USGS Hawaiian Volcano Observatory staff traveled to American Samoa in August and September to repair and service the territory's volcano monitoring network and conduct joint K-12 outreach with local emergency management partners, the observatory reported in its weekly Volcano Watch article.
The two-week trip was led by HVO geologist Natalia Deligne, who wrote the September 24 article. American Samoa falls within HVO's area of responsibility, as both the Hawaiian and Samoan archipelagoes exist because of hot spot volcanism, and staff have returned at least once a year since 2022 to bolster collaborations with local partners and maintain the monitoring network established that year.
In July 2022, earthquakes at Taʻū volcano shook the remote Manuʻa Islands for six weeks as the volcano experienced unrest. Seismic unrest subsided and returned to background levels in September 2022. When the unrest started in late July 2022, there were no volcano or earthquake monitoring stations in American Samoa; HVO rapidly installed a seismic network by mid-August, and two GPS stations were installed in early September, one of which has since been removed.
All five inhabited islands of American Samoa are volcanic. Tutuila, the main population center, last erupted around 1,500 years ago, and archaeologists have found ceramics below and above volcanic ash from that eruption. Ofu-Olosega volcano, about 60 miles (100 kilometers) east of Tutuila, erupted in 1866. Dr. Rev. Turner, a missionary traveling in the area, described the offshore eruption, which sent ash through the ocean to an estimated 2,000 feet (600 meters) above sea level. The most violent part of the two-month eruption lasted about three days, exposing the nearest community to ash and volcanic gas and causing residents to retreat to a safer location.
The most recent eruption of Taʻū volcano is unknown, but the 2022 seismic unrest shows it remains potentially active. Vailuluʻu, a submarine volcano about 30 miles (45 kilometers) east of Taʻū Island, last had a confirmed eruption in 2003, though more recent activity may have occurred.
Although American Samoa's volcanoes are all designated low threat, the eruptive history and the 2022 Taʻū unrest point to the importance of monitoring across the territory. The seismic network is also used by the USGS National Earthquake Information Center and the NOAA Pacific Tsunami Warning Center to locate earthquakes and assess potential tsunamis across the South Pacific.
During the visit, HVO worked with the NOAA National Weather Service Weather Forecast Office of Pago Pago and the American Samoa Department of Homeland Security to reach the three elementary schools and the sole high school of the Manuʻa Islands. HVO presented on volcanoes and earthquakes, NWS covered hurricanes and effects anticipated as the current El Nino event progresses, and ASDHS focused on tsunami preparedness. HVO also performed critical maintenance, including extensive vegetation clearing and replacement of station components affected by rapid vegetation growth and sea spray.
Four years on from the 2022 unrest, HVO said it continues to strengthen bonds with local partners and communities, noting that while it remotely monitors American Samoa most of the year, the annual visits are essential for maintaining and strengthening partnerships and the monitoring network.