In the days leading up to November 15th of 2022, there was an apparent increase in earthquakes
in the vicinity of the town of San Miguel in El Salvador, many of which were large enough
to be felt.
Then, on November 15th at 8:15 am local time, the adjacent San Miguel volcano explosively
erupted, sending a plume of ash several hundred meters into the air.
Over the next 12 hours, several dozen more explosions occurred which were all relatively
small in magnitude.
Overnight, the low intensity explosions continued, which created some incandescence at the summit
crater as bombs of lava were ejected.
What had just begun was an example of yet another small scale phreatomagmatic eruption
of the San Miguel volcano, marking its first eruption in several years.
San Miguel is now the 47th volcano to be actively erupting, and due to the hundreds of thousands
of people which live adjacent to this volcano, it is obvious for a large number of people.
As a result, a local government agency in El Salvador implemented a 3 kilometer, or
slightly under 1.9 mile exclusion zone around the volcano.
For context, the San Miguel volcano is located in southeast El Salvador where it is 11.5
kilometers west southwest of a city which goes by the same name.
Like other adjacent volcanoes, San Miguel exists due to an offshore tectonic plate collision
to the south of the country.
There, the Cocos Plate is subducting underneath the Caribbean Plate.
The melted material from this collision then migrates upwards until it on occasion erupts
onto the surface, forming a chain of volcanoes.
Looking at San Miguel from satellite, it becomes immediately obvious that despite being a stratovolcano,
it tends to erupt rather low silica basalt composition lavas.
This can be observed via abundant red clasts of scoria which cover the volcano's summit,
being deposited largely through mildly explosive strombolian eruptive activity.
As one of the most active volcanoes in El Salvador, San Miguel has erupted 31 times
since 1699.
The vast majority of these eruptions occurred at the volcano's summit crater and were relatively
small, depositing small amounts of ash within a several kilometer radius of the volcano
and in more recent times occasionally disrupting regional air traffic.
In a manner of speaking, San Miguel's latest eruption and its overall recent eruptive activity
is quite similar to Mount Kerinci in Indonesia.
They both produce intermittent phreatomagmatic explosions which are relatively small, whose
most destructive effects are generally damaging local farms by contaminating them with small
amounts of ash.
Despite this fact, San Miguel can and has in certain circumstances caused significant
property damage.
This occurred not through highly explosive eruptions but rather through effusive flank
eruptions.
These have produced flows of lava which can within hours to days travel up to 11 kilometers
from San Miguel's summit.
Around a half dozen of San Miguel's historical eruptions have produced flank lava flows,
but several of these stayed within a 4 kilometer radius of its summit.
While flank effusive eruptions from cinder and spatter cones can technically occur in
any direction around the volcano, they appear to be most likely to originate from a north-northwest
trend which runs through San Miguel's two most obvious flank lava flows.
Although San Miguel appears to have only produced small scale explosive eruptions throughout
its geologic history, there is some debate as to whether a larger eruption occurred in
the past several thousand years.
One paper suggested a VEI 4 explosive eruption occurred while another found no evidence that
this volcano has ever produced a highly explosive event.
Regardless of the very low likelihood of a repeat event occurring, the possibility of
such is still nonzero.
Luckily, there has not been any abundant uplift detected at San Miguel in the last week, while
its carbon dioxide emissions only increased slightly from 500 to 600 parts per million
before erupting.
As a result, San Miguel's latest eruption will likely be small, and there is not yet
any evidence that a flank eruption will occur.
Thanks for watching!
If you would like to request a specific topic, please leave a comment below!
Additionally, I would like to give a special thanks to @lol_iyoutube for granting me permission
to use his footage of several of El Salvador's volcanoes!