Most Recent Weekly Report: 24 August-30 August 2022 Cite this Report

Data from seismometers recently installed on Tutuila, Ta’u, and Ofu-Olosega islands of American Samoa to monitor an ongoing seismic swarm indicated that the events were related to Ta’u Island and not Ofu-Olosega. HVO lowered the Volcano Alert Level to Normal and the Aviation Color Code to Green on 26 August. The report warned residents of Ofu-Olosega that they could still be significantly affected by events that may take place on or around Ta’u Island.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)

Weekly Reports - Index

2022: August

24 August-30 August 2022 Cite this Report

Data from seismometers recently installed on Tutuila, Ta’u, and Ofu-Olosega islands of American Samoa to monitor an ongoing seismic swarm indicated that the events were related to Ta’u Island and not Ofu-Olosega. HVO lowered the Volcano Alert Level to Normal and the Aviation Color Code to Green on 26 August. The report warned residents of Ofu-Olosega that they could still be significantly affected by events that may take place on or around Ta’u Island.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)

17 August-23 August 2022 Cite this Report

HVO reported that an earthquake swarm in the Manu’a Islands of American Samoa continued to be recorded and felt by residents of Ta’u Island and Ofu-Olosega. About 20 earthquakes per hour were recorded by four microseismometers distributed on Tutuila, Ta’u, and Ofu-Olosega Islands. The largest events were estimated to be between magnitudes 2 and 3; most events are too small to be felt. Analysis of the seismic data indicated that the earthquakes were occurring beneath or around the Manu’a Islands, likely closer to Ta’u rather than Ofu-Olosega, though the exact locations, depths, and magnitudes were unknown. The number, size, and frequency of earthquakes recorded by instruments and being felt by people and on both islands indicated that seismicity was above background levels; HVO changed the Volcano Alert Level to Advisory and the Aviation Color Code to Yellow for both volcanoes. Earthquakes continued to be recorded at around the same rate during 20-22 August. Two additional seismometers were installed on Ta’u during 22-23 August.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)

The Global Volcanism Program has no Bulletin Reports available for Ofu-Olosega.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Cones
Feature Name	Feature Type	Elevation	Latitude	Longitude
A'ofa	Shield volcano	494 m	14° 10' 30" S	169° 39' 47" W
Fatuaga Point	Cone	230 m	14° 10' 7" S	169° 38' 18" W
Maga Point	Cone	23 m	14° 11' 32" S	169° 36' 45" W
Nu'u	Tuff cone	76 m	14° 10' 4" S	169° 41' 5" W
Sili	Shield volcano
Tauga Point	Tuff cone	249 m	14° 9' 48" S	169° 40' 21" W
To'aga	Cone

Basic Data Volcano Number Last Known Eruption Elevation Latitude Longitude 244010 1866 CE 639 m / 2,096 ft 14.175°S 169.618°W Morphology Volcano Landform Shield Volcano Types Shield(s) Caldera Pyroclastic cone(s) Rock Types Major Basalt / Picro-Basalt Trachybasalt / Tephrite Basanite Tectonic Setting Subduction zone Oceanic crust (< 15 km) Population Within 5 km Within 10 km Within 30 km Within 100 km 220 384 1,387 1,387

Geological Summary The two triangle-shaped islands of Ofu and Olosega in eastern Samoa, with a combined length of 6 km, are separated by a narrow strait. The islands are formed by two eroded, coalescing basaltic shield volcanoes whose slopes dip to the east and west. Steep cliffs up to 600-m high truncate the northern and southern sides of the islands. The narrow, steep-sided ridge forming the eastern tip of Ofu Island consists of a dike complex. The shield volcano on Ofu is cut on the north by the A'ofa caldera; bathymetry suggests that a caldera may also exist on the Sili shield volcano of Olosega. The Nu'utele tuff cone, forming a small crescent-shaped island immediately off the west end of Ofu Island, is Holocene in age. A submarine eruption took place in 1866 at the opposite end of the two islands, 3 km SE of Olosega, along the ridge connecting Olosega with Ta'u Island. References The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior. Richard J J, 1962. Kermadec, Tonga and Samoa. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 13: 1-38. Stearns H T, 1944. Geology of the Samoan Islands. Geol Soc Amer Bull, 55: 1279-1332. Stice G D, 1968. Petrology of the Manu'a Islands, Samoa. Contr Mineral Petr, 19: 343-357. Stice G D, McCoy F W, 1968. The geology of the Manu'a Islands, Samoa. Pacific Sci, 22: 427-457. Walker G P L, Eyre P R, 1995. Dike complexes in American Samoa. J. Volcanol. Geotherm. Res., 69: 241-254.

Eruptive History

There is data available for 1 confirmed Holocene eruptive periods.

Deformation History

There is no Deformation History data available for Ofu-Olosega.

Emission History

There is no Emissions History data available for Ofu-Olosega.

Photo Gallery

Clouds drape the tops of the two islands of Ofu (left) and Olosega (right) in eastern Samoa in this International Space Station image (N is to the top left). The islands, 6 km in combined length, are separated by a narrow strait. They are formed by two eroded, coalescing basaltic shield volcanoes truncated by mostly-submarine calderas. A submarine eruption took place in 1866 about 3 km SE of Olosega, along the ridge connecting Olosega with Ta'u Island.

NASA International Space Station image ISS002-E-6878, 2001 (http://eol.jsc.nasa.gov/). A narrow strait (just left of center) separates the two triangular islands of Ofu (left) and Olosega (right) in eastern Samoa. The islands are formed by two eroded, coalescing shield volcanoes. The narrow, steep-sided ridge forming the W side of Ofu Island is cut by volcanic dikes and an intrusive plug forms the sharp spire on Ofu Island to the left. A submarine eruption took place in 1866 at the far end of the two islands, 3 km SE of Olosega, along the ridge connecting Olosega with Ta'u Island.

Photo by Peter Craig, 1995 (U.S. National Park Service). Ofu (left) and Olosega (right) in eastern Samoa are parts of the same volcano separated by the Asaga Strait, with the island group reaching nearly 9 km across (including the smaller island to the west), shown in this 29 October 2018 Sentinel-2 satellite image (N is at the top). The islands have likely been shaped by flank failures with resulting debris avalanches below sea level.

Satellite image courtesy of Copernicus Sentinel Data, 2018.

GVP Map Holdings

Maps are not currently available due to technical issues.

Smithsonian Sample Collections Database

There are no samples for Ofu-Olosega in the Smithsonian's NMNH Department of Mineral Sciences Rock and Ore collection.

External Sites

Copernicus Browser	The Copernicus Browser replaced the Sentinel Hub Playground browser in 2023, to provide access to Earth observation archives from the Copernicus Data Space Ecosystem, the main distribution platform for data from the EU Copernicus missions.
MIROVA	Middle InfraRed Observation of Volcanic Activity (MIROVA) is a near real time volcanic hot-spot detection system based on the analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) data. In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity.
MODVOLC Thermal Alerts	Using infrared satellite Moderate Resolution Imaging Spectroradiometer (MODIS) data, scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, developed an automated system called MODVOLC to map thermal hot-spots in near real time. For each MODIS image, the algorithm automatically scans each 1 km pixel within it to check for high-temperature hot-spots. When one is found the date, time, location, and intensity are recorded. MODIS looks at every square km of the Earth every 48 hours, once during the day and once during the night, and the presence of two MODIS sensors in space allows at least four hot-spot observations every two days. Each day updated global maps are compiled to display the locations of all hot spots detected in the previous 24 hours. There is a drop-down list with volcano names which allow users to 'zoom-in' and examine the distribution of hot-spots at a variety of spatial scales.
WOVOdat    Single Volcano View    Temporal Evolution of Unrest    Side by Side Volcanoes	WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore. GVMID Data on Volcano Monitoring Infrastructure The Global Volcano Monitoring Infrastructure Database GVMID, is aimed at documenting and improving capabilities of volcano monitoring from the ground and space. GVMID should provide a snapshot and baseline view of the techniques and instrumentation that are in place at various volcanoes, which can be use by volcano observatories as reference to setup new monitoring system or improving networks at a specific volcano. These data will allow identification of what monitoring gaps exist, which can be then targeted by remote sensing infrastructure and future instrument deployments.
Volcanic Hazard Maps	The IAVCEI Commission on Volcanic Hazards and Risk has a Volcanic Hazard Maps database designed to serve as a resource for hazard mappers (or other interested parties) to explore how common issues in hazard map development have been addressed at different volcanoes, in different countries, for different hazards, and for different intended audiences. In addition to the comprehensive, searchable Volcanic Hazard Maps Database, this website contains information about diversity of volcanic hazard maps, illustrated using examples from the database. This site is for educational purposes related to volcanic hazard maps. Hazard maps found on this website should not be used for emergency purposes. For the most recent, official hazard map for a particular volcano, please seek out the proper institutional authorities on the matter.
IRIS seismic stations/networks	Incorporated Research Institutions for Seismology (IRIS) Data Services map showing the location of seismic stations from all available networks (permanent or temporary) within a radius of 0.18° (about 20 km at mid-latitudes) from the given location of Ofu-Olosega. Users can customize a variety of filters and options in the left panel. Note that if there are no stations are known the map will default to show the entire world with a "No data matched request" error notice.
UNAVCO GPS/GNSS stations	Geodetic Data Services map from UNAVCO showing the location of GPS/GNSS stations from all available networks (permanent or temporary) within a radius of 20 km from the given location of Ofu-Olosega. Users can customize the data search based on station or network names, location, and time window. Requires Adobe Flash Player.
DECADE Data	The DECADE portal, still in the developmental stage, serves as an example of the proposed interoperability between The Smithsonian Institution's Global Volcanism Program, the Mapping Gas Emissions (MaGa) Database, and the EarthChem Geochemical Portal. The Deep Earth Carbon Degassing (DECADE) initiative seeks to use new and established technologies to determine accurate global fluxes of volcanic CO2 to the atmosphere, but installing CO2 monitoring networks on 20 of the world's 150 most actively degassing volcanoes. The group uses related laboratory-based studies (direct gas sampling and analysis, melt inclusions) to provide new data for direct degassing of deep earth carbon to the atmosphere.
Large Eruptions of Ofu-Olosega	Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
EarthChem	EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).