In the last several days, much attention in the world of volcanology had been on the erupting
Mauna Loa volcano in Hawaii.
However, on the 1 year anniversary of a destructive eruption at the Semeru volcano in Indonesia,
another damaging eruption occurred.
On December 4th of 2022, Semeru began producing a series of unusually long travelling pyroclastic
flows, which rapidly swept down its flanks at a speed of more than 150 kilometers per
hour, going on to travel up to 7.5 kilometers away from its summit.
However, as the minutes progressed, the size of explosions and length of pyroclastic flows
continued to increase until a record setting eruption occurred.
At about 11 AM local time, a continuous sub-plinian eruption occurred, sending a plume of ash
high into the atmosphere.
Part of the lava dome subsequently collapsed, releasing a pyroclastic flow which swept down
a riverbed, destroying many structures adjacent to it.
As the pyroclastic flow made a slight turn at a distance of 12 kilometers away, a camera
which recorded the whole sequence was destroyed.
Then, two hours later an even more energetic pyroclastic flow passed the same spot, going
on to travel up to 18.7 kilometers or 11.6 miles away from Semeru's summit, marking its
longest pyroclastic density current on record.
The aftermath of this flow showed a destroyed and scorched landscape where it touched, and
in some areas more than 1 meter or 3 feet thick of still steaming pyroclastic material
was deposited on the ground.
As the eruption plume drifted away from the volcano to the west, it caused ash to rain
down over a wide area.
What had just occurred was an unusually large vulcanian and perhaps sub-plinian eruption
of the Semeru volcano, which was nearly identical to its destructive eruption exactly 1 year
ago.
However, although the 2021 eruption caused a number of casualties, this eruption has
so far not caused any although this fact is still uncertain.
Whereas the 2021 eruption occurred without much warning, the latest eruption occurred
after a series of increasingly voluminous flows which when combined with the fact that
many at risk areas were completely or near completely evacuated may have led to no casualties
occurring.
Due to the fact that an eruption is ongoing, Semeru's alert level was raised to its highest
level, aka from a 3 to a 4, an extended evacuation radius was implemented.
This exclusion zone encompassed an area around the entire volcano to a distance of 8 kilometers
from Semeru's summit, in addition to a distance of 19 kilometers along a prominent drainage
to the southeast and within 500 meters of it.
I had reported on early warning signs of a near future explosive eruption at this volcano
all the way back on October 30th.
Although Semeru was already erupting at the time, it underwent a period of rapid uplift,
indicating the influx of a new and large batch of magma.
Over a span of several days, the volcano was pushed upwards by a rate of approximately
2 centimeters or 4/5th of an inch each day.
Then, for a period of more than 30 hours straight sensors recorded a continuous harmonic tremor,
which is generally caused by the rapid movement of magma and volcanic gasses, often preceding
a volcanic eruption.
At the time, I specifically predicted that an explosive eruption which was larger than
Semeru's December 4th 2021 eruption would occur, and that is exactly what happened.
Although the aforementioned tremor and uplift would eventually pause, it went on to reappear
around 12 days ago.
As pressure built up underneath Semeru's active lava dome, it soon reached an overpressure
situation.
This caused the overlying rock to fracture and then partially collapse, generating the
eruption which just occurred.
I want to remind everyone who lives near Semeru that its eruption is still not over.
More long travelling pyroclastic flows could occur with little or no warning so please
stay away from the volcano.
Thanks for watching and please stay safe!
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