Located to the east of Madagascar is one of the most beautiful and scenic volcanic complexes
on the planet.
Here, the island of Reunion contains several caldera remnants which contain a 1,600 meter
or 1 mile high sheer cliff and several towns within them.
However, while this volcano is extinct, the one to the southeast represents one of the
most active volcanoes on the planet.
Known as Piton de la Fournaise, it is a massive primarily basalt composition shield volcano
which has been erupting intermittently for around 530,000 years.
While its eruptions have been primarily effusive, you might notice several distinct scars in
the landscape to the west of the volcano's summit.
These steep valleys and cliffs represent the site of three massive caldera forming eruptions,
where parts of the island slid to the east in unthinkably large landslides.
These large volume eruptions occurred 250,000 years ago, 65,000 years ago, and in 2700 BCE,
the latter of which consisted of an explosive eruption the same order of magnitude as the
1980 eruption of Mount Saint Helens.
While this volcano has not erupted since January 17th of 2022, it has been showing significant
signs of unrest which suggest that an eruption might occur in the short or mid term future.
Since then, the summit of Piton de la Fournaise has slowly been pushed upwards due to the
refilling of the volcano's underlying magma chamber.
By the end of August, the magma chamber had been mostly filled, causing significant pressure
to build.
This resulted in a series of earthquakes which began occurring at an increasing frequency
on August 26th.
By 4 days later, the number of quakes had spiked to unusually high levels, and were
occurring at between 1 and 3 kilometers in depth.
Over the first week of September, these quakes got shallower and shallower, with some only
occurring a few hundred meters below the surface.
Finally, on September 7th, at 4:54 pm local time, a rapid increase in earthquakes and
the uplift of the volcano's summit occurred.
A seismic crisis had begun, and it was fully possible that an eruption would occur in the
next several minutes to hours as magma was definitely on the move.
As a result, the entire volcano was closed off temporarily.
It is now a day later, and the intrusion of magma stopped at a shallow depth below the
surface, meaning an eruption did not occur.
While this individual seismic crisis is over, an eruption is quite likely by the end of
2022 although this is not a certainty.
However, an eruption could still occur much sooner.
About a third of Piton de la Fournaise's recent eruptions have been preceded by failed intrusions
like what just occurred in the days before an eruption began.
Since Piton de Fournaise's magma chamber contains a significant amount of pressure, and this
pressure will only be relieved by another magmatic intrusion, an eruption could occur
in the next week or two with only a few minutes to hours of advanced notice before a new eruption
begins.
While eruptions have occurred at a distance away from the volcano's main summit, and at
cinder cones, it does not appear that any sort of new eruption will do this.
Magmatic uplift has been centered at the volcano's summit, meaning any sort of new eruption would
begin there and be primarily effusive.
Of course, Piton de la Fournaise much like Kilauea in Hawaii occasionally produces minor
to moderate ash emissions, with many eruptions being rated on the volcanic explosivity index
as a 1 or a 2.
This means that whenever an eruption does occur, it might temporarily ground regional
air traffic as the safe amount of ash particles for an airplane engine is very close to 0.
While many lava flows produced at Piton de la Fournaise only travel a few hundred meters
to a few kilometers, there is always a possibility that a longer distance lava flow might be
generated, travelling all the way to the ocean.
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