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Volcanoes in American Samoa

Volcanic activity in American Samoa is within the area of responsibility of the U.S. Geological Survey’s Hawaiian Volcano Observatory, based in Hilo on the Island of Hawai‘i. Tutuila, Ofu-Olosega and Ta‘ū are potentially active volcanoes within the United States Territory of American Samoa. All are considered low threat.

 

Flag of American Samoa
Flag of American Samoa

American Samoa volcanoes formed from a hotspot

 

Volcanoes in American Samoa formed from hotspot volcanism. As the Pacific Plate passes northwest over the Samoan hotspot, eruptions form submarine volcanoes and islands. This is similar to how the Hawaiian Islands form as the Pacific Plate passes over the Hawaiian hotspot. The islands in American Samoa are the tops of large shield volcanoes, most of which are below the ocean surface.

Volcanoes in American Samoa are progressively younger closer to the hotspot. Volcanoes formed from the Samoan hotspot's eruptions are primarily basaltic shield volcanoes, with summit calderas and rift zones where eruptions are more likely to occur.  Eruptions from hotspot volcanoes typically include slow-moving lava flows and low-level explosions of lava that are localized to a small area. Information about these hazards, which are similar to those in Hawaii, can be found at this HVO website: https://www.usgs.gov/observatories/hvo/hazards.

Tutuila Island, Ofu-Olosega, and Ta‘ū Island are volcanoes in American Samoa that are considered potentially active. The youngest dated eruption in American Samoa is on Tutuila Island from approximately 1700–1400 years ago. However, submarine eruptions have occurred more recently at two locations in the past two centuries. Currently, the Samoa hotspot is considered to be located beneath Vailuluʻu seamount, a submarine volcano about 45 kilometers (28 miles) east of Taʻū Island.

 

Active volcanoes in American Samoa:

 

Color map of islands and nearby bathymetry
This reference map depicts the topography and bathymetry of the volcanoes in the Manu‘a Islands, American Samoa, where seismic unrest has been ongoing for several weeks. The highest elevation in the area is Lata Mountain on Ta‘ū Island, standing 3,179 feet (969 meters) above sea level. The bathymetry data—courtesy of the National Oceanic and Atmospheric Administration (NOAA), Maxar/DigitalGlobe, and the University of Hawai‘i School of Ocean & Earth Science & Technology (SOEST)—depicts submarine topography in high-resolution down to 1,148 feet (350 meters) below sea level, and at coarser resolution to greater depths. A shallow submarine ridge extends to the northwest from Ta‘ū Island towards Olosega Island; it was along this ridge that a submarine eruption occurred in 1866. There are now 3 broadband seismometers (pink circles) and 4 microseismometers (pink squares) monitoring seismic activity in the Manu‘a Islands.

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