On April 15th, 2022, a swarm of earthquakes began underneath the Ruang stratovolcano in
northeast Indonesia.
Over the next 24 hours, a series of 35 volcano tectonic quakes occurred.
For context, this was the same number of earthquakes seen in the last 2 weeks, indicating a greatly
increased level of activity.
These quakes were caused by a new intrusion of magma at depth, which could eventually
result in a volcanic eruption.
The following day, a series of 50 magmatic earthquakes occurred in the first 5 hours
of the morning.
As a result, Ruang's alert level has been raised from green to yellow, indicating an
increased likelihood of an eruption.
So, how deep is this new intrusion of magma?
How likely is an eruption?
This video will answer these two questions, and discuss this highly dangerous volcano.
The Ruang 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.
Several hundred residents live on this small volcanic island which measures 4.7 kilometers
wide and 4.4 kilometers long.
In its center is a 410 meter wide crater which represents where the vast majority of historical
eruptions have occurred.
Several remnants of blocky lava domes are located within, while the scars of older volcanic
craters can be seen outside the crater.
On the exterior of the volcano are blocky lobes of basaltic andesite and andesite lava
which formed during prolonged eruptions.
This 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 is continuing to increase at Ruang, as earthquakes have
been measured at between 3.1 and 7.1 kilometers depth.
The shallowest quakes are likely hydrothermal in origin, so the new intrusion of magma is
probably at between 4 and 7 kilometers depth.
Although this magma is at shallow depths, it is statistically unlikely to reach the
surface and produce an eruption.
Nevertheless, an eruption is still quite plausible as its chances are in the double digit percentage
range, despite most magmatic intrusions never reaching the surface.
Due to the increasing likelihood of an eruption, the government has advised people to remain
out of the following areas; within 1500 meters of Ruang's main crater, and within 2500 meters
of Ruang's east, southeast, south, and southwestern sectors.
Those sectors are most likely to be the site of pyroclastic flows which will easily overflow
the crater as the topography generally guides them in that direction.
Since the island is quite small, it would need to be fully evacuated during any eruption,
as people would have less than 75 seconds to escape if a superheated gas current was
heading their way.
Ruang's largest known eruption lasted for 5 days in 2002, which sent a plume of ash
to a height of 16 kilometers.
If a repeat of this eruption was to occur, the entire island would be put at risk.
Also, Ruang is one of a select group of dangerous volcanoes which have produced volcanic tsunamis
as part of the island is structurally unstable.
In 1871, a lava flow produced by a small eruption caused a slope of the volcano to overload
with weight, making 100 million cubic meters of rock slide into the ocean.
This generated a wave up to 25 meters in height, which devastated several regional islands.
While a repeat of this tsunami is unlikely, volcanoes that have produced prior tsunamis
are far more likely to produce future tsunamis.
With this being said, if an eruption was to occur it would most likely not cause a tsunami
and be completely confined to the island it is situated on, as part of a small VEI 1 or
VEI 2 sequence.
However, prior volcanic eruptions have thrown bombs of lava as far as 7 kilometers distant,
so the possibility of further evacuations on the adjacent island exists.
Thanks for watching.
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