Ofu-Olosega

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  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 14.175°S
  • 169.618°W

  • 639 m
    2096 ft

  • 244010
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

The Global Volcanism Program has no activity reports for Ofu-Olosega.

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

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

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.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
1866 Sep 12 1866 Nov 15 ± 5 days Confirmed 2 Historical Observations Submarine vent 3 km SE of 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 14° 10' 30" S 169° 38' 13" W
Maga Point Cone 14° 11' 53" S 169° 37' 0" W
Nu'u Tuff cone 14° 10' 0" S 169° 40' 59" W
Sili Shield volcano
Tauga Point Tuff cone 14° 10' 5" S 169° 40' 44" W
To'aga Cone
Clouds drape the tops of the two triangle-shaped islands of Ofu (left) and Olosega (right) in eastern Samoa in this Space Shuttle image (with north to the upper 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 Space Shuttle image ISS002-E-6878, 2001 (http://eol.jsc.nasa.gov/).
A narrow strait (just left of center) separates the two triangle-shaped islands of Ofu (left) and Olosega (right) in eastern Samoa. The islands are formed by two eroded, coalescing basaltic shield volcanoes. The narrow, steep-sided ridge forming the western side of Ofu Island is cut by volcanic dikes, and an intrusive plug forms the sharp spire at the left on Ofu Island. 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).

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

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 Volc Geotherm Res, 69: 241-254.

Volcano Types

Shield(s)
Caldera
Pyroclastic cone(s)

Tectonic Setting

Subduction zone
Oceanic crust (< 15 km)

Rock Types

Major
Basalt / Picro-Basalt
Trachybasalt / Tephrite Basanite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
220
384
1,387
1,387

Affiliated Databases

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).
WOVOdat 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.
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).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.