Seven of the nine islands in the Azores Island chain contain active volcanoes, with only
the islands of Corvo and Santa Maria being extinct.
This volcanic nature was reminded to the islands inhabitants when a swarm of several thousand
earthquakes occurred in the timespan of a week on the island of Sao Jorge in March of
2022, with the quakes being caused by a fresh intrusion of magma representing more than
10 million cubic meters of material at a depth of several kilometers.
Luckily, that intrusion stalled, although the area above it is still the site of an
elevated number of earthquakes.
Because of this, another volcano in the Azores island chain that is also producing suspicious
signs has somewhat slipped under the radar of many news agencies, despite the fact that
it has been at a raised alert level ever since August 1st of 2022, Terceira.
This initial increase in alert level was caused by an elevated rate of magnitude 1.5 or higher
earthquakes occurring, which beforehand occurred at a rate of 1 every 5 months but afterwards
occurred at a rate of 3 to 5 a month, underneath sections of the Santa Barbara volcanic cone.
Since then, the number of earthquakes has very slowly albeit somewhat exponentially
continued to increase, as best shown via this chart.
This fact has become all the more pronounced since April 30th 2023, when I received a half
dozen messages from various citizens who lived on the island of Terceira who were concerned
by earthquakes which struck on that day.
Although the magnitude 2.7 and 3.6 quakes which occurred that day were not all that
remarkable, what is important is that they represented the two largest quakes thus far
since it appears that Santa Barbara's hydrothermal system seemingly reactivated.
Following this, the last 7 days in May have been the site of 10 volcano tectonic earthquakes
which is a record high in the 2020s beneath this volcanic cone.
And now, the majority of days on Terceira are producing at least one volcanic earthquake
large enough to be felt on a section of the island.
As a quick note, everything for the rest of the video which I am about to say is highly
speculative and not currently proven by facts.
With this being said, here is my opinion based analysis on the situation.
Despite the lack of uplift which do not worry I have looked for every week during 2023 but
not detected on Terceira, in my opinion, magma still might be moving underneath this volcano.
My best educated guess would place a 1600 meter long sill beneath a section of Santa
Barbara's western flank at a depth of 6 to 8 kilometers.
In an attempt to explain why uplift is not occurring, I suggest that new material is
stopping within a largely empty magma chamber which might be presently refilling.
Now, while this could technically result in a new volcanic eruption which would have an
explosive component to it, odds suggest that a volcanic eruption will most likely not occur,
and whatever is going on underneath this volcano will eventually fade without an eruption.
For some context, Terceira has been the site of 11 earthquake swarms or elevated periods
of seismic activity underneath various volcanic centers on the island ever since it was settled
by Europeans in the 1500s.
Occurring at a rate of once every 45 years or so, only 3 of these 11 periods resulted
in a volcanic eruption, with submarine eruptions occurring in 1867 and 1998 to 2000 and a land
based eruption in 1761.
Since the current earthquakes are not centered offshore, I want to note that it appears somewhat
similar to the preceding earthquake sequence in 1760.
In the year before Terceira erupted, a slow albeit somewhat exponential increase in earthquakes
occurred month over month until finally the rate produced a very large spike.
However, that sequence produced two things that the ongoing sequence so far has not.
One it produced ground deformation.
And two, although not for a known reason, it caused a series of fumaroles at the Furnas
do Enxofre site to suddenly produce less rather than more gas while this was ongoing.
At the present, gas emissions have not seemingly changed.
Now with all of this being said, the current earthquake sequence could simply be explained
by a change in the volcano's hydrothermal system without a fresh intrusion of magma
occurring.
We simply do not know yet.
Becuase of all of this activity, on my 0 to 10 opinion based volcanic unrest scale, I
would place Terceira as a 3.
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