The Krakatau volcano had been continuously erupting, with intermittent low level bursts
of activity since at least April 15th of 2022.
Then, on April 22nd at 5:00 pm local time, the data on the RSAM instrument which measures
overall seismic activity suddenly spiked.
This correlated to a sudden and dramatic increase in volcanic activity at Krakatau's central
vent, leading to a series of phreatic explosions due to the interaction of groundwater with
shallow magma.
Soon after, dramatic lava fountaining began, sending a near continuous column of lava several
hundred meters into the air.
This material eventually fell back to the ground, creating a series of lava flows which
moved down Krakatau's slopes.
By noon of April 23rd, one of these lava flows reached the western and southwestern portions
of the overall island.
This rapid lava effusion and lava fountaining subsequently transitioned to an ash dense
plume which rose to a height of 3 kilometers.
What had just occurred was a paroxysm of the Krakatau volcano; essentially, a short yet
violent burst in activity representing the volcano's largest eruptive event since April
11th of 2020.
For context, the Krakatoa volcano is located in southwest Indonesia where it is halfway
between the islands of Java and Sumatra.
The volcanic complex of Krakatoa consists of four distinct islands.
The outer three islands represent the edge of a 9 kilometer wide caldera which, according
to preliminary evidence from local scientists, formed in a catastrophic eruption in either
535 or 540 CE.
In the 1300 years following this collapse, a new volcanic cone grew out of the sea, rising
to a height of 800 meters or 2,625 feet.
This central island would later be destroyed in 1883 in a mid end VEI 6 eruption, creating
35 meter high tsunamis.
After several decades of dormancy, a new volcanic cone grew out of the youngest caldera called
Anak Krakatau, finally emerging above the surface in 1927.
Between 1927 and 2018, it produced frequent strombolian to vulcanian eruptions, growing
this new island to a height of 338 meters or 1,100 feet tall.
However, during this time, eruptive activity slowly caused the southwestern slope of the
volcano to become greatly oversteepened, leading to a large degree of structural instability.
Then, on December 22nd of 2018, 260 million cubic meters of rock slid into the ocean,
generating another destructive tsunami.
This obliterated a large section of Krakatau's edifice above water, causing its summit to
drop to a height of a mere 110 meters above sea level.
In the years since, only small to moderate sized eruptions occurred, creating a crater
lake just above sea level.
This week's eruption has quickly constructed a large brand new cinder cone, most likely
covering the crater lake, which was constructed to a height of 100 meters in a mere 48 hours.
I do want to note that this figure is not official, but rather was an estimate given
by several eyewitnesses who have been watching the ongoing eruption and compared the new
cone's height to that of known features on the island.
The rapid growth witnessed here may seem extreme but has historical precedent.
In 1943, a cinder cone known as Paricutin grew to a height of 50 meters in only 24 hours.
This rapid growth phase has caused some local residents to become worried about the possibility
of another tsunami occurring.
The good news is that a tsunami is highly unlikely and should not be worried about at
this time.
There is currently no long term signs suggesting structural instability in the southwest slope,
which triggered the last tsunami in 2018.
At the present, the best indication of whether Krakatoa will show increasing or decreasing
levels of volcanic activity are its sulfur dioxide emissions as this correlates very
strongly to the amount of shallow magma present.
Krakatoa's sulfur dioxide emissions were only 28 tons a day on April 14th, but by April
23rd was releasing 9,219 tons a day.
At the present, sulfur dioxide emissions are relatively stable, meaning that intense eruptive
activity should continue.
As a result, Krakatoa's alert level was raised from 2 to 3, and a 5 kilometer exclusion zone
was ordered around the volcano.
Thanks for watching.
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