It is now day 25 of Iceland’s newest eruption of the Fagradalsfjall volcano. Lava has so far
spread across an area of 1.5 square kilometers or 0.58 square miles during this timespan, and I
estimate that a total of 15 million cubic meters of molten rock has been ejected. Any of the tens
of thousands of people who viewed this eruption whether in person or through online livestreams
might have noticed that the lava is behaving slightly different when compared to the 2021
and 2022 eruptions. This assertion is supported by the geochemistry of the recently erupted lava,
although, the differences appear to be minor. To help display these differences, I present a
total alkali versus silica chart, and have added on the compositions of several Icelandic eruptions
from other volcanoes for reference. And now, here is where Fagradalsfjall's eruptions fell in 2021,
2022, and 2023. As you can see, the erupted lava is getting negligibly more silica and alkali rich,
which is leading to an every so slight increase in viscosity. Thus, the lavas erupted in 2021 were
able to move at a maximum speed several percent higher than the current 2023 eruption. While
this pattern could be a fluke, it suggests that some magma at depth emplaced in 2021 is slightly
evolving through fractional crystallization, which is then emerging alongside actual fresh magma
from the mantle during subsequent eruptions. While the current eruption is still ongoing,
it is quite obvious to everyone that the eruption is in its waning stages. Now, lava barely spatters
above the active spatter cone at times, and the lava lake within it has noticeably dropped when
compared to 48 hours ago. The question on everyone's mind is simply "when will this
eruption end, and will I even have time to visit it?" While the initial eruptive rate on day 1 hour
1 of this eruption was 70 cubic meters per second, it has now dropped to less than 5%
of that original value on day 24, barely producing around 3 cubic meters per second. The last time a
separate vent of Fagradalsfjall dropped to 3 cubic meters per second, the eruption only continued for
another 6 days. That was in 2022. However, the current eruption, although it has continuously
decreased which each day producing less lava than the prior day, has decreased in intensity at about
70% slower than the 2022 eruption. Thus, although we do not know when this eruption will end,
in my opinion I suggest that the eruption could end between August 8th and August 13th of 2023.
Regardless, we can definitely say that lava is struggling to be erupted out of
the primary crater, with large spatters beyond the crater rim edge being almost nonexistent.
Despite the greatly decreased amount of erupted rock, an unusually tall albeit brief lava fountain
occurred at around 1:30 am local time on July 30th, with fragments at the peak of the fountain
taking 6 full seconds to reach the ground. Thus, I estimate that the brief lava fountain
which lasted for less than 15 seconds ejected molten rock 176 meters or 577 feet into the air.
Although this is not a definitive measurement, Fagradalsfjall's eruptions seem to only be
actively occurring if the tremor chart for at least 1 of the 3 values is reading a number above
4500. As you can see, this value is still above that threshold, so the eruption is still ongoing.
Despite the decreasing eruptive intensity, the volcano is still emitting several thousand tons
of sulfur dioxide each day. Although you cannot directly see this gas, you can see the effects of
it as when sunlight passes through the material, it returns an unusually bright blue haze.
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