It is now day 6 of the eruption of the Meradalir fissure in the Krysuvik volcanic system of
Iceland.
Due to a lava effusion rate higher than a similar eruption which occurred in 2021, construction
of a towering spatter cone has already begun.
When I visited the ongoing eruption on August 6th, I used the time it took for fragments
of lava to fall to estimate the spatter cone's height, reaching a figure of about 15 meters
or 49 feet tall.
Whereas at the beginning of the eruption the area simply had a fissure which rather evenly
erupted rates of material along its entire length, there are now only 4 vents erupting
molten rock.
So, what happened?
Simply put, the existing vents began absorbing each other.
What used to be perhaps a dozen vents is now only 4, and eventually this will become only
a singular vent.
The exact same sequence of events occurred during the 6 month long eruption of Geldingadalir
in 2021, building a tall spatter cone which also acted as its primary vent.
However, before this spatter cone was constructed, it was simply also a fissure, whose abundant
vents later became a series of small spatter cones which then became a single tall cone.
While the rate of lava effusion was 32 cubic meters per second on day 1 of the eruption,
it has since decreased to around 18 cubic meters per second.
Despite being a significant decrease, the eruptive rate is still nearly double what
Geldingadalir averaged in 2021.
As a result, the current eruption seems to be progressing through recognizable stages
at a faster rate than than its precedessor.
These stages can tell us what type of eruptive activity to expect in the upcoming weeks to
months and are as follows.
First, a small fissure erupts along a relatively straight line, ejecting lava several dozen
meters into the air.
As the area becomes buried by a layer of lava, the strongest vents siphon material from other
nearby vents rendering them inactive.
Thus, what was initially a fissure of material becomes a series of closely spaced spatter
cones.
Eventually, the largest of these spatter cones will become the dominant singular vent.
While this process is ongoing, continued fissure propagation will also occur, lengthening the
eruptive fissure.
What was initially a continuous stream of molten rock with lava fountains will then
become an intermittent one as the supply of fresh magma to the surface is outpaced by
the rate at which the spatter cone can erupt it.
This subsequently turns into a series of eruptions which act like Yellowstone's Old Faithful
Geyser.
Pressure beneath the cone builds until it is released upwards, resulting in several
minutes of lava fountains which may reach heights exceeding 500 meters.
After the magma is drained from the intermediate shallow chamber, a complete lack of eruptive
activity occurs for several minutes as it repressurizes.
As the days progress, the length of time between these bursts of activity will slowly increase,
meaning a geyser like eruption which occurred once every 5 minutes may instead only occur
once every 10 and then 15 minutes.
The geyser-like activity will then stop altogether, being replaced by weak continuous lava effusion.
This in time will eventually weaken until no fresh lava emerges, ending the eruption.
While the ongoing eruption does have a higher rate of lava effusion then its predecessor,
it is still rather low in the context of effusive eruptions around the planet.
While it is higher than the average rate Kilauea erupted at from 1983 to 2017, it is lower
than the typical eruptive rate of Mauna Loa, whose last eruption averaged 138 cubic meters
per second.
Also, the similar fissure eruption of the Bardarbunga volcano resulted in a rate of
94.9 cubic meters per second.
And, all of these are lower than the famous miniature flood basalt like eruption of Laki
in Iceland during 1783 which averaged 700 cubic meters per second.
For the immediate future, eruptive activity should continue at a high rate at Meradalir.
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