On May 6th, 2022, a swarm of earthquakes began to the northwest of the city of Grindavik
in Iceland.
These quakes were not tectonic in origin, but rather occurred due to the movement of
magma.
Over the next 11 days, more than 3,300 earthquakes occurred, the largest of which was a magnitude
4.3.
This occurred alongside magmatic uplift over dozens of square kilometers.
As a result, the alert level of the Reykjanes volcano which spans several hundred square
kilometers of ground was raised from green to yellow on May 15th.
As displayed by this map courtesy of the Iceland Met Office, the ground uplift is centered
2.5 kilometers north-northwest of the city of Grindavik.
The ongoing intrusion of magma is currently at between 3 and 5 kilometers depth with a
volume of approximately 1.5 million cubic meters.
While this may sound like a lot of material, as it could fill 6,000 olympic sized swimming
pools, this is rather small for a magmatic intrusion.
Although there isn't a strong correlation, generally speaking the smaller an intrusion
of magma is, the less likely it is to reach the surface.
Regardless of its small size, this magmatic intrusion is quite interesting for a number
of reasons.
For context, the Reykjanes peninsula consists of 4 separate poorly defined volcanic systems.
While these systems can individually erupt, they tend to erupt in relatively rapid succession
during a period of prolonged elevated volcanic activity.
The last such period of elevated activity on the peninsula resulted in a series of 18
eruptions between 840 and 1240 AD.
The reason I am bringing this up is when Geldingadalir erupted in early 2021 many scientists said
that we were at the beginning of a several decade to several century long period of intensified
volcanic activity on the peninsula.
I agree with this assessment, but think the unrest truly began in early 2020.
That year, the alert level of the Reykjanes volcano was also raised to yellow on two separate
occasions as three different magmatic intrusions occurred just southwest of the geothermal
power plant at between 3 and 4 kilometers in depth.
Thus, since 2020 a total of 6 magmatic intrusions on the peninsula have occurred and only 1
so far has resulted in a volcanic eruption.
Ignoring the odds an eruption will or will not occur, lets suppose that a brand new volcanic
eruption did occur.
Where would the lava flow and what would it look like?
Near Grindavik, we have two post ice age era lava flows which provide approximations of
what the eruption would be like and where it would flow.
These eruptions both occurred to the northwest in 400 BC and 1240 AD.
Both eruptions had an explosive component to them, rating on the volcanic explosivity
index between a 1 and a 2.
If a repeat event of similar intensity were to occur today, the nearby city of Grindavik
could expect to see between a dusting to 4 centimeters in total ashfall.
The 400 BC eruption was the more explosive of the group, resulting in a lava flow which
expanded in all directions but generally flowed towards the south and southwest.
A better comparison to the current situation is the 1240 AD eruption, where several spatter
cones erupted close to where the ongoing uplift is, sending lava towards a natural low point
between two higher rock edifices.
Taking this into account and overlaying the current topography of the region, a new eruption
would be most likely to send lava flows in two directions as labeled on screen.
The area to the north of Grindavik has a bowl shaped area so any new lava would pool for
an extended length of time before heading towards the town.
This pathway could easily be blocked via an earthen dam if an eruption were to occur.
The main lava flow would however move to the west before turning south.
Due to the general flat terrain of the area, such a lava flow might expand and take out
several structures on the southwest edge of Grindavik.
Of course, everything just said is hypothetical, and we do not know if an eruption will occur.
Thanks for watching.
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