krysuvik volcanic
system, as a shallow intrusion of magma generated more than 8,000 earthquakes, the largest of
which was a magnitude 5.5.
While this would eventually result in a new volcanic eruption, minor volcanic activity
began also occurring at another volcano in Iceland.
On August 2nd at 12:42 pm local time, an earthquake swarm began at the Grimsvotn volcano specifically
in the eastern section of its caldera complex.
These quakes largely occurred at unusually shallow depths of 1 to 2 kilometers, which
was highly suspicious.
Since these quakes occurred in combination with minor amounts of volcanic uplift which
had been ongoing since late March of 2022, Grimsvotn's alert level was subsequently raised
from green to yellow.
` For context, the Grimsvotn volcano is located
220 kilometers east of Rekjavik, where it is located under a massive ice sheet known
as Vatnajökull.
This glacier is the site of 6 highly active volcanoes which each have erupted or are suspected
to have erupted in the last 300 years.
In a manner of speaking, this glacier could be considered the volcano capital of the country.
The reason why volcanic eruptions are so common here relates to why volcanism exists in Iceland.
In the mantle underlying the nation in a hotspot which supplies molten rock to the surface
just like seen in the Canary Islands or the Hawaiian Island chain.
This hotspot is currently centered between the Grimsvotn and Bardabunga volcanoes, and
as a result, they are incredibly active.
In fact, Grimsvotn is considered to be the most active volcano in the country, erupting
about once every 9 to 14 years.
Several eruptions since 1930 occurred on the southern wall of its central caldera complex.
Its last eruption in 2011 was no different, ejecting 0.8 cubic kilometers of basaltic
tephra in what was nearly a VEI 5 eruption.
In addition to other effects, this 8 day long eruption caused more than 900 flight cancellations
across Europe.
However, not all of Grimsvotn's recent eruptions have occurred from within its caldera.
To the southwest, Grimsvotn is linked with a series of lengthy fissure systems.
One of these fissure systems produced Grimsvotn's most famous eruptions, when from 1783 to 1785
a 27 kilometer long fissure with 140 craters and vents erupted, producing massive amounts
of basaltic lava in what could almost be considered a miniature flood basalt.
By the time the so called Laki eruption had ended, 565 square kilometers of land had been
covered in molten rock by 14.7 cubic kilometers of material.
While earthquake swarms and long term uplift are both signs of volcanic activity, there
is a crucial third sign at Grimsvotn which has not yet occurred with its latest unrest.
When this volcano's fumaroles are heated to unusually high levels, or lava begins erupting
beneath the ice sheet, it causes large amounts of glacial runoff to occur in what is known
as a jökulhlaup.
The last group of notable jökulhlaups occurred during November and December of 2021, when
Grimsvotn was also at a raised alert level.
Thus, for now, it does not appear that magma is rapidly moving towards the surface, unlike
what recently occurred at the Krysuvik volcanic system.
The true root cause of these quakes is still relatively unclear, with possible causes ranging
from minor magma movement to hydrothermal fluid movement, local tectonics, or they could
simply be glacier earthquakes.
Glacier earthquakes are most frequently observed at volcanoes which have glaciers in the northern
hemisphere during the hottest months of July and August, which is when the highest rate
of glacial retreat occurs.
This removes pressure on underlying faults, which beforehand were partially prevented
from moving due to overlying mass, generating an earthquake.
While the latest episode of unrest at Grimsvotn is not as remarkable as what was witnessed
during November to December of last year, it is still early, so a close eye will be
kept on this volcano for the time being.
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