Earthquake swarm in American Samoa likely related to Taʻū volcano or the nearby submarine Vailuluʻu
An earthquake swarm is occurring in the Manuʻa islands of American Samoa. These earthquakes are most likely related to either Taʻū volcano or the nearby submarine Vailuluʻu volcano, according to the USGS.
- Residents of the Manuʻa group of islands in American Samoa continue to feel earthquakes. Reports from National Park of American Samoa staff and Taʻū residents suggest that the activity began on July 26.
- Since August 10, earthquakes have also been reported by residents of Ofu and Olosega islands.
- Reports suggest that the earthquakes vary in intensity, but are generally short, sharp jolts. The earthquakes are more likely to be felt by people indoors at rest and along the coast, where buildings sit on sediment that amplifies shaking. These factors are probably responsible for the variability in reporting.
- Based on the reports, these earthquakes are probably related to either Taʻū or Vailuluʻu volcanoes.
- Scientists are investigating earthquakes and unconfirmed reports of other activity. Several residents of Taʻū reported loud booming noises on Wednesday night, August 10; no other noises have been reported since then.
- Scientists plan to install additional instruments to monitor earthquakes and other activity in the coming week.
- Taʻū is a shield volcano with rift zones to the northeast and northwest; the last eruption of Taʻū occurred in 1866 as a submarine cone that formed between Taʻū and Ofu-Olosega islands.
- Vailuluʻu is a submarine seamount whose summit is about 600 m (1 970 feet) below sea level. The last eruption of Vailuluʻu was in 2003, during which a cone formed within the summit caldera.
The earthquake activity reported to date suggests a local volcanic source, according to an analysis performed by the USGS.1
Due to limited earthquake monitoring equipment, the exact location of these earthquakes is currently unknown.
The precise location of these earthquakes is still unclear due to a lack of seismic monitoring equipment.
According to the USGS, not all earthquake swarms result in eruptions. Current low-level seismic activity may persist and fluctuate in intensity for days to months without an eruption.
However, it’s also conceivable that the swarm represents an early warning sign of an impending eruption.
“At this time, we cannot determine which of these possibilities is more likely,” scientists at the Hawaiian Volcano Observatory (HVO) said. Sharing of information related to the unrest was assigned to HVO.
Experts at the Pago Pago National Weather Service Office, USGS Volcano Hazards Program, NOAA Pacific Tsunami Warning Center, NOAA-IOC International Tsunami Information Center, and USGS National Earthquake Information Center are working together with the American Samoa EOC to understand the source of these earthquakes better. The Samoa Meteorological Service is also reporting increased seismicity south or east of Tutuila Island.
Dr. Natalia Deligne of the US Geological Survey Hawaiian Volcano Observatory (HVO) arrived on August 11 in Pago Pago and is consulting with local authorities on the situation. Additional HVO personnel and earthquake detection instruments are expected to arrive in American Samoa next week. Dr. Charles McCreery, Director of the Pacific Tsunami Warning Center, will arrive next Monday to advise tsunami concerns.
Currently, the volcanoes of American Samoa are monitored remotely by satellites and a distant seismic station in Apia, Samoa. These devices may be able to detect major explosive activity in American Samoa, but the absence of ground-based monitoring stations at the volcanoes precludes early warning of any new activity.
With the existing real-time earthquake-monitoring network in American Samoa, the earthquakes’ locations and magnitudes cannot be precisely determined, but HVO scientists plan to install additional earthquake monitoring instruments in the coming weeks.
It is unclear if this unrest will escalate to a volcanic eruption, HVO said.
Volcanic hazards associated with eruptions in American Samoa could include volcanic gases, low-level explosions of lava localized to a small area, lava flows, earthquake shaking, and tsunami.
A submarine volcanic eruption or landslide can generate a tsunami. The Pacific Tsunami Warning Center will issue a warning if they detect earthquake activity that is likely to cause a tsunami. However, volcanic eruptions do not usually generate large enough earthquakes to warrant a tsunami warning. If there is a tsunami from a nearby volcanic eruption, residents of the Manuʻa islands and elsewhere in American Samoa are more likely to experience natural warning signs before receiving an official tsunami warning.
If you are at the coast, heed the natural tsunami warning signs. If you feel a strong or long-duration earthquake, see a sudden rise or fall of the ocean, hear a loud roar from the ocean, or see a large aerial plume from an eruption, a tsunami may follow, and you should immediately move to higher ground.
The 10 km (6.2 miles) wide Ta’u Island, located at the E end of the Samoan islands, is ringed by sea cliffs. It is the emergent portion of the large Lata shield volcano.
A major flank collapse event around 22 ka resulted in the steep scarps on the southern side of the island. Two smaller shields were constructed along rift zones at the NW and NE tips of the island.
The NW corner of the island has a tuff-cone complex that ejected large dunite xenoliths and coral blocks. Numerous Holocene post-caldera cones occur at the summit and on the flanks.2
Vailulu’u, a massive basaltic seamount not discovered until 1975, rises 4 200 m (13 780 feet) from the sea floor to a depth of 590 m (1 935 feet) about one-third of the way between Ta’u and Rose islands at the E end of the American Samoas. It is considered to mark the current location of the Samoan hotspot.
The summit contains a 2 km (1.2 miles) wide, 400 m (1 312 feet) deep oval-shaped caldera. Two principal rift zones extend E and W from the summit, parallel to the trend of the hotspot. A third less prominent rift extends SE of the summit.
The rift zones and escarpments produced by mass wasting phenomena give the seamount a star-shaped pattern. On July 10, 1973, explosions were recorded by SOFAR (hydrophone records of underwater acoustic signals). An earthquake swarm in 1995 may have been related to an eruption. Turbid water above the summit shows evidence of ongoing hydrothermal plume activity.3
1 HAWAIIAN VOLCANO OBSERVATORY INFORMATION STATEMENT – U.S. Geological Survey – Saturday, August 13, 2022, 04:38 UTC
2 Ta’u – Geological summary – GVP
3 Vailulu’u – Gelogical summary – GVP
Featured image credit: TW/SAM, Google
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