On May 9th, 2022, a swarm of earthquakes began underneath one of the most dangerous stratovolcanoes
in all of Indonesia.
Over the next 24 hours, a series of 177 volcano tectonic quakes occurred underneath the Mount
Awu volcano.
For context, these quakes have been occurring at elevated levels since the volcano's alert
level was raised to yellow on December 12th of 2021.
This spike in seismic activity likely correlates to a new intrusion of magma at depth which
is moving in a non horizontal direction through Awu's magma conduits.
This new intrusion could eventually result in a volcanic eruption, although one is still
unlikely at the present.
As a result, authorities have told residents to stay outside a 1 kilometer radius of Awu's
summit crater.
Keeping a close eye on Awu is very important as its numerous explosive eruptions since
1640 have resulted in the deaths of more than 8,000 people.
The Mount Awu volcano is located in far northeastern Indonesia, where it is one of a chain of islands
which stretch between Sulawesi and Mindanao in the Philippines.
Awu is the northernmost and only active of 4 volcanoes which formed the island of Sangihe.
Its most prominent feature is a 1.5 kilometer wide and 400 meter deep crater which contains
a lava dome that formed in 2004.
Surrounding this crater is an area largely devoid of vegetation due to volcanic gas emissions.
The Mount Awu volcano is located in a highly unusual geologic setting.
To the east are two closely spaced subduction zones.
Inbetween them is the Molucca Sea Plate, which is being subducted underneath two other regional
plates.
The melted crust from these collisions then migrates upwards before erupting on the surface,
forming two chains of volcanoes.
Both of these volcanic arcs are highly active and have ongoing eruptions.
At the present, earthquake activity has remained far above background levels, as earthquakes
have been measured at between 0.88 and 7 kilometers in depth.
The shallowest quakes are likely hydrothermal in origin, so the new intrusion of magma is
probably at between 3 and 7 kilometers depth.
Although this magma is at shallow depths, it is statistically unlikely to reach the
surface and produce an eruption.
With this being said, May 9th was not the first time during 2022 that a sudden and dramatic
spike in earthquakes occurred at Awu.
In early January a similar series of events occurred, leading to a day with 98 volcano
tectonic earthquakes.
However, earthquake activity subsequently dropped, returning to much lower but still
elevated levels.
This is what will most likely will occur with the latest earthquake swarm although anything
is possible.
Although elevated gas emissions have not been detected coming from the crater, this does
not mean that shallow magma is not present.
Rather, it is quite likely that the lava dome capping Awu's summit crater is acting as a
caprock, preventing gasses from escaping.
Awu's numerous deadly eruptions all followed a similar pattern.
A large lava dome was first built which acted as a caprock.
Gasses, magma, and pressure then would build underneath this dome.
Eventually, the pressure becomes too great and the volcanic dome is destroyed, ejecting
large fragments of rock and the acidic crater lake if one exists at that time, causing fragments
to reach several kilometers distant.
The released eruption column then collapses downwards, releasing pyroclastic flows which
have raced more than 5 kilometers distant.
This is what occurred during VEI 3 eruptions during 1856 and 1892 which each resulted in
the deaths of more than 1,500 residents.
In 1966 an eruption an order of magnitude larger injured more than 1,000 people primarily
through falling fragments of the destroyed lava dome, resulting in the destruction of
9 villages and more than 3,000 homes.
In the case of that eruption, the lava dome in question was originally built by a less
explosive eruption from 1930 to 1931.
Thus, if an eruption was to occur in the next several days to weeks, it would likely destroy
the existing 2004 lava dome rather than add to it.
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