Honolulu, HAWAII — It's been one year since Taʻu volcano in American Samoa started shaking residents of the Manuʻa Islands (Ofu-Olosega and Ta‘u Islands). Fortunately, there have been no additional earthquakes since the volcanic unrest ended last October. This month, USGS staff will be returning to American Samoa to do outreach, strengthen relationships with partners, and maintain the monitoring network.

The first felt earthquake was reported just over a year ago, on July 26, 2022. Over the next six weeks — until early September 2022, hundreds of earthquakes were felt throughout the Manuʻa Islands; one earthquake was felt as far away as Tutuila. The events were highly unusual for American Samoa, so much so that the islands did not have any volcano monitoring equipment when the unrest began.

In response to the unrest, the U.S. Geological Survey (USGS) Hawaiian Volcano Observatory (HVO) rapidly deployed staff and monitoring equipment in August and September 2022. HVO established a rapid monitoring network across American Samoa, and kept the local community, federal and local partners informed on the dynamic situation. In December 2022, a few months after the unrest ended, a small team returned to service the newly established monitoring network.

In August 2023, two HVO scientists will return to American Samoa for two weeks. We are looking forward to being back during less shaky (literally) conditions.

HVO staff will conduct outreach with our partners at the National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) Pago Pago Office. Outreach events are planned for the Manuʻa Islands on August 7 and 8, with further community meetings, media interviews, and other events on Tutuila over the following week.

We will also maintain and service the volcano and earthquake monitoring network, with assistance from the NWS Pago Pago Office. The network also provides important data for earthquake and tsunami monitoring across the southwest Pacific region.

On Taʻu Island, we will replace the TAU broadband seismometer, located on northwest of Taʻu Island, as it was damaged during a lightning storm on May 5, 2023, and is currently offline. We will also improve the telemetry—how data is transmitted so that it can be analyzed from afar—for the broadband seismometer on eastern Tutuila.

Considering that there was no monitoring network in place at the start of the 2022 unrest, we do not know how many earthquakes occurred during the entire 2022 earthquake swarm. A hydrophone (similar to an underwater microphone) on Wake Island, about 4,500 kilometers (2,800 miles) northwest of Taʻu, detected activity that provides a useful overview of how the earthquake swarm evolved—it began in late July, peaked in mid-August, was mostly over by early to mid-September, and definitively ended in early October (see the attached figure).

By August 20, 2022, the rapidly deployed monitoring network had enough stations for the USGS to locate earthquakes of magnitude (M) 2.5 or greater. Between August 20 and September 11, 2022, 301 earthquakes, that were M2.5 or greater, occurred north of Taʻu Island. As the seismic unrest eased back into background activity, between September 11 and October 6, 2022, an additional 8 earthquakes occurred. Most of these final earthquakes were not felt by local residents.

The 2022 earthquake swarm in American Samoa is a reminder that these islands are formed by volcanoes that have the potential to erupt someday.

The network of instruments in American Samoa now allows the USGS to monitor the volcanoes, which have remained quiet since the 2022 unrest ended.

Map of the American Samoa volcano-monitoring network (top). Data from Wake Island hydrograph (located about 4,500 km, or 2,900 miles, northwest of Taʻū Island) shows the general trend in the number of events during the 2022 earthquake swarm (bottom left). Locations for larger earthquakes (M2.5 and greater) are available starting August 20, 2022 (bottom right). [USGS National Earthquake Information Center]

More information on volcanoes in American Samoa is also available on the HVO website at https://www.usgs.gov/observatories/hvo/volcanoes-american-samoa.