In the United States, 3 volcanoes are actively erupting.
Two of these erupting volcanoes are Pavlof and Great Sitkin in Alaska, while the third
is Kilauea in Hawaii.
However, due to unusual activity in another area there is a possibility that not one but
two volcanoes could join this list.
In American Samoa, a highly unusual earthquake swarm has been ongoing since at least July
26th of 2022, repeatedly jolting several of the area's islands.
This earthquake swarm has involved hundreds of earthquakes, the largest of which were
in the magnitude 2 to 3 range.
These quakes are not occurring due to local tectonics but rather the movement of magma
at depth.
While the exact location of these quakes has been difficult to pin down due to lack of
close seismic stations, this gap has been narrowed during the past several days as additional
stations were put in place.
Initially, the earthquake swarms were believed to have occurred somewhere between the volcanic
island of Ta'u and the highly active Vailulu'u seamount to the east.
However, more recently Vailulu'u was ruled out as the source of these quakes.
Instead, the ongoing earthquake swarms are occurring close to if not beneath Ta'u island
with some secondary activity possibly originating at the islands of Ofu-Olosega.
As a result, the alert level of both Ta'u and Ofu-Olosega was raised from white indicating
a lack of sufficient monitoring equipment to yellow meaning an advisory alert level.
While having vastly different appearances, both lush rainforest covered islands have
produced eruptions at some point during the Holocene, indicating the time period of the
last 11,700 years.
To the north, the island of Ofu is connected to the island of Olosega via a narrow bridge.
These two closely spaced islands represent the above sea level portions of two massive
shield volcanoes which rise 4,500 meters or 14,763 feet above the seafloor.
While deeply eroded and containing a series of cliffs, the Ofu island produced a single
or group of explosive eruptions around 10,000 years ago, forming the edge of a notable tuff
cone just offshore of the main island.
Additionally, a more recent eruption occurred to the southeast of the Olosega island at
a submarine vent just offshore of it in 1866.
To the southeast, the larger Ta'u island has a profile more typical of a shield volcano,
with one exception; its summit and southern flanks are breached by a massive collapse
scar to the south, marking the site of a large landslide approximately 22,000 years ago.
This island which only has an area of about 17 square miles has several young looking
spatter and cinder cones on its flanks.
Interestingly, one of these features which formed in an explosive eruption and is known
as a tuff cone surrounds a portion of one of the island's settlements.
While the exact age of these features is unclear, they form two areas of activity where geologically
recent eruptions have occurred.
Despite the implied low silica content of magmas at these volcanoes, several populated
areas could be put at risk due to a future eruption, and there is a possibility that
an eruption would be explosive due to the interaction of magma with seawater or groundwater.
An eruption would be more likely to be explosive if it occurred at shallow depths along the
coastline or in shallow water.
While scientists are currently not sure exactly where the earthquakes are precisely centered,
there are three possibilities.
Possibility one is that a magmatic intrusion is ongoing at a submarine ridge between Ta'u
and Ofu-Olosega, which could eventually result in a surtseyan explosive eruption at shallow
depths.
Possibility 2 is that a magmatic intrusion by sheer coincidence is ongoing at both Ta'u
and Ofu-Olosega, which could result in two separate eruptions.
Possibility 3 is that a magmatic intrusion is ongoing at Ta'u, and regional uplift of
the crust might be causing associated non volcanic earthquakes on the two islands to
the northwest.
Whichever is the case might be revealed as the days progress and more data is collected.
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