Ofu-Olosega Volcano

Updated: Sep 12, 2025 07:27 GMT - refresh

Shield volcanoes

United States, Samoan Islands, -14.18°S / -169.62°W

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Summit height: 639 m / 2,096 ft

Current status: normal or dormant (1 out of 5)

Last update: 31 Aug 2022 (Smithsonian / USGS Weekly Volcanic Activity Report)

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Typical eruption style: unspecified
Ofu-Olosega volcano eruptions: 1866

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Background

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.
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Smithsonian / GVP volcano information

Ofu-Olosega Volcano Photos

Epong frying tofu dices (Photo: Tom Pfeiffer)

Coloful autumn (Photo: Tom Pfeiffer)

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Significant volcanic eruptions: Ofu-Olosega volcano

In the past 10,000 years, Ofu-Olosega has had only one confirmed historic eruption in 1866.

The table below lists all known eruptions (date in bold face) of Ofu-Olosega volcano in historic times and during the past 10,000 years. Updates on the most recent volcanic activity of Ofu-Olosega can be found on the news page of Ofu-Olosega volcano.

Date	Note	VEI
1866 Sep 12 - Nov 15 ±5 d.	Submarine vent 3 km SE of Olosega Historical obs./docs.	2
1866 Sep 12 (eruption 1866 Sep 12 - Nov 15 ±5 d.)	Tsunami recorded Historical obs./docs.	2	Info
1866 Sep 12: 1866, September 12, Samoan Islands. An underwater volcano erupted in the vicinity of the Manua Islands. The first indications of it were weak shocks, felt on September 7 by the inhabitants of the islands of Tau and Olosega, which are part of that archipelago. These shocks occurred at an average of four per hour, and the vibrations continued into the following day. Thirty-nine shocks occurred during the night of September 9. After dinner on the 12th a disturbance in the sea commenced at a distance of approximately 3 km (1 1/2 miles) from the island of Olosega and 8 km (4 1/2 miles) from the island of Tau...The destruction continued all that day and through part of the next. This was followed by an underwater eruption with its usual manifestations. On the 15th of September the eruption was repeated, and each hour approximately 50 eruptions occurred...During this time large pieces of lava floated up to the surface of the ocean, and tremors were felt on the islands. A column of thick smoke, rising to a height of about 600 m (2,000 ft), completely darkened the sky. Although the eruption did not reveal open flames, gleams of fire could be observed on two or three occasions. The sea was extremely disturbed and for a distance of 20 km (10 miles) glittered with a phosphorescent light. Many dead fish floated to the surface and were cast upon the shore. After three days, the frequency of the eruptions began to abate, although even on the 11th of November three or four explosions per hour could be counted. The products of the eruption were not thrown up to such a significant height as previously, now no higher than 5-10 m (20-30 feet). The condition of the vegetation on the Manua Islands suggests that this area had not seen very severe eruptions for at least 80-100 years. (above from reference #415). Start Date: 1866 Sep 12, Stop date: 1866 Nov 15 ± 5 days. Certainty Confirmed, VEI 2, Historical Observations. Submarine vent 3 km SE of Olosega. (reference #2432) Cited references #415 Soloviev, S.L., and Ch.N. Go (1975): A catalogue of tsunamis on the eastern shore of the Pacific Ocean [dates include 1513-1968]. Academy of Sciences of the USSR, Nauka Publishing House, Moscow, 204 p. [Canadian Translation of Fisheries and Aquatic Sciences no. 5078, 1984, translation available from Canada Institute for Scientific and Technical Information, National Research Council, Ottawa, Ontario, Canada K1A OS2, 293 p.] #2432 Venzke, E., R.W. Wunderman, L. McClelland, T. Simkin, J.F. Luhr, L. Siebert, and G. Mayberry (eds.) (2002-): Global Volcanism, 1968 to the Present. Smithsonian Institution, Global Volcanism Program Digital Information Series, GVP-4 (http://www.volcano.si.edu/reports/). Source: NOAA National Centers for Environmental Information (NCEI), Global Significant Earthquake Database. doi:10.7289/V5TD9V7K

Date

Note

VEI

Deaths

Damage

1866 Sep 12 - Nov 15 ±5 d.

Submarine vent 3 km SE of Olosega

Historical obs./docs.

1866 Sep 12

(eruption 1866 Sep 12 - Nov 15 ±5 d.)

Tsunami recorded

Historical obs./docs.

Info

1866 Sep 12:
1866, September 12, Samoan Islands. An underwater volcano erupted in the vicinity of the Manua Islands. The first indications of it were weak shocks, felt on September 7 by the inhabitants of the islands of Tau and Olosega, which are part of that archipelago. These shocks occurred at an average of four per hour, and the vibrations continued into the following day. Thirty-nine shocks occurred during the night of September 9.
After dinner on the 12th a disturbance in the sea commenced at a distance of approximately 3 km (1 1/2 miles) from the island of Olosega and 8 km (4 1/2 miles) from the island of Tau...The destruction continued all that day and through part of the next. This was followed by an underwater eruption with its usual manifestations. On the 15th of September the eruption was repeated, and each hour approximately 50 eruptions occurred...During this time large pieces of lava floated up to the surface of the ocean, and tremors were felt on the islands. A column of thick smoke, rising to a height of about 600 m (2,000 ft), completely darkened the sky.

Although the eruption did not reveal open flames, gleams of fire could be observed on two or three occasions. The sea was extremely disturbed and for a distance of 20 km (10 miles) glittered with a phosphorescent light. Many dead fish floated to the surface and were cast upon the shore.

After three days, the frequency of the eruptions began to abate, although even on the 11th of November three or four explosions per hour could be counted. The products of the eruption were not thrown up to such a significant height as previously, now no higher than 5-10 m (20-30 feet). The condition of the vegetation on the Manua Islands suggests that this area had not seen very severe eruptions for at least 80-100 years.

(above from reference #415).

Start Date: 1866 Sep 12, Stop date: 1866 Nov 15 ± 5 days. Certainty Confirmed, VEI 2, Historical Observations. Submarine vent 3 km SE of Olosega. (reference #2432)

Cited references

#415 Soloviev, S.L., and Ch.N. Go (1975): A catalogue of tsunamis on the eastern shore of the Pacific Ocean [dates include 1513-1968]. Academy of Sciences of the USSR, Nauka Publishing House, Moscow, 204 p. [Canadian Translation of Fisheries and Aquatic Sciences no. 5078, 1984, translation available from Canada Institute for Scientific and Technical Information, National Research Council, Ottawa, Ontario, Canada K1A OS2, 293 p.]
#2432 Venzke, E., R.W. Wunderman, L. McClelland, T. Simkin, J.F. Luhr, L. Siebert, and G. Mayberry (eds.) (2002-): Global Volcanism, 1968 to the Present. Smithsonian Institution, Global Volcanism Program Digital Information Series, GVP-4 (http://www.volcano.si.edu/reports/).

Source: NOAA National Centers for Environmental Information (NCEI), Global Significant Earthquake Database. doi:10.7289/V5TD9V7K

Remark:

Our list of volcanic eruptions closely follows the database of eruptions of the Smithsonian's Global Volcanism Project (GVP), the internationally most recognized data source for volcanic eruptions, but also includes significant eruptive episodes or related volcano events. "Volcanic eruptions" are usually to be understood as sequences of individual eruptive episodes that can follow each other, or even overlap (if several vents are involved), and can last many years, decades or even longer. For example, the current activity of Stromboli volcano is understood as a single eruption that has been ongoing since 1934.

Sources: NOAA National Centers for Environmental Information (NCEI), Global Significant Volcanic Eruptions Database. doi:10.7289/V5TD9V7K | Global Volcanism Project / Smithsonian Institution

Ofu-Olosega Volcano FAQ

+When was the last eruption of Ofu-Olosega volcano?

The last confirmed eruption of Ofu-Olosega occurred in 1866.

+How often does Ofu-Olosega volcano erupt?

Since 1866, Ofu-Olosega volcano has had at least 1 historically documented eruptions. This means that it erupts on average every 159 years.

+When was the largest eruption of Ofu-Olosega volcano?

The largest eruption of Ofu-Olosega volcano in historic times occurred in 1866. It ranks as a strombolian to vulcanian eruption with a magnitude 2 on the VEI (Volcanic Explosivity Index) scale.

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Ofu-Olosega Volcano Maps

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