In the early morning hours of September 10th of 2022, a new volcanic eruption began at
a shallow submarine volcano in Tonga.
This new eruption was not occurring at the now infamous Hunga Tonga Hunga Ha'apai volcano,
which was obliterated in the planet's largest explosive eruption in 31 years earlier this
year, but rather at a different volcano known as Home Reef.
Before the eruption began, this volcano whose edifice began at a depth of 1100 meters below
the seafloor had a summit at a mere 10 meters or 33 feet below sea level.
The reason it was so shallow was because this volcano has twice formed a temporary volcanic
island, rising above sea level in both 1984 and 2006.
Because of this, it took less than 12 hours of erupting for Home Reef to one again climb
above the ocean surface, forming what at the time was measured by Tonga Geological Services
to be an island 70 meters wide and with a summit 10 meters above sea level.
While the two previous eruptions whose lengths were measured only lasted 5 and 10 days, this
eruption is now in its 15th day.
And, strangely, unlike the two prior eruptions it appears to be unusually nonexplosive.
During this time, the new island of Home Reef has grown from 70 meters to 170 meters to
182 meters wide and now the most recent measurement is 218 meters wide.
While this new island is growing at a rate which is slower than prior eruptions which
formed temporary islands up to 1500 meters wide, something is quite different.
While prior eruptions built islands primarily out of ash, although it has not been completely
confirmed, it appears that this newest island is instead being built out of viscous dacite
lava.
Using satellite imagery from the Tonga Geological Services which is a bit higher resolution
than the NASA imagery being shown here, you can see what appear to be individual flows
of viscous lava.
Thus, while Home Reef does produce lava which has the potential to produce a far more explosive
than that produced at Hunga Tonga Hunga Ha'apai, there is clearly another factor in play.
I speculate that Home Reef's eruptions produce lava that has a lower amount of volatile gasses
than seen at Hunga Tonga Hunga Ha'apai.
While prior eruptions from this volcano have resulted in towering plumes of volcanic material
which reached above 10 kilometers in height, the plume during this eruption has regularly
been under 2,000 meters in height.
Using this information, we can estimate the volcanic explosivity index rating of the ongoing
eruption.
Based on comparing it to typical eruption plume heights, the ongoing eruption seems
to best fit a volcanic explosivity index rating of a 1 or a low 2.
While prior eruptions from this volcano were explosive throughout the entire length of
the eruption, the ongoing eruption did not produce any amount of measurable ash until
its 11th day.
In total, while the volcano has produced more than 70 total individual eruptions since September
10th, only 2 of them produced quantities of ash.
This is a bit exciting, as it further infers that the newest island contains a substantial
volume of lava rather than ash.
While volcanic ash islands such as those produced from Sete Cidades in 1811, Home Reef in 1984
and 2006, or Fukutoku Okanoba in 2021 tend to wash away quite quickly, typically within
2 years, lava rich islands tend to remain for decades if not longer.
This is the reason why the expanded island created by the Nishinoshima volcano has remained,
as you can see by the abundance of more erosion resistant lava it created.
In other words, if the Home Reef volcano truly is producing a lava rich mainly effusive eruption,
there is a good chance that we might now have the world's newest semi-permanent volcanic
island.
I want to note that prior eruptions of this volcano have distributed explosively erupted
rafts of pumice to the shores of Fiji and Australia.
However, I have yet to see evidence of any similarly large rafts from the ongoing eruption.
Regardless, the Tonga Geological Services have ordered all ships to stay at least 4
kilometers away from the ongoing eruption.
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