Volcano Watch: From aloha to talofa; Hawaiian Volcano Observatory monitors American Samoa
“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. Today’s article is by Hawaiian Volcano Observatory geologist Natalia Deligne.
Hawaiian Volcano Observatory staff during a 2-week trip in August and September to American Samoa repaired and serviced the volcano monitoring network and conducted joint outreach to schoolchildren in grades K-12 with local emergency management partners.
Earthquakes in July 2022 at Taʻū volcano shook the remote Manuʻa Islands of American Samoa for 6 weeks as the volcano experienced volcanic unrest; fortunately for the communities of Taʻū Island and nearby Ofu-Olosega Islands (also a volcano), seismic unrest subsided and returned to background levels of activity in September 2022.
As American Samoa is within Hawaiian Volcano Observatory’s area of responsibility (the Hawaiian and Samoan archipelagoes exist because of hot spot volcanism), observatory staff have visited at least once a year since 2022 to bolster collaborations with local partners and maintain the newly established volcano (and earthquake) monitoring network.
All five inhabited islands of American Samoa are volcanic. The main population center Tutuila and nearby Aunuʻu Island are part of Tutuila volcano.
Tutuila last erupted about 1,500 years ago. Archaeologists found ceramics below and above volcanic ash associated with this eruption, indicating human settlement at the very least before and after the eruption.
About 60 miles east of Tutuila, Ofu-Olosega volcano erupted in 1866.
Dr. the Rev. Turner, a missionary traveling in 1866 in the area described the offshore eruption, which erupted ash to altitudes of an estimated 2,000 feet above sea level through the ocean. The most violent part of the 2-month-long eruption lasted about 3 days, exposing the nearest community to ash and volcanic gas, causing them to retreat to a safer location on the island.
Turner noted there were no oral traditions recalling previous eruptive activity here (human settlement of the Manuʻa Islands is thought to have occurred about 3,000 years ago).
We do not currently know when the most recent eruption of Taʻū volcano was, but the seismic unrest in 2022 shows it remains potentially active.
When unrest started 4 years ago, there was no volcano or earthquake monitoring stations in American Samoa. Hawaiian Volcano Observatory rapidly installed a seismic network by mid-August.
Two GPS stations were then installed in early September; one has since been removed. Analysis of the seismic data indicates unrest was centered underneath the northern distal flank of Taʻū volcano.
Similar to the Hawaiian Islands and Kamaʻehuakanaloa, Vailuluʻu is a submarine volcano about 30 miles east of Taʻū Island. Repeat oceanic surveys during the past several decades recorded changes to the seamount consistent with eruptive activity.
The most recent confirmed eruption was in 2003, although there might have been more recent activity since.
Although the volcanoes of American Samoa are all designated as low threat volcanoes — in contrast, Kīlauea and Mauna Loa in Hawai’i are very high threat volcanoes — the eruptive activity described above coupled with the 2022 Taʻū unrest point to the importance of volcano monitoring throughout the territory.
The seismic network in American Samoa is also used by National Earthquake Information Center and National Oceanic and Atmospheric Administration Pacific Tsunami Warning Center to locate earthquakes and assess for potential tsunami throughout the South Pacific.
What did Hawaiian Volcano Observatory staff do in their most recent visit to American Samoa?
Working closely with National Weather Service forecast office in Pago Pago:
- Staff visited the Manuʻa Islands.
- The two agencies, along with American Samoa Department of Homeland Security, did outreach in the three elementary schools and sole high school of the Manuʻa Islands.
- Hawaiian Volcano Observatory presented about volcanoes and earthquakes.
- National Weather Service covered hurricanes and impacts anticipated as an El Nino weather event progresses.
- American Samoa Department of Homeland Security focused on tsunami preparedness.
Hawaiian Volcano Observatory also performed critical maintenance of the monitoring network.
Rapid vegetation growth and sea spray greatly affected one of the monitoring stations, requiring extensive vegetation clearing and replacement of some station components.
National Weather Service and National Oceanic and Atmospheric Administration Global Monitoring Laboratory American Samoa Atmospheric Baseline Observatory provided critical and greatly appreciated support to Hawaiian Volcano Observatory staff in the undertaking.
Four years on from the 2022 Taʻū volcano unrest, Hawaiian Volcano Observatory continues to strengthen bonds with local partners and communities in American Samoa.
While most of the year the observatory — based in Hawai‘i on the Big Island — remotely keeps an eye on American Samoa, the annual visits are essential for maintaining and strengthening partnerships and the territory’s monitoring network.
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VOLCANO ACTIVITY UPDATES
KĪLAUEA volcano
VOLCANO ALERT LEVEL: Watch
Kīlauea has erupted episodically since Dec. 23, 2024, within its summit caldera. Lava flows have intermittently erupted from the north vent since Sept. 22, with glow and spatter sometimes visible in the south and west vents.
Six new vents that erupted from Sept. 14-16 in Halemaʻumaʻu are no longer active.
Irregular summit region inflation, along with earthquakes in and around the caldera, signaled that Kīlauea’s summit region is at a high level of pressurization.
No unusual activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.
WHAT’S NEXT: Current conditions remain favorable for another fountaining episode or change in eruptive activity if inflation returns.
MAUNA LOA volcano
VOLCANO ALERT LEVEL: Normal
Mauna Loa is not erupting. Read the most recent monthly Mauna Loa activity update online.
Hawaiian Volcano Observatory continues to closely monitor Kīlauea and Mauna Loa.
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EARTHQUAKE ACTIVITY UPDATES
Four earthquakes were reported felt during the past week throughout the Hawaiian Islands:
- MAGNITUDE-3.2 earthquake at 2:05 p.m. Sept. 23 located 9 miles south-southeast of Hōnaunau-Nāpōʻopoʻo at a depth of 4 miles.
- MAGNITUDE-2.8 earthquake at 7:05 a.m. Sept. 18 located 5 miles south of Waimea at a depth of 6 miles.
- MAGNITUDE-2.5 earthquake at 7:03 a.m. Sept. 18 located 6 miles east of Waikōloa at a depth of 5 miles.
- MAGNITUDE-4.1 earthquake at 8:36 p.m. Sept. 17 located 3 miles south of Pāhala at a depth of 7 miles.
Visit the Hawaiian Volcano Observatory website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.
